1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
3 @c Free Software Foundation, Inc.
4 @c This is part of the GCC manual.
5 @c For copying conditions, see the file gcc.texi.
6
7 @ignore
8 @c man begin INCLUDE
9 @include gcc-vers.texi
10 @c man end
11
12 @c man begin COPYRIGHT
13 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
14 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
15 Free Software Foundation, Inc.
16
17 Permission is granted to copy, distribute and/or modify this document
18 under the terms of the GNU Free Documentation License, Version 1.2 or
19 any later version published by the Free Software Foundation; with the
20 Invariant Sections being ``GNU General Public License'' and ``Funding
21 Free Software'', the Front-Cover texts being (a) (see below), and with
22 the Back-Cover Texts being (b) (see below). A copy of the license is
23 included in the gfdl(7) man page.
24
25 (a) The FSF's Front-Cover Text is:
26
27 A GNU Manual
28
29 (b) The FSF's Back-Cover Text is:
30
31 You have freedom to copy and modify this GNU Manual, like GNU
32 software. Copies published by the Free Software Foundation raise
33 funds for GNU development.
34 @c man end
35 @c Set file name and title for the man page.
36 @setfilename gcc
37 @settitle GNU project C and C++ compiler
38 @c man begin SYNOPSIS
39 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
40 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
41 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
42 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
43 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
44 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
45 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
46
47 Only the most useful options are listed here; see below for the
48 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
49 @c man end
50 @c man begin SEEALSO
51 gpl(7), gfdl(7), fsf-funding(7),
52 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
53 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
54 @file{ld}, @file{binutils} and @file{gdb}.
55 @c man end
56 @c man begin BUGS
57 For instructions on reporting bugs, see
58 @w{@value{BUGURL}}.
59 @c man end
60 @c man begin AUTHOR
61 See the Info entry for @command{gcc}, or
62 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
63 for contributors to GCC@.
64 @c man end
65 @end ignore
66
67 @node Invoking GCC
68 @chapter GCC Command Options
69 @cindex GCC command options
70 @cindex command options
71 @cindex options, GCC command
72
73 @c man begin DESCRIPTION
74 When you invoke GCC, it normally does preprocessing, compilation,
75 assembly and linking. The ``overall options'' allow you to stop this
76 process at an intermediate stage. For example, the @option{-c} option
77 says not to run the linker. Then the output consists of object files
78 output by the assembler.
79
80 Other options are passed on to one stage of processing. Some options
81 control the preprocessor and others the compiler itself. Yet other
82 options control the assembler and linker; most of these are not
83 documented here, since you rarely need to use any of them.
84
85 @cindex C compilation options
86 Most of the command line options that you can use with GCC are useful
87 for C programs; when an option is only useful with another language
88 (usually C++), the explanation says so explicitly. If the description
89 for a particular option does not mention a source language, you can use
90 that option with all supported languages.
91
92 @cindex C++ compilation options
93 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
94 options for compiling C++ programs.
95
96 @cindex grouping options
97 @cindex options, grouping
98 The @command{gcc} program accepts options and file names as operands. Many
99 options have multi-letter names; therefore multiple single-letter options
100 may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d
101 -v}}.
102
103 @cindex order of options
104 @cindex options, order
105 You can mix options and other arguments. For the most part, the order
106 you use doesn't matter. Order does matter when you use several
107 options of the same kind; for example, if you specify @option{-L} more
108 than once, the directories are searched in the order specified. Also,
109 the placement of the @option{-l} option is significant.
110
111 Many options have long names starting with @samp{-f} or with
112 @samp{-W}---for example,
113 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
114 these have both positive and negative forms; the negative form of
115 @option{-ffoo} would be @option{-fno-foo}. This manual documents
116 only one of these two forms, whichever one is not the default.
117
118 @c man end
119
120 @xref{Option Index}, for an index to GCC's options.
121
122 @menu
123 * Option Summary:: Brief list of all options, without explanations.
124 * Overall Options:: Controlling the kind of output:
125 an executable, object files, assembler files,
126 or preprocessed source.
127 * Invoking G++:: Compiling C++ programs.
128 * C Dialect Options:: Controlling the variant of C language compiled.
129 * C++ Dialect Options:: Variations on C++.
130 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
131 and Objective-C++.
132 * Language Independent Options:: Controlling how diagnostics should be
133 formatted.
134 * Warning Options:: How picky should the compiler be?
135 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
136 * Optimize Options:: How much optimization?
137 * Preprocessor Options:: Controlling header files and macro definitions.
138 Also, getting dependency information for Make.
139 * Assembler Options:: Passing options to the assembler.
140 * Link Options:: Specifying libraries and so on.
141 * Directory Options:: Where to find header files and libraries.
142 Where to find the compiler executable files.
143 * Spec Files:: How to pass switches to sub-processes.
144 * Target Options:: Running a cross-compiler, or an old version of GCC.
145 * Submodel Options:: Specifying minor hardware or convention variations,
146 such as 68010 vs 68020.
147 * Code Gen Options:: Specifying conventions for function calls, data layout
148 and register usage.
149 * Environment Variables:: Env vars that affect GCC.
150 * Precompiled Headers:: Compiling a header once, and using it many times.
151 * Running Protoize:: Automatically adding or removing function prototypes.
152 @end menu
153
154 @c man begin OPTIONS
155
156 @node Option Summary
157 @section Option Summary
158
159 Here is a summary of all the options, grouped by type. Explanations are
160 in the following sections.
161
162 @table @emph
163 @item Overall Options
164 @xref{Overall Options,,Options Controlling the Kind of Output}.
165 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
166 -x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol
167 --version -wrapper@@@var{file}}
168
169 @item C Language Options
170 @xref{C Dialect Options,,Options Controlling C Dialect}.
171 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
172 -aux-info @var{filename} @gol
173 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
174 -fhosted -ffreestanding -fopenmp -fms-extensions @gol
175 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
176 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
177 -fsigned-bitfields -fsigned-char @gol
178 -funsigned-bitfields -funsigned-char}
179
180 @item C++ Language Options
181 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
182 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
183 -fconserve-space -ffriend-injection @gol
184 -fno-elide-constructors @gol
185 -fno-enforce-eh-specs @gol
186 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
187 -fno-implicit-templates @gol
188 -fno-implicit-inline-templates @gol
189 -fno-implement-inlines -fms-extensions @gol
190 -fno-nonansi-builtins -fno-operator-names @gol
191 -fno-optional-diags -fpermissive @gol
192 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
193 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
194 -fno-default-inline -fvisibility-inlines-hidden @gol
195 -fvisibility-ms-compat @gol
196 -Wabi -Wctor-dtor-privacy @gol
197 -Wnon-virtual-dtor -Wreorder @gol
198 -Weffc++ -Wstrict-null-sentinel @gol
199 -Wno-non-template-friend -Wold-style-cast @gol
200 -Woverloaded-virtual -Wno-pmf-conversions @gol
201 -Wsign-promo}
202
203 @item Objective-C and Objective-C++ Language Options
204 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
205 Objective-C and Objective-C++ Dialects}.
206 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
207 -fgnu-runtime -fnext-runtime @gol
208 -fno-nil-receivers @gol
209 -fobjc-call-cxx-cdtors @gol
210 -fobjc-direct-dispatch @gol
211 -fobjc-exceptions @gol
212 -fobjc-gc @gol
213 -freplace-objc-classes @gol
214 -fzero-link @gol
215 -gen-decls @gol
216 -Wassign-intercept @gol
217 -Wno-protocol -Wselector @gol
218 -Wstrict-selector-match @gol
219 -Wundeclared-selector}
220
221 @item Language Independent Options
222 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
223 @gccoptlist{-fmessage-length=@var{n} @gol
224 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
225 -fdiagnostics-show-option}
226
227 @item Warning Options
228 @xref{Warning Options,,Options to Request or Suppress Warnings}.
229 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
230 -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
231 -Wno-attributes -Wno-builtin-macro-redefined @gol
232 -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
233 -Wchar-subscripts -Wclobbered -Wcomment @gol
234 -Wconversion -Wcoverage-mismatch -Wno-deprecated @gol
235 -Wno-deprecated-declarations -Wdisabled-optimization @gol
236 -Wno-div-by-zero -Wempty-body -Wenum-compare -Wno-endif-labels @gol
237 -Werror -Werror=* @gol
238 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
239 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol
240 -Wformat-security -Wformat-y2k @gol
241 -Wframe-larger-than=@var{len} -Wignored-qualifiers @gol
242 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
243 -Winit-self -Winline @gol
244 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
245 -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol
246 -Wlogical-op -Wlong-long @gol
247 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
248 -Wmissing-format-attribute -Wmissing-include-dirs @gol
249 -Wmissing-noreturn -Wno-mudflap @gol
250 -Wno-multichar -Wnonnull -Wno-overflow @gol
251 -Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded @gol
252 -Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
253 -Wpointer-arith -Wno-pointer-to-int-cast @gol
254 -Wredundant-decls @gol
255 -Wreturn-type -Wsequence-point -Wshadow @gol
256 -Wsign-compare -Wsign-conversion -Wstack-protector @gol
257 -Wstrict-aliasing -Wstrict-aliasing=n @gol
258 -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
259 -Wswitch -Wswitch-default -Wswitch-enum -Wsync-nand @gol
260 -Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized @gol
261 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
262 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
263 -Wunused-value -Wunused-variable @gol
264 -Wvariadic-macros -Wvla @gol
265 -Wvolatile-register-var -Wwrite-strings}
266
267 @item C and Objective-C-only Warning Options
268 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
269 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
270 -Wold-style-declaration -Wold-style-definition @gol
271 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
272 -Wdeclaration-after-statement -Wpointer-sign}
273
274 @item Debugging Options
275 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
276 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
277 -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
278 -fdump-noaddr -fdump-unnumbered @gol
279 -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
280 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
281 -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
282 -fdump-statistics @gol
283 -fdump-tree-all @gol
284 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
285 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
286 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
287 -fdump-tree-ch @gol
288 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
289 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
290 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
291 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
292 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
293 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
294 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
295 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
296 -fdump-tree-nrv -fdump-tree-vect @gol
297 -fdump-tree-sink @gol
298 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
299 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
300 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
301 -ftree-vectorizer-verbose=@var{n} @gol
302 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
303 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
304 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
305 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
306 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
307 -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
308 -ftest-coverage -ftime-report -fvar-tracking @gol
309 -g -g@var{level} -gcoff -gdwarf-2 @gol
310 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
311 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
312 -fdebug-prefix-map=@var{old}=@var{new} @gol
313 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
314 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
315 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
316 -print-multi-directory -print-multi-lib @gol
317 -print-prog-name=@var{program} -print-search-dirs -Q @gol
318 -print-sysroot -print-sysroot-headers-suffix @gol
319 -save-temps -time}
320
321 @item Optimization Options
322 @xref{Optimize Options,,Options that Control Optimization}.
323 @gccoptlist{
324 -falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol
325 -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
326 -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
327 -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
328 -fcheck-data-deps -fconserve-stack -fcprop-registers -fcrossjumping @gol
329 -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range @gol
330 -fdata-sections -fdce -fdce @gol
331 -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse @gol
332 -fearly-inlining -fexpensive-optimizations -ffast-math @gol
333 -ffinite-math-only -ffloat-store -fforward-propagate @gol
334 -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm @gol
335 -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining @gol
336 -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
337 -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-matrix-reorg -fipa-pta @gol
338 -fipa-pure-const -fipa-reference -fipa-struct-reorg @gol
339 -fipa-type-escape -fira-algorithm=@var{algorithm} @gol
340 -fira-region=@var{region} -fira-coalesce -fno-ira-share-save-slots @gol
341 -fno-ira-share-spill-slots -fira-verbose=@var{n} @gol
342 -fivopts -fkeep-inline-functions -fkeep-static-consts @gol
343 -floop-block -floop-interchange -floop-strip-mine @gol
344 -fmerge-all-constants -fmerge-constants -fmodulo-sched @gol
345 -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap @gol
346 -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline @gol
347 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
348 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
349 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
350 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
351 -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol
352 -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays @gol
353 -fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol
354 -fprofile-generate=@var{path} @gol
355 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
356 -freciprocal-math -fregmove -frename-registers -freorder-blocks @gol
357 -freorder-blocks-and-partition -freorder-functions @gol
358 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
359 -frounding-math -frtl-abstract-sequences -fsched2-use-superblocks @gol
360 -fsched2-use-traces -fsched-spec-load -fsched-spec-load-dangerous @gol
361 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
362 -fschedule-insns -fschedule-insns2 -fsection-anchors -fsee @gol
363 -fselective-scheduling -fselective-scheduling2 @gol
364 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
365 -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
366 -fsplit-wide-types -fstack-protector -fstack-protector-all @gol
367 -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
368 -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
369 -ftree-copyrename -ftree-dce @gol
370 -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im @gol
371 -ftree-loop-distribution @gol
372 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
373 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-reassoc @gol
374 -ftree-sink -ftree-sra -ftree-switch-conversion @gol
375 -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol
376 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
377 -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
378 -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol
379 -fwhole-program @gol
380 --param @var{name}=@var{value}
381 -O -O0 -O1 -O2 -O3 -Os}
382
383 @item Preprocessor Options
384 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
385 @gccoptlist{-A@var{question}=@var{answer} @gol
386 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
387 -C -dD -dI -dM -dN @gol
388 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
389 -idirafter @var{dir} @gol
390 -include @var{file} -imacros @var{file} @gol
391 -iprefix @var{file} -iwithprefix @var{dir} @gol
392 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
393 -imultilib @var{dir} -isysroot @var{dir} @gol
394 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
395 -P -fworking-directory -remap @gol
396 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
397 -Xpreprocessor @var{option}}
398
399 @item Assembler Option
400 @xref{Assembler Options,,Passing Options to the Assembler}.
401 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
402
403 @item Linker Options
404 @xref{Link Options,,Options for Linking}.
405 @gccoptlist{@var{object-file-name} -l@var{library} @gol
406 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
407 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
408 -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
409 -u @var{symbol}}
410
411 @item Directory Options
412 @xref{Directory Options,,Options for Directory Search}.
413 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
414 -specs=@var{file} -I- --sysroot=@var{dir}}
415
416 @item Target Options
417 @c I wrote this xref this way to avoid overfull hbox. -- rms
418 @xref{Target Options}.
419 @gccoptlist{-V @var{version} -b @var{machine}}
420
421 @item Machine Dependent Options
422 @xref{Submodel Options,,Hardware Models and Configurations}.
423 @c This list is ordered alphanumerically by subsection name.
424 @c Try and put the significant identifier (CPU or system) first,
425 @c so users have a clue at guessing where the ones they want will be.
426
427 @emph{ARC Options}
428 @gccoptlist{-EB -EL @gol
429 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
430 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
431
432 @emph{ARM Options}
433 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
434 -mabi=@var{name} @gol
435 -mapcs-stack-check -mno-apcs-stack-check @gol
436 -mapcs-float -mno-apcs-float @gol
437 -mapcs-reentrant -mno-apcs-reentrant @gol
438 -msched-prolog -mno-sched-prolog @gol
439 -mlittle-endian -mbig-endian -mwords-little-endian @gol
440 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
441 -mthumb-interwork -mno-thumb-interwork @gol
442 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
443 -mstructure-size-boundary=@var{n} @gol
444 -mabort-on-noreturn @gol
445 -mlong-calls -mno-long-calls @gol
446 -msingle-pic-base -mno-single-pic-base @gol
447 -mpic-register=@var{reg} @gol
448 -mnop-fun-dllimport @gol
449 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
450 -mpoke-function-name @gol
451 -mthumb -marm @gol
452 -mtpcs-frame -mtpcs-leaf-frame @gol
453 -mcaller-super-interworking -mcallee-super-interworking @gol
454 -mtp=@var{name} @gol
455 -mword-relocations @gol
456 -mfix-cortex-m3-ldrd}
457
458 @emph{AVR Options}
459 @gccoptlist{-mmcu=@var{mcu} -msize -mno-interrupts @gol
460 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
461
462 @emph{Blackfin Options}
463 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
464 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
465 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
466 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
467 -mno-id-shared-library -mshared-library-id=@var{n} @gol
468 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
469 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
470 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol
471 -micplb}
472
473 @emph{CRIS Options}
474 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
475 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
476 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
477 -mstack-align -mdata-align -mconst-align @gol
478 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
479 -melf -maout -melinux -mlinux -sim -sim2 @gol
480 -mmul-bug-workaround -mno-mul-bug-workaround}
481
482 @emph{CRX Options}
483 @gccoptlist{-mmac -mpush-args}
484
485 @emph{Darwin Options}
486 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
487 -arch_only -bind_at_load -bundle -bundle_loader @gol
488 -client_name -compatibility_version -current_version @gol
489 -dead_strip @gol
490 -dependency-file -dylib_file -dylinker_install_name @gol
491 -dynamic -dynamiclib -exported_symbols_list @gol
492 -filelist -flat_namespace -force_cpusubtype_ALL @gol
493 -force_flat_namespace -headerpad_max_install_names @gol
494 -iframework @gol
495 -image_base -init -install_name -keep_private_externs @gol
496 -multi_module -multiply_defined -multiply_defined_unused @gol
497 -noall_load -no_dead_strip_inits_and_terms @gol
498 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
499 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
500 -private_bundle -read_only_relocs -sectalign @gol
501 -sectobjectsymbols -whyload -seg1addr @gol
502 -sectcreate -sectobjectsymbols -sectorder @gol
503 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
504 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
505 -segprot -segs_read_only_addr -segs_read_write_addr @gol
506 -single_module -static -sub_library -sub_umbrella @gol
507 -twolevel_namespace -umbrella -undefined @gol
508 -unexported_symbols_list -weak_reference_mismatches @gol
509 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
510 -mkernel -mone-byte-bool}
511
512 @emph{DEC Alpha Options}
513 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
514 -mieee -mieee-with-inexact -mieee-conformant @gol
515 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
516 -mtrap-precision=@var{mode} -mbuild-constants @gol
517 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
518 -mbwx -mmax -mfix -mcix @gol
519 -mfloat-vax -mfloat-ieee @gol
520 -mexplicit-relocs -msmall-data -mlarge-data @gol
521 -msmall-text -mlarge-text @gol
522 -mmemory-latency=@var{time}}
523
524 @emph{DEC Alpha/VMS Options}
525 @gccoptlist{-mvms-return-codes}
526
527 @emph{FR30 Options}
528 @gccoptlist{-msmall-model -mno-lsim}
529
530 @emph{FRV Options}
531 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
532 -mhard-float -msoft-float @gol
533 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
534 -mdouble -mno-double @gol
535 -mmedia -mno-media -mmuladd -mno-muladd @gol
536 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
537 -mlinked-fp -mlong-calls -malign-labels @gol
538 -mlibrary-pic -macc-4 -macc-8 @gol
539 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
540 -moptimize-membar -mno-optimize-membar @gol
541 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
542 -mvliw-branch -mno-vliw-branch @gol
543 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
544 -mno-nested-cond-exec -mtomcat-stats @gol
545 -mTLS -mtls @gol
546 -mcpu=@var{cpu}}
547
548 @emph{GNU/Linux Options}
549 @gccoptlist{-muclibc}
550
551 @emph{H8/300 Options}
552 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
553
554 @emph{HPPA Options}
555 @gccoptlist{-march=@var{architecture-type} @gol
556 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
557 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
558 -mfixed-range=@var{register-range} @gol
559 -mjump-in-delay -mlinker-opt -mlong-calls @gol
560 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
561 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
562 -mno-jump-in-delay -mno-long-load-store @gol
563 -mno-portable-runtime -mno-soft-float @gol
564 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
565 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
566 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
567 -munix=@var{unix-std} -nolibdld -static -threads}
568
569 @emph{i386 and x86-64 Options}
570 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
571 -mfpmath=@var{unit} @gol
572 -masm=@var{dialect} -mno-fancy-math-387 @gol
573 -mno-fp-ret-in-387 -msoft-float @gol
574 -mno-wide-multiply -mrtd -malign-double @gol
575 -mpreferred-stack-boundary=@var{num}
576 -mincoming-stack-boundary=@var{num}
577 -mcld -mcx16 -msahf -mrecip @gol
578 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
579 -maes -mpclmul @gol
580 -msse4a -m3dnow -mpopcnt -mabm -msse5 @gol
581 -mthreads -mno-align-stringops -minline-all-stringops @gol
582 -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
583 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
584 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
585 -mveclibabi=@var{type} -mpc32 -mpc64 -mpc80 -mstackrealign @gol
586 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
587 -mcmodel=@var{code-model} @gol
588 -m32 -m64 -mlarge-data-threshold=@var{num} @gol
589 -mfused-madd -mno-fused-madd -msse2avx}
590
591 @emph{IA-64 Options}
592 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
593 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
594 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
595 -minline-float-divide-max-throughput @gol
596 -minline-int-divide-min-latency @gol
597 -minline-int-divide-max-throughput @gol
598 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
599 -mno-dwarf2-asm -mearly-stop-bits @gol
600 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
601 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64 @gol
602 -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec @gol
603 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
604 -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose @gol
605 -mno-sched-prefer-non-data-spec-insns @gol
606 -mno-sched-prefer-non-control-spec-insns @gol
607 -mno-sched-count-spec-in-critical-path}
608
609 @emph{M32R/D Options}
610 @gccoptlist{-m32r2 -m32rx -m32r @gol
611 -mdebug @gol
612 -malign-loops -mno-align-loops @gol
613 -missue-rate=@var{number} @gol
614 -mbranch-cost=@var{number} @gol
615 -mmodel=@var{code-size-model-type} @gol
616 -msdata=@var{sdata-type} @gol
617 -mno-flush-func -mflush-func=@var{name} @gol
618 -mno-flush-trap -mflush-trap=@var{number} @gol
619 -G @var{num}}
620
621 @emph{M32C Options}
622 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
623
624 @emph{M680x0 Options}
625 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune}
626 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
627 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
628 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
629 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
630 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
631 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
632 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
633 -mxgot -mno-xgot}
634
635 @emph{M68hc1x Options}
636 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
637 -mauto-incdec -minmax -mlong-calls -mshort @gol
638 -msoft-reg-count=@var{count}}
639
640 @emph{MCore Options}
641 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
642 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
643 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
644 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
645 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
646
647 @emph{MIPS Options}
648 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
649 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol
650 -mips64 -mips64r2 @gol
651 -mips16 -mno-mips16 -mflip-mips16 @gol
652 -minterlink-mips16 -mno-interlink-mips16 @gol
653 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
654 -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
655 -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol
656 -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
657 -mfpu=@var{fpu-type} @gol
658 -msmartmips -mno-smartmips @gol
659 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
660 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
661 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
662 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
663 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
664 -membedded-data -mno-embedded-data @gol
665 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
666 -mcode-readable=@var{setting} @gol
667 -msplit-addresses -mno-split-addresses @gol
668 -mexplicit-relocs -mno-explicit-relocs @gol
669 -mcheck-zero-division -mno-check-zero-division @gol
670 -mdivide-traps -mdivide-breaks @gol
671 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
672 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
673 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
674 -mfix-r10000 -mno-fix-r10000 -mfix-vr4120 -mno-fix-vr4120 @gol
675 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol
676 -mflush-func=@var{func} -mno-flush-func @gol
677 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
678 -mfp-exceptions -mno-fp-exceptions @gol
679 -mvr4130-align -mno-vr4130-align}
680
681 @emph{MMIX Options}
682 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
683 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
684 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
685 -mno-base-addresses -msingle-exit -mno-single-exit}
686
687 @emph{MN10300 Options}
688 @gccoptlist{-mmult-bug -mno-mult-bug @gol
689 -mam33 -mno-am33 @gol
690 -mam33-2 -mno-am33-2 @gol
691 -mreturn-pointer-on-d0 @gol
692 -mno-crt0 -mrelax}
693
694 @emph{PDP-11 Options}
695 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
696 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
697 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
698 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
699 -mbranch-expensive -mbranch-cheap @gol
700 -msplit -mno-split -munix-asm -mdec-asm}
701
702 @emph{picoChip Options}
703 @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N}
704 -msymbol-as-address -mno-inefficient-warnings}
705
706 @emph{PowerPC Options}
707 See RS/6000 and PowerPC Options.
708
709 @emph{RS/6000 and PowerPC Options}
710 @gccoptlist{-mcpu=@var{cpu-type} @gol
711 -mtune=@var{cpu-type} @gol
712 -mpower -mno-power -mpower2 -mno-power2 @gol
713 -mpowerpc -mpowerpc64 -mno-powerpc @gol
714 -maltivec -mno-altivec @gol
715 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
716 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
717 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
718 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
719 -mnew-mnemonics -mold-mnemonics @gol
720 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
721 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
722 -malign-power -malign-natural @gol
723 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
724 -msingle-float -mdouble-float -msimple-fpu @gol
725 -mstring -mno-string -mupdate -mno-update @gol
726 -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol
727 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
728 -mstrict-align -mno-strict-align -mrelocatable @gol
729 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
730 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
731 -mdynamic-no-pic -maltivec -mswdiv @gol
732 -mprioritize-restricted-insns=@var{priority} @gol
733 -msched-costly-dep=@var{dependence_type} @gol
734 -minsert-sched-nops=@var{scheme} @gol
735 -mcall-sysv -mcall-netbsd @gol
736 -maix-struct-return -msvr4-struct-return @gol
737 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
738 -misel -mno-isel @gol
739 -misel=yes -misel=no @gol
740 -mspe -mno-spe @gol
741 -mspe=yes -mspe=no @gol
742 -mpaired @gol
743 -mgen-cell-microcode -mwarn-cell-microcode @gol
744 -mvrsave -mno-vrsave @gol
745 -mmulhw -mno-mulhw @gol
746 -mdlmzb -mno-dlmzb @gol
747 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
748 -mprototype -mno-prototype @gol
749 -msim -mmvme -mads -myellowknife -memb -msdata @gol
750 -msdata=@var{opt} -mvxworks -G @var{num} -pthread}
751
752 @emph{S/390 and zSeries Options}
753 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
754 -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
755 -mlong-double-64 -mlong-double-128 @gol
756 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
757 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
758 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
759 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
760 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
761
762 @emph{Score Options}
763 @gccoptlist{-meb -mel @gol
764 -mnhwloop @gol
765 -muls @gol
766 -mmac @gol
767 -mscore5 -mscore5u -mscore7 -mscore7d}
768
769 @emph{SH Options}
770 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
771 -m4-nofpu -m4-single-only -m4-single -m4 @gol
772 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
773 -m5-64media -m5-64media-nofpu @gol
774 -m5-32media -m5-32media-nofpu @gol
775 -m5-compact -m5-compact-nofpu @gol
776 -mb -ml -mdalign -mrelax @gol
777 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
778 -mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
779 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
780 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
781 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
782 -minvalid-symbols}
783
784 @emph{SPARC Options}
785 @gccoptlist{-mcpu=@var{cpu-type} @gol
786 -mtune=@var{cpu-type} @gol
787 -mcmodel=@var{code-model} @gol
788 -m32 -m64 -mapp-regs -mno-app-regs @gol
789 -mfaster-structs -mno-faster-structs @gol
790 -mfpu -mno-fpu -mhard-float -msoft-float @gol
791 -mhard-quad-float -msoft-quad-float @gol
792 -mimpure-text -mno-impure-text @gol
793 -mno-integer-ldd-std -mlittle-endian @gol
794 -mstack-bias -mno-stack-bias @gol
795 -munaligned-doubles -mno-unaligned-doubles @gol
796 -mv8plus -mno-v8plus -mvis -mno-vis
797 -threads -pthreads -pthread}
798
799 @emph{SPU Options}
800 @gccoptlist{-mwarn-reloc -merror-reloc @gol
801 -msafe-dma -munsafe-dma @gol
802 -mbranch-hints @gol
803 -msmall-mem -mlarge-mem -mstdmain @gol
804 -mfixed-range=@var{register-range}}
805
806 @emph{System V Options}
807 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
808
809 @emph{V850 Options}
810 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
811 -mprolog-function -mno-prolog-function -mspace @gol
812 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
813 -mapp-regs -mno-app-regs @gol
814 -mdisable-callt -mno-disable-callt @gol
815 -mv850e1 @gol
816 -mv850e @gol
817 -mv850 -mbig-switch}
818
819 @emph{VAX Options}
820 @gccoptlist{-mg -mgnu -munix}
821
822 @emph{VxWorks Options}
823 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
824 -Xbind-lazy -Xbind-now}
825
826 @emph{x86-64 Options}
827 See i386 and x86-64 Options.
828
829 @emph{i386 and x86-64 Windows Options}
830 @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll
831 -mnop-fun-dllimport -mthread -mwin32 -mwindows}
832
833 @emph{Xstormy16 Options}
834 @gccoptlist{-msim}
835
836 @emph{Xtensa Options}
837 @gccoptlist{-mconst16 -mno-const16 @gol
838 -mfused-madd -mno-fused-madd @gol
839 -mserialize-volatile -mno-serialize-volatile @gol
840 -mtext-section-literals -mno-text-section-literals @gol
841 -mtarget-align -mno-target-align @gol
842 -mlongcalls -mno-longcalls}
843
844 @emph{zSeries Options}
845 See S/390 and zSeries Options.
846
847 @item Code Generation Options
848 @xref{Code Gen Options,,Options for Code Generation Conventions}.
849 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
850 -ffixed-@var{reg} -fexceptions @gol
851 -fnon-call-exceptions -funwind-tables @gol
852 -fasynchronous-unwind-tables @gol
853 -finhibit-size-directive -finstrument-functions @gol
854 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
855 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
856 -fno-common -fno-ident @gol
857 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
858 -fno-jump-tables @gol
859 -frecord-gcc-switches @gol
860 -freg-struct-return -fshort-enums @gol
861 -fshort-double -fshort-wchar @gol
862 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
863 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
864 -fno-stack-limit -fargument-alias -fargument-noalias @gol
865 -fargument-noalias-global -fargument-noalias-anything @gol
866 -fleading-underscore -ftls-model=@var{model} @gol
867 -ftrapv -fwrapv -fbounds-check @gol
868 -fvisibility}
869 @end table
870
871 @menu
872 * Overall Options:: Controlling the kind of output:
873 an executable, object files, assembler files,
874 or preprocessed source.
875 * C Dialect Options:: Controlling the variant of C language compiled.
876 * C++ Dialect Options:: Variations on C++.
877 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
878 and Objective-C++.
879 * Language Independent Options:: Controlling how diagnostics should be
880 formatted.
881 * Warning Options:: How picky should the compiler be?
882 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
883 * Optimize Options:: How much optimization?
884 * Preprocessor Options:: Controlling header files and macro definitions.
885 Also, getting dependency information for Make.
886 * Assembler Options:: Passing options to the assembler.
887 * Link Options:: Specifying libraries and so on.
888 * Directory Options:: Where to find header files and libraries.
889 Where to find the compiler executable files.
890 * Spec Files:: How to pass switches to sub-processes.
891 * Target Options:: Running a cross-compiler, or an old version of GCC.
892 @end menu
893
894 @node Overall Options
895 @section Options Controlling the Kind of Output
896
897 Compilation can involve up to four stages: preprocessing, compilation
898 proper, assembly and linking, always in that order. GCC is capable of
899 preprocessing and compiling several files either into several
900 assembler input files, or into one assembler input file; then each
901 assembler input file produces an object file, and linking combines all
902 the object files (those newly compiled, and those specified as input)
903 into an executable file.
904
905 @cindex file name suffix
906 For any given input file, the file name suffix determines what kind of
907 compilation is done:
908
909 @table @gcctabopt
910 @item @var{file}.c
911 C source code which must be preprocessed.
912
913 @item @var{file}.i
914 C source code which should not be preprocessed.
915
916 @item @var{file}.ii
917 C++ source code which should not be preprocessed.
918
919 @item @var{file}.m
920 Objective-C source code. Note that you must link with the @file{libobjc}
921 library to make an Objective-C program work.
922
923 @item @var{file}.mi
924 Objective-C source code which should not be preprocessed.
925
926 @item @var{file}.mm
927 @itemx @var{file}.M
928 Objective-C++ source code. Note that you must link with the @file{libobjc}
929 library to make an Objective-C++ program work. Note that @samp{.M} refers
930 to a literal capital M@.
931
932 @item @var{file}.mii
933 Objective-C++ source code which should not be preprocessed.
934
935 @item @var{file}.h
936 C, C++, Objective-C or Objective-C++ header file to be turned into a
937 precompiled header.
938
939 @item @var{file}.cc
940 @itemx @var{file}.cp
941 @itemx @var{file}.cxx
942 @itemx @var{file}.cpp
943 @itemx @var{file}.CPP
944 @itemx @var{file}.c++
945 @itemx @var{file}.C
946 C++ source code which must be preprocessed. Note that in @samp{.cxx},
947 the last two letters must both be literally @samp{x}. Likewise,
948 @samp{.C} refers to a literal capital C@.
949
950 @item @var{file}.mm
951 @itemx @var{file}.M
952 Objective-C++ source code which must be preprocessed.
953
954 @item @var{file}.mii
955 Objective-C++ source code which should not be preprocessed.
956
957 @item @var{file}.hh
958 @itemx @var{file}.H
959 @itemx @var{file}.hp
960 @itemx @var{file}.hxx
961 @itemx @var{file}.hpp
962 @itemx @var{file}.HPP
963 @itemx @var{file}.h++
964 @itemx @var{file}.tcc
965 C++ header file to be turned into a precompiled header.
966
967 @item @var{file}.f
968 @itemx @var{file}.for
969 @itemx @var{file}.ftn
970 Fixed form Fortran source code which should not be preprocessed.
971
972 @item @var{file}.F
973 @itemx @var{file}.FOR
974 @itemx @var{file}.fpp
975 @itemx @var{file}.FPP
976 @itemx @var{file}.FTN
977 Fixed form Fortran source code which must be preprocessed (with the traditional
978 preprocessor).
979
980 @item @var{file}.f90
981 @itemx @var{file}.f95
982 @itemx @var{file}.f03
983 @itemx @var{file}.f08
984 Free form Fortran source code which should not be preprocessed.
985
986 @item @var{file}.F90
987 @itemx @var{file}.F95
988 @itemx @var{file}.F03
989 @itemx @var{file}.F08
990 Free form Fortran source code which must be preprocessed (with the
991 traditional preprocessor).
992
993 @c FIXME: Descriptions of Java file types.
994 @c @var{file}.java
995 @c @var{file}.class
996 @c @var{file}.zip
997 @c @var{file}.jar
998
999 @item @var{file}.ads
1000 Ada source code file which contains a library unit declaration (a
1001 declaration of a package, subprogram, or generic, or a generic
1002 instantiation), or a library unit renaming declaration (a package,
1003 generic, or subprogram renaming declaration). Such files are also
1004 called @dfn{specs}.
1005
1006 @item @var{file}.adb
1007 Ada source code file containing a library unit body (a subprogram or
1008 package body). Such files are also called @dfn{bodies}.
1009
1010 @c GCC also knows about some suffixes for languages not yet included:
1011 @c Pascal:
1012 @c @var{file}.p
1013 @c @var{file}.pas
1014 @c Ratfor:
1015 @c @var{file}.r
1016
1017 @item @var{file}.s
1018 Assembler code.
1019
1020 @item @var{file}.S
1021 @itemx @var{file}.sx
1022 Assembler code which must be preprocessed.
1023
1024 @item @var{other}
1025 An object file to be fed straight into linking.
1026 Any file name with no recognized suffix is treated this way.
1027 @end table
1028
1029 @opindex x
1030 You can specify the input language explicitly with the @option{-x} option:
1031
1032 @table @gcctabopt
1033 @item -x @var{language}
1034 Specify explicitly the @var{language} for the following input files
1035 (rather than letting the compiler choose a default based on the file
1036 name suffix). This option applies to all following input files until
1037 the next @option{-x} option. Possible values for @var{language} are:
1038 @smallexample
1039 c c-header c-cpp-output
1040 c++ c++-header c++-cpp-output
1041 objective-c objective-c-header objective-c-cpp-output
1042 objective-c++ objective-c++-header objective-c++-cpp-output
1043 assembler assembler-with-cpp
1044 ada
1045 f77 f77-cpp-input f95 f95-cpp-input
1046 java
1047 @end smallexample
1048
1049 @item -x none
1050 Turn off any specification of a language, so that subsequent files are
1051 handled according to their file name suffixes (as they are if @option{-x}
1052 has not been used at all).
1053
1054 @item -pass-exit-codes
1055 @opindex pass-exit-codes
1056 Normally the @command{gcc} program will exit with the code of 1 if any
1057 phase of the compiler returns a non-success return code. If you specify
1058 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1059 numerically highest error produced by any phase that returned an error
1060 indication. The C, C++, and Fortran frontends return 4, if an internal
1061 compiler error is encountered.
1062 @end table
1063
1064 If you only want some of the stages of compilation, you can use
1065 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1066 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1067 @command{gcc} is to stop. Note that some combinations (for example,
1068 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1069
1070 @table @gcctabopt
1071 @item -c
1072 @opindex c
1073 Compile or assemble the source files, but do not link. The linking
1074 stage simply is not done. The ultimate output is in the form of an
1075 object file for each source file.
1076
1077 By default, the object file name for a source file is made by replacing
1078 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1079
1080 Unrecognized input files, not requiring compilation or assembly, are
1081 ignored.
1082
1083 @item -S
1084 @opindex S
1085 Stop after the stage of compilation proper; do not assemble. The output
1086 is in the form of an assembler code file for each non-assembler input
1087 file specified.
1088
1089 By default, the assembler file name for a source file is made by
1090 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1091
1092 Input files that don't require compilation are ignored.
1093
1094 @item -E
1095 @opindex E
1096 Stop after the preprocessing stage; do not run the compiler proper. The
1097 output is in the form of preprocessed source code, which is sent to the
1098 standard output.
1099
1100 Input files which don't require preprocessing are ignored.
1101
1102 @cindex output file option
1103 @item -o @var{file}
1104 @opindex o
1105 Place output in file @var{file}. This applies regardless to whatever
1106 sort of output is being produced, whether it be an executable file,
1107 an object file, an assembler file or preprocessed C code.
1108
1109 If @option{-o} is not specified, the default is to put an executable
1110 file in @file{a.out}, the object file for
1111 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1112 assembler file in @file{@var{source}.s}, a precompiled header file in
1113 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1114 standard output.
1115
1116 @item -v
1117 @opindex v
1118 Print (on standard error output) the commands executed to run the stages
1119 of compilation. Also print the version number of the compiler driver
1120 program and of the preprocessor and the compiler proper.
1121
1122 @item -###
1123 @opindex ###
1124 Like @option{-v} except the commands are not executed and all command
1125 arguments are quoted. This is useful for shell scripts to capture the
1126 driver-generated command lines.
1127
1128 @item -pipe
1129 @opindex pipe
1130 Use pipes rather than temporary files for communication between the
1131 various stages of compilation. This fails to work on some systems where
1132 the assembler is unable to read from a pipe; but the GNU assembler has
1133 no trouble.
1134
1135 @item -combine
1136 @opindex combine
1137 If you are compiling multiple source files, this option tells the driver
1138 to pass all the source files to the compiler at once (for those
1139 languages for which the compiler can handle this). This will allow
1140 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1141 language for which this is supported is C@. If you pass source files for
1142 multiple languages to the driver, using this option, the driver will invoke
1143 the compiler(s) that support IMA once each, passing each compiler all the
1144 source files appropriate for it. For those languages that do not support
1145 IMA this option will be ignored, and the compiler will be invoked once for
1146 each source file in that language. If you use this option in conjunction
1147 with @option{-save-temps}, the compiler will generate multiple
1148 pre-processed files
1149 (one for each source file), but only one (combined) @file{.o} or
1150 @file{.s} file.
1151
1152 @item --help
1153 @opindex help
1154 Print (on the standard output) a description of the command line options
1155 understood by @command{gcc}. If the @option{-v} option is also specified
1156 then @option{--help} will also be passed on to the various processes
1157 invoked by @command{gcc}, so that they can display the command line options
1158 they accept. If the @option{-Wextra} option has also been specified
1159 (prior to the @option{--help} option), then command line options which
1160 have no documentation associated with them will also be displayed.
1161
1162 @item --target-help
1163 @opindex target-help
1164 Print (on the standard output) a description of target-specific command
1165 line options for each tool. For some targets extra target-specific
1166 information may also be printed.
1167
1168 @item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]}
1169 Print (on the standard output) a description of the command line
1170 options understood by the compiler that fit into all specified classes
1171 and qualifiers. These are the supported classes:
1172
1173 @table @asis
1174 @item @samp{optimizers}
1175 This will display all of the optimization options supported by the
1176 compiler.
1177
1178 @item @samp{warnings}
1179 This will display all of the options controlling warning messages
1180 produced by the compiler.
1181
1182 @item @samp{target}
1183 This will display target-specific options. Unlike the
1184 @option{--target-help} option however, target-specific options of the
1185 linker and assembler will not be displayed. This is because those
1186 tools do not currently support the extended @option{--help=} syntax.
1187
1188 @item @samp{params}
1189 This will display the values recognized by the @option{--param}
1190 option.
1191
1192 @item @var{language}
1193 This will display the options supported for @var{language}, where
1194 @var{language} is the name of one of the languages supported in this
1195 version of GCC.
1196
1197 @item @samp{common}
1198 This will display the options that are common to all languages.
1199 @end table
1200
1201 These are the supported qualifiers:
1202
1203 @table @asis
1204 @item @samp{undocumented}
1205 Display only those options which are undocumented.
1206
1207 @item @samp{joined}
1208 Display options which take an argument that appears after an equal
1209 sign in the same continuous piece of text, such as:
1210 @samp{--help=target}.
1211
1212 @item @samp{separate}
1213 Display options which take an argument that appears as a separate word
1214 following the original option, such as: @samp{-o output-file}.
1215 @end table
1216
1217 Thus for example to display all the undocumented target-specific
1218 switches supported by the compiler the following can be used:
1219
1220 @smallexample
1221 --help=target,undocumented
1222 @end smallexample
1223
1224 The sense of a qualifier can be inverted by prefixing it with the
1225 @samp{^} character, so for example to display all binary warning
1226 options (i.e., ones that are either on or off and that do not take an
1227 argument), which have a description the following can be used:
1228
1229 @smallexample
1230 --help=warnings,^joined,^undocumented
1231 @end smallexample
1232
1233 The argument to @option{--help=} should not consist solely of inverted
1234 qualifiers.
1235
1236 Combining several classes is possible, although this usually
1237 restricts the output by so much that there is nothing to display. One
1238 case where it does work however is when one of the classes is
1239 @var{target}. So for example to display all the target-specific
1240 optimization options the following can be used:
1241
1242 @smallexample
1243 --help=target,optimizers
1244 @end smallexample
1245
1246 The @option{--help=} option can be repeated on the command line. Each
1247 successive use will display its requested class of options, skipping
1248 those that have already been displayed.
1249
1250 If the @option{-Q} option appears on the command line before the
1251 @option{--help=} option, then the descriptive text displayed by
1252 @option{--help=} is changed. Instead of describing the displayed
1253 options, an indication is given as to whether the option is enabled,
1254 disabled or set to a specific value (assuming that the compiler
1255 knows this at the point where the @option{--help=} option is used).
1256
1257 Here is a truncated example from the ARM port of @command{gcc}:
1258
1259 @smallexample
1260 % gcc -Q -mabi=2 --help=target -c
1261 The following options are target specific:
1262 -mabi= 2
1263 -mabort-on-noreturn [disabled]
1264 -mapcs [disabled]
1265 @end smallexample
1266
1267 The output is sensitive to the effects of previous command line
1268 options, so for example it is possible to find out which optimizations
1269 are enabled at @option{-O2} by using:
1270
1271 @smallexample
1272 -Q -O2 --help=optimizers
1273 @end smallexample
1274
1275 Alternatively you can discover which binary optimizations are enabled
1276 by @option{-O3} by using:
1277
1278 @smallexample
1279 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1280 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1281 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1282 @end smallexample
1283
1284 @item --version
1285 @opindex version
1286 Display the version number and copyrights of the invoked GCC@.
1287
1288 @item -wrapper
1289 @opindex wrapper
1290 Invoke all subcommands under a wrapper program. It takes a single
1291 comma separated list as an argument, which will be used to invoke
1292 the wrapper:
1293
1294 @smallexample
1295 gcc -c t.c -wrapper gdb,--args
1296 @end smallexample
1297
1298 This will invoke all subprograms of gcc under "gdb --args",
1299 thus cc1 invocation will be "gdb --args cc1 ...".
1300
1301 @include @value{srcdir}/../libiberty/at-file.texi
1302 @end table
1303
1304 @node Invoking G++
1305 @section Compiling C++ Programs
1306
1307 @cindex suffixes for C++ source
1308 @cindex C++ source file suffixes
1309 C++ source files conventionally use one of the suffixes @samp{.C},
1310 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1311 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1312 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1313 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1314 files with these names and compiles them as C++ programs even if you
1315 call the compiler the same way as for compiling C programs (usually
1316 with the name @command{gcc}).
1317
1318 @findex g++
1319 @findex c++
1320 However, the use of @command{gcc} does not add the C++ library.
1321 @command{g++} is a program that calls GCC and treats @samp{.c},
1322 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1323 files unless @option{-x} is used, and automatically specifies linking
1324 against the C++ library. This program is also useful when
1325 precompiling a C header file with a @samp{.h} extension for use in C++
1326 compilations. On many systems, @command{g++} is also installed with
1327 the name @command{c++}.
1328
1329 @cindex invoking @command{g++}
1330 When you compile C++ programs, you may specify many of the same
1331 command-line options that you use for compiling programs in any
1332 language; or command-line options meaningful for C and related
1333 languages; or options that are meaningful only for C++ programs.
1334 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1335 explanations of options for languages related to C@.
1336 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1337 explanations of options that are meaningful only for C++ programs.
1338
1339 @node C Dialect Options
1340 @section Options Controlling C Dialect
1341 @cindex dialect options
1342 @cindex language dialect options
1343 @cindex options, dialect
1344
1345 The following options control the dialect of C (or languages derived
1346 from C, such as C++, Objective-C and Objective-C++) that the compiler
1347 accepts:
1348
1349 @table @gcctabopt
1350 @cindex ANSI support
1351 @cindex ISO support
1352 @item -ansi
1353 @opindex ansi
1354 In C mode, this is equivalent to @samp{-std=c89}. In C++ mode, it is
1355 equivalent to @samp{-std=c++98}.
1356
1357 This turns off certain features of GCC that are incompatible with ISO
1358 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1359 such as the @code{asm} and @code{typeof} keywords, and
1360 predefined macros such as @code{unix} and @code{vax} that identify the
1361 type of system you are using. It also enables the undesirable and
1362 rarely used ISO trigraph feature. For the C compiler,
1363 it disables recognition of C++ style @samp{//} comments as well as
1364 the @code{inline} keyword.
1365
1366 The alternate keywords @code{__asm__}, @code{__extension__},
1367 @code{__inline__} and @code{__typeof__} continue to work despite
1368 @option{-ansi}. You would not want to use them in an ISO C program, of
1369 course, but it is useful to put them in header files that might be included
1370 in compilations done with @option{-ansi}. Alternate predefined macros
1371 such as @code{__unix__} and @code{__vax__} are also available, with or
1372 without @option{-ansi}.
1373
1374 The @option{-ansi} option does not cause non-ISO programs to be
1375 rejected gratuitously. For that, @option{-pedantic} is required in
1376 addition to @option{-ansi}. @xref{Warning Options}.
1377
1378 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1379 option is used. Some header files may notice this macro and refrain
1380 from declaring certain functions or defining certain macros that the
1381 ISO standard doesn't call for; this is to avoid interfering with any
1382 programs that might use these names for other things.
1383
1384 Functions that would normally be built in but do not have semantics
1385 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1386 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1387 built-in functions provided by GCC}, for details of the functions
1388 affected.
1389
1390 @item -std=
1391 @opindex std
1392 Determine the language standard. @xref{Standards,,Language Standards
1393 Supported by GCC}, for details of these standard versions. This option
1394 is currently only supported when compiling C or C++.
1395
1396 The compiler can accept several base standards, such as @samp{c89} or
1397 @samp{c++98}, and GNU dialects of those standards, such as
1398 @samp{gnu89} or @samp{gnu++98}. By specifying a base standard, the
1399 compiler will accept all programs following that standard and those
1400 using GNU extensions that do not contradict it. For example,
1401 @samp{-std=c89} turns off certain features of GCC that are
1402 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1403 keywords, but not other GNU extensions that do not have a meaning in
1404 ISO C90, such as omitting the middle term of a @code{?:}
1405 expression. On the other hand, by specifying a GNU dialect of a
1406 standard, all features the compiler support are enabled, even when
1407 those features change the meaning of the base standard and some
1408 strict-conforming programs may be rejected. The particular standard
1409 is used by @option{-pedantic} to identify which features are GNU
1410 extensions given that version of the standard. For example
1411 @samp{-std=gnu89 -pedantic} would warn about C++ style @samp{//}
1412 comments, while @samp{-std=gnu99 -pedantic} would not.
1413
1414 A value for this option must be provided; possible values are
1415
1416 @table @samp
1417 @item c89
1418 @itemx iso9899:1990
1419 Support all ISO C90 programs (certain GNU extensions that conflict
1420 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1421
1422 @item iso9899:199409
1423 ISO C90 as modified in amendment 1.
1424
1425 @item c99
1426 @itemx c9x
1427 @itemx iso9899:1999
1428 @itemx iso9899:199x
1429 ISO C99. Note that this standard is not yet fully supported; see
1430 @w{@uref{http://gcc.gnu.org/gcc-4.4/c99status.html}} for more information. The
1431 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1432
1433 @item gnu89
1434 GNU dialect of ISO C90 (including some C99 features). This
1435 is the default for C code.
1436
1437 @item gnu99
1438 @itemx gnu9x
1439 GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC,
1440 this will become the default. The name @samp{gnu9x} is deprecated.
1441
1442 @item c++98
1443 The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
1444 C++ code.
1445
1446 @item gnu++98
1447 GNU dialect of @option{-std=c++98}. This is the default for
1448 C++ code.
1449
1450 @item c++0x
1451 The working draft of the upcoming ISO C++0x standard. This option
1452 enables experimental features that are likely to be included in
1453 C++0x. The working draft is constantly changing, and any feature that is
1454 enabled by this flag may be removed from future versions of GCC if it is
1455 not part of the C++0x standard.
1456
1457 @item gnu++0x
1458 GNU dialect of @option{-std=c++0x}. This option enables
1459 experimental features that may be removed in future versions of GCC.
1460 @end table
1461
1462 @item -fgnu89-inline
1463 @opindex fgnu89-inline
1464 The option @option{-fgnu89-inline} tells GCC to use the traditional
1465 GNU semantics for @code{inline} functions when in C99 mode.
1466 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1467 is accepted and ignored by GCC versions 4.1.3 up to but not including
1468 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1469 C99 mode. Using this option is roughly equivalent to adding the
1470 @code{gnu_inline} function attribute to all inline functions
1471 (@pxref{Function Attributes}).
1472
1473 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1474 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1475 specifies the default behavior). This option was first supported in
1476 GCC 4.3. This option is not supported in C89 or gnu89 mode.
1477
1478 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1479 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1480 in effect for @code{inline} functions. @xref{Common Predefined
1481 Macros,,,cpp,The C Preprocessor}.
1482
1483 @item -aux-info @var{filename}
1484 @opindex aux-info
1485 Output to the given filename prototyped declarations for all functions
1486 declared and/or defined in a translation unit, including those in header
1487 files. This option is silently ignored in any language other than C@.
1488
1489 Besides declarations, the file indicates, in comments, the origin of
1490 each declaration (source file and line), whether the declaration was
1491 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1492 @samp{O} for old, respectively, in the first character after the line
1493 number and the colon), and whether it came from a declaration or a
1494 definition (@samp{C} or @samp{F}, respectively, in the following
1495 character). In the case of function definitions, a K&R-style list of
1496 arguments followed by their declarations is also provided, inside
1497 comments, after the declaration.
1498
1499 @item -fno-asm
1500 @opindex fno-asm
1501 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1502 keyword, so that code can use these words as identifiers. You can use
1503 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1504 instead. @option{-ansi} implies @option{-fno-asm}.
1505
1506 In C++, this switch only affects the @code{typeof} keyword, since
1507 @code{asm} and @code{inline} are standard keywords. You may want to
1508 use the @option{-fno-gnu-keywords} flag instead, which has the same
1509 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1510 switch only affects the @code{asm} and @code{typeof} keywords, since
1511 @code{inline} is a standard keyword in ISO C99.
1512
1513 @item -fno-builtin
1514 @itemx -fno-builtin-@var{function}
1515 @opindex fno-builtin
1516 @cindex built-in functions
1517 Don't recognize built-in functions that do not begin with
1518 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1519 functions provided by GCC}, for details of the functions affected,
1520 including those which are not built-in functions when @option{-ansi} or
1521 @option{-std} options for strict ISO C conformance are used because they
1522 do not have an ISO standard meaning.
1523
1524 GCC normally generates special code to handle certain built-in functions
1525 more efficiently; for instance, calls to @code{alloca} may become single
1526 instructions that adjust the stack directly, and calls to @code{memcpy}
1527 may become inline copy loops. The resulting code is often both smaller
1528 and faster, but since the function calls no longer appear as such, you
1529 cannot set a breakpoint on those calls, nor can you change the behavior
1530 of the functions by linking with a different library. In addition,
1531 when a function is recognized as a built-in function, GCC may use
1532 information about that function to warn about problems with calls to
1533 that function, or to generate more efficient code, even if the
1534 resulting code still contains calls to that function. For example,
1535 warnings are given with @option{-Wformat} for bad calls to
1536 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1537 known not to modify global memory.
1538
1539 With the @option{-fno-builtin-@var{function}} option
1540 only the built-in function @var{function} is
1541 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1542 function is named that is not built-in in this version of GCC, this
1543 option is ignored. There is no corresponding
1544 @option{-fbuiltin-@var{function}} option; if you wish to enable
1545 built-in functions selectively when using @option{-fno-builtin} or
1546 @option{-ffreestanding}, you may define macros such as:
1547
1548 @smallexample
1549 #define abs(n) __builtin_abs ((n))
1550 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1551 @end smallexample
1552
1553 @item -fhosted
1554 @opindex fhosted
1555 @cindex hosted environment
1556
1557 Assert that compilation takes place in a hosted environment. This implies
1558 @option{-fbuiltin}. A hosted environment is one in which the
1559 entire standard library is available, and in which @code{main} has a return
1560 type of @code{int}. Examples are nearly everything except a kernel.
1561 This is equivalent to @option{-fno-freestanding}.
1562
1563 @item -ffreestanding
1564 @opindex ffreestanding
1565 @cindex hosted environment
1566
1567 Assert that compilation takes place in a freestanding environment. This
1568 implies @option{-fno-builtin}. A freestanding environment
1569 is one in which the standard library may not exist, and program startup may
1570 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1571 This is equivalent to @option{-fno-hosted}.
1572
1573 @xref{Standards,,Language Standards Supported by GCC}, for details of
1574 freestanding and hosted environments.
1575
1576 @item -fopenmp
1577 @opindex fopenmp
1578 @cindex openmp parallel
1579 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1580 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1581 compiler generates parallel code according to the OpenMP Application
1582 Program Interface v2.5 @w{@uref{http://www.openmp.org/}}. This option
1583 implies @option{-pthread}, and thus is only supported on targets that
1584 have support for @option{-pthread}.
1585
1586 @item -fms-extensions
1587 @opindex fms-extensions
1588 Accept some non-standard constructs used in Microsoft header files.
1589
1590 Some cases of unnamed fields in structures and unions are only
1591 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1592 fields within structs/unions}, for details.
1593
1594 @item -trigraphs
1595 @opindex trigraphs
1596 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1597 options for strict ISO C conformance) implies @option{-trigraphs}.
1598
1599 @item -no-integrated-cpp
1600 @opindex no-integrated-cpp
1601 Performs a compilation in two passes: preprocessing and compiling. This
1602 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1603 @option{-B} option. The user supplied compilation step can then add in
1604 an additional preprocessing step after normal preprocessing but before
1605 compiling. The default is to use the integrated cpp (internal cpp)
1606
1607 The semantics of this option will change if "cc1", "cc1plus", and
1608 "cc1obj" are merged.
1609
1610 @cindex traditional C language
1611 @cindex C language, traditional
1612 @item -traditional
1613 @itemx -traditional-cpp
1614 @opindex traditional-cpp
1615 @opindex traditional
1616 Formerly, these options caused GCC to attempt to emulate a pre-standard
1617 C compiler. They are now only supported with the @option{-E} switch.
1618 The preprocessor continues to support a pre-standard mode. See the GNU
1619 CPP manual for details.
1620
1621 @item -fcond-mismatch
1622 @opindex fcond-mismatch
1623 Allow conditional expressions with mismatched types in the second and
1624 third arguments. The value of such an expression is void. This option
1625 is not supported for C++.
1626
1627 @item -flax-vector-conversions
1628 @opindex flax-vector-conversions
1629 Allow implicit conversions between vectors with differing numbers of
1630 elements and/or incompatible element types. This option should not be
1631 used for new code.
1632
1633 @item -funsigned-char
1634 @opindex funsigned-char
1635 Let the type @code{char} be unsigned, like @code{unsigned char}.
1636
1637 Each kind of machine has a default for what @code{char} should
1638 be. It is either like @code{unsigned char} by default or like
1639 @code{signed char} by default.
1640
1641 Ideally, a portable program should always use @code{signed char} or
1642 @code{unsigned char} when it depends on the signedness of an object.
1643 But many programs have been written to use plain @code{char} and
1644 expect it to be signed, or expect it to be unsigned, depending on the
1645 machines they were written for. This option, and its inverse, let you
1646 make such a program work with the opposite default.
1647
1648 The type @code{char} is always a distinct type from each of
1649 @code{signed char} or @code{unsigned char}, even though its behavior
1650 is always just like one of those two.
1651
1652 @item -fsigned-char
1653 @opindex fsigned-char
1654 Let the type @code{char} be signed, like @code{signed char}.
1655
1656 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1657 the negative form of @option{-funsigned-char}. Likewise, the option
1658 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1659
1660 @item -fsigned-bitfields
1661 @itemx -funsigned-bitfields
1662 @itemx -fno-signed-bitfields
1663 @itemx -fno-unsigned-bitfields
1664 @opindex fsigned-bitfields
1665 @opindex funsigned-bitfields
1666 @opindex fno-signed-bitfields
1667 @opindex fno-unsigned-bitfields
1668 These options control whether a bit-field is signed or unsigned, when the
1669 declaration does not use either @code{signed} or @code{unsigned}. By
1670 default, such a bit-field is signed, because this is consistent: the
1671 basic integer types such as @code{int} are signed types.
1672 @end table
1673
1674 @node C++ Dialect Options
1675 @section Options Controlling C++ Dialect
1676
1677 @cindex compiler options, C++
1678 @cindex C++ options, command line
1679 @cindex options, C++
1680 This section describes the command-line options that are only meaningful
1681 for C++ programs; but you can also use most of the GNU compiler options
1682 regardless of what language your program is in. For example, you
1683 might compile a file @code{firstClass.C} like this:
1684
1685 @smallexample
1686 g++ -g -frepo -O -c firstClass.C
1687 @end smallexample
1688
1689 @noindent
1690 In this example, only @option{-frepo} is an option meant
1691 only for C++ programs; you can use the other options with any
1692 language supported by GCC@.
1693
1694 Here is a list of options that are @emph{only} for compiling C++ programs:
1695
1696 @table @gcctabopt
1697
1698 @item -fabi-version=@var{n}
1699 @opindex fabi-version
1700 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1701 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1702 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1703 the version that conforms most closely to the C++ ABI specification.
1704 Therefore, the ABI obtained using version 0 will change as ABI bugs
1705 are fixed.
1706
1707 The default is version 2.
1708
1709 @item -fno-access-control
1710 @opindex fno-access-control
1711 Turn off all access checking. This switch is mainly useful for working
1712 around bugs in the access control code.
1713
1714 @item -fcheck-new
1715 @opindex fcheck-new
1716 Check that the pointer returned by @code{operator new} is non-null
1717 before attempting to modify the storage allocated. This check is
1718 normally unnecessary because the C++ standard specifies that
1719 @code{operator new} will only return @code{0} if it is declared
1720 @samp{throw()}, in which case the compiler will always check the
1721 return value even without this option. In all other cases, when
1722 @code{operator new} has a non-empty exception specification, memory
1723 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1724 @samp{new (nothrow)}.
1725
1726 @item -fconserve-space
1727 @opindex fconserve-space
1728 Put uninitialized or runtime-initialized global variables into the
1729 common segment, as C does. This saves space in the executable at the
1730 cost of not diagnosing duplicate definitions. If you compile with this
1731 flag and your program mysteriously crashes after @code{main()} has
1732 completed, you may have an object that is being destroyed twice because
1733 two definitions were merged.
1734
1735 This option is no longer useful on most targets, now that support has
1736 been added for putting variables into BSS without making them common.
1737
1738 @item -fno-deduce-init-list
1739 @opindex fno-deduce-init-list
1740 Disable deduction of a template type parameter as
1741 std::initializer_list from a brace-enclosed initializer list, i.e.
1742
1743 @smallexample
1744 template <class T> auto forward(T t) -> decltype (realfn (t))
1745 @{
1746 return realfn (t);
1747 @}
1748
1749 void f()
1750 @{
1751 forward(@{1,2@}); // call forward<std::initializer_list<int>>
1752 @}
1753 @end smallexample
1754
1755 This option is present because this deduction is an extension to the
1756 current specification in the C++0x working draft, and there was
1757 some concern about potential overload resolution problems.
1758
1759 @item -ffriend-injection
1760 @opindex ffriend-injection
1761 Inject friend functions into the enclosing namespace, so that they are
1762 visible outside the scope of the class in which they are declared.
1763 Friend functions were documented to work this way in the old Annotated
1764 C++ Reference Manual, and versions of G++ before 4.1 always worked
1765 that way. However, in ISO C++ a friend function which is not declared
1766 in an enclosing scope can only be found using argument dependent
1767 lookup. This option causes friends to be injected as they were in
1768 earlier releases.
1769
1770 This option is for compatibility, and may be removed in a future
1771 release of G++.
1772
1773 @item -fno-elide-constructors
1774 @opindex fno-elide-constructors
1775 The C++ standard allows an implementation to omit creating a temporary
1776 which is only used to initialize another object of the same type.
1777 Specifying this option disables that optimization, and forces G++ to
1778 call the copy constructor in all cases.
1779
1780 @item -fno-enforce-eh-specs
1781 @opindex fno-enforce-eh-specs
1782 Don't generate code to check for violation of exception specifications
1783 at runtime. This option violates the C++ standard, but may be useful
1784 for reducing code size in production builds, much like defining
1785 @samp{NDEBUG}. This does not give user code permission to throw
1786 exceptions in violation of the exception specifications; the compiler
1787 will still optimize based on the specifications, so throwing an
1788 unexpected exception will result in undefined behavior.
1789
1790 @item -ffor-scope
1791 @itemx -fno-for-scope
1792 @opindex ffor-scope
1793 @opindex fno-for-scope
1794 If @option{-ffor-scope} is specified, the scope of variables declared in
1795 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1796 as specified by the C++ standard.
1797 If @option{-fno-for-scope} is specified, the scope of variables declared in
1798 a @i{for-init-statement} extends to the end of the enclosing scope,
1799 as was the case in old versions of G++, and other (traditional)
1800 implementations of C++.
1801
1802 The default if neither flag is given to follow the standard,
1803 but to allow and give a warning for old-style code that would
1804 otherwise be invalid, or have different behavior.
1805
1806 @item -fno-gnu-keywords
1807 @opindex fno-gnu-keywords
1808 Do not recognize @code{typeof} as a keyword, so that code can use this
1809 word as an identifier. You can use the keyword @code{__typeof__} instead.
1810 @option{-ansi} implies @option{-fno-gnu-keywords}.
1811
1812 @item -fno-implicit-templates
1813 @opindex fno-implicit-templates
1814 Never emit code for non-inline templates which are instantiated
1815 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1816 @xref{Template Instantiation}, for more information.
1817
1818 @item -fno-implicit-inline-templates
1819 @opindex fno-implicit-inline-templates
1820 Don't emit code for implicit instantiations of inline templates, either.
1821 The default is to handle inlines differently so that compiles with and
1822 without optimization will need the same set of explicit instantiations.
1823
1824 @item -fno-implement-inlines
1825 @opindex fno-implement-inlines
1826 To save space, do not emit out-of-line copies of inline functions
1827 controlled by @samp{#pragma implementation}. This will cause linker
1828 errors if these functions are not inlined everywhere they are called.
1829
1830 @item -fms-extensions
1831 @opindex fms-extensions
1832 Disable pedantic warnings about constructs used in MFC, such as implicit
1833 int and getting a pointer to member function via non-standard syntax.
1834
1835 @item -fno-nonansi-builtins
1836 @opindex fno-nonansi-builtins
1837 Disable built-in declarations of functions that are not mandated by
1838 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1839 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1840
1841 @item -fno-operator-names
1842 @opindex fno-operator-names
1843 Do not treat the operator name keywords @code{and}, @code{bitand},
1844 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1845 synonyms as keywords.
1846
1847 @item -fno-optional-diags
1848 @opindex fno-optional-diags
1849 Disable diagnostics that the standard says a compiler does not need to
1850 issue. Currently, the only such diagnostic issued by G++ is the one for
1851 a name having multiple meanings within a class.
1852
1853 @item -fpermissive
1854 @opindex fpermissive
1855 Downgrade some diagnostics about nonconformant code from errors to
1856 warnings. Thus, using @option{-fpermissive} will allow some
1857 nonconforming code to compile.
1858
1859 @item -frepo
1860 @opindex frepo
1861 Enable automatic template instantiation at link time. This option also
1862 implies @option{-fno-implicit-templates}. @xref{Template
1863 Instantiation}, for more information.
1864
1865 @item -fno-rtti
1866 @opindex fno-rtti
1867 Disable generation of information about every class with virtual
1868 functions for use by the C++ runtime type identification features
1869 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1870 of the language, you can save some space by using this flag. Note that
1871 exception handling uses the same information, but it will generate it as
1872 needed. The @samp{dynamic_cast} operator can still be used for casts that
1873 do not require runtime type information, i.e.@: casts to @code{void *} or to
1874 unambiguous base classes.
1875
1876 @item -fstats
1877 @opindex fstats
1878 Emit statistics about front-end processing at the end of the compilation.
1879 This information is generally only useful to the G++ development team.
1880
1881 @item -ftemplate-depth-@var{n}
1882 @opindex ftemplate-depth
1883 Set the maximum instantiation depth for template classes to @var{n}.
1884 A limit on the template instantiation depth is needed to detect
1885 endless recursions during template class instantiation. ANSI/ISO C++
1886 conforming programs must not rely on a maximum depth greater than 17.
1887
1888 @item -fno-threadsafe-statics
1889 @opindex fno-threadsafe-statics
1890 Do not emit the extra code to use the routines specified in the C++
1891 ABI for thread-safe initialization of local statics. You can use this
1892 option to reduce code size slightly in code that doesn't need to be
1893 thread-safe.
1894
1895 @item -fuse-cxa-atexit
1896 @opindex fuse-cxa-atexit
1897 Register destructors for objects with static storage duration with the
1898 @code{__cxa_atexit} function rather than the @code{atexit} function.
1899 This option is required for fully standards-compliant handling of static
1900 destructors, but will only work if your C library supports
1901 @code{__cxa_atexit}.
1902
1903 @item -fno-use-cxa-get-exception-ptr
1904 @opindex fno-use-cxa-get-exception-ptr
1905 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1906 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1907 if the runtime routine is not available.
1908
1909 @item -fvisibility-inlines-hidden
1910 @opindex fvisibility-inlines-hidden
1911 This switch declares that the user does not attempt to compare
1912 pointers to inline methods where the addresses of the two functions
1913 were taken in different shared objects.
1914
1915 The effect of this is that GCC may, effectively, mark inline methods with
1916 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1917 appear in the export table of a DSO and do not require a PLT indirection
1918 when used within the DSO@. Enabling this option can have a dramatic effect
1919 on load and link times of a DSO as it massively reduces the size of the
1920 dynamic export table when the library makes heavy use of templates.
1921
1922 The behavior of this switch is not quite the same as marking the
1923 methods as hidden directly, because it does not affect static variables
1924 local to the function or cause the compiler to deduce that
1925 the function is defined in only one shared object.
1926
1927 You may mark a method as having a visibility explicitly to negate the
1928 effect of the switch for that method. For example, if you do want to
1929 compare pointers to a particular inline method, you might mark it as
1930 having default visibility. Marking the enclosing class with explicit
1931 visibility will have no effect.
1932
1933 Explicitly instantiated inline methods are unaffected by this option
1934 as their linkage might otherwise cross a shared library boundary.
1935 @xref{Template Instantiation}.
1936
1937 @item -fvisibility-ms-compat
1938 @opindex fvisibility-ms-compat
1939 This flag attempts to use visibility settings to make GCC's C++
1940 linkage model compatible with that of Microsoft Visual Studio.
1941
1942 The flag makes these changes to GCC's linkage model:
1943
1944 @enumerate
1945 @item
1946 It sets the default visibility to @code{hidden}, like
1947 @option{-fvisibility=hidden}.
1948
1949 @item
1950 Types, but not their members, are not hidden by default.
1951
1952 @item
1953 The One Definition Rule is relaxed for types without explicit
1954 visibility specifications which are defined in more than one different
1955 shared object: those declarations are permitted if they would have
1956 been permitted when this option was not used.
1957 @end enumerate
1958
1959 In new code it is better to use @option{-fvisibility=hidden} and
1960 export those classes which are intended to be externally visible.
1961 Unfortunately it is possible for code to rely, perhaps accidentally,
1962 on the Visual Studio behavior.
1963
1964 Among the consequences of these changes are that static data members
1965 of the same type with the same name but defined in different shared
1966 objects will be different, so changing one will not change the other;
1967 and that pointers to function members defined in different shared
1968 objects may not compare equal. When this flag is given, it is a
1969 violation of the ODR to define types with the same name differently.
1970
1971 @item -fno-weak
1972 @opindex fno-weak
1973 Do not use weak symbol support, even if it is provided by the linker.
1974 By default, G++ will use weak symbols if they are available. This
1975 option exists only for testing, and should not be used by end-users;
1976 it will result in inferior code and has no benefits. This option may
1977 be removed in a future release of G++.
1978
1979 @item -nostdinc++
1980 @opindex nostdinc++
1981 Do not search for header files in the standard directories specific to
1982 C++, but do still search the other standard directories. (This option
1983 is used when building the C++ library.)
1984 @end table
1985
1986 In addition, these optimization, warning, and code generation options
1987 have meanings only for C++ programs:
1988
1989 @table @gcctabopt
1990 @item -fno-default-inline
1991 @opindex fno-default-inline
1992 Do not assume @samp{inline} for functions defined inside a class scope.
1993 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1994 functions will have linkage like inline functions; they just won't be
1995 inlined by default.
1996
1997 @item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)}
1998 @opindex Wabi
1999 @opindex Wno-abi
2000 Warn when G++ generates code that is probably not compatible with the
2001 vendor-neutral C++ ABI@. Although an effort has been made to warn about
2002 all such cases, there are probably some cases that are not warned about,
2003 even though G++ is generating incompatible code. There may also be
2004 cases where warnings are emitted even though the code that is generated
2005 will be compatible.
2006
2007 You should rewrite your code to avoid these warnings if you are
2008 concerned about the fact that code generated by G++ may not be binary
2009 compatible with code generated by other compilers.
2010
2011 The known incompatibilities at this point include:
2012
2013 @itemize @bullet
2014
2015 @item
2016 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
2017 pack data into the same byte as a base class. For example:
2018
2019 @smallexample
2020 struct A @{ virtual void f(); int f1 : 1; @};
2021 struct B : public A @{ int f2 : 1; @};
2022 @end smallexample
2023
2024 @noindent
2025 In this case, G++ will place @code{B::f2} into the same byte
2026 as@code{A::f1}; other compilers will not. You can avoid this problem
2027 by explicitly padding @code{A} so that its size is a multiple of the
2028 byte size on your platform; that will cause G++ and other compilers to
2029 layout @code{B} identically.
2030
2031 @item
2032 Incorrect handling of tail-padding for virtual bases. G++ does not use
2033 tail padding when laying out virtual bases. For example:
2034
2035 @smallexample
2036 struct A @{ virtual void f(); char c1; @};
2037 struct B @{ B(); char c2; @};
2038 struct C : public A, public virtual B @{@};
2039 @end smallexample
2040
2041 @noindent
2042 In this case, G++ will not place @code{B} into the tail-padding for
2043 @code{A}; other compilers will. You can avoid this problem by
2044 explicitly padding @code{A} so that its size is a multiple of its
2045 alignment (ignoring virtual base classes); that will cause G++ and other
2046 compilers to layout @code{C} identically.
2047
2048 @item
2049 Incorrect handling of bit-fields with declared widths greater than that
2050 of their underlying types, when the bit-fields appear in a union. For
2051 example:
2052
2053 @smallexample
2054 union U @{ int i : 4096; @};
2055 @end smallexample
2056
2057 @noindent
2058 Assuming that an @code{int} does not have 4096 bits, G++ will make the
2059 union too small by the number of bits in an @code{int}.
2060
2061 @item
2062 Empty classes can be placed at incorrect offsets. For example:
2063
2064 @smallexample
2065 struct A @{@};
2066
2067 struct B @{
2068 A a;
2069 virtual void f ();
2070 @};
2071
2072 struct C : public B, public A @{@};
2073 @end smallexample
2074
2075 @noindent
2076 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
2077 it should be placed at offset zero. G++ mistakenly believes that the
2078 @code{A} data member of @code{B} is already at offset zero.
2079
2080 @item
2081 Names of template functions whose types involve @code{typename} or
2082 template template parameters can be mangled incorrectly.
2083
2084 @smallexample
2085 template <typename Q>
2086 void f(typename Q::X) @{@}
2087
2088 template <template <typename> class Q>
2089 void f(typename Q<int>::X) @{@}
2090 @end smallexample
2091
2092 @noindent
2093 Instantiations of these templates may be mangled incorrectly.
2094
2095 @end itemize
2096
2097 It also warns psABI related changes. The known psABI changes at this
2098 point include:
2099
2100 @itemize @bullet
2101
2102 @item
2103 For SYSV/x86-64, when passing union with long double, it is changed to
2104 pass in memory as specified in psABI. For example:
2105
2106 @smallexample
2107 union U @{
2108 long double ld;
2109 int i;
2110 @};
2111 @end smallexample
2112
2113 @noindent
2114 @code{union U} will always be passed in memory.
2115
2116 @end itemize
2117
2118 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2119 @opindex Wctor-dtor-privacy
2120 @opindex Wno-ctor-dtor-privacy
2121 Warn when a class seems unusable because all the constructors or
2122 destructors in that class are private, and it has neither friends nor
2123 public static member functions.
2124
2125 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2126 @opindex Wnon-virtual-dtor
2127 @opindex Wno-non-virtual-dtor
2128 Warn when a class has virtual functions and accessible non-virtual
2129 destructor, in which case it would be possible but unsafe to delete
2130 an instance of a derived class through a pointer to the base class.
2131 This warning is also enabled if -Weffc++ is specified.
2132
2133 @item -Wreorder @r{(C++ and Objective-C++ only)}
2134 @opindex Wreorder
2135 @opindex Wno-reorder
2136 @cindex reordering, warning
2137 @cindex warning for reordering of member initializers
2138 Warn when the order of member initializers given in the code does not
2139 match the order in which they must be executed. For instance:
2140
2141 @smallexample
2142 struct A @{
2143 int i;
2144 int j;
2145 A(): j (0), i (1) @{ @}
2146 @};
2147 @end smallexample
2148
2149 The compiler will rearrange the member initializers for @samp{i}
2150 and @samp{j} to match the declaration order of the members, emitting
2151 a warning to that effect. This warning is enabled by @option{-Wall}.
2152 @end table
2153
2154 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2155
2156 @table @gcctabopt
2157 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2158 @opindex Weffc++
2159 @opindex Wno-effc++
2160 Warn about violations of the following style guidelines from Scott Meyers'
2161 @cite{Effective C++} book:
2162
2163 @itemize @bullet
2164 @item
2165 Item 11: Define a copy constructor and an assignment operator for classes
2166 with dynamically allocated memory.
2167
2168 @item
2169 Item 12: Prefer initialization to assignment in constructors.
2170
2171 @item
2172 Item 14: Make destructors virtual in base classes.
2173
2174 @item
2175 Item 15: Have @code{operator=} return a reference to @code{*this}.
2176
2177 @item
2178 Item 23: Don't try to return a reference when you must return an object.
2179
2180 @end itemize
2181
2182 Also warn about violations of the following style guidelines from
2183 Scott Meyers' @cite{More Effective C++} book:
2184
2185 @itemize @bullet
2186 @item
2187 Item 6: Distinguish between prefix and postfix forms of increment and
2188 decrement operators.
2189
2190 @item
2191 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2192
2193 @end itemize
2194
2195 When selecting this option, be aware that the standard library
2196 headers do not obey all of these guidelines; use @samp{grep -v}
2197 to filter out those warnings.
2198
2199 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2200 @opindex Wstrict-null-sentinel
2201 @opindex Wno-strict-null-sentinel
2202 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2203 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2204 to @code{__null}. Although it is a null pointer constant not a null pointer,
2205 it is guaranteed to be of the same size as a pointer. But this use is
2206 not portable across different compilers.
2207
2208 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2209 @opindex Wno-non-template-friend
2210 @opindex Wnon-template-friend
2211 Disable warnings when non-templatized friend functions are declared
2212 within a template. Since the advent of explicit template specification
2213 support in G++, if the name of the friend is an unqualified-id (i.e.,
2214 @samp{friend foo(int)}), the C++ language specification demands that the
2215 friend declare or define an ordinary, nontemplate function. (Section
2216 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2217 could be interpreted as a particular specialization of a templatized
2218 function. Because this non-conforming behavior is no longer the default
2219 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2220 check existing code for potential trouble spots and is on by default.
2221 This new compiler behavior can be turned off with
2222 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2223 but disables the helpful warning.
2224
2225 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2226 @opindex Wold-style-cast
2227 @opindex Wno-old-style-cast
2228 Warn if an old-style (C-style) cast to a non-void type is used within
2229 a C++ program. The new-style casts (@samp{dynamic_cast},
2230 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2231 less vulnerable to unintended effects and much easier to search for.
2232
2233 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2234 @opindex Woverloaded-virtual
2235 @opindex Wno-overloaded-virtual
2236 @cindex overloaded virtual fn, warning
2237 @cindex warning for overloaded virtual fn
2238 Warn when a function declaration hides virtual functions from a
2239 base class. For example, in:
2240
2241 @smallexample
2242 struct A @{
2243 virtual void f();
2244 @};
2245
2246 struct B: public A @{
2247 void f(int);
2248 @};
2249 @end smallexample
2250
2251 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2252 like:
2253
2254 @smallexample
2255 B* b;
2256 b->f();
2257 @end smallexample
2258
2259 will fail to compile.
2260
2261 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2262 @opindex Wno-pmf-conversions
2263 @opindex Wpmf-conversions
2264 Disable the diagnostic for converting a bound pointer to member function
2265 to a plain pointer.
2266
2267 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2268 @opindex Wsign-promo
2269 @opindex Wno-sign-promo
2270 Warn when overload resolution chooses a promotion from unsigned or
2271 enumerated type to a signed type, over a conversion to an unsigned type of
2272 the same size. Previous versions of G++ would try to preserve
2273 unsignedness, but the standard mandates the current behavior.
2274
2275 @smallexample
2276 struct A @{
2277 operator int ();
2278 A& operator = (int);
2279 @};
2280
2281 main ()
2282 @{
2283 A a,b;
2284 a = b;
2285 @}
2286 @end smallexample
2287
2288 In this example, G++ will synthesize a default @samp{A& operator =
2289 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2290 @end table
2291
2292 @node Objective-C and Objective-C++ Dialect Options
2293 @section Options Controlling Objective-C and Objective-C++ Dialects
2294
2295 @cindex compiler options, Objective-C and Objective-C++
2296 @cindex Objective-C and Objective-C++ options, command line
2297 @cindex options, Objective-C and Objective-C++
2298 (NOTE: This manual does not describe the Objective-C and Objective-C++
2299 languages themselves. See @xref{Standards,,Language Standards
2300 Supported by GCC}, for references.)
2301
2302 This section describes the command-line options that are only meaningful
2303 for Objective-C and Objective-C++ programs, but you can also use most of
2304 the language-independent GNU compiler options.
2305 For example, you might compile a file @code{some_class.m} like this:
2306
2307 @smallexample
2308 gcc -g -fgnu-runtime -O -c some_class.m
2309 @end smallexample
2310
2311 @noindent
2312 In this example, @option{-fgnu-runtime} is an option meant only for
2313 Objective-C and Objective-C++ programs; you can use the other options with
2314 any language supported by GCC@.
2315
2316 Note that since Objective-C is an extension of the C language, Objective-C
2317 compilations may also use options specific to the C front-end (e.g.,
2318 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2319 C++-specific options (e.g., @option{-Wabi}).
2320
2321 Here is a list of options that are @emph{only} for compiling Objective-C
2322 and Objective-C++ programs:
2323
2324 @table @gcctabopt
2325 @item -fconstant-string-class=@var{class-name}
2326 @opindex fconstant-string-class
2327 Use @var{class-name} as the name of the class to instantiate for each
2328 literal string specified with the syntax @code{@@"@dots{}"}. The default
2329 class name is @code{NXConstantString} if the GNU runtime is being used, and
2330 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2331 @option{-fconstant-cfstrings} option, if also present, will override the
2332 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2333 to be laid out as constant CoreFoundation strings.
2334
2335 @item -fgnu-runtime
2336 @opindex fgnu-runtime
2337 Generate object code compatible with the standard GNU Objective-C
2338 runtime. This is the default for most types of systems.
2339
2340 @item -fnext-runtime
2341 @opindex fnext-runtime
2342 Generate output compatible with the NeXT runtime. This is the default
2343 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2344 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2345 used.
2346
2347 @item -fno-nil-receivers
2348 @opindex fno-nil-receivers
2349 Assume that all Objective-C message dispatches (e.g.,
2350 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2351 is not @code{nil}. This allows for more efficient entry points in the runtime
2352 to be used. Currently, this option is only available in conjunction with
2353 the NeXT runtime on Mac OS X 10.3 and later.
2354
2355 @item -fobjc-call-cxx-cdtors
2356 @opindex fobjc-call-cxx-cdtors
2357 For each Objective-C class, check if any of its instance variables is a
2358 C++ object with a non-trivial default constructor. If so, synthesize a
2359 special @code{- (id) .cxx_construct} instance method that will run
2360 non-trivial default constructors on any such instance variables, in order,
2361 and then return @code{self}. Similarly, check if any instance variable
2362 is a C++ object with a non-trivial destructor, and if so, synthesize a
2363 special @code{- (void) .cxx_destruct} method that will run
2364 all such default destructors, in reverse order.
2365
2366 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2367 thusly generated will only operate on instance variables declared in the
2368 current Objective-C class, and not those inherited from superclasses. It
2369 is the responsibility of the Objective-C runtime to invoke all such methods
2370 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2371 will be invoked by the runtime immediately after a new object
2372 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2373 be invoked immediately before the runtime deallocates an object instance.
2374
2375 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2376 support for invoking the @code{- (id) .cxx_construct} and
2377 @code{- (void) .cxx_destruct} methods.
2378
2379 @item -fobjc-direct-dispatch
2380 @opindex fobjc-direct-dispatch
2381 Allow fast jumps to the message dispatcher. On Darwin this is
2382 accomplished via the comm page.
2383
2384 @item -fobjc-exceptions
2385 @opindex fobjc-exceptions
2386 Enable syntactic support for structured exception handling in Objective-C,
2387 similar to what is offered by C++ and Java. This option is
2388 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2389 earlier.
2390
2391 @smallexample
2392 @@try @{
2393 @dots{}
2394 @@throw expr;
2395 @dots{}
2396 @}
2397 @@catch (AnObjCClass *exc) @{
2398 @dots{}
2399 @@throw expr;
2400 @dots{}
2401 @@throw;
2402 @dots{}
2403 @}
2404 @@catch (AnotherClass *exc) @{
2405 @dots{}
2406 @}
2407 @@catch (id allOthers) @{
2408 @dots{}
2409 @}
2410 @@finally @{
2411 @dots{}
2412 @@throw expr;
2413 @dots{}
2414 @}
2415 @end smallexample
2416
2417 The @code{@@throw} statement may appear anywhere in an Objective-C or
2418 Objective-C++ program; when used inside of a @code{@@catch} block, the
2419 @code{@@throw} may appear without an argument (as shown above), in which case
2420 the object caught by the @code{@@catch} will be rethrown.
2421
2422 Note that only (pointers to) Objective-C objects may be thrown and
2423 caught using this scheme. When an object is thrown, it will be caught
2424 by the nearest @code{@@catch} clause capable of handling objects of that type,
2425 analogously to how @code{catch} blocks work in C++ and Java. A
2426 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2427 any and all Objective-C exceptions not caught by previous @code{@@catch}
2428 clauses (if any).
2429
2430 The @code{@@finally} clause, if present, will be executed upon exit from the
2431 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2432 regardless of whether any exceptions are thrown, caught or rethrown
2433 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2434 of the @code{finally} clause in Java.
2435
2436 There are several caveats to using the new exception mechanism:
2437
2438 @itemize @bullet
2439 @item
2440 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2441 idioms provided by the @code{NSException} class, the new
2442 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2443 systems, due to additional functionality needed in the (NeXT) Objective-C
2444 runtime.
2445
2446 @item
2447 As mentioned above, the new exceptions do not support handling
2448 types other than Objective-C objects. Furthermore, when used from
2449 Objective-C++, the Objective-C exception model does not interoperate with C++
2450 exceptions at this time. This means you cannot @code{@@throw} an exception
2451 from Objective-C and @code{catch} it in C++, or vice versa
2452 (i.e., @code{throw @dots{} @@catch}).
2453 @end itemize
2454
2455 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2456 blocks for thread-safe execution:
2457
2458 @smallexample
2459 @@synchronized (ObjCClass *guard) @{
2460 @dots{}
2461 @}
2462 @end smallexample
2463
2464 Upon entering the @code{@@synchronized} block, a thread of execution shall
2465 first check whether a lock has been placed on the corresponding @code{guard}
2466 object by another thread. If it has, the current thread shall wait until
2467 the other thread relinquishes its lock. Once @code{guard} becomes available,
2468 the current thread will place its own lock on it, execute the code contained in
2469 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2470 making @code{guard} available to other threads).
2471
2472 Unlike Java, Objective-C does not allow for entire methods to be marked
2473 @code{@@synchronized}. Note that throwing exceptions out of
2474 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2475 to be unlocked properly.
2476
2477 @item -fobjc-gc
2478 @opindex fobjc-gc
2479 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2480
2481 @item -freplace-objc-classes
2482 @opindex freplace-objc-classes
2483 Emit a special marker instructing @command{ld(1)} not to statically link in
2484 the resulting object file, and allow @command{dyld(1)} to load it in at
2485 run time instead. This is used in conjunction with the Fix-and-Continue
2486 debugging mode, where the object file in question may be recompiled and
2487 dynamically reloaded in the course of program execution, without the need
2488 to restart the program itself. Currently, Fix-and-Continue functionality
2489 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2490 and later.
2491
2492 @item -fzero-link
2493 @opindex fzero-link
2494 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2495 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2496 compile time) with static class references that get initialized at load time,
2497 which improves run-time performance. Specifying the @option{-fzero-link} flag
2498 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2499 to be retained. This is useful in Zero-Link debugging mode, since it allows
2500 for individual class implementations to be modified during program execution.
2501
2502 @item -gen-decls
2503 @opindex gen-decls
2504 Dump interface declarations for all classes seen in the source file to a
2505 file named @file{@var{sourcename}.decl}.
2506
2507 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
2508 @opindex Wassign-intercept
2509 @opindex Wno-assign-intercept
2510 Warn whenever an Objective-C assignment is being intercepted by the
2511 garbage collector.
2512
2513 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
2514 @opindex Wno-protocol
2515 @opindex Wprotocol
2516 If a class is declared to implement a protocol, a warning is issued for
2517 every method in the protocol that is not implemented by the class. The
2518 default behavior is to issue a warning for every method not explicitly
2519 implemented in the class, even if a method implementation is inherited
2520 from the superclass. If you use the @option{-Wno-protocol} option, then
2521 methods inherited from the superclass are considered to be implemented,
2522 and no warning is issued for them.
2523
2524 @item -Wselector @r{(Objective-C and Objective-C++ only)}
2525 @opindex Wselector
2526 @opindex Wno-selector
2527 Warn if multiple methods of different types for the same selector are
2528 found during compilation. The check is performed on the list of methods
2529 in the final stage of compilation. Additionally, a check is performed
2530 for each selector appearing in a @code{@@selector(@dots{})}
2531 expression, and a corresponding method for that selector has been found
2532 during compilation. Because these checks scan the method table only at
2533 the end of compilation, these warnings are not produced if the final
2534 stage of compilation is not reached, for example because an error is
2535 found during compilation, or because the @option{-fsyntax-only} option is
2536 being used.
2537
2538 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
2539 @opindex Wstrict-selector-match
2540 @opindex Wno-strict-selector-match
2541 Warn if multiple methods with differing argument and/or return types are
2542 found for a given selector when attempting to send a message using this
2543 selector to a receiver of type @code{id} or @code{Class}. When this flag
2544 is off (which is the default behavior), the compiler will omit such warnings
2545 if any differences found are confined to types which share the same size
2546 and alignment.
2547
2548 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
2549 @opindex Wundeclared-selector
2550 @opindex Wno-undeclared-selector
2551 Warn if a @code{@@selector(@dots{})} expression referring to an
2552 undeclared selector is found. A selector is considered undeclared if no
2553 method with that name has been declared before the
2554 @code{@@selector(@dots{})} expression, either explicitly in an
2555 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2556 an @code{@@implementation} section. This option always performs its
2557 checks as soon as a @code{@@selector(@dots{})} expression is found,
2558 while @option{-Wselector} only performs its checks in the final stage of
2559 compilation. This also enforces the coding style convention
2560 that methods and selectors must be declared before being used.
2561
2562 @item -print-objc-runtime-info
2563 @opindex print-objc-runtime-info
2564 Generate C header describing the largest structure that is passed by
2565 value, if any.
2566
2567 @end table
2568
2569 @node Language Independent Options
2570 @section Options to Control Diagnostic Messages Formatting
2571 @cindex options to control diagnostics formatting
2572 @cindex diagnostic messages
2573 @cindex message formatting
2574
2575 Traditionally, diagnostic messages have been formatted irrespective of
2576 the output device's aspect (e.g.@: its width, @dots{}). The options described
2577 below can be used to control the diagnostic messages formatting
2578 algorithm, e.g.@: how many characters per line, how often source location
2579 information should be reported. Right now, only the C++ front end can
2580 honor these options. However it is expected, in the near future, that
2581 the remaining front ends would be able to digest them correctly.
2582
2583 @table @gcctabopt
2584 @item -fmessage-length=@var{n}
2585 @opindex fmessage-length
2586 Try to format error messages so that they fit on lines of about @var{n}
2587 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2588 the front ends supported by GCC@. If @var{n} is zero, then no
2589 line-wrapping will be done; each error message will appear on a single
2590 line.
2591
2592 @opindex fdiagnostics-show-location
2593 @item -fdiagnostics-show-location=once
2594 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2595 reporter to emit @emph{once} source location information; that is, in
2596 case the message is too long to fit on a single physical line and has to
2597 be wrapped, the source location won't be emitted (as prefix) again,
2598 over and over, in subsequent continuation lines. This is the default
2599 behavior.
2600
2601 @item -fdiagnostics-show-location=every-line
2602 Only meaningful in line-wrapping mode. Instructs the diagnostic
2603 messages reporter to emit the same source location information (as
2604 prefix) for physical lines that result from the process of breaking
2605 a message which is too long to fit on a single line.
2606
2607 @item -fdiagnostics-show-option
2608 @opindex fdiagnostics-show-option
2609 This option instructs the diagnostic machinery to add text to each
2610 diagnostic emitted, which indicates which command line option directly
2611 controls that diagnostic, when such an option is known to the
2612 diagnostic machinery.
2613
2614 @item -Wcoverage-mismatch
2615 @opindex Wcoverage-mismatch
2616 Warn if feedback profiles do not match when using the
2617 @option{-fprofile-use} option.
2618 If a source file was changed between @option{-fprofile-gen} and
2619 @option{-fprofile-use}, the files with the profile feedback can fail
2620 to match the source file and GCC can not use the profile feedback
2621 information. By default, GCC emits an error message in this case.
2622 The option @option{-Wcoverage-mismatch} emits a warning instead of an
2623 error. GCC does not use appropriate feedback profiles, so using this
2624 option can result in poorly optimized code. This option is useful
2625 only in the case of very minor changes such as bug fixes to an
2626 existing code-base.
2627
2628 @end table
2629
2630 @node Warning Options
2631 @section Options to Request or Suppress Warnings
2632 @cindex options to control warnings
2633 @cindex warning messages
2634 @cindex messages, warning
2635 @cindex suppressing warnings
2636
2637 Warnings are diagnostic messages that report constructions which
2638 are not inherently erroneous but which are risky or suggest there
2639 may have been an error.
2640
2641 The following language-independent options do not enable specific
2642 warnings but control the kinds of diagnostics produced by GCC.
2643
2644 @table @gcctabopt
2645 @cindex syntax checking
2646 @item -fsyntax-only
2647 @opindex fsyntax-only
2648 Check the code for syntax errors, but don't do anything beyond that.
2649
2650 @item -w
2651 @opindex w
2652 Inhibit all warning messages.
2653
2654 @item -Werror
2655 @opindex Werror
2656 @opindex Wno-error
2657 Make all warnings into errors.
2658
2659 @item -Werror=
2660 @opindex Werror=
2661 @opindex Wno-error=
2662 Make the specified warning into an error. The specifier for a warning
2663 is appended, for example @option{-Werror=switch} turns the warnings
2664 controlled by @option{-Wswitch} into errors. This switch takes a
2665 negative form, to be used to negate @option{-Werror} for specific
2666 warnings, for example @option{-Wno-error=switch} makes
2667 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
2668 is in effect. You can use the @option{-fdiagnostics-show-option}
2669 option to have each controllable warning amended with the option which
2670 controls it, to determine what to use with this option.
2671
2672 Note that specifying @option{-Werror=}@var{foo} automatically implies
2673 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
2674 imply anything.
2675
2676 @item -Wfatal-errors
2677 @opindex Wfatal-errors
2678 @opindex Wno-fatal-errors
2679 This option causes the compiler to abort compilation on the first error
2680 occurred rather than trying to keep going and printing further error
2681 messages.
2682
2683 @end table
2684
2685 You can request many specific warnings with options beginning
2686 @samp{-W}, for example @option{-Wimplicit} to request warnings on
2687 implicit declarations. Each of these specific warning options also
2688 has a negative form beginning @samp{-Wno-} to turn off warnings; for
2689 example, @option{-Wno-implicit}. This manual lists only one of the
2690 two forms, whichever is not the default. For further,
2691 language-specific options also refer to @ref{C++ Dialect Options} and
2692 @ref{Objective-C and Objective-C++ Dialect Options}.
2693
2694 @table @gcctabopt
2695 @item -pedantic
2696 @opindex pedantic
2697 Issue all the warnings demanded by strict ISO C and ISO C++;
2698 reject all programs that use forbidden extensions, and some other
2699 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2700 version of the ISO C standard specified by any @option{-std} option used.
2701
2702 Valid ISO C and ISO C++ programs should compile properly with or without
2703 this option (though a rare few will require @option{-ansi} or a
2704 @option{-std} option specifying the required version of ISO C)@. However,
2705 without this option, certain GNU extensions and traditional C and C++
2706 features are supported as well. With this option, they are rejected.
2707
2708 @option{-pedantic} does not cause warning messages for use of the
2709 alternate keywords whose names begin and end with @samp{__}. Pedantic
2710 warnings are also disabled in the expression that follows
2711 @code{__extension__}. However, only system header files should use
2712 these escape routes; application programs should avoid them.
2713 @xref{Alternate Keywords}.
2714
2715 Some users try to use @option{-pedantic} to check programs for strict ISO
2716 C conformance. They soon find that it does not do quite what they want:
2717 it finds some non-ISO practices, but not all---only those for which
2718 ISO C @emph{requires} a diagnostic, and some others for which
2719 diagnostics have been added.
2720
2721 A feature to report any failure to conform to ISO C might be useful in
2722 some instances, but would require considerable additional work and would
2723 be quite different from @option{-pedantic}. We don't have plans to
2724 support such a feature in the near future.
2725
2726 Where the standard specified with @option{-std} represents a GNU
2727 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2728 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2729 extended dialect is based. Warnings from @option{-pedantic} are given
2730 where they are required by the base standard. (It would not make sense
2731 for such warnings to be given only for features not in the specified GNU
2732 C dialect, since by definition the GNU dialects of C include all
2733 features the compiler supports with the given option, and there would be
2734 nothing to warn about.)
2735
2736 @item -pedantic-errors
2737 @opindex pedantic-errors
2738 Like @option{-pedantic}, except that errors are produced rather than
2739 warnings.
2740
2741 @item -Wall
2742 @opindex Wall
2743 @opindex Wno-all
2744 This enables all the warnings about constructions that some users
2745 consider questionable, and that are easy to avoid (or modify to
2746 prevent the warning), even in conjunction with macros. This also
2747 enables some language-specific warnings described in @ref{C++ Dialect
2748 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
2749
2750 @option{-Wall} turns on the following warning flags:
2751
2752 @gccoptlist{-Waddress @gol
2753 -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol
2754 -Wc++0x-compat @gol
2755 -Wchar-subscripts @gol
2756 -Wimplicit-int @gol
2757 -Wimplicit-function-declaration @gol
2758 -Wcomment @gol
2759 -Wformat @gol
2760 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
2761 -Wmissing-braces @gol
2762 -Wnonnull @gol
2763 -Wparentheses @gol
2764 -Wpointer-sign @gol
2765 -Wreorder @gol
2766 -Wreturn-type @gol
2767 -Wsequence-point @gol
2768 -Wsign-compare @r{(only in C++)} @gol
2769 -Wstrict-aliasing @gol
2770 -Wstrict-overflow=1 @gol
2771 -Wswitch @gol
2772 -Wtrigraphs @gol
2773 -Wuninitialized @gol
2774 -Wunknown-pragmas @gol
2775 -Wunused-function @gol
2776 -Wunused-label @gol
2777 -Wunused-value @gol
2778 -Wunused-variable @gol
2779 -Wvolatile-register-var @gol
2780 }
2781
2782 Note that some warning flags are not implied by @option{-Wall}. Some of
2783 them warn about constructions that users generally do not consider
2784 questionable, but which occasionally you might wish to check for;
2785 others warn about constructions that are necessary or hard to avoid in
2786 some cases, and there is no simple way to modify the code to suppress
2787 the warning. Some of them are enabled by @option{-Wextra} but many of
2788 them must be enabled individually.
2789
2790 @item -Wextra
2791 @opindex W
2792 @opindex Wextra
2793 @opindex Wno-extra
2794 This enables some extra warning flags that are not enabled by
2795 @option{-Wall}. (This option used to be called @option{-W}. The older
2796 name is still supported, but the newer name is more descriptive.)
2797
2798 @gccoptlist{-Wclobbered @gol
2799 -Wempty-body @gol
2800 -Wignored-qualifiers @gol
2801 -Wmissing-field-initializers @gol
2802 -Wmissing-parameter-type @r{(C only)} @gol
2803 -Wold-style-declaration @r{(C only)} @gol
2804 -Woverride-init @gol
2805 -Wsign-compare @gol
2806 -Wtype-limits @gol
2807 -Wuninitialized @gol
2808 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2809 }
2810
2811 The option @option{-Wextra} also prints warning messages for the
2812 following cases:
2813
2814 @itemize @bullet
2815
2816 @item
2817 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2818 @samp{>}, or @samp{>=}.
2819
2820 @item
2821 (C++ only) An enumerator and a non-enumerator both appear in a
2822 conditional expression.
2823
2824 @item
2825 (C++ only) Ambiguous virtual bases.
2826
2827 @item
2828 (C++ only) Subscripting an array which has been declared @samp{register}.
2829
2830 @item
2831 (C++ only) Taking the address of a variable which has been declared
2832 @samp{register}.
2833
2834 @item
2835 (C++ only) A base class is not initialized in a derived class' copy
2836 constructor.
2837
2838 @end itemize
2839
2840 @item -Wchar-subscripts
2841 @opindex Wchar-subscripts
2842 @opindex Wno-char-subscripts
2843 Warn if an array subscript has type @code{char}. This is a common cause
2844 of error, as programmers often forget that this type is signed on some
2845 machines.
2846 This warning is enabled by @option{-Wall}.
2847
2848 @item -Wcomment
2849 @opindex Wcomment
2850 @opindex Wno-comment
2851 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2852 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2853 This warning is enabled by @option{-Wall}.
2854
2855 @item -Wformat
2856 @opindex Wformat
2857 @opindex Wno-format
2858 @opindex ffreestanding
2859 @opindex fno-builtin
2860 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2861 the arguments supplied have types appropriate to the format string
2862 specified, and that the conversions specified in the format string make
2863 sense. This includes standard functions, and others specified by format
2864 attributes (@pxref{Function Attributes}), in the @code{printf},
2865 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2866 not in the C standard) families (or other target-specific families).
2867 Which functions are checked without format attributes having been
2868 specified depends on the standard version selected, and such checks of
2869 functions without the attribute specified are disabled by
2870 @option{-ffreestanding} or @option{-fno-builtin}.
2871
2872 The formats are checked against the format features supported by GNU
2873 libc version 2.2. These include all ISO C90 and C99 features, as well
2874 as features from the Single Unix Specification and some BSD and GNU
2875 extensions. Other library implementations may not support all these
2876 features; GCC does not support warning about features that go beyond a
2877 particular library's limitations. However, if @option{-pedantic} is used
2878 with @option{-Wformat}, warnings will be given about format features not
2879 in the selected standard version (but not for @code{strfmon} formats,
2880 since those are not in any version of the C standard). @xref{C Dialect
2881 Options,,Options Controlling C Dialect}.
2882
2883 Since @option{-Wformat} also checks for null format arguments for
2884 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2885
2886 @option{-Wformat} is included in @option{-Wall}. For more control over some
2887 aspects of format checking, the options @option{-Wformat-y2k},
2888 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2889 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2890 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2891
2892 @item -Wformat-y2k
2893 @opindex Wformat-y2k
2894 @opindex Wno-format-y2k
2895 If @option{-Wformat} is specified, also warn about @code{strftime}
2896 formats which may yield only a two-digit year.
2897
2898 @item -Wno-format-contains-nul
2899 @opindex Wno-format-contains-nul
2900 @opindex Wformat-contains-nul
2901 If @option{-Wformat} is specified, do not warn about format strings that
2902 contain NUL bytes.
2903
2904 @item -Wno-format-extra-args
2905 @opindex Wno-format-extra-args
2906 @opindex Wformat-extra-args
2907 If @option{-Wformat} is specified, do not warn about excess arguments to a
2908 @code{printf} or @code{scanf} format function. The C standard specifies
2909 that such arguments are ignored.
2910
2911 Where the unused arguments lie between used arguments that are
2912 specified with @samp{$} operand number specifications, normally
2913 warnings are still given, since the implementation could not know what
2914 type to pass to @code{va_arg} to skip the unused arguments. However,
2915 in the case of @code{scanf} formats, this option will suppress the
2916 warning if the unused arguments are all pointers, since the Single
2917 Unix Specification says that such unused arguments are allowed.
2918
2919 @item -Wno-format-zero-length @r{(C and Objective-C only)}
2920 @opindex Wno-format-zero-length
2921 @opindex Wformat-zero-length
2922 If @option{-Wformat} is specified, do not warn about zero-length formats.
2923 The C standard specifies that zero-length formats are allowed.
2924
2925 @item -Wformat-nonliteral
2926 @opindex Wformat-nonliteral
2927 @opindex Wno-format-nonliteral
2928 If @option{-Wformat} is specified, also warn if the format string is not a
2929 string literal and so cannot be checked, unless the format function
2930 takes its format arguments as a @code{va_list}.
2931
2932 @item -Wformat-security
2933 @opindex Wformat-security
2934 @opindex Wno-format-security
2935 If @option{-Wformat} is specified, also warn about uses of format
2936 functions that represent possible security problems. At present, this
2937 warns about calls to @code{printf} and @code{scanf} functions where the
2938 format string is not a string literal and there are no format arguments,
2939 as in @code{printf (foo);}. This may be a security hole if the format
2940 string came from untrusted input and contains @samp{%n}. (This is
2941 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2942 in future warnings may be added to @option{-Wformat-security} that are not
2943 included in @option{-Wformat-nonliteral}.)
2944
2945 @item -Wformat=2
2946 @opindex Wformat=2
2947 @opindex Wno-format=2
2948 Enable @option{-Wformat} plus format checks not included in
2949 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2950 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2951
2952 @item -Wnonnull @r{(C and Objective-C only)}
2953 @opindex Wnonnull
2954 @opindex Wno-nonnull
2955 Warn about passing a null pointer for arguments marked as
2956 requiring a non-null value by the @code{nonnull} function attribute.
2957
2958 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2959 can be disabled with the @option{-Wno-nonnull} option.
2960
2961 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2962 @opindex Winit-self
2963 @opindex Wno-init-self
2964 Warn about uninitialized variables which are initialized with themselves.
2965 Note this option can only be used with the @option{-Wuninitialized} option.
2966
2967 For example, GCC will warn about @code{i} being uninitialized in the
2968 following snippet only when @option{-Winit-self} has been specified:
2969 @smallexample
2970 @group
2971 int f()
2972 @{
2973 int i = i;
2974 return i;
2975 @}
2976 @end group
2977 @end smallexample
2978
2979 @item -Wimplicit-int @r{(C and Objective-C only)}
2980 @opindex Wimplicit-int
2981 @opindex Wno-implicit-int
2982 Warn when a declaration does not specify a type.
2983 This warning is enabled by @option{-Wall}.
2984
2985 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
2986 @opindex Wimplicit-function-declaration
2987 @opindex Wno-implicit-function-declaration
2988 Give a warning whenever a function is used before being declared. In
2989 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
2990 enabled by default and it is made into an error by
2991 @option{-pedantic-errors}. This warning is also enabled by
2992 @option{-Wall}.
2993
2994 @item -Wimplicit
2995 @opindex Wimplicit
2996 @opindex Wno-implicit
2997 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2998 This warning is enabled by @option{-Wall}.
2999
3000 @item -Wignored-qualifiers @r{(C and C++ only)}
3001 @opindex Wignored-qualifiers
3002 @opindex Wno-ignored-qualifiers
3003 Warn if the return type of a function has a type qualifier
3004 such as @code{const}. For ISO C such a type qualifier has no effect,
3005 since the value returned by a function is not an lvalue.
3006 For C++, the warning is only emitted for scalar types or @code{void}.
3007 ISO C prohibits qualified @code{void} return types on function
3008 definitions, so such return types always receive a warning
3009 even without this option.
3010
3011 This warning is also enabled by @option{-Wextra}.
3012
3013 @item -Wmain
3014 @opindex Wmain
3015 @opindex Wno-main
3016 Warn if the type of @samp{main} is suspicious. @samp{main} should be
3017 a function with external linkage, returning int, taking either zero
3018 arguments, two, or three arguments of appropriate types. This warning
3019 is enabled by default in C++ and is enabled by either @option{-Wall}
3020 or @option{-pedantic}.
3021
3022 @item -Wmissing-braces
3023 @opindex Wmissing-braces
3024 @opindex Wno-missing-braces
3025 Warn if an aggregate or union initializer is not fully bracketed. In
3026 the following example, the initializer for @samp{a} is not fully
3027 bracketed, but that for @samp{b} is fully bracketed.
3028
3029 @smallexample
3030 int a[2][2] = @{ 0, 1, 2, 3 @};
3031 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
3032 @end smallexample
3033
3034 This warning is enabled by @option{-Wall}.
3035
3036 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
3037 @opindex Wmissing-include-dirs
3038 @opindex Wno-missing-include-dirs
3039 Warn if a user-supplied include directory does not exist.
3040
3041 @item -Wparentheses
3042 @opindex Wparentheses
3043 @opindex Wno-parentheses
3044 Warn if parentheses are omitted in certain contexts, such
3045 as when there is an assignment in a context where a truth value
3046 is expected, or when operators are nested whose precedence people
3047 often get confused about.
3048
3049 Also warn if a comparison like @samp{x<=y<=z} appears; this is
3050 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
3051 interpretation from that of ordinary mathematical notation.
3052
3053 Also warn about constructions where there may be confusion to which
3054 @code{if} statement an @code{else} branch belongs. Here is an example of
3055 such a case:
3056
3057 @smallexample
3058 @group
3059 @{
3060 if (a)
3061 if (b)
3062 foo ();
3063 else
3064 bar ();
3065 @}
3066 @end group
3067 @end smallexample
3068
3069 In C/C++, every @code{else} branch belongs to the innermost possible
3070 @code{if} statement, which in this example is @code{if (b)}. This is
3071 often not what the programmer expected, as illustrated in the above
3072 example by indentation the programmer chose. When there is the
3073 potential for this confusion, GCC will issue a warning when this flag
3074 is specified. To eliminate the warning, add explicit braces around
3075 the innermost @code{if} statement so there is no way the @code{else}
3076 could belong to the enclosing @code{if}. The resulting code would
3077 look like this:
3078
3079 @smallexample
3080 @group
3081 @{
3082 if (a)
3083 @{
3084 if (b)
3085 foo ();
3086 else
3087 bar ();
3088 @}
3089 @}
3090 @end group
3091 @end smallexample
3092
3093 This warning is enabled by @option{-Wall}.
3094
3095 @item -Wsequence-point
3096 @opindex Wsequence-point
3097 @opindex Wno-sequence-point
3098 Warn about code that may have undefined semantics because of violations
3099 of sequence point rules in the C and C++ standards.
3100
3101 The C and C++ standards defines the order in which expressions in a C/C++
3102 program are evaluated in terms of @dfn{sequence points}, which represent
3103 a partial ordering between the execution of parts of the program: those
3104 executed before the sequence point, and those executed after it. These
3105 occur after the evaluation of a full expression (one which is not part
3106 of a larger expression), after the evaluation of the first operand of a
3107 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3108 function is called (but after the evaluation of its arguments and the
3109 expression denoting the called function), and in certain other places.
3110 Other than as expressed by the sequence point rules, the order of
3111 evaluation of subexpressions of an expression is not specified. All
3112 these rules describe only a partial order rather than a total order,
3113 since, for example, if two functions are called within one expression
3114 with no sequence point between them, the order in which the functions
3115 are called is not specified. However, the standards committee have
3116 ruled that function calls do not overlap.
3117
3118 It is not specified when between sequence points modifications to the
3119 values of objects take effect. Programs whose behavior depends on this
3120 have undefined behavior; the C and C++ standards specify that ``Between
3121 the previous and next sequence point an object shall have its stored
3122 value modified at most once by the evaluation of an expression.
3123 Furthermore, the prior value shall be read only to determine the value
3124 to be stored.''. If a program breaks these rules, the results on any
3125 particular implementation are entirely unpredictable.
3126
3127 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3128 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3129 diagnosed by this option, and it may give an occasional false positive
3130 result, but in general it has been found fairly effective at detecting
3131 this sort of problem in programs.
3132
3133 The standard is worded confusingly, therefore there is some debate
3134 over the precise meaning of the sequence point rules in subtle cases.
3135 Links to discussions of the problem, including proposed formal
3136 definitions, may be found on the GCC readings page, at
3137 @w{@uref{http://gcc.gnu.org/readings.html}}.
3138
3139 This warning is enabled by @option{-Wall} for C and C++.
3140
3141 @item -Wreturn-type
3142 @opindex Wreturn-type
3143 @opindex Wno-return-type
3144 Warn whenever a function is defined with a return-type that defaults
3145 to @code{int}. Also warn about any @code{return} statement with no
3146 return-value in a function whose return-type is not @code{void}
3147 (falling off the end of the function body is considered returning
3148 without a value), and about a @code{return} statement with a
3149 expression in a function whose return-type is @code{void}.
3150
3151 For C++, a function without return type always produces a diagnostic
3152 message, even when @option{-Wno-return-type} is specified. The only
3153 exceptions are @samp{main} and functions defined in system headers.
3154
3155 This warning is enabled by @option{-Wall}.
3156
3157 @item -Wswitch
3158 @opindex Wswitch
3159 @opindex Wno-switch
3160 Warn whenever a @code{switch} statement has an index of enumerated type
3161 and lacks a @code{case} for one or more of the named codes of that
3162 enumeration. (The presence of a @code{default} label prevents this
3163 warning.) @code{case} labels outside the enumeration range also
3164 provoke warnings when this option is used.
3165 This warning is enabled by @option{-Wall}.
3166
3167 @item -Wswitch-default
3168 @opindex Wswitch-default
3169 @opindex Wno-switch-default
3170 Warn whenever a @code{switch} statement does not have a @code{default}
3171 case.
3172
3173 @item -Wswitch-enum
3174 @opindex Wswitch-enum
3175 @opindex Wno-switch-enum
3176 Warn whenever a @code{switch} statement has an index of enumerated type
3177 and lacks a @code{case} for one or more of the named codes of that
3178 enumeration. @code{case} labels outside the enumeration range also
3179 provoke warnings when this option is used.
3180
3181 @item -Wsync-nand @r{(C and C++ only)}
3182 @opindex Wsync-nand
3183 @opindex Wno-sync-nand
3184 Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
3185 built-in functions are used. These functions changed semantics in GCC 4.4.
3186
3187 @item -Wtrigraphs
3188 @opindex Wtrigraphs
3189 @opindex Wno-trigraphs
3190 Warn if any trigraphs are encountered that might change the meaning of
3191 the program (trigraphs within comments are not warned about).
3192 This warning is enabled by @option{-Wall}.
3193
3194 @item -Wunused-function
3195 @opindex Wunused-function
3196 @opindex Wno-unused-function
3197 Warn whenever a static function is declared but not defined or a
3198 non-inline static function is unused.
3199 This warning is enabled by @option{-Wall}.
3200
3201 @item -Wunused-label
3202 @opindex Wunused-label
3203 @opindex Wno-unused-label
3204 Warn whenever a label is declared but not used.
3205 This warning is enabled by @option{-Wall}.
3206
3207 To suppress this warning use the @samp{unused} attribute
3208 (@pxref{Variable Attributes}).
3209
3210 @item -Wunused-parameter
3211 @opindex Wunused-parameter
3212 @opindex Wno-unused-parameter
3213 Warn whenever a function parameter is unused aside from its declaration.
3214
3215 To suppress this warning use the @samp{unused} attribute
3216 (@pxref{Variable Attributes}).
3217
3218 @item -Wunused-variable
3219 @opindex Wunused-variable
3220 @opindex Wno-unused-variable
3221 Warn whenever a local variable or non-constant static variable is unused
3222 aside from its declaration.
3223 This warning is enabled by @option{-Wall}.
3224
3225 To suppress this warning use the @samp{unused} attribute
3226 (@pxref{Variable Attributes}).
3227
3228 @item -Wunused-value
3229 @opindex Wunused-value
3230 @opindex Wno-unused-value
3231 Warn whenever a statement computes a result that is explicitly not
3232 used. To suppress this warning cast the unused expression to
3233 @samp{void}. This includes an expression-statement or the left-hand
3234 side of a comma expression that contains no side effects. For example,
3235 an expression such as @samp{x[i,j]} will cause a warning, while
3236 @samp{x[(void)i,j]} will not.
3237
3238 This warning is enabled by @option{-Wall}.
3239
3240 @item -Wunused
3241 @opindex Wunused
3242 @opindex Wno-unused
3243 All the above @option{-Wunused} options combined.
3244
3245 In order to get a warning about an unused function parameter, you must
3246 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
3247 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
3248
3249 @item -Wuninitialized
3250 @opindex Wuninitialized
3251 @opindex Wno-uninitialized
3252 Warn if an automatic variable is used without first being initialized
3253 or if a variable may be clobbered by a @code{setjmp} call. In C++,
3254 warn if a non-static reference or non-static @samp{const} member
3255 appears in a class without constructors.
3256
3257 If you want to warn about code which uses the uninitialized value of the
3258 variable in its own initializer, use the @option{-Winit-self} option.
3259
3260 These warnings occur for individual uninitialized or clobbered
3261 elements of structure, union or array variables as well as for
3262 variables which are uninitialized or clobbered as a whole. They do
3263 not occur for variables or elements declared @code{volatile}. Because
3264 these warnings depend on optimization, the exact variables or elements
3265 for which there are warnings will depend on the precise optimization
3266 options and version of GCC used.
3267
3268 Note that there may be no warning about a variable that is used only
3269 to compute a value that itself is never used, because such
3270 computations may be deleted by data flow analysis before the warnings
3271 are printed.
3272
3273 These warnings are made optional because GCC is not smart
3274 enough to see all the reasons why the code might be correct
3275 despite appearing to have an error. Here is one example of how
3276 this can happen:
3277
3278 @smallexample
3279 @group
3280 @{
3281 int x;
3282 switch (y)
3283 @{
3284 case 1: x = 1;
3285 break;
3286 case 2: x = 4;
3287 break;
3288 case 3: x = 5;
3289 @}
3290 foo (x);
3291 @}
3292 @end group
3293 @end smallexample
3294
3295 @noindent
3296 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
3297 always initialized, but GCC doesn't know this. Here is
3298 another common case:
3299
3300 @smallexample
3301 @{
3302 int save_y;
3303 if (change_y) save_y = y, y = new_y;
3304 @dots{}
3305 if (change_y) y = save_y;
3306 @}
3307 @end smallexample
3308
3309 @noindent
3310 This has no bug because @code{save_y} is used only if it is set.
3311
3312 @cindex @code{longjmp} warnings
3313 This option also warns when a non-volatile automatic variable might be
3314 changed by a call to @code{longjmp}. These warnings as well are possible
3315 only in optimizing compilation.
3316
3317 The compiler sees only the calls to @code{setjmp}. It cannot know
3318 where @code{longjmp} will be called; in fact, a signal handler could
3319 call it at any point in the code. As a result, you may get a warning
3320 even when there is in fact no problem because @code{longjmp} cannot
3321 in fact be called at the place which would cause a problem.
3322
3323 Some spurious warnings can be avoided if you declare all the functions
3324 you use that never return as @code{noreturn}. @xref{Function
3325 Attributes}.
3326
3327 This warning is enabled by @option{-Wall} or @option{-Wextra}.
3328
3329 @item -Wunknown-pragmas
3330 @opindex Wunknown-pragmas
3331 @opindex Wno-unknown-pragmas
3332 @cindex warning for unknown pragmas
3333 @cindex unknown pragmas, warning
3334 @cindex pragmas, warning of unknown
3335 Warn when a #pragma directive is encountered which is not understood by
3336 GCC@. If this command line option is used, warnings will even be issued
3337 for unknown pragmas in system header files. This is not the case if
3338 the warnings were only enabled by the @option{-Wall} command line option.
3339
3340 @item -Wno-pragmas
3341 @opindex Wno-pragmas
3342 @opindex Wpragmas
3343 Do not warn about misuses of pragmas, such as incorrect parameters,
3344 invalid syntax, or conflicts between pragmas. See also
3345 @samp{-Wunknown-pragmas}.
3346
3347 @item -Wstrict-aliasing
3348 @opindex Wstrict-aliasing
3349 @opindex Wno-strict-aliasing
3350 This option is only active when @option{-fstrict-aliasing} is active.
3351 It warns about code which might break the strict aliasing rules that the
3352 compiler is using for optimization. The warning does not catch all
3353 cases, but does attempt to catch the more common pitfalls. It is
3354 included in @option{-Wall}.
3355 It is equivalent to @option{-Wstrict-aliasing=3}
3356
3357 @item -Wstrict-aliasing=n
3358 @opindex Wstrict-aliasing=n
3359 @opindex Wno-strict-aliasing=n
3360 This option is only active when @option{-fstrict-aliasing} is active.
3361 It warns about code which might break the strict aliasing rules that the
3362 compiler is using for optimization.
3363 Higher levels correspond to higher accuracy (fewer false positives).
3364 Higher levels also correspond to more effort, similar to the way -O works.
3365 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3366 with n=3.
3367
3368 Level 1: Most aggressive, quick, least accurate.
3369 Possibly useful when higher levels
3370 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3371 false negatives. However, it has many false positives.
3372 Warns for all pointer conversions between possibly incompatible types,
3373 even if never dereferenced. Runs in the frontend only.
3374
3375 Level 2: Aggressive, quick, not too precise.
3376 May still have many false positives (not as many as level 1 though),
3377 and few false negatives (but possibly more than level 1).
3378 Unlike level 1, it only warns when an address is taken. Warns about
3379 incomplete types. Runs in the frontend only.
3380
3381 Level 3 (default for @option{-Wstrict-aliasing}):
3382 Should have very few false positives and few false
3383 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3384 Takes care of the common punn+dereference pattern in the frontend:
3385 @code{*(int*)&some_float}.
3386 If optimization is enabled, it also runs in the backend, where it deals
3387 with multiple statement cases using flow-sensitive points-to information.
3388 Only warns when the converted pointer is dereferenced.
3389 Does not warn about incomplete types.
3390
3391 @item -Wstrict-overflow
3392 @itemx -Wstrict-overflow=@var{n}
3393 @opindex Wstrict-overflow
3394 @opindex Wno-strict-overflow
3395 This option is only active when @option{-fstrict-overflow} is active.
3396 It warns about cases where the compiler optimizes based on the
3397 assumption that signed overflow does not occur. Note that it does not
3398 warn about all cases where the code might overflow: it only warns
3399 about cases where the compiler implements some optimization. Thus
3400 this warning depends on the optimization level.
3401
3402 An optimization which assumes that signed overflow does not occur is
3403 perfectly safe if the values of the variables involved are such that
3404 overflow never does, in fact, occur. Therefore this warning can
3405 easily give a false positive: a warning about code which is not
3406 actually a problem. To help focus on important issues, several
3407 warning levels are defined. No warnings are issued for the use of
3408 undefined signed overflow when estimating how many iterations a loop
3409 will require, in particular when determining whether a loop will be
3410 executed at all.
3411
3412 @table @gcctabopt
3413 @item -Wstrict-overflow=1
3414 Warn about cases which are both questionable and easy to avoid. For
3415 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3416 compiler will simplify this to @code{1}. This level of
3417 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3418 are not, and must be explicitly requested.
3419
3420 @item -Wstrict-overflow=2
3421 Also warn about other cases where a comparison is simplified to a
3422 constant. For example: @code{abs (x) >= 0}. This can only be
3423 simplified when @option{-fstrict-overflow} is in effect, because
3424 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3425 zero. @option{-Wstrict-overflow} (with no level) is the same as
3426 @option{-Wstrict-overflow=2}.
3427
3428 @item -Wstrict-overflow=3
3429 Also warn about other cases where a comparison is simplified. For
3430 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3431
3432 @item -Wstrict-overflow=4
3433 Also warn about other simplifications not covered by the above cases.
3434 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3435
3436 @item -Wstrict-overflow=5
3437 Also warn about cases where the compiler reduces the magnitude of a
3438 constant involved in a comparison. For example: @code{x + 2 > y} will
3439 be simplified to @code{x + 1 >= y}. This is reported only at the
3440 highest warning level because this simplification applies to many
3441 comparisons, so this warning level will give a very large number of
3442 false positives.
3443 @end table
3444
3445 @item -Warray-bounds
3446 @opindex Wno-array-bounds
3447 @opindex Warray-bounds
3448 This option is only active when @option{-ftree-vrp} is active
3449 (default for -O2 and above). It warns about subscripts to arrays
3450 that are always out of bounds. This warning is enabled by @option{-Wall}.
3451
3452 @item -Wno-div-by-zero
3453 @opindex Wno-div-by-zero
3454 @opindex Wdiv-by-zero
3455 Do not warn about compile-time integer division by zero. Floating point
3456 division by zero is not warned about, as it can be a legitimate way of
3457 obtaining infinities and NaNs.
3458
3459 @item -Wsystem-headers
3460 @opindex Wsystem-headers
3461 @opindex Wno-system-headers
3462 @cindex warnings from system headers
3463 @cindex system headers, warnings from
3464 Print warning messages for constructs found in system header files.
3465 Warnings from system headers are normally suppressed, on the assumption
3466 that they usually do not indicate real problems and would only make the
3467 compiler output harder to read. Using this command line option tells
3468 GCC to emit warnings from system headers as if they occurred in user
3469 code. However, note that using @option{-Wall} in conjunction with this
3470 option will @emph{not} warn about unknown pragmas in system
3471 headers---for that, @option{-Wunknown-pragmas} must also be used.
3472
3473 @item -Wfloat-equal
3474 @opindex Wfloat-equal
3475 @opindex Wno-float-equal
3476 Warn if floating point values are used in equality comparisons.
3477
3478 The idea behind this is that sometimes it is convenient (for the
3479 programmer) to consider floating-point values as approximations to
3480 infinitely precise real numbers. If you are doing this, then you need
3481 to compute (by analyzing the code, or in some other way) the maximum or
3482 likely maximum error that the computation introduces, and allow for it
3483 when performing comparisons (and when producing output, but that's a
3484 different problem). In particular, instead of testing for equality, you
3485 would check to see whether the two values have ranges that overlap; and
3486 this is done with the relational operators, so equality comparisons are
3487 probably mistaken.
3488
3489 @item -Wtraditional @r{(C and Objective-C only)}
3490 @opindex Wtraditional
3491 @opindex Wno-traditional
3492 Warn about certain constructs that behave differently in traditional and
3493 ISO C@. Also warn about ISO C constructs that have no traditional C
3494 equivalent, and/or problematic constructs which should be avoided.
3495
3496 @itemize @bullet
3497 @item
3498 Macro parameters that appear within string literals in the macro body.
3499 In traditional C macro replacement takes place within string literals,
3500 but does not in ISO C@.
3501
3502 @item
3503 In traditional C, some preprocessor directives did not exist.
3504 Traditional preprocessors would only consider a line to be a directive
3505 if the @samp{#} appeared in column 1 on the line. Therefore
3506 @option{-Wtraditional} warns about directives that traditional C
3507 understands but would ignore because the @samp{#} does not appear as the
3508 first character on the line. It also suggests you hide directives like
3509 @samp{#pragma} not understood by traditional C by indenting them. Some
3510 traditional implementations would not recognize @samp{#elif}, so it
3511 suggests avoiding it altogether.
3512
3513 @item
3514 A function-like macro that appears without arguments.
3515
3516 @item
3517 The unary plus operator.
3518
3519 @item
3520 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3521 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3522 constants.) Note, these suffixes appear in macros defined in the system
3523 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3524 Use of these macros in user code might normally lead to spurious
3525 warnings, however GCC's integrated preprocessor has enough context to
3526 avoid warning in these cases.
3527
3528 @item
3529 A function declared external in one block and then used after the end of
3530 the block.
3531
3532 @item
3533 A @code{switch} statement has an operand of type @code{long}.
3534
3535 @item
3536 A non-@code{static} function declaration follows a @code{static} one.
3537 This construct is not accepted by some traditional C compilers.
3538
3539 @item
3540 The ISO type of an integer constant has a different width or
3541 signedness from its traditional type. This warning is only issued if
3542 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3543 typically represent bit patterns, are not warned about.
3544
3545 @item
3546 Usage of ISO string concatenation is detected.
3547
3548 @item
3549 Initialization of automatic aggregates.
3550
3551 @item
3552 Identifier conflicts with labels. Traditional C lacks a separate
3553 namespace for labels.
3554
3555 @item
3556 Initialization of unions. If the initializer is zero, the warning is
3557 omitted. This is done under the assumption that the zero initializer in
3558 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3559 initializer warnings and relies on default initialization to zero in the
3560 traditional C case.
3561
3562 @item
3563 Conversions by prototypes between fixed/floating point values and vice
3564 versa. The absence of these prototypes when compiling with traditional
3565 C would cause serious problems. This is a subset of the possible
3566 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3567
3568 @item
3569 Use of ISO C style function definitions. This warning intentionally is
3570 @emph{not} issued for prototype declarations or variadic functions
3571 because these ISO C features will appear in your code when using
3572 libiberty's traditional C compatibility macros, @code{PARAMS} and
3573 @code{VPARAMS}. This warning is also bypassed for nested functions
3574 because that feature is already a GCC extension and thus not relevant to
3575 traditional C compatibility.
3576 @end itemize
3577
3578 @item -Wtraditional-conversion @r{(C and Objective-C only)}
3579 @opindex Wtraditional-conversion
3580 @opindex Wno-traditional-conversion
3581 Warn if a prototype causes a type conversion that is different from what
3582 would happen to the same argument in the absence of a prototype. This
3583 includes conversions of fixed point to floating and vice versa, and
3584 conversions changing the width or signedness of a fixed point argument
3585 except when the same as the default promotion.
3586
3587 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
3588 @opindex Wdeclaration-after-statement
3589 @opindex Wno-declaration-after-statement
3590 Warn when a declaration is found after a statement in a block. This
3591 construct, known from C++, was introduced with ISO C99 and is by default
3592 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3593 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3594
3595 @item -Wundef
3596 @opindex Wundef
3597 @opindex Wno-undef
3598 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3599
3600 @item -Wno-endif-labels
3601 @opindex Wno-endif-labels
3602 @opindex Wendif-labels
3603 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3604
3605 @item -Wshadow
3606 @opindex Wshadow
3607 @opindex Wno-shadow
3608 Warn whenever a local variable shadows another local variable, parameter or
3609 global variable or whenever a built-in function is shadowed.
3610
3611 @item -Wlarger-than=@var{len}
3612 @opindex Wlarger-than=@var{len}
3613 @opindex Wlarger-than-@var{len}
3614 Warn whenever an object of larger than @var{len} bytes is defined.
3615
3616 @item -Wframe-larger-than=@var{len}
3617 @opindex Wframe-larger-than
3618 Warn if the size of a function frame is larger than @var{len} bytes.
3619 The computation done to determine the stack frame size is approximate
3620 and not conservative.
3621 The actual requirements may be somewhat greater than @var{len}
3622 even if you do not get a warning. In addition, any space allocated
3623 via @code{alloca}, variable-length arrays, or related constructs
3624 is not included by the compiler when determining
3625 whether or not to issue a warning.
3626
3627 @item -Wunsafe-loop-optimizations
3628 @opindex Wunsafe-loop-optimizations
3629 @opindex Wno-unsafe-loop-optimizations
3630 Warn if the loop cannot be optimized because the compiler could not
3631 assume anything on the bounds of the loop indices. With
3632 @option{-funsafe-loop-optimizations} warn if the compiler made
3633 such assumptions.
3634
3635 @item -Wno-pedantic-ms-format @r{(MinGW targets only)}
3636 @opindex Wno-pedantic-ms-format
3637 @opindex Wpedantic-ms-format
3638 Disables the warnings about non-ISO @code{printf} / @code{scanf} format
3639 width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets
3640 depending on the MS runtime, when you are using the options @option{-Wformat}
3641 and @option{-pedantic} without gnu-extensions.
3642
3643 @item -Wpointer-arith
3644 @opindex Wpointer-arith
3645 @opindex Wno-pointer-arith
3646 Warn about anything that depends on the ``size of'' a function type or
3647 of @code{void}. GNU C assigns these types a size of 1, for
3648 convenience in calculations with @code{void *} pointers and pointers
3649 to functions. In C++, warn also when an arithmetic operation involves
3650 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3651
3652 @item -Wtype-limits
3653 @opindex Wtype-limits
3654 @opindex Wno-type-limits
3655 Warn if a comparison is always true or always false due to the limited
3656 range of the data type, but do not warn for constant expressions. For
3657 example, warn if an unsigned variable is compared against zero with
3658 @samp{<} or @samp{>=}. This warning is also enabled by
3659 @option{-Wextra}.
3660
3661 @item -Wbad-function-cast @r{(C and Objective-C only)}
3662 @opindex Wbad-function-cast
3663 @opindex Wno-bad-function-cast
3664 Warn whenever a function call is cast to a non-matching type.
3665 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3666
3667 @item -Wc++-compat @r{(C and Objective-C only)}
3668 Warn about ISO C constructs that are outside of the common subset of
3669 ISO C and ISO C++, e.g.@: request for implicit conversion from
3670 @code{void *} to a pointer to non-@code{void} type.
3671
3672 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3673 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3674 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3675 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3676
3677 @item -Wcast-qual
3678 @opindex Wcast-qual
3679 @opindex Wno-cast-qual
3680 Warn whenever a pointer is cast so as to remove a type qualifier from
3681 the target type. For example, warn if a @code{const char *} is cast
3682 to an ordinary @code{char *}.
3683
3684 @item -Wcast-align
3685 @opindex Wcast-align
3686 @opindex Wno-cast-align
3687 Warn whenever a pointer is cast such that the required alignment of the
3688 target is increased. For example, warn if a @code{char *} is cast to
3689 an @code{int *} on machines where integers can only be accessed at
3690 two- or four-byte boundaries.
3691
3692 @item -Wwrite-strings
3693 @opindex Wwrite-strings
3694 @opindex Wno-write-strings
3695 When compiling C, give string constants the type @code{const
3696 char[@var{length}]} so that copying the address of one into a
3697 non-@code{const} @code{char *} pointer will get a warning. These
3698 warnings will help you find at compile time code that can try to write
3699 into a string constant, but only if you have been very careful about
3700 using @code{const} in declarations and prototypes. Otherwise, it will
3701 just be a nuisance. This is why we did not make @option{-Wall} request
3702 these warnings.
3703
3704 When compiling C++, warn about the deprecated conversion from string
3705 literals to @code{char *}. This warning is enabled by default for C++
3706 programs.
3707
3708 @item -Wclobbered
3709 @opindex Wclobbered
3710 @opindex Wno-clobbered
3711 Warn for variables that might be changed by @samp{longjmp} or
3712 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
3713
3714 @item -Wconversion
3715 @opindex Wconversion
3716 @opindex Wno-conversion
3717 Warn for implicit conversions that may alter a value. This includes
3718 conversions between real and integer, like @code{abs (x)} when
3719 @code{x} is @code{double}; conversions between signed and unsigned,
3720 like @code{unsigned ui = -1}; and conversions to smaller types, like
3721 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3722 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3723 changed by the conversion like in @code{abs (2.0)}. Warnings about
3724 conversions between signed and unsigned integers can be disabled by
3725 using @option{-Wno-sign-conversion}.
3726
3727 For C++, also warn for conversions between @code{NULL} and non-pointer
3728 types; confusing overload resolution for user-defined conversions; and
3729 conversions that will never use a type conversion operator:
3730 conversions to @code{void}, the same type, a base class or a reference
3731 to them. Warnings about conversions between signed and unsigned
3732 integers are disabled by default in C++ unless
3733 @option{-Wsign-conversion} is explicitly enabled.
3734
3735 @item -Wempty-body
3736 @opindex Wempty-body
3737 @opindex Wno-empty-body
3738 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
3739 while} statement. This warning is also enabled by @option{-Wextra}.
3740
3741 @item -Wenum-compare @r{(C++ and Objective-C++ only)}
3742 @opindex Wenum-compare
3743 @opindex Wno-enum-compare
3744 Warn about a comparison between values of different enum types. This
3745 warning is enabled by default.
3746
3747 @item -Wsign-compare
3748 @opindex Wsign-compare
3749 @opindex Wno-sign-compare
3750 @cindex warning for comparison of signed and unsigned values
3751 @cindex comparison of signed and unsigned values, warning
3752 @cindex signed and unsigned values, comparison warning
3753 Warn when a comparison between signed and unsigned values could produce
3754 an incorrect result when the signed value is converted to unsigned.
3755 This warning is also enabled by @option{-Wextra}; to get the other warnings
3756 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3757
3758 @item -Wsign-conversion
3759 @opindex Wsign-conversion
3760 @opindex Wno-sign-conversion
3761 Warn for implicit conversions that may change the sign of an integer
3762 value, like assigning a signed integer expression to an unsigned
3763 integer variable. An explicit cast silences the warning. In C, this
3764 option is enabled also by @option{-Wconversion}.
3765
3766 @item -Waddress
3767 @opindex Waddress
3768 @opindex Wno-address
3769 Warn about suspicious uses of memory addresses. These include using
3770 the address of a function in a conditional expression, such as
3771 @code{void func(void); if (func)}, and comparisons against the memory
3772 address of a string literal, such as @code{if (x == "abc")}. Such
3773 uses typically indicate a programmer error: the address of a function
3774 always evaluates to true, so their use in a conditional usually
3775 indicate that the programmer forgot the parentheses in a function
3776 call; and comparisons against string literals result in unspecified
3777 behavior and are not portable in C, so they usually indicate that the
3778 programmer intended to use @code{strcmp}. This warning is enabled by
3779 @option{-Wall}.
3780
3781 @item -Wlogical-op
3782 @opindex Wlogical-op
3783 @opindex Wno-logical-op
3784 Warn about suspicious uses of logical operators in expressions.
3785 This includes using logical operators in contexts where a
3786 bit-wise operator is likely to be expected.
3787
3788 @item -Waggregate-return
3789 @opindex Waggregate-return
3790 @opindex Wno-aggregate-return
3791 Warn if any functions that return structures or unions are defined or
3792 called. (In languages where you can return an array, this also elicits
3793 a warning.)
3794
3795 @item -Wno-attributes
3796 @opindex Wno-attributes
3797 @opindex Wattributes
3798 Do not warn if an unexpected @code{__attribute__} is used, such as
3799 unrecognized attributes, function attributes applied to variables,
3800 etc. This will not stop errors for incorrect use of supported
3801 attributes.
3802
3803 @item -Wno-builtin-macro-redefined
3804 @opindex Wno-builtin-macro-redefined
3805 @opindex Wbuiltin-macro-redefined
3806 Do not warn if certain built-in macros are redefined. This suppresses
3807 warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__},
3808 @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}.
3809
3810 @item -Wstrict-prototypes @r{(C and Objective-C only)}
3811 @opindex Wstrict-prototypes
3812 @opindex Wno-strict-prototypes
3813 Warn if a function is declared or defined without specifying the
3814 argument types. (An old-style function definition is permitted without
3815 a warning if preceded by a declaration which specifies the argument
3816 types.)
3817
3818 @item -Wold-style-declaration @r{(C and Objective-C only)}
3819 @opindex Wold-style-declaration
3820 @opindex Wno-old-style-declaration
3821 Warn for obsolescent usages, according to the C Standard, in a
3822 declaration. For example, warn if storage-class specifiers like
3823 @code{static} are not the first things in a declaration. This warning
3824 is also enabled by @option{-Wextra}.
3825
3826 @item -Wold-style-definition @r{(C and Objective-C only)}
3827 @opindex Wold-style-definition
3828 @opindex Wno-old-style-definition
3829 Warn if an old-style function definition is used. A warning is given
3830 even if there is a previous prototype.
3831
3832 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
3833 @opindex Wmissing-parameter-type
3834 @opindex Wno-missing-parameter-type
3835 A function parameter is declared without a type specifier in K&R-style
3836 functions:
3837
3838 @smallexample
3839 void foo(bar) @{ @}
3840 @end smallexample
3841
3842 This warning is also enabled by @option{-Wextra}.
3843
3844 @item -Wmissing-prototypes @r{(C and Objective-C only)}
3845 @opindex Wmissing-prototypes
3846 @opindex Wno-missing-prototypes
3847 Warn if a global function is defined without a previous prototype
3848 declaration. This warning is issued even if the definition itself
3849 provides a prototype. The aim is to detect global functions that fail
3850 to be declared in header files.
3851
3852 @item -Wmissing-declarations
3853 @opindex Wmissing-declarations
3854 @opindex Wno-missing-declarations
3855 Warn if a global function is defined without a previous declaration.
3856 Do so even if the definition itself provides a prototype.
3857 Use this option to detect global functions that are not declared in
3858 header files. In C++, no warnings are issued for function templates,
3859 or for inline functions, or for functions in anonymous namespaces.
3860
3861 @item -Wmissing-field-initializers
3862 @opindex Wmissing-field-initializers
3863 @opindex Wno-missing-field-initializers
3864 @opindex W
3865 @opindex Wextra
3866 @opindex Wno-extra
3867 Warn if a structure's initializer has some fields missing. For
3868 example, the following code would cause such a warning, because
3869 @code{x.h} is implicitly zero:
3870
3871 @smallexample
3872 struct s @{ int f, g, h; @};
3873 struct s x = @{ 3, 4 @};
3874 @end smallexample
3875
3876 This option does not warn about designated initializers, so the following
3877 modification would not trigger a warning:
3878
3879 @smallexample
3880 struct s @{ int f, g, h; @};
3881 struct s x = @{ .f = 3, .g = 4 @};
3882 @end smallexample
3883
3884 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3885 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3886
3887 @item -Wmissing-noreturn
3888 @opindex Wmissing-noreturn
3889 @opindex Wno-missing-noreturn
3890 Warn about functions which might be candidates for attribute @code{noreturn}.
3891 Note these are only possible candidates, not absolute ones. Care should
3892 be taken to manually verify functions actually do not ever return before
3893 adding the @code{noreturn} attribute, otherwise subtle code generation
3894 bugs could be introduced. You will not get a warning for @code{main} in
3895 hosted C environments.
3896
3897 @item -Wmissing-format-attribute
3898 @opindex Wmissing-format-attribute
3899 @opindex Wno-missing-format-attribute
3900 @opindex Wformat
3901 @opindex Wno-format
3902 Warn about function pointers which might be candidates for @code{format}
3903 attributes. Note these are only possible candidates, not absolute ones.
3904 GCC will guess that function pointers with @code{format} attributes that
3905 are used in assignment, initialization, parameter passing or return
3906 statements should have a corresponding @code{format} attribute in the
3907 resulting type. I.e.@: the left-hand side of the assignment or
3908 initialization, the type of the parameter variable, or the return type
3909 of the containing function respectively should also have a @code{format}
3910 attribute to avoid the warning.
3911
3912 GCC will also warn about function definitions which might be
3913 candidates for @code{format} attributes. Again, these are only
3914 possible candidates. GCC will guess that @code{format} attributes
3915 might be appropriate for any function that calls a function like
3916 @code{vprintf} or @code{vscanf}, but this might not always be the
3917 case, and some functions for which @code{format} attributes are
3918 appropriate may not be detected.
3919
3920 @item -Wno-multichar
3921 @opindex Wno-multichar
3922 @opindex Wmultichar
3923 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3924 Usually they indicate a typo in the user's code, as they have
3925 implementation-defined values, and should not be used in portable code.
3926
3927 @item -Wnormalized=<none|id|nfc|nfkc>
3928 @opindex Wnormalized=
3929 @cindex NFC
3930 @cindex NFKC
3931 @cindex character set, input normalization
3932 In ISO C and ISO C++, two identifiers are different if they are
3933 different sequences of characters. However, sometimes when characters
3934 outside the basic ASCII character set are used, you can have two
3935 different character sequences that look the same. To avoid confusion,
3936 the ISO 10646 standard sets out some @dfn{normalization rules} which
3937 when applied ensure that two sequences that look the same are turned into
3938 the same sequence. GCC can warn you if you are using identifiers which
3939 have not been normalized; this option controls that warning.
3940
3941 There are four levels of warning that GCC supports. The default is
3942 @option{-Wnormalized=nfc}, which warns about any identifier which is
3943 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3944 recommended form for most uses.
3945
3946 Unfortunately, there are some characters which ISO C and ISO C++ allow
3947 in identifiers that when turned into NFC aren't allowable as
3948 identifiers. That is, there's no way to use these symbols in portable
3949 ISO C or C++ and have all your identifiers in NFC@.
3950 @option{-Wnormalized=id} suppresses the warning for these characters.
3951 It is hoped that future versions of the standards involved will correct
3952 this, which is why this option is not the default.
3953
3954 You can switch the warning off for all characters by writing
3955 @option{-Wnormalized=none}. You would only want to do this if you
3956 were using some other normalization scheme (like ``D''), because
3957 otherwise you can easily create bugs that are literally impossible to see.
3958
3959 Some characters in ISO 10646 have distinct meanings but look identical
3960 in some fonts or display methodologies, especially once formatting has
3961 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3962 LETTER N'', will display just like a regular @code{n} which has been
3963 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3964 normalization scheme to convert all these into a standard form as
3965 well, and GCC will warn if your code is not in NFKC if you use
3966 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3967 about every identifier that contains the letter O because it might be
3968 confused with the digit 0, and so is not the default, but may be
3969 useful as a local coding convention if the programming environment is
3970 unable to be fixed to display these characters distinctly.
3971
3972 @item -Wno-deprecated
3973 @opindex Wno-deprecated
3974 @opindex Wdeprecated
3975 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
3976
3977 @item -Wno-deprecated-declarations
3978 @opindex Wno-deprecated-declarations
3979 @opindex Wdeprecated-declarations
3980 Do not warn about uses of functions (@pxref{Function Attributes}),
3981 variables (@pxref{Variable Attributes}), and types (@pxref{Type
3982 Attributes}) marked as deprecated by using the @code{deprecated}
3983 attribute.
3984
3985 @item -Wno-overflow
3986 @opindex Wno-overflow
3987 @opindex Woverflow
3988 Do not warn about compile-time overflow in constant expressions.
3989
3990 @item -Woverride-init @r{(C and Objective-C only)}
3991 @opindex Woverride-init
3992 @opindex Wno-override-init
3993 @opindex W
3994 @opindex Wextra
3995 @opindex Wno-extra
3996 Warn if an initialized field without side effects is overridden when
3997 using designated initializers (@pxref{Designated Inits, , Designated
3998 Initializers}).
3999
4000 This warning is included in @option{-Wextra}. To get other
4001 @option{-Wextra} warnings without this one, use @samp{-Wextra
4002 -Wno-override-init}.
4003
4004 @item -Wpacked
4005 @opindex Wpacked
4006 @opindex Wno-packed
4007 Warn if a structure is given the packed attribute, but the packed
4008 attribute has no effect on the layout or size of the structure.
4009 Such structures may be mis-aligned for little benefit. For
4010 instance, in this code, the variable @code{f.x} in @code{struct bar}
4011 will be misaligned even though @code{struct bar} does not itself
4012 have the packed attribute:
4013
4014 @smallexample
4015 @group
4016 struct foo @{
4017 int x;
4018 char a, b, c, d;
4019 @} __attribute__((packed));
4020 struct bar @{
4021 char z;
4022 struct foo f;
4023 @};
4024 @end group
4025 @end smallexample
4026
4027 @item -Wpacked-bitfield-compat
4028 @opindex Wpacked-bitfield-compat
4029 @opindex Wno-packed-bitfield-compat
4030 The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute
4031 on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but
4032 the change can lead to differences in the structure layout. GCC
4033 informs you when the offset of such a field has changed in GCC 4.4.
4034 For example there is no longer a 4-bit padding between field @code{a}
4035 and @code{b} in this structure:
4036
4037 @smallexample
4038 struct foo
4039 @{
4040 char a:4;
4041 char b:8;
4042 @} __attribute__ ((packed));
4043 @end smallexample
4044
4045 This warning is enabled by default. Use
4046 @option{-Wno-packed-bitfield-compat} to disable this warning.
4047
4048 @item -Wpadded
4049 @opindex Wpadded
4050 @opindex Wno-padded
4051 Warn if padding is included in a structure, either to align an element
4052 of the structure or to align the whole structure. Sometimes when this
4053 happens it is possible to rearrange the fields of the structure to
4054 reduce the padding and so make the structure smaller.
4055
4056 @item -Wredundant-decls
4057 @opindex Wredundant-decls
4058 @opindex Wno-redundant-decls
4059 Warn if anything is declared more than once in the same scope, even in
4060 cases where multiple declaration is valid and changes nothing.
4061
4062 @item -Wnested-externs @r{(C and Objective-C only)}
4063 @opindex Wnested-externs
4064 @opindex Wno-nested-externs
4065 Warn if an @code{extern} declaration is encountered within a function.
4066
4067 @item -Wunreachable-code
4068 @opindex Wunreachable-code
4069 @opindex Wno-unreachable-code
4070 Warn if the compiler detects that code will never be executed.
4071
4072 This option is intended to warn when the compiler detects that at
4073 least a whole line of source code will never be executed, because
4074 some condition is never satisfied or because it is after a
4075 procedure that never returns.
4076
4077 It is possible for this option to produce a warning even though there
4078 are circumstances under which part of the affected line can be executed,
4079 so care should be taken when removing apparently-unreachable code.
4080
4081 For instance, when a function is inlined, a warning may mean that the
4082 line is unreachable in only one inlined copy of the function.
4083
4084 This option is not made part of @option{-Wall} because in a debugging
4085 version of a program there is often substantial code which checks
4086 correct functioning of the program and is, hopefully, unreachable
4087 because the program does work. Another common use of unreachable
4088 code is to provide behavior which is selectable at compile-time.
4089
4090 @item -Winline
4091 @opindex Winline
4092 @opindex Wno-inline
4093 Warn if a function can not be inlined and it was declared as inline.
4094 Even with this option, the compiler will not warn about failures to
4095 inline functions declared in system headers.
4096
4097 The compiler uses a variety of heuristics to determine whether or not
4098 to inline a function. For example, the compiler takes into account
4099 the size of the function being inlined and the amount of inlining
4100 that has already been done in the current function. Therefore,
4101 seemingly insignificant changes in the source program can cause the
4102 warnings produced by @option{-Winline} to appear or disappear.
4103
4104 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
4105 @opindex Wno-invalid-offsetof
4106 @opindex Winvalid-offsetof
4107 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
4108 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
4109 to a non-POD type is undefined. In existing C++ implementations,
4110 however, @samp{offsetof} typically gives meaningful results even when
4111 applied to certain kinds of non-POD types. (Such as a simple
4112 @samp{struct} that fails to be a POD type only by virtue of having a
4113 constructor.) This flag is for users who are aware that they are
4114 writing nonportable code and who have deliberately chosen to ignore the
4115 warning about it.
4116
4117 The restrictions on @samp{offsetof} may be relaxed in a future version
4118 of the C++ standard.
4119
4120 @item -Wno-int-to-pointer-cast @r{(C and Objective-C only)}
4121 @opindex Wno-int-to-pointer-cast
4122 @opindex Wint-to-pointer-cast
4123 Suppress warnings from casts to pointer type of an integer of a
4124 different size.
4125
4126 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
4127 @opindex Wno-pointer-to-int-cast
4128 @opindex Wpointer-to-int-cast
4129 Suppress warnings from casts from a pointer to an integer type of a
4130 different size.
4131
4132 @item -Winvalid-pch
4133 @opindex Winvalid-pch
4134 @opindex Wno-invalid-pch
4135 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
4136 the search path but can't be used.
4137
4138 @item -Wlong-long
4139 @opindex Wlong-long
4140 @opindex Wno-long-long
4141 Warn if @samp{long long} type is used. This is default. To inhibit
4142 the warning messages, use @option{-Wno-long-long}. Flags
4143 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
4144 only when @option{-pedantic} flag is used.
4145
4146 @item -Wvariadic-macros
4147 @opindex Wvariadic-macros
4148 @opindex Wno-variadic-macros
4149 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
4150 alternate syntax when in pedantic ISO C99 mode. This is default.
4151 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
4152
4153 @item -Wvla
4154 @opindex Wvla
4155 @opindex Wno-vla
4156 Warn if variable length array is used in the code.
4157 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
4158 the variable length array.
4159
4160 @item -Wvolatile-register-var
4161 @opindex Wvolatile-register-var
4162 @opindex Wno-volatile-register-var
4163 Warn if a register variable is declared volatile. The volatile
4164 modifier does not inhibit all optimizations that may eliminate reads
4165 and/or writes to register variables. This warning is enabled by
4166 @option{-Wall}.
4167
4168 @item -Wdisabled-optimization
4169 @opindex Wdisabled-optimization
4170 @opindex Wno-disabled-optimization
4171 Warn if a requested optimization pass is disabled. This warning does
4172 not generally indicate that there is anything wrong with your code; it
4173 merely indicates that GCC's optimizers were unable to handle the code
4174 effectively. Often, the problem is that your code is too big or too
4175 complex; GCC will refuse to optimize programs when the optimization
4176 itself is likely to take inordinate amounts of time.
4177
4178 @item -Wpointer-sign @r{(C and Objective-C only)}
4179 @opindex Wpointer-sign
4180 @opindex Wno-pointer-sign
4181 Warn for pointer argument passing or assignment with different signedness.
4182 This option is only supported for C and Objective-C@. It is implied by
4183 @option{-Wall} and by @option{-pedantic}, which can be disabled with
4184 @option{-Wno-pointer-sign}.
4185
4186 @item -Wstack-protector
4187 @opindex Wstack-protector
4188 @opindex Wno-stack-protector
4189 This option is only active when @option{-fstack-protector} is active. It
4190 warns about functions that will not be protected against stack smashing.
4191
4192 @item -Wno-mudflap
4193 @opindex Wno-mudflap
4194 Suppress warnings about constructs that cannot be instrumented by
4195 @option{-fmudflap}.
4196
4197 @item -Woverlength-strings
4198 @opindex Woverlength-strings
4199 @opindex Wno-overlength-strings
4200 Warn about string constants which are longer than the ``minimum
4201 maximum'' length specified in the C standard. Modern compilers
4202 generally allow string constants which are much longer than the
4203 standard's minimum limit, but very portable programs should avoid
4204 using longer strings.
4205
4206 The limit applies @emph{after} string constant concatenation, and does
4207 not count the trailing NUL@. In C89, the limit was 509 characters; in
4208 C99, it was raised to 4095. C++98 does not specify a normative
4209 minimum maximum, so we do not diagnose overlength strings in C++@.
4210
4211 This option is implied by @option{-pedantic}, and can be disabled with
4212 @option{-Wno-overlength-strings}.
4213 @end table
4214
4215 @node Debugging Options
4216 @section Options for Debugging Your Program or GCC
4217 @cindex options, debugging
4218 @cindex debugging information options
4219
4220 GCC has various special options that are used for debugging
4221 either your program or GCC:
4222
4223 @table @gcctabopt
4224 @item -g
4225 @opindex g
4226 Produce debugging information in the operating system's native format
4227 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
4228 information.
4229
4230 On most systems that use stabs format, @option{-g} enables use of extra
4231 debugging information that only GDB can use; this extra information
4232 makes debugging work better in GDB but will probably make other debuggers
4233 crash or
4234 refuse to read the program. If you want to control for certain whether
4235 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
4236 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
4237
4238 GCC allows you to use @option{-g} with
4239 @option{-O}. The shortcuts taken by optimized code may occasionally
4240 produce surprising results: some variables you declared may not exist
4241 at all; flow of control may briefly move where you did not expect it;
4242 some statements may not be executed because they compute constant
4243 results or their values were already at hand; some statements may
4244 execute in different places because they were moved out of loops.
4245
4246 Nevertheless it proves possible to debug optimized output. This makes
4247 it reasonable to use the optimizer for programs that might have bugs.
4248
4249 The following options are useful when GCC is generated with the
4250 capability for more than one debugging format.
4251
4252 @item -ggdb
4253 @opindex ggdb
4254 Produce debugging information for use by GDB@. This means to use the
4255 most expressive format available (DWARF 2, stabs, or the native format
4256 if neither of those are supported), including GDB extensions if at all
4257 possible.
4258
4259 @item -gstabs
4260 @opindex gstabs
4261 Produce debugging information in stabs format (if that is supported),
4262 without GDB extensions. This is the format used by DBX on most BSD
4263 systems. On MIPS, Alpha and System V Release 4 systems this option
4264 produces stabs debugging output which is not understood by DBX or SDB@.
4265 On System V Release 4 systems this option requires the GNU assembler.
4266
4267 @item -feliminate-unused-debug-symbols
4268 @opindex feliminate-unused-debug-symbols
4269 Produce debugging information in stabs format (if that is supported),
4270 for only symbols that are actually used.
4271
4272 @item -femit-class-debug-always
4273 Instead of emitting debugging information for a C++ class in only one
4274 object file, emit it in all object files using the class. This option
4275 should be used only with debuggers that are unable to handle the way GCC
4276 normally emits debugging information for classes because using this
4277 option will increase the size of debugging information by as much as a
4278 factor of two.
4279
4280 @item -gstabs+
4281 @opindex gstabs+
4282 Produce debugging information in stabs format (if that is supported),
4283 using GNU extensions understood only by the GNU debugger (GDB)@. The
4284 use of these extensions is likely to make other debuggers crash or
4285 refuse to read the program.
4286
4287 @item -gcoff
4288 @opindex gcoff
4289 Produce debugging information in COFF format (if that is supported).
4290 This is the format used by SDB on most System V systems prior to
4291 System V Release 4.
4292
4293 @item -gxcoff
4294 @opindex gxcoff
4295 Produce debugging information in XCOFF format (if that is supported).
4296 This is the format used by the DBX debugger on IBM RS/6000 systems.
4297
4298 @item -gxcoff+
4299 @opindex gxcoff+
4300 Produce debugging information in XCOFF format (if that is supported),
4301 using GNU extensions understood only by the GNU debugger (GDB)@. The
4302 use of these extensions is likely to make other debuggers crash or
4303 refuse to read the program, and may cause assemblers other than the GNU
4304 assembler (GAS) to fail with an error.
4305
4306 @item -gdwarf-2
4307 @opindex gdwarf-2
4308 Produce debugging information in DWARF version 2 format (if that is
4309 supported). This is the format used by DBX on IRIX 6. With this
4310 option, GCC uses features of DWARF version 3 when they are useful;
4311 version 3 is upward compatible with version 2, but may still cause
4312 problems for older debuggers.
4313
4314 @item -gvms
4315 @opindex gvms
4316 Produce debugging information in VMS debug format (if that is
4317 supported). This is the format used by DEBUG on VMS systems.
4318
4319 @item -g@var{level}
4320 @itemx -ggdb@var{level}
4321 @itemx -gstabs@var{level}
4322 @itemx -gcoff@var{level}
4323 @itemx -gxcoff@var{level}
4324 @itemx -gvms@var{level}
4325 Request debugging information and also use @var{level} to specify how
4326 much information. The default level is 2.
4327
4328 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4329 @option{-g}.
4330
4331 Level 1 produces minimal information, enough for making backtraces in
4332 parts of the program that you don't plan to debug. This includes
4333 descriptions of functions and external variables, but no information
4334 about local variables and no line numbers.
4335
4336 Level 3 includes extra information, such as all the macro definitions
4337 present in the program. Some debuggers support macro expansion when
4338 you use @option{-g3}.
4339
4340 @option{-gdwarf-2} does not accept a concatenated debug level, because
4341 GCC used to support an option @option{-gdwarf} that meant to generate
4342 debug information in version 1 of the DWARF format (which is very
4343 different from version 2), and it would have been too confusing. That
4344 debug format is long obsolete, but the option cannot be changed now.
4345 Instead use an additional @option{-g@var{level}} option to change the
4346 debug level for DWARF2.
4347
4348 @item -feliminate-dwarf2-dups
4349 @opindex feliminate-dwarf2-dups
4350 Compress DWARF2 debugging information by eliminating duplicated
4351 information about each symbol. This option only makes sense when
4352 generating DWARF2 debugging information with @option{-gdwarf-2}.
4353
4354 @item -femit-struct-debug-baseonly
4355 Emit debug information for struct-like types
4356 only when the base name of the compilation source file
4357 matches the base name of file in which the struct was defined.
4358
4359 This option substantially reduces the size of debugging information,
4360 but at significant potential loss in type information to the debugger.
4361 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4362 See @option{-femit-struct-debug-detailed} for more detailed control.
4363
4364 This option works only with DWARF 2.
4365
4366 @item -femit-struct-debug-reduced
4367 Emit debug information for struct-like types
4368 only when the base name of the compilation source file
4369 matches the base name of file in which the type was defined,
4370 unless the struct is a template or defined in a system header.
4371
4372 This option significantly reduces the size of debugging information,
4373 with some potential loss in type information to the debugger.
4374 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4375 See @option{-femit-struct-debug-detailed} for more detailed control.
4376
4377 This option works only with DWARF 2.
4378
4379 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4380 Specify the struct-like types
4381 for which the compiler will generate debug information.
4382 The intent is to reduce duplicate struct debug information
4383 between different object files within the same program.
4384
4385 This option is a detailed version of
4386 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4387 which will serve for most needs.
4388
4389 A specification has the syntax
4390 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4391
4392 The optional first word limits the specification to
4393 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4394 A struct type is used directly when it is the type of a variable, member.
4395 Indirect uses arise through pointers to structs.
4396 That is, when use of an incomplete struct would be legal, the use is indirect.
4397 An example is
4398 @samp{struct one direct; struct two * indirect;}.
4399
4400 The optional second word limits the specification to
4401 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4402 Generic structs are a bit complicated to explain.
4403 For C++, these are non-explicit specializations of template classes,
4404 or non-template classes within the above.
4405 Other programming languages have generics,
4406 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4407
4408 The third word specifies the source files for those
4409 structs for which the compiler will emit debug information.
4410 The values @samp{none} and @samp{any} have the normal meaning.
4411 The value @samp{base} means that
4412 the base of name of the file in which the type declaration appears
4413 must match the base of the name of the main compilation file.
4414 In practice, this means that
4415 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4416 but types declared in other header will not.
4417 The value @samp{sys} means those types satisfying @samp{base}
4418 or declared in system or compiler headers.
4419
4420 You may need to experiment to determine the best settings for your application.
4421
4422 The default is @samp{-femit-struct-debug-detailed=all}.
4423
4424 This option works only with DWARF 2.
4425
4426 @item -fno-merge-debug-strings
4427 @opindex fmerge-debug-strings
4428 @opindex fno-merge-debug-strings
4429 Direct the linker to not merge together strings in the debugging
4430 information which are identical in different object files. Merging is
4431 not supported by all assemblers or linkers. Merging decreases the size
4432 of the debug information in the output file at the cost of increasing
4433 link processing time. Merging is enabled by default.
4434
4435 @item -fdebug-prefix-map=@var{old}=@var{new}
4436 @opindex fdebug-prefix-map
4437 When compiling files in directory @file{@var{old}}, record debugging
4438 information describing them as in @file{@var{new}} instead.
4439
4440 @item -fno-dwarf2-cfi-asm
4441 @opindex fdwarf2-cfi-asm
4442 @opindex fno-dwarf2-cfi-asm
4443 Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section
4444 instead of using GAS @code{.cfi_*} directives.
4445
4446 @cindex @command{prof}
4447 @item -p
4448 @opindex p
4449 Generate extra code to write profile information suitable for the
4450 analysis program @command{prof}. You must use this option when compiling
4451 the source files you want data about, and you must also use it when
4452 linking.
4453
4454 @cindex @command{gprof}
4455 @item -pg
4456 @opindex pg
4457 Generate extra code to write profile information suitable for the
4458 analysis program @command{gprof}. You must use this option when compiling
4459 the source files you want data about, and you must also use it when
4460 linking.
4461
4462 @item -Q
4463 @opindex Q
4464 Makes the compiler print out each function name as it is compiled, and
4465 print some statistics about each pass when it finishes.
4466
4467 @item -ftime-report
4468 @opindex ftime-report
4469 Makes the compiler print some statistics about the time consumed by each
4470 pass when it finishes.
4471
4472 @item -fmem-report
4473 @opindex fmem-report
4474 Makes the compiler print some statistics about permanent memory
4475 allocation when it finishes.
4476
4477 @item -fpre-ipa-mem-report
4478 @opindex fpre-ipa-mem-report
4479 @item -fpost-ipa-mem-report
4480 @opindex fpost-ipa-mem-report
4481 Makes the compiler print some statistics about permanent memory
4482 allocation before or after interprocedural optimization.
4483
4484 @item -fprofile-arcs
4485 @opindex fprofile-arcs
4486 Add code so that program flow @dfn{arcs} are instrumented. During
4487 execution the program records how many times each branch and call is
4488 executed and how many times it is taken or returns. When the compiled
4489 program exits it saves this data to a file called
4490 @file{@var{auxname}.gcda} for each source file. The data may be used for
4491 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4492 test coverage analysis (@option{-ftest-coverage}). Each object file's
4493 @var{auxname} is generated from the name of the output file, if
4494 explicitly specified and it is not the final executable, otherwise it is
4495 the basename of the source file. In both cases any suffix is removed
4496 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4497 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4498 @xref{Cross-profiling}.
4499
4500 @cindex @command{gcov}
4501 @item --coverage
4502 @opindex coverage
4503
4504 This option is used to compile and link code instrumented for coverage
4505 analysis. The option is a synonym for @option{-fprofile-arcs}
4506 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4507 linking). See the documentation for those options for more details.
4508
4509 @itemize
4510
4511 @item
4512 Compile the source files with @option{-fprofile-arcs} plus optimization
4513 and code generation options. For test coverage analysis, use the
4514 additional @option{-ftest-coverage} option. You do not need to profile
4515 every source file in a program.
4516
4517 @item
4518 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4519 (the latter implies the former).
4520
4521 @item
4522 Run the program on a representative workload to generate the arc profile
4523 information. This may be repeated any number of times. You can run
4524 concurrent instances of your program, and provided that the file system
4525 supports locking, the data files will be correctly updated. Also
4526 @code{fork} calls are detected and correctly handled (double counting
4527 will not happen).
4528
4529 @item
4530 For profile-directed optimizations, compile the source files again with
4531 the same optimization and code generation options plus
4532 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4533 Control Optimization}).
4534
4535 @item
4536 For test coverage analysis, use @command{gcov} to produce human readable
4537 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4538 @command{gcov} documentation for further information.
4539
4540 @end itemize
4541
4542 With @option{-fprofile-arcs}, for each function of your program GCC
4543 creates a program flow graph, then finds a spanning tree for the graph.
4544 Only arcs that are not on the spanning tree have to be instrumented: the
4545 compiler adds code to count the number of times that these arcs are
4546 executed. When an arc is the only exit or only entrance to a block, the
4547 instrumentation code can be added to the block; otherwise, a new basic
4548 block must be created to hold the instrumentation code.
4549
4550 @need 2000
4551 @item -ftest-coverage
4552 @opindex ftest-coverage
4553 Produce a notes file that the @command{gcov} code-coverage utility
4554 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4555 show program coverage. Each source file's note file is called
4556 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4557 above for a description of @var{auxname} and instructions on how to
4558 generate test coverage data. Coverage data will match the source files
4559 more closely, if you do not optimize.
4560
4561 @item -fdbg-cnt-list
4562 @opindex fdbg-cnt-list
4563 Print the name and the counter upperbound for all debug counters.
4564
4565 @item -fdbg-cnt=@var{counter-value-list}
4566 @opindex fdbg-cnt
4567 Set the internal debug counter upperbound. @var{counter-value-list}
4568 is a comma-separated list of @var{name}:@var{value} pairs
4569 which sets the upperbound of each debug counter @var{name} to @var{value}.
4570 All debug counters have the initial upperbound of @var{UINT_MAX},
4571 thus dbg_cnt() returns true always unless the upperbound is set by this option.
4572 e.g. With -fdbg-cnt=dce:10,tail_call:0
4573 dbg_cnt(dce) will return true only for first 10 invocations
4574 and dbg_cnt(tail_call) will return false always.
4575
4576 @item -d@var{letters}
4577 @itemx -fdump-rtl-@var{pass}
4578 @opindex d
4579 Says to make debugging dumps during compilation at times specified by
4580 @var{letters}. This is used for debugging the RTL-based passes of the
4581 compiler. The file names for most of the dumps are made by appending a
4582 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
4583 from the name of the output file, if explicitly specified and it is not
4584 an executable, otherwise it is the basename of the source file. These
4585 switches may have different effects when @option{-E} is used for
4586 preprocessing.
4587
4588 Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
4589 @option{-d} option @var{letters}. Here are the possible
4590 letters for use in @var{pass} and @var{letters}, and their meanings:
4591
4592 @table @gcctabopt
4593
4594 @item -fdump-rtl-alignments
4595 @opindex fdump-rtl-alignments
4596 Dump after branch alignments have been computed.
4597
4598 @item -fdump-rtl-asmcons
4599 @opindex fdump-rtl-asmcons
4600 Dump after fixing rtl statements that have unsatisfied in/out constraints.
4601
4602 @item -fdump-rtl-auto_inc_dec
4603 @opindex fdump-rtl-auto_inc_dec
4604 Dump after auto-inc-dec discovery. This pass is only run on
4605 architectures that have auto inc or auto dec instructions.
4606
4607 @item -fdump-rtl-barriers
4608 @opindex fdump-rtl-barriers
4609 Dump after cleaning up the barrier instructions.
4610
4611 @item -fdump-rtl-bbpart
4612 @opindex fdump-rtl-bbpart
4613 Dump after partitioning hot and cold basic blocks.
4614
4615 @item -fdump-rtl-bbro
4616 @opindex fdump-rtl-bbro
4617 Dump after block reordering.
4618
4619 @item -fdump-rtl-btl1
4620 @itemx -fdump-rtl-btl2
4621 @opindex fdump-rtl-btl2
4622 @opindex fdump-rtl-btl2
4623 @option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping
4624 after the two branch
4625 target load optimization passes.
4626
4627 @item -fdump-rtl-bypass
4628 @opindex fdump-rtl-bypass
4629 Dump after jump bypassing and control flow optimizations.
4630
4631 @item -fdump-rtl-combine
4632 @opindex fdump-rtl-combine
4633 Dump after the RTL instruction combination pass.
4634
4635 @item -fdump-rtl-compgotos
4636 @opindex fdump-rtl-compgotos
4637 Dump after duplicating the computed gotos.
4638
4639 @item -fdump-rtl-ce1
4640 @itemx -fdump-rtl-ce2
4641 @itemx -fdump-rtl-ce3
4642 @opindex fdump-rtl-ce1
4643 @opindex fdump-rtl-ce2
4644 @opindex fdump-rtl-ce3
4645 @option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and
4646 @option{-fdump-rtl-ce3} enable dumping after the three
4647 if conversion passes.
4648
4649 @itemx -fdump-rtl-cprop_hardreg
4650 @opindex fdump-rtl-cprop_hardreg
4651 Dump after hard register copy propagation.
4652
4653 @itemx -fdump-rtl-csa
4654 @opindex fdump-rtl-csa
4655 Dump after combining stack adjustments.
4656
4657 @item -fdump-rtl-cse1
4658 @itemx -fdump-rtl-cse2
4659 @opindex fdump-rtl-cse1
4660 @opindex fdump-rtl-cse2
4661 @option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after
4662 the two common sub-expression elimination passes.
4663
4664 @itemx -fdump-rtl-dce
4665 @opindex fdump-rtl-dce
4666 Dump after the standalone dead code elimination passes.
4667
4668 @itemx -fdump-rtl-dbr
4669 @opindex fdump-rtl-dbr
4670 Dump after delayed branch scheduling.
4671
4672 @item -fdump-rtl-dce1
4673 @itemx -fdump-rtl-dce2
4674 @opindex fdump-rtl-dce1
4675 @opindex fdump-rtl-dce2
4676 @option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after
4677 the two dead store elimination passes.
4678
4679 @item -fdump-rtl-eh
4680 @opindex fdump-rtl-eh
4681 Dump after finalization of EH handling code.
4682
4683 @item -fdump-rtl-eh_ranges
4684 @opindex fdump-rtl-eh_ranges
4685 Dump after conversion of EH handling range regions.
4686
4687 @item -fdump-rtl-expand
4688 @opindex fdump-rtl-expand
4689 Dump after RTL generation.
4690
4691 @item -fdump-rtl-fwprop1
4692 @itemx -fdump-rtl-fwprop2
4693 @opindex fdump-rtl-fwprop1
4694 @opindex fdump-rtl-fwprop2
4695 @option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable
4696 dumping after the two forward propagation passes.
4697
4698 @item -fdump-rtl-gcse1
4699 @itemx -fdump-rtl-gcse2
4700 @opindex fdump-rtl-gcse1
4701 @opindex fdump-rtl-gcse2
4702 @option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping
4703 after global common subexpression elimination.
4704
4705 @item -fdump-rtl-init-regs
4706 @opindex fdump-rtl-init-regs
4707 Dump after the initialization of the registers.
4708
4709 @item -fdump-rtl-initvals
4710 @opindex fdump-rtl-initvals
4711 Dump after the computation of the initial value sets.
4712
4713 @itemx -fdump-rtl-into_cfglayout
4714 @opindex fdump-rtl-into_cfglayout
4715 Dump after converting to cfglayout mode.
4716
4717 @item -fdump-rtl-ira
4718 @opindex fdump-rtl-ira
4719 Dump after iterated register allocation.
4720
4721 @item -fdump-rtl-jump
4722 @opindex fdump-rtl-jump
4723 Dump after the second jump optimization.
4724
4725 @item -fdump-rtl-loop2
4726 @opindex fdump-rtl-loop2
4727 @option{-fdump-rtl-loop2} enables dumping after the rtl
4728 loop optimization passes.
4729
4730 @item -fdump-rtl-mach
4731 @opindex fdump-rtl-mach
4732 Dump after performing the machine dependent reorganization pass, if that
4733 pass exists.
4734
4735 @item -fdump-rtl-mode_sw
4736 @opindex fdump-rtl-mode_sw
4737 Dump after removing redundant mode switches.
4738
4739 @item -fdump-rtl-rnreg
4740 @opindex fdump-rtl-rnreg
4741 Dump after register renumbering.
4742
4743 @itemx -fdump-rtl-outof_cfglayout
4744 @opindex fdump-rtl-outof_cfglayout
4745 Dump after converting from cfglayout mode.
4746
4747 @item -fdump-rtl-peephole2
4748 @opindex fdump-rtl-peephole2
4749 Dump after the peephole pass.
4750
4751 @item -fdump-rtl-postreload
4752 @opindex fdump-rtl-postreload
4753 Dump after post-reload optimizations.
4754
4755 @itemx -fdump-rtl-pro_and_epilogue
4756 @opindex fdump-rtl-pro_and_epilogue
4757 Dump after generating the function pro and epilogues.
4758
4759 @item -fdump-rtl-regmove
4760 @opindex fdump-rtl-regmove
4761 Dump after the register move pass.
4762
4763 @item -fdump-rtl-sched1
4764 @itemx -fdump-rtl-sched2
4765 @opindex fdump-rtl-sched1
4766 @opindex fdump-rtl-sched2
4767 @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping
4768 after the basic block scheduling passes.
4769
4770 @item -fdump-rtl-see
4771 @opindex fdump-rtl-see
4772 Dump after sign extension elimination.
4773
4774 @item -fdump-rtl-seqabstr
4775 @opindex fdump-rtl-seqabstr
4776 Dump after common sequence discovery.
4777
4778 @item -fdump-rtl-shorten
4779 @opindex fdump-rtl-shorten
4780 Dump after shortening branches.
4781
4782 @item -fdump-rtl-sibling
4783 @opindex fdump-rtl-sibling
4784 Dump after sibling call optimizations.
4785
4786 @item -fdump-rtl-split1
4787 @itemx -fdump-rtl-split2
4788 @itemx -fdump-rtl-split3
4789 @itemx -fdump-rtl-split4
4790 @itemx -fdump-rtl-split5
4791 @opindex fdump-rtl-split1
4792 @opindex fdump-rtl-split2
4793 @opindex fdump-rtl-split3
4794 @opindex fdump-rtl-split4
4795 @opindex fdump-rtl-split5
4796 @option{-fdump-rtl-split1}, @option{-fdump-rtl-split2},
4797 @option{-fdump-rtl-split3}, @option{-fdump-rtl-split4} and
4798 @option{-fdump-rtl-split5} enable dumping after five rounds of
4799 instruction splitting.
4800
4801 @item -fdump-rtl-sms
4802 @opindex fdump-rtl-sms
4803 Dump after modulo scheduling. This pass is only run on some
4804 architectures.
4805
4806 @item -fdump-rtl-stack
4807 @opindex fdump-rtl-stack
4808 Dump after conversion from GCC's "flat register file" registers to the
4809 x87's stack-like registers. This pass is only run on x86 variants.
4810
4811 @item -fdump-rtl-subreg1
4812 @itemx -fdump-rtl-subreg2
4813 @opindex fdump-rtl-subreg1
4814 @opindex fdump-rtl-subreg2
4815 @option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after
4816 the two subreg expansion passes.
4817
4818 @item -fdump-rtl-unshare
4819 @opindex fdump-rtl-unshare
4820 Dump after all rtl has been unshared.
4821
4822 @item -fdump-rtl-vartrack
4823 @opindex fdump-rtl-vartrack
4824 Dump after variable tracking.
4825
4826 @item -fdump-rtl-vregs
4827 @opindex fdump-rtl-vregs
4828 Dump after converting virtual registers to hard registers.
4829
4830 @item -fdump-rtl-web
4831 @opindex fdump-rtl-web
4832 Dump after live range splitting.
4833
4834 @item -fdump-rtl-regclass
4835 @itemx -fdump-rtl-subregs_of_mode_init
4836 @itemx -fdump-rtl-subregs_of_mode_finish
4837 @itemx -fdump-rtl-dfinit
4838 @itemx -fdump-rtl-dfinish
4839 @opindex fdump-rtl-regclass
4840 @opindex fdump-rtl-subregs_of_mode_init
4841 @opindex fdump-rtl-subregs_of_mode_finish
4842 @opindex fdump-rtl-dfinit
4843 @opindex fdump-rtl-dfinish
4844 These dumps are defined but always produce empty files.
4845
4846 @item -fdump-rtl-all
4847 @opindex fdump-rtl-all
4848 Produce all the dumps listed above.
4849
4850 @item -dA
4851 @opindex dA
4852 Annotate the assembler output with miscellaneous debugging information.
4853
4854 @item -dD
4855 @opindex dD
4856 Dump all macro definitions, at the end of preprocessing, in addition to
4857 normal output.
4858
4859 @item -dH
4860 @opindex dH
4861 Produce a core dump whenever an error occurs.
4862
4863 @item -dm
4864 @opindex dm
4865 Print statistics on memory usage, at the end of the run, to
4866 standard error.
4867
4868 @item -dp
4869 @opindex dp
4870 Annotate the assembler output with a comment indicating which
4871 pattern and alternative was used. The length of each instruction is
4872 also printed.
4873
4874 @item -dP
4875 @opindex dP
4876 Dump the RTL in the assembler output as a comment before each instruction.
4877 Also turns on @option{-dp} annotation.
4878
4879 @item -dv
4880 @opindex dv
4881 For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
4882 dump a representation of the control flow graph suitable for viewing with VCG
4883 to @file{@var{file}.@var{pass}.vcg}.
4884
4885 @item -dx
4886 @opindex dx
4887 Just generate RTL for a function instead of compiling it. Usually used
4888 with @option{-fdump-rtl-expand}.
4889
4890 @item -dy
4891 @opindex dy
4892 Dump debugging information during parsing, to standard error.
4893 @end table
4894
4895 @item -fdump-noaddr
4896 @opindex fdump-noaddr
4897 When doing debugging dumps, suppress address output. This makes it more
4898 feasible to use diff on debugging dumps for compiler invocations with
4899 different compiler binaries and/or different
4900 text / bss / data / heap / stack / dso start locations.
4901
4902 @item -fdump-unnumbered
4903 @opindex fdump-unnumbered
4904 When doing debugging dumps, suppress instruction numbers and address output.
4905 This makes it more feasible to use diff on debugging dumps for compiler
4906 invocations with different options, in particular with and without
4907 @option{-g}.
4908
4909 @item -fdump-translation-unit @r{(C++ only)}
4910 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
4911 @opindex fdump-translation-unit
4912 Dump a representation of the tree structure for the entire translation
4913 unit to a file. The file name is made by appending @file{.tu} to the
4914 source file name. If the @samp{-@var{options}} form is used, @var{options}
4915 controls the details of the dump as described for the
4916 @option{-fdump-tree} options.
4917
4918 @item -fdump-class-hierarchy @r{(C++ only)}
4919 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
4920 @opindex fdump-class-hierarchy
4921 Dump a representation of each class's hierarchy and virtual function
4922 table layout to a file. The file name is made by appending @file{.class}
4923 to the source file name. If the @samp{-@var{options}} form is used,
4924 @var{options} controls the details of the dump as described for the
4925 @option{-fdump-tree} options.
4926
4927 @item -fdump-ipa-@var{switch}
4928 @opindex fdump-ipa
4929 Control the dumping at various stages of inter-procedural analysis
4930 language tree to a file. The file name is generated by appending a switch
4931 specific suffix to the source file name. The following dumps are possible:
4932
4933 @table @samp
4934 @item all
4935 Enables all inter-procedural analysis dumps.
4936
4937 @item cgraph
4938 Dumps information about call-graph optimization, unused function removal,
4939 and inlining decisions.
4940
4941 @item inline
4942 Dump after function inlining.
4943
4944 @end table
4945
4946 @item -fdump-statistics-@var{option}
4947 @opindex -fdump-statistics
4948 Enable and control dumping of pass statistics in a separate file. The
4949 file name is generated by appending a suffix ending in @samp{.statistics}
4950 to the source file name. If the @samp{-@var{option}} form is used,
4951 @samp{-stats} will cause counters to be summed over the whole compilation unit
4952 while @samp{-details} will dump every event as the passes generate them.
4953 The default with no option is to sum counters for each function compiled.
4954
4955 @item -fdump-tree-@var{switch}
4956 @itemx -fdump-tree-@var{switch}-@var{options}
4957 @opindex fdump-tree
4958 Control the dumping at various stages of processing the intermediate
4959 language tree to a file. The file name is generated by appending a switch
4960 specific suffix to the source file name. If the @samp{-@var{options}}
4961 form is used, @var{options} is a list of @samp{-} separated options that
4962 control the details of the dump. Not all options are applicable to all
4963 dumps, those which are not meaningful will be ignored. The following
4964 options are available
4965
4966 @table @samp
4967 @item address
4968 Print the address of each node. Usually this is not meaningful as it
4969 changes according to the environment and source file. Its primary use
4970 is for tying up a dump file with a debug environment.
4971 @item slim
4972 Inhibit dumping of members of a scope or body of a function merely
4973 because that scope has been reached. Only dump such items when they
4974 are directly reachable by some other path. When dumping pretty-printed
4975 trees, this option inhibits dumping the bodies of control structures.
4976 @item raw
4977 Print a raw representation of the tree. By default, trees are
4978 pretty-printed into a C-like representation.
4979 @item details
4980 Enable more detailed dumps (not honored by every dump option).
4981 @item stats
4982 Enable dumping various statistics about the pass (not honored by every dump
4983 option).
4984 @item blocks
4985 Enable showing basic block boundaries (disabled in raw dumps).
4986 @item vops
4987 Enable showing virtual operands for every statement.
4988 @item lineno
4989 Enable showing line numbers for statements.
4990 @item uid
4991 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4992 @item verbose
4993 Enable showing the tree dump for each statement.
4994 @item all
4995 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
4996 and @option{lineno}.
4997 @end table
4998
4999 The following tree dumps are possible:
5000 @table @samp
5001
5002 @item original
5003 Dump before any tree based optimization, to @file{@var{file}.original}.
5004
5005 @item optimized
5006 Dump after all tree based optimization, to @file{@var{file}.optimized}.
5007
5008 @item gimple
5009 @opindex fdump-tree-gimple
5010 Dump each function before and after the gimplification pass to a file. The
5011 file name is made by appending @file{.gimple} to the source file name.
5012
5013 @item cfg
5014 @opindex fdump-tree-cfg
5015 Dump the control flow graph of each function to a file. The file name is
5016 made by appending @file{.cfg} to the source file name.
5017
5018 @item vcg
5019 @opindex fdump-tree-vcg
5020 Dump the control flow graph of each function to a file in VCG format. The
5021 file name is made by appending @file{.vcg} to the source file name. Note
5022 that if the file contains more than one function, the generated file cannot
5023 be used directly by VCG@. You will need to cut and paste each function's
5024 graph into its own separate file first.
5025
5026 @item ch
5027 @opindex fdump-tree-ch
5028 Dump each function after copying loop headers. The file name is made by
5029 appending @file{.ch} to the source file name.
5030
5031 @item ssa
5032 @opindex fdump-tree-ssa
5033 Dump SSA related information to a file. The file name is made by appending
5034 @file{.ssa} to the source file name.
5035
5036 @item alias
5037 @opindex fdump-tree-alias
5038 Dump aliasing information for each function. The file name is made by
5039 appending @file{.alias} to the source file name.
5040
5041 @item ccp
5042 @opindex fdump-tree-ccp
5043 Dump each function after CCP@. The file name is made by appending
5044 @file{.ccp} to the source file name.
5045
5046 @item storeccp
5047 @opindex fdump-tree-storeccp
5048 Dump each function after STORE-CCP@. The file name is made by appending
5049 @file{.storeccp} to the source file name.
5050
5051 @item pre
5052 @opindex fdump-tree-pre
5053 Dump trees after partial redundancy elimination. The file name is made
5054 by appending @file{.pre} to the source file name.
5055
5056 @item fre
5057 @opindex fdump-tree-fre
5058 Dump trees after full redundancy elimination. The file name is made
5059 by appending @file{.fre} to the source file name.
5060
5061 @item copyprop
5062 @opindex fdump-tree-copyprop
5063 Dump trees after copy propagation. The file name is made
5064 by appending @file{.copyprop} to the source file name.
5065
5066 @item store_copyprop
5067 @opindex fdump-tree-store_copyprop
5068 Dump trees after store copy-propagation. The file name is made
5069 by appending @file{.store_copyprop} to the source file name.
5070
5071 @item dce
5072 @opindex fdump-tree-dce
5073 Dump each function after dead code elimination. The file name is made by
5074 appending @file{.dce} to the source file name.
5075
5076 @item mudflap
5077 @opindex fdump-tree-mudflap
5078 Dump each function after adding mudflap instrumentation. The file name is
5079 made by appending @file{.mudflap} to the source file name.
5080
5081 @item sra
5082 @opindex fdump-tree-sra
5083 Dump each function after performing scalar replacement of aggregates. The
5084 file name is made by appending @file{.sra} to the source file name.
5085
5086 @item sink
5087 @opindex fdump-tree-sink
5088 Dump each function after performing code sinking. The file name is made
5089 by appending @file{.sink} to the source file name.
5090
5091 @item dom
5092 @opindex fdump-tree-dom
5093 Dump each function after applying dominator tree optimizations. The file
5094 name is made by appending @file{.dom} to the source file name.
5095
5096 @item dse
5097 @opindex fdump-tree-dse
5098 Dump each function after applying dead store elimination. The file
5099 name is made by appending @file{.dse} to the source file name.
5100
5101 @item phiopt
5102 @opindex fdump-tree-phiopt
5103 Dump each function after optimizing PHI nodes into straightline code. The file
5104 name is made by appending @file{.phiopt} to the source file name.
5105
5106 @item forwprop
5107 @opindex fdump-tree-forwprop
5108 Dump each function after forward propagating single use variables. The file
5109 name is made by appending @file{.forwprop} to the source file name.
5110
5111 @item copyrename
5112 @opindex fdump-tree-copyrename
5113 Dump each function after applying the copy rename optimization. The file
5114 name is made by appending @file{.copyrename} to the source file name.
5115
5116 @item nrv
5117 @opindex fdump-tree-nrv
5118 Dump each function after applying the named return value optimization on
5119 generic trees. The file name is made by appending @file{.nrv} to the source
5120 file name.
5121
5122 @item vect
5123 @opindex fdump-tree-vect
5124 Dump each function after applying vectorization of loops. The file name is
5125 made by appending @file{.vect} to the source file name.
5126
5127 @item vrp
5128 @opindex fdump-tree-vrp
5129 Dump each function after Value Range Propagation (VRP). The file name
5130 is made by appending @file{.vrp} to the source file name.
5131
5132 @item all
5133 @opindex fdump-tree-all
5134 Enable all the available tree dumps with the flags provided in this option.
5135 @end table
5136
5137 @item -ftree-vectorizer-verbose=@var{n}
5138 @opindex ftree-vectorizer-verbose
5139 This option controls the amount of debugging output the vectorizer prints.
5140 This information is written to standard error, unless
5141 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
5142 in which case it is output to the usual dump listing file, @file{.vect}.
5143 For @var{n}=0 no diagnostic information is reported.
5144 If @var{n}=1 the vectorizer reports each loop that got vectorized,
5145 and the total number of loops that got vectorized.
5146 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
5147 the first analysis phase (vect_analyze_loop_form) - i.e.@: countable,
5148 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
5149 level that @option{-fdump-tree-vect-stats} uses.
5150 Higher verbosity levels mean either more information dumped for each
5151 reported loop, or same amount of information reported for more loops:
5152 If @var{n}=3, alignment related information is added to the reports.
5153 If @var{n}=4, data-references related information (e.g.@: memory dependences,
5154 memory access-patterns) is added to the reports.
5155 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
5156 that did not pass the first analysis phase (i.e., may not be countable, or
5157 may have complicated control-flow).
5158 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
5159 For @var{n}=7, all the information the vectorizer generates during its
5160 analysis and transformation is reported. This is the same verbosity level
5161 that @option{-fdump-tree-vect-details} uses.
5162
5163 @item -frandom-seed=@var{string}
5164 @opindex frandom-string
5165 This option provides a seed that GCC uses when it would otherwise use
5166 random numbers. It is used to generate certain symbol names
5167 that have to be different in every compiled file. It is also used to
5168 place unique stamps in coverage data files and the object files that
5169 produce them. You can use the @option{-frandom-seed} option to produce
5170 reproducibly identical object files.
5171
5172 The @var{string} should be different for every file you compile.
5173
5174 @item -fsched-verbose=@var{n}
5175 @opindex fsched-verbose
5176 On targets that use instruction scheduling, this option controls the
5177 amount of debugging output the scheduler prints. This information is
5178 written to standard error, unless @option{-fdump-rtl-sched1} or
5179 @option{-fdump-rtl-sched2} is specified, in which case it is output
5180 to the usual dump listing file, @file{.sched} or @file{.sched2}
5181 respectively. However for @var{n} greater than nine, the output is
5182 always printed to standard error.
5183
5184 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
5185 same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
5186 For @var{n} greater than one, it also output basic block probabilities,
5187 detailed ready list information and unit/insn info. For @var{n} greater
5188 than two, it includes RTL at abort point, control-flow and regions info.
5189 And for @var{n} over four, @option{-fsched-verbose} also includes
5190 dependence info.
5191
5192 @item -save-temps
5193 @opindex save-temps
5194 Store the usual ``temporary'' intermediate files permanently; place them
5195 in the current directory and name them based on the source file. Thus,
5196 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
5197 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
5198 preprocessed @file{foo.i} output file even though the compiler now
5199 normally uses an integrated preprocessor.
5200
5201 When used in combination with the @option{-x} command line option,
5202 @option{-save-temps} is sensible enough to avoid over writing an
5203 input source file with the same extension as an intermediate file.
5204 The corresponding intermediate file may be obtained by renaming the
5205 source file before using @option{-save-temps}.
5206
5207 @item -time
5208 @opindex time
5209 Report the CPU time taken by each subprocess in the compilation
5210 sequence. For C source files, this is the compiler proper and assembler
5211 (plus the linker if linking is done). The output looks like this:
5212
5213 @smallexample
5214 # cc1 0.12 0.01
5215 # as 0.00 0.01
5216 @end smallexample
5217
5218 The first number on each line is the ``user time'', that is time spent
5219 executing the program itself. The second number is ``system time'',
5220 time spent executing operating system routines on behalf of the program.
5221 Both numbers are in seconds.
5222
5223 @item -fvar-tracking
5224 @opindex fvar-tracking
5225 Run variable tracking pass. It computes where variables are stored at each
5226 position in code. Better debugging information is then generated
5227 (if the debugging information format supports this information).
5228
5229 It is enabled by default when compiling with optimization (@option{-Os},
5230 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
5231 the debug info format supports it.
5232
5233 @item -print-file-name=@var{library}
5234 @opindex print-file-name
5235 Print the full absolute name of the library file @var{library} that
5236 would be used when linking---and don't do anything else. With this
5237 option, GCC does not compile or link anything; it just prints the
5238 file name.
5239
5240 @item -print-multi-directory
5241 @opindex print-multi-directory
5242 Print the directory name corresponding to the multilib selected by any
5243 other switches present in the command line. This directory is supposed
5244 to exist in @env{GCC_EXEC_PREFIX}.
5245
5246 @item -print-multi-lib
5247 @opindex print-multi-lib
5248 Print the mapping from multilib directory names to compiler switches
5249 that enable them. The directory name is separated from the switches by
5250 @samp{;}, and each switch starts with an @samp{@@} instead of the
5251 @samp{-}, without spaces between multiple switches. This is supposed to
5252 ease shell-processing.
5253
5254 @item -print-prog-name=@var{program}
5255 @opindex print-prog-name
5256 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
5257
5258 @item -print-libgcc-file-name
5259 @opindex print-libgcc-file-name
5260 Same as @option{-print-file-name=libgcc.a}.
5261
5262 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
5263 but you do want to link with @file{libgcc.a}. You can do
5264
5265 @smallexample
5266 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
5267 @end smallexample
5268
5269 @item -print-search-dirs
5270 @opindex print-search-dirs
5271 Print the name of the configured installation directory and a list of
5272 program and library directories @command{gcc} will search---and don't do anything else.
5273
5274 This is useful when @command{gcc} prints the error message
5275 @samp{installation problem, cannot exec cpp0: No such file or directory}.
5276 To resolve this you either need to put @file{cpp0} and the other compiler
5277 components where @command{gcc} expects to find them, or you can set the environment
5278 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
5279 Don't forget the trailing @samp{/}.
5280 @xref{Environment Variables}.
5281
5282 @item -print-sysroot
5283 @opindex print-sysroot
5284 Print the target sysroot directory that will be used during
5285 compilation. This is the target sysroot specified either at configure
5286 time or using the @option{--sysroot} option, possibly with an extra
5287 suffix that depends on compilation options. If no target sysroot is
5288 specified, the option prints nothing.
5289
5290 @item -print-sysroot-headers-suffix
5291 @opindex print-sysroot-headers-suffix
5292 Print the suffix added to the target sysroot when searching for
5293 headers, or give an error if the compiler is not configured with such
5294 a suffix---and don't do anything else.
5295
5296 @item -dumpmachine
5297 @opindex dumpmachine
5298 Print the compiler's target machine (for example,
5299 @samp{i686-pc-linux-gnu})---and don't do anything else.
5300
5301 @item -dumpversion
5302 @opindex dumpversion
5303 Print the compiler version (for example, @samp{3.0})---and don't do
5304 anything else.
5305
5306 @item -dumpspecs
5307 @opindex dumpspecs
5308 Print the compiler's built-in specs---and don't do anything else. (This
5309 is used when GCC itself is being built.) @xref{Spec Files}.
5310
5311 @item -feliminate-unused-debug-types
5312 @opindex feliminate-unused-debug-types
5313 Normally, when producing DWARF2 output, GCC will emit debugging
5314 information for all types declared in a compilation
5315 unit, regardless of whether or not they are actually used
5316 in that compilation unit. Sometimes this is useful, such as
5317 if, in the debugger, you want to cast a value to a type that is
5318 not actually used in your program (but is declared). More often,
5319 however, this results in a significant amount of wasted space.
5320 With this option, GCC will avoid producing debug symbol output
5321 for types that are nowhere used in the source file being compiled.
5322 @end table
5323
5324 @node Optimize Options
5325 @section Options That Control Optimization
5326 @cindex optimize options
5327 @cindex options, optimization
5328
5329 These options control various sorts of optimizations.
5330
5331 Without any optimization option, the compiler's goal is to reduce the
5332 cost of compilation and to make debugging produce the expected
5333 results. Statements are independent: if you stop the program with a
5334 breakpoint between statements, you can then assign a new value to any
5335 variable or change the program counter to any other statement in the
5336 function and get exactly the results you would expect from the source
5337 code.
5338
5339 Turning on optimization flags makes the compiler attempt to improve
5340 the performance and/or code size at the expense of compilation time
5341 and possibly the ability to debug the program.
5342
5343 The compiler performs optimization based on the knowledge it has of the
5344 program. Compiling multiple files at once to a single output file mode allows
5345 the compiler to use information gained from all of the files when compiling
5346 each of them.
5347
5348 Not all optimizations are controlled directly by a flag. Only
5349 optimizations that have a flag are listed.
5350
5351 @table @gcctabopt
5352 @item -O
5353 @itemx -O1
5354 @opindex O
5355 @opindex O1
5356 Optimize. Optimizing compilation takes somewhat more time, and a lot
5357 more memory for a large function.
5358
5359 With @option{-O}, the compiler tries to reduce code size and execution
5360 time, without performing any optimizations that take a great deal of
5361 compilation time.
5362
5363 @option{-O} turns on the following optimization flags:
5364 @gccoptlist{
5365 -fauto-inc-dec @gol
5366 -fcprop-registers @gol
5367 -fdce @gol
5368 -fdefer-pop @gol
5369 -fdelayed-branch @gol
5370 -fdse @gol
5371 -fguess-branch-probability @gol
5372 -fif-conversion2 @gol
5373 -fif-conversion @gol
5374 -finline-small-functions @gol
5375 -fipa-pure-const @gol
5376 -fipa-reference @gol
5377 -fmerge-constants
5378 -fsplit-wide-types @gol
5379 -ftree-builtin-call-dce @gol
5380 -ftree-ccp @gol
5381 -ftree-ch @gol
5382 -ftree-copyrename @gol
5383 -ftree-dce @gol
5384 -ftree-dominator-opts @gol
5385 -ftree-dse @gol
5386 -ftree-fre @gol
5387 -ftree-sra @gol
5388 -ftree-ter @gol
5389 -funit-at-a-time}
5390
5391 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5392 where doing so does not interfere with debugging.
5393
5394 @item -O2
5395 @opindex O2
5396 Optimize even more. GCC performs nearly all supported optimizations
5397 that do not involve a space-speed tradeoff.
5398 As compared to @option{-O}, this option increases both compilation time
5399 and the performance of the generated code.
5400
5401 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5402 also turns on the following optimization flags:
5403 @gccoptlist{-fthread-jumps @gol
5404 -falign-functions -falign-jumps @gol
5405 -falign-loops -falign-labels @gol
5406 -fcaller-saves @gol
5407 -fcrossjumping @gol
5408 -fcse-follow-jumps -fcse-skip-blocks @gol
5409 -fdelete-null-pointer-checks @gol
5410 -fexpensive-optimizations @gol
5411 -fgcse -fgcse-lm @gol
5412 -findirect-inlining @gol
5413 -foptimize-sibling-calls @gol
5414 -fpeephole2 @gol
5415 -fregmove @gol
5416 -freorder-blocks -freorder-functions @gol
5417 -frerun-cse-after-loop @gol
5418 -fsched-interblock -fsched-spec @gol
5419 -fschedule-insns -fschedule-insns2 @gol
5420 -fstrict-aliasing -fstrict-overflow @gol
5421 -ftree-switch-conversion @gol
5422 -ftree-pre @gol
5423 -ftree-vrp}
5424
5425 Please note the warning under @option{-fgcse} about
5426 invoking @option{-O2} on programs that use computed gotos.
5427
5428 @item -O3
5429 @opindex O3
5430 Optimize yet more. @option{-O3} turns on all optimizations specified
5431 by @option{-O2} and also turns on the @option{-finline-functions},
5432 @option{-funswitch-loops}, @option{-fpredictive-commoning},
5433 @option{-fgcse-after-reload} and @option{-ftree-vectorize} options.
5434
5435 @item -O0
5436 @opindex O0
5437 Reduce compilation time and make debugging produce the expected
5438 results. This is the default.
5439
5440 @item -Os
5441 @opindex Os
5442 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5443 do not typically increase code size. It also performs further
5444 optimizations designed to reduce code size.
5445
5446 @option{-Os} disables the following optimization flags:
5447 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5448 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5449 -fprefetch-loop-arrays -ftree-vect-loop-version}
5450
5451 If you use multiple @option{-O} options, with or without level numbers,
5452 the last such option is the one that is effective.
5453 @end table
5454
5455 Options of the form @option{-f@var{flag}} specify machine-independent
5456 flags. Most flags have both positive and negative forms; the negative
5457 form of @option{-ffoo} would be @option{-fno-foo}. In the table
5458 below, only one of the forms is listed---the one you typically will
5459 use. You can figure out the other form by either removing @samp{no-}
5460 or adding it.
5461
5462 The following options control specific optimizations. They are either
5463 activated by @option{-O} options or are related to ones that are. You
5464 can use the following flags in the rare cases when ``fine-tuning'' of
5465 optimizations to be performed is desired.
5466
5467 @table @gcctabopt
5468 @item -fno-default-inline
5469 @opindex fno-default-inline
5470 Do not make member functions inline by default merely because they are
5471 defined inside the class scope (C++ only). Otherwise, when you specify
5472 @w{@option{-O}}, member functions defined inside class scope are compiled
5473 inline by default; i.e., you don't need to add @samp{inline} in front of
5474 the member function name.
5475
5476 @item -fno-defer-pop
5477 @opindex fno-defer-pop
5478 Always pop the arguments to each function call as soon as that function
5479 returns. For machines which must pop arguments after a function call,
5480 the compiler normally lets arguments accumulate on the stack for several
5481 function calls and pops them all at once.
5482
5483 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5484
5485 @item -fforward-propagate
5486 @opindex fforward-propagate
5487 Perform a forward propagation pass on RTL@. The pass tries to combine two
5488 instructions and checks if the result can be simplified. If loop unrolling
5489 is active, two passes are performed and the second is scheduled after
5490 loop unrolling.
5491
5492 This option is enabled by default at optimization levels @option{-O2},
5493 @option{-O3}, @option{-Os}.
5494
5495 @item -fomit-frame-pointer
5496 @opindex fomit-frame-pointer
5497 Don't keep the frame pointer in a register for functions that
5498 don't need one. This avoids the instructions to save, set up and
5499 restore frame pointers; it also makes an extra register available
5500 in many functions. @strong{It also makes debugging impossible on
5501 some machines.}
5502
5503 On some machines, such as the VAX, this flag has no effect, because
5504 the standard calling sequence automatically handles the frame pointer
5505 and nothing is saved by pretending it doesn't exist. The
5506 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
5507 whether a target machine supports this flag. @xref{Registers,,Register
5508 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
5509
5510 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5511
5512 @item -foptimize-sibling-calls
5513 @opindex foptimize-sibling-calls
5514 Optimize sibling and tail recursive calls.
5515
5516 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5517
5518 @item -fno-inline
5519 @opindex fno-inline
5520 Don't pay attention to the @code{inline} keyword. Normally this option
5521 is used to keep the compiler from expanding any functions inline.
5522 Note that if you are not optimizing, no functions can be expanded inline.
5523
5524 @item -finline-small-functions
5525 @opindex finline-small-functions
5526 Integrate functions into their callers when their body is smaller than expected
5527 function call code (so overall size of program gets smaller). The compiler
5528 heuristically decides which functions are simple enough to be worth integrating
5529 in this way.
5530
5531 Enabled at level @option{-O2}.
5532
5533 @item -findirect-inlining
5534 @opindex findirect-inlining
5535 Inline also indirect calls that are discovered to be known at compile
5536 time thanks to previous inlining. This option has any effect only
5537 when inlining itself is turned on by the @option{-finline-functions}
5538 or @option{-finline-small-functions} options.
5539
5540 Enabled at level @option{-O2}.
5541
5542 @item -finline-functions
5543 @opindex finline-functions
5544 Integrate all simple functions into their callers. The compiler
5545 heuristically decides which functions are simple enough to be worth
5546 integrating in this way.
5547
5548 If all calls to a given function are integrated, and the function is
5549 declared @code{static}, then the function is normally not output as
5550 assembler code in its own right.
5551
5552 Enabled at level @option{-O3}.
5553
5554 @item -finline-functions-called-once
5555 @opindex finline-functions-called-once
5556 Consider all @code{static} functions called once for inlining into their
5557 caller even if they are not marked @code{inline}. If a call to a given
5558 function is integrated, then the function is not output as assembler code
5559 in its own right.
5560
5561 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
5562
5563 @item -fearly-inlining
5564 @opindex fearly-inlining
5565 Inline functions marked by @code{always_inline} and functions whose body seems
5566 smaller than the function call overhead early before doing
5567 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
5568 makes profiling significantly cheaper and usually inlining faster on programs
5569 having large chains of nested wrapper functions.
5570
5571 Enabled by default.
5572
5573 @item -finline-limit=@var{n}
5574 @opindex finline-limit
5575 By default, GCC limits the size of functions that can be inlined. This flag
5576 allows coarse control of this limit. @var{n} is the size of functions that
5577 can be inlined in number of pseudo instructions.
5578
5579 Inlining is actually controlled by a number of parameters, which may be
5580 specified individually by using @option{--param @var{name}=@var{value}}.
5581 The @option{-finline-limit=@var{n}} option sets some of these parameters
5582 as follows:
5583
5584 @table @gcctabopt
5585 @item max-inline-insns-single
5586 is set to @var{n}/2.
5587 @item max-inline-insns-auto
5588 is set to @var{n}/2.
5589 @end table
5590
5591 See below for a documentation of the individual
5592 parameters controlling inlining and for the defaults of these parameters.
5593
5594 @emph{Note:} there may be no value to @option{-finline-limit} that results
5595 in default behavior.
5596
5597 @emph{Note:} pseudo instruction represents, in this particular context, an
5598 abstract measurement of function's size. In no way does it represent a count
5599 of assembly instructions and as such its exact meaning might change from one
5600 release to an another.
5601
5602 @item -fkeep-inline-functions
5603 @opindex fkeep-inline-functions
5604 In C, emit @code{static} functions that are declared @code{inline}
5605 into the object file, even if the function has been inlined into all
5606 of its callers. This switch does not affect functions using the
5607 @code{extern inline} extension in GNU C89@. In C++, emit any and all
5608 inline functions into the object file.
5609
5610 @item -fkeep-static-consts
5611 @opindex fkeep-static-consts
5612 Emit variables declared @code{static const} when optimization isn't turned
5613 on, even if the variables aren't referenced.
5614
5615 GCC enables this option by default. If you want to force the compiler to
5616 check if the variable was referenced, regardless of whether or not
5617 optimization is turned on, use the @option{-fno-keep-static-consts} option.
5618
5619 @item -fmerge-constants
5620 @opindex fmerge-constants
5621 Attempt to merge identical constants (string constants and floating point
5622 constants) across compilation units.
5623
5624 This option is the default for optimized compilation if the assembler and
5625 linker support it. Use @option{-fno-merge-constants} to inhibit this
5626 behavior.
5627
5628 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5629
5630 @item -fmerge-all-constants
5631 @opindex fmerge-all-constants
5632 Attempt to merge identical constants and identical variables.
5633
5634 This option implies @option{-fmerge-constants}. In addition to
5635 @option{-fmerge-constants} this considers e.g.@: even constant initialized
5636 arrays or initialized constant variables with integral or floating point
5637 types. Languages like C or C++ require each variable, including multiple
5638 instances of the same variable in recursive calls, to have distinct locations,
5639 so using this option will result in non-conforming
5640 behavior.
5641
5642 @item -fmodulo-sched
5643 @opindex fmodulo-sched
5644 Perform swing modulo scheduling immediately before the first scheduling
5645 pass. This pass looks at innermost loops and reorders their
5646 instructions by overlapping different iterations.
5647
5648 @item -fmodulo-sched-allow-regmoves
5649 @opindex fmodulo-sched-allow-regmoves
5650 Perform more aggressive SMS based modulo scheduling with register moves
5651 allowed. By setting this flag certain anti-dependences edges will be
5652 deleted which will trigger the generation of reg-moves based on the
5653 life-range analysis. This option is effective only with
5654 @option{-fmodulo-sched} enabled.
5655
5656 @item -fno-branch-count-reg
5657 @opindex fno-branch-count-reg
5658 Do not use ``decrement and branch'' instructions on a count register,
5659 but instead generate a sequence of instructions that decrement a
5660 register, compare it against zero, then branch based upon the result.
5661 This option is only meaningful on architectures that support such
5662 instructions, which include x86, PowerPC, IA-64 and S/390.
5663
5664 The default is @option{-fbranch-count-reg}.
5665
5666 @item -fno-function-cse
5667 @opindex fno-function-cse
5668 Do not put function addresses in registers; make each instruction that
5669 calls a constant function contain the function's address explicitly.
5670
5671 This option results in less efficient code, but some strange hacks
5672 that alter the assembler output may be confused by the optimizations
5673 performed when this option is not used.
5674
5675 The default is @option{-ffunction-cse}
5676
5677 @item -fno-zero-initialized-in-bss
5678 @opindex fno-zero-initialized-in-bss
5679 If the target supports a BSS section, GCC by default puts variables that
5680 are initialized to zero into BSS@. This can save space in the resulting
5681 code.
5682
5683 This option turns off this behavior because some programs explicitly
5684 rely on variables going to the data section. E.g., so that the
5685 resulting executable can find the beginning of that section and/or make
5686 assumptions based on that.
5687
5688 The default is @option{-fzero-initialized-in-bss}.
5689
5690 @item -fmudflap -fmudflapth -fmudflapir
5691 @opindex fmudflap
5692 @opindex fmudflapth
5693 @opindex fmudflapir
5694 @cindex bounds checking
5695 @cindex mudflap
5696 For front-ends that support it (C and C++), instrument all risky
5697 pointer/array dereferencing operations, some standard library
5698 string/heap functions, and some other associated constructs with
5699 range/validity tests. Modules so instrumented should be immune to
5700 buffer overflows, invalid heap use, and some other classes of C/C++
5701 programming errors. The instrumentation relies on a separate runtime
5702 library (@file{libmudflap}), which will be linked into a program if
5703 @option{-fmudflap} is given at link time. Run-time behavior of the
5704 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
5705 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
5706 for its options.
5707
5708 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
5709 link if your program is multi-threaded. Use @option{-fmudflapir}, in
5710 addition to @option{-fmudflap} or @option{-fmudflapth}, if
5711 instrumentation should ignore pointer reads. This produces less
5712 instrumentation (and therefore faster execution) and still provides
5713 some protection against outright memory corrupting writes, but allows
5714 erroneously read data to propagate within a program.
5715
5716 @item -fthread-jumps
5717 @opindex fthread-jumps
5718 Perform optimizations where we check to see if a jump branches to a
5719 location where another comparison subsumed by the first is found. If
5720 so, the first branch is redirected to either the destination of the
5721 second branch or a point immediately following it, depending on whether
5722 the condition is known to be true or false.
5723
5724 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5725
5726 @item -fsplit-wide-types
5727 @opindex fsplit-wide-types
5728 When using a type that occupies multiple registers, such as @code{long
5729 long} on a 32-bit system, split the registers apart and allocate them
5730 independently. This normally generates better code for those types,
5731 but may make debugging more difficult.
5732
5733 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
5734 @option{-Os}.
5735
5736 @item -fcse-follow-jumps
5737 @opindex fcse-follow-jumps
5738 In common subexpression elimination (CSE), scan through jump instructions
5739 when the target of the jump is not reached by any other path. For
5740 example, when CSE encounters an @code{if} statement with an
5741 @code{else} clause, CSE will follow the jump when the condition
5742 tested is false.
5743
5744 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5745
5746 @item -fcse-skip-blocks
5747 @opindex fcse-skip-blocks
5748 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
5749 follow jumps which conditionally skip over blocks. When CSE
5750 encounters a simple @code{if} statement with no else clause,
5751 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
5752 body of the @code{if}.
5753
5754 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5755
5756 @item -frerun-cse-after-loop
5757 @opindex frerun-cse-after-loop
5758 Re-run common subexpression elimination after loop optimizations has been
5759 performed.
5760
5761 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5762
5763 @item -fgcse
5764 @opindex fgcse
5765 Perform a global common subexpression elimination pass.
5766 This pass also performs global constant and copy propagation.
5767
5768 @emph{Note:} When compiling a program using computed gotos, a GCC
5769 extension, you may get better runtime performance if you disable
5770 the global common subexpression elimination pass by adding
5771 @option{-fno-gcse} to the command line.
5772
5773 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5774
5775 @item -fgcse-lm
5776 @opindex fgcse-lm
5777 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
5778 attempt to move loads which are only killed by stores into themselves. This
5779 allows a loop containing a load/store sequence to be changed to a load outside
5780 the loop, and a copy/store within the loop.
5781
5782 Enabled by default when gcse is enabled.
5783
5784 @item -fgcse-sm
5785 @opindex fgcse-sm
5786 When @option{-fgcse-sm} is enabled, a store motion pass is run after
5787 global common subexpression elimination. This pass will attempt to move
5788 stores out of loops. When used in conjunction with @option{-fgcse-lm},
5789 loops containing a load/store sequence can be changed to a load before
5790 the loop and a store after the loop.
5791
5792 Not enabled at any optimization level.
5793
5794 @item -fgcse-las
5795 @opindex fgcse-las
5796 When @option{-fgcse-las} is enabled, the global common subexpression
5797 elimination pass eliminates redundant loads that come after stores to the
5798 same memory location (both partial and full redundancies).
5799
5800 Not enabled at any optimization level.
5801
5802 @item -fgcse-after-reload
5803 @opindex fgcse-after-reload
5804 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
5805 pass is performed after reload. The purpose of this pass is to cleanup
5806 redundant spilling.
5807
5808 @item -funsafe-loop-optimizations
5809 @opindex funsafe-loop-optimizations
5810 If given, the loop optimizer will assume that loop indices do not
5811 overflow, and that the loops with nontrivial exit condition are not
5812 infinite. This enables a wider range of loop optimizations even if
5813 the loop optimizer itself cannot prove that these assumptions are valid.
5814 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
5815 if it finds this kind of loop.
5816
5817 @item -fcrossjumping
5818 @opindex fcrossjumping
5819 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
5820 resulting code may or may not perform better than without cross-jumping.
5821
5822 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5823
5824 @item -fauto-inc-dec
5825 @opindex fauto-inc-dec
5826 Combine increments or decrements of addresses with memory accesses.
5827 This pass is always skipped on architectures that do not have
5828 instructions to support this. Enabled by default at @option{-O} and
5829 higher on architectures that support this.
5830
5831 @item -fdce
5832 @opindex fdce
5833 Perform dead code elimination (DCE) on RTL@.
5834 Enabled by default at @option{-O} and higher.
5835
5836 @item -fdse
5837 @opindex fdse
5838 Perform dead store elimination (DSE) on RTL@.
5839 Enabled by default at @option{-O} and higher.
5840
5841 @item -fif-conversion
5842 @opindex fif-conversion
5843 Attempt to transform conditional jumps into branch-less equivalents. This
5844 include use of conditional moves, min, max, set flags and abs instructions, and
5845 some tricks doable by standard arithmetics. The use of conditional execution
5846 on chips where it is available is controlled by @code{if-conversion2}.
5847
5848 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5849
5850 @item -fif-conversion2
5851 @opindex fif-conversion2
5852 Use conditional execution (where available) to transform conditional jumps into
5853 branch-less equivalents.
5854
5855 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5856
5857 @item -fdelete-null-pointer-checks
5858 @opindex fdelete-null-pointer-checks
5859 Use global dataflow analysis to identify and eliminate useless checks
5860 for null pointers. The compiler assumes that dereferencing a null
5861 pointer would have halted the program. If a pointer is checked after
5862 it has already been dereferenced, it cannot be null.
5863
5864 In some environments, this assumption is not true, and programs can
5865 safely dereference null pointers. Use
5866 @option{-fno-delete-null-pointer-checks} to disable this optimization
5867 for programs which depend on that behavior.
5868
5869 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5870
5871 @item -fexpensive-optimizations
5872 @opindex fexpensive-optimizations
5873 Perform a number of minor optimizations that are relatively expensive.
5874
5875 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5876
5877 @item -foptimize-register-move
5878 @itemx -fregmove
5879 @opindex foptimize-register-move
5880 @opindex fregmove
5881 Attempt to reassign register numbers in move instructions and as
5882 operands of other simple instructions in order to maximize the amount of
5883 register tying. This is especially helpful on machines with two-operand
5884 instructions.
5885
5886 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
5887 optimization.
5888
5889 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5890
5891 @item -fira-algorithm=@var{algorithm}
5892 Use specified coloring algorithm for the integrated register
5893 allocator. The @var{algorithm} argument should be @code{priority} or
5894 @code{CB}. The first algorithm specifies Chow's priority coloring,
5895 the second one specifies Chaitin-Briggs coloring. The second
5896 algorithm can be unimplemented for some architectures. If it is
5897 implemented, it is the default because Chaitin-Briggs coloring as a
5898 rule generates a better code.
5899
5900 @item -fira-region=@var{region}
5901 Use specified regions for the integrated register allocator. The
5902 @var{region} argument should be one of @code{all}, @code{mixed}, or
5903 @code{one}. The first value means using all loops as register
5904 allocation regions, the second value which is the default means using
5905 all loops except for loops with small register pressure as the
5906 regions, and third one means using all function as a single region.
5907 The first value can give best result for machines with small size and
5908 irregular register set, the third one results in faster and generates
5909 decent code and the smallest size code, and the default value usually
5910 give the best results in most cases and for most architectures.
5911
5912 @item -fira-coalesce
5913 @opindex fira-coalesce
5914 Do optimistic register coalescing. This option might be profitable for
5915 architectures with big regular register files.
5916
5917 @item -fno-ira-share-save-slots
5918 @opindex fno-ira-share-save-slots
5919 Switch off sharing stack slots used for saving call used hard
5920 registers living through a call. Each hard register will get a
5921 separate stack slot and as a result function stack frame will be
5922 bigger.
5923
5924 @item -fno-ira-share-spill-slots
5925 @opindex fno-ira-share-spill-slots
5926 Switch off sharing stack slots allocated for pseudo-registers. Each
5927 pseudo-register which did not get a hard register will get a separate
5928 stack slot and as a result function stack frame will be bigger.
5929
5930 @item -fira-verbose=@var{n}
5931 @opindex fira-verbose
5932 Set up how verbose dump file for the integrated register allocator
5933 will be. Default value is 5. If the value is greater or equal to 10,
5934 the dump file will be stderr as if the value were @var{n} minus 10.
5935
5936 @item -fdelayed-branch
5937 @opindex fdelayed-branch
5938 If supported for the target machine, attempt to reorder instructions
5939 to exploit instruction slots available after delayed branch
5940 instructions.
5941
5942 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5943
5944 @item -fschedule-insns
5945 @opindex fschedule-insns
5946 If supported for the target machine, attempt to reorder instructions to
5947 eliminate execution stalls due to required data being unavailable. This
5948 helps machines that have slow floating point or memory load instructions
5949 by allowing other instructions to be issued until the result of the load
5950 or floating point instruction is required.
5951
5952 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5953
5954 @item -fschedule-insns2
5955 @opindex fschedule-insns2
5956 Similar to @option{-fschedule-insns}, but requests an additional pass of
5957 instruction scheduling after register allocation has been done. This is
5958 especially useful on machines with a relatively small number of
5959 registers and where memory load instructions take more than one cycle.
5960
5961 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5962
5963 @item -fno-sched-interblock
5964 @opindex fno-sched-interblock
5965 Don't schedule instructions across basic blocks. This is normally
5966 enabled by default when scheduling before register allocation, i.e.@:
5967 with @option{-fschedule-insns} or at @option{-O2} or higher.
5968
5969 @item -fno-sched-spec
5970 @opindex fno-sched-spec
5971 Don't allow speculative motion of non-load instructions. This is normally
5972 enabled by default when scheduling before register allocation, i.e.@:
5973 with @option{-fschedule-insns} or at @option{-O2} or higher.
5974
5975 @item -fsched-spec-load
5976 @opindex fsched-spec-load
5977 Allow speculative motion of some load instructions. This only makes
5978 sense when scheduling before register allocation, i.e.@: with
5979 @option{-fschedule-insns} or at @option{-O2} or higher.
5980
5981 @item -fsched-spec-load-dangerous
5982 @opindex fsched-spec-load-dangerous
5983 Allow speculative motion of more load instructions. This only makes
5984 sense when scheduling before register allocation, i.e.@: with
5985 @option{-fschedule-insns} or at @option{-O2} or higher.
5986
5987 @item -fsched-stalled-insns
5988 @itemx -fsched-stalled-insns=@var{n}
5989 @opindex fsched-stalled-insns
5990 Define how many insns (if any) can be moved prematurely from the queue
5991 of stalled insns into the ready list, during the second scheduling pass.
5992 @option{-fno-sched-stalled-insns} means that no insns will be moved
5993 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
5994 on how many queued insns can be moved prematurely.
5995 @option{-fsched-stalled-insns} without a value is equivalent to
5996 @option{-fsched-stalled-insns=1}.
5997
5998 @item -fsched-stalled-insns-dep
5999 @itemx -fsched-stalled-insns-dep=@var{n}
6000 @opindex fsched-stalled-insns-dep
6001 Define how many insn groups (cycles) will be examined for a dependency
6002 on a stalled insn that is candidate for premature removal from the queue
6003 of stalled insns. This has an effect only during the second scheduling pass,
6004 and only if @option{-fsched-stalled-insns} is used.
6005 @option{-fno-sched-stalled-insns-dep} is equivalent to
6006 @option{-fsched-stalled-insns-dep=0}.
6007 @option{-fsched-stalled-insns-dep} without a value is equivalent to
6008 @option{-fsched-stalled-insns-dep=1}.
6009
6010 @item -fsched2-use-superblocks
6011 @opindex fsched2-use-superblocks
6012 When scheduling after register allocation, do use superblock scheduling
6013 algorithm. Superblock scheduling allows motion across basic block boundaries
6014 resulting on faster schedules. This option is experimental, as not all machine
6015 descriptions used by GCC model the CPU closely enough to avoid unreliable
6016 results from the algorithm.
6017
6018 This only makes sense when scheduling after register allocation, i.e.@: with
6019 @option{-fschedule-insns2} or at @option{-O2} or higher.
6020
6021 @item -fsched2-use-traces
6022 @opindex fsched2-use-traces
6023 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
6024 allocation and additionally perform code duplication in order to increase the
6025 size of superblocks using tracer pass. See @option{-ftracer} for details on
6026 trace formation.
6027
6028 This mode should produce faster but significantly longer programs. Also
6029 without @option{-fbranch-probabilities} the traces constructed may not
6030 match the reality and hurt the performance. This only makes
6031 sense when scheduling after register allocation, i.e.@: with
6032 @option{-fschedule-insns2} or at @option{-O2} or higher.
6033
6034 @item -fsee
6035 @opindex fsee
6036 Eliminate redundant sign extension instructions and move the non-redundant
6037 ones to optimal placement using lazy code motion (LCM).
6038
6039 @item -freschedule-modulo-scheduled-loops
6040 @opindex freschedule-modulo-scheduled-loops
6041 The modulo scheduling comes before the traditional scheduling, if a loop
6042 was modulo scheduled we may want to prevent the later scheduling passes
6043 from changing its schedule, we use this option to control that.
6044
6045 @item -fselective-scheduling
6046 @opindex fselective-scheduling
6047 Schedule instructions using selective scheduling algorithm. Selective
6048 scheduling runs instead of the first scheduler pass.
6049
6050 @item -fselective-scheduling2
6051 @opindex fselective-scheduling2
6052 Schedule instructions using selective scheduling algorithm. Selective
6053 scheduling runs instead of the second scheduler pass.
6054
6055 @item -fsel-sched-pipelining
6056 @opindex fsel-sched-pipelining
6057 Enable software pipelining of innermost loops during selective scheduling.
6058 This option has no effect until one of @option{-fselective-scheduling} or
6059 @option{-fselective-scheduling2} is turned on.
6060
6061 @item -fsel-sched-pipelining-outer-loops
6062 @opindex fsel-sched-pipelining-outer-loops
6063 When pipelining loops during selective scheduling, also pipeline outer loops.
6064 This option has no effect until @option{-fsel-sched-pipelining} is turned on.
6065
6066 @item -fcaller-saves
6067 @opindex fcaller-saves
6068 Enable values to be allocated in registers that will be clobbered by
6069 function calls, by emitting extra instructions to save and restore the
6070 registers around such calls. Such allocation is done only when it
6071 seems to result in better code than would otherwise be produced.
6072
6073 This option is always enabled by default on certain machines, usually
6074 those which have no call-preserved registers to use instead.
6075
6076 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6077
6078 @item -fconserve-stack
6079 @opindex fconserve-stack
6080 Attempt to minimize stack usage. The compiler will attempt to use less
6081 stack space, even if that makes the program slower. This option
6082 implies setting the @option{large-stack-frame} parameter to 100
6083 and the @option{large-stack-frame-growth} parameter to 400.
6084
6085 @item -ftree-reassoc
6086 @opindex ftree-reassoc
6087 Perform reassociation on trees. This flag is enabled by default
6088 at @option{-O} and higher.
6089
6090 @item -ftree-pre
6091 @opindex ftree-pre
6092 Perform partial redundancy elimination (PRE) on trees. This flag is
6093 enabled by default at @option{-O2} and @option{-O3}.
6094
6095 @item -ftree-fre
6096 @opindex ftree-fre
6097 Perform full redundancy elimination (FRE) on trees. The difference
6098 between FRE and PRE is that FRE only considers expressions
6099 that are computed on all paths leading to the redundant computation.
6100 This analysis is faster than PRE, though it exposes fewer redundancies.
6101 This flag is enabled by default at @option{-O} and higher.
6102
6103 @item -ftree-copy-prop
6104 @opindex ftree-copy-prop
6105 Perform copy propagation on trees. This pass eliminates unnecessary
6106 copy operations. This flag is enabled by default at @option{-O} and
6107 higher.
6108
6109 @item -fipa-pure-const
6110 @opindex fipa-pure-const
6111 Discover which functions are pure or constant.
6112 Enabled by default at @option{-O} and higher.
6113
6114 @item -fipa-reference
6115 @opindex fipa-reference
6116 Discover which static variables do not escape cannot escape the
6117 compilation unit.
6118 Enabled by default at @option{-O} and higher.
6119
6120 @item -fipa-struct-reorg
6121 @opindex fipa-struct-reorg
6122 Perform structure reorganization optimization, that change C-like structures
6123 layout in order to better utilize spatial locality. This transformation is
6124 affective for programs containing arrays of structures. Available in two
6125 compilation modes: profile-based (enabled with @option{-fprofile-generate})
6126 or static (which uses built-in heuristics). Require @option{-fipa-type-escape}
6127 to provide the safety of this transformation. It works only in whole program
6128 mode, so it requires @option{-fwhole-program} and @option{-combine} to be
6129 enabled. Structures considered @samp{cold} by this transformation are not
6130 affected (see @option{--param struct-reorg-cold-struct-ratio=@var{value}}).
6131
6132 With this flag, the program debug info reflects a new structure layout.
6133
6134 @item -fipa-pta
6135 @opindex fipa-pta
6136 Perform interprocedural pointer analysis. This option is experimental
6137 and does not affect generated code.
6138
6139 @item -fipa-cp
6140 @opindex fipa-cp
6141 Perform interprocedural constant propagation.
6142 This optimization analyzes the program to determine when values passed
6143 to functions are constants and then optimizes accordingly.
6144 This optimization can substantially increase performance
6145 if the application has constants passed to functions.
6146 This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
6147
6148 @item -fipa-cp-clone
6149 @opindex fipa-cp-clone
6150 Perform function cloning to make interprocedural constant propagation stronger.
6151 When enabled, interprocedural constant propagation will perform function cloning
6152 when externally visible function can be called with constant arguments.
6153 Because this optimization can create multiple copies of functions,
6154 it may significantly increase code size
6155 (see @option{--param ipcp-unit-growth=@var{value}}).
6156 This flag is enabled by default at @option{-O3}.
6157
6158 @item -fipa-matrix-reorg
6159 @opindex fipa-matrix-reorg
6160 Perform matrix flattening and transposing.
6161 Matrix flattening tries to replace a m-dimensional matrix
6162 with its equivalent n-dimensional matrix, where n < m.
6163 This reduces the level of indirection needed for accessing the elements
6164 of the matrix. The second optimization is matrix transposing that
6165 attempts to change the order of the matrix's dimensions in order to
6166 improve cache locality.
6167 Both optimizations need the @option{-fwhole-program} flag.
6168 Transposing is enabled only if profiling information is available.
6169
6170
6171 @item -ftree-sink
6172 @opindex ftree-sink
6173 Perform forward store motion on trees. This flag is
6174 enabled by default at @option{-O} and higher.
6175
6176 @item -ftree-ccp
6177 @opindex ftree-ccp
6178 Perform sparse conditional constant propagation (CCP) on trees. This
6179 pass only operates on local scalar variables and is enabled by default
6180 at @option{-O} and higher.
6181
6182 @item -ftree-switch-conversion
6183 Perform conversion of simple initializations in a switch to
6184 initializations from a scalar array. This flag is enabled by default
6185 at @option{-O2} and higher.
6186
6187 @item -ftree-dce
6188 @opindex ftree-dce
6189 Perform dead code elimination (DCE) on trees. This flag is enabled by
6190 default at @option{-O} and higher.
6191
6192 @item -ftree-builtin-call-dce
6193 @opindex ftree-builtin-call-dce
6194 Perform conditional dead code elimination (DCE) for calls to builtin functions
6195 that may set @code{errno} but are otherwise side-effect free. This flag is
6196 enabled by default at @option{-O2} and higher if @option{-Os} is not also
6197 specified.
6198
6199 @item -ftree-dominator-opts
6200 @opindex ftree-dominator-opts
6201 Perform a variety of simple scalar cleanups (constant/copy
6202 propagation, redundancy elimination, range propagation and expression
6203 simplification) based on a dominator tree traversal. This also
6204 performs jump threading (to reduce jumps to jumps). This flag is
6205 enabled by default at @option{-O} and higher.
6206
6207 @item -ftree-dse
6208 @opindex ftree-dse
6209 Perform dead store elimination (DSE) on trees. A dead store is a store into
6210 a memory location which will later be overwritten by another store without
6211 any intervening loads. In this case the earlier store can be deleted. This
6212 flag is enabled by default at @option{-O} and higher.
6213
6214 @item -ftree-ch
6215 @opindex ftree-ch
6216 Perform loop header copying on trees. This is beneficial since it increases
6217 effectiveness of code motion optimizations. It also saves one jump. This flag
6218 is enabled by default at @option{-O} and higher. It is not enabled
6219 for @option{-Os}, since it usually increases code size.
6220
6221 @item -ftree-loop-optimize
6222 @opindex ftree-loop-optimize
6223 Perform loop optimizations on trees. This flag is enabled by default
6224 at @option{-O} and higher.
6225
6226 @item -ftree-loop-linear
6227 @opindex ftree-loop-linear
6228 Perform linear loop transformations on tree. This flag can improve cache
6229 performance and allow further loop optimizations to take place.
6230
6231 @item -floop-interchange
6232 Perform loop interchange transformations on loops. Interchanging two
6233 nested loops switches the inner and outer loops. For example, given a
6234 loop like:
6235 @smallexample
6236 DO J = 1, M
6237 DO I = 1, N
6238 A(J, I) = A(J, I) * C
6239 ENDDO
6240 ENDDO
6241 @end smallexample
6242 loop interchange will transform the loop as if the user had written:
6243 @smallexample
6244 DO I = 1, N
6245 DO J = 1, M
6246 A(J, I) = A(J, I) * C
6247 ENDDO
6248 ENDDO
6249 @end smallexample
6250 which can be beneficial when @code{N} is larger than the caches,
6251 because in Fortran, the elements of an array are stored in memory
6252 contiguously by column, and the original loop iterates over rows,
6253 potentially creating at each access a cache miss. This optimization
6254 applies to all the languages supported by GCC and is not limited to
6255 Fortran. To use this code transformation, GCC has to be configured
6256 with @option{--with-ppl} and @option{--with-cloog} to enable the
6257 Graphite loop transformation infrastructure.
6258
6259 @item -floop-strip-mine
6260 Perform loop strip mining transformations on loops. Strip mining
6261 splits a loop into two nested loops. The outer loop has strides
6262 equal to the strip size and the inner loop has strides of the
6263 original loop within a strip. For example, given a loop like:
6264 @smallexample
6265 DO I = 1, N
6266 A(I) = A(I) + C
6267 ENDDO
6268 @end smallexample
6269 loop strip mining will transform the loop as if the user had written:
6270 @smallexample
6271 DO II = 1, N, 4
6272 DO I = II, min (II + 3, N)
6273 A(I) = A(I) + C
6274 ENDDO
6275 ENDDO
6276 @end smallexample
6277 This optimization applies to all the languages supported by GCC and is
6278 not limited to Fortran. To use this code transformation, GCC has to
6279 be configured with @option{--with-ppl} and @option{--with-cloog} to
6280 enable the Graphite loop transformation infrastructure.
6281
6282 @item -floop-block
6283 Perform loop blocking transformations on loops. Blocking strip mines
6284 each loop in the loop nest such that the memory accesses of the
6285 element loops fit inside caches. For example, given a loop like:
6286 @smallexample
6287 DO I = 1, N
6288 DO J = 1, M
6289 A(J, I) = B(I) + C(J)
6290 ENDDO
6291 ENDDO
6292 @end smallexample
6293 loop blocking will transform the loop as if the user had written:
6294 @smallexample
6295 DO II = 1, N, 64
6296 DO JJ = 1, M, 64
6297 DO I = II, min (II + 63, N)
6298 DO J = JJ, min (JJ + 63, M)
6299 A(J, I) = B(I) + C(J)
6300 ENDDO
6301 ENDDO
6302 ENDDO
6303 ENDDO
6304 @end smallexample
6305 which can be beneficial when @code{M} is larger than the caches,
6306 because the innermost loop will iterate over a smaller amount of data
6307 that can be kept in the caches. This optimization applies to all the
6308 languages supported by GCC and is not limited to Fortran. To use this
6309 code transformation, GCC has to be configured with @option{--with-ppl}
6310 and @option{--with-cloog} to enable the Graphite loop transformation
6311 infrastructure.
6312
6313 @item -fcheck-data-deps
6314 @opindex fcheck-data-deps
6315 Compare the results of several data dependence analyzers. This option
6316 is used for debugging the data dependence analyzers.
6317
6318 @item -ftree-loop-distribution
6319 Perform loop distribution. This flag can improve cache performance on
6320 big loop bodies and allow further loop optimizations, like
6321 parallelization or vectorization, to take place. For example, the loop
6322 @smallexample
6323 DO I = 1, N
6324 A(I) = B(I) + C
6325 D(I) = E(I) * F
6326 ENDDO
6327 @end smallexample
6328 is transformed to
6329 @smallexample
6330 DO I = 1, N
6331 A(I) = B(I) + C
6332 ENDDO
6333 DO I = 1, N
6334 D(I) = E(I) * F
6335 ENDDO
6336 @end smallexample
6337
6338 @item -ftree-loop-im
6339 @opindex ftree-loop-im
6340 Perform loop invariant motion on trees. This pass moves only invariants that
6341 would be hard to handle at RTL level (function calls, operations that expand to
6342 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
6343 operands of conditions that are invariant out of the loop, so that we can use
6344 just trivial invariantness analysis in loop unswitching. The pass also includes
6345 store motion.
6346
6347 @item -ftree-loop-ivcanon
6348 @opindex ftree-loop-ivcanon
6349 Create a canonical counter for number of iterations in the loop for that
6350 determining number of iterations requires complicated analysis. Later
6351 optimizations then may determine the number easily. Useful especially
6352 in connection with unrolling.
6353
6354 @item -fivopts
6355 @opindex fivopts
6356 Perform induction variable optimizations (strength reduction, induction
6357 variable merging and induction variable elimination) on trees.
6358
6359 @item -ftree-parallelize-loops=n
6360 @opindex ftree-parallelize-loops
6361 Parallelize loops, i.e., split their iteration space to run in n threads.
6362 This is only possible for loops whose iterations are independent
6363 and can be arbitrarily reordered. The optimization is only
6364 profitable on multiprocessor machines, for loops that are CPU-intensive,
6365 rather than constrained e.g.@: by memory bandwidth. This option
6366 implies @option{-pthread}, and thus is only supported on targets
6367 that have support for @option{-pthread}.
6368
6369 @item -ftree-sra
6370 @opindex ftree-sra
6371 Perform scalar replacement of aggregates. This pass replaces structure
6372 references with scalars to prevent committing structures to memory too
6373 early. This flag is enabled by default at @option{-O} and higher.
6374
6375 @item -ftree-copyrename
6376 @opindex ftree-copyrename
6377 Perform copy renaming on trees. This pass attempts to rename compiler
6378 temporaries to other variables at copy locations, usually resulting in
6379 variable names which more closely resemble the original variables. This flag
6380 is enabled by default at @option{-O} and higher.
6381
6382 @item -ftree-ter
6383 @opindex ftree-ter
6384 Perform temporary expression replacement during the SSA->normal phase. Single
6385 use/single def temporaries are replaced at their use location with their
6386 defining expression. This results in non-GIMPLE code, but gives the expanders
6387 much more complex trees to work on resulting in better RTL generation. This is
6388 enabled by default at @option{-O} and higher.
6389
6390 @item -ftree-vectorize
6391 @opindex ftree-vectorize
6392 Perform loop vectorization on trees. This flag is enabled by default at
6393 @option{-O3}.
6394
6395 @item -ftree-vect-loop-version
6396 @opindex ftree-vect-loop-version
6397 Perform loop versioning when doing loop vectorization on trees. When a loop
6398 appears to be vectorizable except that data alignment or data dependence cannot
6399 be determined at compile time then vectorized and non-vectorized versions of
6400 the loop are generated along with runtime checks for alignment or dependence
6401 to control which version is executed. This option is enabled by default
6402 except at level @option{-Os} where it is disabled.
6403
6404 @item -fvect-cost-model
6405 @opindex fvect-cost-model
6406 Enable cost model for vectorization.
6407
6408 @item -ftree-vrp
6409 @opindex ftree-vrp
6410 Perform Value Range Propagation on trees. This is similar to the
6411 constant propagation pass, but instead of values, ranges of values are
6412 propagated. This allows the optimizers to remove unnecessary range
6413 checks like array bound checks and null pointer checks. This is
6414 enabled by default at @option{-O2} and higher. Null pointer check
6415 elimination is only done if @option{-fdelete-null-pointer-checks} is
6416 enabled.
6417
6418 @item -ftracer
6419 @opindex ftracer
6420 Perform tail duplication to enlarge superblock size. This transformation
6421 simplifies the control flow of the function allowing other optimizations to do
6422 better job.
6423
6424 @item -funroll-loops
6425 @opindex funroll-loops
6426 Unroll loops whose number of iterations can be determined at compile
6427 time or upon entry to the loop. @option{-funroll-loops} implies
6428 @option{-frerun-cse-after-loop}. This option makes code larger,
6429 and may or may not make it run faster.
6430
6431 @item -funroll-all-loops
6432 @opindex funroll-all-loops
6433 Unroll all loops, even if their number of iterations is uncertain when
6434 the loop is entered. This usually makes programs run more slowly.
6435 @option{-funroll-all-loops} implies the same options as
6436 @option{-funroll-loops},
6437
6438 @item -fsplit-ivs-in-unroller
6439 @opindex fsplit-ivs-in-unroller
6440 Enables expressing of values of induction variables in later iterations
6441 of the unrolled loop using the value in the first iteration. This breaks
6442 long dependency chains, thus improving efficiency of the scheduling passes.
6443
6444 Combination of @option{-fweb} and CSE is often sufficient to obtain the
6445 same effect. However in cases the loop body is more complicated than
6446 a single basic block, this is not reliable. It also does not work at all
6447 on some of the architectures due to restrictions in the CSE pass.
6448
6449 This optimization is enabled by default.
6450
6451 @item -fvariable-expansion-in-unroller
6452 @opindex fvariable-expansion-in-unroller
6453 With this option, the compiler will create multiple copies of some
6454 local variables when unrolling a loop which can result in superior code.
6455
6456 @item -fpredictive-commoning
6457 @opindex fpredictive-commoning
6458 Perform predictive commoning optimization, i.e., reusing computations
6459 (especially memory loads and stores) performed in previous
6460 iterations of loops.
6461
6462 This option is enabled at level @option{-O3}.
6463
6464 @item -fprefetch-loop-arrays
6465 @opindex fprefetch-loop-arrays
6466 If supported by the target machine, generate instructions to prefetch
6467 memory to improve the performance of loops that access large arrays.
6468
6469 This option may generate better or worse code; results are highly
6470 dependent on the structure of loops within the source code.
6471
6472 Disabled at level @option{-Os}.
6473
6474 @item -fno-peephole
6475 @itemx -fno-peephole2
6476 @opindex fno-peephole
6477 @opindex fno-peephole2
6478 Disable any machine-specific peephole optimizations. The difference
6479 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
6480 are implemented in the compiler; some targets use one, some use the
6481 other, a few use both.
6482
6483 @option{-fpeephole} is enabled by default.
6484 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6485
6486 @item -fno-guess-branch-probability
6487 @opindex fno-guess-branch-probability
6488 Do not guess branch probabilities using heuristics.
6489
6490 GCC will use heuristics to guess branch probabilities if they are
6491 not provided by profiling feedback (@option{-fprofile-arcs}). These
6492 heuristics are based on the control flow graph. If some branch probabilities
6493 are specified by @samp{__builtin_expect}, then the heuristics will be
6494 used to guess branch probabilities for the rest of the control flow graph,
6495 taking the @samp{__builtin_expect} info into account. The interactions
6496 between the heuristics and @samp{__builtin_expect} can be complex, and in
6497 some cases, it may be useful to disable the heuristics so that the effects
6498 of @samp{__builtin_expect} are easier to understand.
6499
6500 The default is @option{-fguess-branch-probability} at levels
6501 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6502
6503 @item -freorder-blocks
6504 @opindex freorder-blocks
6505 Reorder basic blocks in the compiled function in order to reduce number of
6506 taken branches and improve code locality.
6507
6508 Enabled at levels @option{-O2}, @option{-O3}.
6509
6510 @item -freorder-blocks-and-partition
6511 @opindex freorder-blocks-and-partition
6512 In addition to reordering basic blocks in the compiled function, in order
6513 to reduce number of taken branches, partitions hot and cold basic blocks
6514 into separate sections of the assembly and .o files, to improve
6515 paging and cache locality performance.
6516
6517 This optimization is automatically turned off in the presence of
6518 exception handling, for linkonce sections, for functions with a user-defined
6519 section attribute and on any architecture that does not support named
6520 sections.
6521
6522 @item -freorder-functions
6523 @opindex freorder-functions
6524 Reorder functions in the object file in order to
6525 improve code locality. This is implemented by using special
6526 subsections @code{.text.hot} for most frequently executed functions and
6527 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
6528 the linker so object file format must support named sections and linker must
6529 place them in a reasonable way.
6530
6531 Also profile feedback must be available in to make this option effective. See
6532 @option{-fprofile-arcs} for details.
6533
6534 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6535
6536 @item -fstrict-aliasing
6537 @opindex fstrict-aliasing
6538 Allow the compiler to assume the strictest aliasing rules applicable to
6539 the language being compiled. For C (and C++), this activates
6540 optimizations based on the type of expressions. In particular, an
6541 object of one type is assumed never to reside at the same address as an
6542 object of a different type, unless the types are almost the same. For
6543 example, an @code{unsigned int} can alias an @code{int}, but not a
6544 @code{void*} or a @code{double}. A character type may alias any other
6545 type.
6546
6547 @anchor{Type-punning}Pay special attention to code like this:
6548 @smallexample
6549 union a_union @{
6550 int i;
6551 double d;
6552 @};
6553
6554 int f() @{
6555 union a_union t;
6556 t.d = 3.0;
6557 return t.i;
6558 @}
6559 @end smallexample
6560 The practice of reading from a different union member than the one most
6561 recently written to (called ``type-punning'') is common. Even with
6562 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
6563 is accessed through the union type. So, the code above will work as
6564 expected. @xref{Structures unions enumerations and bit-fields
6565 implementation}. However, this code might not:
6566 @smallexample
6567 int f() @{
6568 union a_union t;
6569 int* ip;
6570 t.d = 3.0;
6571 ip = &t.i;
6572 return *ip;
6573 @}
6574 @end smallexample
6575
6576 Similarly, access by taking the address, casting the resulting pointer
6577 and dereferencing the result has undefined behavior, even if the cast
6578 uses a union type, e.g.:
6579 @smallexample
6580 int f() @{
6581 double d = 3.0;
6582 return ((union a_union *) &d)->i;
6583 @}
6584 @end smallexample
6585
6586 The @option{-fstrict-aliasing} option is enabled at levels
6587 @option{-O2}, @option{-O3}, @option{-Os}.
6588
6589 @item -fstrict-overflow
6590 @opindex fstrict-overflow
6591 Allow the compiler to assume strict signed overflow rules, depending
6592 on the language being compiled. For C (and C++) this means that
6593 overflow when doing arithmetic with signed numbers is undefined, which
6594 means that the compiler may assume that it will not happen. This
6595 permits various optimizations. For example, the compiler will assume
6596 that an expression like @code{i + 10 > i} will always be true for
6597 signed @code{i}. This assumption is only valid if signed overflow is
6598 undefined, as the expression is false if @code{i + 10} overflows when
6599 using twos complement arithmetic. When this option is in effect any
6600 attempt to determine whether an operation on signed numbers will
6601 overflow must be written carefully to not actually involve overflow.
6602
6603 This option also allows the compiler to assume strict pointer
6604 semantics: given a pointer to an object, if adding an offset to that
6605 pointer does not produce a pointer to the same object, the addition is
6606 undefined. This permits the compiler to conclude that @code{p + u >
6607 p} is always true for a pointer @code{p} and unsigned integer
6608 @code{u}. This assumption is only valid because pointer wraparound is
6609 undefined, as the expression is false if @code{p + u} overflows using
6610 twos complement arithmetic.
6611
6612 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
6613 that integer signed overflow is fully defined: it wraps. When
6614 @option{-fwrapv} is used, there is no difference between
6615 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
6616 integers. With @option{-fwrapv} certain types of overflow are
6617 permitted. For example, if the compiler gets an overflow when doing
6618 arithmetic on constants, the overflowed value can still be used with
6619 @option{-fwrapv}, but not otherwise.
6620
6621 The @option{-fstrict-overflow} option is enabled at levels
6622 @option{-O2}, @option{-O3}, @option{-Os}.
6623
6624 @item -falign-functions
6625 @itemx -falign-functions=@var{n}
6626 @opindex falign-functions
6627 Align the start of functions to the next power-of-two greater than
6628 @var{n}, skipping up to @var{n} bytes. For instance,
6629 @option{-falign-functions=32} aligns functions to the next 32-byte
6630 boundary, but @option{-falign-functions=24} would align to the next
6631 32-byte boundary only if this can be done by skipping 23 bytes or less.
6632
6633 @option{-fno-align-functions} and @option{-falign-functions=1} are
6634 equivalent and mean that functions will not be aligned.
6635
6636 Some assemblers only support this flag when @var{n} is a power of two;
6637 in that case, it is rounded up.
6638
6639 If @var{n} is not specified or is zero, use a machine-dependent default.
6640
6641 Enabled at levels @option{-O2}, @option{-O3}.
6642
6643 @item -falign-labels
6644 @itemx -falign-labels=@var{n}
6645 @opindex falign-labels
6646 Align all branch targets to a power-of-two boundary, skipping up to
6647 @var{n} bytes like @option{-falign-functions}. This option can easily
6648 make code slower, because it must insert dummy operations for when the
6649 branch target is reached in the usual flow of the code.
6650
6651 @option{-fno-align-labels} and @option{-falign-labels=1} are
6652 equivalent and mean that labels will not be aligned.
6653
6654 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
6655 are greater than this value, then their values are used instead.
6656
6657 If @var{n} is not specified or is zero, use a machine-dependent default
6658 which is very likely to be @samp{1}, meaning no alignment.
6659
6660 Enabled at levels @option{-O2}, @option{-O3}.
6661
6662 @item -falign-loops
6663 @itemx -falign-loops=@var{n}
6664 @opindex falign-loops
6665 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
6666 like @option{-falign-functions}. The hope is that the loop will be
6667 executed many times, which will make up for any execution of the dummy
6668 operations.
6669
6670 @option{-fno-align-loops} and @option{-falign-loops=1} are
6671 equivalent and mean that loops will not be aligned.
6672
6673 If @var{n} is not specified or is zero, use a machine-dependent default.
6674
6675 Enabled at levels @option{-O2}, @option{-O3}.
6676
6677 @item -falign-jumps
6678 @itemx -falign-jumps=@var{n}
6679 @opindex falign-jumps
6680 Align branch targets to a power-of-two boundary, for branch targets
6681 where the targets can only be reached by jumping, skipping up to @var{n}
6682 bytes like @option{-falign-functions}. In this case, no dummy operations
6683 need be executed.
6684
6685 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
6686 equivalent and mean that loops will not be aligned.
6687
6688 If @var{n} is not specified or is zero, use a machine-dependent default.
6689
6690 Enabled at levels @option{-O2}, @option{-O3}.
6691
6692 @item -funit-at-a-time
6693 @opindex funit-at-a-time
6694 This option is left for compatibility reasons. @option{-funit-at-a-time}
6695 has no effect, while @option{-fno-unit-at-a-time} implies
6696 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
6697
6698 Enabled by default.
6699
6700 @item -fno-toplevel-reorder
6701 @opindex fno-toplevel-reorder
6702 Do not reorder top-level functions, variables, and @code{asm}
6703 statements. Output them in the same order that they appear in the
6704 input file. When this option is used, unreferenced static variables
6705 will not be removed. This option is intended to support existing code
6706 which relies on a particular ordering. For new code, it is better to
6707 use attributes.
6708
6709 Enabled at level @option{-O0}. When disabled explicitly, it also imply
6710 @option{-fno-section-anchors} that is otherwise enabled at @option{-O0} on some
6711 targets.
6712
6713 @item -fweb
6714 @opindex fweb
6715 Constructs webs as commonly used for register allocation purposes and assign
6716 each web individual pseudo register. This allows the register allocation pass
6717 to operate on pseudos directly, but also strengthens several other optimization
6718 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
6719 however, make debugging impossible, since variables will no longer stay in a
6720 ``home register''.
6721
6722 Enabled by default with @option{-funroll-loops}.
6723
6724 @item -fwhole-program
6725 @opindex fwhole-program
6726 Assume that the current compilation unit represents whole program being
6727 compiled. All public functions and variables with the exception of @code{main}
6728 and those merged by attribute @code{externally_visible} become static functions
6729 and in a affect gets more aggressively optimized by interprocedural optimizers.
6730 While this option is equivalent to proper use of @code{static} keyword for
6731 programs consisting of single file, in combination with option
6732 @option{--combine} this flag can be used to compile most of smaller scale C
6733 programs since the functions and variables become local for the whole combined
6734 compilation unit, not for the single source file itself.
6735
6736 This option is not supported for Fortran programs.
6737
6738 @item -fcprop-registers
6739 @opindex fcprop-registers
6740 After register allocation and post-register allocation instruction splitting,
6741 we perform a copy-propagation pass to try to reduce scheduling dependencies
6742 and occasionally eliminate the copy.
6743
6744 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6745
6746 @item -fprofile-correction
6747 @opindex fprofile-correction
6748 Profiles collected using an instrumented binary for multi-threaded programs may
6749 be inconsistent due to missed counter updates. When this option is specified,
6750 GCC will use heuristics to correct or smooth out such inconsistencies. By
6751 default, GCC will emit an error message when an inconsistent profile is detected.
6752
6753 @item -fprofile-dir=@var{path}
6754 @opindex fprofile-dir
6755
6756 Set the directory to search the profile data files in to @var{path}.
6757 This option affects only the profile data generated by
6758 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
6759 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
6760 and its related options.
6761 By default, GCC will use the current directory as @var{path}
6762 thus the profile data file will appear in the same directory as the object file.
6763
6764 @item -fprofile-generate
6765 @itemx -fprofile-generate=@var{path}
6766 @opindex fprofile-generate
6767
6768 Enable options usually used for instrumenting application to produce
6769 profile useful for later recompilation with profile feedback based
6770 optimization. You must use @option{-fprofile-generate} both when
6771 compiling and when linking your program.
6772
6773 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
6774
6775 If @var{path} is specified, GCC will look at the @var{path} to find
6776 the profile feedback data files. See @option{-fprofile-dir}.
6777
6778 @item -fprofile-use
6779 @itemx -fprofile-use=@var{path}
6780 @opindex fprofile-use
6781 Enable profile feedback directed optimizations, and optimizations
6782 generally profitable only with profile feedback available.
6783
6784 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
6785 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
6786
6787 By default, GCC emits an error message if the feedback profiles do not
6788 match the source code. This error can be turned into a warning by using
6789 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
6790 code.
6791
6792 If @var{path} is specified, GCC will look at the @var{path} to find
6793 the profile feedback data files. See @option{-fprofile-dir}.
6794 @end table
6795
6796 The following options control compiler behavior regarding floating
6797 point arithmetic. These options trade off between speed and
6798 correctness. All must be specifically enabled.
6799
6800 @table @gcctabopt
6801 @item -ffloat-store
6802 @opindex ffloat-store
6803 Do not store floating point variables in registers, and inhibit other
6804 options that might change whether a floating point value is taken from a
6805 register or memory.
6806
6807 @cindex floating point precision
6808 This option prevents undesirable excess precision on machines such as
6809 the 68000 where the floating registers (of the 68881) keep more
6810 precision than a @code{double} is supposed to have. Similarly for the
6811 x86 architecture. For most programs, the excess precision does only
6812 good, but a few programs rely on the precise definition of IEEE floating
6813 point. Use @option{-ffloat-store} for such programs, after modifying
6814 them to store all pertinent intermediate computations into variables.
6815
6816 @item -ffast-math
6817 @opindex ffast-math
6818 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
6819 @option{-ffinite-math-only}, @option{-fno-rounding-math},
6820 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
6821
6822 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
6823
6824 This option is not turned on by any @option{-O} option since
6825 it can result in incorrect output for programs which depend on
6826 an exact implementation of IEEE or ISO rules/specifications for
6827 math functions. It may, however, yield faster code for programs
6828 that do not require the guarantees of these specifications.
6829
6830 @item -fno-math-errno
6831 @opindex fno-math-errno
6832 Do not set ERRNO after calling math functions that are executed
6833 with a single instruction, e.g., sqrt. A program that relies on
6834 IEEE exceptions for math error handling may want to use this flag
6835 for speed while maintaining IEEE arithmetic compatibility.
6836
6837 This option is not turned on by any @option{-O} option since
6838 it can result in incorrect output for programs which depend on
6839 an exact implementation of IEEE or ISO rules/specifications for
6840 math functions. It may, however, yield faster code for programs
6841 that do not require the guarantees of these specifications.
6842
6843 The default is @option{-fmath-errno}.
6844
6845 On Darwin systems, the math library never sets @code{errno}. There is
6846 therefore no reason for the compiler to consider the possibility that
6847 it might, and @option{-fno-math-errno} is the default.
6848
6849 @item -funsafe-math-optimizations
6850 @opindex funsafe-math-optimizations
6851
6852 Allow optimizations for floating-point arithmetic that (a) assume
6853 that arguments and results are valid and (b) may violate IEEE or
6854 ANSI standards. When used at link-time, it may include libraries
6855 or startup files that change the default FPU control word or other
6856 similar optimizations.
6857
6858 This option is not turned on by any @option{-O} option since
6859 it can result in incorrect output for programs which depend on
6860 an exact implementation of IEEE or ISO rules/specifications for
6861 math functions. It may, however, yield faster code for programs
6862 that do not require the guarantees of these specifications.
6863 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
6864 @option{-fassociative-math} and @option{-freciprocal-math}.
6865
6866 The default is @option{-fno-unsafe-math-optimizations}.
6867
6868 @item -fassociative-math
6869 @opindex fassociative-math
6870
6871 Allow re-association of operands in series of floating-point operations.
6872 This violates the ISO C and C++ language standard by possibly changing
6873 computation result. NOTE: re-ordering may change the sign of zero as
6874 well as ignore NaNs and inhibit or create underflow or overflow (and
6875 thus cannot be used on a code which relies on rounding behavior like
6876 @code{(x + 2**52) - 2**52)}. May also reorder floating-point comparisons
6877 and thus may not be used when ordered comparisons are required.
6878 This option requires that both @option{-fno-signed-zeros} and
6879 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
6880 much sense with @option{-frounding-math}.
6881
6882 The default is @option{-fno-associative-math}.
6883
6884 @item -freciprocal-math
6885 @opindex freciprocal-math
6886
6887 Allow the reciprocal of a value to be used instead of dividing by
6888 the value if this enables optimizations. For example @code{x / y}
6889 can be replaced with @code{x * (1/y)} which is useful if @code{(1/y)}
6890 is subject to common subexpression elimination. Note that this loses
6891 precision and increases the number of flops operating on the value.
6892
6893 The default is @option{-fno-reciprocal-math}.
6894
6895 @item -ffinite-math-only
6896 @opindex ffinite-math-only
6897 Allow optimizations for floating-point arithmetic that assume
6898 that arguments and results are not NaNs or +-Infs.
6899
6900 This option is not turned on by any @option{-O} option since
6901 it can result in incorrect output for programs which depend on
6902 an exact implementation of IEEE or ISO rules/specifications for
6903 math functions. It may, however, yield faster code for programs
6904 that do not require the guarantees of these specifications.
6905
6906 The default is @option{-fno-finite-math-only}.
6907
6908 @item -fno-signed-zeros
6909 @opindex fno-signed-zeros
6910 Allow optimizations for floating point arithmetic that ignore the
6911 signedness of zero. IEEE arithmetic specifies the behavior of
6912 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
6913 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
6914 This option implies that the sign of a zero result isn't significant.
6915
6916 The default is @option{-fsigned-zeros}.
6917
6918 @item -fno-trapping-math
6919 @opindex fno-trapping-math
6920 Compile code assuming that floating-point operations cannot generate
6921 user-visible traps. These traps include division by zero, overflow,
6922 underflow, inexact result and invalid operation. This option requires
6923 that @option{-fno-signaling-nans} be in effect. Setting this option may
6924 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
6925
6926 This option should never be turned on by any @option{-O} option since
6927 it can result in incorrect output for programs which depend on
6928 an exact implementation of IEEE or ISO rules/specifications for
6929 math functions.
6930
6931 The default is @option{-ftrapping-math}.
6932
6933 @item -frounding-math
6934 @opindex frounding-math
6935 Disable transformations and optimizations that assume default floating
6936 point rounding behavior. This is round-to-zero for all floating point
6937 to integer conversions, and round-to-nearest for all other arithmetic
6938 truncations. This option should be specified for programs that change
6939 the FP rounding mode dynamically, or that may be executed with a
6940 non-default rounding mode. This option disables constant folding of
6941 floating point expressions at compile-time (which may be affected by
6942 rounding mode) and arithmetic transformations that are unsafe in the
6943 presence of sign-dependent rounding modes.
6944
6945 The default is @option{-fno-rounding-math}.
6946
6947 This option is experimental and does not currently guarantee to
6948 disable all GCC optimizations that are affected by rounding mode.
6949 Future versions of GCC may provide finer control of this setting
6950 using C99's @code{FENV_ACCESS} pragma. This command line option
6951 will be used to specify the default state for @code{FENV_ACCESS}.
6952
6953 @item -frtl-abstract-sequences
6954 @opindex frtl-abstract-sequences
6955 It is a size optimization method. This option is to find identical
6956 sequences of code, which can be turned into pseudo-procedures and
6957 then replace all occurrences with calls to the newly created
6958 subroutine. It is kind of an opposite of @option{-finline-functions}.
6959 This optimization runs at RTL level.
6960
6961 @item -fsignaling-nans
6962 @opindex fsignaling-nans
6963 Compile code assuming that IEEE signaling NaNs may generate user-visible
6964 traps during floating-point operations. Setting this option disables
6965 optimizations that may change the number of exceptions visible with
6966 signaling NaNs. This option implies @option{-ftrapping-math}.
6967
6968 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
6969 be defined.
6970
6971 The default is @option{-fno-signaling-nans}.
6972
6973 This option is experimental and does not currently guarantee to
6974 disable all GCC optimizations that affect signaling NaN behavior.
6975
6976 @item -fsingle-precision-constant
6977 @opindex fsingle-precision-constant
6978 Treat floating point constant as single precision constant instead of
6979 implicitly converting it to double precision constant.
6980
6981 @item -fcx-limited-range
6982 @opindex fcx-limited-range
6983 When enabled, this option states that a range reduction step is not
6984 needed when performing complex division. Also, there is no checking
6985 whether the result of a complex multiplication or division is @code{NaN
6986 + I*NaN}, with an attempt to rescue the situation in that case. The
6987 default is @option{-fno-cx-limited-range}, but is enabled by
6988 @option{-ffast-math}.
6989
6990 This option controls the default setting of the ISO C99
6991 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
6992 all languages.
6993
6994 @item -fcx-fortran-rules
6995 @opindex fcx-fortran-rules
6996 Complex multiplication and division follow Fortran rules. Range
6997 reduction is done as part of complex division, but there is no checking
6998 whether the result of a complex multiplication or division is @code{NaN
6999 + I*NaN}, with an attempt to rescue the situation in that case.
7000
7001 The default is @option{-fno-cx-fortran-rules}.
7002
7003 @end table
7004
7005 The following options control optimizations that may improve
7006 performance, but are not enabled by any @option{-O} options. This
7007 section includes experimental options that may produce broken code.
7008
7009 @table @gcctabopt
7010 @item -fbranch-probabilities
7011 @opindex fbranch-probabilities
7012 After running a program compiled with @option{-fprofile-arcs}
7013 (@pxref{Debugging Options,, Options for Debugging Your Program or
7014 @command{gcc}}), you can compile it a second time using
7015 @option{-fbranch-probabilities}, to improve optimizations based on
7016 the number of times each branch was taken. When the program
7017 compiled with @option{-fprofile-arcs} exits it saves arc execution
7018 counts to a file called @file{@var{sourcename}.gcda} for each source
7019 file. The information in this data file is very dependent on the
7020 structure of the generated code, so you must use the same source code
7021 and the same optimization options for both compilations.
7022
7023 With @option{-fbranch-probabilities}, GCC puts a
7024 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
7025 These can be used to improve optimization. Currently, they are only
7026 used in one place: in @file{reorg.c}, instead of guessing which path a
7027 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
7028 exactly determine which path is taken more often.
7029
7030 @item -fprofile-values
7031 @opindex fprofile-values
7032 If combined with @option{-fprofile-arcs}, it adds code so that some
7033 data about values of expressions in the program is gathered.
7034
7035 With @option{-fbranch-probabilities}, it reads back the data gathered
7036 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
7037 notes to instructions for their later usage in optimizations.
7038
7039 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
7040
7041 @item -fvpt
7042 @opindex fvpt
7043 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
7044 a code to gather information about values of expressions.
7045
7046 With @option{-fbranch-probabilities}, it reads back the data gathered
7047 and actually performs the optimizations based on them.
7048 Currently the optimizations include specialization of division operation
7049 using the knowledge about the value of the denominator.
7050
7051 @item -frename-registers
7052 @opindex frename-registers
7053 Attempt to avoid false dependencies in scheduled code by making use
7054 of registers left over after register allocation. This optimization
7055 will most benefit processors with lots of registers. Depending on the
7056 debug information format adopted by the target, however, it can
7057 make debugging impossible, since variables will no longer stay in
7058 a ``home register''.
7059
7060 Enabled by default with @option{-funroll-loops}.
7061
7062 @item -ftracer
7063 @opindex ftracer
7064 Perform tail duplication to enlarge superblock size. This transformation
7065 simplifies the control flow of the function allowing other optimizations to do
7066 better job.
7067
7068 Enabled with @option{-fprofile-use}.
7069
7070 @item -funroll-loops
7071 @opindex funroll-loops
7072 Unroll loops whose number of iterations can be determined at compile time or
7073 upon entry to the loop. @option{-funroll-loops} implies
7074 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
7075 It also turns on complete loop peeling (i.e.@: complete removal of loops with
7076 small constant number of iterations). This option makes code larger, and may
7077 or may not make it run faster.
7078
7079 Enabled with @option{-fprofile-use}.
7080
7081 @item -funroll-all-loops
7082 @opindex funroll-all-loops
7083 Unroll all loops, even if their number of iterations is uncertain when
7084 the loop is entered. This usually makes programs run more slowly.
7085 @option{-funroll-all-loops} implies the same options as
7086 @option{-funroll-loops}.
7087
7088 @item -fpeel-loops
7089 @opindex fpeel-loops
7090 Peels the loops for that there is enough information that they do not
7091 roll much (from profile feedback). It also turns on complete loop peeling
7092 (i.e.@: complete removal of loops with small constant number of iterations).
7093
7094 Enabled with @option{-fprofile-use}.
7095
7096 @item -fmove-loop-invariants
7097 @opindex fmove-loop-invariants
7098 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
7099 at level @option{-O1}
7100
7101 @item -funswitch-loops
7102 @opindex funswitch-loops
7103 Move branches with loop invariant conditions out of the loop, with duplicates
7104 of the loop on both branches (modified according to result of the condition).
7105
7106 @item -ffunction-sections
7107 @itemx -fdata-sections
7108 @opindex ffunction-sections
7109 @opindex fdata-sections
7110 Place each function or data item into its own section in the output
7111 file if the target supports arbitrary sections. The name of the
7112 function or the name of the data item determines the section's name
7113 in the output file.
7114
7115 Use these options on systems where the linker can perform optimizations
7116 to improve locality of reference in the instruction space. Most systems
7117 using the ELF object format and SPARC processors running Solaris 2 have
7118 linkers with such optimizations. AIX may have these optimizations in
7119 the future.
7120
7121 Only use these options when there are significant benefits from doing
7122 so. When you specify these options, the assembler and linker will
7123 create larger object and executable files and will also be slower.
7124 You will not be able to use @code{gprof} on all systems if you
7125 specify this option and you may have problems with debugging if
7126 you specify both this option and @option{-g}.
7127
7128 @item -fbranch-target-load-optimize
7129 @opindex fbranch-target-load-optimize
7130 Perform branch target register load optimization before prologue / epilogue
7131 threading.
7132 The use of target registers can typically be exposed only during reload,
7133 thus hoisting loads out of loops and doing inter-block scheduling needs
7134 a separate optimization pass.
7135
7136 @item -fbranch-target-load-optimize2
7137 @opindex fbranch-target-load-optimize2
7138 Perform branch target register load optimization after prologue / epilogue
7139 threading.
7140
7141 @item -fbtr-bb-exclusive
7142 @opindex fbtr-bb-exclusive
7143 When performing branch target register load optimization, don't reuse
7144 branch target registers in within any basic block.
7145
7146 @item -fstack-protector
7147 @opindex fstack-protector
7148 Emit extra code to check for buffer overflows, such as stack smashing
7149 attacks. This is done by adding a guard variable to functions with
7150 vulnerable objects. This includes functions that call alloca, and
7151 functions with buffers larger than 8 bytes. The guards are initialized
7152 when a function is entered and then checked when the function exits.
7153 If a guard check fails, an error message is printed and the program exits.
7154
7155 @item -fstack-protector-all
7156 @opindex fstack-protector-all
7157 Like @option{-fstack-protector} except that all functions are protected.
7158
7159 @item -fsection-anchors
7160 @opindex fsection-anchors
7161 Try to reduce the number of symbolic address calculations by using
7162 shared ``anchor'' symbols to address nearby objects. This transformation
7163 can help to reduce the number of GOT entries and GOT accesses on some
7164 targets.
7165
7166 For example, the implementation of the following function @code{foo}:
7167
7168 @smallexample
7169 static int a, b, c;
7170 int foo (void) @{ return a + b + c; @}
7171 @end smallexample
7172
7173 would usually calculate the addresses of all three variables, but if you
7174 compile it with @option{-fsection-anchors}, it will access the variables
7175 from a common anchor point instead. The effect is similar to the
7176 following pseudocode (which isn't valid C):
7177
7178 @smallexample
7179 int foo (void)
7180 @{
7181 register int *xr = &x;
7182 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
7183 @}
7184 @end smallexample
7185
7186 Not all targets support this option.
7187
7188 @item --param @var{name}=@var{value}
7189 @opindex param
7190 In some places, GCC uses various constants to control the amount of
7191 optimization that is done. For example, GCC will not inline functions
7192 that contain more that a certain number of instructions. You can
7193 control some of these constants on the command-line using the
7194 @option{--param} option.
7195
7196 The names of specific parameters, and the meaning of the values, are
7197 tied to the internals of the compiler, and are subject to change
7198 without notice in future releases.
7199
7200 In each case, the @var{value} is an integer. The allowable choices for
7201 @var{name} are given in the following table:
7202
7203 @table @gcctabopt
7204 @item sra-max-structure-size
7205 The maximum structure size, in bytes, at which the scalar replacement
7206 of aggregates (SRA) optimization will perform block copies. The
7207 default value, 0, implies that GCC will select the most appropriate
7208 size itself.
7209
7210 @item sra-field-structure-ratio
7211 The threshold ratio (as a percentage) between instantiated fields and
7212 the complete structure size. We say that if the ratio of the number
7213 of bytes in instantiated fields to the number of bytes in the complete
7214 structure exceeds this parameter, then block copies are not used. The
7215 default is 75.
7216
7217 @item struct-reorg-cold-struct-ratio
7218 The threshold ratio (as a percentage) between a structure frequency
7219 and the frequency of the hottest structure in the program. This parameter
7220 is used by struct-reorg optimization enabled by @option{-fipa-struct-reorg}.
7221 We say that if the ratio of a structure frequency, calculated by profiling,
7222 to the hottest structure frequency in the program is less than this
7223 parameter, then structure reorganization is not applied to this structure.
7224 The default is 10.
7225
7226 @item predictable-branch-cost-outcome
7227 When branch is predicted to be taken with probability lower than this threshold
7228 (in percent), then it is considered well predictable. The default is 10.
7229
7230 @item max-crossjump-edges
7231 The maximum number of incoming edges to consider for crossjumping.
7232 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
7233 the number of edges incoming to each block. Increasing values mean
7234 more aggressive optimization, making the compile time increase with
7235 probably small improvement in executable size.
7236
7237 @item min-crossjump-insns
7238 The minimum number of instructions which must be matched at the end
7239 of two blocks before crossjumping will be performed on them. This
7240 value is ignored in the case where all instructions in the block being
7241 crossjumped from are matched. The default value is 5.
7242
7243 @item max-grow-copy-bb-insns
7244 The maximum code size expansion factor when copying basic blocks
7245 instead of jumping. The expansion is relative to a jump instruction.
7246 The default value is 8.
7247
7248 @item max-goto-duplication-insns
7249 The maximum number of instructions to duplicate to a block that jumps
7250 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
7251 passes, GCC factors computed gotos early in the compilation process,
7252 and unfactors them as late as possible. Only computed jumps at the
7253 end of a basic blocks with no more than max-goto-duplication-insns are
7254 unfactored. The default value is 8.
7255
7256 @item max-delay-slot-insn-search
7257 The maximum number of instructions to consider when looking for an
7258 instruction to fill a delay slot. If more than this arbitrary number of
7259 instructions is searched, the time savings from filling the delay slot
7260 will be minimal so stop searching. Increasing values mean more
7261 aggressive optimization, making the compile time increase with probably
7262 small improvement in executable run time.
7263
7264 @item max-delay-slot-live-search
7265 When trying to fill delay slots, the maximum number of instructions to
7266 consider when searching for a block with valid live register
7267 information. Increasing this arbitrarily chosen value means more
7268 aggressive optimization, increasing the compile time. This parameter
7269 should be removed when the delay slot code is rewritten to maintain the
7270 control-flow graph.
7271
7272 @item max-gcse-memory
7273 The approximate maximum amount of memory that will be allocated in
7274 order to perform the global common subexpression elimination
7275 optimization. If more memory than specified is required, the
7276 optimization will not be done.
7277
7278 @item max-gcse-passes
7279 The maximum number of passes of GCSE to run. The default is 1.
7280
7281 @item max-pending-list-length
7282 The maximum number of pending dependencies scheduling will allow
7283 before flushing the current state and starting over. Large functions
7284 with few branches or calls can create excessively large lists which
7285 needlessly consume memory and resources.
7286
7287 @item max-inline-insns-single
7288 Several parameters control the tree inliner used in gcc.
7289 This number sets the maximum number of instructions (counted in GCC's
7290 internal representation) in a single function that the tree inliner
7291 will consider for inlining. This only affects functions declared
7292 inline and methods implemented in a class declaration (C++).
7293 The default value is 450.
7294
7295 @item max-inline-insns-auto
7296 When you use @option{-finline-functions} (included in @option{-O3}),
7297 a lot of functions that would otherwise not be considered for inlining
7298 by the compiler will be investigated. To those functions, a different
7299 (more restrictive) limit compared to functions declared inline can
7300 be applied.
7301 The default value is 90.
7302
7303 @item large-function-insns
7304 The limit specifying really large functions. For functions larger than this
7305 limit after inlining, inlining is constrained by
7306 @option{--param large-function-growth}. This parameter is useful primarily
7307 to avoid extreme compilation time caused by non-linear algorithms used by the
7308 backend.
7309 The default value is 2700.
7310
7311 @item large-function-growth
7312 Specifies maximal growth of large function caused by inlining in percents.
7313 The default value is 100 which limits large function growth to 2.0 times
7314 the original size.
7315
7316 @item large-unit-insns
7317 The limit specifying large translation unit. Growth caused by inlining of
7318 units larger than this limit is limited by @option{--param inline-unit-growth}.
7319 For small units this might be too tight (consider unit consisting of function A
7320 that is inline and B that just calls A three time. If B is small relative to
7321 A, the growth of unit is 300\% and yet such inlining is very sane. For very
7322 large units consisting of small inlineable functions however the overall unit
7323 growth limit is needed to avoid exponential explosion of code size. Thus for
7324 smaller units, the size is increased to @option{--param large-unit-insns}
7325 before applying @option{--param inline-unit-growth}. The default is 10000
7326
7327 @item inline-unit-growth
7328 Specifies maximal overall growth of the compilation unit caused by inlining.
7329 The default value is 30 which limits unit growth to 1.3 times the original
7330 size.
7331
7332 @item ipcp-unit-growth
7333 Specifies maximal overall growth of the compilation unit caused by
7334 interprocedural constant propagation. The default value is 10 which limits
7335 unit growth to 1.1 times the original size.
7336
7337 @item large-stack-frame
7338 The limit specifying large stack frames. While inlining the algorithm is trying
7339 to not grow past this limit too much. Default value is 256 bytes.
7340
7341 @item large-stack-frame-growth
7342 Specifies maximal growth of large stack frames caused by inlining in percents.
7343 The default value is 1000 which limits large stack frame growth to 11 times
7344 the original size.
7345
7346 @item max-inline-insns-recursive
7347 @itemx max-inline-insns-recursive-auto
7348 Specifies maximum number of instructions out-of-line copy of self recursive inline
7349 function can grow into by performing recursive inlining.
7350
7351 For functions declared inline @option{--param max-inline-insns-recursive} is
7352 taken into account. For function not declared inline, recursive inlining
7353 happens only when @option{-finline-functions} (included in @option{-O3}) is
7354 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
7355 default value is 450.
7356
7357 @item max-inline-recursive-depth
7358 @itemx max-inline-recursive-depth-auto
7359 Specifies maximum recursion depth used by the recursive inlining.
7360
7361 For functions declared inline @option{--param max-inline-recursive-depth} is
7362 taken into account. For function not declared inline, recursive inlining
7363 happens only when @option{-finline-functions} (included in @option{-O3}) is
7364 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
7365 default value is 8.
7366
7367 @item min-inline-recursive-probability
7368 Recursive inlining is profitable only for function having deep recursion
7369 in average and can hurt for function having little recursion depth by
7370 increasing the prologue size or complexity of function body to other
7371 optimizers.
7372
7373 When profile feedback is available (see @option{-fprofile-generate}) the actual
7374 recursion depth can be guessed from probability that function will recurse via
7375 given call expression. This parameter limits inlining only to call expression
7376 whose probability exceeds given threshold (in percents). The default value is
7377 10.
7378
7379 @item inline-call-cost
7380 Specify cost of call instruction relative to simple arithmetics operations
7381 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
7382 functions and at the same time increases size of leaf function that is believed to
7383 reduce function size by being inlined. In effect it increases amount of
7384 inlining for code having large abstraction penalty (many functions that just
7385 pass the arguments to other functions) and decrease inlining for code with low
7386 abstraction penalty. The default value is 12.
7387
7388 @item min-vect-loop-bound
7389 The minimum number of iterations under which a loop will not get vectorized
7390 when @option{-ftree-vectorize} is used. The number of iterations after
7391 vectorization needs to be greater than the value specified by this option
7392 to allow vectorization. The default value is 0.
7393
7394 @item max-unrolled-insns
7395 The maximum number of instructions that a loop should have if that loop
7396 is unrolled, and if the loop is unrolled, it determines how many times
7397 the loop code is unrolled.
7398
7399 @item max-average-unrolled-insns
7400 The maximum number of instructions biased by probabilities of their execution
7401 that a loop should have if that loop is unrolled, and if the loop is unrolled,
7402 it determines how many times the loop code is unrolled.
7403
7404 @item max-unroll-times
7405 The maximum number of unrollings of a single loop.
7406
7407 @item max-peeled-insns
7408 The maximum number of instructions that a loop should have if that loop
7409 is peeled, and if the loop is peeled, it determines how many times
7410 the loop code is peeled.
7411
7412 @item max-peel-times
7413 The maximum number of peelings of a single loop.
7414
7415 @item max-completely-peeled-insns
7416 The maximum number of insns of a completely peeled loop.
7417
7418 @item max-completely-peel-times
7419 The maximum number of iterations of a loop to be suitable for complete peeling.
7420
7421 @item max-completely-peel-loop-nest-depth
7422 The maximum depth of a loop nest suitable for complete peeling.
7423
7424 @item max-unswitch-insns
7425 The maximum number of insns of an unswitched loop.
7426
7427 @item max-unswitch-level
7428 The maximum number of branches unswitched in a single loop.
7429
7430 @item lim-expensive
7431 The minimum cost of an expensive expression in the loop invariant motion.
7432
7433 @item iv-consider-all-candidates-bound
7434 Bound on number of candidates for induction variables below that
7435 all candidates are considered for each use in induction variable
7436 optimizations. Only the most relevant candidates are considered
7437 if there are more candidates, to avoid quadratic time complexity.
7438
7439 @item iv-max-considered-uses
7440 The induction variable optimizations give up on loops that contain more
7441 induction variable uses.
7442
7443 @item iv-always-prune-cand-set-bound
7444 If number of candidates in the set is smaller than this value,
7445 we always try to remove unnecessary ivs from the set during its
7446 optimization when a new iv is added to the set.
7447
7448 @item scev-max-expr-size
7449 Bound on size of expressions used in the scalar evolutions analyzer.
7450 Large expressions slow the analyzer.
7451
7452 @item omega-max-vars
7453 The maximum number of variables in an Omega constraint system.
7454 The default value is 128.
7455
7456 @item omega-max-geqs
7457 The maximum number of inequalities in an Omega constraint system.
7458 The default value is 256.
7459
7460 @item omega-max-eqs
7461 The maximum number of equalities in an Omega constraint system.
7462 The default value is 128.
7463
7464 @item omega-max-wild-cards
7465 The maximum number of wildcard variables that the Omega solver will
7466 be able to insert. The default value is 18.
7467
7468 @item omega-hash-table-size
7469 The size of the hash table in the Omega solver. The default value is
7470 550.
7471
7472 @item omega-max-keys
7473 The maximal number of keys used by the Omega solver. The default
7474 value is 500.
7475
7476 @item omega-eliminate-redundant-constraints
7477 When set to 1, use expensive methods to eliminate all redundant
7478 constraints. The default value is 0.
7479
7480 @item vect-max-version-for-alignment-checks
7481 The maximum number of runtime checks that can be performed when
7482 doing loop versioning for alignment in the vectorizer. See option
7483 ftree-vect-loop-version for more information.
7484
7485 @item vect-max-version-for-alias-checks
7486 The maximum number of runtime checks that can be performed when
7487 doing loop versioning for alias in the vectorizer. See option
7488 ftree-vect-loop-version for more information.
7489
7490 @item max-iterations-to-track
7491
7492 The maximum number of iterations of a loop the brute force algorithm
7493 for analysis of # of iterations of the loop tries to evaluate.
7494
7495 @item hot-bb-count-fraction
7496 Select fraction of the maximal count of repetitions of basic block in program
7497 given basic block needs to have to be considered hot.
7498
7499 @item hot-bb-frequency-fraction
7500 Select fraction of the maximal frequency of executions of basic block in
7501 function given basic block needs to have to be considered hot
7502
7503 @item max-predicted-iterations
7504 The maximum number of loop iterations we predict statically. This is useful
7505 in cases where function contain single loop with known bound and other loop
7506 with unknown. We predict the known number of iterations correctly, while
7507 the unknown number of iterations average to roughly 10. This means that the
7508 loop without bounds would appear artificially cold relative to the other one.
7509
7510 @item align-threshold
7511
7512 Select fraction of the maximal frequency of executions of basic block in
7513 function given basic block will get aligned.
7514
7515 @item align-loop-iterations
7516
7517 A loop expected to iterate at lest the selected number of iterations will get
7518 aligned.
7519
7520 @item tracer-dynamic-coverage
7521 @itemx tracer-dynamic-coverage-feedback
7522
7523 This value is used to limit superblock formation once the given percentage of
7524 executed instructions is covered. This limits unnecessary code size
7525 expansion.
7526
7527 The @option{tracer-dynamic-coverage-feedback} is used only when profile
7528 feedback is available. The real profiles (as opposed to statically estimated
7529 ones) are much less balanced allowing the threshold to be larger value.
7530
7531 @item tracer-max-code-growth
7532 Stop tail duplication once code growth has reached given percentage. This is
7533 rather hokey argument, as most of the duplicates will be eliminated later in
7534 cross jumping, so it may be set to much higher values than is the desired code
7535 growth.
7536
7537 @item tracer-min-branch-ratio
7538
7539 Stop reverse growth when the reverse probability of best edge is less than this
7540 threshold (in percent).
7541
7542 @item tracer-min-branch-ratio
7543 @itemx tracer-min-branch-ratio-feedback
7544
7545 Stop forward growth if the best edge do have probability lower than this
7546 threshold.
7547
7548 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
7549 compilation for profile feedback and one for compilation without. The value
7550 for compilation with profile feedback needs to be more conservative (higher) in
7551 order to make tracer effective.
7552
7553 @item max-cse-path-length
7554
7555 Maximum number of basic blocks on path that cse considers. The default is 10.
7556
7557 @item max-cse-insns
7558 The maximum instructions CSE process before flushing. The default is 1000.
7559
7560 @item max-aliased-vops
7561
7562 Maximum number of virtual operands per function allowed to represent
7563 aliases before triggering the alias partitioning heuristic. Alias
7564 partitioning reduces compile times and memory consumption needed for
7565 aliasing at the expense of precision loss in alias information. The
7566 default value for this parameter is 100 for -O1, 500 for -O2 and 1000
7567 for -O3.
7568
7569 Notice that if a function contains more memory statements than the
7570 value of this parameter, it is not really possible to achieve this
7571 reduction. In this case, the compiler will use the number of memory
7572 statements as the value for @option{max-aliased-vops}.
7573
7574 @item avg-aliased-vops
7575
7576 Average number of virtual operands per statement allowed to represent
7577 aliases before triggering the alias partitioning heuristic. This
7578 works in conjunction with @option{max-aliased-vops}. If a function
7579 contains more than @option{max-aliased-vops} virtual operators, then
7580 memory symbols will be grouped into memory partitions until either the
7581 total number of virtual operators is below @option{max-aliased-vops}
7582 or the average number of virtual operators per memory statement is
7583 below @option{avg-aliased-vops}. The default value for this parameter
7584 is 1 for -O1 and -O2, and 3 for -O3.
7585
7586 @item ggc-min-expand
7587
7588 GCC uses a garbage collector to manage its own memory allocation. This
7589 parameter specifies the minimum percentage by which the garbage
7590 collector's heap should be allowed to expand between collections.
7591 Tuning this may improve compilation speed; it has no effect on code
7592 generation.
7593
7594 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
7595 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
7596 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
7597 GCC is not able to calculate RAM on a particular platform, the lower
7598 bound of 30% is used. Setting this parameter and
7599 @option{ggc-min-heapsize} to zero causes a full collection to occur at
7600 every opportunity. This is extremely slow, but can be useful for
7601 debugging.
7602
7603 @item ggc-min-heapsize
7604
7605 Minimum size of the garbage collector's heap before it begins bothering
7606 to collect garbage. The first collection occurs after the heap expands
7607 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
7608 tuning this may improve compilation speed, and has no effect on code
7609 generation.
7610
7611 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
7612 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
7613 with a lower bound of 4096 (four megabytes) and an upper bound of
7614 131072 (128 megabytes). If GCC is not able to calculate RAM on a
7615 particular platform, the lower bound is used. Setting this parameter
7616 very large effectively disables garbage collection. Setting this
7617 parameter and @option{ggc-min-expand} to zero causes a full collection
7618 to occur at every opportunity.
7619
7620 @item max-reload-search-insns
7621 The maximum number of instruction reload should look backward for equivalent
7622 register. Increasing values mean more aggressive optimization, making the
7623 compile time increase with probably slightly better performance. The default
7624 value is 100.
7625
7626 @item max-cselib-memory-locations
7627 The maximum number of memory locations cselib should take into account.
7628 Increasing values mean more aggressive optimization, making the compile time
7629 increase with probably slightly better performance. The default value is 500.
7630
7631 @item reorder-blocks-duplicate
7632 @itemx reorder-blocks-duplicate-feedback
7633
7634 Used by basic block reordering pass to decide whether to use unconditional
7635 branch or duplicate the code on its destination. Code is duplicated when its
7636 estimated size is smaller than this value multiplied by the estimated size of
7637 unconditional jump in the hot spots of the program.
7638
7639 The @option{reorder-block-duplicate-feedback} is used only when profile
7640 feedback is available and may be set to higher values than
7641 @option{reorder-block-duplicate} since information about the hot spots is more
7642 accurate.
7643
7644 @item max-sched-ready-insns
7645 The maximum number of instructions ready to be issued the scheduler should
7646 consider at any given time during the first scheduling pass. Increasing
7647 values mean more thorough searches, making the compilation time increase
7648 with probably little benefit. The default value is 100.
7649
7650 @item max-sched-region-blocks
7651 The maximum number of blocks in a region to be considered for
7652 interblock scheduling. The default value is 10.
7653
7654 @item max-pipeline-region-blocks
7655 The maximum number of blocks in a region to be considered for
7656 pipelining in the selective scheduler. The default value is 15.
7657
7658 @item max-sched-region-insns
7659 The maximum number of insns in a region to be considered for
7660 interblock scheduling. The default value is 100.
7661
7662 @item max-pipeline-region-insns
7663 The maximum number of insns in a region to be considered for
7664 pipelining in the selective scheduler. The default value is 200.
7665
7666 @item min-spec-prob
7667 The minimum probability (in percents) of reaching a source block
7668 for interblock speculative scheduling. The default value is 40.
7669
7670 @item max-sched-extend-regions-iters
7671 The maximum number of iterations through CFG to extend regions.
7672 0 - disable region extension,
7673 N - do at most N iterations.
7674 The default value is 0.
7675
7676 @item max-sched-insn-conflict-delay
7677 The maximum conflict delay for an insn to be considered for speculative motion.
7678 The default value is 3.
7679
7680 @item sched-spec-prob-cutoff
7681 The minimal probability of speculation success (in percents), so that
7682 speculative insn will be scheduled.
7683 The default value is 40.
7684
7685 @item sched-mem-true-dep-cost
7686 Minimal distance (in CPU cycles) between store and load targeting same
7687 memory locations. The default value is 1.
7688
7689 @item selsched-max-lookahead
7690 The maximum size of the lookahead window of selective scheduling. It is a
7691 depth of search for available instructions.
7692 The default value is 50.
7693
7694 @item selsched-max-sched-times
7695 The maximum number of times that an instruction will be scheduled during
7696 selective scheduling. This is the limit on the number of iterations
7697 through which the instruction may be pipelined. The default value is 2.
7698
7699 @item selsched-max-insns-to-rename
7700 The maximum number of best instructions in the ready list that are considered
7701 for renaming in the selective scheduler. The default value is 2.
7702
7703 @item max-last-value-rtl
7704 The maximum size measured as number of RTLs that can be recorded in an expression
7705 in combiner for a pseudo register as last known value of that register. The default
7706 is 10000.
7707
7708 @item integer-share-limit
7709 Small integer constants can use a shared data structure, reducing the
7710 compiler's memory usage and increasing its speed. This sets the maximum
7711 value of a shared integer constant. The default value is 256.
7712
7713 @item min-virtual-mappings
7714 Specifies the minimum number of virtual mappings in the incremental
7715 SSA updater that should be registered to trigger the virtual mappings
7716 heuristic defined by virtual-mappings-ratio. The default value is
7717 100.
7718
7719 @item virtual-mappings-ratio
7720 If the number of virtual mappings is virtual-mappings-ratio bigger
7721 than the number of virtual symbols to be updated, then the incremental
7722 SSA updater switches to a full update for those symbols. The default
7723 ratio is 3.
7724
7725 @item ssp-buffer-size
7726 The minimum size of buffers (i.e.@: arrays) that will receive stack smashing
7727 protection when @option{-fstack-protection} is used.
7728
7729 @item max-jump-thread-duplication-stmts
7730 Maximum number of statements allowed in a block that needs to be
7731 duplicated when threading jumps.
7732
7733 @item max-fields-for-field-sensitive
7734 Maximum number of fields in a structure we will treat in
7735 a field sensitive manner during pointer analysis. The default is zero
7736 for -O0, and -O1 and 100 for -Os, -O2, and -O3.
7737
7738 @item prefetch-latency
7739 Estimate on average number of instructions that are executed before
7740 prefetch finishes. The distance we prefetch ahead is proportional
7741 to this constant. Increasing this number may also lead to less
7742 streams being prefetched (see @option{simultaneous-prefetches}).
7743
7744 @item simultaneous-prefetches
7745 Maximum number of prefetches that can run at the same time.
7746
7747 @item l1-cache-line-size
7748 The size of cache line in L1 cache, in bytes.
7749
7750 @item l1-cache-size
7751 The size of L1 cache, in kilobytes.
7752
7753 @item l2-cache-size
7754 The size of L2 cache, in kilobytes.
7755
7756 @item use-canonical-types
7757 Whether the compiler should use the ``canonical'' type system. By
7758 default, this should always be 1, which uses a more efficient internal
7759 mechanism for comparing types in C++ and Objective-C++. However, if
7760 bugs in the canonical type system are causing compilation failures,
7761 set this value to 0 to disable canonical types.
7762
7763 @item switch-conversion-max-branch-ratio
7764 Switch initialization conversion will refuse to create arrays that are
7765 bigger than @option{switch-conversion-max-branch-ratio} times the number of
7766 branches in the switch.
7767
7768 @item max-partial-antic-length
7769 Maximum length of the partial antic set computed during the tree
7770 partial redundancy elimination optimization (@option{-ftree-pre}) when
7771 optimizing at @option{-O3} and above. For some sorts of source code
7772 the enhanced partial redundancy elimination optimization can run away,
7773 consuming all of the memory available on the host machine. This
7774 parameter sets a limit on the length of the sets that are computed,
7775 which prevents the runaway behavior. Setting a value of 0 for
7776 this parameter will allow an unlimited set length.
7777
7778 @item sccvn-max-scc-size
7779 Maximum size of a strongly connected component (SCC) during SCCVN
7780 processing. If this limit is hit, SCCVN processing for the whole
7781 function will not be done and optimizations depending on it will
7782 be disabled. The default maximum SCC size is 10000.
7783
7784 @item ira-max-loops-num
7785 IRA uses a regional register allocation by default. If a function
7786 contains loops more than number given by the parameter, only at most
7787 given number of the most frequently executed loops will form regions
7788 for the regional register allocation. The default value of the
7789 parameter is 100.
7790
7791 @item ira-max-conflict-table-size
7792 Although IRA uses a sophisticated algorithm of compression conflict
7793 table, the table can be still big for huge functions. If the conflict
7794 table for a function could be more than size in MB given by the
7795 parameter, the conflict table is not built and faster, simpler, and
7796 lower quality register allocation algorithm will be used. The
7797 algorithm do not use pseudo-register conflicts. The default value of
7798 the parameter is 2000.
7799
7800 @item loop-invariant-max-bbs-in-loop
7801 Loop invariant motion can be very expensive, both in compile time and
7802 in amount of needed compile time memory, with very large loops. Loops
7803 with more basic blocks than this parameter won't have loop invariant
7804 motion optimization performed on them. The default value of the
7805 parameter is 1000 for -O1 and 10000 for -O2 and above.
7806
7807 @end table
7808 @end table
7809
7810 @node Preprocessor Options
7811 @section Options Controlling the Preprocessor
7812 @cindex preprocessor options
7813 @cindex options, preprocessor
7814
7815 These options control the C preprocessor, which is run on each C source
7816 file before actual compilation.
7817
7818 If you use the @option{-E} option, nothing is done except preprocessing.
7819 Some of these options make sense only together with @option{-E} because
7820 they cause the preprocessor output to be unsuitable for actual
7821 compilation.
7822
7823 @table @gcctabopt
7824 @item -Wp,@var{option}
7825 @opindex Wp
7826 You can use @option{-Wp,@var{option}} to bypass the compiler driver
7827 and pass @var{option} directly through to the preprocessor. If
7828 @var{option} contains commas, it is split into multiple options at the
7829 commas. However, many options are modified, translated or interpreted
7830 by the compiler driver before being passed to the preprocessor, and
7831 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
7832 interface is undocumented and subject to change, so whenever possible
7833 you should avoid using @option{-Wp} and let the driver handle the
7834 options instead.
7835
7836 @item -Xpreprocessor @var{option}
7837 @opindex Xpreprocessor
7838 Pass @var{option} as an option to the preprocessor. You can use this to
7839 supply system-specific preprocessor options which GCC does not know how to
7840 recognize.
7841
7842 If you want to pass an option that takes an argument, you must use
7843 @option{-Xpreprocessor} twice, once for the option and once for the argument.
7844 @end table
7845
7846 @include cppopts.texi
7847
7848 @node Assembler Options
7849 @section Passing Options to the Assembler
7850
7851 @c prevent bad page break with this line
7852 You can pass options to the assembler.
7853
7854 @table @gcctabopt
7855 @item -Wa,@var{option}
7856 @opindex Wa
7857 Pass @var{option} as an option to the assembler. If @var{option}
7858 contains commas, it is split into multiple options at the commas.
7859
7860 @item -Xassembler @var{option}
7861 @opindex Xassembler
7862 Pass @var{option} as an option to the assembler. You can use this to
7863 supply system-specific assembler options which GCC does not know how to
7864 recognize.
7865
7866 If you want to pass an option that takes an argument, you must use
7867 @option{-Xassembler} twice, once for the option and once for the argument.
7868
7869 @end table
7870
7871 @node Link Options
7872 @section Options for Linking
7873 @cindex link options
7874 @cindex options, linking
7875
7876 These options come into play when the compiler links object files into
7877 an executable output file. They are meaningless if the compiler is
7878 not doing a link step.
7879
7880 @table @gcctabopt
7881 @cindex file names
7882 @item @var{object-file-name}
7883 A file name that does not end in a special recognized suffix is
7884 considered to name an object file or library. (Object files are
7885 distinguished from libraries by the linker according to the file
7886 contents.) If linking is done, these object files are used as input
7887 to the linker.
7888
7889 @item -c
7890 @itemx -S
7891 @itemx -E
7892 @opindex c
7893 @opindex S
7894 @opindex E
7895 If any of these options is used, then the linker is not run, and
7896 object file names should not be used as arguments. @xref{Overall
7897 Options}.
7898
7899 @cindex Libraries
7900 @item -l@var{library}
7901 @itemx -l @var{library}
7902 @opindex l
7903 Search the library named @var{library} when linking. (The second
7904 alternative with the library as a separate argument is only for
7905 POSIX compliance and is not recommended.)
7906
7907 It makes a difference where in the command you write this option; the
7908 linker searches and processes libraries and object files in the order they
7909 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
7910 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
7911 to functions in @samp{z}, those functions may not be loaded.
7912
7913 The linker searches a standard list of directories for the library,
7914 which is actually a file named @file{lib@var{library}.a}. The linker
7915 then uses this file as if it had been specified precisely by name.
7916
7917 The directories searched include several standard system directories
7918 plus any that you specify with @option{-L}.
7919
7920 Normally the files found this way are library files---archive files
7921 whose members are object files. The linker handles an archive file by
7922 scanning through it for members which define symbols that have so far
7923 been referenced but not defined. But if the file that is found is an
7924 ordinary object file, it is linked in the usual fashion. The only
7925 difference between using an @option{-l} option and specifying a file name
7926 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
7927 and searches several directories.
7928
7929 @item -lobjc
7930 @opindex lobjc
7931 You need this special case of the @option{-l} option in order to
7932 link an Objective-C or Objective-C++ program.
7933
7934 @item -nostartfiles
7935 @opindex nostartfiles
7936 Do not use the standard system startup files when linking.
7937 The standard system libraries are used normally, unless @option{-nostdlib}
7938 or @option{-nodefaultlibs} is used.
7939
7940 @item -nodefaultlibs
7941 @opindex nodefaultlibs
7942 Do not use the standard system libraries when linking.
7943 Only the libraries you specify will be passed to the linker.
7944 The standard startup files are used normally, unless @option{-nostartfiles}
7945 is used. The compiler may generate calls to @code{memcmp},
7946 @code{memset}, @code{memcpy} and @code{memmove}.
7947 These entries are usually resolved by entries in
7948 libc. These entry points should be supplied through some other
7949 mechanism when this option is specified.
7950
7951 @item -nostdlib
7952 @opindex nostdlib
7953 Do not use the standard system startup files or libraries when linking.
7954 No startup files and only the libraries you specify will be passed to
7955 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
7956 @code{memcpy} and @code{memmove}.
7957 These entries are usually resolved by entries in
7958 libc. These entry points should be supplied through some other
7959 mechanism when this option is specified.
7960
7961 @cindex @option{-lgcc}, use with @option{-nostdlib}
7962 @cindex @option{-nostdlib} and unresolved references
7963 @cindex unresolved references and @option{-nostdlib}
7964 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
7965 @cindex @option{-nodefaultlibs} and unresolved references
7966 @cindex unresolved references and @option{-nodefaultlibs}
7967 One of the standard libraries bypassed by @option{-nostdlib} and
7968 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
7969 that GCC uses to overcome shortcomings of particular machines, or special
7970 needs for some languages.
7971 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
7972 Collection (GCC) Internals},
7973 for more discussion of @file{libgcc.a}.)
7974 In most cases, you need @file{libgcc.a} even when you want to avoid
7975 other standard libraries. In other words, when you specify @option{-nostdlib}
7976 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
7977 This ensures that you have no unresolved references to internal GCC
7978 library subroutines. (For example, @samp{__main}, used to ensure C++
7979 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
7980 GNU Compiler Collection (GCC) Internals}.)
7981
7982 @item -pie
7983 @opindex pie
7984 Produce a position independent executable on targets which support it.
7985 For predictable results, you must also specify the same set of options
7986 that were used to generate code (@option{-fpie}, @option{-fPIE},
7987 or model suboptions) when you specify this option.
7988
7989 @item -rdynamic
7990 @opindex rdynamic
7991 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
7992 that support it. This instructs the linker to add all symbols, not
7993 only used ones, to the dynamic symbol table. This option is needed
7994 for some uses of @code{dlopen} or to allow obtaining backtraces
7995 from within a program.
7996
7997 @item -s
7998 @opindex s
7999 Remove all symbol table and relocation information from the executable.
8000
8001 @item -static
8002 @opindex static
8003 On systems that support dynamic linking, this prevents linking with the shared
8004 libraries. On other systems, this option has no effect.
8005
8006 @item -shared
8007 @opindex shared
8008 Produce a shared object which can then be linked with other objects to
8009 form an executable. Not all systems support this option. For predictable
8010 results, you must also specify the same set of options that were used to
8011 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
8012 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
8013 needs to build supplementary stub code for constructors to work. On
8014 multi-libbed systems, @samp{gcc -shared} must select the correct support
8015 libraries to link against. Failing to supply the correct flags may lead
8016 to subtle defects. Supplying them in cases where they are not necessary
8017 is innocuous.}
8018
8019 @item -shared-libgcc
8020 @itemx -static-libgcc
8021 @opindex shared-libgcc
8022 @opindex static-libgcc
8023 On systems that provide @file{libgcc} as a shared library, these options
8024 force the use of either the shared or static version respectively.
8025 If no shared version of @file{libgcc} was built when the compiler was
8026 configured, these options have no effect.
8027
8028 There are several situations in which an application should use the
8029 shared @file{libgcc} instead of the static version. The most common
8030 of these is when the application wishes to throw and catch exceptions
8031 across different shared libraries. In that case, each of the libraries
8032 as well as the application itself should use the shared @file{libgcc}.
8033
8034 Therefore, the G++ and GCJ drivers automatically add
8035 @option{-shared-libgcc} whenever you build a shared library or a main
8036 executable, because C++ and Java programs typically use exceptions, so
8037 this is the right thing to do.
8038
8039 If, instead, you use the GCC driver to create shared libraries, you may
8040 find that they will not always be linked with the shared @file{libgcc}.
8041 If GCC finds, at its configuration time, that you have a non-GNU linker
8042 or a GNU linker that does not support option @option{--eh-frame-hdr},
8043 it will link the shared version of @file{libgcc} into shared libraries
8044 by default. Otherwise, it will take advantage of the linker and optimize
8045 away the linking with the shared version of @file{libgcc}, linking with
8046 the static version of libgcc by default. This allows exceptions to
8047 propagate through such shared libraries, without incurring relocation
8048 costs at library load time.
8049
8050 However, if a library or main executable is supposed to throw or catch
8051 exceptions, you must link it using the G++ or GCJ driver, as appropriate
8052 for the languages used in the program, or using the option
8053 @option{-shared-libgcc}, such that it is linked with the shared
8054 @file{libgcc}.
8055
8056 @item -symbolic
8057 @opindex symbolic
8058 Bind references to global symbols when building a shared object. Warn
8059 about any unresolved references (unless overridden by the link editor
8060 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
8061 this option.
8062
8063 @item -T @var{script}
8064 @opindex T
8065 @cindex linker script
8066 Use @var{script} as the linker script. This option is supported by most
8067 systems using the GNU linker. On some targets, such as bare-board
8068 targets without an operating system, the @option{-T} option may be required
8069 when linking to avoid references to undefined symbols.
8070
8071 @item -Xlinker @var{option}
8072 @opindex Xlinker
8073 Pass @var{option} as an option to the linker. You can use this to
8074 supply system-specific linker options which GCC does not know how to
8075 recognize.
8076
8077 If you want to pass an option that takes a separate argument, you must use
8078 @option{-Xlinker} twice, once for the option and once for the argument.
8079 For example, to pass @option{-assert definitions}, you must write
8080 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
8081 @option{-Xlinker "-assert definitions"}, because this passes the entire
8082 string as a single argument, which is not what the linker expects.
8083
8084 When using the GNU linker, it is usually more convenient to pass
8085 arguments to linker options using the @option{@var{option}=@var{value}}
8086 syntax than as separate arguments. For example, you can specify
8087 @samp{-Xlinker -Map=output.map} rather than
8088 @samp{-Xlinker -Map -Xlinker output.map}. Other linkers may not support
8089 this syntax for command-line options.
8090
8091 @item -Wl,@var{option}
8092 @opindex Wl
8093 Pass @var{option} as an option to the linker. If @var{option} contains
8094 commas, it is split into multiple options at the commas. You can use this
8095 syntax to pass an argument to the option.
8096 For example, @samp{-Wl,-Map,output.map} passes @samp{-Map output.map} to the
8097 linker. When using the GNU linker, you can also get the same effect with
8098 @samp{-Wl,-Map=output.map}.
8099
8100 @item -u @var{symbol}
8101 @opindex u
8102 Pretend the symbol @var{symbol} is undefined, to force linking of
8103 library modules to define it. You can use @option{-u} multiple times with
8104 different symbols to force loading of additional library modules.
8105 @end table
8106
8107 @node Directory Options
8108 @section Options for Directory Search
8109 @cindex directory options
8110 @cindex options, directory search
8111 @cindex search path
8112
8113 These options specify directories to search for header files, for
8114 libraries and for parts of the compiler:
8115
8116 @table @gcctabopt
8117 @item -I@var{dir}
8118 @opindex I
8119 Add the directory @var{dir} to the head of the list of directories to be
8120 searched for header files. This can be used to override a system header
8121 file, substituting your own version, since these directories are
8122 searched before the system header file directories. However, you should
8123 not use this option to add directories that contain vendor-supplied
8124 system header files (use @option{-isystem} for that). If you use more than
8125 one @option{-I} option, the directories are scanned in left-to-right
8126 order; the standard system directories come after.
8127
8128 If a standard system include directory, or a directory specified with
8129 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
8130 option will be ignored. The directory will still be searched but as a
8131 system directory at its normal position in the system include chain.
8132 This is to ensure that GCC's procedure to fix buggy system headers and
8133 the ordering for the include_next directive are not inadvertently changed.
8134 If you really need to change the search order for system directories,
8135 use the @option{-nostdinc} and/or @option{-isystem} options.
8136
8137 @item -iquote@var{dir}
8138 @opindex iquote
8139 Add the directory @var{dir} to the head of the list of directories to
8140 be searched for header files only for the case of @samp{#include
8141 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
8142 otherwise just like @option{-I}.
8143
8144 @item -L@var{dir}
8145 @opindex L
8146 Add directory @var{dir} to the list of directories to be searched
8147 for @option{-l}.
8148
8149 @item -B@var{prefix}
8150 @opindex B
8151 This option specifies where to find the executables, libraries,
8152 include files, and data files of the compiler itself.
8153
8154 The compiler driver program runs one or more of the subprograms
8155 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
8156 @var{prefix} as a prefix for each program it tries to run, both with and
8157 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
8158
8159 For each subprogram to be run, the compiler driver first tries the
8160 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
8161 was not specified, the driver tries two standard prefixes, which are
8162 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
8163 those results in a file name that is found, the unmodified program
8164 name is searched for using the directories specified in your
8165 @env{PATH} environment variable.
8166
8167 The compiler will check to see if the path provided by the @option{-B}
8168 refers to a directory, and if necessary it will add a directory
8169 separator character at the end of the path.
8170
8171 @option{-B} prefixes that effectively specify directory names also apply
8172 to libraries in the linker, because the compiler translates these
8173 options into @option{-L} options for the linker. They also apply to
8174 includes files in the preprocessor, because the compiler translates these
8175 options into @option{-isystem} options for the preprocessor. In this case,
8176 the compiler appends @samp{include} to the prefix.
8177
8178 The run-time support file @file{libgcc.a} can also be searched for using
8179 the @option{-B} prefix, if needed. If it is not found there, the two
8180 standard prefixes above are tried, and that is all. The file is left
8181 out of the link if it is not found by those means.
8182
8183 Another way to specify a prefix much like the @option{-B} prefix is to use
8184 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
8185 Variables}.
8186
8187 As a special kludge, if the path provided by @option{-B} is
8188 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
8189 9, then it will be replaced by @file{[dir/]include}. This is to help
8190 with boot-strapping the compiler.
8191
8192 @item -specs=@var{file}
8193 @opindex specs
8194 Process @var{file} after the compiler reads in the standard @file{specs}
8195 file, in order to override the defaults that the @file{gcc} driver
8196 program uses when determining what switches to pass to @file{cc1},
8197 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
8198 @option{-specs=@var{file}} can be specified on the command line, and they
8199 are processed in order, from left to right.
8200
8201 @item --sysroot=@var{dir}
8202 @opindex sysroot
8203 Use @var{dir} as the logical root directory for headers and libraries.
8204 For example, if the compiler would normally search for headers in
8205 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
8206 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
8207
8208 If you use both this option and the @option{-isysroot} option, then
8209 the @option{--sysroot} option will apply to libraries, but the
8210 @option{-isysroot} option will apply to header files.
8211
8212 The GNU linker (beginning with version 2.16) has the necessary support
8213 for this option. If your linker does not support this option, the
8214 header file aspect of @option{--sysroot} will still work, but the
8215 library aspect will not.
8216
8217 @item -I-
8218 @opindex I-
8219 This option has been deprecated. Please use @option{-iquote} instead for
8220 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
8221 Any directories you specify with @option{-I} options before the @option{-I-}
8222 option are searched only for the case of @samp{#include "@var{file}"};
8223 they are not searched for @samp{#include <@var{file}>}.
8224
8225 If additional directories are specified with @option{-I} options after
8226 the @option{-I-}, these directories are searched for all @samp{#include}
8227 directives. (Ordinarily @emph{all} @option{-I} directories are used
8228 this way.)
8229
8230 In addition, the @option{-I-} option inhibits the use of the current
8231 directory (where the current input file came from) as the first search
8232 directory for @samp{#include "@var{file}"}. There is no way to
8233 override this effect of @option{-I-}. With @option{-I.} you can specify
8234 searching the directory which was current when the compiler was
8235 invoked. That is not exactly the same as what the preprocessor does
8236 by default, but it is often satisfactory.
8237
8238 @option{-I-} does not inhibit the use of the standard system directories
8239 for header files. Thus, @option{-I-} and @option{-nostdinc} are
8240 independent.
8241 @end table
8242
8243 @c man end
8244
8245 @node Spec Files
8246 @section Specifying subprocesses and the switches to pass to them
8247 @cindex Spec Files
8248
8249 @command{gcc} is a driver program. It performs its job by invoking a
8250 sequence of other programs to do the work of compiling, assembling and
8251 linking. GCC interprets its command-line parameters and uses these to
8252 deduce which programs it should invoke, and which command-line options
8253 it ought to place on their command lines. This behavior is controlled
8254 by @dfn{spec strings}. In most cases there is one spec string for each
8255 program that GCC can invoke, but a few programs have multiple spec
8256 strings to control their behavior. The spec strings built into GCC can
8257 be overridden by using the @option{-specs=} command-line switch to specify
8258 a spec file.
8259
8260 @dfn{Spec files} are plaintext files that are used to construct spec
8261 strings. They consist of a sequence of directives separated by blank
8262 lines. The type of directive is determined by the first non-whitespace
8263 character on the line and it can be one of the following:
8264
8265 @table @code
8266 @item %@var{command}
8267 Issues a @var{command} to the spec file processor. The commands that can
8268 appear here are:
8269
8270 @table @code
8271 @item %include <@var{file}>
8272 @cindex %include
8273 Search for @var{file} and insert its text at the current point in the
8274 specs file.
8275
8276 @item %include_noerr <@var{file}>
8277 @cindex %include_noerr
8278 Just like @samp{%include}, but do not generate an error message if the include
8279 file cannot be found.
8280
8281 @item %rename @var{old_name} @var{new_name}
8282 @cindex %rename
8283 Rename the spec string @var{old_name} to @var{new_name}.
8284
8285 @end table
8286
8287 @item *[@var{spec_name}]:
8288 This tells the compiler to create, override or delete the named spec
8289 string. All lines after this directive up to the next directive or
8290 blank line are considered to be the text for the spec string. If this
8291 results in an empty string then the spec will be deleted. (Or, if the
8292 spec did not exist, then nothing will happened.) Otherwise, if the spec
8293 does not currently exist a new spec will be created. If the spec does
8294 exist then its contents will be overridden by the text of this
8295 directive, unless the first character of that text is the @samp{+}
8296 character, in which case the text will be appended to the spec.
8297
8298 @item [@var{suffix}]:
8299 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
8300 and up to the next directive or blank line are considered to make up the
8301 spec string for the indicated suffix. When the compiler encounters an
8302 input file with the named suffix, it will processes the spec string in
8303 order to work out how to compile that file. For example:
8304
8305 @smallexample
8306 .ZZ:
8307 z-compile -input %i
8308 @end smallexample
8309
8310 This says that any input file whose name ends in @samp{.ZZ} should be
8311 passed to the program @samp{z-compile}, which should be invoked with the
8312 command-line switch @option{-input} and with the result of performing the
8313 @samp{%i} substitution. (See below.)
8314
8315 As an alternative to providing a spec string, the text that follows a
8316 suffix directive can be one of the following:
8317
8318 @table @code
8319 @item @@@var{language}
8320 This says that the suffix is an alias for a known @var{language}. This is
8321 similar to using the @option{-x} command-line switch to GCC to specify a
8322 language explicitly. For example:
8323
8324 @smallexample
8325 .ZZ:
8326 @@c++
8327 @end smallexample
8328
8329 Says that .ZZ files are, in fact, C++ source files.
8330
8331 @item #@var{name}
8332 This causes an error messages saying:
8333
8334 @smallexample
8335 @var{name} compiler not installed on this system.
8336 @end smallexample
8337 @end table
8338
8339 GCC already has an extensive list of suffixes built into it.
8340 This directive will add an entry to the end of the list of suffixes, but
8341 since the list is searched from the end backwards, it is effectively
8342 possible to override earlier entries using this technique.
8343
8344 @end table
8345
8346 GCC has the following spec strings built into it. Spec files can
8347 override these strings or create their own. Note that individual
8348 targets can also add their own spec strings to this list.
8349
8350 @smallexample
8351 asm Options to pass to the assembler
8352 asm_final Options to pass to the assembler post-processor
8353 cpp Options to pass to the C preprocessor
8354 cc1 Options to pass to the C compiler
8355 cc1plus Options to pass to the C++ compiler
8356 endfile Object files to include at the end of the link
8357 link Options to pass to the linker
8358 lib Libraries to include on the command line to the linker
8359 libgcc Decides which GCC support library to pass to the linker
8360 linker Sets the name of the linker
8361 predefines Defines to be passed to the C preprocessor
8362 signed_char Defines to pass to CPP to say whether @code{char} is signed
8363 by default
8364 startfile Object files to include at the start of the link
8365 @end smallexample
8366
8367 Here is a small example of a spec file:
8368
8369 @smallexample
8370 %rename lib old_lib
8371
8372 *lib:
8373 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
8374 @end smallexample
8375
8376 This example renames the spec called @samp{lib} to @samp{old_lib} and
8377 then overrides the previous definition of @samp{lib} with a new one.
8378 The new definition adds in some extra command-line options before
8379 including the text of the old definition.
8380
8381 @dfn{Spec strings} are a list of command-line options to be passed to their
8382 corresponding program. In addition, the spec strings can contain
8383 @samp{%}-prefixed sequences to substitute variable text or to
8384 conditionally insert text into the command line. Using these constructs
8385 it is possible to generate quite complex command lines.
8386
8387 Here is a table of all defined @samp{%}-sequences for spec
8388 strings. Note that spaces are not generated automatically around the
8389 results of expanding these sequences. Therefore you can concatenate them
8390 together or combine them with constant text in a single argument.
8391
8392 @table @code
8393 @item %%
8394 Substitute one @samp{%} into the program name or argument.
8395
8396 @item %i
8397 Substitute the name of the input file being processed.
8398
8399 @item %b
8400 Substitute the basename of the input file being processed.
8401 This is the substring up to (and not including) the last period
8402 and not including the directory.
8403
8404 @item %B
8405 This is the same as @samp{%b}, but include the file suffix (text after
8406 the last period).
8407
8408 @item %d
8409 Marks the argument containing or following the @samp{%d} as a
8410 temporary file name, so that that file will be deleted if GCC exits
8411 successfully. Unlike @samp{%g}, this contributes no text to the
8412 argument.
8413
8414 @item %g@var{suffix}
8415 Substitute a file name that has suffix @var{suffix} and is chosen
8416 once per compilation, and mark the argument in the same way as
8417 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
8418 name is now chosen in a way that is hard to predict even when previously
8419 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
8420 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
8421 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
8422 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
8423 was simply substituted with a file name chosen once per compilation,
8424 without regard to any appended suffix (which was therefore treated
8425 just like ordinary text), making such attacks more likely to succeed.
8426
8427 @item %u@var{suffix}
8428 Like @samp{%g}, but generates a new temporary file name even if
8429 @samp{%u@var{suffix}} was already seen.
8430
8431 @item %U@var{suffix}
8432 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
8433 new one if there is no such last file name. In the absence of any
8434 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
8435 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
8436 would involve the generation of two distinct file names, one
8437 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
8438 simply substituted with a file name chosen for the previous @samp{%u},
8439 without regard to any appended suffix.
8440
8441 @item %j@var{suffix}
8442 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
8443 writable, and if save-temps is off; otherwise, substitute the name
8444 of a temporary file, just like @samp{%u}. This temporary file is not
8445 meant for communication between processes, but rather as a junk
8446 disposal mechanism.
8447
8448 @item %|@var{suffix}
8449 @itemx %m@var{suffix}
8450 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
8451 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
8452 all. These are the two most common ways to instruct a program that it
8453 should read from standard input or write to standard output. If you
8454 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
8455 construct: see for example @file{f/lang-specs.h}.
8456
8457 @item %.@var{SUFFIX}
8458 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
8459 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
8460 terminated by the next space or %.
8461
8462 @item %w
8463 Marks the argument containing or following the @samp{%w} as the
8464 designated output file of this compilation. This puts the argument
8465 into the sequence of arguments that @samp{%o} will substitute later.
8466
8467 @item %o
8468 Substitutes the names of all the output files, with spaces
8469 automatically placed around them. You should write spaces
8470 around the @samp{%o} as well or the results are undefined.
8471 @samp{%o} is for use in the specs for running the linker.
8472 Input files whose names have no recognized suffix are not compiled
8473 at all, but they are included among the output files, so they will
8474 be linked.
8475
8476 @item %O
8477 Substitutes the suffix for object files. Note that this is
8478 handled specially when it immediately follows @samp{%g, %u, or %U},
8479 because of the need for those to form complete file names. The
8480 handling is such that @samp{%O} is treated exactly as if it had already
8481 been substituted, except that @samp{%g, %u, and %U} do not currently
8482 support additional @var{suffix} characters following @samp{%O} as they would
8483 following, for example, @samp{.o}.
8484
8485 @item %p
8486 Substitutes the standard macro predefinitions for the
8487 current target machine. Use this when running @code{cpp}.
8488
8489 @item %P
8490 Like @samp{%p}, but puts @samp{__} before and after the name of each
8491 predefined macro, except for macros that start with @samp{__} or with
8492 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
8493 C@.
8494
8495 @item %I
8496 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
8497 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
8498 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
8499 and @option{-imultilib} as necessary.
8500
8501 @item %s
8502 Current argument is the name of a library or startup file of some sort.
8503 Search for that file in a standard list of directories and substitute
8504 the full name found.
8505
8506 @item %e@var{str}
8507 Print @var{str} as an error message. @var{str} is terminated by a newline.
8508 Use this when inconsistent options are detected.
8509
8510 @item %(@var{name})
8511 Substitute the contents of spec string @var{name} at this point.
8512
8513 @item %[@var{name}]
8514 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
8515
8516 @item %x@{@var{option}@}
8517 Accumulate an option for @samp{%X}.
8518
8519 @item %X
8520 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
8521 spec string.
8522
8523 @item %Y
8524 Output the accumulated assembler options specified by @option{-Wa}.
8525
8526 @item %Z
8527 Output the accumulated preprocessor options specified by @option{-Wp}.
8528
8529 @item %a
8530 Process the @code{asm} spec. This is used to compute the
8531 switches to be passed to the assembler.
8532
8533 @item %A
8534 Process the @code{asm_final} spec. This is a spec string for
8535 passing switches to an assembler post-processor, if such a program is
8536 needed.
8537
8538 @item %l
8539 Process the @code{link} spec. This is the spec for computing the
8540 command line passed to the linker. Typically it will make use of the
8541 @samp{%L %G %S %D and %E} sequences.
8542
8543 @item %D
8544 Dump out a @option{-L} option for each directory that GCC believes might
8545 contain startup files. If the target supports multilibs then the
8546 current multilib directory will be prepended to each of these paths.
8547
8548 @item %L
8549 Process the @code{lib} spec. This is a spec string for deciding which
8550 libraries should be included on the command line to the linker.
8551
8552 @item %G
8553 Process the @code{libgcc} spec. This is a spec string for deciding
8554 which GCC support library should be included on the command line to the linker.
8555
8556 @item %S
8557 Process the @code{startfile} spec. This is a spec for deciding which
8558 object files should be the first ones passed to the linker. Typically
8559 this might be a file named @file{crt0.o}.
8560
8561 @item %E
8562 Process the @code{endfile} spec. This is a spec string that specifies
8563 the last object files that will be passed to the linker.
8564
8565 @item %C
8566 Process the @code{cpp} spec. This is used to construct the arguments
8567 to be passed to the C preprocessor.
8568
8569 @item %1
8570 Process the @code{cc1} spec. This is used to construct the options to be
8571 passed to the actual C compiler (@samp{cc1}).
8572
8573 @item %2
8574 Process the @code{cc1plus} spec. This is used to construct the options to be
8575 passed to the actual C++ compiler (@samp{cc1plus}).
8576
8577 @item %*
8578 Substitute the variable part of a matched option. See below.
8579 Note that each comma in the substituted string is replaced by
8580 a single space.
8581
8582 @item %<@code{S}
8583 Remove all occurrences of @code{-S} from the command line. Note---this
8584 command is position dependent. @samp{%} commands in the spec string
8585 before this one will see @code{-S}, @samp{%} commands in the spec string
8586 after this one will not.
8587
8588 @item %:@var{function}(@var{args})
8589 Call the named function @var{function}, passing it @var{args}.
8590 @var{args} is first processed as a nested spec string, then split
8591 into an argument vector in the usual fashion. The function returns
8592 a string which is processed as if it had appeared literally as part
8593 of the current spec.
8594
8595 The following built-in spec functions are provided:
8596
8597 @table @code
8598 @item @code{getenv}
8599 The @code{getenv} spec function takes two arguments: an environment
8600 variable name and a string. If the environment variable is not
8601 defined, a fatal error is issued. Otherwise, the return value is the
8602 value of the environment variable concatenated with the string. For
8603 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
8604
8605 @smallexample
8606 %:getenv(TOPDIR /include)
8607 @end smallexample
8608
8609 expands to @file{/path/to/top/include}.
8610
8611 @item @code{if-exists}
8612 The @code{if-exists} spec function takes one argument, an absolute
8613 pathname to a file. If the file exists, @code{if-exists} returns the
8614 pathname. Here is a small example of its usage:
8615
8616 @smallexample
8617 *startfile:
8618 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
8619 @end smallexample
8620
8621 @item @code{if-exists-else}
8622 The @code{if-exists-else} spec function is similar to the @code{if-exists}
8623 spec function, except that it takes two arguments. The first argument is
8624 an absolute pathname to a file. If the file exists, @code{if-exists-else}
8625 returns the pathname. If it does not exist, it returns the second argument.
8626 This way, @code{if-exists-else} can be used to select one file or another,
8627 based on the existence of the first. Here is a small example of its usage:
8628
8629 @smallexample
8630 *startfile:
8631 crt0%O%s %:if-exists(crti%O%s) \
8632 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
8633 @end smallexample
8634
8635 @item @code{replace-outfile}
8636 The @code{replace-outfile} spec function takes two arguments. It looks for the
8637 first argument in the outfiles array and replaces it with the second argument. Here
8638 is a small example of its usage:
8639
8640 @smallexample
8641 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
8642 @end smallexample
8643
8644 @item @code{print-asm-header}
8645 The @code{print-asm-header} function takes no arguments and simply
8646 prints a banner like:
8647
8648 @smallexample
8649 Assembler options
8650 =================
8651
8652 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
8653 @end smallexample
8654
8655 It is used to separate compiler options from assembler options
8656 in the @option{--target-help} output.
8657 @end table
8658
8659 @item %@{@code{S}@}
8660 Substitutes the @code{-S} switch, if that switch was given to GCC@.
8661 If that switch was not specified, this substitutes nothing. Note that
8662 the leading dash is omitted when specifying this option, and it is
8663 automatically inserted if the substitution is performed. Thus the spec
8664 string @samp{%@{foo@}} would match the command-line option @option{-foo}
8665 and would output the command line option @option{-foo}.
8666
8667 @item %W@{@code{S}@}
8668 Like %@{@code{S}@} but mark last argument supplied within as a file to be
8669 deleted on failure.
8670
8671 @item %@{@code{S}*@}
8672 Substitutes all the switches specified to GCC whose names start
8673 with @code{-S}, but which also take an argument. This is used for
8674 switches like @option{-o}, @option{-D}, @option{-I}, etc.
8675 GCC considers @option{-o foo} as being
8676 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
8677 text, including the space. Thus two arguments would be generated.
8678
8679 @item %@{@code{S}*&@code{T}*@}
8680 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
8681 (the order of @code{S} and @code{T} in the spec is not significant).
8682 There can be any number of ampersand-separated variables; for each the
8683 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
8684
8685 @item %@{@code{S}:@code{X}@}
8686 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
8687
8688 @item %@{!@code{S}:@code{X}@}
8689 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
8690
8691 @item %@{@code{S}*:@code{X}@}
8692 Substitutes @code{X} if one or more switches whose names start with
8693 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
8694 once, no matter how many such switches appeared. However, if @code{%*}
8695 appears somewhere in @code{X}, then @code{X} will be substituted once
8696 for each matching switch, with the @code{%*} replaced by the part of
8697 that switch that matched the @code{*}.
8698
8699 @item %@{.@code{S}:@code{X}@}
8700 Substitutes @code{X}, if processing a file with suffix @code{S}.
8701
8702 @item %@{!.@code{S}:@code{X}@}
8703 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
8704
8705 @item %@{,@code{S}:@code{X}@}
8706 Substitutes @code{X}, if processing a file for language @code{S}.
8707
8708 @item %@{!,@code{S}:@code{X}@}
8709 Substitutes @code{X}, if not processing a file for language @code{S}.
8710
8711 @item %@{@code{S}|@code{P}:@code{X}@}
8712 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
8713 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
8714 @code{*} sequences as well, although they have a stronger binding than
8715 the @samp{|}. If @code{%*} appears in @code{X}, all of the
8716 alternatives must be starred, and only the first matching alternative
8717 is substituted.
8718
8719 For example, a spec string like this:
8720
8721 @smallexample
8722 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
8723 @end smallexample
8724
8725 will output the following command-line options from the following input
8726 command-line options:
8727
8728 @smallexample
8729 fred.c -foo -baz
8730 jim.d -bar -boggle
8731 -d fred.c -foo -baz -boggle
8732 -d jim.d -bar -baz -boggle
8733 @end smallexample
8734
8735 @item %@{S:X; T:Y; :D@}
8736
8737 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
8738 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
8739 be as many clauses as you need. This may be combined with @code{.},
8740 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
8741
8742
8743 @end table
8744
8745 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
8746 construct may contain other nested @samp{%} constructs or spaces, or
8747 even newlines. They are processed as usual, as described above.
8748 Trailing white space in @code{X} is ignored. White space may also
8749 appear anywhere on the left side of the colon in these constructs,
8750 except between @code{.} or @code{*} and the corresponding word.
8751
8752 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
8753 handled specifically in these constructs. If another value of
8754 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
8755 @option{-W} switch is found later in the command line, the earlier
8756 switch value is ignored, except with @{@code{S}*@} where @code{S} is
8757 just one letter, which passes all matching options.
8758
8759 The character @samp{|} at the beginning of the predicate text is used to
8760 indicate that a command should be piped to the following command, but
8761 only if @option{-pipe} is specified.
8762
8763 It is built into GCC which switches take arguments and which do not.
8764 (You might think it would be useful to generalize this to allow each
8765 compiler's spec to say which switches take arguments. But this cannot
8766 be done in a consistent fashion. GCC cannot even decide which input
8767 files have been specified without knowing which switches take arguments,
8768 and it must know which input files to compile in order to tell which
8769 compilers to run).
8770
8771 GCC also knows implicitly that arguments starting in @option{-l} are to be
8772 treated as compiler output files, and passed to the linker in their
8773 proper position among the other output files.
8774
8775 @c man begin OPTIONS
8776
8777 @node Target Options
8778 @section Specifying Target Machine and Compiler Version
8779 @cindex target options
8780 @cindex cross compiling
8781 @cindex specifying machine version
8782 @cindex specifying compiler version and target machine
8783 @cindex compiler version, specifying
8784 @cindex target machine, specifying
8785
8786 The usual way to run GCC is to run the executable called @file{gcc}, or
8787 @file{<machine>-gcc} when cross-compiling, or
8788 @file{<machine>-gcc-<version>} to run a version other than the one that
8789 was installed last. Sometimes this is inconvenient, so GCC provides
8790 options that will switch to another cross-compiler or version.
8791
8792 @table @gcctabopt
8793 @item -b @var{machine}
8794 @opindex b
8795 The argument @var{machine} specifies the target machine for compilation.
8796
8797 The value to use for @var{machine} is the same as was specified as the
8798 machine type when configuring GCC as a cross-compiler. For
8799 example, if a cross-compiler was configured with @samp{configure
8800 arm-elf}, meaning to compile for an arm processor with elf binaries,
8801 then you would specify @option{-b arm-elf} to run that cross compiler.
8802 Because there are other options beginning with @option{-b}, the
8803 configuration must contain a hyphen, or @option{-b} alone should be one
8804 argument followed by the configuration in the next argument.
8805
8806 @item -V @var{version}
8807 @opindex V
8808 The argument @var{version} specifies which version of GCC to run.
8809 This is useful when multiple versions are installed. For example,
8810 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
8811 @end table
8812
8813 The @option{-V} and @option{-b} options work by running the
8814 @file{<machine>-gcc-<version>} executable, so there's no real reason to
8815 use them if you can just run that directly.
8816
8817 @node Submodel Options
8818 @section Hardware Models and Configurations
8819 @cindex submodel options
8820 @cindex specifying hardware config
8821 @cindex hardware models and configurations, specifying
8822 @cindex machine dependent options
8823
8824 Earlier we discussed the standard option @option{-b} which chooses among
8825 different installed compilers for completely different target
8826 machines, such as VAX vs.@: 68000 vs.@: 80386.
8827
8828 In addition, each of these target machine types can have its own
8829 special options, starting with @samp{-m}, to choose among various
8830 hardware models or configurations---for example, 68010 vs 68020,
8831 floating coprocessor or none. A single installed version of the
8832 compiler can compile for any model or configuration, according to the
8833 options specified.
8834
8835 Some configurations of the compiler also support additional special
8836 options, usually for compatibility with other compilers on the same
8837 platform.
8838
8839 @c This list is ordered alphanumerically by subsection name.
8840 @c It should be the same order and spelling as these options are listed
8841 @c in Machine Dependent Options
8842
8843 @menu
8844 * ARC Options::
8845 * ARM Options::
8846 * AVR Options::
8847 * Blackfin Options::
8848 * CRIS Options::
8849 * CRX Options::
8850 * Darwin Options::
8851 * DEC Alpha Options::
8852 * DEC Alpha/VMS Options::
8853 * FR30 Options::
8854 * FRV Options::
8855 * GNU/Linux Options::
8856 * H8/300 Options::
8857 * HPPA Options::
8858 * i386 and x86-64 Options::
8859 * i386 and x86-64 Windows Options::
8860 * IA-64 Options::
8861 * M32C Options::
8862 * M32R/D Options::
8863 * M680x0 Options::
8864 * M68hc1x Options::
8865 * MCore Options::
8866 * MIPS Options::
8867 * MMIX Options::
8868 * MN10300 Options::
8869 * PDP-11 Options::
8870 * picoChip Options::
8871 * PowerPC Options::
8872 * RS/6000 and PowerPC Options::
8873 * S/390 and zSeries Options::
8874 * Score Options::
8875 * SH Options::
8876 * SPARC Options::
8877 * SPU Options::
8878 * System V Options::
8879 * V850 Options::
8880 * VAX Options::
8881 * VxWorks Options::
8882 * x86-64 Options::
8883 * Xstormy16 Options::
8884 * Xtensa Options::
8885 * zSeries Options::
8886 @end menu
8887
8888 @node ARC Options
8889 @subsection ARC Options
8890 @cindex ARC Options
8891
8892 These options are defined for ARC implementations:
8893
8894 @table @gcctabopt
8895 @item -EL
8896 @opindex EL
8897 Compile code for little endian mode. This is the default.
8898
8899 @item -EB
8900 @opindex EB
8901 Compile code for big endian mode.
8902
8903 @item -mmangle-cpu
8904 @opindex mmangle-cpu
8905 Prepend the name of the cpu to all public symbol names.
8906 In multiple-processor systems, there are many ARC variants with different
8907 instruction and register set characteristics. This flag prevents code
8908 compiled for one cpu to be linked with code compiled for another.
8909 No facility exists for handling variants that are ``almost identical''.
8910 This is an all or nothing option.
8911
8912 @item -mcpu=@var{cpu}
8913 @opindex mcpu
8914 Compile code for ARC variant @var{cpu}.
8915 Which variants are supported depend on the configuration.
8916 All variants support @option{-mcpu=base}, this is the default.
8917
8918 @item -mtext=@var{text-section}
8919 @itemx -mdata=@var{data-section}
8920 @itemx -mrodata=@var{readonly-data-section}
8921 @opindex mtext
8922 @opindex mdata
8923 @opindex mrodata
8924 Put functions, data, and readonly data in @var{text-section},
8925 @var{data-section}, and @var{readonly-data-section} respectively
8926 by default. This can be overridden with the @code{section} attribute.
8927 @xref{Variable Attributes}.
8928
8929 @item -mfix-cortex-m3-ldrd
8930 @opindex mfix-cortex-m3-ldrd
8931 Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions
8932 with overlapping destination and base registers are used. This option avoids
8933 generating these instructions. This option is enabled by default when
8934 @option{-mcpu=cortex-m3} is specified.
8935
8936 @end table
8937
8938 @node ARM Options
8939 @subsection ARM Options
8940 @cindex ARM options
8941
8942 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
8943 architectures:
8944
8945 @table @gcctabopt
8946 @item -mabi=@var{name}
8947 @opindex mabi
8948 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
8949 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
8950
8951 @item -mapcs-frame
8952 @opindex mapcs-frame
8953 Generate a stack frame that is compliant with the ARM Procedure Call
8954 Standard for all functions, even if this is not strictly necessary for
8955 correct execution of the code. Specifying @option{-fomit-frame-pointer}
8956 with this option will cause the stack frames not to be generated for
8957 leaf functions. The default is @option{-mno-apcs-frame}.
8958
8959 @item -mapcs
8960 @opindex mapcs
8961 This is a synonym for @option{-mapcs-frame}.
8962
8963 @ignore
8964 @c not currently implemented
8965 @item -mapcs-stack-check
8966 @opindex mapcs-stack-check
8967 Generate code to check the amount of stack space available upon entry to
8968 every function (that actually uses some stack space). If there is
8969 insufficient space available then either the function
8970 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
8971 called, depending upon the amount of stack space required. The run time
8972 system is required to provide these functions. The default is
8973 @option{-mno-apcs-stack-check}, since this produces smaller code.
8974
8975 @c not currently implemented
8976 @item -mapcs-float
8977 @opindex mapcs-float
8978 Pass floating point arguments using the float point registers. This is
8979 one of the variants of the APCS@. This option is recommended if the
8980 target hardware has a floating point unit or if a lot of floating point
8981 arithmetic is going to be performed by the code. The default is
8982 @option{-mno-apcs-float}, since integer only code is slightly increased in
8983 size if @option{-mapcs-float} is used.
8984
8985 @c not currently implemented
8986 @item -mapcs-reentrant
8987 @opindex mapcs-reentrant
8988 Generate reentrant, position independent code. The default is
8989 @option{-mno-apcs-reentrant}.
8990 @end ignore
8991
8992 @item -mthumb-interwork
8993 @opindex mthumb-interwork
8994 Generate code which supports calling between the ARM and Thumb
8995 instruction sets. Without this option the two instruction sets cannot
8996 be reliably used inside one program. The default is
8997 @option{-mno-thumb-interwork}, since slightly larger code is generated
8998 when @option{-mthumb-interwork} is specified.
8999
9000 @item -mno-sched-prolog
9001 @opindex mno-sched-prolog
9002 Prevent the reordering of instructions in the function prolog, or the
9003 merging of those instruction with the instructions in the function's
9004 body. This means that all functions will start with a recognizable set
9005 of instructions (or in fact one of a choice from a small set of
9006 different function prologues), and this information can be used to
9007 locate the start if functions inside an executable piece of code. The
9008 default is @option{-msched-prolog}.
9009
9010 @item -mfloat-abi=@var{name}
9011 @opindex mfloat-abi
9012 Specifies which floating-point ABI to use. Permissible values
9013 are: @samp{soft}, @samp{softfp} and @samp{hard}.
9014
9015 Specifying @samp{soft} causes GCC to generate output containing
9016 library calls for floating-point operations.
9017 @samp{softfp} allows the generation of code using hardware floating-point
9018 instructions, but still uses the soft-float calling conventions.
9019 @samp{hard} allows generation of floating-point instructions
9020 and uses FPU-specific calling conventions.
9021
9022 Using @option{-mfloat-abi=hard} with VFP coprocessors is not supported.
9023 Use @option{-mfloat-abi=softfp} with the appropriate @option{-mfpu} option
9024 to allow the compiler to generate code that makes use of the hardware
9025 floating-point capabilities for these CPUs.
9026
9027 The default depends on the specific target configuration. Note that
9028 the hard-float and soft-float ABIs are not link-compatible; you must
9029 compile your entire program with the same ABI, and link with a
9030 compatible set of libraries.
9031
9032 @item -mhard-float
9033 @opindex mhard-float
9034 Equivalent to @option{-mfloat-abi=hard}.
9035
9036 @item -msoft-float
9037 @opindex msoft-float
9038 Equivalent to @option{-mfloat-abi=soft}.
9039
9040 @item -mlittle-endian
9041 @opindex mlittle-endian
9042 Generate code for a processor running in little-endian mode. This is
9043 the default for all standard configurations.
9044
9045 @item -mbig-endian
9046 @opindex mbig-endian
9047 Generate code for a processor running in big-endian mode; the default is
9048 to compile code for a little-endian processor.
9049
9050 @item -mwords-little-endian
9051 @opindex mwords-little-endian
9052 This option only applies when generating code for big-endian processors.
9053 Generate code for a little-endian word order but a big-endian byte
9054 order. That is, a byte order of the form @samp{32107654}. Note: this
9055 option should only be used if you require compatibility with code for
9056 big-endian ARM processors generated by versions of the compiler prior to
9057 2.8.
9058
9059 @item -mcpu=@var{name}
9060 @opindex mcpu
9061 This specifies the name of the target ARM processor. GCC uses this name
9062 to determine what kind of instructions it can emit when generating
9063 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
9064 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
9065 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
9066 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
9067 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
9068 @samp{arm720},
9069 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
9070 @samp{arm710t}, @samp{arm720t}, @samp{arm740t},
9071 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
9072 @samp{strongarm1110},
9073 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
9074 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
9075 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
9076 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
9077 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
9078 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
9079 @samp{arm1156t2-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
9080 @samp{cortex-a8}, @samp{cortex-a9},
9081 @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-m3},
9082 @samp{cortex-m1},
9083 @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
9084
9085 @item -mtune=@var{name}
9086 @opindex mtune
9087 This option is very similar to the @option{-mcpu=} option, except that
9088 instead of specifying the actual target processor type, and hence
9089 restricting which instructions can be used, it specifies that GCC should
9090 tune the performance of the code as if the target were of the type
9091 specified in this option, but still choosing the instructions that it
9092 will generate based on the cpu specified by a @option{-mcpu=} option.
9093 For some ARM implementations better performance can be obtained by using
9094 this option.
9095
9096 @item -march=@var{name}
9097 @opindex march
9098 This specifies the name of the target ARM architecture. GCC uses this
9099 name to determine what kind of instructions it can emit when generating
9100 assembly code. This option can be used in conjunction with or instead
9101 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
9102 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
9103 @samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te},
9104 @samp{armv6}, @samp{armv6j},
9105 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
9106 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m},
9107 @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
9108
9109 @item -mfpu=@var{name}
9110 @itemx -mfpe=@var{number}
9111 @itemx -mfp=@var{number}
9112 @opindex mfpu
9113 @opindex mfpe
9114 @opindex mfp
9115 This specifies what floating point hardware (or hardware emulation) is
9116 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
9117 @samp{fpe3}, @samp{maverick}, @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-d16} and
9118 @samp{neon}. @option{-mfp} and @option{-mfpe}
9119 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
9120 with older versions of GCC@.
9121
9122 If @option{-msoft-float} is specified this specifies the format of
9123 floating point values.
9124
9125 @item -mstructure-size-boundary=@var{n}
9126 @opindex mstructure-size-boundary
9127 The size of all structures and unions will be rounded up to a multiple
9128 of the number of bits set by this option. Permissible values are 8, 32
9129 and 64. The default value varies for different toolchains. For the COFF
9130 targeted toolchain the default value is 8. A value of 64 is only allowed
9131 if the underlying ABI supports it.
9132
9133 Specifying the larger number can produce faster, more efficient code, but
9134 can also increase the size of the program. Different values are potentially
9135 incompatible. Code compiled with one value cannot necessarily expect to
9136 work with code or libraries compiled with another value, if they exchange
9137 information using structures or unions.
9138
9139 @item -mabort-on-noreturn
9140 @opindex mabort-on-noreturn
9141 Generate a call to the function @code{abort} at the end of a
9142 @code{noreturn} function. It will be executed if the function tries to
9143 return.
9144
9145 @item -mlong-calls
9146 @itemx -mno-long-calls
9147 @opindex mlong-calls
9148 @opindex mno-long-calls
9149 Tells the compiler to perform function calls by first loading the
9150 address of the function into a register and then performing a subroutine
9151 call on this register. This switch is needed if the target function
9152 will lie outside of the 64 megabyte addressing range of the offset based
9153 version of subroutine call instruction.
9154
9155 Even if this switch is enabled, not all function calls will be turned
9156 into long calls. The heuristic is that static functions, functions
9157 which have the @samp{short-call} attribute, functions that are inside
9158 the scope of a @samp{#pragma no_long_calls} directive and functions whose
9159 definitions have already been compiled within the current compilation
9160 unit, will not be turned into long calls. The exception to this rule is
9161 that weak function definitions, functions with the @samp{long-call}
9162 attribute or the @samp{section} attribute, and functions that are within
9163 the scope of a @samp{#pragma long_calls} directive, will always be
9164 turned into long calls.
9165
9166 This feature is not enabled by default. Specifying
9167 @option{-mno-long-calls} will restore the default behavior, as will
9168 placing the function calls within the scope of a @samp{#pragma
9169 long_calls_off} directive. Note these switches have no effect on how
9170 the compiler generates code to handle function calls via function
9171 pointers.
9172
9173 @item -msingle-pic-base
9174 @opindex msingle-pic-base
9175 Treat the register used for PIC addressing as read-only, rather than
9176 loading it in the prologue for each function. The run-time system is
9177 responsible for initializing this register with an appropriate value
9178 before execution begins.
9179
9180 @item -mpic-register=@var{reg}
9181 @opindex mpic-register
9182 Specify the register to be used for PIC addressing. The default is R10
9183 unless stack-checking is enabled, when R9 is used.
9184
9185 @item -mcirrus-fix-invalid-insns
9186 @opindex mcirrus-fix-invalid-insns
9187 @opindex mno-cirrus-fix-invalid-insns
9188 Insert NOPs into the instruction stream to in order to work around
9189 problems with invalid Maverick instruction combinations. This option
9190 is only valid if the @option{-mcpu=ep9312} option has been used to
9191 enable generation of instructions for the Cirrus Maverick floating
9192 point co-processor. This option is not enabled by default, since the
9193 problem is only present in older Maverick implementations. The default
9194 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
9195 switch.
9196
9197 @item -mpoke-function-name
9198 @opindex mpoke-function-name
9199 Write the name of each function into the text section, directly
9200 preceding the function prologue. The generated code is similar to this:
9201
9202 @smallexample
9203 t0
9204 .ascii "arm_poke_function_name", 0
9205 .align
9206 t1
9207 .word 0xff000000 + (t1 - t0)
9208 arm_poke_function_name
9209 mov ip, sp
9210 stmfd sp!, @{fp, ip, lr, pc@}
9211 sub fp, ip, #4
9212 @end smallexample
9213
9214 When performing a stack backtrace, code can inspect the value of
9215 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
9216 location @code{pc - 12} and the top 8 bits are set, then we know that
9217 there is a function name embedded immediately preceding this location
9218 and has length @code{((pc[-3]) & 0xff000000)}.
9219
9220 @item -mthumb
9221 @opindex mthumb
9222 Generate code for the Thumb instruction set. The default is to
9223 use the 32-bit ARM instruction set.
9224 This option automatically enables either 16-bit Thumb-1 or
9225 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
9226 and @option{-march=@var{name}} options.
9227
9228 @item -mtpcs-frame
9229 @opindex mtpcs-frame
9230 Generate a stack frame that is compliant with the Thumb Procedure Call
9231 Standard for all non-leaf functions. (A leaf function is one that does
9232 not call any other functions.) The default is @option{-mno-tpcs-frame}.
9233
9234 @item -mtpcs-leaf-frame
9235 @opindex mtpcs-leaf-frame
9236 Generate a stack frame that is compliant with the Thumb Procedure Call
9237 Standard for all leaf functions. (A leaf function is one that does
9238 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
9239
9240 @item -mcallee-super-interworking
9241 @opindex mcallee-super-interworking
9242 Gives all externally visible functions in the file being compiled an ARM
9243 instruction set header which switches to Thumb mode before executing the
9244 rest of the function. This allows these functions to be called from
9245 non-interworking code.
9246
9247 @item -mcaller-super-interworking
9248 @opindex mcaller-super-interworking
9249 Allows calls via function pointers (including virtual functions) to
9250 execute correctly regardless of whether the target code has been
9251 compiled for interworking or not. There is a small overhead in the cost
9252 of executing a function pointer if this option is enabled.
9253
9254 @item -mtp=@var{name}
9255 @opindex mtp
9256 Specify the access model for the thread local storage pointer. The valid
9257 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
9258 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
9259 (supported in the arm6k architecture), and @option{auto}, which uses the
9260 best available method for the selected processor. The default setting is
9261 @option{auto}.
9262
9263 @item -mword-relocations
9264 @opindex mword-relocations
9265 Only generate absolute relocations on word sized values (i.e. R_ARM_ABS32).
9266 This is enabled by default on targets (uClinux, SymbianOS) where the runtime
9267 loader imposes this restriction, and when @option{-fpic} or @option{-fPIC}
9268 is specified.
9269
9270 @end table
9271
9272 @node AVR Options
9273 @subsection AVR Options
9274 @cindex AVR Options
9275
9276 These options are defined for AVR implementations:
9277
9278 @table @gcctabopt
9279 @item -mmcu=@var{mcu}
9280 @opindex mmcu
9281 Specify ATMEL AVR instruction set or MCU type.
9282
9283 Instruction set avr1 is for the minimal AVR core, not supported by the C
9284 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9285 attiny11, attiny12, attiny15, attiny28).
9286
9287 Instruction set avr2 (default) is for the classic AVR core with up to
9288 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9289 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9290 at90c8534, at90s8535).
9291
9292 Instruction set avr3 is for the classic AVR core with up to 128K program
9293 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9294
9295 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9296 memory space (MCU types: atmega8, atmega83, atmega85).
9297
9298 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9299 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9300 atmega64, atmega128, at43usb355, at94k).
9301
9302 @item -msize
9303 @opindex msize
9304 Output instruction sizes to the asm file.
9305
9306 @item -mno-interrupts
9307 @opindex mno-interrupts
9308 Generated code is not compatible with hardware interrupts.
9309 Code size will be smaller.
9310
9311 @item -mcall-prologues
9312 @opindex mcall-prologues
9313 Functions prologues/epilogues expanded as call to appropriate
9314 subroutines. Code size will be smaller.
9315
9316 @item -mno-tablejump
9317 @opindex mno-tablejump
9318 Do not generate tablejump insns which sometimes increase code size.
9319 The option is now deprecated in favor of the equivalent
9320 @option{-fno-jump-tables}
9321
9322 @item -mtiny-stack
9323 @opindex mtiny-stack
9324 Change only the low 8 bits of the stack pointer.
9325
9326 @item -mint8
9327 @opindex mint8
9328 Assume int to be 8 bit integer. This affects the sizes of all types: A
9329 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
9330 and long long will be 4 bytes. Please note that this option does not
9331 comply to the C standards, but it will provide you with smaller code
9332 size.
9333 @end table
9334
9335 @node Blackfin Options
9336 @subsection Blackfin Options
9337 @cindex Blackfin Options
9338
9339 @table @gcctabopt
9340 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
9341 @opindex mcpu=
9342 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
9343 can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518},
9344 @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526},
9345 @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
9346 @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
9347 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
9348 @samp{bf561}.
9349 The optional @var{sirevision} specifies the silicon revision of the target
9350 Blackfin processor. Any workarounds available for the targeted silicon revision
9351 will be enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
9352 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
9353 will be enabled. The @code{__SILICON_REVISION__} macro is defined to two
9354 hexadecimal digits representing the major and minor numbers in the silicon
9355 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
9356 is not defined. If @var{sirevision} is @samp{any}, the
9357 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
9358 If this optional @var{sirevision} is not used, GCC assumes the latest known
9359 silicon revision of the targeted Blackfin processor.
9360
9361 Support for @samp{bf561} is incomplete. For @samp{bf561},
9362 Only the processor macro is defined.
9363 Without this option, @samp{bf532} is used as the processor by default.
9364 The corresponding predefined processor macros for @var{cpu} is to
9365 be defined. And for @samp{bfin-elf} toolchain, this causes the hardware BSP
9366 provided by libgloss to be linked in if @option{-msim} is not given.
9367
9368 @item -msim
9369 @opindex msim
9370 Specifies that the program will be run on the simulator. This causes
9371 the simulator BSP provided by libgloss to be linked in. This option
9372 has effect only for @samp{bfin-elf} toolchain.
9373 Certain other options, such as @option{-mid-shared-library} and
9374 @option{-mfdpic}, imply @option{-msim}.
9375
9376 @item -momit-leaf-frame-pointer
9377 @opindex momit-leaf-frame-pointer
9378 Don't keep the frame pointer in a register for leaf functions. This
9379 avoids the instructions to save, set up and restore frame pointers and
9380 makes an extra register available in leaf functions. The option
9381 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9382 which might make debugging harder.
9383
9384 @item -mspecld-anomaly
9385 @opindex mspecld-anomaly
9386 When enabled, the compiler will ensure that the generated code does not
9387 contain speculative loads after jump instructions. If this option is used,
9388 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
9389
9390 @item -mno-specld-anomaly
9391 @opindex mno-specld-anomaly
9392 Don't generate extra code to prevent speculative loads from occurring.
9393
9394 @item -mcsync-anomaly
9395 @opindex mcsync-anomaly
9396 When enabled, the compiler will ensure that the generated code does not
9397 contain CSYNC or SSYNC instructions too soon after conditional branches.
9398 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
9399
9400 @item -mno-csync-anomaly
9401 @opindex mno-csync-anomaly
9402 Don't generate extra code to prevent CSYNC or SSYNC instructions from
9403 occurring too soon after a conditional branch.
9404
9405 @item -mlow-64k
9406 @opindex mlow-64k
9407 When enabled, the compiler is free to take advantage of the knowledge that
9408 the entire program fits into the low 64k of memory.
9409
9410 @item -mno-low-64k
9411 @opindex mno-low-64k
9412 Assume that the program is arbitrarily large. This is the default.
9413
9414 @item -mstack-check-l1
9415 @opindex mstack-check-l1
9416 Do stack checking using information placed into L1 scratchpad memory by the
9417 uClinux kernel.
9418
9419 @item -mid-shared-library
9420 @opindex mid-shared-library
9421 Generate code that supports shared libraries via the library ID method.
9422 This allows for execute in place and shared libraries in an environment
9423 without virtual memory management. This option implies @option{-fPIC}.
9424 With a @samp{bfin-elf} target, this option implies @option{-msim}.
9425
9426 @item -mno-id-shared-library
9427 @opindex mno-id-shared-library
9428 Generate code that doesn't assume ID based shared libraries are being used.
9429 This is the default.
9430
9431 @item -mleaf-id-shared-library
9432 @opindex mleaf-id-shared-library
9433 Generate code that supports shared libraries via the library ID method,
9434 but assumes that this library or executable won't link against any other
9435 ID shared libraries. That allows the compiler to use faster code for jumps
9436 and calls.
9437
9438 @item -mno-leaf-id-shared-library
9439 @opindex mno-leaf-id-shared-library
9440 Do not assume that the code being compiled won't link against any ID shared
9441 libraries. Slower code will be generated for jump and call insns.
9442
9443 @item -mshared-library-id=n
9444 @opindex mshared-library-id
9445 Specified the identification number of the ID based shared library being
9446 compiled. Specifying a value of 0 will generate more compact code, specifying
9447 other values will force the allocation of that number to the current
9448 library but is no more space or time efficient than omitting this option.
9449
9450 @item -msep-data
9451 @opindex msep-data
9452 Generate code that allows the data segment to be located in a different
9453 area of memory from the text segment. This allows for execute in place in
9454 an environment without virtual memory management by eliminating relocations
9455 against the text section.
9456
9457 @item -mno-sep-data
9458 @opindex mno-sep-data
9459 Generate code that assumes that the data segment follows the text segment.
9460 This is the default.
9461
9462 @item -mlong-calls
9463 @itemx -mno-long-calls
9464 @opindex mlong-calls
9465 @opindex mno-long-calls
9466 Tells the compiler to perform function calls by first loading the
9467 address of the function into a register and then performing a subroutine
9468 call on this register. This switch is needed if the target function
9469 will lie outside of the 24 bit addressing range of the offset based
9470 version of subroutine call instruction.
9471
9472 This feature is not enabled by default. Specifying
9473 @option{-mno-long-calls} will restore the default behavior. Note these
9474 switches have no effect on how the compiler generates code to handle
9475 function calls via function pointers.
9476
9477 @item -mfast-fp
9478 @opindex mfast-fp
9479 Link with the fast floating-point library. This library relaxes some of
9480 the IEEE floating-point standard's rules for checking inputs against
9481 Not-a-Number (NAN), in the interest of performance.
9482
9483 @item -minline-plt
9484 @opindex minline-plt
9485 Enable inlining of PLT entries in function calls to functions that are
9486 not known to bind locally. It has no effect without @option{-mfdpic}.
9487
9488 @item -mmulticore
9489 @opindex mmulticore
9490 Build standalone application for multicore Blackfin processor. Proper
9491 start files and link scripts will be used to support multicore.
9492 This option defines @code{__BFIN_MULTICORE}. It can only be used with
9493 @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. It can be used with
9494 @option{-mcorea} or @option{-mcoreb}. If it's used without
9495 @option{-mcorea} or @option{-mcoreb}, single application/dual core
9496 programming model is used. In this model, the main function of Core B
9497 should be named as coreb_main. If it's used with @option{-mcorea} or
9498 @option{-mcoreb}, one application per core programming model is used.
9499 If this option is not used, single core application programming
9500 model is used.
9501
9502 @item -mcorea
9503 @opindex mcorea
9504 Build standalone application for Core A of BF561 when using
9505 one application per core programming model. Proper start files
9506 and link scripts will be used to support Core A. This option
9507 defines @code{__BFIN_COREA}. It must be used with @option{-mmulticore}.
9508
9509 @item -mcoreb
9510 @opindex mcoreb
9511 Build standalone application for Core B of BF561 when using
9512 one application per core programming model. Proper start files
9513 and link scripts will be used to support Core B. This option
9514 defines @code{__BFIN_COREB}. When this option is used, coreb_main
9515 should be used instead of main. It must be used with
9516 @option{-mmulticore}.
9517
9518 @item -msdram
9519 @opindex msdram
9520 Build standalone application for SDRAM. Proper start files and
9521 link scripts will be used to put the application into SDRAM.
9522 Loader should initialize SDRAM before loading the application
9523 into SDRAM. This option defines @code{__BFIN_SDRAM}.
9524
9525 @item -micplb
9526 @opindex micplb
9527 Assume that ICPLBs are enabled at runtime. This has an effect on certain
9528 anomaly workarounds. For Linux targets, the default is to assume ICPLBs
9529 are enabled; for standalone applications the default is off.
9530 @end table
9531
9532 @node CRIS Options
9533 @subsection CRIS Options
9534 @cindex CRIS Options
9535
9536 These options are defined specifically for the CRIS ports.
9537
9538 @table @gcctabopt
9539 @item -march=@var{architecture-type}
9540 @itemx -mcpu=@var{architecture-type}
9541 @opindex march
9542 @opindex mcpu
9543 Generate code for the specified architecture. The choices for
9544 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9545 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
9546 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9547 @samp{v10}.
9548
9549 @item -mtune=@var{architecture-type}
9550 @opindex mtune
9551 Tune to @var{architecture-type} everything applicable about the generated
9552 code, except for the ABI and the set of available instructions. The
9553 choices for @var{architecture-type} are the same as for
9554 @option{-march=@var{architecture-type}}.
9555
9556 @item -mmax-stack-frame=@var{n}
9557 @opindex mmax-stack-frame
9558 Warn when the stack frame of a function exceeds @var{n} bytes.
9559
9560 @item -metrax4
9561 @itemx -metrax100
9562 @opindex metrax4
9563 @opindex metrax100
9564 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9565 @option{-march=v3} and @option{-march=v8} respectively.
9566
9567 @item -mmul-bug-workaround
9568 @itemx -mno-mul-bug-workaround
9569 @opindex mmul-bug-workaround
9570 @opindex mno-mul-bug-workaround
9571 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
9572 models where it applies. This option is active by default.
9573
9574 @item -mpdebug
9575 @opindex mpdebug
9576 Enable CRIS-specific verbose debug-related information in the assembly
9577 code. This option also has the effect to turn off the @samp{#NO_APP}
9578 formatted-code indicator to the assembler at the beginning of the
9579 assembly file.
9580
9581 @item -mcc-init
9582 @opindex mcc-init
9583 Do not use condition-code results from previous instruction; always emit
9584 compare and test instructions before use of condition codes.
9585
9586 @item -mno-side-effects
9587 @opindex mno-side-effects
9588 Do not emit instructions with side-effects in addressing modes other than
9589 post-increment.
9590
9591 @item -mstack-align
9592 @itemx -mno-stack-align
9593 @itemx -mdata-align
9594 @itemx -mno-data-align
9595 @itemx -mconst-align
9596 @itemx -mno-const-align
9597 @opindex mstack-align
9598 @opindex mno-stack-align
9599 @opindex mdata-align
9600 @opindex mno-data-align
9601 @opindex mconst-align
9602 @opindex mno-const-align
9603 These options (no-options) arranges (eliminate arrangements) for the
9604 stack-frame, individual data and constants to be aligned for the maximum
9605 single data access size for the chosen CPU model. The default is to
9606 arrange for 32-bit alignment. ABI details such as structure layout are
9607 not affected by these options.
9608
9609 @item -m32-bit
9610 @itemx -m16-bit
9611 @itemx -m8-bit
9612 @opindex m32-bit
9613 @opindex m16-bit
9614 @opindex m8-bit
9615 Similar to the stack- data- and const-align options above, these options
9616 arrange for stack-frame, writable data and constants to all be 32-bit,
9617 16-bit or 8-bit aligned. The default is 32-bit alignment.
9618
9619 @item -mno-prologue-epilogue
9620 @itemx -mprologue-epilogue
9621 @opindex mno-prologue-epilogue
9622 @opindex mprologue-epilogue
9623 With @option{-mno-prologue-epilogue}, the normal function prologue and
9624 epilogue that sets up the stack-frame are omitted and no return
9625 instructions or return sequences are generated in the code. Use this
9626 option only together with visual inspection of the compiled code: no
9627 warnings or errors are generated when call-saved registers must be saved,
9628 or storage for local variable needs to be allocated.
9629
9630 @item -mno-gotplt
9631 @itemx -mgotplt
9632 @opindex mno-gotplt
9633 @opindex mgotplt
9634 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9635 instruction sequences that load addresses for functions from the PLT part
9636 of the GOT rather than (traditional on other architectures) calls to the
9637 PLT@. The default is @option{-mgotplt}.
9638
9639 @item -melf
9640 @opindex melf
9641 Legacy no-op option only recognized with the cris-axis-elf and
9642 cris-axis-linux-gnu targets.
9643
9644 @item -mlinux
9645 @opindex mlinux
9646 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9647
9648 @item -sim
9649 @opindex sim
9650 This option, recognized for the cris-axis-elf arranges
9651 to link with input-output functions from a simulator library. Code,
9652 initialized data and zero-initialized data are allocated consecutively.
9653
9654 @item -sim2
9655 @opindex sim2
9656 Like @option{-sim}, but pass linker options to locate initialized data at
9657 0x40000000 and zero-initialized data at 0x80000000.
9658 @end table
9659
9660 @node CRX Options
9661 @subsection CRX Options
9662 @cindex CRX Options
9663
9664 These options are defined specifically for the CRX ports.
9665
9666 @table @gcctabopt
9667
9668 @item -mmac
9669 @opindex mmac
9670 Enable the use of multiply-accumulate instructions. Disabled by default.
9671
9672 @item -mpush-args
9673 @opindex mpush-args
9674 Push instructions will be used to pass outgoing arguments when functions
9675 are called. Enabled by default.
9676 @end table
9677
9678 @node Darwin Options
9679 @subsection Darwin Options
9680 @cindex Darwin options
9681
9682 These options are defined for all architectures running the Darwin operating
9683 system.
9684
9685 FSF GCC on Darwin does not create ``fat'' object files; it will create
9686 an object file for the single architecture that it was built to
9687 target. Apple's GCC on Darwin does create ``fat'' files if multiple
9688 @option{-arch} options are used; it does so by running the compiler or
9689 linker multiple times and joining the results together with
9690 @file{lipo}.
9691
9692 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
9693 @samp{i686}) is determined by the flags that specify the ISA
9694 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
9695 @option{-force_cpusubtype_ALL} option can be used to override this.
9696
9697 The Darwin tools vary in their behavior when presented with an ISA
9698 mismatch. The assembler, @file{as}, will only permit instructions to
9699 be used that are valid for the subtype of the file it is generating,
9700 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
9701 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
9702 and print an error if asked to create a shared library with a less
9703 restrictive subtype than its input files (for instance, trying to put
9704 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
9705 for executables, @file{ld}, will quietly give the executable the most
9706 restrictive subtype of any of its input files.
9707
9708 @table @gcctabopt
9709 @item -F@var{dir}
9710 @opindex F
9711 Add the framework directory @var{dir} to the head of the list of
9712 directories to be searched for header files. These directories are
9713 interleaved with those specified by @option{-I} options and are
9714 scanned in a left-to-right order.
9715
9716 A framework directory is a directory with frameworks in it. A
9717 framework is a directory with a @samp{"Headers"} and/or
9718 @samp{"PrivateHeaders"} directory contained directly in it that ends
9719 in @samp{".framework"}. The name of a framework is the name of this
9720 directory excluding the @samp{".framework"}. Headers associated with
9721 the framework are found in one of those two directories, with
9722 @samp{"Headers"} being searched first. A subframework is a framework
9723 directory that is in a framework's @samp{"Frameworks"} directory.
9724 Includes of subframework headers can only appear in a header of a
9725 framework that contains the subframework, or in a sibling subframework
9726 header. Two subframeworks are siblings if they occur in the same
9727 framework. A subframework should not have the same name as a
9728 framework, a warning will be issued if this is violated. Currently a
9729 subframework cannot have subframeworks, in the future, the mechanism
9730 may be extended to support this. The standard frameworks can be found
9731 in @samp{"/System/Library/Frameworks"} and
9732 @samp{"/Library/Frameworks"}. An example include looks like
9733 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
9734 the name of the framework and header.h is found in the
9735 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
9736
9737 @item -iframework@var{dir}
9738 @opindex iframework
9739 Like @option{-F} except the directory is a treated as a system
9740 directory. The main difference between this @option{-iframework} and
9741 @option{-F} is that with @option{-iframework} the compiler does not
9742 warn about constructs contained within header files found via
9743 @var{dir}. This option is valid only for the C family of languages.
9744
9745 @item -gused
9746 @opindex gused
9747 Emit debugging information for symbols that are used. For STABS
9748 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
9749 This is by default ON@.
9750
9751 @item -gfull
9752 @opindex gfull
9753 Emit debugging information for all symbols and types.
9754
9755 @item -mmacosx-version-min=@var{version}
9756 The earliest version of MacOS X that this executable will run on
9757 is @var{version}. Typical values of @var{version} include @code{10.1},
9758 @code{10.2}, and @code{10.3.9}.
9759
9760 If the compiler was built to use the system's headers by default,
9761 then the default for this option is the system version on which the
9762 compiler is running, otherwise the default is to make choices which
9763 are compatible with as many systems and code bases as possible.
9764
9765 @item -mkernel
9766 @opindex mkernel
9767 Enable kernel development mode. The @option{-mkernel} option sets
9768 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
9769 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
9770 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
9771 applicable. This mode also sets @option{-mno-altivec},
9772 @option{-msoft-float}, @option{-fno-builtin} and
9773 @option{-mlong-branch} for PowerPC targets.
9774
9775 @item -mone-byte-bool
9776 @opindex mone-byte-bool
9777 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
9778 By default @samp{sizeof(bool)} is @samp{4} when compiling for
9779 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
9780 option has no effect on x86.
9781
9782 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
9783 to generate code that is not binary compatible with code generated
9784 without that switch. Using this switch may require recompiling all
9785 other modules in a program, including system libraries. Use this
9786 switch to conform to a non-default data model.
9787
9788 @item -mfix-and-continue
9789 @itemx -ffix-and-continue
9790 @itemx -findirect-data
9791 @opindex mfix-and-continue
9792 @opindex ffix-and-continue
9793 @opindex findirect-data
9794 Generate code suitable for fast turn around development. Needed to
9795 enable gdb to dynamically load @code{.o} files into already running
9796 programs. @option{-findirect-data} and @option{-ffix-and-continue}
9797 are provided for backwards compatibility.
9798
9799 @item -all_load
9800 @opindex all_load
9801 Loads all members of static archive libraries.
9802 See man ld(1) for more information.
9803
9804 @item -arch_errors_fatal
9805 @opindex arch_errors_fatal
9806 Cause the errors having to do with files that have the wrong architecture
9807 to be fatal.
9808
9809 @item -bind_at_load
9810 @opindex bind_at_load
9811 Causes the output file to be marked such that the dynamic linker will
9812 bind all undefined references when the file is loaded or launched.
9813
9814 @item -bundle
9815 @opindex bundle
9816 Produce a Mach-o bundle format file.
9817 See man ld(1) for more information.
9818
9819 @item -bundle_loader @var{executable}
9820 @opindex bundle_loader
9821 This option specifies the @var{executable} that will be loading the build
9822 output file being linked. See man ld(1) for more information.
9823
9824 @item -dynamiclib
9825 @opindex dynamiclib
9826 When passed this option, GCC will produce a dynamic library instead of
9827 an executable when linking, using the Darwin @file{libtool} command.
9828
9829 @item -force_cpusubtype_ALL
9830 @opindex force_cpusubtype_ALL
9831 This causes GCC's output file to have the @var{ALL} subtype, instead of
9832 one controlled by the @option{-mcpu} or @option{-march} option.
9833
9834 @item -allowable_client @var{client_name}
9835 @itemx -client_name
9836 @itemx -compatibility_version
9837 @itemx -current_version
9838 @itemx -dead_strip
9839 @itemx -dependency-file
9840 @itemx -dylib_file
9841 @itemx -dylinker_install_name
9842 @itemx -dynamic
9843 @itemx -exported_symbols_list
9844 @itemx -filelist
9845 @itemx -flat_namespace
9846 @itemx -force_flat_namespace
9847 @itemx -headerpad_max_install_names
9848 @itemx -image_base
9849 @itemx -init
9850 @itemx -install_name
9851 @itemx -keep_private_externs
9852 @itemx -multi_module
9853 @itemx -multiply_defined
9854 @itemx -multiply_defined_unused
9855 @itemx -noall_load
9856 @itemx -no_dead_strip_inits_and_terms
9857 @itemx -nofixprebinding
9858 @itemx -nomultidefs
9859 @itemx -noprebind
9860 @itemx -noseglinkedit
9861 @itemx -pagezero_size
9862 @itemx -prebind
9863 @itemx -prebind_all_twolevel_modules
9864 @itemx -private_bundle
9865 @itemx -read_only_relocs
9866 @itemx -sectalign
9867 @itemx -sectobjectsymbols
9868 @itemx -whyload
9869 @itemx -seg1addr
9870 @itemx -sectcreate
9871 @itemx -sectobjectsymbols
9872 @itemx -sectorder
9873 @itemx -segaddr
9874 @itemx -segs_read_only_addr
9875 @itemx -segs_read_write_addr
9876 @itemx -seg_addr_table
9877 @itemx -seg_addr_table_filename
9878 @itemx -seglinkedit
9879 @itemx -segprot
9880 @itemx -segs_read_only_addr
9881 @itemx -segs_read_write_addr
9882 @itemx -single_module
9883 @itemx -static
9884 @itemx -sub_library
9885 @itemx -sub_umbrella
9886 @itemx -twolevel_namespace
9887 @itemx -umbrella
9888 @itemx -undefined
9889 @itemx -unexported_symbols_list
9890 @itemx -weak_reference_mismatches
9891 @itemx -whatsloaded
9892 @opindex allowable_client
9893 @opindex client_name
9894 @opindex compatibility_version
9895 @opindex current_version
9896 @opindex dead_strip
9897 @opindex dependency-file
9898 @opindex dylib_file
9899 @opindex dylinker_install_name
9900 @opindex dynamic
9901 @opindex exported_symbols_list
9902 @opindex filelist
9903 @opindex flat_namespace
9904 @opindex force_flat_namespace
9905 @opindex headerpad_max_install_names
9906 @opindex image_base
9907 @opindex init
9908 @opindex install_name
9909 @opindex keep_private_externs
9910 @opindex multi_module
9911 @opindex multiply_defined
9912 @opindex multiply_defined_unused
9913 @opindex noall_load
9914 @opindex no_dead_strip_inits_and_terms
9915 @opindex nofixprebinding
9916 @opindex nomultidefs
9917 @opindex noprebind
9918 @opindex noseglinkedit
9919 @opindex pagezero_size
9920 @opindex prebind
9921 @opindex prebind_all_twolevel_modules
9922 @opindex private_bundle
9923 @opindex read_only_relocs
9924 @opindex sectalign
9925 @opindex sectobjectsymbols
9926 @opindex whyload
9927 @opindex seg1addr
9928 @opindex sectcreate
9929 @opindex sectobjectsymbols
9930 @opindex sectorder
9931 @opindex segaddr
9932 @opindex segs_read_only_addr
9933 @opindex segs_read_write_addr
9934 @opindex seg_addr_table
9935 @opindex seg_addr_table_filename
9936 @opindex seglinkedit
9937 @opindex segprot
9938 @opindex segs_read_only_addr
9939 @opindex segs_read_write_addr
9940 @opindex single_module
9941 @opindex static
9942 @opindex sub_library
9943 @opindex sub_umbrella
9944 @opindex twolevel_namespace
9945 @opindex umbrella
9946 @opindex undefined
9947 @opindex unexported_symbols_list
9948 @opindex weak_reference_mismatches
9949 @opindex whatsloaded
9950 These options are passed to the Darwin linker. The Darwin linker man page
9951 describes them in detail.
9952 @end table
9953
9954 @node DEC Alpha Options
9955 @subsection DEC Alpha Options
9956
9957 These @samp{-m} options are defined for the DEC Alpha implementations:
9958
9959 @table @gcctabopt
9960 @item -mno-soft-float
9961 @itemx -msoft-float
9962 @opindex mno-soft-float
9963 @opindex msoft-float
9964 Use (do not use) the hardware floating-point instructions for
9965 floating-point operations. When @option{-msoft-float} is specified,
9966 functions in @file{libgcc.a} will be used to perform floating-point
9967 operations. Unless they are replaced by routines that emulate the
9968 floating-point operations, or compiled in such a way as to call such
9969 emulations routines, these routines will issue floating-point
9970 operations. If you are compiling for an Alpha without floating-point
9971 operations, you must ensure that the library is built so as not to call
9972 them.
9973
9974 Note that Alpha implementations without floating-point operations are
9975 required to have floating-point registers.
9976
9977 @item -mfp-reg
9978 @itemx -mno-fp-regs
9979 @opindex mfp-reg
9980 @opindex mno-fp-regs
9981 Generate code that uses (does not use) the floating-point register set.
9982 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
9983 register set is not used, floating point operands are passed in integer
9984 registers as if they were integers and floating-point results are passed
9985 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
9986 so any function with a floating-point argument or return value called by code
9987 compiled with @option{-mno-fp-regs} must also be compiled with that
9988 option.
9989
9990 A typical use of this option is building a kernel that does not use,
9991 and hence need not save and restore, any floating-point registers.
9992
9993 @item -mieee
9994 @opindex mieee
9995 The Alpha architecture implements floating-point hardware optimized for
9996 maximum performance. It is mostly compliant with the IEEE floating
9997 point standard. However, for full compliance, software assistance is
9998 required. This option generates code fully IEEE compliant code
9999 @emph{except} that the @var{inexact-flag} is not maintained (see below).
10000 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
10001 defined during compilation. The resulting code is less efficient but is
10002 able to correctly support denormalized numbers and exceptional IEEE
10003 values such as not-a-number and plus/minus infinity. Other Alpha
10004 compilers call this option @option{-ieee_with_no_inexact}.
10005
10006 @item -mieee-with-inexact
10007 @opindex mieee-with-inexact
10008 This is like @option{-mieee} except the generated code also maintains
10009 the IEEE @var{inexact-flag}. Turning on this option causes the
10010 generated code to implement fully-compliant IEEE math. In addition to
10011 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
10012 macro. On some Alpha implementations the resulting code may execute
10013 significantly slower than the code generated by default. Since there is
10014 very little code that depends on the @var{inexact-flag}, you should
10015 normally not specify this option. Other Alpha compilers call this
10016 option @option{-ieee_with_inexact}.
10017
10018 @item -mfp-trap-mode=@var{trap-mode}
10019 @opindex mfp-trap-mode
10020 This option controls what floating-point related traps are enabled.
10021 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
10022 The trap mode can be set to one of four values:
10023
10024 @table @samp
10025 @item n
10026 This is the default (normal) setting. The only traps that are enabled
10027 are the ones that cannot be disabled in software (e.g., division by zero
10028 trap).
10029
10030 @item u
10031 In addition to the traps enabled by @samp{n}, underflow traps are enabled
10032 as well.
10033
10034 @item su
10035 Like @samp{u}, but the instructions are marked to be safe for software
10036 completion (see Alpha architecture manual for details).
10037
10038 @item sui
10039 Like @samp{su}, but inexact traps are enabled as well.
10040 @end table
10041
10042 @item -mfp-rounding-mode=@var{rounding-mode}
10043 @opindex mfp-rounding-mode
10044 Selects the IEEE rounding mode. Other Alpha compilers call this option
10045 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
10046 of:
10047
10048 @table @samp
10049 @item n
10050 Normal IEEE rounding mode. Floating point numbers are rounded towards
10051 the nearest machine number or towards the even machine number in case
10052 of a tie.
10053
10054 @item m
10055 Round towards minus infinity.
10056
10057 @item c
10058 Chopped rounding mode. Floating point numbers are rounded towards zero.
10059
10060 @item d
10061 Dynamic rounding mode. A field in the floating point control register
10062 (@var{fpcr}, see Alpha architecture reference manual) controls the
10063 rounding mode in effect. The C library initializes this register for
10064 rounding towards plus infinity. Thus, unless your program modifies the
10065 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
10066 @end table
10067
10068 @item -mtrap-precision=@var{trap-precision}
10069 @opindex mtrap-precision
10070 In the Alpha architecture, floating point traps are imprecise. This
10071 means without software assistance it is impossible to recover from a
10072 floating trap and program execution normally needs to be terminated.
10073 GCC can generate code that can assist operating system trap handlers
10074 in determining the exact location that caused a floating point trap.
10075 Depending on the requirements of an application, different levels of
10076 precisions can be selected:
10077
10078 @table @samp
10079 @item p
10080 Program precision. This option is the default and means a trap handler
10081 can only identify which program caused a floating point exception.
10082
10083 @item f
10084 Function precision. The trap handler can determine the function that
10085 caused a floating point exception.
10086
10087 @item i
10088 Instruction precision. The trap handler can determine the exact
10089 instruction that caused a floating point exception.
10090 @end table
10091
10092 Other Alpha compilers provide the equivalent options called
10093 @option{-scope_safe} and @option{-resumption_safe}.
10094
10095 @item -mieee-conformant
10096 @opindex mieee-conformant
10097 This option marks the generated code as IEEE conformant. You must not
10098 use this option unless you also specify @option{-mtrap-precision=i} and either
10099 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
10100 is to emit the line @samp{.eflag 48} in the function prologue of the
10101 generated assembly file. Under DEC Unix, this has the effect that
10102 IEEE-conformant math library routines will be linked in.
10103
10104 @item -mbuild-constants
10105 @opindex mbuild-constants
10106 Normally GCC examines a 32- or 64-bit integer constant to
10107 see if it can construct it from smaller constants in two or three
10108 instructions. If it cannot, it will output the constant as a literal and
10109 generate code to load it from the data segment at runtime.
10110
10111 Use this option to require GCC to construct @emph{all} integer constants
10112 using code, even if it takes more instructions (the maximum is six).
10113
10114 You would typically use this option to build a shared library dynamic
10115 loader. Itself a shared library, it must relocate itself in memory
10116 before it can find the variables and constants in its own data segment.
10117
10118 @item -malpha-as
10119 @itemx -mgas
10120 @opindex malpha-as
10121 @opindex mgas
10122 Select whether to generate code to be assembled by the vendor-supplied
10123 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
10124
10125 @item -mbwx
10126 @itemx -mno-bwx
10127 @itemx -mcix
10128 @itemx -mno-cix
10129 @itemx -mfix
10130 @itemx -mno-fix
10131 @itemx -mmax
10132 @itemx -mno-max
10133 @opindex mbwx
10134 @opindex mno-bwx
10135 @opindex mcix
10136 @opindex mno-cix
10137 @opindex mfix
10138 @opindex mno-fix
10139 @opindex mmax
10140 @opindex mno-max
10141 Indicate whether GCC should generate code to use the optional BWX,
10142 CIX, FIX and MAX instruction sets. The default is to use the instruction
10143 sets supported by the CPU type specified via @option{-mcpu=} option or that
10144 of the CPU on which GCC was built if none was specified.
10145
10146 @item -mfloat-vax
10147 @itemx -mfloat-ieee
10148 @opindex mfloat-vax
10149 @opindex mfloat-ieee
10150 Generate code that uses (does not use) VAX F and G floating point
10151 arithmetic instead of IEEE single and double precision.
10152
10153 @item -mexplicit-relocs
10154 @itemx -mno-explicit-relocs
10155 @opindex mexplicit-relocs
10156 @opindex mno-explicit-relocs
10157 Older Alpha assemblers provided no way to generate symbol relocations
10158 except via assembler macros. Use of these macros does not allow
10159 optimal instruction scheduling. GNU binutils as of version 2.12
10160 supports a new syntax that allows the compiler to explicitly mark
10161 which relocations should apply to which instructions. This option
10162 is mostly useful for debugging, as GCC detects the capabilities of
10163 the assembler when it is built and sets the default accordingly.
10164
10165 @item -msmall-data
10166 @itemx -mlarge-data
10167 @opindex msmall-data
10168 @opindex mlarge-data
10169 When @option{-mexplicit-relocs} is in effect, static data is
10170 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
10171 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
10172 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
10173 16-bit relocations off of the @code{$gp} register. This limits the
10174 size of the small data area to 64KB, but allows the variables to be
10175 directly accessed via a single instruction.
10176
10177 The default is @option{-mlarge-data}. With this option the data area
10178 is limited to just below 2GB@. Programs that require more than 2GB of
10179 data must use @code{malloc} or @code{mmap} to allocate the data in the
10180 heap instead of in the program's data segment.
10181
10182 When generating code for shared libraries, @option{-fpic} implies
10183 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
10184
10185 @item -msmall-text
10186 @itemx -mlarge-text
10187 @opindex msmall-text
10188 @opindex mlarge-text
10189 When @option{-msmall-text} is used, the compiler assumes that the
10190 code of the entire program (or shared library) fits in 4MB, and is
10191 thus reachable with a branch instruction. When @option{-msmall-data}
10192 is used, the compiler can assume that all local symbols share the
10193 same @code{$gp} value, and thus reduce the number of instructions
10194 required for a function call from 4 to 1.
10195
10196 The default is @option{-mlarge-text}.
10197
10198 @item -mcpu=@var{cpu_type}
10199 @opindex mcpu
10200 Set the instruction set and instruction scheduling parameters for
10201 machine type @var{cpu_type}. You can specify either the @samp{EV}
10202 style name or the corresponding chip number. GCC supports scheduling
10203 parameters for the EV4, EV5 and EV6 family of processors and will
10204 choose the default values for the instruction set from the processor
10205 you specify. If you do not specify a processor type, GCC will default
10206 to the processor on which the compiler was built.
10207
10208 Supported values for @var{cpu_type} are
10209
10210 @table @samp
10211 @item ev4
10212 @itemx ev45
10213 @itemx 21064
10214 Schedules as an EV4 and has no instruction set extensions.
10215
10216 @item ev5
10217 @itemx 21164
10218 Schedules as an EV5 and has no instruction set extensions.
10219
10220 @item ev56
10221 @itemx 21164a
10222 Schedules as an EV5 and supports the BWX extension.
10223
10224 @item pca56
10225 @itemx 21164pc
10226 @itemx 21164PC
10227 Schedules as an EV5 and supports the BWX and MAX extensions.
10228
10229 @item ev6
10230 @itemx 21264
10231 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
10232
10233 @item ev67
10234 @itemx 21264a
10235 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
10236 @end table
10237
10238 Native Linux/GNU toolchains also support the value @samp{native},
10239 which selects the best architecture option for the host processor.
10240 @option{-mcpu=native} has no effect if GCC does not recognize
10241 the processor.
10242
10243 @item -mtune=@var{cpu_type}
10244 @opindex mtune
10245 Set only the instruction scheduling parameters for machine type
10246 @var{cpu_type}. The instruction set is not changed.
10247
10248 Native Linux/GNU toolchains also support the value @samp{native},
10249 which selects the best architecture option for the host processor.
10250 @option{-mtune=native} has no effect if GCC does not recognize
10251 the processor.
10252
10253 @item -mmemory-latency=@var{time}
10254 @opindex mmemory-latency
10255 Sets the latency the scheduler should assume for typical memory
10256 references as seen by the application. This number is highly
10257 dependent on the memory access patterns used by the application
10258 and the size of the external cache on the machine.
10259
10260 Valid options for @var{time} are
10261
10262 @table @samp
10263 @item @var{number}
10264 A decimal number representing clock cycles.
10265
10266 @item L1
10267 @itemx L2
10268 @itemx L3
10269 @itemx main
10270 The compiler contains estimates of the number of clock cycles for
10271 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
10272 (also called Dcache, Scache, and Bcache), as well as to main memory.
10273 Note that L3 is only valid for EV5.
10274
10275 @end table
10276 @end table
10277
10278 @node DEC Alpha/VMS Options
10279 @subsection DEC Alpha/VMS Options
10280
10281 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
10282
10283 @table @gcctabopt
10284 @item -mvms-return-codes
10285 @opindex mvms-return-codes
10286 Return VMS condition codes from main. The default is to return POSIX
10287 style condition (e.g.@: error) codes.
10288 @end table
10289
10290 @node FR30 Options
10291 @subsection FR30 Options
10292 @cindex FR30 Options
10293
10294 These options are defined specifically for the FR30 port.
10295
10296 @table @gcctabopt
10297
10298 @item -msmall-model
10299 @opindex msmall-model
10300 Use the small address space model. This can produce smaller code, but
10301 it does assume that all symbolic values and addresses will fit into a
10302 20-bit range.
10303
10304 @item -mno-lsim
10305 @opindex mno-lsim
10306 Assume that run-time support has been provided and so there is no need
10307 to include the simulator library (@file{libsim.a}) on the linker
10308 command line.
10309
10310 @end table
10311
10312 @node FRV Options
10313 @subsection FRV Options
10314 @cindex FRV Options
10315
10316 @table @gcctabopt
10317 @item -mgpr-32
10318 @opindex mgpr-32
10319
10320 Only use the first 32 general purpose registers.
10321
10322 @item -mgpr-64
10323 @opindex mgpr-64
10324
10325 Use all 64 general purpose registers.
10326
10327 @item -mfpr-32
10328 @opindex mfpr-32
10329
10330 Use only the first 32 floating point registers.
10331
10332 @item -mfpr-64
10333 @opindex mfpr-64
10334
10335 Use all 64 floating point registers
10336
10337 @item -mhard-float
10338 @opindex mhard-float
10339
10340 Use hardware instructions for floating point operations.
10341
10342 @item -msoft-float
10343 @opindex msoft-float
10344
10345 Use library routines for floating point operations.
10346
10347 @item -malloc-cc
10348 @opindex malloc-cc
10349
10350 Dynamically allocate condition code registers.
10351
10352 @item -mfixed-cc
10353 @opindex mfixed-cc
10354
10355 Do not try to dynamically allocate condition code registers, only
10356 use @code{icc0} and @code{fcc0}.
10357
10358 @item -mdword
10359 @opindex mdword
10360
10361 Change ABI to use double word insns.
10362
10363 @item -mno-dword
10364 @opindex mno-dword
10365
10366 Do not use double word instructions.
10367
10368 @item -mdouble
10369 @opindex mdouble
10370
10371 Use floating point double instructions.
10372
10373 @item -mno-double
10374 @opindex mno-double
10375
10376 Do not use floating point double instructions.
10377
10378 @item -mmedia
10379 @opindex mmedia
10380
10381 Use media instructions.
10382
10383 @item -mno-media
10384 @opindex mno-media
10385
10386 Do not use media instructions.
10387
10388 @item -mmuladd
10389 @opindex mmuladd
10390
10391 Use multiply and add/subtract instructions.
10392
10393 @item -mno-muladd
10394 @opindex mno-muladd
10395
10396 Do not use multiply and add/subtract instructions.
10397
10398 @item -mfdpic
10399 @opindex mfdpic
10400
10401 Select the FDPIC ABI, that uses function descriptors to represent
10402 pointers to functions. Without any PIC/PIE-related options, it
10403 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
10404 assumes GOT entries and small data are within a 12-bit range from the
10405 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
10406 are computed with 32 bits.
10407 With a @samp{bfin-elf} target, this option implies @option{-msim}.
10408
10409 @item -minline-plt
10410 @opindex minline-plt
10411
10412 Enable inlining of PLT entries in function calls to functions that are
10413 not known to bind locally. It has no effect without @option{-mfdpic}.
10414 It's enabled by default if optimizing for speed and compiling for
10415 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
10416 optimization option such as @option{-O3} or above is present in the
10417 command line.
10418
10419 @item -mTLS
10420 @opindex TLS
10421
10422 Assume a large TLS segment when generating thread-local code.
10423
10424 @item -mtls
10425 @opindex tls
10426
10427 Do not assume a large TLS segment when generating thread-local code.
10428
10429 @item -mgprel-ro
10430 @opindex mgprel-ro
10431
10432 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
10433 that is known to be in read-only sections. It's enabled by default,
10434 except for @option{-fpic} or @option{-fpie}: even though it may help
10435 make the global offset table smaller, it trades 1 instruction for 4.
10436 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
10437 one of which may be shared by multiple symbols, and it avoids the need
10438 for a GOT entry for the referenced symbol, so it's more likely to be a
10439 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
10440
10441 @item -multilib-library-pic
10442 @opindex multilib-library-pic
10443
10444 Link with the (library, not FD) pic libraries. It's implied by
10445 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
10446 @option{-fpic} without @option{-mfdpic}. You should never have to use
10447 it explicitly.
10448
10449 @item -mlinked-fp
10450 @opindex mlinked-fp
10451
10452 Follow the EABI requirement of always creating a frame pointer whenever
10453 a stack frame is allocated. This option is enabled by default and can
10454 be disabled with @option{-mno-linked-fp}.
10455
10456 @item -mlong-calls
10457 @opindex mlong-calls
10458
10459 Use indirect addressing to call functions outside the current
10460 compilation unit. This allows the functions to be placed anywhere
10461 within the 32-bit address space.
10462
10463 @item -malign-labels
10464 @opindex malign-labels
10465
10466 Try to align labels to an 8-byte boundary by inserting nops into the
10467 previous packet. This option only has an effect when VLIW packing
10468 is enabled. It doesn't create new packets; it merely adds nops to
10469 existing ones.
10470
10471 @item -mlibrary-pic
10472 @opindex mlibrary-pic
10473
10474 Generate position-independent EABI code.
10475
10476 @item -macc-4
10477 @opindex macc-4
10478
10479 Use only the first four media accumulator registers.
10480
10481 @item -macc-8
10482 @opindex macc-8
10483
10484 Use all eight media accumulator registers.
10485
10486 @item -mpack
10487 @opindex mpack
10488
10489 Pack VLIW instructions.
10490
10491 @item -mno-pack
10492 @opindex mno-pack
10493
10494 Do not pack VLIW instructions.
10495
10496 @item -mno-eflags
10497 @opindex mno-eflags
10498
10499 Do not mark ABI switches in e_flags.
10500
10501 @item -mcond-move
10502 @opindex mcond-move
10503
10504 Enable the use of conditional-move instructions (default).
10505
10506 This switch is mainly for debugging the compiler and will likely be removed
10507 in a future version.
10508
10509 @item -mno-cond-move
10510 @opindex mno-cond-move
10511
10512 Disable the use of conditional-move instructions.
10513
10514 This switch is mainly for debugging the compiler and will likely be removed
10515 in a future version.
10516
10517 @item -mscc
10518 @opindex mscc
10519
10520 Enable the use of conditional set instructions (default).
10521
10522 This switch is mainly for debugging the compiler and will likely be removed
10523 in a future version.
10524
10525 @item -mno-scc
10526 @opindex mno-scc
10527
10528 Disable the use of conditional set instructions.
10529
10530 This switch is mainly for debugging the compiler and will likely be removed
10531 in a future version.
10532
10533 @item -mcond-exec
10534 @opindex mcond-exec
10535
10536 Enable the use of conditional execution (default).
10537
10538 This switch is mainly for debugging the compiler and will likely be removed
10539 in a future version.
10540
10541 @item -mno-cond-exec
10542 @opindex mno-cond-exec
10543
10544 Disable the use of conditional execution.
10545
10546 This switch is mainly for debugging the compiler and will likely be removed
10547 in a future version.
10548
10549 @item -mvliw-branch
10550 @opindex mvliw-branch
10551
10552 Run a pass to pack branches into VLIW instructions (default).
10553
10554 This switch is mainly for debugging the compiler and will likely be removed
10555 in a future version.
10556
10557 @item -mno-vliw-branch
10558 @opindex mno-vliw-branch
10559
10560 Do not run a pass to pack branches into VLIW instructions.
10561
10562 This switch is mainly for debugging the compiler and will likely be removed
10563 in a future version.
10564
10565 @item -mmulti-cond-exec
10566 @opindex mmulti-cond-exec
10567
10568 Enable optimization of @code{&&} and @code{||} in conditional execution
10569 (default).
10570
10571 This switch is mainly for debugging the compiler and will likely be removed
10572 in a future version.
10573
10574 @item -mno-multi-cond-exec
10575 @opindex mno-multi-cond-exec
10576
10577 Disable optimization of @code{&&} and @code{||} in conditional execution.
10578
10579 This switch is mainly for debugging the compiler and will likely be removed
10580 in a future version.
10581
10582 @item -mnested-cond-exec
10583 @opindex mnested-cond-exec
10584
10585 Enable nested conditional execution optimizations (default).
10586
10587 This switch is mainly for debugging the compiler and will likely be removed
10588 in a future version.
10589
10590 @item -mno-nested-cond-exec
10591 @opindex mno-nested-cond-exec
10592
10593 Disable nested conditional execution optimizations.
10594
10595 This switch is mainly for debugging the compiler and will likely be removed
10596 in a future version.
10597
10598 @item -moptimize-membar
10599 @opindex moptimize-membar
10600
10601 This switch removes redundant @code{membar} instructions from the
10602 compiler generated code. It is enabled by default.
10603
10604 @item -mno-optimize-membar
10605 @opindex mno-optimize-membar
10606
10607 This switch disables the automatic removal of redundant @code{membar}
10608 instructions from the generated code.
10609
10610 @item -mtomcat-stats
10611 @opindex mtomcat-stats
10612
10613 Cause gas to print out tomcat statistics.
10614
10615 @item -mcpu=@var{cpu}
10616 @opindex mcpu
10617
10618 Select the processor type for which to generate code. Possible values are
10619 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
10620 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
10621
10622 @end table
10623
10624 @node GNU/Linux Options
10625 @subsection GNU/Linux Options
10626
10627 These @samp{-m} options are defined for GNU/Linux targets:
10628
10629 @table @gcctabopt
10630 @item -mglibc
10631 @opindex mglibc
10632 Use the GNU C library instead of uClibc. This is the default except
10633 on @samp{*-*-linux-*uclibc*} targets.
10634
10635 @item -muclibc
10636 @opindex muclibc
10637 Use uClibc instead of the GNU C library. This is the default on
10638 @samp{*-*-linux-*uclibc*} targets.
10639 @end table
10640
10641 @node H8/300 Options
10642 @subsection H8/300 Options
10643
10644 These @samp{-m} options are defined for the H8/300 implementations:
10645
10646 @table @gcctabopt
10647 @item -mrelax
10648 @opindex mrelax
10649 Shorten some address references at link time, when possible; uses the
10650 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
10651 ld, Using ld}, for a fuller description.
10652
10653 @item -mh
10654 @opindex mh
10655 Generate code for the H8/300H@.
10656
10657 @item -ms
10658 @opindex ms
10659 Generate code for the H8S@.
10660
10661 @item -mn
10662 @opindex mn
10663 Generate code for the H8S and H8/300H in the normal mode. This switch
10664 must be used either with @option{-mh} or @option{-ms}.
10665
10666 @item -ms2600
10667 @opindex ms2600
10668 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
10669
10670 @item -mint32
10671 @opindex mint32
10672 Make @code{int} data 32 bits by default.
10673
10674 @item -malign-300
10675 @opindex malign-300
10676 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
10677 The default for the H8/300H and H8S is to align longs and floats on 4
10678 byte boundaries.
10679 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
10680 This option has no effect on the H8/300.
10681 @end table
10682
10683 @node HPPA Options
10684 @subsection HPPA Options
10685 @cindex HPPA Options
10686
10687 These @samp{-m} options are defined for the HPPA family of computers:
10688
10689 @table @gcctabopt
10690 @item -march=@var{architecture-type}
10691 @opindex march
10692 Generate code for the specified architecture. The choices for
10693 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
10694 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
10695 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
10696 architecture option for your machine. Code compiled for lower numbered
10697 architectures will run on higher numbered architectures, but not the
10698 other way around.
10699
10700 @item -mpa-risc-1-0
10701 @itemx -mpa-risc-1-1
10702 @itemx -mpa-risc-2-0
10703 @opindex mpa-risc-1-0
10704 @opindex mpa-risc-1-1
10705 @opindex mpa-risc-2-0
10706 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
10707
10708 @item -mbig-switch
10709 @opindex mbig-switch
10710 Generate code suitable for big switch tables. Use this option only if
10711 the assembler/linker complain about out of range branches within a switch
10712 table.
10713
10714 @item -mjump-in-delay
10715 @opindex mjump-in-delay
10716 Fill delay slots of function calls with unconditional jump instructions
10717 by modifying the return pointer for the function call to be the target
10718 of the conditional jump.
10719
10720 @item -mdisable-fpregs
10721 @opindex mdisable-fpregs
10722 Prevent floating point registers from being used in any manner. This is
10723 necessary for compiling kernels which perform lazy context switching of
10724 floating point registers. If you use this option and attempt to perform
10725 floating point operations, the compiler will abort.
10726
10727 @item -mdisable-indexing
10728 @opindex mdisable-indexing
10729 Prevent the compiler from using indexing address modes. This avoids some
10730 rather obscure problems when compiling MIG generated code under MACH@.
10731
10732 @item -mno-space-regs
10733 @opindex mno-space-regs
10734 Generate code that assumes the target has no space registers. This allows
10735 GCC to generate faster indirect calls and use unscaled index address modes.
10736
10737 Such code is suitable for level 0 PA systems and kernels.
10738
10739 @item -mfast-indirect-calls
10740 @opindex mfast-indirect-calls
10741 Generate code that assumes calls never cross space boundaries. This
10742 allows GCC to emit code which performs faster indirect calls.
10743
10744 This option will not work in the presence of shared libraries or nested
10745 functions.
10746
10747 @item -mfixed-range=@var{register-range}
10748 @opindex mfixed-range
10749 Generate code treating the given register range as fixed registers.
10750 A fixed register is one that the register allocator can not use. This is
10751 useful when compiling kernel code. A register range is specified as
10752 two registers separated by a dash. Multiple register ranges can be
10753 specified separated by a comma.
10754
10755 @item -mlong-load-store
10756 @opindex mlong-load-store
10757 Generate 3-instruction load and store sequences as sometimes required by
10758 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
10759 the HP compilers.
10760
10761 @item -mportable-runtime
10762 @opindex mportable-runtime
10763 Use the portable calling conventions proposed by HP for ELF systems.
10764
10765 @item -mgas
10766 @opindex mgas
10767 Enable the use of assembler directives only GAS understands.
10768
10769 @item -mschedule=@var{cpu-type}
10770 @opindex mschedule
10771 Schedule code according to the constraints for the machine type
10772 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
10773 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
10774 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
10775 proper scheduling option for your machine. The default scheduling is
10776 @samp{8000}.
10777
10778 @item -mlinker-opt
10779 @opindex mlinker-opt
10780 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
10781 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
10782 linkers in which they give bogus error messages when linking some programs.
10783
10784 @item -msoft-float
10785 @opindex msoft-float
10786 Generate output containing library calls for floating point.
10787 @strong{Warning:} the requisite libraries are not available for all HPPA
10788 targets. Normally the facilities of the machine's usual C compiler are
10789 used, but this cannot be done directly in cross-compilation. You must make
10790 your own arrangements to provide suitable library functions for
10791 cross-compilation.
10792
10793 @option{-msoft-float} changes the calling convention in the output file;
10794 therefore, it is only useful if you compile @emph{all} of a program with
10795 this option. In particular, you need to compile @file{libgcc.a}, the
10796 library that comes with GCC, with @option{-msoft-float} in order for
10797 this to work.
10798
10799 @item -msio
10800 @opindex msio
10801 Generate the predefine, @code{_SIO}, for server IO@. The default is
10802 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
10803 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
10804 options are available under HP-UX and HI-UX@.
10805
10806 @item -mgnu-ld
10807 @opindex gnu-ld
10808 Use GNU ld specific options. This passes @option{-shared} to ld when
10809 building a shared library. It is the default when GCC is configured,
10810 explicitly or implicitly, with the GNU linker. This option does not
10811 have any affect on which ld is called, it only changes what parameters
10812 are passed to that ld. The ld that is called is determined by the
10813 @option{--with-ld} configure option, GCC's program search path, and
10814 finally by the user's @env{PATH}. The linker used by GCC can be printed
10815 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
10816 on the 64 bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10817
10818 @item -mhp-ld
10819 @opindex hp-ld
10820 Use HP ld specific options. This passes @option{-b} to ld when building
10821 a shared library and passes @option{+Accept TypeMismatch} to ld on all
10822 links. It is the default when GCC is configured, explicitly or
10823 implicitly, with the HP linker. This option does not have any affect on
10824 which ld is called, it only changes what parameters are passed to that
10825 ld. The ld that is called is determined by the @option{--with-ld}
10826 configure option, GCC's program search path, and finally by the user's
10827 @env{PATH}. The linker used by GCC can be printed using @samp{which
10828 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
10829 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10830
10831 @item -mlong-calls
10832 @opindex mno-long-calls
10833 Generate code that uses long call sequences. This ensures that a call
10834 is always able to reach linker generated stubs. The default is to generate
10835 long calls only when the distance from the call site to the beginning
10836 of the function or translation unit, as the case may be, exceeds a
10837 predefined limit set by the branch type being used. The limits for
10838 normal calls are 7,600,000 and 240,000 bytes, respectively for the
10839 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
10840 240,000 bytes.
10841
10842 Distances are measured from the beginning of functions when using the
10843 @option{-ffunction-sections} option, or when using the @option{-mgas}
10844 and @option{-mno-portable-runtime} options together under HP-UX with
10845 the SOM linker.
10846
10847 It is normally not desirable to use this option as it will degrade
10848 performance. However, it may be useful in large applications,
10849 particularly when partial linking is used to build the application.
10850
10851 The types of long calls used depends on the capabilities of the
10852 assembler and linker, and the type of code being generated. The
10853 impact on systems that support long absolute calls, and long pic
10854 symbol-difference or pc-relative calls should be relatively small.
10855 However, an indirect call is used on 32-bit ELF systems in pic code
10856 and it is quite long.
10857
10858 @item -munix=@var{unix-std}
10859 @opindex march
10860 Generate compiler predefines and select a startfile for the specified
10861 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
10862 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
10863 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
10864 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
10865 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
10866 and later.
10867
10868 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
10869 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
10870 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
10871 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
10872 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
10873 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
10874
10875 It is @emph{important} to note that this option changes the interfaces
10876 for various library routines. It also affects the operational behavior
10877 of the C library. Thus, @emph{extreme} care is needed in using this
10878 option.
10879
10880 Library code that is intended to operate with more than one UNIX
10881 standard must test, set and restore the variable @var{__xpg4_extended_mask}
10882 as appropriate. Most GNU software doesn't provide this capability.
10883
10884 @item -nolibdld
10885 @opindex nolibdld
10886 Suppress the generation of link options to search libdld.sl when the
10887 @option{-static} option is specified on HP-UX 10 and later.
10888
10889 @item -static
10890 @opindex static
10891 The HP-UX implementation of setlocale in libc has a dependency on
10892 libdld.sl. There isn't an archive version of libdld.sl. Thus,
10893 when the @option{-static} option is specified, special link options
10894 are needed to resolve this dependency.
10895
10896 On HP-UX 10 and later, the GCC driver adds the necessary options to
10897 link with libdld.sl when the @option{-static} option is specified.
10898 This causes the resulting binary to be dynamic. On the 64-bit port,
10899 the linkers generate dynamic binaries by default in any case. The
10900 @option{-nolibdld} option can be used to prevent the GCC driver from
10901 adding these link options.
10902
10903 @item -threads
10904 @opindex threads
10905 Add support for multithreading with the @dfn{dce thread} library
10906 under HP-UX@. This option sets flags for both the preprocessor and
10907 linker.
10908 @end table
10909
10910 @node i386 and x86-64 Options
10911 @subsection Intel 386 and AMD x86-64 Options
10912 @cindex i386 Options
10913 @cindex x86-64 Options
10914 @cindex Intel 386 Options
10915 @cindex AMD x86-64 Options
10916
10917 These @samp{-m} options are defined for the i386 and x86-64 family of
10918 computers:
10919
10920 @table @gcctabopt
10921 @item -mtune=@var{cpu-type}
10922 @opindex mtune
10923 Tune to @var{cpu-type} everything applicable about the generated code, except
10924 for the ABI and the set of available instructions. The choices for
10925 @var{cpu-type} are:
10926 @table @emph
10927 @item generic
10928 Produce code optimized for the most common IA32/AMD64/EM64T processors.
10929 If you know the CPU on which your code will run, then you should use
10930 the corresponding @option{-mtune} option instead of
10931 @option{-mtune=generic}. But, if you do not know exactly what CPU users
10932 of your application will have, then you should use this option.
10933
10934 As new processors are deployed in the marketplace, the behavior of this
10935 option will change. Therefore, if you upgrade to a newer version of
10936 GCC, the code generated option will change to reflect the processors
10937 that were most common when that version of GCC was released.
10938
10939 There is no @option{-march=generic} option because @option{-march}
10940 indicates the instruction set the compiler can use, and there is no
10941 generic instruction set applicable to all processors. In contrast,
10942 @option{-mtune} indicates the processor (or, in this case, collection of
10943 processors) for which the code is optimized.
10944 @item native
10945 This selects the CPU to tune for at compilation time by determining
10946 the processor type of the compiling machine. Using @option{-mtune=native}
10947 will produce code optimized for the local machine under the constraints
10948 of the selected instruction set. Using @option{-march=native} will
10949 enable all instruction subsets supported by the local machine (hence
10950 the result might not run on different machines).
10951 @item i386
10952 Original Intel's i386 CPU@.
10953 @item i486
10954 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
10955 @item i586, pentium
10956 Intel Pentium CPU with no MMX support.
10957 @item pentium-mmx
10958 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
10959 @item pentiumpro
10960 Intel PentiumPro CPU@.
10961 @item i686
10962 Same as @code{generic}, but when used as @code{march} option, PentiumPro
10963 instruction set will be used, so the code will run on all i686 family chips.
10964 @item pentium2
10965 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
10966 @item pentium3, pentium3m
10967 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
10968 support.
10969 @item pentium-m
10970 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
10971 support. Used by Centrino notebooks.
10972 @item pentium4, pentium4m
10973 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
10974 @item prescott
10975 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
10976 set support.
10977 @item nocona
10978 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
10979 SSE2 and SSE3 instruction set support.
10980 @item core2
10981 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
10982 instruction set support.
10983 @item k6
10984 AMD K6 CPU with MMX instruction set support.
10985 @item k6-2, k6-3
10986 Improved versions of AMD K6 CPU with MMX and 3dNOW!@: instruction set support.
10987 @item athlon, athlon-tbird
10988 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and SSE prefetch instructions
10989 support.
10990 @item athlon-4, athlon-xp, athlon-mp
10991 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and full SSE
10992 instruction set support.
10993 @item k8, opteron, athlon64, athlon-fx
10994 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
10995 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW!@: and 64-bit instruction set extensions.)
10996 @item k8-sse3, opteron-sse3, athlon64-sse3
10997 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
10998 @item amdfam10, barcelona
10999 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
11000 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3dNOW!, enhanced 3dNOW!, ABM and 64-bit
11001 instruction set extensions.)
11002 @item winchip-c6
11003 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
11004 set support.
11005 @item winchip2
11006 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!@:
11007 instruction set support.
11008 @item c3
11009 Via C3 CPU with MMX and 3dNOW!@: instruction set support. (No scheduling is
11010 implemented for this chip.)
11011 @item c3-2
11012 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
11013 implemented for this chip.)
11014 @item geode
11015 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
11016 @end table
11017
11018 While picking a specific @var{cpu-type} will schedule things appropriately
11019 for that particular chip, the compiler will not generate any code that
11020 does not run on the i386 without the @option{-march=@var{cpu-type}} option
11021 being used.
11022
11023 @item -march=@var{cpu-type}
11024 @opindex march
11025 Generate instructions for the machine type @var{cpu-type}. The choices
11026 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
11027 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
11028
11029 @item -mcpu=@var{cpu-type}
11030 @opindex mcpu
11031 A deprecated synonym for @option{-mtune}.
11032
11033 @item -mfpmath=@var{unit}
11034 @opindex march
11035 Generate floating point arithmetics for selected unit @var{unit}. The choices
11036 for @var{unit} are:
11037
11038 @table @samp
11039 @item 387
11040 Use the standard 387 floating point coprocessor present majority of chips and
11041 emulated otherwise. Code compiled with this option will run almost everywhere.
11042 The temporary results are computed in 80bit precision instead of precision
11043 specified by the type resulting in slightly different results compared to most
11044 of other chips. See @option{-ffloat-store} for more detailed description.
11045
11046 This is the default choice for i386 compiler.
11047
11048 @item sse
11049 Use scalar floating point instructions present in the SSE instruction set.
11050 This instruction set is supported by Pentium3 and newer chips, in the AMD line
11051 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
11052 instruction set supports only single precision arithmetics, thus the double and
11053 extended precision arithmetics is still done using 387. Later version, present
11054 only in Pentium4 and the future AMD x86-64 chips supports double precision
11055 arithmetics too.
11056
11057 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
11058 or @option{-msse2} switches to enable SSE extensions and make this option
11059 effective. For the x86-64 compiler, these extensions are enabled by default.
11060
11061 The resulting code should be considerably faster in the majority of cases and avoid
11062 the numerical instability problems of 387 code, but may break some existing
11063 code that expects temporaries to be 80bit.
11064
11065 This is the default choice for the x86-64 compiler.
11066
11067 @item sse,387
11068 @itemx sse+387
11069 @itemx both
11070 Attempt to utilize both instruction sets at once. This effectively double the
11071 amount of available registers and on chips with separate execution units for
11072 387 and SSE the execution resources too. Use this option with care, as it is
11073 still experimental, because the GCC register allocator does not model separate
11074 functional units well resulting in instable performance.
11075 @end table
11076
11077 @item -masm=@var{dialect}
11078 @opindex masm=@var{dialect}
11079 Output asm instructions using selected @var{dialect}. Supported
11080 choices are @samp{intel} or @samp{att} (the default one). Darwin does
11081 not support @samp{intel}.
11082
11083 @item -mieee-fp
11084 @itemx -mno-ieee-fp
11085 @opindex mieee-fp
11086 @opindex mno-ieee-fp
11087 Control whether or not the compiler uses IEEE floating point
11088 comparisons. These handle correctly the case where the result of a
11089 comparison is unordered.
11090
11091 @item -msoft-float
11092 @opindex msoft-float
11093 Generate output containing library calls for floating point.
11094 @strong{Warning:} the requisite libraries are not part of GCC@.
11095 Normally the facilities of the machine's usual C compiler are used, but
11096 this can't be done directly in cross-compilation. You must make your
11097 own arrangements to provide suitable library functions for
11098 cross-compilation.
11099
11100 On machines where a function returns floating point results in the 80387
11101 register stack, some floating point opcodes may be emitted even if
11102 @option{-msoft-float} is used.
11103
11104 @item -mno-fp-ret-in-387
11105 @opindex mno-fp-ret-in-387
11106 Do not use the FPU registers for return values of functions.
11107
11108 The usual calling convention has functions return values of types
11109 @code{float} and @code{double} in an FPU register, even if there
11110 is no FPU@. The idea is that the operating system should emulate
11111 an FPU@.
11112
11113 The option @option{-mno-fp-ret-in-387} causes such values to be returned
11114 in ordinary CPU registers instead.
11115
11116 @item -mno-fancy-math-387
11117 @opindex mno-fancy-math-387
11118 Some 387 emulators do not support the @code{sin}, @code{cos} and
11119 @code{sqrt} instructions for the 387. Specify this option to avoid
11120 generating those instructions. This option is the default on FreeBSD,
11121 OpenBSD and NetBSD@. This option is overridden when @option{-march}
11122 indicates that the target cpu will always have an FPU and so the
11123 instruction will not need emulation. As of revision 2.6.1, these
11124 instructions are not generated unless you also use the
11125 @option{-funsafe-math-optimizations} switch.
11126
11127 @item -malign-double
11128 @itemx -mno-align-double
11129 @opindex malign-double
11130 @opindex mno-align-double
11131 Control whether GCC aligns @code{double}, @code{long double}, and
11132 @code{long long} variables on a two word boundary or a one word
11133 boundary. Aligning @code{double} variables on a two word boundary will
11134 produce code that runs somewhat faster on a @samp{Pentium} at the
11135 expense of more memory.
11136
11137 On x86-64, @option{-malign-double} is enabled by default.
11138
11139 @strong{Warning:} if you use the @option{-malign-double} switch,
11140 structures containing the above types will be aligned differently than
11141 the published application binary interface specifications for the 386
11142 and will not be binary compatible with structures in code compiled
11143 without that switch.
11144
11145 @item -m96bit-long-double
11146 @itemx -m128bit-long-double
11147 @opindex m96bit-long-double
11148 @opindex m128bit-long-double
11149 These switches control the size of @code{long double} type. The i386
11150 application binary interface specifies the size to be 96 bits,
11151 so @option{-m96bit-long-double} is the default in 32 bit mode.
11152
11153 Modern architectures (Pentium and newer) would prefer @code{long double}
11154 to be aligned to an 8 or 16 byte boundary. In arrays or structures
11155 conforming to the ABI, this would not be possible. So specifying a
11156 @option{-m128bit-long-double} will align @code{long double}
11157 to a 16 byte boundary by padding the @code{long double} with an additional
11158 32 bit zero.
11159
11160 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
11161 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
11162
11163 Notice that neither of these options enable any extra precision over the x87
11164 standard of 80 bits for a @code{long double}.
11165
11166 @strong{Warning:} if you override the default value for your target ABI, the
11167 structures and arrays containing @code{long double} variables will change
11168 their size as well as function calling convention for function taking
11169 @code{long double} will be modified. Hence they will not be binary
11170 compatible with arrays or structures in code compiled without that switch.
11171
11172 @item -mlarge-data-threshold=@var{number}
11173 @opindex mlarge-data-threshold=@var{number}
11174 When @option{-mcmodel=medium} is specified, the data greater than
11175 @var{threshold} are placed in large data section. This value must be the
11176 same across all object linked into the binary and defaults to 65535.
11177
11178 @item -mrtd
11179 @opindex mrtd
11180 Use a different function-calling convention, in which functions that
11181 take a fixed number of arguments return with the @code{ret} @var{num}
11182 instruction, which pops their arguments while returning. This saves one
11183 instruction in the caller since there is no need to pop the arguments
11184 there.
11185
11186 You can specify that an individual function is called with this calling
11187 sequence with the function attribute @samp{stdcall}. You can also
11188 override the @option{-mrtd} option by using the function attribute
11189 @samp{cdecl}. @xref{Function Attributes}.
11190
11191 @strong{Warning:} this calling convention is incompatible with the one
11192 normally used on Unix, so you cannot use it if you need to call
11193 libraries compiled with the Unix compiler.
11194
11195 Also, you must provide function prototypes for all functions that
11196 take variable numbers of arguments (including @code{printf});
11197 otherwise incorrect code will be generated for calls to those
11198 functions.
11199
11200 In addition, seriously incorrect code will result if you call a
11201 function with too many arguments. (Normally, extra arguments are
11202 harmlessly ignored.)
11203
11204 @item -mregparm=@var{num}
11205 @opindex mregparm
11206 Control how many registers are used to pass integer arguments. By
11207 default, no registers are used to pass arguments, and at most 3
11208 registers can be used. You can control this behavior for a specific
11209 function by using the function attribute @samp{regparm}.
11210 @xref{Function Attributes}.
11211
11212 @strong{Warning:} if you use this switch, and
11213 @var{num} is nonzero, then you must build all modules with the same
11214 value, including any libraries. This includes the system libraries and
11215 startup modules.
11216
11217 @item -msseregparm
11218 @opindex msseregparm
11219 Use SSE register passing conventions for float and double arguments
11220 and return values. You can control this behavior for a specific
11221 function by using the function attribute @samp{sseregparm}.
11222 @xref{Function Attributes}.
11223
11224 @strong{Warning:} if you use this switch then you must build all
11225 modules with the same value, including any libraries. This includes
11226 the system libraries and startup modules.
11227
11228 @item -mpc32
11229 @itemx -mpc64
11230 @itemx -mpc80
11231 @opindex mpc32
11232 @opindex mpc64
11233 @opindex mpc80
11234
11235 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
11236 is specified, the significands of results of floating-point operations are
11237 rounded to 24 bits (single precision); @option{-mpc64} rounds the
11238 significands of results of floating-point operations to 53 bits (double
11239 precision) and @option{-mpc80} rounds the significands of results of
11240 floating-point operations to 64 bits (extended double precision), which is
11241 the default. When this option is used, floating-point operations in higher
11242 precisions are not available to the programmer without setting the FPU
11243 control word explicitly.
11244
11245 Setting the rounding of floating-point operations to less than the default
11246 80 bits can speed some programs by 2% or more. Note that some mathematical
11247 libraries assume that extended precision (80 bit) floating-point operations
11248 are enabled by default; routines in such libraries could suffer significant
11249 loss of accuracy, typically through so-called "catastrophic cancellation",
11250 when this option is used to set the precision to less than extended precision.
11251
11252 @item -mstackrealign
11253 @opindex mstackrealign
11254 Realign the stack at entry. On the Intel x86, the @option{-mstackrealign}
11255 option will generate an alternate prologue and epilogue that realigns the
11256 runtime stack if necessary. This supports mixing legacy codes that keep
11257 a 4-byte aligned stack with modern codes that keep a 16-byte stack for
11258 SSE compatibility. See also the attribute @code{force_align_arg_pointer},
11259 applicable to individual functions.
11260
11261 @item -mpreferred-stack-boundary=@var{num}
11262 @opindex mpreferred-stack-boundary
11263 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
11264 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
11265 the default is 4 (16 bytes or 128 bits).
11266
11267 @item -mincoming-stack-boundary=@var{num}
11268 @opindex mincoming-stack-boundary
11269 Assume the incoming stack is aligned to a 2 raised to @var{num} byte
11270 boundary. If @option{-mincoming-stack-boundary} is not specified,
11271 the one specified by @option{-mpreferred-stack-boundary} will be used.
11272
11273 On Pentium and PentiumPro, @code{double} and @code{long double} values
11274 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
11275 suffer significant run time performance penalties. On Pentium III, the
11276 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
11277 properly if it is not 16 byte aligned.
11278
11279 To ensure proper alignment of this values on the stack, the stack boundary
11280 must be as aligned as that required by any value stored on the stack.
11281 Further, every function must be generated such that it keeps the stack
11282 aligned. Thus calling a function compiled with a higher preferred
11283 stack boundary from a function compiled with a lower preferred stack
11284 boundary will most likely misalign the stack. It is recommended that
11285 libraries that use callbacks always use the default setting.
11286
11287 This extra alignment does consume extra stack space, and generally
11288 increases code size. Code that is sensitive to stack space usage, such
11289 as embedded systems and operating system kernels, may want to reduce the
11290 preferred alignment to @option{-mpreferred-stack-boundary=2}.
11291
11292 @item -mmmx
11293 @itemx -mno-mmx
11294 @itemx -msse
11295 @itemx -mno-sse
11296 @itemx -msse2
11297 @itemx -mno-sse2
11298 @itemx -msse3
11299 @itemx -mno-sse3
11300 @itemx -mssse3
11301 @itemx -mno-ssse3
11302 @itemx -msse4.1
11303 @itemx -mno-sse4.1
11304 @itemx -msse4.2
11305 @itemx -mno-sse4.2
11306 @itemx -msse4
11307 @itemx -mno-sse4
11308 @itemx -mavx
11309 @itemx -mno-avx
11310 @itemx -maes
11311 @itemx -mno-aes
11312 @itemx -mpclmul
11313 @itemx -mno-pclmul
11314 @itemx -msse4a
11315 @itemx -mno-sse4a
11316 @itemx -msse5
11317 @itemx -mno-sse5
11318 @itemx -m3dnow
11319 @itemx -mno-3dnow
11320 @itemx -mpopcnt
11321 @itemx -mno-popcnt
11322 @itemx -mabm
11323 @itemx -mno-abm
11324 @opindex mmmx
11325 @opindex mno-mmx
11326 @opindex msse
11327 @opindex mno-sse
11328 @opindex m3dnow
11329 @opindex mno-3dnow
11330 These switches enable or disable the use of instructions in the MMX,
11331 SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, SSE4A, SSE5, ABM or
11332 3DNow!@: extended instruction sets.
11333 These extensions are also available as built-in functions: see
11334 @ref{X86 Built-in Functions}, for details of the functions enabled and
11335 disabled by these switches.
11336
11337 To have SSE/SSE2 instructions generated automatically from floating-point
11338 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
11339
11340 GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it
11341 generates new AVX instructions or AVX equivalence for all SSEx instructions
11342 when needed.
11343
11344 These options will enable GCC to use these extended instructions in
11345 generated code, even without @option{-mfpmath=sse}. Applications which
11346 perform runtime CPU detection must compile separate files for each
11347 supported architecture, using the appropriate flags. In particular,
11348 the file containing the CPU detection code should be compiled without
11349 these options.
11350
11351 @item -mcld
11352 @opindex mcld
11353 This option instructs GCC to emit a @code{cld} instruction in the prologue
11354 of functions that use string instructions. String instructions depend on
11355 the DF flag to select between autoincrement or autodecrement mode. While the
11356 ABI specifies the DF flag to be cleared on function entry, some operating
11357 systems violate this specification by not clearing the DF flag in their
11358 exception dispatchers. The exception handler can be invoked with the DF flag
11359 set which leads to wrong direction mode, when string instructions are used.
11360 This option can be enabled by default on 32-bit x86 targets by configuring
11361 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
11362 instructions can be suppressed with the @option{-mno-cld} compiler option
11363 in this case.
11364
11365 @item -mcx16
11366 @opindex mcx16
11367 This option will enable GCC to use CMPXCHG16B instruction in generated code.
11368 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
11369 data types. This is useful for high resolution counters that could be updated
11370 by multiple processors (or cores). This instruction is generated as part of
11371 atomic built-in functions: see @ref{Atomic Builtins} for details.
11372
11373 @item -msahf
11374 @opindex msahf
11375 This option will enable GCC to use SAHF instruction in generated 64-bit code.
11376 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
11377 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
11378 SAHF are load and store instructions, respectively, for certain status flags.
11379 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
11380 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
11381
11382 @item -mrecip
11383 @opindex mrecip
11384 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
11385 vectorized variants RCPPS and RSQRTPS) with an additional Newton-Raphson step
11386 to increase precision instead of DIVSS and SQRTSS (and their vectorized
11387 variants) for single precision floating point arguments. These instructions
11388 are generated only when @option{-funsafe-math-optimizations} is enabled
11389 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
11390 Note that while the throughput of the sequence is higher than the throughput
11391 of the non-reciprocal instruction, the precision of the sequence can be
11392 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
11393
11394 @item -mveclibabi=@var{type}
11395 @opindex mveclibabi
11396 Specifies the ABI type to use for vectorizing intrinsics using an
11397 external library. Supported types are @code{svml} for the Intel short
11398 vector math library and @code{acml} for the AMD math core library style
11399 of interfacing. GCC will currently emit calls to @code{vmldExp2},
11400 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
11401 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
11402 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
11403 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
11404 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
11405 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
11406 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
11407 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
11408 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
11409 function type when @option{-mveclibabi=svml} is used and @code{__vrd2_sin},
11410 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
11411 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
11412 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
11413 @code{__vrs4_log10f} and @code{__vrs4_powf} for corresponding function type
11414 when @option{-mveclibabi=acml} is used. Both @option{-ftree-vectorize} and
11415 @option{-funsafe-math-optimizations} have to be enabled. A SVML or ACML ABI
11416 compatible library will have to be specified at link time.
11417
11418 @item -mpush-args
11419 @itemx -mno-push-args
11420 @opindex mpush-args
11421 @opindex mno-push-args
11422 Use PUSH operations to store outgoing parameters. This method is shorter
11423 and usually equally fast as method using SUB/MOV operations and is enabled
11424 by default. In some cases disabling it may improve performance because of
11425 improved scheduling and reduced dependencies.
11426
11427 @item -maccumulate-outgoing-args
11428 @opindex maccumulate-outgoing-args
11429 If enabled, the maximum amount of space required for outgoing arguments will be
11430 computed in the function prologue. This is faster on most modern CPUs
11431 because of reduced dependencies, improved scheduling and reduced stack usage
11432 when preferred stack boundary is not equal to 2. The drawback is a notable
11433 increase in code size. This switch implies @option{-mno-push-args}.
11434
11435 @item -mthreads
11436 @opindex mthreads
11437 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
11438 on thread-safe exception handling must compile and link all code with the
11439 @option{-mthreads} option. When compiling, @option{-mthreads} defines
11440 @option{-D_MT}; when linking, it links in a special thread helper library
11441 @option{-lmingwthrd} which cleans up per thread exception handling data.
11442
11443 @item -mno-align-stringops
11444 @opindex mno-align-stringops
11445 Do not align destination of inlined string operations. This switch reduces
11446 code size and improves performance in case the destination is already aligned,
11447 but GCC doesn't know about it.
11448
11449 @item -minline-all-stringops
11450 @opindex minline-all-stringops
11451 By default GCC inlines string operations only when destination is known to be
11452 aligned at least to 4 byte boundary. This enables more inlining, increase code
11453 size, but may improve performance of code that depends on fast memcpy, strlen
11454 and memset for short lengths.
11455
11456 @item -minline-stringops-dynamically
11457 @opindex minline-stringops-dynamically
11458 For string operation of unknown size, inline runtime checks so for small
11459 blocks inline code is used, while for large blocks library call is used.
11460
11461 @item -mstringop-strategy=@var{alg}
11462 @opindex mstringop-strategy=@var{alg}
11463 Overwrite internal decision heuristic about particular algorithm to inline
11464 string operation with. The allowed values are @code{rep_byte},
11465 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
11466 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
11467 expanding inline loop, @code{libcall} for always expanding library call.
11468
11469 @item -momit-leaf-frame-pointer
11470 @opindex momit-leaf-frame-pointer
11471 Don't keep the frame pointer in a register for leaf functions. This
11472 avoids the instructions to save, set up and restore frame pointers and
11473 makes an extra register available in leaf functions. The option
11474 @option{-fomit-frame-pointer} removes the frame pointer for all functions
11475 which might make debugging harder.
11476
11477 @item -mtls-direct-seg-refs
11478 @itemx -mno-tls-direct-seg-refs
11479 @opindex mtls-direct-seg-refs
11480 Controls whether TLS variables may be accessed with offsets from the
11481 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
11482 or whether the thread base pointer must be added. Whether or not this
11483 is legal depends on the operating system, and whether it maps the
11484 segment to cover the entire TLS area.
11485
11486 For systems that use GNU libc, the default is on.
11487
11488 @item -mfused-madd
11489 @itemx -mno-fused-madd
11490 @opindex mfused-madd
11491 Enable automatic generation of fused floating point multiply-add instructions
11492 if the ISA supports such instructions. The -mfused-madd option is on by
11493 default. The fused multiply-add instructions have a different
11494 rounding behavior compared to executing a multiply followed by an add.
11495
11496 @item -msse2avx
11497 @itemx -mno-sse2avx
11498 @opindex msse2avx
11499 Specify that the assembler should encode SSE instructions with VEX
11500 prefix. The option @option{-mavx} turns this on by default.
11501 @end table
11502
11503 These @samp{-m} switches are supported in addition to the above
11504 on AMD x86-64 processors in 64-bit environments.
11505
11506 @table @gcctabopt
11507 @item -m32
11508 @itemx -m64
11509 @opindex m32
11510 @opindex m64
11511 Generate code for a 32-bit or 64-bit environment.
11512 The 32-bit environment sets int, long and pointer to 32 bits and
11513 generates code that runs on any i386 system.
11514 The 64-bit environment sets int to 32 bits and long and pointer
11515 to 64 bits and generates code for AMD's x86-64 architecture. For
11516 darwin only the -m64 option turns off the @option{-fno-pic} and
11517 @option{-mdynamic-no-pic} options.
11518
11519 @item -mno-red-zone
11520 @opindex no-red-zone
11521 Do not use a so called red zone for x86-64 code. The red zone is mandated
11522 by the x86-64 ABI, it is a 128-byte area beyond the location of the
11523 stack pointer that will not be modified by signal or interrupt handlers
11524 and therefore can be used for temporary data without adjusting the stack
11525 pointer. The flag @option{-mno-red-zone} disables this red zone.
11526
11527 @item -mcmodel=small
11528 @opindex mcmodel=small
11529 Generate code for the small code model: the program and its symbols must
11530 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
11531 Programs can be statically or dynamically linked. This is the default
11532 code model.
11533
11534 @item -mcmodel=kernel
11535 @opindex mcmodel=kernel
11536 Generate code for the kernel code model. The kernel runs in the
11537 negative 2 GB of the address space.
11538 This model has to be used for Linux kernel code.
11539
11540 @item -mcmodel=medium
11541 @opindex mcmodel=medium
11542 Generate code for the medium model: The program is linked in the lower 2
11543 GB of the address space. Small symbols are also placed there. Symbols
11544 with sizes larger than @option{-mlarge-data-threshold} are put into
11545 large data or bss sections and can be located above 2GB. Programs can
11546 be statically or dynamically linked.
11547
11548 @item -mcmodel=large
11549 @opindex mcmodel=large
11550 Generate code for the large model: This model makes no assumptions
11551 about addresses and sizes of sections.
11552
11553 @item -msave-args
11554 @opindex msave-args
11555 Save integer arguments on the stack at function entry.
11556 @end table
11557
11558 @node IA-64 Options
11559 @subsection IA-64 Options
11560 @cindex IA-64 Options
11561
11562 These are the @samp{-m} options defined for the Intel IA-64 architecture.
11563
11564 @table @gcctabopt
11565 @item -mbig-endian
11566 @opindex mbig-endian
11567 Generate code for a big endian target. This is the default for HP-UX@.
11568
11569 @item -mlittle-endian
11570 @opindex mlittle-endian
11571 Generate code for a little endian target. This is the default for AIX5
11572 and GNU/Linux.
11573
11574 @item -mgnu-as
11575 @itemx -mno-gnu-as
11576 @opindex mgnu-as
11577 @opindex mno-gnu-as
11578 Generate (or don't) code for the GNU assembler. This is the default.
11579 @c Also, this is the default if the configure option @option{--with-gnu-as}
11580 @c is used.
11581
11582 @item -mgnu-ld
11583 @itemx -mno-gnu-ld
11584 @opindex mgnu-ld
11585 @opindex mno-gnu-ld
11586 Generate (or don't) code for the GNU linker. This is the default.
11587 @c Also, this is the default if the configure option @option{--with-gnu-ld}
11588 @c is used.
11589
11590 @item -mno-pic
11591 @opindex mno-pic
11592 Generate code that does not use a global pointer register. The result
11593 is not position independent code, and violates the IA-64 ABI@.
11594
11595 @item -mvolatile-asm-stop
11596 @itemx -mno-volatile-asm-stop
11597 @opindex mvolatile-asm-stop
11598 @opindex mno-volatile-asm-stop
11599 Generate (or don't) a stop bit immediately before and after volatile asm
11600 statements.
11601
11602 @item -mregister-names
11603 @itemx -mno-register-names
11604 @opindex mregister-names
11605 @opindex mno-register-names
11606 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
11607 the stacked registers. This may make assembler output more readable.
11608
11609 @item -mno-sdata
11610 @itemx -msdata
11611 @opindex mno-sdata
11612 @opindex msdata
11613 Disable (or enable) optimizations that use the small data section. This may
11614 be useful for working around optimizer bugs.
11615
11616 @item -mconstant-gp
11617 @opindex mconstant-gp
11618 Generate code that uses a single constant global pointer value. This is
11619 useful when compiling kernel code.
11620
11621 @item -mauto-pic
11622 @opindex mauto-pic
11623 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
11624 This is useful when compiling firmware code.
11625
11626 @item -minline-float-divide-min-latency
11627 @opindex minline-float-divide-min-latency
11628 Generate code for inline divides of floating point values
11629 using the minimum latency algorithm.
11630
11631 @item -minline-float-divide-max-throughput
11632 @opindex minline-float-divide-max-throughput
11633 Generate code for inline divides of floating point values
11634 using the maximum throughput algorithm.
11635
11636 @item -minline-int-divide-min-latency
11637 @opindex minline-int-divide-min-latency
11638 Generate code for inline divides of integer values
11639 using the minimum latency algorithm.
11640
11641 @item -minline-int-divide-max-throughput
11642 @opindex minline-int-divide-max-throughput
11643 Generate code for inline divides of integer values
11644 using the maximum throughput algorithm.
11645
11646 @item -minline-sqrt-min-latency
11647 @opindex minline-sqrt-min-latency
11648 Generate code for inline square roots
11649 using the minimum latency algorithm.
11650
11651 @item -minline-sqrt-max-throughput
11652 @opindex minline-sqrt-max-throughput
11653 Generate code for inline square roots
11654 using the maximum throughput algorithm.
11655
11656 @item -mno-dwarf2-asm
11657 @itemx -mdwarf2-asm
11658 @opindex mno-dwarf2-asm
11659 @opindex mdwarf2-asm
11660 Don't (or do) generate assembler code for the DWARF2 line number debugging
11661 info. This may be useful when not using the GNU assembler.
11662
11663 @item -mearly-stop-bits
11664 @itemx -mno-early-stop-bits
11665 @opindex mearly-stop-bits
11666 @opindex mno-early-stop-bits
11667 Allow stop bits to be placed earlier than immediately preceding the
11668 instruction that triggered the stop bit. This can improve instruction
11669 scheduling, but does not always do so.
11670
11671 @item -mfixed-range=@var{register-range}
11672 @opindex mfixed-range
11673 Generate code treating the given register range as fixed registers.
11674 A fixed register is one that the register allocator can not use. This is
11675 useful when compiling kernel code. A register range is specified as
11676 two registers separated by a dash. Multiple register ranges can be
11677 specified separated by a comma.
11678
11679 @item -mtls-size=@var{tls-size}
11680 @opindex mtls-size
11681 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
11682 64.
11683
11684 @item -mtune=@var{cpu-type}
11685 @opindex mtune
11686 Tune the instruction scheduling for a particular CPU, Valid values are
11687 itanium, itanium1, merced, itanium2, and mckinley.
11688
11689 @item -mt
11690 @itemx -pthread
11691 @opindex mt
11692 @opindex pthread
11693 Add support for multithreading using the POSIX threads library. This
11694 option sets flags for both the preprocessor and linker. It does
11695 not affect the thread safety of object code produced by the compiler or
11696 that of libraries supplied with it. These are HP-UX specific flags.
11697
11698 @item -milp32
11699 @itemx -mlp64
11700 @opindex milp32
11701 @opindex mlp64
11702 Generate code for a 32-bit or 64-bit environment.
11703 The 32-bit environment sets int, long and pointer to 32 bits.
11704 The 64-bit environment sets int to 32 bits and long and pointer
11705 to 64 bits. These are HP-UX specific flags.
11706
11707 @item -mno-sched-br-data-spec
11708 @itemx -msched-br-data-spec
11709 @opindex mno-sched-br-data-spec
11710 @opindex msched-br-data-spec
11711 (Dis/En)able data speculative scheduling before reload.
11712 This will result in generation of the ld.a instructions and
11713 the corresponding check instructions (ld.c / chk.a).
11714 The default is 'disable'.
11715
11716 @item -msched-ar-data-spec
11717 @itemx -mno-sched-ar-data-spec
11718 @opindex msched-ar-data-spec
11719 @opindex mno-sched-ar-data-spec
11720 (En/Dis)able data speculative scheduling after reload.
11721 This will result in generation of the ld.a instructions and
11722 the corresponding check instructions (ld.c / chk.a).
11723 The default is 'enable'.
11724
11725 @item -mno-sched-control-spec
11726 @itemx -msched-control-spec
11727 @opindex mno-sched-control-spec
11728 @opindex msched-control-spec
11729 (Dis/En)able control speculative scheduling. This feature is
11730 available only during region scheduling (i.e.@: before reload).
11731 This will result in generation of the ld.s instructions and
11732 the corresponding check instructions chk.s .
11733 The default is 'disable'.
11734
11735 @item -msched-br-in-data-spec
11736 @itemx -mno-sched-br-in-data-spec
11737 @opindex msched-br-in-data-spec
11738 @opindex mno-sched-br-in-data-spec
11739 (En/Dis)able speculative scheduling of the instructions that
11740 are dependent on the data speculative loads before reload.
11741 This is effective only with @option{-msched-br-data-spec} enabled.
11742 The default is 'enable'.
11743
11744 @item -msched-ar-in-data-spec
11745 @itemx -mno-sched-ar-in-data-spec
11746 @opindex msched-ar-in-data-spec
11747 @opindex mno-sched-ar-in-data-spec
11748 (En/Dis)able speculative scheduling of the instructions that
11749 are dependent on the data speculative loads after reload.
11750 This is effective only with @option{-msched-ar-data-spec} enabled.
11751 The default is 'enable'.
11752
11753 @item -msched-in-control-spec
11754 @itemx -mno-sched-in-control-spec
11755 @opindex msched-in-control-spec
11756 @opindex mno-sched-in-control-spec
11757 (En/Dis)able speculative scheduling of the instructions that
11758 are dependent on the control speculative loads.
11759 This is effective only with @option{-msched-control-spec} enabled.
11760 The default is 'enable'.
11761
11762 @item -msched-ldc
11763 @itemx -mno-sched-ldc
11764 @opindex msched-ldc
11765 @opindex mno-sched-ldc
11766 (En/Dis)able use of simple data speculation checks ld.c .
11767 If disabled, only chk.a instructions will be emitted to check
11768 data speculative loads.
11769 The default is 'enable'.
11770
11771 @item -mno-sched-control-ldc
11772 @itemx -msched-control-ldc
11773 @opindex mno-sched-control-ldc
11774 @opindex msched-control-ldc
11775 (Dis/En)able use of ld.c instructions to check control speculative loads.
11776 If enabled, in case of control speculative load with no speculatively
11777 scheduled dependent instructions this load will be emitted as ld.sa and
11778 ld.c will be used to check it.
11779 The default is 'disable'.
11780
11781 @item -mno-sched-spec-verbose
11782 @itemx -msched-spec-verbose
11783 @opindex mno-sched-spec-verbose
11784 @opindex msched-spec-verbose
11785 (Dis/En)able printing of the information about speculative motions.
11786
11787 @item -mno-sched-prefer-non-data-spec-insns
11788 @itemx -msched-prefer-non-data-spec-insns
11789 @opindex mno-sched-prefer-non-data-spec-insns
11790 @opindex msched-prefer-non-data-spec-insns
11791 If enabled, data speculative instructions will be chosen for schedule
11792 only if there are no other choices at the moment. This will make
11793 the use of the data speculation much more conservative.
11794 The default is 'disable'.
11795
11796 @item -mno-sched-prefer-non-control-spec-insns
11797 @itemx -msched-prefer-non-control-spec-insns
11798 @opindex mno-sched-prefer-non-control-spec-insns
11799 @opindex msched-prefer-non-control-spec-insns
11800 If enabled, control speculative instructions will be chosen for schedule
11801 only if there are no other choices at the moment. This will make
11802 the use of the control speculation much more conservative.
11803 The default is 'disable'.
11804
11805 @item -mno-sched-count-spec-in-critical-path
11806 @itemx -msched-count-spec-in-critical-path
11807 @opindex mno-sched-count-spec-in-critical-path
11808 @opindex msched-count-spec-in-critical-path
11809 If enabled, speculative dependencies will be considered during
11810 computation of the instructions priorities. This will make the use of the
11811 speculation a bit more conservative.
11812 The default is 'disable'.
11813
11814 @end table
11815
11816 @node M32C Options
11817 @subsection M32C Options
11818 @cindex M32C options
11819
11820 @table @gcctabopt
11821 @item -mcpu=@var{name}
11822 @opindex mcpu=
11823 Select the CPU for which code is generated. @var{name} may be one of
11824 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
11825 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
11826 the M32C/80 series.
11827
11828 @item -msim
11829 @opindex msim
11830 Specifies that the program will be run on the simulator. This causes
11831 an alternate runtime library to be linked in which supports, for
11832 example, file I/O@. You must not use this option when generating
11833 programs that will run on real hardware; you must provide your own
11834 runtime library for whatever I/O functions are needed.
11835
11836 @item -memregs=@var{number}
11837 @opindex memregs=
11838 Specifies the number of memory-based pseudo-registers GCC will use
11839 during code generation. These pseudo-registers will be used like real
11840 registers, so there is a tradeoff between GCC's ability to fit the
11841 code into available registers, and the performance penalty of using
11842 memory instead of registers. Note that all modules in a program must
11843 be compiled with the same value for this option. Because of that, you
11844 must not use this option with the default runtime libraries gcc
11845 builds.
11846
11847 @end table
11848
11849 @node M32R/D Options
11850 @subsection M32R/D Options
11851 @cindex M32R/D options
11852
11853 These @option{-m} options are defined for Renesas M32R/D architectures:
11854
11855 @table @gcctabopt
11856 @item -m32r2
11857 @opindex m32r2
11858 Generate code for the M32R/2@.
11859
11860 @item -m32rx
11861 @opindex m32rx
11862 Generate code for the M32R/X@.
11863
11864 @item -m32r
11865 @opindex m32r
11866 Generate code for the M32R@. This is the default.
11867
11868 @item -mmodel=small
11869 @opindex mmodel=small
11870 Assume all objects live in the lower 16MB of memory (so that their addresses
11871 can be loaded with the @code{ld24} instruction), and assume all subroutines
11872 are reachable with the @code{bl} instruction.
11873 This is the default.
11874
11875 The addressability of a particular object can be set with the
11876 @code{model} attribute.
11877
11878 @item -mmodel=medium
11879 @opindex mmodel=medium
11880 Assume objects may be anywhere in the 32-bit address space (the compiler
11881 will generate @code{seth/add3} instructions to load their addresses), and
11882 assume all subroutines are reachable with the @code{bl} instruction.
11883
11884 @item -mmodel=large
11885 @opindex mmodel=large
11886 Assume objects may be anywhere in the 32-bit address space (the compiler
11887 will generate @code{seth/add3} instructions to load their addresses), and
11888 assume subroutines may not be reachable with the @code{bl} instruction
11889 (the compiler will generate the much slower @code{seth/add3/jl}
11890 instruction sequence).
11891
11892 @item -msdata=none
11893 @opindex msdata=none
11894 Disable use of the small data area. Variables will be put into
11895 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
11896 @code{section} attribute has been specified).
11897 This is the default.
11898
11899 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
11900 Objects may be explicitly put in the small data area with the
11901 @code{section} attribute using one of these sections.
11902
11903 @item -msdata=sdata
11904 @opindex msdata=sdata
11905 Put small global and static data in the small data area, but do not
11906 generate special code to reference them.
11907
11908 @item -msdata=use
11909 @opindex msdata=use
11910 Put small global and static data in the small data area, and generate
11911 special instructions to reference them.
11912
11913 @item -G @var{num}
11914 @opindex G
11915 @cindex smaller data references
11916 Put global and static objects less than or equal to @var{num} bytes
11917 into the small data or bss sections instead of the normal data or bss
11918 sections. The default value of @var{num} is 8.
11919 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
11920 for this option to have any effect.
11921
11922 All modules should be compiled with the same @option{-G @var{num}} value.
11923 Compiling with different values of @var{num} may or may not work; if it
11924 doesn't the linker will give an error message---incorrect code will not be
11925 generated.
11926
11927 @item -mdebug
11928 @opindex mdebug
11929 Makes the M32R specific code in the compiler display some statistics
11930 that might help in debugging programs.
11931
11932 @item -malign-loops
11933 @opindex malign-loops
11934 Align all loops to a 32-byte boundary.
11935
11936 @item -mno-align-loops
11937 @opindex mno-align-loops
11938 Do not enforce a 32-byte alignment for loops. This is the default.
11939
11940 @item -missue-rate=@var{number}
11941 @opindex missue-rate=@var{number}
11942 Issue @var{number} instructions per cycle. @var{number} can only be 1
11943 or 2.
11944
11945 @item -mbranch-cost=@var{number}
11946 @opindex mbranch-cost=@var{number}
11947 @var{number} can only be 1 or 2. If it is 1 then branches will be
11948 preferred over conditional code, if it is 2, then the opposite will
11949 apply.
11950
11951 @item -mflush-trap=@var{number}
11952 @opindex mflush-trap=@var{number}
11953 Specifies the trap number to use to flush the cache. The default is
11954 12. Valid numbers are between 0 and 15 inclusive.
11955
11956 @item -mno-flush-trap
11957 @opindex mno-flush-trap
11958 Specifies that the cache cannot be flushed by using a trap.
11959
11960 @item -mflush-func=@var{name}
11961 @opindex mflush-func=@var{name}
11962 Specifies the name of the operating system function to call to flush
11963 the cache. The default is @emph{_flush_cache}, but a function call
11964 will only be used if a trap is not available.
11965
11966 @item -mno-flush-func
11967 @opindex mno-flush-func
11968 Indicates that there is no OS function for flushing the cache.
11969
11970 @end table
11971
11972 @node M680x0 Options
11973 @subsection M680x0 Options
11974 @cindex M680x0 options
11975
11976 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
11977 The default settings depend on which architecture was selected when
11978 the compiler was configured; the defaults for the most common choices
11979 are given below.
11980
11981 @table @gcctabopt
11982 @item -march=@var{arch}
11983 @opindex march
11984 Generate code for a specific M680x0 or ColdFire instruction set
11985 architecture. Permissible values of @var{arch} for M680x0
11986 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
11987 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
11988 architectures are selected according to Freescale's ISA classification
11989 and the permissible values are: @samp{isaa}, @samp{isaaplus},
11990 @samp{isab} and @samp{isac}.
11991
11992 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
11993 code for a ColdFire target. The @var{arch} in this macro is one of the
11994 @option{-march} arguments given above.
11995
11996 When used together, @option{-march} and @option{-mtune} select code
11997 that runs on a family of similar processors but that is optimized
11998 for a particular microarchitecture.
11999
12000 @item -mcpu=@var{cpu}
12001 @opindex mcpu
12002 Generate code for a specific M680x0 or ColdFire processor.
12003 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
12004 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
12005 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
12006 below, which also classifies the CPUs into families:
12007
12008 @multitable @columnfractions 0.20 0.80
12009 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
12010 @item @samp{51qe} @tab @samp{51qe}
12011 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
12012 @item @samp{5206e} @tab @samp{5206e}
12013 @item @samp{5208} @tab @samp{5207} @samp{5208}
12014 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
12015 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
12016 @item @samp{5216} @tab @samp{5214} @samp{5216}
12017 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
12018 @item @samp{5225} @tab @samp{5224} @samp{5225}
12019 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
12020 @item @samp{5249} @tab @samp{5249}
12021 @item @samp{5250} @tab @samp{5250}
12022 @item @samp{5271} @tab @samp{5270} @samp{5271}
12023 @item @samp{5272} @tab @samp{5272}
12024 @item @samp{5275} @tab @samp{5274} @samp{5275}
12025 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
12026 @item @samp{5307} @tab @samp{5307}
12027 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
12028 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
12029 @item @samp{5407} @tab @samp{5407}
12030 @item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485}
12031 @end multitable
12032
12033 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
12034 @var{arch} is compatible with @var{cpu}. Other combinations of
12035 @option{-mcpu} and @option{-march} are rejected.
12036
12037 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
12038 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
12039 where the value of @var{family} is given by the table above.
12040
12041 @item -mtune=@var{tune}
12042 @opindex mtune
12043 Tune the code for a particular microarchitecture, within the
12044 constraints set by @option{-march} and @option{-mcpu}.
12045 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
12046 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
12047 and @samp{cpu32}. The ColdFire microarchitectures
12048 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
12049
12050 You can also use @option{-mtune=68020-40} for code that needs
12051 to run relatively well on 68020, 68030 and 68040 targets.
12052 @option{-mtune=68020-60} is similar but includes 68060 targets
12053 as well. These two options select the same tuning decisions as
12054 @option{-m68020-40} and @option{-m68020-60} respectively.
12055
12056 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
12057 when tuning for 680x0 architecture @var{arch}. It also defines
12058 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
12059 option is used. If gcc is tuning for a range of architectures,
12060 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
12061 it defines the macros for every architecture in the range.
12062
12063 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
12064 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
12065 of the arguments given above.
12066
12067 @item -m68000
12068 @itemx -mc68000
12069 @opindex m68000
12070 @opindex mc68000
12071 Generate output for a 68000. This is the default
12072 when the compiler is configured for 68000-based systems.
12073 It is equivalent to @option{-march=68000}.
12074
12075 Use this option for microcontrollers with a 68000 or EC000 core,
12076 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
12077
12078 @item -m68010
12079 @opindex m68010
12080 Generate output for a 68010. This is the default
12081 when the compiler is configured for 68010-based systems.
12082 It is equivalent to @option{-march=68010}.
12083
12084 @item -m68020
12085 @itemx -mc68020
12086 @opindex m68020
12087 @opindex mc68020
12088 Generate output for a 68020. This is the default
12089 when the compiler is configured for 68020-based systems.
12090 It is equivalent to @option{-march=68020}.
12091
12092 @item -m68030
12093 @opindex m68030
12094 Generate output for a 68030. This is the default when the compiler is
12095 configured for 68030-based systems. It is equivalent to
12096 @option{-march=68030}.
12097
12098 @item -m68040
12099 @opindex m68040
12100 Generate output for a 68040. This is the default when the compiler is
12101 configured for 68040-based systems. It is equivalent to
12102 @option{-march=68040}.
12103
12104 This option inhibits the use of 68881/68882 instructions that have to be
12105 emulated by software on the 68040. Use this option if your 68040 does not
12106 have code to emulate those instructions.
12107
12108 @item -m68060
12109 @opindex m68060
12110 Generate output for a 68060. This is the default when the compiler is
12111 configured for 68060-based systems. It is equivalent to
12112 @option{-march=68060}.
12113
12114 This option inhibits the use of 68020 and 68881/68882 instructions that
12115 have to be emulated by software on the 68060. Use this option if your 68060
12116 does not have code to emulate those instructions.
12117
12118 @item -mcpu32
12119 @opindex mcpu32
12120 Generate output for a CPU32. This is the default
12121 when the compiler is configured for CPU32-based systems.
12122 It is equivalent to @option{-march=cpu32}.
12123
12124 Use this option for microcontrollers with a
12125 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
12126 68336, 68340, 68341, 68349 and 68360.
12127
12128 @item -m5200
12129 @opindex m5200
12130 Generate output for a 520X ColdFire CPU@. This is the default
12131 when the compiler is configured for 520X-based systems.
12132 It is equivalent to @option{-mcpu=5206}, and is now deprecated
12133 in favor of that option.
12134
12135 Use this option for microcontroller with a 5200 core, including
12136 the MCF5202, MCF5203, MCF5204 and MCF5206.
12137
12138 @item -m5206e
12139 @opindex m5206e
12140 Generate output for a 5206e ColdFire CPU@. The option is now
12141 deprecated in favor of the equivalent @option{-mcpu=5206e}.
12142
12143 @item -m528x
12144 @opindex m528x
12145 Generate output for a member of the ColdFire 528X family.
12146 The option is now deprecated in favor of the equivalent
12147 @option{-mcpu=528x}.
12148
12149 @item -m5307
12150 @opindex m5307
12151 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
12152 in favor of the equivalent @option{-mcpu=5307}.
12153
12154 @item -m5407
12155 @opindex m5407
12156 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
12157 in favor of the equivalent @option{-mcpu=5407}.
12158
12159 @item -mcfv4e
12160 @opindex mcfv4e
12161 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
12162 This includes use of hardware floating point instructions.
12163 The option is equivalent to @option{-mcpu=547x}, and is now
12164 deprecated in favor of that option.
12165
12166 @item -m68020-40
12167 @opindex m68020-40
12168 Generate output for a 68040, without using any of the new instructions.
12169 This results in code which can run relatively efficiently on either a
12170 68020/68881 or a 68030 or a 68040. The generated code does use the
12171 68881 instructions that are emulated on the 68040.
12172
12173 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
12174
12175 @item -m68020-60
12176 @opindex m68020-60
12177 Generate output for a 68060, without using any of the new instructions.
12178 This results in code which can run relatively efficiently on either a
12179 68020/68881 or a 68030 or a 68040. The generated code does use the
12180 68881 instructions that are emulated on the 68060.
12181
12182 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
12183
12184 @item -mhard-float
12185 @itemx -m68881
12186 @opindex mhard-float
12187 @opindex m68881
12188 Generate floating-point instructions. This is the default for 68020
12189 and above, and for ColdFire devices that have an FPU@. It defines the
12190 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
12191 on ColdFire targets.
12192
12193 @item -msoft-float
12194 @opindex msoft-float
12195 Do not generate floating-point instructions; use library calls instead.
12196 This is the default for 68000, 68010, and 68832 targets. It is also
12197 the default for ColdFire devices that have no FPU.
12198
12199 @item -mdiv
12200 @itemx -mno-div
12201 @opindex mdiv
12202 @opindex mno-div
12203 Generate (do not generate) ColdFire hardware divide and remainder
12204 instructions. If @option{-march} is used without @option{-mcpu},
12205 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
12206 architectures. Otherwise, the default is taken from the target CPU
12207 (either the default CPU, or the one specified by @option{-mcpu}). For
12208 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
12209 @option{-mcpu=5206e}.
12210
12211 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
12212
12213 @item -mshort
12214 @opindex mshort
12215 Consider type @code{int} to be 16 bits wide, like @code{short int}.
12216 Additionally, parameters passed on the stack are also aligned to a
12217 16-bit boundary even on targets whose API mandates promotion to 32-bit.
12218
12219 @item -mno-short
12220 @opindex mno-short
12221 Do not consider type @code{int} to be 16 bits wide. This is the default.
12222
12223 @item -mnobitfield
12224 @itemx -mno-bitfield
12225 @opindex mnobitfield
12226 @opindex mno-bitfield
12227 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
12228 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
12229
12230 @item -mbitfield
12231 @opindex mbitfield
12232 Do use the bit-field instructions. The @option{-m68020} option implies
12233 @option{-mbitfield}. This is the default if you use a configuration
12234 designed for a 68020.
12235
12236 @item -mrtd
12237 @opindex mrtd
12238 Use a different function-calling convention, in which functions
12239 that take a fixed number of arguments return with the @code{rtd}
12240 instruction, which pops their arguments while returning. This
12241 saves one instruction in the caller since there is no need to pop
12242 the arguments there.
12243
12244 This calling convention is incompatible with the one normally
12245 used on Unix, so you cannot use it if you need to call libraries
12246 compiled with the Unix compiler.
12247
12248 Also, you must provide function prototypes for all functions that
12249 take variable numbers of arguments (including @code{printf});
12250 otherwise incorrect code will be generated for calls to those
12251 functions.
12252
12253 In addition, seriously incorrect code will result if you call a
12254 function with too many arguments. (Normally, extra arguments are
12255 harmlessly ignored.)
12256
12257 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
12258 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
12259
12260 @item -mno-rtd
12261 @opindex mno-rtd
12262 Do not use the calling conventions selected by @option{-mrtd}.
12263 This is the default.
12264
12265 @item -malign-int
12266 @itemx -mno-align-int
12267 @opindex malign-int
12268 @opindex mno-align-int
12269 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
12270 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
12271 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
12272 Aligning variables on 32-bit boundaries produces code that runs somewhat
12273 faster on processors with 32-bit busses at the expense of more memory.
12274
12275 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
12276 align structures containing the above types differently than
12277 most published application binary interface specifications for the m68k.
12278
12279 @item -mpcrel
12280 @opindex mpcrel
12281 Use the pc-relative addressing mode of the 68000 directly, instead of
12282 using a global offset table. At present, this option implies @option{-fpic},
12283 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
12284 not presently supported with @option{-mpcrel}, though this could be supported for
12285 68020 and higher processors.
12286
12287 @item -mno-strict-align
12288 @itemx -mstrict-align
12289 @opindex mno-strict-align
12290 @opindex mstrict-align
12291 Do not (do) assume that unaligned memory references will be handled by
12292 the system.
12293
12294 @item -msep-data
12295 Generate code that allows the data segment to be located in a different
12296 area of memory from the text segment. This allows for execute in place in
12297 an environment without virtual memory management. This option implies
12298 @option{-fPIC}.
12299
12300 @item -mno-sep-data
12301 Generate code that assumes that the data segment follows the text segment.
12302 This is the default.
12303
12304 @item -mid-shared-library
12305 Generate code that supports shared libraries via the library ID method.
12306 This allows for execute in place and shared libraries in an environment
12307 without virtual memory management. This option implies @option{-fPIC}.
12308
12309 @item -mno-id-shared-library
12310 Generate code that doesn't assume ID based shared libraries are being used.
12311 This is the default.
12312
12313 @item -mshared-library-id=n
12314 Specified the identification number of the ID based shared library being
12315 compiled. Specifying a value of 0 will generate more compact code, specifying
12316 other values will force the allocation of that number to the current
12317 library but is no more space or time efficient than omitting this option.
12318
12319 @item -mxgot
12320 @itemx -mno-xgot
12321 @opindex mxgot
12322 @opindex mno-xgot
12323 When generating position-independent code for ColdFire, generate code
12324 that works if the GOT has more than 8192 entries. This code is
12325 larger and slower than code generated without this option. On M680x0
12326 processors, this option is not needed; @option{-fPIC} suffices.
12327
12328 GCC normally uses a single instruction to load values from the GOT@.
12329 While this is relatively efficient, it only works if the GOT
12330 is smaller than about 64k. Anything larger causes the linker
12331 to report an error such as:
12332
12333 @cindex relocation truncated to fit (ColdFire)
12334 @smallexample
12335 relocation truncated to fit: R_68K_GOT16O foobar
12336 @end smallexample
12337
12338 If this happens, you should recompile your code with @option{-mxgot}.
12339 It should then work with very large GOTs. However, code generated with
12340 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
12341 the value of a global symbol.
12342
12343 Note that some linkers, including newer versions of the GNU linker,
12344 can create multiple GOTs and sort GOT entries. If you have such a linker,
12345 you should only need to use @option{-mxgot} when compiling a single
12346 object file that accesses more than 8192 GOT entries. Very few do.
12347
12348 These options have no effect unless GCC is generating
12349 position-independent code.
12350
12351 @end table
12352
12353 @node M68hc1x Options
12354 @subsection M68hc1x Options
12355 @cindex M68hc1x options
12356
12357 These are the @samp{-m} options defined for the 68hc11 and 68hc12
12358 microcontrollers. The default values for these options depends on
12359 which style of microcontroller was selected when the compiler was configured;
12360 the defaults for the most common choices are given below.
12361
12362 @table @gcctabopt
12363 @item -m6811
12364 @itemx -m68hc11
12365 @opindex m6811
12366 @opindex m68hc11
12367 Generate output for a 68HC11. This is the default
12368 when the compiler is configured for 68HC11-based systems.
12369
12370 @item -m6812
12371 @itemx -m68hc12
12372 @opindex m6812
12373 @opindex m68hc12
12374 Generate output for a 68HC12. This is the default
12375 when the compiler is configured for 68HC12-based systems.
12376
12377 @item -m68S12
12378 @itemx -m68hcs12
12379 @opindex m68S12
12380 @opindex m68hcs12
12381 Generate output for a 68HCS12.
12382
12383 @item -mauto-incdec
12384 @opindex mauto-incdec
12385 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
12386 addressing modes.
12387
12388 @item -minmax
12389 @itemx -nominmax
12390 @opindex minmax
12391 @opindex mnominmax
12392 Enable the use of 68HC12 min and max instructions.
12393
12394 @item -mlong-calls
12395 @itemx -mno-long-calls
12396 @opindex mlong-calls
12397 @opindex mno-long-calls
12398 Treat all calls as being far away (near). If calls are assumed to be
12399 far away, the compiler will use the @code{call} instruction to
12400 call a function and the @code{rtc} instruction for returning.
12401
12402 @item -mshort
12403 @opindex mshort
12404 Consider type @code{int} to be 16 bits wide, like @code{short int}.
12405
12406 @item -msoft-reg-count=@var{count}
12407 @opindex msoft-reg-count
12408 Specify the number of pseudo-soft registers which are used for the
12409 code generation. The maximum number is 32. Using more pseudo-soft
12410 register may or may not result in better code depending on the program.
12411 The default is 4 for 68HC11 and 2 for 68HC12.
12412
12413 @end table
12414
12415 @node MCore Options
12416 @subsection MCore Options
12417 @cindex MCore options
12418
12419 These are the @samp{-m} options defined for the Motorola M*Core
12420 processors.
12421
12422 @table @gcctabopt
12423
12424 @item -mhardlit
12425 @itemx -mno-hardlit
12426 @opindex mhardlit
12427 @opindex mno-hardlit
12428 Inline constants into the code stream if it can be done in two
12429 instructions or less.
12430
12431 @item -mdiv
12432 @itemx -mno-div
12433 @opindex mdiv
12434 @opindex mno-div
12435 Use the divide instruction. (Enabled by default).
12436
12437 @item -mrelax-immediate
12438 @itemx -mno-relax-immediate
12439 @opindex mrelax-immediate
12440 @opindex mno-relax-immediate
12441 Allow arbitrary sized immediates in bit operations.
12442
12443 @item -mwide-bitfields
12444 @itemx -mno-wide-bitfields
12445 @opindex mwide-bitfields
12446 @opindex mno-wide-bitfields
12447 Always treat bit-fields as int-sized.
12448
12449 @item -m4byte-functions
12450 @itemx -mno-4byte-functions
12451 @opindex m4byte-functions
12452 @opindex mno-4byte-functions
12453 Force all functions to be aligned to a four byte boundary.
12454
12455 @item -mcallgraph-data
12456 @itemx -mno-callgraph-data
12457 @opindex mcallgraph-data
12458 @opindex mno-callgraph-data
12459 Emit callgraph information.
12460
12461 @item -mslow-bytes
12462 @itemx -mno-slow-bytes
12463 @opindex mslow-bytes
12464 @opindex mno-slow-bytes
12465 Prefer word access when reading byte quantities.
12466
12467 @item -mlittle-endian
12468 @itemx -mbig-endian
12469 @opindex mlittle-endian
12470 @opindex mbig-endian
12471 Generate code for a little endian target.
12472
12473 @item -m210
12474 @itemx -m340
12475 @opindex m210
12476 @opindex m340
12477 Generate code for the 210 processor.
12478
12479 @item -mno-lsim
12480 @opindex no-lsim
12481 Assume that run-time support has been provided and so omit the
12482 simulator library (@file{libsim.a)} from the linker command line.
12483
12484 @item -mstack-increment=@var{size}
12485 @opindex mstack-increment
12486 Set the maximum amount for a single stack increment operation. Large
12487 values can increase the speed of programs which contain functions
12488 that need a large amount of stack space, but they can also trigger a
12489 segmentation fault if the stack is extended too much. The default
12490 value is 0x1000.
12491
12492 @end table
12493
12494 @node MIPS Options
12495 @subsection MIPS Options
12496 @cindex MIPS options
12497
12498 @table @gcctabopt
12499
12500 @item -EB
12501 @opindex EB
12502 Generate big-endian code.
12503
12504 @item -EL
12505 @opindex EL
12506 Generate little-endian code. This is the default for @samp{mips*el-*-*}
12507 configurations.
12508
12509 @item -march=@var{arch}
12510 @opindex march
12511 Generate code that will run on @var{arch}, which can be the name of a
12512 generic MIPS ISA, or the name of a particular processor.
12513 The ISA names are:
12514 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
12515 @samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}.
12516 The processor names are:
12517 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
12518 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
12519 @samp{5kc}, @samp{5kf},
12520 @samp{20kc},
12521 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
12522 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
12523 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
12524 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
12525 @samp{loongson2e}, @samp{loongson2f},
12526 @samp{m4k},
12527 @samp{octeon},
12528 @samp{orion},
12529 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
12530 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
12531 @samp{rm7000}, @samp{rm9000},
12532 @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000},
12533 @samp{sb1},
12534 @samp{sr71000},
12535 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
12536 @samp{vr5000}, @samp{vr5400}, @samp{vr5500}
12537 and @samp{xlr}.
12538 The special value @samp{from-abi} selects the
12539 most compatible architecture for the selected ABI (that is,
12540 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
12541
12542 Native Linux/GNU toolchains also support the value @samp{native},
12543 which selects the best architecture option for the host processor.
12544 @option{-march=native} has no effect if GCC does not recognize
12545 the processor.
12546
12547 In processor names, a final @samp{000} can be abbreviated as @samp{k}
12548 (for example, @samp{-march=r2k}). Prefixes are optional, and
12549 @samp{vr} may be written @samp{r}.
12550
12551 Names of the form @samp{@var{n}f2_1} refer to processors with
12552 FPUs clocked at half the rate of the core, names of the form
12553 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
12554 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
12555 processors with FPUs clocked a ratio of 3:2 with respect to the core.
12556 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
12557 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
12558 accepted as synonyms for @samp{@var{n}f1_1}.
12559
12560 GCC defines two macros based on the value of this option. The first
12561 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
12562 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
12563 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
12564 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
12565 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
12566
12567 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
12568 above. In other words, it will have the full prefix and will not
12569 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
12570 the macro names the resolved architecture (either @samp{"mips1"} or
12571 @samp{"mips3"}). It names the default architecture when no
12572 @option{-march} option is given.
12573
12574 @item -mtune=@var{arch}
12575 @opindex mtune
12576 Optimize for @var{arch}. Among other things, this option controls
12577 the way instructions are scheduled, and the perceived cost of arithmetic
12578 operations. The list of @var{arch} values is the same as for
12579 @option{-march}.
12580
12581 When this option is not used, GCC will optimize for the processor
12582 specified by @option{-march}. By using @option{-march} and
12583 @option{-mtune} together, it is possible to generate code that will
12584 run on a family of processors, but optimize the code for one
12585 particular member of that family.
12586
12587 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
12588 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
12589 @samp{-march} ones described above.
12590
12591 @item -mips1
12592 @opindex mips1
12593 Equivalent to @samp{-march=mips1}.
12594
12595 @item -mips2
12596 @opindex mips2
12597 Equivalent to @samp{-march=mips2}.
12598
12599 @item -mips3
12600 @opindex mips3
12601 Equivalent to @samp{-march=mips3}.
12602
12603 @item -mips4
12604 @opindex mips4
12605 Equivalent to @samp{-march=mips4}.
12606
12607 @item -mips32
12608 @opindex mips32
12609 Equivalent to @samp{-march=mips32}.
12610
12611 @item -mips32r2
12612 @opindex mips32r2
12613 Equivalent to @samp{-march=mips32r2}.
12614
12615 @item -mips64
12616 @opindex mips64
12617 Equivalent to @samp{-march=mips64}.
12618
12619 @item -mips64r2
12620 @opindex mips64r2
12621 Equivalent to @samp{-march=mips64r2}.
12622
12623 @item -mips16
12624 @itemx -mno-mips16
12625 @opindex mips16
12626 @opindex mno-mips16
12627 Generate (do not generate) MIPS16 code. If GCC is targetting a
12628 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
12629
12630 MIPS16 code generation can also be controlled on a per-function basis
12631 by means of @code{mips16} and @code{nomips16} attributes.
12632 @xref{Function Attributes}, for more information.
12633
12634 @item -mflip-mips16
12635 @opindex mflip-mips16
12636 Generate MIPS16 code on alternating functions. This option is provided
12637 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
12638 not intended for ordinary use in compiling user code.
12639
12640 @item -minterlink-mips16
12641 @itemx -mno-interlink-mips16
12642 @opindex minterlink-mips16
12643 @opindex mno-interlink-mips16
12644 Require (do not require) that non-MIPS16 code be link-compatible with
12645 MIPS16 code.
12646
12647 For example, non-MIPS16 code cannot jump directly to MIPS16 code;
12648 it must either use a call or an indirect jump. @option{-minterlink-mips16}
12649 therefore disables direct jumps unless GCC knows that the target of the
12650 jump is not MIPS16.
12651
12652 @item -mabi=32
12653 @itemx -mabi=o64
12654 @itemx -mabi=n32
12655 @itemx -mabi=64
12656 @itemx -mabi=eabi
12657 @opindex mabi=32
12658 @opindex mabi=o64
12659 @opindex mabi=n32
12660 @opindex mabi=64
12661 @opindex mabi=eabi
12662 Generate code for the given ABI@.
12663
12664 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
12665 generates 64-bit code when you select a 64-bit architecture, but you
12666 can use @option{-mgp32} to get 32-bit code instead.
12667
12668 For information about the O64 ABI, see
12669 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
12670
12671 GCC supports a variant of the o32 ABI in which floating-point registers
12672 are 64 rather than 32 bits wide. You can select this combination with
12673 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
12674 and @samp{mfhc1} instructions and is therefore only supported for
12675 MIPS32R2 processors.
12676
12677 The register assignments for arguments and return values remain the
12678 same, but each scalar value is passed in a single 64-bit register
12679 rather than a pair of 32-bit registers. For example, scalar
12680 floating-point values are returned in @samp{$f0} only, not a
12681 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
12682 remains the same, but all 64 bits are saved.
12683
12684 @item -mabicalls
12685 @itemx -mno-abicalls
12686 @opindex mabicalls
12687 @opindex mno-abicalls
12688 Generate (do not generate) code that is suitable for SVR4-style
12689 dynamic objects. @option{-mabicalls} is the default for SVR4-based
12690 systems.
12691
12692 @item -mshared
12693 @itemx -mno-shared
12694 Generate (do not generate) code that is fully position-independent,
12695 and that can therefore be linked into shared libraries. This option
12696 only affects @option{-mabicalls}.
12697
12698 All @option{-mabicalls} code has traditionally been position-independent,
12699 regardless of options like @option{-fPIC} and @option{-fpic}. However,
12700 as an extension, the GNU toolchain allows executables to use absolute
12701 accesses for locally-binding symbols. It can also use shorter GP
12702 initialization sequences and generate direct calls to locally-defined
12703 functions. This mode is selected by @option{-mno-shared}.
12704
12705 @option{-mno-shared} depends on binutils 2.16 or higher and generates
12706 objects that can only be linked by the GNU linker. However, the option
12707 does not affect the ABI of the final executable; it only affects the ABI
12708 of relocatable objects. Using @option{-mno-shared} will generally make
12709 executables both smaller and quicker.
12710
12711 @option{-mshared} is the default.
12712
12713 @item -mplt
12714 @itemx -mno-plt
12715 @opindex mplt
12716 @opindex mno-plt
12717 Assume (do not assume) that the static and dynamic linkers
12718 support PLTs and copy relocations. This option only affects
12719 @samp{-mno-shared -mabicalls}. For the n64 ABI, this option
12720 has no effect without @samp{-msym32}.
12721
12722 You can make @option{-mplt} the default by configuring
12723 GCC with @option{--with-mips-plt}. The default is
12724 @option{-mno-plt} otherwise.
12725
12726 @item -mxgot
12727 @itemx -mno-xgot
12728 @opindex mxgot
12729 @opindex mno-xgot
12730 Lift (do not lift) the usual restrictions on the size of the global
12731 offset table.
12732
12733 GCC normally uses a single instruction to load values from the GOT@.
12734 While this is relatively efficient, it will only work if the GOT
12735 is smaller than about 64k. Anything larger will cause the linker
12736 to report an error such as:
12737
12738 @cindex relocation truncated to fit (MIPS)
12739 @smallexample
12740 relocation truncated to fit: R_MIPS_GOT16 foobar
12741 @end smallexample
12742
12743 If this happens, you should recompile your code with @option{-mxgot}.
12744 It should then work with very large GOTs, although it will also be
12745 less efficient, since it will take three instructions to fetch the
12746 value of a global symbol.
12747
12748 Note that some linkers can create multiple GOTs. If you have such a
12749 linker, you should only need to use @option{-mxgot} when a single object
12750 file accesses more than 64k's worth of GOT entries. Very few do.
12751
12752 These options have no effect unless GCC is generating position
12753 independent code.
12754
12755 @item -mgp32
12756 @opindex mgp32
12757 Assume that general-purpose registers are 32 bits wide.
12758
12759 @item -mgp64
12760 @opindex mgp64
12761 Assume that general-purpose registers are 64 bits wide.
12762
12763 @item -mfp32
12764 @opindex mfp32
12765 Assume that floating-point registers are 32 bits wide.
12766
12767 @item -mfp64
12768 @opindex mfp64
12769 Assume that floating-point registers are 64 bits wide.
12770
12771 @item -mhard-float
12772 @opindex mhard-float
12773 Use floating-point coprocessor instructions.
12774
12775 @item -msoft-float
12776 @opindex msoft-float
12777 Do not use floating-point coprocessor instructions. Implement
12778 floating-point calculations using library calls instead.
12779
12780 @item -msingle-float
12781 @opindex msingle-float
12782 Assume that the floating-point coprocessor only supports single-precision
12783 operations.
12784
12785 @item -mdouble-float
12786 @opindex mdouble-float
12787 Assume that the floating-point coprocessor supports double-precision
12788 operations. This is the default.
12789
12790 @item -mllsc
12791 @itemx -mno-llsc
12792 @opindex mllsc
12793 @opindex mno-llsc
12794 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
12795 implement atomic memory built-in functions. When neither option is
12796 specified, GCC will use the instructions if the target architecture
12797 supports them.
12798
12799 @option{-mllsc} is useful if the runtime environment can emulate the
12800 instructions and @option{-mno-llsc} can be useful when compiling for
12801 nonstandard ISAs. You can make either option the default by
12802 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
12803 respectively. @option{--with-llsc} is the default for some
12804 configurations; see the installation documentation for details.
12805
12806 @item -mdsp
12807 @itemx -mno-dsp
12808 @opindex mdsp
12809 @opindex mno-dsp
12810 Use (do not use) revision 1 of the MIPS DSP ASE@.
12811 @xref{MIPS DSP Built-in Functions}. This option defines the
12812 preprocessor macro @samp{__mips_dsp}. It also defines
12813 @samp{__mips_dsp_rev} to 1.
12814
12815 @item -mdspr2
12816 @itemx -mno-dspr2
12817 @opindex mdspr2
12818 @opindex mno-dspr2
12819 Use (do not use) revision 2 of the MIPS DSP ASE@.
12820 @xref{MIPS DSP Built-in Functions}. This option defines the
12821 preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}.
12822 It also defines @samp{__mips_dsp_rev} to 2.
12823
12824 @item -msmartmips
12825 @itemx -mno-smartmips
12826 @opindex msmartmips
12827 @opindex mno-smartmips
12828 Use (do not use) the MIPS SmartMIPS ASE.
12829
12830 @item -mpaired-single
12831 @itemx -mno-paired-single
12832 @opindex mpaired-single
12833 @opindex mno-paired-single
12834 Use (do not use) paired-single floating-point instructions.
12835 @xref{MIPS Paired-Single Support}. This option requires
12836 hardware floating-point support to be enabled.
12837
12838 @item -mdmx
12839 @itemx -mno-mdmx
12840 @opindex mdmx
12841 @opindex mno-mdmx
12842 Use (do not use) MIPS Digital Media Extension instructions.
12843 This option can only be used when generating 64-bit code and requires
12844 hardware floating-point support to be enabled.
12845
12846 @item -mips3d
12847 @itemx -mno-mips3d
12848 @opindex mips3d
12849 @opindex mno-mips3d
12850 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
12851 The option @option{-mips3d} implies @option{-mpaired-single}.
12852
12853 @item -mmt
12854 @itemx -mno-mt
12855 @opindex mmt
12856 @opindex mno-mt
12857 Use (do not use) MT Multithreading instructions.
12858
12859 @item -mlong64
12860 @opindex mlong64
12861 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
12862 an explanation of the default and the way that the pointer size is
12863 determined.
12864
12865 @item -mlong32
12866 @opindex mlong32
12867 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
12868
12869 The default size of @code{int}s, @code{long}s and pointers depends on
12870 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
12871 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
12872 32-bit @code{long}s. Pointers are the same size as @code{long}s,
12873 or the same size as integer registers, whichever is smaller.
12874
12875 @item -msym32
12876 @itemx -mno-sym32
12877 @opindex msym32
12878 @opindex mno-sym32
12879 Assume (do not assume) that all symbols have 32-bit values, regardless
12880 of the selected ABI@. This option is useful in combination with
12881 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
12882 to generate shorter and faster references to symbolic addresses.
12883
12884 @item -G @var{num}
12885 @opindex G
12886 Put definitions of externally-visible data in a small data section
12887 if that data is no bigger than @var{num} bytes. GCC can then access
12888 the data more efficiently; see @option{-mgpopt} for details.
12889
12890 The default @option{-G} option depends on the configuration.
12891
12892 @item -mlocal-sdata
12893 @itemx -mno-local-sdata
12894 @opindex mlocal-sdata
12895 @opindex mno-local-sdata
12896 Extend (do not extend) the @option{-G} behavior to local data too,
12897 such as to static variables in C@. @option{-mlocal-sdata} is the
12898 default for all configurations.
12899
12900 If the linker complains that an application is using too much small data,
12901 you might want to try rebuilding the less performance-critical parts with
12902 @option{-mno-local-sdata}. You might also want to build large
12903 libraries with @option{-mno-local-sdata}, so that the libraries leave
12904 more room for the main program.
12905
12906 @item -mextern-sdata
12907 @itemx -mno-extern-sdata
12908 @opindex mextern-sdata
12909 @opindex mno-extern-sdata
12910 Assume (do not assume) that externally-defined data will be in
12911 a small data section if that data is within the @option{-G} limit.
12912 @option{-mextern-sdata} is the default for all configurations.
12913
12914 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
12915 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
12916 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
12917 is placed in a small data section. If @var{Var} is defined by another
12918 module, you must either compile that module with a high-enough
12919 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
12920 definition. If @var{Var} is common, you must link the application
12921 with a high-enough @option{-G} setting.
12922
12923 The easiest way of satisfying these restrictions is to compile
12924 and link every module with the same @option{-G} option. However,
12925 you may wish to build a library that supports several different
12926 small data limits. You can do this by compiling the library with
12927 the highest supported @option{-G} setting and additionally using
12928 @option{-mno-extern-sdata} to stop the library from making assumptions
12929 about externally-defined data.
12930
12931 @item -mgpopt
12932 @itemx -mno-gpopt
12933 @opindex mgpopt
12934 @opindex mno-gpopt
12935 Use (do not use) GP-relative accesses for symbols that are known to be
12936 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
12937 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
12938 configurations.
12939
12940 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
12941 might not hold the value of @code{_gp}. For example, if the code is
12942 part of a library that might be used in a boot monitor, programs that
12943 call boot monitor routines will pass an unknown value in @code{$gp}.
12944 (In such situations, the boot monitor itself would usually be compiled
12945 with @option{-G0}.)
12946
12947 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
12948 @option{-mno-extern-sdata}.
12949
12950 @item -membedded-data
12951 @itemx -mno-embedded-data
12952 @opindex membedded-data
12953 @opindex mno-embedded-data
12954 Allocate variables to the read-only data section first if possible, then
12955 next in the small data section if possible, otherwise in data. This gives
12956 slightly slower code than the default, but reduces the amount of RAM required
12957 when executing, and thus may be preferred for some embedded systems.
12958
12959 @item -muninit-const-in-rodata
12960 @itemx -mno-uninit-const-in-rodata
12961 @opindex muninit-const-in-rodata
12962 @opindex mno-uninit-const-in-rodata
12963 Put uninitialized @code{const} variables in the read-only data section.
12964 This option is only meaningful in conjunction with @option{-membedded-data}.
12965
12966 @item -mcode-readable=@var{setting}
12967 @opindex mcode-readable
12968 Specify whether GCC may generate code that reads from executable sections.
12969 There are three possible settings:
12970
12971 @table @gcctabopt
12972 @item -mcode-readable=yes
12973 Instructions may freely access executable sections. This is the
12974 default setting.
12975
12976 @item -mcode-readable=pcrel
12977 MIPS16 PC-relative load instructions can access executable sections,
12978 but other instructions must not do so. This option is useful on 4KSc
12979 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
12980 It is also useful on processors that can be configured to have a dual
12981 instruction/data SRAM interface and that, like the M4K, automatically
12982 redirect PC-relative loads to the instruction RAM.
12983
12984 @item -mcode-readable=no
12985 Instructions must not access executable sections. This option can be
12986 useful on targets that are configured to have a dual instruction/data
12987 SRAM interface but that (unlike the M4K) do not automatically redirect
12988 PC-relative loads to the instruction RAM.
12989 @end table
12990
12991 @item -msplit-addresses
12992 @itemx -mno-split-addresses
12993 @opindex msplit-addresses
12994 @opindex mno-split-addresses
12995 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
12996 relocation operators. This option has been superseded by
12997 @option{-mexplicit-relocs} but is retained for backwards compatibility.
12998
12999 @item -mexplicit-relocs
13000 @itemx -mno-explicit-relocs
13001 @opindex mexplicit-relocs
13002 @opindex mno-explicit-relocs
13003 Use (do not use) assembler relocation operators when dealing with symbolic
13004 addresses. The alternative, selected by @option{-mno-explicit-relocs},
13005 is to use assembler macros instead.
13006
13007 @option{-mexplicit-relocs} is the default if GCC was configured
13008 to use an assembler that supports relocation operators.
13009
13010 @item -mcheck-zero-division
13011 @itemx -mno-check-zero-division
13012 @opindex mcheck-zero-division
13013 @opindex mno-check-zero-division
13014 Trap (do not trap) on integer division by zero.
13015
13016 The default is @option{-mcheck-zero-division}.
13017
13018 @item -mdivide-traps
13019 @itemx -mdivide-breaks
13020 @opindex mdivide-traps
13021 @opindex mdivide-breaks
13022 MIPS systems check for division by zero by generating either a
13023 conditional trap or a break instruction. Using traps results in
13024 smaller code, but is only supported on MIPS II and later. Also, some
13025 versions of the Linux kernel have a bug that prevents trap from
13026 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
13027 allow conditional traps on architectures that support them and
13028 @option{-mdivide-breaks} to force the use of breaks.
13029
13030 The default is usually @option{-mdivide-traps}, but this can be
13031 overridden at configure time using @option{--with-divide=breaks}.
13032 Divide-by-zero checks can be completely disabled using
13033 @option{-mno-check-zero-division}.
13034
13035 @item -mmemcpy
13036 @itemx -mno-memcpy
13037 @opindex mmemcpy
13038 @opindex mno-memcpy
13039 Force (do not force) the use of @code{memcpy()} for non-trivial block
13040 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
13041 most constant-sized copies.
13042
13043 @item -mlong-calls
13044 @itemx -mno-long-calls
13045 @opindex mlong-calls
13046 @opindex mno-long-calls
13047 Disable (do not disable) use of the @code{jal} instruction. Calling
13048 functions using @code{jal} is more efficient but requires the caller
13049 and callee to be in the same 256 megabyte segment.
13050
13051 This option has no effect on abicalls code. The default is
13052 @option{-mno-long-calls}.
13053
13054 @item -mmad
13055 @itemx -mno-mad
13056 @opindex mmad
13057 @opindex mno-mad
13058 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
13059 instructions, as provided by the R4650 ISA@.
13060
13061 @item -mfused-madd
13062 @itemx -mno-fused-madd
13063 @opindex mfused-madd
13064 @opindex mno-fused-madd
13065 Enable (disable) use of the floating point multiply-accumulate
13066 instructions, when they are available. The default is
13067 @option{-mfused-madd}.
13068
13069 When multiply-accumulate instructions are used, the intermediate
13070 product is calculated to infinite precision and is not subject to
13071 the FCSR Flush to Zero bit. This may be undesirable in some
13072 circumstances.
13073
13074 @item -nocpp
13075 @opindex nocpp
13076 Tell the MIPS assembler to not run its preprocessor over user
13077 assembler files (with a @samp{.s} suffix) when assembling them.
13078
13079 @item -mfix-r4000
13080 @itemx -mno-fix-r4000
13081 @opindex mfix-r4000
13082 @opindex mno-fix-r4000
13083 Work around certain R4000 CPU errata:
13084 @itemize @minus
13085 @item
13086 A double-word or a variable shift may give an incorrect result if executed
13087 immediately after starting an integer division.
13088 @item
13089 A double-word or a variable shift may give an incorrect result if executed
13090 while an integer multiplication is in progress.
13091 @item
13092 An integer division may give an incorrect result if started in a delay slot
13093 of a taken branch or a jump.
13094 @end itemize
13095
13096 @item -mfix-r4400
13097 @itemx -mno-fix-r4400
13098 @opindex mfix-r4400
13099 @opindex mno-fix-r4400
13100 Work around certain R4400 CPU errata:
13101 @itemize @minus
13102 @item
13103 A double-word or a variable shift may give an incorrect result if executed
13104 immediately after starting an integer division.
13105 @end itemize
13106
13107 @item -mfix-r10000
13108 @itemx -mno-fix-r10000
13109 @opindex mfix-r10000
13110 @opindex mno-fix-r10000
13111 Work around certain R10000 errata:
13112 @itemize @minus
13113 @item
13114 @code{ll}/@code{sc} sequences may not behave atomically on revisions
13115 prior to 3.0. They may deadlock on revisions 2.6 and earlier.
13116 @end itemize
13117
13118 This option can only be used if the target architecture supports
13119 branch-likely instructions. @option{-mfix-r10000} is the default when
13120 @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default
13121 otherwise.
13122
13123 @item -mfix-vr4120
13124 @itemx -mno-fix-vr4120
13125 @opindex mfix-vr4120
13126 Work around certain VR4120 errata:
13127 @itemize @minus
13128 @item
13129 @code{dmultu} does not always produce the correct result.
13130 @item
13131 @code{div} and @code{ddiv} do not always produce the correct result if one
13132 of the operands is negative.
13133 @end itemize
13134 The workarounds for the division errata rely on special functions in
13135 @file{libgcc.a}. At present, these functions are only provided by
13136 the @code{mips64vr*-elf} configurations.
13137
13138 Other VR4120 errata require a nop to be inserted between certain pairs of
13139 instructions. These errata are handled by the assembler, not by GCC itself.
13140
13141 @item -mfix-vr4130
13142 @opindex mfix-vr4130
13143 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
13144 workarounds are implemented by the assembler rather than by GCC,
13145 although GCC will avoid using @code{mflo} and @code{mfhi} if the
13146 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
13147 instructions are available instead.
13148
13149 @item -mfix-sb1
13150 @itemx -mno-fix-sb1
13151 @opindex mfix-sb1
13152 Work around certain SB-1 CPU core errata.
13153 (This flag currently works around the SB-1 revision 2
13154 ``F1'' and ``F2'' floating point errata.)
13155
13156 @item -mr10k-cache-barrier=@var{setting}
13157 @opindex mr10k-cache-barrier
13158 Specify whether GCC should insert cache barriers to avoid the
13159 side-effects of speculation on R10K processors.
13160
13161 In common with many processors, the R10K tries to predict the outcome
13162 of a conditional branch and speculatively executes instructions from
13163 the ``taken'' branch. It later aborts these instructions if the
13164 predicted outcome was wrong. However, on the R10K, even aborted
13165 instructions can have side effects.
13166
13167 This problem only affects kernel stores and, depending on the system,
13168 kernel loads. As an example, a speculatively-executed store may load
13169 the target memory into cache and mark the cache line as dirty, even if
13170 the store itself is later aborted. If a DMA operation writes to the
13171 same area of memory before the ``dirty'' line is flushed, the cached
13172 data will overwrite the DMA-ed data. See the R10K processor manual
13173 for a full description, including other potential problems.
13174
13175 One workaround is to insert cache barrier instructions before every memory
13176 access that might be speculatively executed and that might have side
13177 effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}}
13178 controls GCC's implementation of this workaround. It assumes that
13179 aborted accesses to any byte in the following regions will not have
13180 side effects:
13181
13182 @enumerate
13183 @item
13184 the memory occupied by the current function's stack frame;
13185
13186 @item
13187 the memory occupied by an incoming stack argument;
13188
13189 @item
13190 the memory occupied by an object with a link-time-constant address.
13191 @end enumerate
13192
13193 It is the kernel's responsibility to ensure that speculative
13194 accesses to these regions are indeed safe.
13195
13196 If the input program contains a function declaration such as:
13197
13198 @smallexample
13199 void foo (void);
13200 @end smallexample
13201
13202 then the implementation of @code{foo} must allow @code{j foo} and
13203 @code{jal foo} to be executed speculatively. GCC honors this
13204 restriction for functions it compiles itself. It expects non-GCC
13205 functions (such as hand-written assembly code) to do the same.
13206
13207 The option has three forms:
13208
13209 @table @gcctabopt
13210 @item -mr10k-cache-barrier=load-store
13211 Insert a cache barrier before a load or store that might be
13212 speculatively executed and that might have side effects even
13213 if aborted.
13214
13215 @item -mr10k-cache-barrier=store
13216 Insert a cache barrier before a store that might be speculatively
13217 executed and that might have side effects even if aborted.
13218
13219 @item -mr10k-cache-barrier=none
13220 Disable the insertion of cache barriers. This is the default setting.
13221 @end table
13222
13223 @item -mflush-func=@var{func}
13224 @itemx -mno-flush-func
13225 @opindex mflush-func
13226 Specifies the function to call to flush the I and D caches, or to not
13227 call any such function. If called, the function must take the same
13228 arguments as the common @code{_flush_func()}, that is, the address of the
13229 memory range for which the cache is being flushed, the size of the
13230 memory range, and the number 3 (to flush both caches). The default
13231 depends on the target GCC was configured for, but commonly is either
13232 @samp{_flush_func} or @samp{__cpu_flush}.
13233
13234 @item mbranch-cost=@var{num}
13235 @opindex mbranch-cost
13236 Set the cost of branches to roughly @var{num} ``simple'' instructions.
13237 This cost is only a heuristic and is not guaranteed to produce
13238 consistent results across releases. A zero cost redundantly selects
13239 the default, which is based on the @option{-mtune} setting.
13240
13241 @item -mbranch-likely
13242 @itemx -mno-branch-likely
13243 @opindex mbranch-likely
13244 @opindex mno-branch-likely
13245 Enable or disable use of Branch Likely instructions, regardless of the
13246 default for the selected architecture. By default, Branch Likely
13247 instructions may be generated if they are supported by the selected
13248 architecture. An exception is for the MIPS32 and MIPS64 architectures
13249 and processors which implement those architectures; for those, Branch
13250 Likely instructions will not be generated by default because the MIPS32
13251 and MIPS64 architectures specifically deprecate their use.
13252
13253 @item -mfp-exceptions
13254 @itemx -mno-fp-exceptions
13255 @opindex mfp-exceptions
13256 Specifies whether FP exceptions are enabled. This affects how we schedule
13257 FP instructions for some processors. The default is that FP exceptions are
13258 enabled.
13259
13260 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
13261 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
13262 FP pipe.
13263
13264 @item -mvr4130-align
13265 @itemx -mno-vr4130-align
13266 @opindex mvr4130-align
13267 The VR4130 pipeline is two-way superscalar, but can only issue two
13268 instructions together if the first one is 8-byte aligned. When this
13269 option is enabled, GCC will align pairs of instructions that it
13270 thinks should execute in parallel.
13271
13272 This option only has an effect when optimizing for the VR4130.
13273 It normally makes code faster, but at the expense of making it bigger.
13274 It is enabled by default at optimization level @option{-O3}.
13275 @end table
13276
13277 @node MMIX Options
13278 @subsection MMIX Options
13279 @cindex MMIX Options
13280
13281 These options are defined for the MMIX:
13282
13283 @table @gcctabopt
13284 @item -mlibfuncs
13285 @itemx -mno-libfuncs
13286 @opindex mlibfuncs
13287 @opindex mno-libfuncs
13288 Specify that intrinsic library functions are being compiled, passing all
13289 values in registers, no matter the size.
13290
13291 @item -mepsilon
13292 @itemx -mno-epsilon
13293 @opindex mepsilon
13294 @opindex mno-epsilon
13295 Generate floating-point comparison instructions that compare with respect
13296 to the @code{rE} epsilon register.
13297
13298 @item -mabi=mmixware
13299 @itemx -mabi=gnu
13300 @opindex mabi-mmixware
13301 @opindex mabi=gnu
13302 Generate code that passes function parameters and return values that (in
13303 the called function) are seen as registers @code{$0} and up, as opposed to
13304 the GNU ABI which uses global registers @code{$231} and up.
13305
13306 @item -mzero-extend
13307 @itemx -mno-zero-extend
13308 @opindex mzero-extend
13309 @opindex mno-zero-extend
13310 When reading data from memory in sizes shorter than 64 bits, use (do not
13311 use) zero-extending load instructions by default, rather than
13312 sign-extending ones.
13313
13314 @item -mknuthdiv
13315 @itemx -mno-knuthdiv
13316 @opindex mknuthdiv
13317 @opindex mno-knuthdiv
13318 Make the result of a division yielding a remainder have the same sign as
13319 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
13320 remainder follows the sign of the dividend. Both methods are
13321 arithmetically valid, the latter being almost exclusively used.
13322
13323 @item -mtoplevel-symbols
13324 @itemx -mno-toplevel-symbols
13325 @opindex mtoplevel-symbols
13326 @opindex mno-toplevel-symbols
13327 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
13328 code can be used with the @code{PREFIX} assembly directive.
13329
13330 @item -melf
13331 @opindex melf
13332 Generate an executable in the ELF format, rather than the default
13333 @samp{mmo} format used by the @command{mmix} simulator.
13334
13335 @item -mbranch-predict
13336 @itemx -mno-branch-predict
13337 @opindex mbranch-predict
13338 @opindex mno-branch-predict
13339 Use (do not use) the probable-branch instructions, when static branch
13340 prediction indicates a probable branch.
13341
13342 @item -mbase-addresses
13343 @itemx -mno-base-addresses
13344 @opindex mbase-addresses
13345 @opindex mno-base-addresses
13346 Generate (do not generate) code that uses @emph{base addresses}. Using a
13347 base address automatically generates a request (handled by the assembler
13348 and the linker) for a constant to be set up in a global register. The
13349 register is used for one or more base address requests within the range 0
13350 to 255 from the value held in the register. The generally leads to short
13351 and fast code, but the number of different data items that can be
13352 addressed is limited. This means that a program that uses lots of static
13353 data may require @option{-mno-base-addresses}.
13354
13355 @item -msingle-exit
13356 @itemx -mno-single-exit
13357 @opindex msingle-exit
13358 @opindex mno-single-exit
13359 Force (do not force) generated code to have a single exit point in each
13360 function.
13361 @end table
13362
13363 @node MN10300 Options
13364 @subsection MN10300 Options
13365 @cindex MN10300 options
13366
13367 These @option{-m} options are defined for Matsushita MN10300 architectures:
13368
13369 @table @gcctabopt
13370 @item -mmult-bug
13371 @opindex mmult-bug
13372 Generate code to avoid bugs in the multiply instructions for the MN10300
13373 processors. This is the default.
13374
13375 @item -mno-mult-bug
13376 @opindex mno-mult-bug
13377 Do not generate code to avoid bugs in the multiply instructions for the
13378 MN10300 processors.
13379
13380 @item -mam33
13381 @opindex mam33
13382 Generate code which uses features specific to the AM33 processor.
13383
13384 @item -mno-am33
13385 @opindex mno-am33
13386 Do not generate code which uses features specific to the AM33 processor. This
13387 is the default.
13388
13389 @item -mreturn-pointer-on-d0
13390 @opindex mreturn-pointer-on-d0
13391 When generating a function which returns a pointer, return the pointer
13392 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
13393 only in a0, and attempts to call such functions without a prototype
13394 would result in errors. Note that this option is on by default; use
13395 @option{-mno-return-pointer-on-d0} to disable it.
13396
13397 @item -mno-crt0
13398 @opindex mno-crt0
13399 Do not link in the C run-time initialization object file.
13400
13401 @item -mrelax
13402 @opindex mrelax
13403 Indicate to the linker that it should perform a relaxation optimization pass
13404 to shorten branches, calls and absolute memory addresses. This option only
13405 has an effect when used on the command line for the final link step.
13406
13407 This option makes symbolic debugging impossible.
13408 @end table
13409
13410 @node PDP-11 Options
13411 @subsection PDP-11 Options
13412 @cindex PDP-11 Options
13413
13414 These options are defined for the PDP-11:
13415
13416 @table @gcctabopt
13417 @item -mfpu
13418 @opindex mfpu
13419 Use hardware FPP floating point. This is the default. (FIS floating
13420 point on the PDP-11/40 is not supported.)
13421
13422 @item -msoft-float
13423 @opindex msoft-float
13424 Do not use hardware floating point.
13425
13426 @item -mac0
13427 @opindex mac0
13428 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
13429
13430 @item -mno-ac0
13431 @opindex mno-ac0
13432 Return floating-point results in memory. This is the default.
13433
13434 @item -m40
13435 @opindex m40
13436 Generate code for a PDP-11/40.
13437
13438 @item -m45
13439 @opindex m45
13440 Generate code for a PDP-11/45. This is the default.
13441
13442 @item -m10
13443 @opindex m10
13444 Generate code for a PDP-11/10.
13445
13446 @item -mbcopy-builtin
13447 @opindex bcopy-builtin
13448 Use inline @code{movmemhi} patterns for copying memory. This is the
13449 default.
13450
13451 @item -mbcopy
13452 @opindex mbcopy
13453 Do not use inline @code{movmemhi} patterns for copying memory.
13454
13455 @item -mint16
13456 @itemx -mno-int32
13457 @opindex mint16
13458 @opindex mno-int32
13459 Use 16-bit @code{int}. This is the default.
13460
13461 @item -mint32
13462 @itemx -mno-int16
13463 @opindex mint32
13464 @opindex mno-int16
13465 Use 32-bit @code{int}.
13466
13467 @item -mfloat64
13468 @itemx -mno-float32
13469 @opindex mfloat64
13470 @opindex mno-float32
13471 Use 64-bit @code{float}. This is the default.
13472
13473 @item -mfloat32
13474 @itemx -mno-float64
13475 @opindex mfloat32
13476 @opindex mno-float64
13477 Use 32-bit @code{float}.
13478
13479 @item -mabshi
13480 @opindex mabshi
13481 Use @code{abshi2} pattern. This is the default.
13482
13483 @item -mno-abshi
13484 @opindex mno-abshi
13485 Do not use @code{abshi2} pattern.
13486
13487 @item -mbranch-expensive
13488 @opindex mbranch-expensive
13489 Pretend that branches are expensive. This is for experimenting with
13490 code generation only.
13491
13492 @item -mbranch-cheap
13493 @opindex mbranch-cheap
13494 Do not pretend that branches are expensive. This is the default.
13495
13496 @item -msplit
13497 @opindex msplit
13498 Generate code for a system with split I&D@.
13499
13500 @item -mno-split
13501 @opindex mno-split
13502 Generate code for a system without split I&D@. This is the default.
13503
13504 @item -munix-asm
13505 @opindex munix-asm
13506 Use Unix assembler syntax. This is the default when configured for
13507 @samp{pdp11-*-bsd}.
13508
13509 @item -mdec-asm
13510 @opindex mdec-asm
13511 Use DEC assembler syntax. This is the default when configured for any
13512 PDP-11 target other than @samp{pdp11-*-bsd}.
13513 @end table
13514
13515 @node picoChip Options
13516 @subsection picoChip Options
13517 @cindex picoChip options
13518
13519 These @samp{-m} options are defined for picoChip implementations:
13520
13521 @table @gcctabopt
13522
13523 @item -mae=@var{ae_type}
13524 @opindex mcpu
13525 Set the instruction set, register set, and instruction scheduling
13526 parameters for array element type @var{ae_type}. Supported values
13527 for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}.
13528
13529 @option{-mae=ANY} selects a completely generic AE type. Code
13530 generated with this option will run on any of the other AE types. The
13531 code will not be as efficient as it would be if compiled for a specific
13532 AE type, and some types of operation (e.g., multiplication) will not
13533 work properly on all types of AE.
13534
13535 @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type
13536 for compiled code, and is the default.
13537
13538 @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this
13539 option may suffer from poor performance of byte (char) manipulation,
13540 since the DSP AE does not provide hardware support for byte load/stores.
13541
13542 @item -msymbol-as-address
13543 Enable the compiler to directly use a symbol name as an address in a
13544 load/store instruction, without first loading it into a
13545 register. Typically, the use of this option will generate larger
13546 programs, which run faster than when the option isn't used. However, the
13547 results vary from program to program, so it is left as a user option,
13548 rather than being permanently enabled.
13549
13550 @item -mno-inefficient-warnings
13551 Disables warnings about the generation of inefficient code. These
13552 warnings can be generated, for example, when compiling code which
13553 performs byte-level memory operations on the MAC AE type. The MAC AE has
13554 no hardware support for byte-level memory operations, so all byte
13555 load/stores must be synthesized from word load/store operations. This is
13556 inefficient and a warning will be generated indicating to the programmer
13557 that they should rewrite the code to avoid byte operations, or to target
13558 an AE type which has the necessary hardware support. This option enables
13559 the warning to be turned off.
13560
13561 @end table
13562
13563 @node PowerPC Options
13564 @subsection PowerPC Options
13565 @cindex PowerPC options
13566
13567 These are listed under @xref{RS/6000 and PowerPC Options}.
13568
13569 @node RS/6000 and PowerPC Options
13570 @subsection IBM RS/6000 and PowerPC Options
13571 @cindex RS/6000 and PowerPC Options
13572 @cindex IBM RS/6000 and PowerPC Options
13573
13574 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
13575 @table @gcctabopt
13576 @item -mpower
13577 @itemx -mno-power
13578 @itemx -mpower2
13579 @itemx -mno-power2
13580 @itemx -mpowerpc
13581 @itemx -mno-powerpc
13582 @itemx -mpowerpc-gpopt
13583 @itemx -mno-powerpc-gpopt
13584 @itemx -mpowerpc-gfxopt
13585 @itemx -mno-powerpc-gfxopt
13586 @itemx -mpowerpc64
13587 @itemx -mno-powerpc64
13588 @itemx -mmfcrf
13589 @itemx -mno-mfcrf
13590 @itemx -mpopcntb
13591 @itemx -mno-popcntb
13592 @itemx -mfprnd
13593 @itemx -mno-fprnd
13594 @itemx -mcmpb
13595 @itemx -mno-cmpb
13596 @itemx -mmfpgpr
13597 @itemx -mno-mfpgpr
13598 @itemx -mhard-dfp
13599 @itemx -mno-hard-dfp
13600 @opindex mpower
13601 @opindex mno-power
13602 @opindex mpower2
13603 @opindex mno-power2
13604 @opindex mpowerpc
13605 @opindex mno-powerpc
13606 @opindex mpowerpc-gpopt
13607 @opindex mno-powerpc-gpopt
13608 @opindex mpowerpc-gfxopt
13609 @opindex mno-powerpc-gfxopt
13610 @opindex mpowerpc64
13611 @opindex mno-powerpc64
13612 @opindex mmfcrf
13613 @opindex mno-mfcrf
13614 @opindex mpopcntb
13615 @opindex mno-popcntb
13616 @opindex mfprnd
13617 @opindex mno-fprnd
13618 @opindex mcmpb
13619 @opindex mno-cmpb
13620 @opindex mmfpgpr
13621 @opindex mno-mfpgpr
13622 @opindex mhard-dfp
13623 @opindex mno-hard-dfp
13624 GCC supports two related instruction set architectures for the
13625 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
13626 instructions supported by the @samp{rios} chip set used in the original
13627 RS/6000 systems and the @dfn{PowerPC} instruction set is the
13628 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
13629 the IBM 4xx, 6xx, and follow-on microprocessors.
13630
13631 Neither architecture is a subset of the other. However there is a
13632 large common subset of instructions supported by both. An MQ
13633 register is included in processors supporting the POWER architecture.
13634
13635 You use these options to specify which instructions are available on the
13636 processor you are using. The default value of these options is
13637 determined when configuring GCC@. Specifying the
13638 @option{-mcpu=@var{cpu_type}} overrides the specification of these
13639 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
13640 rather than the options listed above.
13641
13642 The @option{-mpower} option allows GCC to generate instructions that
13643 are found only in the POWER architecture and to use the MQ register.
13644 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
13645 to generate instructions that are present in the POWER2 architecture but
13646 not the original POWER architecture.
13647
13648 The @option{-mpowerpc} option allows GCC to generate instructions that
13649 are found only in the 32-bit subset of the PowerPC architecture.
13650 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
13651 GCC to use the optional PowerPC architecture instructions in the
13652 General Purpose group, including floating-point square root. Specifying
13653 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
13654 use the optional PowerPC architecture instructions in the Graphics
13655 group, including floating-point select.
13656
13657 The @option{-mmfcrf} option allows GCC to generate the move from
13658 condition register field instruction implemented on the POWER4
13659 processor and other processors that support the PowerPC V2.01
13660 architecture.
13661 The @option{-mpopcntb} option allows GCC to generate the popcount and
13662 double precision FP reciprocal estimate instruction implemented on the
13663 POWER5 processor and other processors that support the PowerPC V2.02
13664 architecture.
13665 The @option{-mfprnd} option allows GCC to generate the FP round to
13666 integer instructions implemented on the POWER5+ processor and other
13667 processors that support the PowerPC V2.03 architecture.
13668 The @option{-mcmpb} option allows GCC to generate the compare bytes
13669 instruction implemented on the POWER6 processor and other processors
13670 that support the PowerPC V2.05 architecture.
13671 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
13672 general purpose register instructions implemented on the POWER6X
13673 processor and other processors that support the extended PowerPC V2.05
13674 architecture.
13675 The @option{-mhard-dfp} option allows GCC to generate the decimal floating
13676 point instructions implemented on some POWER processors.
13677
13678 The @option{-mpowerpc64} option allows GCC to generate the additional
13679 64-bit instructions that are found in the full PowerPC64 architecture
13680 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
13681 @option{-mno-powerpc64}.
13682
13683 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
13684 will use only the instructions in the common subset of both
13685 architectures plus some special AIX common-mode calls, and will not use
13686 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
13687 permits GCC to use any instruction from either architecture and to
13688 allow use of the MQ register; specify this for the Motorola MPC601.
13689
13690 @item -mnew-mnemonics
13691 @itemx -mold-mnemonics
13692 @opindex mnew-mnemonics
13693 @opindex mold-mnemonics
13694 Select which mnemonics to use in the generated assembler code. With
13695 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
13696 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
13697 assembler mnemonics defined for the POWER architecture. Instructions
13698 defined in only one architecture have only one mnemonic; GCC uses that
13699 mnemonic irrespective of which of these options is specified.
13700
13701 GCC defaults to the mnemonics appropriate for the architecture in
13702 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
13703 value of these option. Unless you are building a cross-compiler, you
13704 should normally not specify either @option{-mnew-mnemonics} or
13705 @option{-mold-mnemonics}, but should instead accept the default.
13706
13707 @item -mcpu=@var{cpu_type}
13708 @opindex mcpu
13709 Set architecture type, register usage, choice of mnemonics, and
13710 instruction scheduling parameters for machine type @var{cpu_type}.
13711 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
13712 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
13713 @samp{505}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
13714 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
13715 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
13716 @samp{860}, @samp{970}, @samp{8540}, @samp{e300c2}, @samp{e300c3},
13717 @samp{e500mc}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
13718 @samp{power}, @samp{power2}, @samp{power3}, @samp{power4},
13719 @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x}, @samp{power7}
13720 @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
13721 @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
13722
13723 @option{-mcpu=common} selects a completely generic processor. Code
13724 generated under this option will run on any POWER or PowerPC processor.
13725 GCC will use only the instructions in the common subset of both
13726 architectures, and will not use the MQ register. GCC assumes a generic
13727 processor model for scheduling purposes.
13728
13729 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
13730 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
13731 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
13732 types, with an appropriate, generic processor model assumed for
13733 scheduling purposes.
13734
13735 The other options specify a specific processor. Code generated under
13736 those options will run best on that processor, and may not run at all on
13737 others.
13738
13739 The @option{-mcpu} options automatically enable or disable the
13740 following options:
13741
13742 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
13743 -mnew-mnemonics -mpopcntb -mpower -mpower2 -mpowerpc64 @gol
13744 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
13745 -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr}
13746
13747 The particular options set for any particular CPU will vary between
13748 compiler versions, depending on what setting seems to produce optimal
13749 code for that CPU; it doesn't necessarily reflect the actual hardware's
13750 capabilities. If you wish to set an individual option to a particular
13751 value, you may specify it after the @option{-mcpu} option, like
13752 @samp{-mcpu=970 -mno-altivec}.
13753
13754 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
13755 not enabled or disabled by the @option{-mcpu} option at present because
13756 AIX does not have full support for these options. You may still
13757 enable or disable them individually if you're sure it'll work in your
13758 environment.
13759
13760 @item -mtune=@var{cpu_type}
13761 @opindex mtune
13762 Set the instruction scheduling parameters for machine type
13763 @var{cpu_type}, but do not set the architecture type, register usage, or
13764 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
13765 values for @var{cpu_type} are used for @option{-mtune} as for
13766 @option{-mcpu}. If both are specified, the code generated will use the
13767 architecture, registers, and mnemonics set by @option{-mcpu}, but the
13768 scheduling parameters set by @option{-mtune}.
13769
13770 @item -mswdiv
13771 @itemx -mno-swdiv
13772 @opindex mswdiv
13773 @opindex mno-swdiv
13774 Generate code to compute division as reciprocal estimate and iterative
13775 refinement, creating opportunities for increased throughput. This
13776 feature requires: optional PowerPC Graphics instruction set for single
13777 precision and FRE instruction for double precision, assuming divides
13778 cannot generate user-visible traps, and the domain values not include
13779 Infinities, denormals or zero denominator.
13780
13781 @item -maltivec
13782 @itemx -mno-altivec
13783 @opindex maltivec
13784 @opindex mno-altivec
13785 Generate code that uses (does not use) AltiVec instructions, and also
13786 enable the use of built-in functions that allow more direct access to
13787 the AltiVec instruction set. You may also need to set
13788 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
13789 enhancements.
13790
13791 @item -mvrsave
13792 @itemx -mno-vrsave
13793 @opindex mvrsave
13794 @opindex mno-vrsave
13795 Generate VRSAVE instructions when generating AltiVec code.
13796
13797 @item -mgen-cell-microcode
13798 @opindex mgen-cell-microcode
13799 Generate Cell microcode instructions
13800
13801 @item -mwarn-cell-microcode
13802 @opindex mwarn-cell-microcode
13803 Warning when a Cell microcode instruction is going to emitted. An example
13804 of a Cell microcode instruction is a variable shift.
13805
13806 @item -msecure-plt
13807 @opindex msecure-plt
13808 Generate code that allows ld and ld.so to build executables and shared
13809 libraries with non-exec .plt and .got sections. This is a PowerPC
13810 32-bit SYSV ABI option.
13811
13812 @item -mbss-plt
13813 @opindex mbss-plt
13814 Generate code that uses a BSS .plt section that ld.so fills in, and
13815 requires .plt and .got sections that are both writable and executable.
13816 This is a PowerPC 32-bit SYSV ABI option.
13817
13818 @item -misel
13819 @itemx -mno-isel
13820 @opindex misel
13821 @opindex mno-isel
13822 This switch enables or disables the generation of ISEL instructions.
13823
13824 @item -misel=@var{yes/no}
13825 This switch has been deprecated. Use @option{-misel} and
13826 @option{-mno-isel} instead.
13827
13828 @item -mspe
13829 @itemx -mno-spe
13830 @opindex mspe
13831 @opindex mno-spe
13832 This switch enables or disables the generation of SPE simd
13833 instructions.
13834
13835 @item -mpaired
13836 @itemx -mno-paired
13837 @opindex mpaired
13838 @opindex mno-paired
13839 This switch enables or disables the generation of PAIRED simd
13840 instructions.
13841
13842 @item -mspe=@var{yes/no}
13843 This option has been deprecated. Use @option{-mspe} and
13844 @option{-mno-spe} instead.
13845
13846 @item -mfloat-gprs=@var{yes/single/double/no}
13847 @itemx -mfloat-gprs
13848 @opindex mfloat-gprs
13849 This switch enables or disables the generation of floating point
13850 operations on the general purpose registers for architectures that
13851 support it.
13852
13853 The argument @var{yes} or @var{single} enables the use of
13854 single-precision floating point operations.
13855
13856 The argument @var{double} enables the use of single and
13857 double-precision floating point operations.
13858
13859 The argument @var{no} disables floating point operations on the
13860 general purpose registers.
13861
13862 This option is currently only available on the MPC854x.
13863
13864 @item -m32
13865 @itemx -m64
13866 @opindex m32
13867 @opindex m64
13868 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
13869 targets (including GNU/Linux). The 32-bit environment sets int, long
13870 and pointer to 32 bits and generates code that runs on any PowerPC
13871 variant. The 64-bit environment sets int to 32 bits and long and
13872 pointer to 64 bits, and generates code for PowerPC64, as for
13873 @option{-mpowerpc64}.
13874
13875 @item -mfull-toc
13876 @itemx -mno-fp-in-toc
13877 @itemx -mno-sum-in-toc
13878 @itemx -mminimal-toc
13879 @opindex mfull-toc
13880 @opindex mno-fp-in-toc
13881 @opindex mno-sum-in-toc
13882 @opindex mminimal-toc
13883 Modify generation of the TOC (Table Of Contents), which is created for
13884 every executable file. The @option{-mfull-toc} option is selected by
13885 default. In that case, GCC will allocate at least one TOC entry for
13886 each unique non-automatic variable reference in your program. GCC
13887 will also place floating-point constants in the TOC@. However, only
13888 16,384 entries are available in the TOC@.
13889
13890 If you receive a linker error message that saying you have overflowed
13891 the available TOC space, you can reduce the amount of TOC space used
13892 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
13893 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
13894 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
13895 generate code to calculate the sum of an address and a constant at
13896 run-time instead of putting that sum into the TOC@. You may specify one
13897 or both of these options. Each causes GCC to produce very slightly
13898 slower and larger code at the expense of conserving TOC space.
13899
13900 If you still run out of space in the TOC even when you specify both of
13901 these options, specify @option{-mminimal-toc} instead. This option causes
13902 GCC to make only one TOC entry for every file. When you specify this
13903 option, GCC will produce code that is slower and larger but which
13904 uses extremely little TOC space. You may wish to use this option
13905 only on files that contain less frequently executed code.
13906
13907 @item -maix64
13908 @itemx -maix32
13909 @opindex maix64
13910 @opindex maix32
13911 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
13912 @code{long} type, and the infrastructure needed to support them.
13913 Specifying @option{-maix64} implies @option{-mpowerpc64} and
13914 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
13915 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
13916
13917 @item -mxl-compat
13918 @itemx -mno-xl-compat
13919 @opindex mxl-compat
13920 @opindex mno-xl-compat
13921 Produce code that conforms more closely to IBM XL compiler semantics
13922 when using AIX-compatible ABI@. Pass floating-point arguments to
13923 prototyped functions beyond the register save area (RSA) on the stack
13924 in addition to argument FPRs. Do not assume that most significant
13925 double in 128-bit long double value is properly rounded when comparing
13926 values and converting to double. Use XL symbol names for long double
13927 support routines.
13928
13929 The AIX calling convention was extended but not initially documented to
13930 handle an obscure K&R C case of calling a function that takes the
13931 address of its arguments with fewer arguments than declared. IBM XL
13932 compilers access floating point arguments which do not fit in the
13933 RSA from the stack when a subroutine is compiled without
13934 optimization. Because always storing floating-point arguments on the
13935 stack is inefficient and rarely needed, this option is not enabled by
13936 default and only is necessary when calling subroutines compiled by IBM
13937 XL compilers without optimization.
13938
13939 @item -mpe
13940 @opindex mpe
13941 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
13942 application written to use message passing with special startup code to
13943 enable the application to run. The system must have PE installed in the
13944 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
13945 must be overridden with the @option{-specs=} option to specify the
13946 appropriate directory location. The Parallel Environment does not
13947 support threads, so the @option{-mpe} option and the @option{-pthread}
13948 option are incompatible.
13949
13950 @item -malign-natural
13951 @itemx -malign-power
13952 @opindex malign-natural
13953 @opindex malign-power
13954 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
13955 @option{-malign-natural} overrides the ABI-defined alignment of larger
13956 types, such as floating-point doubles, on their natural size-based boundary.
13957 The option @option{-malign-power} instructs GCC to follow the ABI-specified
13958 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
13959
13960 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
13961 is not supported.
13962
13963 @item -msoft-float
13964 @itemx -mhard-float
13965 @opindex msoft-float
13966 @opindex mhard-float
13967 Generate code that does not use (uses) the floating-point register set.
13968 Software floating point emulation is provided if you use the
13969 @option{-msoft-float} option, and pass the option to GCC when linking.
13970
13971 @item -msingle-float
13972 @itemx -mdouble-float
13973 @opindex msingle-float
13974 @opindex mdouble-float
13975 Generate code for single or double-precision floating point operations.
13976 @option{-mdouble-float} implies @option{-msingle-float}.
13977
13978 @item -msimple-fpu
13979 @opindex msimple-fpu
13980 Do not generate sqrt and div instructions for hardware floating point unit.
13981
13982 @item -mfpu
13983 @opindex mfpu
13984 Specify type of floating point unit. Valid values are @var{sp_lite}
13985 (equivalent to -msingle-float -msimple-fpu), @var{dp_lite} (equivalent
13986 to -mdouble-float -msimple-fpu), @var{sp_full} (equivalent to -msingle-float),
13987 and @var{dp_full} (equivalent to -mdouble-float).
13988
13989 @item -mxilinx-fpu
13990 @opindex mxilinx-fpu
13991 Perform optimizations for floating point unit on Xilinx PPC 405/440.
13992
13993 @item -mmultiple
13994 @itemx -mno-multiple
13995 @opindex mmultiple
13996 @opindex mno-multiple
13997 Generate code that uses (does not use) the load multiple word
13998 instructions and the store multiple word instructions. These
13999 instructions are generated by default on POWER systems, and not
14000 generated on PowerPC systems. Do not use @option{-mmultiple} on little
14001 endian PowerPC systems, since those instructions do not work when the
14002 processor is in little endian mode. The exceptions are PPC740 and
14003 PPC750 which permit the instructions usage in little endian mode.
14004
14005 @item -mstring
14006 @itemx -mno-string
14007 @opindex mstring
14008 @opindex mno-string
14009 Generate code that uses (does not use) the load string instructions
14010 and the store string word instructions to save multiple registers and
14011 do small block moves. These instructions are generated by default on
14012 POWER systems, and not generated on PowerPC systems. Do not use
14013 @option{-mstring} on little endian PowerPC systems, since those
14014 instructions do not work when the processor is in little endian mode.
14015 The exceptions are PPC740 and PPC750 which permit the instructions
14016 usage in little endian mode.
14017
14018 @item -mupdate
14019 @itemx -mno-update
14020 @opindex mupdate
14021 @opindex mno-update
14022 Generate code that uses (does not use) the load or store instructions
14023 that update the base register to the address of the calculated memory
14024 location. These instructions are generated by default. If you use
14025 @option{-mno-update}, there is a small window between the time that the
14026 stack pointer is updated and the address of the previous frame is
14027 stored, which means code that walks the stack frame across interrupts or
14028 signals may get corrupted data.
14029
14030 @item -mavoid-indexed-addresses
14031 @item -mno-avoid-indexed-addresses
14032 @opindex mavoid-indexed-addresses
14033 @opindex mno-avoid-indexed-addresses
14034 Generate code that tries to avoid (not avoid) the use of indexed load
14035 or store instructions. These instructions can incur a performance
14036 penalty on Power6 processors in certain situations, such as when
14037 stepping through large arrays that cross a 16M boundary. This option
14038 is enabled by default when targetting Power6 and disabled otherwise.
14039
14040 @item -mfused-madd
14041 @itemx -mno-fused-madd
14042 @opindex mfused-madd
14043 @opindex mno-fused-madd
14044 Generate code that uses (does not use) the floating point multiply and
14045 accumulate instructions. These instructions are generated by default if
14046 hardware floating is used.
14047
14048 @item -mmulhw
14049 @itemx -mno-mulhw
14050 @opindex mmulhw
14051 @opindex mno-mulhw
14052 Generate code that uses (does not use) the half-word multiply and
14053 multiply-accumulate instructions on the IBM 405, 440 and 464 processors.
14054 These instructions are generated by default when targetting those
14055 processors.
14056
14057 @item -mdlmzb
14058 @itemx -mno-dlmzb
14059 @opindex mdlmzb
14060 @opindex mno-dlmzb
14061 Generate code that uses (does not use) the string-search @samp{dlmzb}
14062 instruction on the IBM 405, 440 and 464 processors. This instruction is
14063 generated by default when targetting those processors.
14064
14065 @item -mno-bit-align
14066 @itemx -mbit-align
14067 @opindex mno-bit-align
14068 @opindex mbit-align
14069 On System V.4 and embedded PowerPC systems do not (do) force structures
14070 and unions that contain bit-fields to be aligned to the base type of the
14071 bit-field.
14072
14073 For example, by default a structure containing nothing but 8
14074 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
14075 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
14076 the structure would be aligned to a 1 byte boundary and be one byte in
14077 size.
14078
14079 @item -mno-strict-align
14080 @itemx -mstrict-align
14081 @opindex mno-strict-align
14082 @opindex mstrict-align
14083 On System V.4 and embedded PowerPC systems do not (do) assume that
14084 unaligned memory references will be handled by the system.
14085
14086 @item -mrelocatable
14087 @itemx -mno-relocatable
14088 @opindex mrelocatable
14089 @opindex mno-relocatable
14090 On embedded PowerPC systems generate code that allows (does not allow)
14091 the program to be relocated to a different address at runtime. If you
14092 use @option{-mrelocatable} on any module, all objects linked together must
14093 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
14094
14095 @item -mrelocatable-lib
14096 @itemx -mno-relocatable-lib
14097 @opindex mrelocatable-lib
14098 @opindex mno-relocatable-lib
14099 On embedded PowerPC systems generate code that allows (does not allow)
14100 the program to be relocated to a different address at runtime. Modules
14101 compiled with @option{-mrelocatable-lib} can be linked with either modules
14102 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
14103 with modules compiled with the @option{-mrelocatable} options.
14104
14105 @item -mno-toc
14106 @itemx -mtoc
14107 @opindex mno-toc
14108 @opindex mtoc
14109 On System V.4 and embedded PowerPC systems do not (do) assume that
14110 register 2 contains a pointer to a global area pointing to the addresses
14111 used in the program.
14112
14113 @item -mlittle
14114 @itemx -mlittle-endian
14115 @opindex mlittle
14116 @opindex mlittle-endian
14117 On System V.4 and embedded PowerPC systems compile code for the
14118 processor in little endian mode. The @option{-mlittle-endian} option is
14119 the same as @option{-mlittle}.
14120
14121 @item -mbig
14122 @itemx -mbig-endian
14123 @opindex mbig
14124 @opindex mbig-endian
14125 On System V.4 and embedded PowerPC systems compile code for the
14126 processor in big endian mode. The @option{-mbig-endian} option is
14127 the same as @option{-mbig}.
14128
14129 @item -mdynamic-no-pic
14130 @opindex mdynamic-no-pic
14131 On Darwin and Mac OS X systems, compile code so that it is not
14132 relocatable, but that its external references are relocatable. The
14133 resulting code is suitable for applications, but not shared
14134 libraries.
14135
14136 @item -mprioritize-restricted-insns=@var{priority}
14137 @opindex mprioritize-restricted-insns
14138 This option controls the priority that is assigned to
14139 dispatch-slot restricted instructions during the second scheduling
14140 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
14141 @var{no/highest/second-highest} priority to dispatch slot restricted
14142 instructions.
14143
14144 @item -msched-costly-dep=@var{dependence_type}
14145 @opindex msched-costly-dep
14146 This option controls which dependences are considered costly
14147 by the target during instruction scheduling. The argument
14148 @var{dependence_type} takes one of the following values:
14149 @var{no}: no dependence is costly,
14150 @var{all}: all dependences are costly,
14151 @var{true_store_to_load}: a true dependence from store to load is costly,
14152 @var{store_to_load}: any dependence from store to load is costly,
14153 @var{number}: any dependence which latency >= @var{number} is costly.
14154
14155 @item -minsert-sched-nops=@var{scheme}
14156 @opindex minsert-sched-nops
14157 This option controls which nop insertion scheme will be used during
14158 the second scheduling pass. The argument @var{scheme} takes one of the
14159 following values:
14160 @var{no}: Don't insert nops.
14161 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
14162 according to the scheduler's grouping.
14163 @var{regroup_exact}: Insert nops to force costly dependent insns into
14164 separate groups. Insert exactly as many nops as needed to force an insn
14165 to a new group, according to the estimated processor grouping.
14166 @var{number}: Insert nops to force costly dependent insns into
14167 separate groups. Insert @var{number} nops to force an insn to a new group.
14168
14169 @item -mcall-sysv
14170 @opindex mcall-sysv
14171 On System V.4 and embedded PowerPC systems compile code using calling
14172 conventions that adheres to the March 1995 draft of the System V
14173 Application Binary Interface, PowerPC processor supplement. This is the
14174 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
14175
14176 @item -mcall-sysv-eabi
14177 @opindex mcall-sysv-eabi
14178 Specify both @option{-mcall-sysv} and @option{-meabi} options.
14179
14180 @item -mcall-sysv-noeabi
14181 @opindex mcall-sysv-noeabi
14182 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
14183
14184 @item -mcall-solaris
14185 @opindex mcall-solaris
14186 On System V.4 and embedded PowerPC systems compile code for the Solaris
14187 operating system.
14188
14189 @item -mcall-linux
14190 @opindex mcall-linux
14191 On System V.4 and embedded PowerPC systems compile code for the
14192 Linux-based GNU system.
14193
14194 @item -mcall-gnu
14195 @opindex mcall-gnu
14196 On System V.4 and embedded PowerPC systems compile code for the
14197 Hurd-based GNU system.
14198
14199 @item -mcall-netbsd
14200 @opindex mcall-netbsd
14201 On System V.4 and embedded PowerPC systems compile code for the
14202 NetBSD operating system.
14203
14204 @item -maix-struct-return
14205 @opindex maix-struct-return
14206 Return all structures in memory (as specified by the AIX ABI)@.
14207
14208 @item -msvr4-struct-return
14209 @opindex msvr4-struct-return
14210 Return structures smaller than 8 bytes in registers (as specified by the
14211 SVR4 ABI)@.
14212
14213 @item -mabi=@var{abi-type}
14214 @opindex mabi
14215 Extend the current ABI with a particular extension, or remove such extension.
14216 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
14217 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
14218
14219 @item -mabi=spe
14220 @opindex mabi=spe
14221 Extend the current ABI with SPE ABI extensions. This does not change
14222 the default ABI, instead it adds the SPE ABI extensions to the current
14223 ABI@.
14224
14225 @item -mabi=no-spe
14226 @opindex mabi=no-spe
14227 Disable Booke SPE ABI extensions for the current ABI@.
14228
14229 @item -mabi=ibmlongdouble
14230 @opindex mabi=ibmlongdouble
14231 Change the current ABI to use IBM extended precision long double.
14232 This is a PowerPC 32-bit SYSV ABI option.
14233
14234 @item -mabi=ieeelongdouble
14235 @opindex mabi=ieeelongdouble
14236 Change the current ABI to use IEEE extended precision long double.
14237 This is a PowerPC 32-bit Linux ABI option.
14238
14239 @item -mprototype
14240 @itemx -mno-prototype
14241 @opindex mprototype
14242 @opindex mno-prototype
14243 On System V.4 and embedded PowerPC systems assume that all calls to
14244 variable argument functions are properly prototyped. Otherwise, the
14245 compiler must insert an instruction before every non prototyped call to
14246 set or clear bit 6 of the condition code register (@var{CR}) to
14247 indicate whether floating point values were passed in the floating point
14248 registers in case the function takes a variable arguments. With
14249 @option{-mprototype}, only calls to prototyped variable argument functions
14250 will set or clear the bit.
14251
14252 @item -msim
14253 @opindex msim
14254 On embedded PowerPC systems, assume that the startup module is called
14255 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
14256 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
14257 configurations.
14258
14259 @item -mmvme
14260 @opindex mmvme
14261 On embedded PowerPC systems, assume that the startup module is called
14262 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
14263 @file{libc.a}.
14264
14265 @item -mads
14266 @opindex mads
14267 On embedded PowerPC systems, assume that the startup module is called
14268 @file{crt0.o} and the standard C libraries are @file{libads.a} and
14269 @file{libc.a}.
14270
14271 @item -myellowknife
14272 @opindex myellowknife
14273 On embedded PowerPC systems, assume that the startup module is called
14274 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
14275 @file{libc.a}.
14276
14277 @item -mvxworks
14278 @opindex mvxworks
14279 On System V.4 and embedded PowerPC systems, specify that you are
14280 compiling for a VxWorks system.
14281
14282 @item -memb
14283 @opindex memb
14284 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
14285 header to indicate that @samp{eabi} extended relocations are used.
14286
14287 @item -meabi
14288 @itemx -mno-eabi
14289 @opindex meabi
14290 @opindex mno-eabi
14291 On System V.4 and embedded PowerPC systems do (do not) adhere to the
14292 Embedded Applications Binary Interface (eabi) which is a set of
14293 modifications to the System V.4 specifications. Selecting @option{-meabi}
14294 means that the stack is aligned to an 8 byte boundary, a function
14295 @code{__eabi} is called to from @code{main} to set up the eabi
14296 environment, and the @option{-msdata} option can use both @code{r2} and
14297 @code{r13} to point to two separate small data areas. Selecting
14298 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
14299 do not call an initialization function from @code{main}, and the
14300 @option{-msdata} option will only use @code{r13} to point to a single
14301 small data area. The @option{-meabi} option is on by default if you
14302 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
14303
14304 @item -msdata=eabi
14305 @opindex msdata=eabi
14306 On System V.4 and embedded PowerPC systems, put small initialized
14307 @code{const} global and static data in the @samp{.sdata2} section, which
14308 is pointed to by register @code{r2}. Put small initialized
14309 non-@code{const} global and static data in the @samp{.sdata} section,
14310 which is pointed to by register @code{r13}. Put small uninitialized
14311 global and static data in the @samp{.sbss} section, which is adjacent to
14312 the @samp{.sdata} section. The @option{-msdata=eabi} option is
14313 incompatible with the @option{-mrelocatable} option. The
14314 @option{-msdata=eabi} option also sets the @option{-memb} option.
14315
14316 @item -msdata=sysv
14317 @opindex msdata=sysv
14318 On System V.4 and embedded PowerPC systems, put small global and static
14319 data in the @samp{.sdata} section, which is pointed to by register
14320 @code{r13}. Put small uninitialized global and static data in the
14321 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
14322 The @option{-msdata=sysv} option is incompatible with the
14323 @option{-mrelocatable} option.
14324
14325 @item -msdata=default
14326 @itemx -msdata
14327 @opindex msdata=default
14328 @opindex msdata
14329 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
14330 compile code the same as @option{-msdata=eabi}, otherwise compile code the
14331 same as @option{-msdata=sysv}.
14332
14333 @item -msdata=data
14334 @opindex msdata=data
14335 On System V.4 and embedded PowerPC systems, put small global
14336 data in the @samp{.sdata} section. Put small uninitialized global
14337 data in the @samp{.sbss} section. Do not use register @code{r13}
14338 to address small data however. This is the default behavior unless
14339 other @option{-msdata} options are used.
14340
14341 @item -msdata=none
14342 @itemx -mno-sdata
14343 @opindex msdata=none
14344 @opindex mno-sdata
14345 On embedded PowerPC systems, put all initialized global and static data
14346 in the @samp{.data} section, and all uninitialized data in the
14347 @samp{.bss} section.
14348
14349 @item -G @var{num}
14350 @opindex G
14351 @cindex smaller data references (PowerPC)
14352 @cindex .sdata/.sdata2 references (PowerPC)
14353 On embedded PowerPC systems, put global and static items less than or
14354 equal to @var{num} bytes into the small data or bss sections instead of
14355 the normal data or bss section. By default, @var{num} is 8. The
14356 @option{-G @var{num}} switch is also passed to the linker.
14357 All modules should be compiled with the same @option{-G @var{num}} value.
14358
14359 @item -mregnames
14360 @itemx -mno-regnames
14361 @opindex mregnames
14362 @opindex mno-regnames
14363 On System V.4 and embedded PowerPC systems do (do not) emit register
14364 names in the assembly language output using symbolic forms.
14365
14366 @item -mlongcall
14367 @itemx -mno-longcall
14368 @opindex mlongcall
14369 @opindex mno-longcall
14370 By default assume that all calls are far away so that a longer more
14371 expensive calling sequence is required. This is required for calls
14372 further than 32 megabytes (33,554,432 bytes) from the current location.
14373 A short call will be generated if the compiler knows
14374 the call cannot be that far away. This setting can be overridden by
14375 the @code{shortcall} function attribute, or by @code{#pragma
14376 longcall(0)}.
14377
14378 Some linkers are capable of detecting out-of-range calls and generating
14379 glue code on the fly. On these systems, long calls are unnecessary and
14380 generate slower code. As of this writing, the AIX linker can do this,
14381 as can the GNU linker for PowerPC/64. It is planned to add this feature
14382 to the GNU linker for 32-bit PowerPC systems as well.
14383
14384 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
14385 callee, L42'', plus a ``branch island'' (glue code). The two target
14386 addresses represent the callee and the ``branch island''. The
14387 Darwin/PPC linker will prefer the first address and generate a ``bl
14388 callee'' if the PPC ``bl'' instruction will reach the callee directly;
14389 otherwise, the linker will generate ``bl L42'' to call the ``branch
14390 island''. The ``branch island'' is appended to the body of the
14391 calling function; it computes the full 32-bit address of the callee
14392 and jumps to it.
14393
14394 On Mach-O (Darwin) systems, this option directs the compiler emit to
14395 the glue for every direct call, and the Darwin linker decides whether
14396 to use or discard it.
14397
14398 In the future, we may cause GCC to ignore all longcall specifications
14399 when the linker is known to generate glue.
14400
14401 @item -pthread
14402 @opindex pthread
14403 Adds support for multithreading with the @dfn{pthreads} library.
14404 This option sets flags for both the preprocessor and linker.
14405
14406 @end table
14407
14408 @node S/390 and zSeries Options
14409 @subsection S/390 and zSeries Options
14410 @cindex S/390 and zSeries Options
14411
14412 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
14413
14414 @table @gcctabopt
14415 @item -mhard-float
14416 @itemx -msoft-float
14417 @opindex mhard-float
14418 @opindex msoft-float
14419 Use (do not use) the hardware floating-point instructions and registers
14420 for floating-point operations. When @option{-msoft-float} is specified,
14421 functions in @file{libgcc.a} will be used to perform floating-point
14422 operations. When @option{-mhard-float} is specified, the compiler
14423 generates IEEE floating-point instructions. This is the default.
14424
14425 @item -mhard-dfp
14426 @itemx -mno-hard-dfp
14427 @opindex mhard-dfp
14428 @opindex mno-hard-dfp
14429 Use (do not use) the hardware decimal-floating-point instructions for
14430 decimal-floating-point operations. When @option{-mno-hard-dfp} is
14431 specified, functions in @file{libgcc.a} will be used to perform
14432 decimal-floating-point operations. When @option{-mhard-dfp} is
14433 specified, the compiler generates decimal-floating-point hardware
14434 instructions. This is the default for @option{-march=z9-ec} or higher.
14435
14436 @item -mlong-double-64
14437 @itemx -mlong-double-128
14438 @opindex mlong-double-64
14439 @opindex mlong-double-128
14440 These switches control the size of @code{long double} type. A size
14441 of 64bit makes the @code{long double} type equivalent to the @code{double}
14442 type. This is the default.
14443
14444 @item -mbackchain
14445 @itemx -mno-backchain
14446 @opindex mbackchain
14447 @opindex mno-backchain
14448 Store (do not store) the address of the caller's frame as backchain pointer
14449 into the callee's stack frame.
14450 A backchain may be needed to allow debugging using tools that do not understand
14451 DWARF-2 call frame information.
14452 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
14453 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
14454 the backchain is placed into the topmost word of the 96/160 byte register
14455 save area.
14456
14457 In general, code compiled with @option{-mbackchain} is call-compatible with
14458 code compiled with @option{-mmo-backchain}; however, use of the backchain
14459 for debugging purposes usually requires that the whole binary is built with
14460 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
14461 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
14462 to build a linux kernel use @option{-msoft-float}.
14463
14464 The default is to not maintain the backchain.
14465
14466 @item -mpacked-stack
14467 @itemx -mno-packed-stack
14468 @opindex mpacked-stack
14469 @opindex mno-packed-stack
14470 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
14471 specified, the compiler uses the all fields of the 96/160 byte register save
14472 area only for their default purpose; unused fields still take up stack space.
14473 When @option{-mpacked-stack} is specified, register save slots are densely
14474 packed at the top of the register save area; unused space is reused for other
14475 purposes, allowing for more efficient use of the available stack space.
14476 However, when @option{-mbackchain} is also in effect, the topmost word of
14477 the save area is always used to store the backchain, and the return address
14478 register is always saved two words below the backchain.
14479
14480 As long as the stack frame backchain is not used, code generated with
14481 @option{-mpacked-stack} is call-compatible with code generated with
14482 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
14483 S/390 or zSeries generated code that uses the stack frame backchain at run
14484 time, not just for debugging purposes. Such code is not call-compatible
14485 with code compiled with @option{-mpacked-stack}. Also, note that the
14486 combination of @option{-mbackchain},
14487 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
14488 to build a linux kernel use @option{-msoft-float}.
14489
14490 The default is to not use the packed stack layout.
14491
14492 @item -msmall-exec
14493 @itemx -mno-small-exec
14494 @opindex msmall-exec
14495 @opindex mno-small-exec
14496 Generate (or do not generate) code using the @code{bras} instruction
14497 to do subroutine calls.
14498 This only works reliably if the total executable size does not
14499 exceed 64k. The default is to use the @code{basr} instruction instead,
14500 which does not have this limitation.
14501
14502 @item -m64
14503 @itemx -m31
14504 @opindex m64
14505 @opindex m31
14506 When @option{-m31} is specified, generate code compliant to the
14507 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
14508 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
14509 particular to generate 64-bit instructions. For the @samp{s390}
14510 targets, the default is @option{-m31}, while the @samp{s390x}
14511 targets default to @option{-m64}.
14512
14513 @item -mzarch
14514 @itemx -mesa
14515 @opindex mzarch
14516 @opindex mesa
14517 When @option{-mzarch} is specified, generate code using the
14518 instructions available on z/Architecture.
14519 When @option{-mesa} is specified, generate code using the
14520 instructions available on ESA/390. Note that @option{-mesa} is
14521 not possible with @option{-m64}.
14522 When generating code compliant to the GNU/Linux for S/390 ABI,
14523 the default is @option{-mesa}. When generating code compliant
14524 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
14525
14526 @item -mmvcle
14527 @itemx -mno-mvcle
14528 @opindex mmvcle
14529 @opindex mno-mvcle
14530 Generate (or do not generate) code using the @code{mvcle} instruction
14531 to perform block moves. When @option{-mno-mvcle} is specified,
14532 use a @code{mvc} loop instead. This is the default unless optimizing for
14533 size.
14534
14535 @item -mdebug
14536 @itemx -mno-debug
14537 @opindex mdebug
14538 @opindex mno-debug
14539 Print (or do not print) additional debug information when compiling.
14540 The default is to not print debug information.
14541
14542 @item -march=@var{cpu-type}
14543 @opindex march
14544 Generate code that will run on @var{cpu-type}, which is the name of a system
14545 representing a certain processor type. Possible values for
14546 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990},
14547 @samp{z9-109}, @samp{z9-ec} and @samp{z10}.
14548 When generating code using the instructions available on z/Architecture,
14549 the default is @option{-march=z900}. Otherwise, the default is
14550 @option{-march=g5}.
14551
14552 @item -mtune=@var{cpu-type}
14553 @opindex mtune
14554 Tune to @var{cpu-type} everything applicable about the generated code,
14555 except for the ABI and the set of available instructions.
14556 The list of @var{cpu-type} values is the same as for @option{-march}.
14557 The default is the value used for @option{-march}.
14558
14559 @item -mtpf-trace
14560 @itemx -mno-tpf-trace
14561 @opindex mtpf-trace
14562 @opindex mno-tpf-trace
14563 Generate code that adds (does not add) in TPF OS specific branches to trace
14564 routines in the operating system. This option is off by default, even
14565 when compiling for the TPF OS@.
14566
14567 @item -mfused-madd
14568 @itemx -mno-fused-madd
14569 @opindex mfused-madd
14570 @opindex mno-fused-madd
14571 Generate code that uses (does not use) the floating point multiply and
14572 accumulate instructions. These instructions are generated by default if
14573 hardware floating point is used.
14574
14575 @item -mwarn-framesize=@var{framesize}
14576 @opindex mwarn-framesize
14577 Emit a warning if the current function exceeds the given frame size. Because
14578 this is a compile time check it doesn't need to be a real problem when the program
14579 runs. It is intended to identify functions which most probably cause
14580 a stack overflow. It is useful to be used in an environment with limited stack
14581 size e.g.@: the linux kernel.
14582
14583 @item -mwarn-dynamicstack
14584 @opindex mwarn-dynamicstack
14585 Emit a warning if the function calls alloca or uses dynamically
14586 sized arrays. This is generally a bad idea with a limited stack size.
14587
14588 @item -mstack-guard=@var{stack-guard}
14589 @itemx -mstack-size=@var{stack-size}
14590 @opindex mstack-guard
14591 @opindex mstack-size
14592 If these options are provided the s390 back end emits additional instructions in
14593 the function prologue which trigger a trap if the stack size is @var{stack-guard}
14594 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
14595 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
14596 the frame size of the compiled function is chosen.
14597 These options are intended to be used to help debugging stack overflow problems.
14598 The additionally emitted code causes only little overhead and hence can also be
14599 used in production like systems without greater performance degradation. The given
14600 values have to be exact powers of 2 and @var{stack-size} has to be greater than
14601 @var{stack-guard} without exceeding 64k.
14602 In order to be efficient the extra code makes the assumption that the stack starts
14603 at an address aligned to the value given by @var{stack-size}.
14604 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
14605 @end table
14606
14607 @node Score Options
14608 @subsection Score Options
14609 @cindex Score Options
14610
14611 These options are defined for Score implementations:
14612
14613 @table @gcctabopt
14614 @item -meb
14615 @opindex meb
14616 Compile code for big endian mode. This is the default.
14617
14618 @item -mel
14619 @opindex mel
14620 Compile code for little endian mode.
14621
14622 @item -mnhwloop
14623 @opindex mnhwloop
14624 Disable generate bcnz instruction.
14625
14626 @item -muls
14627 @opindex muls
14628 Enable generate unaligned load and store instruction.
14629
14630 @item -mmac
14631 @opindex mmac
14632 Enable the use of multiply-accumulate instructions. Disabled by default.
14633
14634 @item -mscore5
14635 @opindex mscore5
14636 Specify the SCORE5 as the target architecture.
14637
14638 @item -mscore5u
14639 @opindex mscore5u
14640 Specify the SCORE5U of the target architecture.
14641
14642 @item -mscore7
14643 @opindex mscore7
14644 Specify the SCORE7 as the target architecture. This is the default.
14645
14646 @item -mscore7d
14647 @opindex mscore7d
14648 Specify the SCORE7D as the target architecture.
14649 @end table
14650
14651 @node SH Options
14652 @subsection SH Options
14653
14654 These @samp{-m} options are defined for the SH implementations:
14655
14656 @table @gcctabopt
14657 @item -m1
14658 @opindex m1
14659 Generate code for the SH1.
14660
14661 @item -m2
14662 @opindex m2
14663 Generate code for the SH2.
14664
14665 @item -m2e
14666 Generate code for the SH2e.
14667
14668 @item -m3
14669 @opindex m3
14670 Generate code for the SH3.
14671
14672 @item -m3e
14673 @opindex m3e
14674 Generate code for the SH3e.
14675
14676 @item -m4-nofpu
14677 @opindex m4-nofpu
14678 Generate code for the SH4 without a floating-point unit.
14679
14680 @item -m4-single-only
14681 @opindex m4-single-only
14682 Generate code for the SH4 with a floating-point unit that only
14683 supports single-precision arithmetic.
14684
14685 @item -m4-single
14686 @opindex m4-single
14687 Generate code for the SH4 assuming the floating-point unit is in
14688 single-precision mode by default.
14689
14690 @item -m4
14691 @opindex m4
14692 Generate code for the SH4.
14693
14694 @item -m4a-nofpu
14695 @opindex m4a-nofpu
14696 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
14697 floating-point unit is not used.
14698
14699 @item -m4a-single-only
14700 @opindex m4a-single-only
14701 Generate code for the SH4a, in such a way that no double-precision
14702 floating point operations are used.
14703
14704 @item -m4a-single
14705 @opindex m4a-single
14706 Generate code for the SH4a assuming the floating-point unit is in
14707 single-precision mode by default.
14708
14709 @item -m4a
14710 @opindex m4a
14711 Generate code for the SH4a.
14712
14713 @item -m4al
14714 @opindex m4al
14715 Same as @option{-m4a-nofpu}, except that it implicitly passes
14716 @option{-dsp} to the assembler. GCC doesn't generate any DSP
14717 instructions at the moment.
14718
14719 @item -mb
14720 @opindex mb
14721 Compile code for the processor in big endian mode.
14722
14723 @item -ml
14724 @opindex ml
14725 Compile code for the processor in little endian mode.
14726
14727 @item -mdalign
14728 @opindex mdalign
14729 Align doubles at 64-bit boundaries. Note that this changes the calling
14730 conventions, and thus some functions from the standard C library will
14731 not work unless you recompile it first with @option{-mdalign}.
14732
14733 @item -mrelax
14734 @opindex mrelax
14735 Shorten some address references at link time, when possible; uses the
14736 linker option @option{-relax}.
14737
14738 @item -mbigtable
14739 @opindex mbigtable
14740 Use 32-bit offsets in @code{switch} tables. The default is to use
14741 16-bit offsets.
14742
14743 @item -mbitops
14744 @opindex mbitops
14745 Enable the use of bit manipulation instructions on SH2A.
14746
14747 @item -mfmovd
14748 @opindex mfmovd
14749 Enable the use of the instruction @code{fmovd}.
14750
14751 @item -mhitachi
14752 @opindex mhitachi
14753 Comply with the calling conventions defined by Renesas.
14754
14755 @item -mrenesas
14756 @opindex mhitachi
14757 Comply with the calling conventions defined by Renesas.
14758
14759 @item -mno-renesas
14760 @opindex mhitachi
14761 Comply with the calling conventions defined for GCC before the Renesas
14762 conventions were available. This option is the default for all
14763 targets of the SH toolchain except for @samp{sh-symbianelf}.
14764
14765 @item -mnomacsave
14766 @opindex mnomacsave
14767 Mark the @code{MAC} register as call-clobbered, even if
14768 @option{-mhitachi} is given.
14769
14770 @item -mieee
14771 @opindex mieee
14772 Increase IEEE-compliance of floating-point code.
14773 At the moment, this is equivalent to @option{-fno-finite-math-only}.
14774 When generating 16 bit SH opcodes, getting IEEE-conforming results for
14775 comparisons of NANs / infinities incurs extra overhead in every
14776 floating point comparison, therefore the default is set to
14777 @option{-ffinite-math-only}.
14778
14779 @item -minline-ic_invalidate
14780 @opindex minline-ic_invalidate
14781 Inline code to invalidate instruction cache entries after setting up
14782 nested function trampolines.
14783 This option has no effect if -musermode is in effect and the selected
14784 code generation option (e.g. -m4) does not allow the use of the icbi
14785 instruction.
14786 If the selected code generation option does not allow the use of the icbi
14787 instruction, and -musermode is not in effect, the inlined code will
14788 manipulate the instruction cache address array directly with an associative
14789 write. This not only requires privileged mode, but it will also
14790 fail if the cache line had been mapped via the TLB and has become unmapped.
14791
14792 @item -misize
14793 @opindex misize
14794 Dump instruction size and location in the assembly code.
14795
14796 @item -mpadstruct
14797 @opindex mpadstruct
14798 This option is deprecated. It pads structures to multiple of 4 bytes,
14799 which is incompatible with the SH ABI@.
14800
14801 @item -mspace
14802 @opindex mspace
14803 Optimize for space instead of speed. Implied by @option{-Os}.
14804
14805 @item -mprefergot
14806 @opindex mprefergot
14807 When generating position-independent code, emit function calls using
14808 the Global Offset Table instead of the Procedure Linkage Table.
14809
14810 @item -musermode
14811 @opindex musermode
14812 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
14813 if the inlined code would not work in user mode.
14814 This is the default when the target is @code{sh-*-linux*}.
14815
14816 @item -multcost=@var{number}
14817 @opindex multcost=@var{number}
14818 Set the cost to assume for a multiply insn.
14819
14820 @item -mdiv=@var{strategy}
14821 @opindex mdiv=@var{strategy}
14822 Set the division strategy to use for SHmedia code. @var{strategy} must be
14823 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
14824 inv:call2, inv:fp .
14825 "fp" performs the operation in floating point. This has a very high latency,
14826 but needs only a few instructions, so it might be a good choice if
14827 your code has enough easily exploitable ILP to allow the compiler to
14828 schedule the floating point instructions together with other instructions.
14829 Division by zero causes a floating point exception.
14830 "inv" uses integer operations to calculate the inverse of the divisor,
14831 and then multiplies the dividend with the inverse. This strategy allows
14832 cse and hoisting of the inverse calculation. Division by zero calculates
14833 an unspecified result, but does not trap.
14834 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
14835 have been found, or if the entire operation has been hoisted to the same
14836 place, the last stages of the inverse calculation are intertwined with the
14837 final multiply to reduce the overall latency, at the expense of using a few
14838 more instructions, and thus offering fewer scheduling opportunities with
14839 other code.
14840 "call" calls a library function that usually implements the inv:minlat
14841 strategy.
14842 This gives high code density for m5-*media-nofpu compilations.
14843 "call2" uses a different entry point of the same library function, where it
14844 assumes that a pointer to a lookup table has already been set up, which
14845 exposes the pointer load to cse / code hoisting optimizations.
14846 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
14847 code generation, but if the code stays unoptimized, revert to the "call",
14848 "call2", or "fp" strategies, respectively. Note that the
14849 potentially-trapping side effect of division by zero is carried by a
14850 separate instruction, so it is possible that all the integer instructions
14851 are hoisted out, but the marker for the side effect stays where it is.
14852 A recombination to fp operations or a call is not possible in that case.
14853 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
14854 that the inverse calculation was nor separated from the multiply, they speed
14855 up division where the dividend fits into 20 bits (plus sign where applicable),
14856 by inserting a test to skip a number of operations in this case; this test
14857 slows down the case of larger dividends. inv20u assumes the case of a such
14858 a small dividend to be unlikely, and inv20l assumes it to be likely.
14859
14860 @item -mdivsi3_libfunc=@var{name}
14861 @opindex mdivsi3_libfunc=@var{name}
14862 Set the name of the library function used for 32 bit signed division to
14863 @var{name}. This only affect the name used in the call and inv:call
14864 division strategies, and the compiler will still expect the same
14865 sets of input/output/clobbered registers as if this option was not present.
14866
14867 @item -mfixed-range=@var{register-range}
14868 @opindex mfixed-range
14869 Generate code treating the given register range as fixed registers.
14870 A fixed register is one that the register allocator can not use. This is
14871 useful when compiling kernel code. A register range is specified as
14872 two registers separated by a dash. Multiple register ranges can be
14873 specified separated by a comma.
14874
14875 @item -madjust-unroll
14876 @opindex madjust-unroll
14877 Throttle unrolling to avoid thrashing target registers.
14878 This option only has an effect if the gcc code base supports the
14879 TARGET_ADJUST_UNROLL_MAX target hook.
14880
14881 @item -mindexed-addressing
14882 @opindex mindexed-addressing
14883 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
14884 This is only safe if the hardware and/or OS implement 32 bit wrap-around
14885 semantics for the indexed addressing mode. The architecture allows the
14886 implementation of processors with 64 bit MMU, which the OS could use to
14887 get 32 bit addressing, but since no current hardware implementation supports
14888 this or any other way to make the indexed addressing mode safe to use in
14889 the 32 bit ABI, the default is -mno-indexed-addressing.
14890
14891 @item -mgettrcost=@var{number}
14892 @opindex mgettrcost=@var{number}
14893 Set the cost assumed for the gettr instruction to @var{number}.
14894 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
14895
14896 @item -mpt-fixed
14897 @opindex mpt-fixed
14898 Assume pt* instructions won't trap. This will generally generate better
14899 scheduled code, but is unsafe on current hardware. The current architecture
14900 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
14901 This has the unintentional effect of making it unsafe to schedule ptabs /
14902 ptrel before a branch, or hoist it out of a loop. For example,
14903 __do_global_ctors, a part of libgcc that runs constructors at program
14904 startup, calls functions in a list which is delimited by @minus{}1. With the
14905 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
14906 That means that all the constructors will be run a bit quicker, but when
14907 the loop comes to the end of the list, the program crashes because ptabs
14908 loads @minus{}1 into a target register. Since this option is unsafe for any
14909 hardware implementing the current architecture specification, the default
14910 is -mno-pt-fixed. Unless the user specifies a specific cost with
14911 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
14912 this deters register allocation using target registers for storing
14913 ordinary integers.
14914
14915 @item -minvalid-symbols
14916 @opindex minvalid-symbols
14917 Assume symbols might be invalid. Ordinary function symbols generated by
14918 the compiler will always be valid to load with movi/shori/ptabs or
14919 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
14920 to generate symbols that will cause ptabs / ptrel to trap.
14921 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
14922 It will then prevent cross-basic-block cse, hoisting and most scheduling
14923 of symbol loads. The default is @option{-mno-invalid-symbols}.
14924 @end table
14925
14926 @node SPARC Options
14927 @subsection SPARC Options
14928 @cindex SPARC options
14929
14930 These @samp{-m} options are supported on the SPARC:
14931
14932 @table @gcctabopt
14933 @item -mno-app-regs
14934 @itemx -mapp-regs
14935 @opindex mno-app-regs
14936 @opindex mapp-regs
14937 Specify @option{-mapp-regs} to generate output using the global registers
14938 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
14939 is the default.
14940
14941 To be fully SVR4 ABI compliant at the cost of some performance loss,
14942 specify @option{-mno-app-regs}. You should compile libraries and system
14943 software with this option.
14944
14945 @item -mfpu
14946 @itemx -mhard-float
14947 @opindex mfpu
14948 @opindex mhard-float
14949 Generate output containing floating point instructions. This is the
14950 default.
14951
14952 @item -mno-fpu
14953 @itemx -msoft-float
14954 @opindex mno-fpu
14955 @opindex msoft-float
14956 Generate output containing library calls for floating point.
14957 @strong{Warning:} the requisite libraries are not available for all SPARC
14958 targets. Normally the facilities of the machine's usual C compiler are
14959 used, but this cannot be done directly in cross-compilation. You must make
14960 your own arrangements to provide suitable library functions for
14961 cross-compilation. The embedded targets @samp{sparc-*-aout} and
14962 @samp{sparclite-*-*} do provide software floating point support.
14963
14964 @option{-msoft-float} changes the calling convention in the output file;
14965 therefore, it is only useful if you compile @emph{all} of a program with
14966 this option. In particular, you need to compile @file{libgcc.a}, the
14967 library that comes with GCC, with @option{-msoft-float} in order for
14968 this to work.
14969
14970 @item -mhard-quad-float
14971 @opindex mhard-quad-float
14972 Generate output containing quad-word (long double) floating point
14973 instructions.
14974
14975 @item -msoft-quad-float
14976 @opindex msoft-quad-float
14977 Generate output containing library calls for quad-word (long double)
14978 floating point instructions. The functions called are those specified
14979 in the SPARC ABI@. This is the default.
14980
14981 As of this writing, there are no SPARC implementations that have hardware
14982 support for the quad-word floating point instructions. They all invoke
14983 a trap handler for one of these instructions, and then the trap handler
14984 emulates the effect of the instruction. Because of the trap handler overhead,
14985 this is much slower than calling the ABI library routines. Thus the
14986 @option{-msoft-quad-float} option is the default.
14987
14988 @item -mno-unaligned-doubles
14989 @itemx -munaligned-doubles
14990 @opindex mno-unaligned-doubles
14991 @opindex munaligned-doubles
14992 Assume that doubles have 8 byte alignment. This is the default.
14993
14994 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
14995 alignment only if they are contained in another type, or if they have an
14996 absolute address. Otherwise, it assumes they have 4 byte alignment.
14997 Specifying this option avoids some rare compatibility problems with code
14998 generated by other compilers. It is not the default because it results
14999 in a performance loss, especially for floating point code.
15000
15001 @item -mno-faster-structs
15002 @itemx -mfaster-structs
15003 @opindex mno-faster-structs
15004 @opindex mfaster-structs
15005 With @option{-mfaster-structs}, the compiler assumes that structures
15006 should have 8 byte alignment. This enables the use of pairs of
15007 @code{ldd} and @code{std} instructions for copies in structure
15008 assignment, in place of twice as many @code{ld} and @code{st} pairs.
15009 However, the use of this changed alignment directly violates the SPARC
15010 ABI@. Thus, it's intended only for use on targets where the developer
15011 acknowledges that their resulting code will not be directly in line with
15012 the rules of the ABI@.
15013
15014 @item -mimpure-text
15015 @opindex mimpure-text
15016 @option{-mimpure-text}, used in addition to @option{-shared}, tells
15017 the compiler to not pass @option{-z text} to the linker when linking a
15018 shared object. Using this option, you can link position-dependent
15019 code into a shared object.
15020
15021 @option{-mimpure-text} suppresses the ``relocations remain against
15022 allocatable but non-writable sections'' linker error message.
15023 However, the necessary relocations will trigger copy-on-write, and the
15024 shared object is not actually shared across processes. Instead of
15025 using @option{-mimpure-text}, you should compile all source code with
15026 @option{-fpic} or @option{-fPIC}.
15027
15028 This option is only available on SunOS and Solaris.
15029
15030 @item -mcpu=@var{cpu_type}
15031 @opindex mcpu
15032 Set the instruction set, register set, and instruction scheduling parameters
15033 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
15034 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
15035 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
15036 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
15037 @samp{ultrasparc3}, @samp{niagara} and @samp{niagara2}.
15038
15039 Default instruction scheduling parameters are used for values that select
15040 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
15041 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
15042
15043 Here is a list of each supported architecture and their supported
15044 implementations.
15045
15046 @smallexample
15047 v7: cypress
15048 v8: supersparc, hypersparc
15049 sparclite: f930, f934, sparclite86x
15050 sparclet: tsc701
15051 v9: ultrasparc, ultrasparc3, niagara, niagara2
15052 @end smallexample
15053
15054 By default (unless configured otherwise), GCC generates code for the V7
15055 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
15056 additionally optimizes it for the Cypress CY7C602 chip, as used in the
15057 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
15058 SPARCStation 1, 2, IPX etc.
15059
15060 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
15061 architecture. The only difference from V7 code is that the compiler emits
15062 the integer multiply and integer divide instructions which exist in SPARC-V8
15063 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
15064 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
15065 2000 series.
15066
15067 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
15068 the SPARC architecture. This adds the integer multiply, integer divide step
15069 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
15070 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
15071 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
15072 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
15073 MB86934 chip, which is the more recent SPARClite with FPU@.
15074
15075 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
15076 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
15077 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
15078 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
15079 optimizes it for the TEMIC SPARClet chip.
15080
15081 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
15082 architecture. This adds 64-bit integer and floating-point move instructions,
15083 3 additional floating-point condition code registers and conditional move
15084 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
15085 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
15086 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
15087 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
15088 @option{-mcpu=niagara}, the compiler additionally optimizes it for
15089 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
15090 additionally optimizes it for Sun UltraSPARC T2 chips.
15091
15092 @item -mtune=@var{cpu_type}
15093 @opindex mtune
15094 Set the instruction scheduling parameters for machine type
15095 @var{cpu_type}, but do not set the instruction set or register set that the
15096 option @option{-mcpu=@var{cpu_type}} would.
15097
15098 The same values for @option{-mcpu=@var{cpu_type}} can be used for
15099 @option{-mtune=@var{cpu_type}}, but the only useful values are those
15100 that select a particular cpu implementation. Those are @samp{cypress},
15101 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
15102 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
15103 @samp{ultrasparc3}, @samp{niagara}, and @samp{niagara2}.
15104
15105 @item -mv8plus
15106 @itemx -mno-v8plus
15107 @opindex mv8plus
15108 @opindex mno-v8plus
15109 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
15110 difference from the V8 ABI is that the global and out registers are
15111 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
15112 mode for all SPARC-V9 processors.
15113
15114 @item -mvis
15115 @itemx -mno-vis
15116 @opindex mvis
15117 @opindex mno-vis
15118 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
15119 Visual Instruction Set extensions. The default is @option{-mno-vis}.
15120
15121 @item -mno-integer-ldd-std
15122 @opindex mno-integer-ldd-std
15123 With @option{-mno-integer-ldd-std}, GCC does not use the @code{ldd}
15124 and @code{std} instructions for integer operands in 32-bit mode. This
15125 is for use with legacy code using 64-bit quantities which are not
15126 64-bit aligned.
15127
15128 @item -massume-32bit-callers
15129 @opindex massume-32bit-callers
15130 With @option{-massume-32bit-callers}, The type promotion of function
15131 arguments is altered such that integer arguments smaller than the word
15132 size are extended in the callee rather than the caller. This is
15133 necessary for system calls from 32bit processes to 64bit kernels in
15134 certain systems. This option should not be used in any situation
15135 other than compiling the kernels of such systems, and has not been
15136 tested outside of that scenario.
15137 @end table
15138
15139 These @samp{-m} options are supported in addition to the above
15140 on SPARC-V9 processors in 64-bit environments:
15141
15142 @table @gcctabopt
15143 @item -mlittle-endian
15144 @opindex mlittle-endian
15145 Generate code for a processor running in little-endian mode. It is only
15146 available for a few configurations and most notably not on Solaris and Linux.
15147
15148 @item -m32
15149 @itemx -m64
15150 @opindex m32
15151 @opindex m64
15152 Generate code for a 32-bit or 64-bit environment.
15153 The 32-bit environment sets int, long and pointer to 32 bits.
15154 The 64-bit environment sets int to 32 bits and long and pointer
15155 to 64 bits.
15156
15157 @item -mcmodel=medlow
15158 @opindex mcmodel=medlow
15159 Generate code for the Medium/Low code model: 64-bit addresses, programs
15160 must be linked in the low 32 bits of memory. Programs can be statically
15161 or dynamically linked.
15162
15163 @item -mcmodel=medmid
15164 @opindex mcmodel=medmid
15165 Generate code for the Medium/Middle code model: 64-bit addresses, programs
15166 must be linked in the low 44 bits of memory, the text and data segments must
15167 be less than 2GB in size and the data segment must be located within 2GB of
15168 the text segment.
15169
15170 @item -mcmodel=medany
15171 @opindex mcmodel=medany
15172 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
15173 may be linked anywhere in memory, the text and data segments must be less
15174 than 2GB in size and the data segment must be located within 2GB of the
15175 text segment.
15176
15177 @item -mcmodel=embmedany
15178 @opindex mcmodel=embmedany
15179 Generate code for the Medium/Anywhere code model for embedded systems:
15180 64-bit addresses, the text and data segments must be less than 2GB in
15181 size, both starting anywhere in memory (determined at link time). The
15182 global register %g4 points to the base of the data segment. Programs
15183 are statically linked and PIC is not supported.
15184
15185 @item -mstack-bias
15186 @itemx -mno-stack-bias
15187 @opindex mstack-bias
15188 @opindex mno-stack-bias
15189 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
15190 frame pointer if present, are offset by @minus{}2047 which must be added back
15191 when making stack frame references. This is the default in 64-bit mode.
15192 Otherwise, assume no such offset is present.
15193 @end table
15194
15195 These switches are supported in addition to the above on Solaris:
15196
15197 @table @gcctabopt
15198 @item -threads
15199 @opindex threads
15200 Add support for multithreading using the Solaris threads library. This
15201 option sets flags for both the preprocessor and linker. This option does
15202 not affect the thread safety of object code produced by the compiler or
15203 that of libraries supplied with it.
15204
15205 @item -pthreads
15206 @opindex pthreads
15207 Add support for multithreading using the POSIX threads library. This
15208 option sets flags for both the preprocessor and linker. This option does
15209 not affect the thread safety of object code produced by the compiler or
15210 that of libraries supplied with it.
15211
15212 @item -pthread
15213 @opindex pthread
15214 This is a synonym for @option{-pthreads}.
15215 @end table
15216
15217 @node SPU Options
15218 @subsection SPU Options
15219 @cindex SPU options
15220
15221 These @samp{-m} options are supported on the SPU:
15222
15223 @table @gcctabopt
15224 @item -mwarn-reloc
15225 @itemx -merror-reloc
15226 @opindex mwarn-reloc
15227 @opindex merror-reloc
15228
15229 The loader for SPU does not handle dynamic relocations. By default, GCC
15230 will give an error when it generates code that requires a dynamic
15231 relocation. @option{-mno-error-reloc} disables the error,
15232 @option{-mwarn-reloc} will generate a warning instead.
15233
15234 @item -msafe-dma
15235 @itemx -munsafe-dma
15236 @opindex msafe-dma
15237 @opindex munsafe-dma
15238
15239 Instructions which initiate or test completion of DMA must not be
15240 reordered with respect to loads and stores of the memory which is being
15241 accessed. Users typically address this problem using the volatile
15242 keyword, but that can lead to inefficient code in places where the
15243 memory is known to not change. Rather than mark the memory as volatile
15244 we treat the DMA instructions as potentially effecting all memory. With
15245 @option{-munsafe-dma} users must use the volatile keyword to protect
15246 memory accesses.
15247
15248 @item -mbranch-hints
15249 @opindex mbranch-hints
15250
15251 By default, GCC will generate a branch hint instruction to avoid
15252 pipeline stalls for always taken or probably taken branches. A hint
15253 will not be generated closer than 8 instructions away from its branch.
15254 There is little reason to disable them, except for debugging purposes,
15255 or to make an object a little bit smaller.
15256
15257 @item -msmall-mem
15258 @itemx -mlarge-mem
15259 @opindex msmall-mem
15260 @opindex mlarge-mem
15261
15262 By default, GCC generates code assuming that addresses are never larger
15263 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
15264 a full 32 bit address.
15265
15266 @item -mstdmain
15267 @opindex mstdmain
15268
15269 By default, GCC links against startup code that assumes the SPU-style
15270 main function interface (which has an unconventional parameter list).
15271 With @option{-mstdmain}, GCC will link your program against startup
15272 code that assumes a C99-style interface to @code{main}, including a
15273 local copy of @code{argv} strings.
15274
15275 @item -mfixed-range=@var{register-range}
15276 @opindex mfixed-range
15277 Generate code treating the given register range as fixed registers.
15278 A fixed register is one that the register allocator can not use. This is
15279 useful when compiling kernel code. A register range is specified as
15280 two registers separated by a dash. Multiple register ranges can be
15281 specified separated by a comma.
15282
15283 @item -mdual-nops
15284 @itemx -mdual-nops=@var{n}
15285 @opindex mdual-nops
15286 By default, GCC will insert nops to increase dual issue when it expects
15287 it to increase performance. @var{n} can be a value from 0 to 10. A
15288 smaller @var{n} will insert fewer nops. 10 is the default, 0 is the
15289 same as @option{-mno-dual-nops}. Disabled with @option{-Os}.
15290
15291 @item -mhint-max-nops=@var{n}
15292 @opindex mhint-max-nops
15293 Maximum number of nops to insert for a branch hint. A branch hint must
15294 be at least 8 instructions away from the branch it is effecting. GCC
15295 will insert up to @var{n} nops to enforce this, otherwise it will not
15296 generate the branch hint.
15297
15298 @item -mhint-max-distance=@var{n}
15299 @opindex mhint-max-distance
15300 The encoding of the branch hint instruction limits the hint to be within
15301 256 instructions of the branch it is effecting. By default, GCC makes
15302 sure it is within 125.
15303
15304 @item -msafe-hints
15305 @opindex msafe-hints
15306 Work around a hardware bug which causes the SPU to stall indefinitely.
15307 By default, GCC will insert the @code{hbrp} instruction to make sure
15308 this stall won't happen.
15309
15310 @end table
15311
15312 @node System V Options
15313 @subsection Options for System V
15314
15315 These additional options are available on System V Release 4 for
15316 compatibility with other compilers on those systems:
15317
15318 @table @gcctabopt
15319 @item -G
15320 @opindex G
15321 Create a shared object.
15322 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
15323
15324 @item -Qy
15325 @opindex Qy
15326 Identify the versions of each tool used by the compiler, in a
15327 @code{.ident} assembler directive in the output.
15328
15329 @item -Qn
15330 @opindex Qn
15331 Refrain from adding @code{.ident} directives to the output file (this is
15332 the default).
15333
15334 @item -YP,@var{dirs}
15335 @opindex YP
15336 Search the directories @var{dirs}, and no others, for libraries
15337 specified with @option{-l}.
15338
15339 @item -Ym,@var{dir}
15340 @opindex Ym
15341 Look in the directory @var{dir} to find the M4 preprocessor.
15342 The assembler uses this option.
15343 @c This is supposed to go with a -Yd for predefined M4 macro files, but
15344 @c the generic assembler that comes with Solaris takes just -Ym.
15345 @end table
15346
15347 @node V850 Options
15348 @subsection V850 Options
15349 @cindex V850 Options
15350
15351 These @samp{-m} options are defined for V850 implementations:
15352
15353 @table @gcctabopt
15354 @item -mlong-calls
15355 @itemx -mno-long-calls
15356 @opindex mlong-calls
15357 @opindex mno-long-calls
15358 Treat all calls as being far away (near). If calls are assumed to be
15359 far away, the compiler will always load the functions address up into a
15360 register, and call indirect through the pointer.
15361
15362 @item -mno-ep
15363 @itemx -mep
15364 @opindex mno-ep
15365 @opindex mep
15366 Do not optimize (do optimize) basic blocks that use the same index
15367 pointer 4 or more times to copy pointer into the @code{ep} register, and
15368 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
15369 option is on by default if you optimize.
15370
15371 @item -mno-prolog-function
15372 @itemx -mprolog-function
15373 @opindex mno-prolog-function
15374 @opindex mprolog-function
15375 Do not use (do use) external functions to save and restore registers
15376 at the prologue and epilogue of a function. The external functions
15377 are slower, but use less code space if more than one function saves
15378 the same number of registers. The @option{-mprolog-function} option
15379 is on by default if you optimize.
15380
15381 @item -mspace
15382 @opindex mspace
15383 Try to make the code as small as possible. At present, this just turns
15384 on the @option{-mep} and @option{-mprolog-function} options.
15385
15386 @item -mtda=@var{n}
15387 @opindex mtda
15388 Put static or global variables whose size is @var{n} bytes or less into
15389 the tiny data area that register @code{ep} points to. The tiny data
15390 area can hold up to 256 bytes in total (128 bytes for byte references).
15391
15392 @item -msda=@var{n}
15393 @opindex msda
15394 Put static or global variables whose size is @var{n} bytes or less into
15395 the small data area that register @code{gp} points to. The small data
15396 area can hold up to 64 kilobytes.
15397
15398 @item -mzda=@var{n}
15399 @opindex mzda
15400 Put static or global variables whose size is @var{n} bytes or less into
15401 the first 32 kilobytes of memory.
15402
15403 @item -mv850
15404 @opindex mv850
15405 Specify that the target processor is the V850.
15406
15407 @item -mbig-switch
15408 @opindex mbig-switch
15409 Generate code suitable for big switch tables. Use this option only if
15410 the assembler/linker complain about out of range branches within a switch
15411 table.
15412
15413 @item -mapp-regs
15414 @opindex mapp-regs
15415 This option will cause r2 and r5 to be used in the code generated by
15416 the compiler. This setting is the default.
15417
15418 @item -mno-app-regs
15419 @opindex mno-app-regs
15420 This option will cause r2 and r5 to be treated as fixed registers.
15421
15422 @item -mv850e1
15423 @opindex mv850e1
15424 Specify that the target processor is the V850E1. The preprocessor
15425 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
15426 this option is used.
15427
15428 @item -mv850e
15429 @opindex mv850e
15430 Specify that the target processor is the V850E@. The preprocessor
15431 constant @samp{__v850e__} will be defined if this option is used.
15432
15433 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
15434 are defined then a default target processor will be chosen and the
15435 relevant @samp{__v850*__} preprocessor constant will be defined.
15436
15437 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
15438 defined, regardless of which processor variant is the target.
15439
15440 @item -mdisable-callt
15441 @opindex mdisable-callt
15442 This option will suppress generation of the CALLT instruction for the
15443 v850e and v850e1 flavors of the v850 architecture. The default is
15444 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
15445
15446 @end table
15447
15448 @node VAX Options
15449 @subsection VAX Options
15450 @cindex VAX options
15451
15452 These @samp{-m} options are defined for the VAX:
15453
15454 @table @gcctabopt
15455 @item -munix
15456 @opindex munix
15457 Do not output certain jump instructions (@code{aobleq} and so on)
15458 that the Unix assembler for the VAX cannot handle across long
15459 ranges.
15460
15461 @item -mgnu
15462 @opindex mgnu
15463 Do output those jump instructions, on the assumption that you
15464 will assemble with the GNU assembler.
15465
15466 @item -mg
15467 @opindex mg
15468 Output code for g-format floating point numbers instead of d-format.
15469 @end table
15470
15471 @node VxWorks Options
15472 @subsection VxWorks Options
15473 @cindex VxWorks Options
15474
15475 The options in this section are defined for all VxWorks targets.
15476 Options specific to the target hardware are listed with the other
15477 options for that target.
15478
15479 @table @gcctabopt
15480 @item -mrtp
15481 @opindex mrtp
15482 GCC can generate code for both VxWorks kernels and real time processes
15483 (RTPs). This option switches from the former to the latter. It also
15484 defines the preprocessor macro @code{__RTP__}.
15485
15486 @item -non-static
15487 @opindex non-static
15488 Link an RTP executable against shared libraries rather than static
15489 libraries. The options @option{-static} and @option{-shared} can
15490 also be used for RTPs (@pxref{Link Options}); @option{-static}
15491 is the default.
15492
15493 @item -Bstatic
15494 @itemx -Bdynamic
15495 @opindex Bstatic
15496 @opindex Bdynamic
15497 These options are passed down to the linker. They are defined for
15498 compatibility with Diab.
15499
15500 @item -Xbind-lazy
15501 @opindex Xbind-lazy
15502 Enable lazy binding of function calls. This option is equivalent to
15503 @option{-Wl,-z,now} and is defined for compatibility with Diab.
15504
15505 @item -Xbind-now
15506 @opindex Xbind-now
15507 Disable lazy binding of function calls. This option is the default and
15508 is defined for compatibility with Diab.
15509 @end table
15510
15511 @node x86-64 Options
15512 @subsection x86-64 Options
15513 @cindex x86-64 options
15514
15515 These are listed under @xref{i386 and x86-64 Options}.
15516
15517 @node i386 and x86-64 Windows Options
15518 @subsection i386 and x86-64 Windows Options
15519 @cindex i386 and x86-64 Windows Options
15520
15521 These additional options are available for Windows targets:
15522
15523 @table @gcctabopt
15524 @item -mconsole
15525 @opindex mconsole
15526 This option is available for Cygwin and MinGW targets. It
15527 specifies that a console application is to be generated, by
15528 instructing the linker to set the PE header subsystem type
15529 required for console applications.
15530 This is the default behaviour for Cygwin and MinGW targets.
15531
15532 @item -mcygwin
15533 @opindex mcygwin
15534 This option is available for Cygwin targets. It specifies that
15535 the Cygwin internal interface is to be used for predefined
15536 preprocessor macros, C runtime libraries and related linker
15537 paths and options. For Cygwin targets this is the default behaviour.
15538 This option is deprecated and will be removed in a future release.
15539
15540 @item -mno-cygwin
15541 @opindex mno-cygwin
15542 This option is available for Cygwin targets. It specifies that
15543 the MinGW internal interface is to be used instead of Cygwin's, by
15544 setting MinGW-related predefined macros and linker paths and default
15545 library options.
15546 This option is deprecated and will be removed in a future release.
15547
15548 @item -mdll
15549 @opindex mdll
15550 This option is available for Cygwin and MinGW targets. It
15551 specifies that a DLL - a dynamic link library - is to be
15552 generated, enabling the selection of the required runtime
15553 startup object and entry point.
15554
15555 @item -mnop-fun-dllimport
15556 @opindex mnop-fun-dllimport
15557 This option is available for Cygwin and MinGW targets. It
15558 specifies that the dllimport attribute should be ignored.
15559
15560 @item -mthread
15561 @opindex mthread
15562 This option is available for MinGW targets. It specifies
15563 that MinGW-specific thread support is to be used.
15564
15565 @item -mwin32
15566 @opindex mwin32
15567 This option is available for Cygwin and MinGW targets. It
15568 specifies that the typical Windows pre-defined macros are to
15569 be set in the pre-processor, but does not influence the choice
15570 of runtime library/startup code.
15571
15572 @item -mwindows
15573 @opindex mwindows
15574 This option is available for Cygwin and MinGW targets. It
15575 specifies that a GUI application is to be generated by
15576 instructing the linker to set the PE header subsystem type
15577 appropriately.
15578 @end table
15579
15580 See also under @ref{i386 and x86-64 Options} for standard options.
15581
15582 @node Xstormy16 Options
15583 @subsection Xstormy16 Options
15584 @cindex Xstormy16 Options
15585
15586 These options are defined for Xstormy16:
15587
15588 @table @gcctabopt
15589 @item -msim
15590 @opindex msim
15591 Choose startup files and linker script suitable for the simulator.
15592 @end table
15593
15594 @node Xtensa Options
15595 @subsection Xtensa Options
15596 @cindex Xtensa Options
15597
15598 These options are supported for Xtensa targets:
15599
15600 @table @gcctabopt
15601 @item -mconst16
15602 @itemx -mno-const16
15603 @opindex mconst16
15604 @opindex mno-const16
15605 Enable or disable use of @code{CONST16} instructions for loading
15606 constant values. The @code{CONST16} instruction is currently not a
15607 standard option from Tensilica. When enabled, @code{CONST16}
15608 instructions are always used in place of the standard @code{L32R}
15609 instructions. The use of @code{CONST16} is enabled by default only if
15610 the @code{L32R} instruction is not available.
15611
15612 @item -mfused-madd
15613 @itemx -mno-fused-madd
15614 @opindex mfused-madd
15615 @opindex mno-fused-madd
15616 Enable or disable use of fused multiply/add and multiply/subtract
15617 instructions in the floating-point option. This has no effect if the
15618 floating-point option is not also enabled. Disabling fused multiply/add
15619 and multiply/subtract instructions forces the compiler to use separate
15620 instructions for the multiply and add/subtract operations. This may be
15621 desirable in some cases where strict IEEE 754-compliant results are
15622 required: the fused multiply add/subtract instructions do not round the
15623 intermediate result, thereby producing results with @emph{more} bits of
15624 precision than specified by the IEEE standard. Disabling fused multiply
15625 add/subtract instructions also ensures that the program output is not
15626 sensitive to the compiler's ability to combine multiply and add/subtract
15627 operations.
15628
15629 @item -mserialize-volatile
15630 @itemx -mno-serialize-volatile
15631 @opindex mserialize-volatile
15632 @opindex mno-serialize-volatile
15633 When this option is enabled, GCC inserts @code{MEMW} instructions before
15634 @code{volatile} memory references to guarantee sequential consistency.
15635 The default is @option{-mserialize-volatile}. Use
15636 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
15637
15638 @item -mtext-section-literals
15639 @itemx -mno-text-section-literals
15640 @opindex mtext-section-literals
15641 @opindex mno-text-section-literals
15642 Control the treatment of literal pools. The default is
15643 @option{-mno-text-section-literals}, which places literals in a separate
15644 section in the output file. This allows the literal pool to be placed
15645 in a data RAM/ROM, and it also allows the linker to combine literal
15646 pools from separate object files to remove redundant literals and
15647 improve code size. With @option{-mtext-section-literals}, the literals
15648 are interspersed in the text section in order to keep them as close as
15649 possible to their references. This may be necessary for large assembly
15650 files.
15651
15652 @item -mtarget-align
15653 @itemx -mno-target-align
15654 @opindex mtarget-align
15655 @opindex mno-target-align
15656 When this option is enabled, GCC instructs the assembler to
15657 automatically align instructions to reduce branch penalties at the
15658 expense of some code density. The assembler attempts to widen density
15659 instructions to align branch targets and the instructions following call
15660 instructions. If there are not enough preceding safe density
15661 instructions to align a target, no widening will be performed. The
15662 default is @option{-mtarget-align}. These options do not affect the
15663 treatment of auto-aligned instructions like @code{LOOP}, which the
15664 assembler will always align, either by widening density instructions or
15665 by inserting no-op instructions.
15666
15667 @item -mlongcalls
15668 @itemx -mno-longcalls
15669 @opindex mlongcalls
15670 @opindex mno-longcalls
15671 When this option is enabled, GCC instructs the assembler to translate
15672 direct calls to indirect calls unless it can determine that the target
15673 of a direct call is in the range allowed by the call instruction. This
15674 translation typically occurs for calls to functions in other source
15675 files. Specifically, the assembler translates a direct @code{CALL}
15676 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
15677 The default is @option{-mno-longcalls}. This option should be used in
15678 programs where the call target can potentially be out of range. This
15679 option is implemented in the assembler, not the compiler, so the
15680 assembly code generated by GCC will still show direct call
15681 instructions---look at the disassembled object code to see the actual
15682 instructions. Note that the assembler will use an indirect call for
15683 every cross-file call, not just those that really will be out of range.
15684 @end table
15685
15686 @node zSeries Options
15687 @subsection zSeries Options
15688 @cindex zSeries options
15689
15690 These are listed under @xref{S/390 and zSeries Options}.
15691
15692 @node Code Gen Options
15693 @section Options for Code Generation Conventions
15694 @cindex code generation conventions
15695 @cindex options, code generation
15696 @cindex run-time options
15697
15698 These machine-independent options control the interface conventions
15699 used in code generation.
15700
15701 Most of them have both positive and negative forms; the negative form
15702 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
15703 one of the forms is listed---the one which is not the default. You
15704 can figure out the other form by either removing @samp{no-} or adding
15705 it.
15706
15707 @table @gcctabopt
15708 @item -fbounds-check
15709 @opindex fbounds-check
15710 For front-ends that support it, generate additional code to check that
15711 indices used to access arrays are within the declared range. This is
15712 currently only supported by the Java and Fortran front-ends, where
15713 this option defaults to true and false respectively.
15714
15715 @item -ftrapv
15716 @opindex ftrapv
15717 This option generates traps for signed overflow on addition, subtraction,
15718 multiplication operations.
15719
15720 @item -fwrapv
15721 @opindex fwrapv
15722 This option instructs the compiler to assume that signed arithmetic
15723 overflow of addition, subtraction and multiplication wraps around
15724 using twos-complement representation. This flag enables some optimizations
15725 and disables others. This option is enabled by default for the Java
15726 front-end, as required by the Java language specification.
15727
15728 @item -fexceptions
15729 @opindex fexceptions
15730 Enable exception handling. Generates extra code needed to propagate
15731 exceptions. For some targets, this implies GCC will generate frame
15732 unwind information for all functions, which can produce significant data
15733 size overhead, although it does not affect execution. If you do not
15734 specify this option, GCC will enable it by default for languages like
15735 C++ which normally require exception handling, and disable it for
15736 languages like C that do not normally require it. However, you may need
15737 to enable this option when compiling C code that needs to interoperate
15738 properly with exception handlers written in C++. You may also wish to
15739 disable this option if you are compiling older C++ programs that don't
15740 use exception handling.
15741
15742 @item -fnon-call-exceptions
15743 @opindex fnon-call-exceptions
15744 Generate code that allows trapping instructions to throw exceptions.
15745 Note that this requires platform-specific runtime support that does
15746 not exist everywhere. Moreover, it only allows @emph{trapping}
15747 instructions to throw exceptions, i.e.@: memory references or floating
15748 point instructions. It does not allow exceptions to be thrown from
15749 arbitrary signal handlers such as @code{SIGALRM}.
15750
15751 @item -funwind-tables
15752 @opindex funwind-tables
15753 Similar to @option{-fexceptions}, except that it will just generate any needed
15754 static data, but will not affect the generated code in any other way.
15755 You will normally not enable this option; instead, a language processor
15756 that needs this handling would enable it on your behalf.
15757
15758 @item -fasynchronous-unwind-tables
15759 @opindex fasynchronous-unwind-tables
15760 Generate unwind table in dwarf2 format, if supported by target machine. The
15761 table is exact at each instruction boundary, so it can be used for stack
15762 unwinding from asynchronous events (such as debugger or garbage collector).
15763
15764 @item -fpcc-struct-return
15765 @opindex fpcc-struct-return
15766 Return ``short'' @code{struct} and @code{union} values in memory like
15767 longer ones, rather than in registers. This convention is less
15768 efficient, but it has the advantage of allowing intercallability between
15769 GCC-compiled files and files compiled with other compilers, particularly
15770 the Portable C Compiler (pcc).
15771
15772 The precise convention for returning structures in memory depends
15773 on the target configuration macros.
15774
15775 Short structures and unions are those whose size and alignment match
15776 that of some integer type.
15777
15778 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
15779 switch is not binary compatible with code compiled with the
15780 @option{-freg-struct-return} switch.
15781 Use it to conform to a non-default application binary interface.
15782
15783 @item -freg-struct-return
15784 @opindex freg-struct-return
15785 Return @code{struct} and @code{union} values in registers when possible.
15786 This is more efficient for small structures than
15787 @option{-fpcc-struct-return}.
15788
15789 If you specify neither @option{-fpcc-struct-return} nor
15790 @option{-freg-struct-return}, GCC defaults to whichever convention is
15791 standard for the target. If there is no standard convention, GCC
15792 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
15793 the principal compiler. In those cases, we can choose the standard, and
15794 we chose the more efficient register return alternative.
15795
15796 @strong{Warning:} code compiled with the @option{-freg-struct-return}
15797 switch is not binary compatible with code compiled with the
15798 @option{-fpcc-struct-return} switch.
15799 Use it to conform to a non-default application binary interface.
15800
15801 @item -fshort-enums
15802 @opindex fshort-enums
15803 Allocate to an @code{enum} type only as many bytes as it needs for the
15804 declared range of possible values. Specifically, the @code{enum} type
15805 will be equivalent to the smallest integer type which has enough room.
15806
15807 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
15808 code that is not binary compatible with code generated without that switch.
15809 Use it to conform to a non-default application binary interface.
15810
15811 @item -fshort-double
15812 @opindex fshort-double
15813 Use the same size for @code{double} as for @code{float}.
15814
15815 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
15816 code that is not binary compatible with code generated without that switch.
15817 Use it to conform to a non-default application binary interface.
15818
15819 @item -fshort-wchar
15820 @opindex fshort-wchar
15821 Override the underlying type for @samp{wchar_t} to be @samp{short
15822 unsigned int} instead of the default for the target. This option is
15823 useful for building programs to run under WINE@.
15824
15825 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
15826 code that is not binary compatible with code generated without that switch.
15827 Use it to conform to a non-default application binary interface.
15828
15829 @item -fno-common
15830 @opindex fno-common
15831 In C code, controls the placement of uninitialized global variables.
15832 Unix C compilers have traditionally permitted multiple definitions of
15833 such variables in different compilation units by placing the variables
15834 in a common block.
15835 This is the behavior specified by @option{-fcommon}, and is the default
15836 for GCC on most targets.
15837 On the other hand, this behavior is not required by ISO C, and on some
15838 targets may carry a speed or code size penalty on variable references.
15839 The @option{-fno-common} option specifies that the compiler should place
15840 uninitialized global variables in the data section of the object file,
15841 rather than generating them as common blocks.
15842 This has the effect that if the same variable is declared
15843 (without @code{extern}) in two different compilations,
15844 you will get a multiple-definition error when you link them.
15845 In this case, you must compile with @option{-fcommon} instead.
15846 Compiling with @option{-fno-common} is useful on targets for which
15847 it provides better performance, or if you wish to verify that the
15848 program will work on other systems which always treat uninitialized
15849 variable declarations this way.
15850
15851 @item -fno-ident
15852 @opindex fno-ident
15853 Ignore the @samp{#ident} directive.
15854
15855 @item -finhibit-size-directive
15856 @opindex finhibit-size-directive
15857 Don't output a @code{.size} assembler directive, or anything else that
15858 would cause trouble if the function is split in the middle, and the
15859 two halves are placed at locations far apart in memory. This option is
15860 used when compiling @file{crtstuff.c}; you should not need to use it
15861 for anything else.
15862
15863 @item -fverbose-asm
15864 @opindex fverbose-asm
15865 Put extra commentary information in the generated assembly code to
15866 make it more readable. This option is generally only of use to those
15867 who actually need to read the generated assembly code (perhaps while
15868 debugging the compiler itself).
15869
15870 @option{-fno-verbose-asm}, the default, causes the
15871 extra information to be omitted and is useful when comparing two assembler
15872 files.
15873
15874 @item -frecord-gcc-switches
15875 @opindex frecord-gcc-switches
15876 This switch causes the command line that was used to invoke the
15877 compiler to be recorded into the object file that is being created.
15878 This switch is only implemented on some targets and the exact format
15879 of the recording is target and binary file format dependent, but it
15880 usually takes the form of a section containing ASCII text. This
15881 switch is related to the @option{-fverbose-asm} switch, but that
15882 switch only records information in the assembler output file as
15883 comments, so it never reaches the object file.
15884
15885 @item -fpic
15886 @opindex fpic
15887 @cindex global offset table
15888 @cindex PIC
15889 Generate position-independent code (PIC) suitable for use in a shared
15890 library, if supported for the target machine. Such code accesses all
15891 constant addresses through a global offset table (GOT)@. The dynamic
15892 loader resolves the GOT entries when the program starts (the dynamic
15893 loader is not part of GCC; it is part of the operating system). If
15894 the GOT size for the linked executable exceeds a machine-specific
15895 maximum size, you get an error message from the linker indicating that
15896 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
15897 instead. (These maximums are 8k on the SPARC and 32k
15898 on the m68k and RS/6000. The 386 has no such limit.)
15899
15900 Position-independent code requires special support, and therefore works
15901 only on certain machines. For the 386, GCC supports PIC for System V
15902 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
15903 position-independent.
15904
15905 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15906 are defined to 1.
15907
15908 @item -fPIC
15909 @opindex fPIC
15910 If supported for the target machine, emit position-independent code,
15911 suitable for dynamic linking and avoiding any limit on the size of the
15912 global offset table. This option makes a difference on the m68k,
15913 PowerPC and SPARC@.
15914
15915 Position-independent code requires special support, and therefore works
15916 only on certain machines.
15917
15918 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15919 are defined to 2.
15920
15921 @item -fpie
15922 @itemx -fPIE
15923 @opindex fpie
15924 @opindex fPIE
15925 These options are similar to @option{-fpic} and @option{-fPIC}, but
15926 generated position independent code can be only linked into executables.
15927 Usually these options are used when @option{-pie} GCC option will be
15928 used during linking.
15929
15930 @option{-fpie} and @option{-fPIE} both define the macros
15931 @code{__pie__} and @code{__PIE__}. The macros have the value 1
15932 for @option{-fpie} and 2 for @option{-fPIE}.
15933
15934 @item -fno-jump-tables
15935 @opindex fno-jump-tables
15936 Do not use jump tables for switch statements even where it would be
15937 more efficient than other code generation strategies. This option is
15938 of use in conjunction with @option{-fpic} or @option{-fPIC} for
15939 building code which forms part of a dynamic linker and cannot
15940 reference the address of a jump table. On some targets, jump tables
15941 do not require a GOT and this option is not needed.
15942
15943 @item -ffixed-@var{reg}
15944 @opindex ffixed
15945 Treat the register named @var{reg} as a fixed register; generated code
15946 should never refer to it (except perhaps as a stack pointer, frame
15947 pointer or in some other fixed role).
15948
15949 @var{reg} must be the name of a register. The register names accepted
15950 are machine-specific and are defined in the @code{REGISTER_NAMES}
15951 macro in the machine description macro file.
15952
15953 This flag does not have a negative form, because it specifies a
15954 three-way choice.
15955
15956 @item -fcall-used-@var{reg}
15957 @opindex fcall-used
15958 Treat the register named @var{reg} as an allocable register that is
15959 clobbered by function calls. It may be allocated for temporaries or
15960 variables that do not live across a call. Functions compiled this way
15961 will not save and restore the register @var{reg}.
15962
15963 It is an error to used this flag with the frame pointer or stack pointer.
15964 Use of this flag for other registers that have fixed pervasive roles in
15965 the machine's execution model will produce disastrous results.
15966
15967 This flag does not have a negative form, because it specifies a
15968 three-way choice.
15969
15970 @item -fcall-saved-@var{reg}
15971 @opindex fcall-saved
15972 Treat the register named @var{reg} as an allocable register saved by
15973 functions. It may be allocated even for temporaries or variables that
15974 live across a call. Functions compiled this way will save and restore
15975 the register @var{reg} if they use it.
15976
15977 It is an error to used this flag with the frame pointer or stack pointer.
15978 Use of this flag for other registers that have fixed pervasive roles in
15979 the machine's execution model will produce disastrous results.
15980
15981 A different sort of disaster will result from the use of this flag for
15982 a register in which function values may be returned.
15983
15984 This flag does not have a negative form, because it specifies a
15985 three-way choice.
15986
15987 @item -fpack-struct[=@var{n}]
15988 @opindex fpack-struct
15989 Without a value specified, pack all structure members together without
15990 holes. When a value is specified (which must be a small power of two), pack
15991 structure members according to this value, representing the maximum
15992 alignment (that is, objects with default alignment requirements larger than
15993 this will be output potentially unaligned at the next fitting location.
15994
15995 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
15996 code that is not binary compatible with code generated without that switch.
15997 Additionally, it makes the code suboptimal.
15998 Use it to conform to a non-default application binary interface.
15999
16000 @item -finstrument-functions
16001 @opindex finstrument-functions
16002 Generate instrumentation calls for entry and exit to functions. Just
16003 after function entry and just before function exit, the following
16004 profiling functions will be called with the address of the current
16005 function and its call site. (On some platforms,
16006 @code{__builtin_return_address} does not work beyond the current
16007 function, so the call site information may not be available to the
16008 profiling functions otherwise.)
16009
16010 @smallexample
16011 void __cyg_profile_func_enter (void *this_fn,
16012 void *call_site);
16013 void __cyg_profile_func_exit (void *this_fn,
16014 void *call_site);
16015 @end smallexample
16016
16017 The first argument is the address of the start of the current function,
16018 which may be looked up exactly in the symbol table.
16019
16020 This instrumentation is also done for functions expanded inline in other
16021 functions. The profiling calls will indicate where, conceptually, the
16022 inline function is entered and exited. This means that addressable
16023 versions of such functions must be available. If all your uses of a
16024 function are expanded inline, this may mean an additional expansion of
16025 code size. If you use @samp{extern inline} in your C code, an
16026 addressable version of such functions must be provided. (This is
16027 normally the case anyways, but if you get lucky and the optimizer always
16028 expands the functions inline, you might have gotten away without
16029 providing static copies.)
16030
16031 A function may be given the attribute @code{no_instrument_function}, in
16032 which case this instrumentation will not be done. This can be used, for
16033 example, for the profiling functions listed above, high-priority
16034 interrupt routines, and any functions from which the profiling functions
16035 cannot safely be called (perhaps signal handlers, if the profiling
16036 routines generate output or allocate memory).
16037
16038 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
16039 @opindex finstrument-functions-exclude-file-list
16040
16041 Set the list of functions that are excluded from instrumentation (see
16042 the description of @code{-finstrument-functions}). If the file that
16043 contains a function definition matches with one of @var{file}, then
16044 that function is not instrumented. The match is done on substrings:
16045 if the @var{file} parameter is a substring of the file name, it is
16046 considered to be a match.
16047
16048 For example,
16049 @code{-finstrument-functions-exclude-file-list=/bits/stl,include/sys}
16050 will exclude any inline function defined in files whose pathnames
16051 contain @code{/bits/stl} or @code{include/sys}.
16052
16053 If, for some reason, you want to include letter @code{','} in one of
16054 @var{sym}, write @code{'\,'}. For example,
16055 @code{-finstrument-functions-exclude-file-list='\,\,tmp'}
16056 (note the single quote surrounding the option).
16057
16058 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
16059 @opindex finstrument-functions-exclude-function-list
16060
16061 This is similar to @code{-finstrument-functions-exclude-file-list},
16062 but this option sets the list of function names to be excluded from
16063 instrumentation. The function name to be matched is its user-visible
16064 name, such as @code{vector<int> blah(const vector<int> &)}, not the
16065 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
16066 match is done on substrings: if the @var{sym} parameter is a substring
16067 of the function name, it is considered to be a match.
16068
16069 @item -fstack-check
16070 @opindex fstack-check
16071 Generate code to verify that you do not go beyond the boundary of the
16072 stack. You should specify this flag if you are running in an
16073 environment with multiple threads, but only rarely need to specify it in
16074 a single-threaded environment since stack overflow is automatically
16075 detected on nearly all systems if there is only one stack.
16076
16077 Note that this switch does not actually cause checking to be done; the
16078 operating system or the language runtime must do that. The switch causes
16079 generation of code to ensure that they see the stack being extended.
16080
16081 You can additionally specify a string parameter: @code{no} means no
16082 checking, @code{generic} means force the use of old-style checking,
16083 @code{specific} means use the best checking method and is equivalent
16084 to bare @option{-fstack-check}.
16085
16086 Old-style checking is a generic mechanism that requires no specific
16087 target support in the compiler but comes with the following drawbacks:
16088
16089 @enumerate
16090 @item
16091 Modified allocation strategy for large objects: they will always be
16092 allocated dynamically if their size exceeds a fixed threshold.
16093
16094 @item
16095 Fixed limit on the size of the static frame of functions: when it is
16096 topped by a particular function, stack checking is not reliable and
16097 a warning is issued by the compiler.
16098
16099 @item
16100 Inefficiency: because of both the modified allocation strategy and the
16101 generic implementation, the performances of the code are hampered.
16102 @end enumerate
16103
16104 Note that old-style stack checking is also the fallback method for
16105 @code{specific} if no target support has been added in the compiler.
16106
16107 @item -fstack-limit-register=@var{reg}
16108 @itemx -fstack-limit-symbol=@var{sym}
16109 @itemx -fno-stack-limit
16110 @opindex fstack-limit-register
16111 @opindex fstack-limit-symbol
16112 @opindex fno-stack-limit
16113 Generate code to ensure that the stack does not grow beyond a certain value,
16114 either the value of a register or the address of a symbol. If the stack
16115 would grow beyond the value, a signal is raised. For most targets,
16116 the signal is raised before the stack overruns the boundary, so
16117 it is possible to catch the signal without taking special precautions.
16118
16119 For instance, if the stack starts at absolute address @samp{0x80000000}
16120 and grows downwards, you can use the flags
16121 @option{-fstack-limit-symbol=__stack_limit} and
16122 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
16123 of 128KB@. Note that this may only work with the GNU linker.
16124
16125 @cindex aliasing of parameters
16126 @cindex parameters, aliased
16127 @item -fargument-alias
16128 @itemx -fargument-noalias
16129 @itemx -fargument-noalias-global
16130 @itemx -fargument-noalias-anything
16131 @opindex fargument-alias
16132 @opindex fargument-noalias
16133 @opindex fargument-noalias-global
16134 @opindex fargument-noalias-anything
16135 Specify the possible relationships among parameters and between
16136 parameters and global data.
16137
16138 @option{-fargument-alias} specifies that arguments (parameters) may
16139 alias each other and may alias global storage.@*
16140 @option{-fargument-noalias} specifies that arguments do not alias
16141 each other, but may alias global storage.@*
16142 @option{-fargument-noalias-global} specifies that arguments do not
16143 alias each other and do not alias global storage.
16144 @option{-fargument-noalias-anything} specifies that arguments do not
16145 alias any other storage.
16146
16147 Each language will automatically use whatever option is required by
16148 the language standard. You should not need to use these options yourself.
16149
16150 @item -fleading-underscore
16151 @opindex fleading-underscore
16152 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
16153 change the way C symbols are represented in the object file. One use
16154 is to help link with legacy assembly code.
16155
16156 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
16157 generate code that is not binary compatible with code generated without that
16158 switch. Use it to conform to a non-default application binary interface.
16159 Not all targets provide complete support for this switch.
16160
16161 @item -ftls-model=@var{model}
16162 @opindex ftls-model
16163 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
16164 The @var{model} argument should be one of @code{global-dynamic},
16165 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
16166
16167 The default without @option{-fpic} is @code{initial-exec}; with
16168 @option{-fpic} the default is @code{global-dynamic}.
16169
16170 @item -fvisibility=@var{default|internal|hidden|protected}
16171 @opindex fvisibility
16172 Set the default ELF image symbol visibility to the specified option---all
16173 symbols will be marked with this unless overridden within the code.
16174 Using this feature can very substantially improve linking and
16175 load times of shared object libraries, produce more optimized
16176 code, provide near-perfect API export and prevent symbol clashes.
16177 It is @strong{strongly} recommended that you use this in any shared objects
16178 you distribute.
16179
16180 Despite the nomenclature, @code{default} always means public ie;
16181 available to be linked against from outside the shared object.
16182 @code{protected} and @code{internal} are pretty useless in real-world
16183 usage so the only other commonly used option will be @code{hidden}.
16184 The default if @option{-fvisibility} isn't specified is
16185 @code{default}, i.e., make every
16186 symbol public---this causes the same behavior as previous versions of
16187 GCC@.
16188
16189 A good explanation of the benefits offered by ensuring ELF
16190 symbols have the correct visibility is given by ``How To Write
16191 Shared Libraries'' by Ulrich Drepper (which can be found at
16192 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
16193 solution made possible by this option to marking things hidden when
16194 the default is public is to make the default hidden and mark things
16195 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
16196 and @code{__attribute__ ((visibility("default")))} instead of
16197 @code{__declspec(dllexport)} you get almost identical semantics with
16198 identical syntax. This is a great boon to those working with
16199 cross-platform projects.
16200
16201 For those adding visibility support to existing code, you may find
16202 @samp{#pragma GCC visibility} of use. This works by you enclosing
16203 the declarations you wish to set visibility for with (for example)
16204 @samp{#pragma GCC visibility push(hidden)} and
16205 @samp{#pragma GCC visibility pop}.
16206 Bear in mind that symbol visibility should be viewed @strong{as
16207 part of the API interface contract} and thus all new code should
16208 always specify visibility when it is not the default ie; declarations
16209 only for use within the local DSO should @strong{always} be marked explicitly
16210 as hidden as so to avoid PLT indirection overheads---making this
16211 abundantly clear also aids readability and self-documentation of the code.
16212 Note that due to ISO C++ specification requirements, operator new and
16213 operator delete must always be of default visibility.
16214
16215 Be aware that headers from outside your project, in particular system
16216 headers and headers from any other library you use, may not be
16217 expecting to be compiled with visibility other than the default. You
16218 may need to explicitly say @samp{#pragma GCC visibility push(default)}
16219 before including any such headers.
16220
16221 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
16222 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
16223 no modifications. However, this means that calls to @samp{extern}
16224 functions with no explicit visibility will use the PLT, so it is more
16225 effective to use @samp{__attribute ((visibility))} and/or
16226 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
16227 declarations should be treated as hidden.
16228
16229 Note that @samp{-fvisibility} does affect C++ vague linkage
16230 entities. This means that, for instance, an exception class that will
16231 be thrown between DSOs must be explicitly marked with default
16232 visibility so that the @samp{type_info} nodes will be unified between
16233 the DSOs.
16234
16235 An overview of these techniques, their benefits and how to use them
16236 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
16237
16238 @end table
16239
16240 @c man end
16241
16242 @node Environment Variables
16243 @section Environment Variables Affecting GCC
16244 @cindex environment variables
16245
16246 @c man begin ENVIRONMENT
16247 This section describes several environment variables that affect how GCC
16248 operates. Some of them work by specifying directories or prefixes to use
16249 when searching for various kinds of files. Some are used to specify other
16250 aspects of the compilation environment.
16251
16252 Note that you can also specify places to search using options such as
16253 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
16254 take precedence over places specified using environment variables, which
16255 in turn take precedence over those specified by the configuration of GCC@.
16256 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
16257 GNU Compiler Collection (GCC) Internals}.
16258
16259 @table @env
16260 @item LANG
16261 @itemx LC_CTYPE
16262 @c @itemx LC_COLLATE
16263 @itemx LC_MESSAGES
16264 @c @itemx LC_MONETARY
16265 @c @itemx LC_NUMERIC
16266 @c @itemx LC_TIME
16267 @itemx LC_ALL
16268 @findex LANG
16269 @findex LC_CTYPE
16270 @c @findex LC_COLLATE
16271 @findex LC_MESSAGES
16272 @c @findex LC_MONETARY
16273 @c @findex LC_NUMERIC
16274 @c @findex LC_TIME
16275 @findex LC_ALL
16276 @cindex locale
16277 These environment variables control the way that GCC uses
16278 localization information that allow GCC to work with different
16279 national conventions. GCC inspects the locale categories
16280 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
16281 so. These locale categories can be set to any value supported by your
16282 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
16283 Kingdom encoded in UTF-8.
16284
16285 The @env{LC_CTYPE} environment variable specifies character
16286 classification. GCC uses it to determine the character boundaries in
16287 a string; this is needed for some multibyte encodings that contain quote
16288 and escape characters that would otherwise be interpreted as a string
16289 end or escape.
16290
16291 The @env{LC_MESSAGES} environment variable specifies the language to
16292 use in diagnostic messages.
16293
16294 If the @env{LC_ALL} environment variable is set, it overrides the value
16295 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
16296 and @env{LC_MESSAGES} default to the value of the @env{LANG}
16297 environment variable. If none of these variables are set, GCC
16298 defaults to traditional C English behavior.
16299
16300 @item TMPDIR
16301 @findex TMPDIR
16302 If @env{TMPDIR} is set, it specifies the directory to use for temporary
16303 files. GCC uses temporary files to hold the output of one stage of
16304 compilation which is to be used as input to the next stage: for example,
16305 the output of the preprocessor, which is the input to the compiler
16306 proper.
16307
16308 @item GCC_EXEC_PREFIX
16309 @findex GCC_EXEC_PREFIX
16310 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
16311 names of the subprograms executed by the compiler. No slash is added
16312 when this prefix is combined with the name of a subprogram, but you can
16313 specify a prefix that ends with a slash if you wish.
16314
16315 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
16316 an appropriate prefix to use based on the pathname it was invoked with.
16317
16318 If GCC cannot find the subprogram using the specified prefix, it
16319 tries looking in the usual places for the subprogram.
16320
16321 The default value of @env{GCC_EXEC_PREFIX} is
16322 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
16323 the installed compiler. In many cases @var{prefix} is the value
16324 of @code{prefix} when you ran the @file{configure} script.
16325
16326 Other prefixes specified with @option{-B} take precedence over this prefix.
16327
16328 This prefix is also used for finding files such as @file{crt0.o} that are
16329 used for linking.
16330
16331 In addition, the prefix is used in an unusual way in finding the
16332 directories to search for header files. For each of the standard
16333 directories whose name normally begins with @samp{/usr/local/lib/gcc}
16334 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
16335 replacing that beginning with the specified prefix to produce an
16336 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
16337 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
16338 These alternate directories are searched first; the standard directories
16339 come next. If a standard directory begins with the configured
16340 @var{prefix} then the value of @var{prefix} is replaced by
16341 @env{GCC_EXEC_PREFIX} when looking for header files.
16342
16343 @item COMPILER_PATH
16344 @findex COMPILER_PATH
16345 The value of @env{COMPILER_PATH} is a colon-separated list of
16346 directories, much like @env{PATH}. GCC tries the directories thus
16347 specified when searching for subprograms, if it can't find the
16348 subprograms using @env{GCC_EXEC_PREFIX}.
16349
16350 @item LIBRARY_PATH
16351 @findex LIBRARY_PATH
16352 The value of @env{LIBRARY_PATH} is a colon-separated list of
16353 directories, much like @env{PATH}. When configured as a native compiler,
16354 GCC tries the directories thus specified when searching for special
16355 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
16356 using GCC also uses these directories when searching for ordinary
16357 libraries for the @option{-l} option (but directories specified with
16358 @option{-L} come first).
16359
16360 @item LANG
16361 @findex LANG
16362 @cindex locale definition
16363 This variable is used to pass locale information to the compiler. One way in
16364 which this information is used is to determine the character set to be used
16365 when character literals, string literals and comments are parsed in C and C++.
16366 When the compiler is configured to allow multibyte characters,
16367 the following values for @env{LANG} are recognized:
16368
16369 @table @samp
16370 @item C-JIS
16371 Recognize JIS characters.
16372 @item C-SJIS
16373 Recognize SJIS characters.
16374 @item C-EUCJP
16375 Recognize EUCJP characters.
16376 @end table
16377
16378 If @env{LANG} is not defined, or if it has some other value, then the
16379 compiler will use mblen and mbtowc as defined by the default locale to
16380 recognize and translate multibyte characters.
16381 @end table
16382
16383 @noindent
16384 Some additional environments variables affect the behavior of the
16385 preprocessor.
16386
16387 @include cppenv.texi
16388
16389 @c man end
16390
16391 @node Precompiled Headers
16392 @section Using Precompiled Headers
16393 @cindex precompiled headers
16394 @cindex speed of compilation
16395
16396 Often large projects have many header files that are included in every
16397 source file. The time the compiler takes to process these header files
16398 over and over again can account for nearly all of the time required to
16399 build the project. To make builds faster, GCC allows users to
16400 `precompile' a header file; then, if builds can use the precompiled
16401 header file they will be much faster.
16402
16403 To create a precompiled header file, simply compile it as you would any
16404 other file, if necessary using the @option{-x} option to make the driver
16405 treat it as a C or C++ header file. You will probably want to use a
16406 tool like @command{make} to keep the precompiled header up-to-date when
16407 the headers it contains change.
16408
16409 A precompiled header file will be searched for when @code{#include} is
16410 seen in the compilation. As it searches for the included file
16411 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
16412 compiler looks for a precompiled header in each directory just before it
16413 looks for the include file in that directory. The name searched for is
16414 the name specified in the @code{#include} with @samp{.gch} appended. If
16415 the precompiled header file can't be used, it is ignored.
16416
16417 For instance, if you have @code{#include "all.h"}, and you have
16418 @file{all.h.gch} in the same directory as @file{all.h}, then the
16419 precompiled header file will be used if possible, and the original
16420 header will be used otherwise.
16421
16422 Alternatively, you might decide to put the precompiled header file in a
16423 directory and use @option{-I} to ensure that directory is searched
16424 before (or instead of) the directory containing the original header.
16425 Then, if you want to check that the precompiled header file is always
16426 used, you can put a file of the same name as the original header in this
16427 directory containing an @code{#error} command.
16428
16429 This also works with @option{-include}. So yet another way to use
16430 precompiled headers, good for projects not designed with precompiled
16431 header files in mind, is to simply take most of the header files used by
16432 a project, include them from another header file, precompile that header
16433 file, and @option{-include} the precompiled header. If the header files
16434 have guards against multiple inclusion, they will be skipped because
16435 they've already been included (in the precompiled header).
16436
16437 If you need to precompile the same header file for different
16438 languages, targets, or compiler options, you can instead make a
16439 @emph{directory} named like @file{all.h.gch}, and put each precompiled
16440 header in the directory, perhaps using @option{-o}. It doesn't matter
16441 what you call the files in the directory, every precompiled header in
16442 the directory will be considered. The first precompiled header
16443 encountered in the directory that is valid for this compilation will
16444 be used; they're searched in no particular order.
16445
16446 There are many other possibilities, limited only by your imagination,
16447 good sense, and the constraints of your build system.
16448
16449 A precompiled header file can be used only when these conditions apply:
16450
16451 @itemize
16452 @item
16453 Only one precompiled header can be used in a particular compilation.
16454
16455 @item
16456 A precompiled header can't be used once the first C token is seen. You
16457 can have preprocessor directives before a precompiled header; you can
16458 even include a precompiled header from inside another header, so long as
16459 there are no C tokens before the @code{#include}.
16460
16461 @item
16462 The precompiled header file must be produced for the same language as
16463 the current compilation. You can't use a C precompiled header for a C++
16464 compilation.
16465
16466 @item
16467 The precompiled header file must have been produced by the same compiler
16468 binary as the current compilation is using.
16469
16470 @item
16471 Any macros defined before the precompiled header is included must
16472 either be defined in the same way as when the precompiled header was
16473 generated, or must not affect the precompiled header, which usually
16474 means that they don't appear in the precompiled header at all.
16475
16476 The @option{-D} option is one way to define a macro before a
16477 precompiled header is included; using a @code{#define} can also do it.
16478 There are also some options that define macros implicitly, like
16479 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
16480 defined this way.
16481
16482 @item If debugging information is output when using the precompiled
16483 header, using @option{-g} or similar, the same kind of debugging information
16484 must have been output when building the precompiled header. However,
16485 a precompiled header built using @option{-g} can be used in a compilation
16486 when no debugging information is being output.
16487
16488 @item The same @option{-m} options must generally be used when building
16489 and using the precompiled header. @xref{Submodel Options},
16490 for any cases where this rule is relaxed.
16491
16492 @item Each of the following options must be the same when building and using
16493 the precompiled header:
16494
16495 @gccoptlist{-fexceptions}
16496
16497 @item
16498 Some other command-line options starting with @option{-f},
16499 @option{-p}, or @option{-O} must be defined in the same way as when
16500 the precompiled header was generated. At present, it's not clear
16501 which options are safe to change and which are not; the safest choice
16502 is to use exactly the same options when generating and using the
16503 precompiled header. The following are known to be safe:
16504
16505 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
16506 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
16507 -fsched-verbose=<number> -fschedule-insns -fvisibility= @gol
16508 -pedantic-errors}
16509
16510 @end itemize
16511
16512 For all of these except the last, the compiler will automatically
16513 ignore the precompiled header if the conditions aren't met. If you
16514 find an option combination that doesn't work and doesn't cause the
16515 precompiled header to be ignored, please consider filing a bug report,
16516 see @ref{Bugs}.
16517
16518 If you do use differing options when generating and using the
16519 precompiled header, the actual behavior will be a mixture of the
16520 behavior for the options. For instance, if you use @option{-g} to
16521 generate the precompiled header but not when using it, you may or may
16522 not get debugging information for routines in the precompiled header.
16523
16524 @node Running Protoize
16525 @section Running Protoize
16526
16527 The program @code{protoize} is an optional part of GCC@. You can use
16528 it to add prototypes to a program, thus converting the program to ISO
16529 C in one respect. The companion program @code{unprotoize} does the
16530 reverse: it removes argument types from any prototypes that are found.
16531
16532 When you run these programs, you must specify a set of source files as
16533 command line arguments. The conversion programs start out by compiling
16534 these files to see what functions they define. The information gathered
16535 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
16536
16537 After scanning comes actual conversion. The specified files are all
16538 eligible to be converted; any files they include (whether sources or
16539 just headers) are eligible as well.
16540
16541 But not all the eligible files are converted. By default,
16542 @code{protoize} and @code{unprotoize} convert only source and header
16543 files in the current directory. You can specify additional directories
16544 whose files should be converted with the @option{-d @var{directory}}
16545 option. You can also specify particular files to exclude with the
16546 @option{-x @var{file}} option. A file is converted if it is eligible, its
16547 directory name matches one of the specified directory names, and its
16548 name within the directory has not been excluded.
16549
16550 Basic conversion with @code{protoize} consists of rewriting most
16551 function definitions and function declarations to specify the types of
16552 the arguments. The only ones not rewritten are those for varargs
16553 functions.
16554
16555 @code{protoize} optionally inserts prototype declarations at the
16556 beginning of the source file, to make them available for any calls that
16557 precede the function's definition. Or it can insert prototype
16558 declarations with block scope in the blocks where undeclared functions
16559 are called.
16560
16561 Basic conversion with @code{unprotoize} consists of rewriting most
16562 function declarations to remove any argument types, and rewriting
16563 function definitions to the old-style pre-ISO form.
16564
16565 Both conversion programs print a warning for any function declaration or
16566 definition that they can't convert. You can suppress these warnings
16567 with @option{-q}.
16568
16569 The output from @code{protoize} or @code{unprotoize} replaces the
16570 original source file. The original file is renamed to a name ending
16571 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
16572 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
16573 for DOS) file already exists, then the source file is simply discarded.
16574
16575 @code{protoize} and @code{unprotoize} both depend on GCC itself to
16576 scan the program and collect information about the functions it uses.
16577 So neither of these programs will work until GCC is installed.
16578
16579 Here is a table of the options you can use with @code{protoize} and
16580 @code{unprotoize}. Each option works with both programs unless
16581 otherwise stated.
16582
16583 @table @code
16584 @item -B @var{directory}
16585 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
16586 usual directory (normally @file{/usr/local/lib}). This file contains
16587 prototype information about standard system functions. This option
16588 applies only to @code{protoize}.
16589
16590 @item -c @var{compilation-options}
16591 Use @var{compilation-options} as the options when running @command{gcc} to
16592 produce the @samp{.X} files. The special option @option{-aux-info} is
16593 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
16594
16595 Note that the compilation options must be given as a single argument to
16596 @code{protoize} or @code{unprotoize}. If you want to specify several
16597 @command{gcc} options, you must quote the entire set of compilation options
16598 to make them a single word in the shell.
16599
16600 There are certain @command{gcc} arguments that you cannot use, because they
16601 would produce the wrong kind of output. These include @option{-g},
16602 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
16603 the @var{compilation-options}, they are ignored.
16604
16605 @item -C
16606 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
16607 systems) instead of @samp{.c}. This is convenient if you are converting
16608 a C program to C++. This option applies only to @code{protoize}.
16609
16610 @item -g
16611 Add explicit global declarations. This means inserting explicit
16612 declarations at the beginning of each source file for each function
16613 that is called in the file and was not declared. These declarations
16614 precede the first function definition that contains a call to an
16615 undeclared function. This option applies only to @code{protoize}.
16616
16617 @item -i @var{string}
16618 Indent old-style parameter declarations with the string @var{string}.
16619 This option applies only to @code{protoize}.
16620
16621 @code{unprotoize} converts prototyped function definitions to old-style
16622 function definitions, where the arguments are declared between the
16623 argument list and the initial @samp{@{}. By default, @code{unprotoize}
16624 uses five spaces as the indentation. If you want to indent with just
16625 one space instead, use @option{-i " "}.
16626
16627 @item -k
16628 Keep the @samp{.X} files. Normally, they are deleted after conversion
16629 is finished.
16630
16631 @item -l
16632 Add explicit local declarations. @code{protoize} with @option{-l} inserts
16633 a prototype declaration for each function in each block which calls the
16634 function without any declaration. This option applies only to
16635 @code{protoize}.
16636
16637 @item -n
16638 Make no real changes. This mode just prints information about the conversions
16639 that would have been done without @option{-n}.
16640
16641 @item -N
16642 Make no @samp{.save} files. The original files are simply deleted.
16643 Use this option with caution.
16644
16645 @item -p @var{program}
16646 Use the program @var{program} as the compiler. Normally, the name
16647 @file{gcc} is used.
16648
16649 @item -q
16650 Work quietly. Most warnings are suppressed.
16651
16652 @item -v
16653 Print the version number, just like @option{-v} for @command{gcc}.
16654 @end table
16655
16656 If you need special compiler options to compile one of your program's
16657 source files, then you should generate that file's @samp{.X} file
16658 specially, by running @command{gcc} on that source file with the
16659 appropriate options and the option @option{-aux-info}. Then run
16660 @code{protoize} on the entire set of files. @code{protoize} will use
16661 the existing @samp{.X} file because it is newer than the source file.
16662 For example:
16663
16664 @smallexample
16665 gcc -Dfoo=bar file1.c -aux-info file1.X
16666 protoize *.c
16667 @end smallexample
16668
16669 @noindent
16670 You need to include the special files along with the rest in the
16671 @code{protoize} command, even though their @samp{.X} files already
16672 exist, because otherwise they won't get converted.
16673
16674 @xref{Protoize Caveats}, for more information on how to use
16675 @code{protoize} successfully.