Included is a revised copy of backtrace.3.
Michael:
I was tempted to use an alternate loop condition in h():
for (sz=1; (sz&(sz-1))==0 && (sz<<=1); ) {
if (NULL==(vec=realloc(vec, sz*sizeof(*vec)))) {
perror("realloc");
exit(EXIT_FAILURE);
}
sz=backtrace(vec, sz);
}
but I anticipated that you feel this is not the place to teach people
about the properties of powers of two. I mention it here in case I
was wrong :)
BTW, |expand -t4 should be useful in the future when I forget your tab
preference.
.\" Copyright (C) 2006 Justin Pryzby <[EMAIL PROTECTED]>
.\"
.\" Permission is hereby granted, free of charge, to any person obtaining
.\" a copy of this software and associated documentation files (the
.\" "Software"), to deal in the Software without restriction, including
.\" without limitation the rights to use, copy, modify, merge, publish,
.\" distribute, sublicense, and/or sell copies of the Software, and to
.\" permit persons to whom the Software is furnished to do so, subject to
.\" the following conditions:
.\"
.\" The above copyright notice and this permission notice shall be
.\" included in all copies or substantial portions of the Software.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
.\" EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
.\" IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
.\" CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
.\" TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
.\" SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
.\"
.\" References:
.\" glibc manual and source
.TH BACKTRACE 3 "2006-05-26" GNU
.
.SH NAME
backtrace, backtrace_symbols, backtrace_symbols_fd \- support for application
self-debugging
.
.SH SYNOPSIS
\fB#include <execinfo.h>
\fBint backtrace(void **\fIbuffer\fP, int \fPsize\fP);
.br
\fBchar **backtrace_symbols(void *const *\fIbuffer\fP, int \fPsize\fP);
.br
\fBvoid backtrace_symbols_fd(void *const *\fIbuffer\fP, int \fPsize\fP, int
\fPfd\fP);
.
.SH DESCRIPTION
\fBbacktrace\fP() stores up to \fIsize\fP return addresses of the
most-recently called functions to the \fIbuffer\fP array.
\fBbacktrace_symbols\fP() accepts in \fIbuffer\fP an array of
\fIsize\fP return addresses, as generated by \fBbacktrace\fP(), and
returns an array of strings describing the functions containing those
addresses.
\fBbacktrace_symbols_fd\fP() accepts the same \fIbuffer\fP and
\fPsize\fP parameters as \fBbacktrace_symbols\fP(), and writes to the
file descriptor \fIfd\fP the same descriptive strings, separated by
newlines.
.
.SH "RETURN VALUE"
\fBbacktrace\fP() returns the number of addresses stored, which is not
greater than \fIsize\fP. If it is less than \fIsize\fP, then the full
stacktrace was stored; if it is equal to \fIsize\fP, then the
stacktrace may have been truncated, in which case, the addresses of
the least-recently called functions are not stored.
\fBbacktrace_symbols\fP() returns an array of \fIsize\fP strings, each
of which contains the function name, offset in bytes from the
beginning of that function, and the return address. The array (but
not the string elements) is allocated with \fBmalloc\fP(), and should
be freed when it is unused. \fBNULL\fP is returned on error.
.
.SH EXAMPLE
.nf
/* make CFLAGS='-W -Wall -O0 -g' LDFLAGS='-rdynamic' gnubt */
#include <execinfo.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int h(void)
{
void **vec=NULL;
size_t sz;
for (sz=1; 1; sz<<=1) {
size_t ret;
if (NULL==(vec=realloc(vec, sz*sizeof(*vec)))) {
perror("realloc");
exit(EXIT_FAILURE);
}
ret=backtrace(vec, sz);
if (ret<sz) {
sz=ret;
break;
}
}
backtrace_symbols_fd(vec, sz, STDOUT_FILENO);
free(vec);
return 0;
}
int g(int n)
{
if (n!=0) return g(n-1);
return h();
}
/* Note the effect of marking a function "static" */
static int f(int n)
{
return g(n);
}
int main(int argc, char **argv)
{
if (argc!=2) {
fprintf(stderr, "Usage: %s <iterations>\n", *argv);
exit(EXIT_FAILURE);
}
return f(atoi(argv[1]));
}
.fi
.
.SH "CONFORMING TO"
These functions are GNU extensions, and should not be used in programs
intended to be portable.
.
.SH NOTES
These functions make some assumptions about how a function's return
address is stored on the stack. Omission of the frame pointers (as
implied by any of \fBgcc\fP's non-zero optimization levels) may
violate those assumptions.
Use of a special linker option may be necessary for
\fBbacktrace_symbols\fP() and \fPbacktrace_symbols_fd\fP() to resolve
the names of the symbols. For the GNU linker \fBld\fP, it is
necessary to pass \fB\-rdynamic\fP. Note that "static" function names
are never exposed, and won't be available in the backtrace.
\fBbacktrace_symbols\fP() requires that \fBmalloc\fP() function
correctly, whereas \fBbacktrace\fP() and \fBbacktrace_symbols_fd\fP()
do not (assuming that their arguments are allocated on the stack).
This is not insignificant in the situations where a backtrace is
useful.
.
.SH SEE ALSO
.BR malloc (3),
.BR dladdr (3),
.BR ld (1),
.BR gcc (1)
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