NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON
BACKTRACE(3) Linux Programmer's Manual BACKTRACE(3)
backtrace, backtrace_symbols, backtrace_symbols_fd - support for application
self-debugging
#include <execinfo.h>
int backtrace(void **buffer, int size);
char **backtrace_symbols(void *const *buffer, int size);
void backtrace_symbols_fd(void *const *buffer, int size, int fd);
backtrace() returns a backtrace for the calling program, in the array pointed
to by buffer. A backtrace is the series of currently active function calls
for the program. Each item in the array pointed to by buffer is of type void
*, and is the return address from the corresponding stack frame. The size
argument specifies the maximum number of addresses that can be stored in
buffer. If the backtrace is larger than size, then the addresses
corresponding to the size most recent function calls are returned; to obtain
the complete backtrace, make sure that buffer and size are large enough.
Given the set of addresses returned by backtrace() in buffer,
backtrace_symbols() translates the addresses into an array of strings that
describe the addresses symbolically. The size argument specifies the number
of addresses in buffer. The symbolic representation of each address consists
of the function name (if this can be determined), a hexadecimal offset into
the function, and the actual return address (in hexadecimal). The address of
the array of string pointers is returned as the function result of
backtrace_symbols(). This array is malloc(3)ed by backtrace_symbols(), and
must be freed by the caller. (The strings pointed to by the array of pointers
need not and should not be freed.)
backtrace_symbols_fd() takes the same buffer and size arguments as
backtrace_symbols(), but instead of returning an array of strings to the
caller, it writes the strings, one per line, to the file descriptor fd.
backtrace_symbols_fd() does not call malloc(3), and so can be employed in
situations where the latter function might fail.
backtrace() returns the number of addresses returned in buffer, which is not
greater than size. If the return value is less than size, then the full
backtrace was stored; if it is equal to size, then it may have been truncated,
in which case the addresses of the oldest stack frames are not returned.
On success, backtrace_symbols() returns a pointer to the array malloc(3)ed by
the call; on error, NULL is returned.
backtrace(), backtrace_symbols(), and backtrace_symbols_fd() are provided in
glibc since version 2.1.
These functions are GNU extensions.
These functions make some assumptions about how a function's return address is
stored on the stack. Note the following:
* Omission of the frame pointers (as implied by any of gcc(1)'s non-zero
optimization levels) may cause these assumptions to be violated.
* Inlined functions do not have stack frames.
* Tail-call optimization causes one stack frame to replace another.
The symbol names may be unavailable without the use of special linker options.
For systems using the GNU linker, it is necessary to use the -rdynamic linker
option. Note that names of "static" functions are not exposed, and won't be
available in the backtrace.
The program below demonstrates the use of backtrace() and backtrace_symbols().
The following shell session shows what we might see when running the program:
$ cc -rdynamic prog.c -o prog
$ ./prog 3
backtrace() returned 8 addresses
./prog(myfunc3+0x5c) [0x80487f0]
./prog [0x8048871]
./prog(myfunc+0x21) [0x8048894]
./prog(myfunc+0x1a) [0x804888d]
./prog(myfunc+0x1a) [0x804888d]
./prog(main+0x65) [0x80488fb]
/lib/libc.so.6(__libc_start_main+0xdc) [0xb7e38f9c]
./prog [0x8048711]
#include <execinfo.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
void
myfunc3(void)
{
int j, nptrs;
#define SIZE 100
void *buffer[100];
char **strings;
nptrs = backtrace(buffer, SIZE);
printf("backtrace() returned %d addresses\n", nptrs);
/* The call backtrace_symbols_fd(buffer, nptrs, STDOUT_FILENO)
would produce similar output to the following: */
strings = backtrace_symbols(buffer, nptrs);
if (strings == NULL) {
perror("backtrace_symbols");
exit(EXIT_FAILURE);
}
for (j = 0; j < nptrs; j++)
printf("%s\n", strings[j]);
free(strings);
}
static void /* "static" means don't export the symbol... */
myfunc2(void)
{
myfunc3();
}
void
myfunc(int ncalls)
{
if (ncalls > 1)
myfunc(ncalls - 1);
else
myfunc2();
}
int
main(int argc, char *argv[])
{
if (argc != 2) {
fprintf(stderr, "%s num-calls\n", argv[0]);
exit(EXIT_FAILURE);
}
myfunc(atoi(argv[1]));
exit(EXIT_SUCCESS);
}
gcc(1), ld(1), dlopen(3), malloc(3)
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
GNU 2008-06-14 BACKTRACE(3)