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6 .TH fex_set_log 3M "12 Jul 2006" "SunOS 5.11" "Mathematical Library Functions"
7 .SH NAME
8 fex_set_log, fex_get_log, fex_set_log_depth, fex_get_log_depth, fex_log_entry
9 \- log retrospective diagnostics for floating point exceptions
10 .SH SYNOPSIS
11 .LP
12 .nf
13 c99 [ \fIflag\fR... ] \fIfile\fR... -lm [ \fIlibrary\fR... ]
14 #include <fenv.h>
15
16 \fBint\fR \fBfex_set_log\fR(\fBFILE *\fR\fIfp\fR);
17 .fi
18
19 .LP
20 .nf
21 \fBFILE *\fR\fBfex_get_log\fR(\fBvoid\fR);
22 .fi
23
24 .LP
25 .nf
26 \fBint\fR \fBfex_set_log_depth\fR(\fBint\fR \fIdepth\fR);
27 .fi
28
29 .LP
30 .nf
31 \fBint\fR \fBfex_get_log_depth\fR(\fBvoid\fR);
32 .fi
33
34 .LP
35 .nf
36 \fBvoid\fR \fBfex_log_entry\fR(\fBconst char *\fR\fImsg\fR);
37 .fi
38
39 .SH DESCRIPTION
40 .sp
41 .LP
42 The \fBfex_set_log()\fR function enables logging of retrospective diagnostic
43 messages regarding floating point exceptions to the file specified by \fIfp\fR.
44 If \fIfp\fR is \fINULL\fR, logging is disabled. When a program starts, logging
45 is initially disabled.
46 .sp
47 .LP
48 The occurrence of any of the twelve exceptions listed in
49 \fBfex_set_handling\fR(3M) constitutes an event that can be logged. To prevent
50 the log from becoming exhorbitantly long, the logging mechanism eliminates
51 redundant entries by two methods. First, each exception is associated with a
52 \fIsite\fR in the program. The site is identified by the address of the
53 instruction that caused the exception together with a stack trace. Only the
54 first exception of a given type to occur at a given site will be logged.
55 Second, when \fBFEX_NONSTOP\fR handling mode is in effect for some exception,
56 only those occurrences of that exception that set its previously clear flag are
57 logged. Clearing a flag using \fBfeclearexcept()\fR allows the next occurrence
58 of the exception to be logged provided it does not occur at a site at which it
59 was previously logged.
60 .sp
61 .LP
62 Each of the different types of invalid operation exceptions can be logged at
63 the same site. Because all invalid operation exceptions share the same flag,
64 however, of those types for which \fBFEX_NONSTOP\fR mode is in effect, only the
65 first exception to set the flag will be logged. When the invalid operation
66 exception is raised by a call to \fBferaiseexcept\fR(3M) or
67 \fBfeupdateenv\fR(3M), which type of invalid operation is logged depends on the
68 implementation.
69 .sp
70 .LP
71 If an exception results in the creation of a log entry, the entry is created at
72 the time the exception occurs and before any exception handling actions
73 selected with \fBfex_set_handling()\fR are taken. In particular, the log entry
74 is available even if the program terminates as a result of the exception. The
75 log entry shows the type of exception, the address of the instruction that
76 caused it, how it will be handled, and the stack trace. If symbols are
77 available, the address of the excepting instruction and the addresses in the
78 stack trace are followed by the names of the corresponding symbols.
79 .sp
80 .LP
81 The \fBfex_get_log()\fR function returns the current log file.
82 .sp
83 .LP
84 The \fBfex_set_log_depth()\fR sets the maximum depth of the stack trace
85 recorded with each exception to \fIdepth\fR stack frames. The default depth is
86 100.
87 .sp
88 .LP
89 The\fBfex_get_log_depth()\fR function returns the current maximum stack trace
90 depth.
91 .sp
92 .LP
93 The \fBfex_log_entry()\fR function adds a user-supplied entry to the log. The
94 entry includes the string pointed to by \fImsg\fR and the stack trace. Like
95 entries for floating point exceptions, redundant user-supplied entries are
96 eliminated: only the first user-supplied entry with a given \fImsg\fR to be
97 requested from a given site will be logged. For the purpose of a user-supplied
98 entry, the site is defined only by the stack trace, which begins with the
99 function that called \fBfex_log_entry()\fR.
100 .SH RETURN VALUES
101 .sp
102 .LP
103 The \fBfex_set_log()\fR function returns a non-zero value if logging is enabled
104 or disabled accordingly and returns 0 otherwise. The \fBfex_set_log_depth()\fR
105 returns a non-zero value if the requested stack trace depth is established
106 (regardless of whether logging is enabled) and returns 0 otherwise.
107 .SH EXAMPLES
108 .sp
109 .LP
110 The following example demonstrates the output generated when a floating point
111 overflow occurs in \fBsscanf\fR(3C).
112 .sp
113 .in +2
114 .nf
115 #include <fenv.h>
116
117 int
118 main() {
119 double x;
120 /*
121 * enable logging of retrospective diagnostics
122 */
123 (void) fex_set_log(stdout);
124 /*
125 * establish default handling for overflows
126 */
127 (void) fex_set_handling(FEX_OVERFLOW, FEX_NONSTOP, NULL);
128 /*
129 * trigger an overflow in sscanf
130 */
131 (void) sscanf("1.0e+400", "%lf", &x);
132 return 0;
133 }
134 .fi
135 .in -2
136
137 .sp
138 .LP
139 The output from the preceding program reads:
140 .sp
141 .in +2
142 .nf
143 Floating point overflow at 0xef71cac4 __base_conversion_set_exceptio
144 n, nonstop mode
145 0xef71cacc __base_conversion_set_exception
146 0xef721820 _decimal_to_double
147 0xef75aba8 number
148 0xef75a94c __doscan_u
149 0xef75ecf8 sscanf
150 0x00010f20 main
151 .fi
152 .in -2
153
154 .sp
155 .LP
156 Recompiling the program or running it on another system can produce different
157 text addresses from those shown above.
158 .SH ATTRIBUTES
159 .sp
160 .LP
161 See \fBattributes\fR(5) for descriptions of the following attributes:
162 .sp
163
164 .sp
165 .TS
166 tab() box;
167 lw(2.75i) lw(2.75i)
168 lw(2.75i) lw(2.75i)
169 .
170 ATTRIBUTE TYPEATTRIBUTE VALUE
171 AvailabilitySUNWlibms, SUNWlmxs
172 Interface StabilityStable
173 MT-LevelMT-Safe (see NOTES)
174 .TE
175
176 .SH SEE ALSO
177 .sp
178 .LP
179 \fBfeclearexcept\fR(3M), \fBfegetenv\fR(3M), \fBferaiseexcept\fR(3M),
180 \fBfeupdateenv\fR(3M), \fBfex_set_handling\fR(3M), \fBattributes\fR(5)
181 .sp
182 .LP
183 \fINumerical Computation Guide\fR
184 .SH NOTES
185 .sp
186 .LP
187 All threads in a process share the same log file. Each call to
188 \fBfex_set_log()\fR preempts the previous one.
189 .sp
190 .LP
191 In addition to the log file itself, two additional file descriptors are used
192 during the creation of a log entry in order to obtain symbol names from the
193 executable and any shared objects it uses. These file descriptors are
194 relinquished once the log entry is written. If the file descriptors cannot be
195 allocated, symbols names are omitted from the stack trace.
196 .sp
197 .LP
198 The functions described on this page automatically install and deinstall
199 \fBSIGFPE\fR handlers and set and clear the trap enable mode bits in the
200 floating point status register as needed. If a program uses these functions
201 and attempts to install a \fBSIGFPE\fR handler or control the trap enable mode
202 bits independently, the resulting behavior is not defined.
203 .sp
204 .LP
205 As described in \fBfex_set_handling()\fR, when a handling function installed in
206 \fBFEX_CUSTOM\fR mode is invoked, all exception traps are disabled (and will
207 not be reenabled while \fBSIGFPE\fR is blocked). Thus, retrospective
208 diagnostic messages are not logged for exceptions that occur within such a
209 handler.