backtrace(3) BSD Library Functions Manual backtrace(3)NAME
backtrace, backtrace_symbols, backtrace_symbols_fd -- call stack backtrace and display functions
SYNOPSIS
#include <execinfo.h>
int
backtrace(void** array, int size);
char**
backtrace_symbols(void* const* array, int size);
void
backtrace_symbols_fd(void* const* array, int size, int fd);
DESCRIPTION
These routines provide a mechanism to examine the current thread's call stack.
backtrace() writes the function return addresses of the current call stack to the array of pointers referenced by array. At most, size
pointers are written. The number of pointers actually written to array is returned.
backtrace_symbols() attempts to transform a call stack obtained by backtrace() into an array of human-readable strings using dladdr(). The
array of strings returned has size elements. It is allocated using malloc() and should be released using free(). There is no need to free
the individual strings in the array.
backtrace_symbols_fd() performs the same operation as backtrace_symbols(), but the resulting strings are immediately written to the file
descriptor fd, and are not returned.
EXAMPLE
#include <execinfo.h>
#include <stdio.h>
...
void* callstack[128];
int i, frames = backtrace(callstack, 128);
char** strs = backtrace_symbols(callstack, frames);
for (i = 0; i < frames; ++i) {
printf("%s
", strs[i]);
}
free(strs);
...
HISTORY
These functions first appeared in Mac OS X 10.5.
SEE ALSO dladdr(3), malloc(3)Mac OS X February 15, 2007 Mac OS X
Check Out this Related Man Page
BACKTRACE(3) Linux Programmer's Manual BACKTRACE(3)NAME
backtrace, backtrace_symbols, backtrace_symbols_fd - support for application self-debugging
SYNOPSIS
#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);
DESCRIPTION
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 corre-
sponding 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.
RETURN VALUE
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.
VERSIONS
backtrace(), backtrace_symbols(), and backtrace_symbols_fd() are provided in glibc since version 2.1.
CONFORMING TO
These functions are GNU extensions.
NOTES
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 nonzero 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.
EXAMPLE
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]
Program source
#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
", 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
", 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
", argv[0]);
exit(EXIT_FAILURE);
}
myfunc(atoi(argv[1]));
exit(EXIT_SUCCESS);
}
SEE ALSO gcc(1), ld(1), dlopen(3), malloc(3)COLOPHON
This page is part of release 3.27 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)