1 .\" Sparse manpage by Josh Triplett
2 .TH sparse "1"
3 .
4 .SH NAME
5 sparse \- Semantic Parser for C
6 .
7 .SH SYNOPSIS
8 .B sparse
9 [\fIWARNING OPTIONS\fR]... \fIfile.c\fR
10 .
11 .SH DESCRIPTION
12 Sparse parses C source and looks for errors, producing warnings on standard
13 error.
14 .P
15 Sparse accepts options controlling the set of warnings to generate. To turn
16 on warnings Sparse does not issue by default, use the corresponding warning
17 option \fB\-Wsomething\fR. Sparse issues some warnings by default; to turn
18 off those warnings, pass the negation of the associated warning option,
19 \fB\-Wno\-something\fR.
20 .
21 .SH WARNING OPTIONS
22 .TP
23 .B \-fmax-warnings=COUNT
24 Set the maximum number of displayed warnings to COUNT, which should be
25 a numerical value or 'unlimited'.
26 The default limit is 100.
27 .
28 .TP
29 .B \-Wsparse\-all
30 Turn on all sparse warnings, except for those explicitly disabled via
31 \fB\-Wno\-something\fR.
32 .TP
33 .B \-Wsparse\-error
34 Turn all sparse warnings into errors.
35 .TP
36 .B \-Waddress\-space
37 Warn about code which mixes pointers to different address spaces.
38
39 Sparse allows an extended attribute
40 .BI __attribute__((address_space( id )))
41 on pointers, which designates a pointer target in address space \fIid\fR (an
42 identifier or a constant integer).
43 With \fB\-Waddress\-space\fR, Sparse treats pointers with
44 identical target types but different address spaces as distinct types and
45 will warn accordingly.
46
47 Sparse will also warn on casts which remove the address space (casts to an
48 integer type or to a plain pointer type). An exception to this is when the
49 destination type is \fBuintptr_t\fR (or \fBunsigned long\fR) since such casts
50 are often used to "get a pointer value representation in an integer type" and
51 such values are independent of the address space.
52
53 To override these warnings, use a type that includes \fB__attribute__((force))\fR.
54
55 Sparse issues these warnings by default. To turn them off, use
56 \fB\-Wno\-address\-space\fR.
57 .
58 .TP
59 .B \-Wbitwise
60 Warn about unsupported operations or type mismatches with restricted integer
61 types.
62
63 Sparse supports an extended attribute, \fB__attribute__((bitwise))\fR, which
64 creates a new restricted integer type from a base integer type, distinct from
65 the base integer type and from any other restricted integer type not declared
66 in the same declaration or \fBtypedef\fR. For example, this allows programs
67 to create \fBtypedef\fRs for integer types with specific endianness. With
68 \fB-Wbitwise\fR, Sparse will warn on any use of a restricted type in
69 arithmetic operations other than bitwise operations, and on any conversion of
70 one restricted type into another, except via a cast that includes
71 \fB__attribute__((force))\fR.
72
73 __bitwise ends up being a "stronger integer separation", one that
74 doesn't allow you to mix with non-bitwise integers, so now it's much
75 harder to lose the type by mistake.
76
77 __bitwise is for *unique types* that cannot be mixed with other
78 types, and that you'd never want to just use as a random integer (the
79 integer 0 is special, though, and gets silently accepted iirc - it's
80 kind of like "NULL" for pointers). So "gfp_t" or the "safe endianness"
81 types would be __bitwise: you can only operate on them by doing
82 specific operations that know about *that* particular type.
83
84 Sparse issues these warnings by default. To turn them off, use
85 \fB\-Wno\-bitwise\fR.
86 .
87 .TP
88 .B \-Wbitwise\-pointer
89 Same as \fB\-Wbitwise\fR but for casts to or from pointers to bitwise types.
90
91 Sparse does not issue these warnings by default.
92 .
93 .TP
94 .B \-Wcast\-from\-as
95 Warn about casts which remove an address space from a pointer type.
96
97 This is similar to \fB\-Waddress\-space\fR but will also warn
98 on casts to \fBunsigned long\fR.
99
100 Sparse does not issues these warnings by default.
101 .
102 .TP
103 .B \-Wcast\-to\-as
104 Warn about casts which add an address space to a pointer type.
105
106 A cast that includes \fB__attribute__((force))\fR will suppress this warning.
107 No warning is generated if the original type is \fBuintptr_t\fR
108 (or \fBunsigned long\fR).
109
110 Sparse does not issue these warnings by default.
111 .
112 .TP
113 .B \-Wcast\-truncate
114 Warn about casts that truncate constant values.
115
116 Sparse issues these warnings by default. To turn them off, use
117 \fB\-Wno\-cast\-truncate\fR.
118 .
119 .TP
120 .B \-Wconstant\-suffix
121 Warn if an integer constant is larger than the maximum representable value
122 of the type indicated by its type suffix (if any). For example, on a
123 system where ints are 32-bit and longs 64-bit, the constant \fB0x100000000U\fR
124 is larger than can be represented by an \fBunsigned int\fR but fits in an
125 \fBunsigned long\fR. So its type is \fBunsigned long\fR but this is not
126 indicated by its suffix. In this case, the warning could be suppressed by
127 using the suffix \fBUL\fR: \fB0x100000000UL\fR.
128
129 Sparse does not issue these warnings by default.
130 .
131 .TP
132 .B \-Wconstexpr-not-const
133 Warn if a non-constant expression is encountered when really expecting a
134 constant expression instead.
135 Currently, this warns when initializing an object of static storage duration
136 with an initializer which is not a constant expression.
137
138 Sparse does not issue these warnings by default.
139 .
140 .TP
141 .B \-Wcontext
142 Warn about potential errors in synchronization or other delimited contexts.
143
144 Sparse supports several means of designating functions or statements that
145 delimit contexts, such as synchronization. Functions with the extended
146 attribute
147 .BI __attribute__((context( expression , in_context , out_context ))
148 require the context \fIexpression\fR (for instance, a lock) to have the value
149 \fIin_context\fR (a constant nonnegative integer) when called, and return with
150 the value \fIout_context\fR (a constant nonnegative integer). For APIs
151 defined via macros, use the statement form
152 .BI __context__( expression , in_value , out_value )
153 in the body of the macro.
154
155 With \fB-Wcontext\fR Sparse will warn when it sees a function change the
156 context without indicating this with a \fBcontext\fR attribute, either by
157 decreasing a context below zero (such as by releasing a lock without acquiring
158 it), or returning with a changed context (such as by acquiring a lock without
159 releasing it). Sparse will also warn about blocks of code which may
160 potentially execute with different contexts.
161
162 Sparse issues these warnings by default. To turn them off, use
163 \fB\-Wno\-context\fR.
164 .
165 .TP
166 .B \-Wdecl
167 Warn about any non-\fBstatic\fR variable or function definition that has no
168 previous declaration.
169
170 Private symbols (functions and variables) internal to a given source file
171 should use \fBstatic\fR, to allow additional compiler optimizations, allow
172 detection of unused symbols, and prevent other code from relying on these
173 internal symbols. Public symbols used by other source files will need
174 declarations visible to those other source files, such as in a header file.
175 All declarations should fall into one of these two categories. Thus, with
176 \fB-Wdecl\fR, Sparse warns about any symbol definition with neither
177 \fBstatic\fR nor a declaration. To fix this warning, declare private symbols
178 \fBstatic\fR, and ensure that the files defining public symbols have the
179 symbol declarations available first (such as by including the appropriate
180 header file).
181
182 Sparse issues these warnings by default. To turn them off, use
183 \fB\-Wno\-decl\fR.
184 .
185 .TP
186 .B \-Wdeclaration-after-statement
187 Warn about declarations that are not at the start of a block.
188
189 These declarations are permitted in C99 but not in C89.
190
191 Sparse issues these warnings by default only when the C dialect is
192 C89 (i.e. -ansi or -std=c89). To turn them off, use
193 \fB\-Wno\-declaration\-after\-statement\fR.
194 .
195 .TP
196 .B \-Wdefault\-bitfield\-sign
197 Warn about any bitfield with no explicit signedness.
198
199 Bitfields have no standard-specified default signedness. (C99 6.7.2) A
200 bitfield without an explicit \fBsigned\fR or \fBunsigned\fR creates a
201 portability problem for software that relies on the available range of values.
202 To fix this, specify the bitfield type as \fBsigned\fR or \fBunsigned\fR
203 explicitly.
204
205 Sparse does not issue these warnings by default.
206 .
207 .TP
208 .B \-Wdesignated\-init
209 Warn about positional initialization of structs marked as requiring designated
210 initializers.
211
212 Sparse allows an attribute
213 .BI __attribute__((designated_init))
214 which marks a struct as requiring designated initializers. Sparse will warn
215 about positional initialization of a struct variable or struct literal of a
216 type that has this attribute.
217
218 Requiring designated initializers for a particular struct type will insulate
219 code using that struct type from changes to the layout of the type, avoiding
220 the need to change initializers for that type unless they initialize a removed
221 or incompatibly changed field.
222
223 Common examples of this type of struct include collections of function pointers
224 for the implementations of a class of related operations, for which the default
225 NULL for an unmentioned field in a designated initializer will correctly
226 indicate the absence of that operation.
227
228 Sparse issues these warnings by default. To turn them off, use
229 \fB\-Wno\-designated\-init\fR.
230 .
231 .TP
232 .B \-Wdo\-while
233 Warn about do-while loops that do not delimit the loop body with braces.
234
235 Sparse does not issue these warnings by default.
236 .
237 .TP
238 .B \-Wenum\-mismatch
239 Warn about the use of an expression of an incorrect \fBenum\fR type when
240 initializing another \fBenum\fR type, assigning to another \fBenum\fR type, or
241 passing an argument to a function which expects another \fBenum\fR type.
242
243 Sparse issues these warnings by default. To turn them off, use
244 \fB\-Wno\-enum\-mismatch\fR.
245 .
246 .TP
247 .B \-Wexternal\-function\-has\-definition
248 Warn about function definitions that are declared with external linkage.
249
250 Sparse issues these warnings by default. To turn them off, use
251 \fB\-Wno\-external\-function\-has\-definition\fR.
252 .
253 .TP
254 .B \-Winit\-cstring
255 Warn about initialization of a char array with a too long constant C string.
256
257 If the size of the char array and the length of the string are the same,
258 there is no space for the last nul char of the string in the array:
259
260 .nf
261 char s[3] = "abc";
262 .fi
263
264 If the array is used as a byte array, not as C string, this
265 warning is just noise. However, if the array is passed to functions
266 dealing with C string like printf(%s) and strcmp, it may cause a
267 trouble.
268
269 Sparse does not issue these warnings by default.
270 .
271 .TP
272 .B \-Wmemcpy\-max\-count
273 Warn about call of \fBmemcpy()\fR, \fBmemset()\fR, \fBcopy_from_user()\fR, or
274 \fBcopy_to_user()\fR with a large compile-time byte count.
275
276 Sparse issues these warnings by default. To turn them off, use
277 \fB\-Wno\-memcpy\-max\-count\fR.
278
279 The limit can be changed with \fB\-fmemcpy\-max\-count=COUNT\fR,
280 the default being \fB100000\fR.
281 .
282 .TP
283 .B \-Wnon\-pointer\-null
284 Warn about the use of 0 as a NULL pointer.
285
286 0 has integer type. NULL has pointer type.
287
288 Sparse issues these warnings by default. To turn them off, use
289 \fB\-Wno\-non\-pointer\-null\fR.
290 .
291 .TP
292 .B \-Wold\-initializer
293 Warn about the use of the pre-C99 GCC syntax for designated initializers.
294
295 C99 provides a standard syntax for designated fields in \fBstruct\fR or
296 \fBunion\fR initializers:
297
298 .nf
299 struct structname var = { .field = value };
300 .fi
301
302 GCC also has an old, non-standard syntax for designated initializers which
303 predates C99:
304
305 .nf
306 struct structname var = { field: value };
307 .fi
308
309 Sparse will warn about the use of GCC's non-standard syntax for designated
310 initializers. To fix this warning, convert designated initializers to use the
311 standard C99 syntax.
312
313 Sparse issues these warnings by default. To turn them off, use
314 \fB\-Wno\-old\-initializer\fR.
315 .
316 .TP
317 .B \-Wone\-bit\-signed\-bitfield
318 Warn about any one-bit \fBsigned\fR bitfields.
319
320 A one-bit \fBsigned\fR bitfield can only have the values 0 and -1, or with
321 some compilers only 0; this results in unexpected behavior for programs which
322 expected the ability to store 0 and 1.
323
324 Sparse issues these warnings by default. To turn them off, use
325 \fB\-Wno\-one\-bit\-signed\-bitfield\fR.
326 .
327 .TP
328 .B \-Wparen\-string
329 Warn about the use of a parenthesized string to initialize an array.
330
331 Standard C syntax does not permit a parenthesized string as an array
332 initializer. GCC allows this syntax as an extension. With
333 \fB\-Wparen\-string\fR, Sparse will warn about this syntax.
334
335 Sparse does not issue these warnings by default.
336 .
337 .TP
338 .B \-Wpointer\-arith
339 Warn about anything that depends on the \fBsizeof\fR a void or function type.
340
341 C99 does not allow the \fBsizeof\fR operator to be applied to function types
342 or to incomplete types such as void. GCC allows \fBsizeof\fR to be applied to
343 these types as an extension and assigns these types a size of \fI1\fR. With
344 \fB\-pointer\-arith\fR, Sparse will warn about pointer arithmetic on void
345 or function pointers, as well as expressions which directly apply the
346 \fBsizeof\fR operator to void or function types.
347
348 Sparse does not issue these warnings by default.
349 .
350 .TP
351 .B \-Wptr\-subtraction\-blows
352 Warn when subtracting two pointers to a type with a non-power-of-two size.
353
354 Subtracting two pointers to a given type gives a difference in terms of the
355 number of items of that type. To generate this value, compilers will usually
356 need to divide the difference by the size of the type, an potentially
357 expensive operation for sizes other than powers of two.
358
359 Code written using pointer subtraction can often use another approach instead,
360 such as array indexing with an explicit array index variable, which may allow
361 compilers to generate more efficient code.
362
363 Sparse does not issue these warnings by default.
364 .
365 .TP
366 .B \-Wreturn\-void
367 Warn if a function with return type void returns a void expression.
368
369 C99 permits this, and in some cases this allows for more generic code in
370 macros that use typeof or take a type as a macro argument. However, some
371 programs consider this poor style, and those programs can use
372 \fB\-Wreturn\-void\fR to get warnings about it.
373
374 Sparse does not issue these warnings by default.
375 .
376 .TP
377 .B \-Wshadow
378 Warn when declaring a symbol which shadows a declaration with the same name in
379 an outer scope.
380
381 Such declarations can lead to error-prone code.
382
383 Sparse does not issue these warnings by default.
384 .
385 .TP
386 .B \-Wshift-count-negative
387 Warn if a shift count is negative.
388
389 Sparse issues these warnings by default.
390 .
391 .TP
392 .B \-Wshift-count-overflow
393 Warn if a shift count is bigger than the operand's width.
394
395 Sparse issues these warnings by default.
396 .
397 .TP
398 .B \-Wsizeof-bool
399 Warn when checking the sizeof a _Bool.
400
401 C99 does not specify the size of a _Bool. GCC, by default, uses \fI1\fR.
402
403 Sparse does not issue these warnings by default.
404 .
405 .TP
406 .B \-Wtransparent\-union
407 Warn about any declaration using the GCC extension
408 \fB__attribute__((transparent_union))\fR.
409
410 Sparse issues these warnings by default. To turn them off, use
411 \fB\-Wno\-transparent\-union\fR.
412 .
413 .TP
414 .B \-Wtypesign
415 Warn when converting a pointer to an integer type into a pointer to an integer
416 type with different signedness.
417
418 Sparse does not issue these warnings by default.
419 .
420 .TP
421 .B \-Wundef
422 Warn about preprocessor conditionals that use the value of an undefined
423 preprocessor symbol.
424
425 Standard C (C99 6.10.1) permits using the value of an undefined preprocessor
426 symbol in preprocessor conditionals, and specifies it has a value of 0.
427 However, this behavior can lead to subtle errors.
428
429 Sparse does not issue these warnings by default.
430 .
431 .SH MISC OPTIONS
432 .TP
433 .B \-gcc-base-dir \fIdir\fR
434 Look for compiler-provided system headers in \fIdir\fR/include/ and \fIdir\fR/include-fixed/.
435 .
436 .TP
437 .B \-multiarch-dir \fIdir\fR
438 Look for system headers in the multiarch subdirectory \fIdir\fR.
439 The \fIdir\fR name would normally take the form of the target's
440 normalized GNU triplet. (e.g. i386-linux-gnu).
441 .
442 .SH DEBUG OPTIONS
443 .TP
444 .B \-fmem-report
445 Report some statistics about memory allocation used by the tool.
446 .
447 .SH OTHER OPTIONS
448 .TP
449 .B \-fdiagnostic-prefix[=PREFIX]
450 Prefix all diagnostics by the given PREFIX, followed by ": ".
451 If no one is given "sparse" is used.
452 The default is to not use a prefix at all.
453 .
454 .TP
455 .B \-fmemcpy-max-count=COUNT
456 Set the limit for the warnings given by \fB-Wmemcpy-max-count\fR.
457 A COUNT of 'unlimited' or '0' will effectively disable the warning.
458 The default limit is 100000.
459 .
460 .TP
461 .B \-ftabstop=WIDTH
462 Set the distance between tab stops. This helps sparse report correct
463 column numbers in warnings or errors. If the value is less than 1 or
464 greater than 100, the option is ignored. The default is 8.
465 .
466 .TP
467 .B \-f[no-]unsigned-char, \-f[no-]signed-char
468 Let plain 'char' be unsigned or signed.
469 By default chars are signed.
470 .
471 .SH SEE ALSO
472 .BR cgcc (1)
473 .
474 .SH HOMEPAGE
475 http://www.kernel.org/pub/software/devel/sparse/
476 .
477 .SH MAILING LIST
478 linux-sparse@vger.kernel.org
479 .
480 .SH CONTRIBUTINGS AND REPORTING BUGS
481 Submission of patches and reporting of bugs, as well as discussions
482 related to Sparse, should be done via the mailing list (linux-sparse@vger.kernel.org)
483 where the development and maintenance is primarily done.
484 You do not have to be subscribed to the list to send a message there.
485
486 Bugs can also be reported and tracked via the Linux kernel's bugzilla:
487 http://bugzilla.kernel.org/enter_bug.cgi?component=Sparse&product=Tools .
488 .
489 .SH AUTHORS
490 Sparse was started by Linus Torvalds.
491 The complete list of contributors can be find at
492 https://www.openhub.net/p/sparse/contributors .
493
494 Luc Van Oostenryck is Sparse's current maintainer.