Provided by: manpages-dev_6.9.1-1_all 
NAME
backtrace, backtrace_symbols, backtrace_symbols_fd - support for application self-debugging
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <execinfo.h>
int backtrace(void *buffer[.size], int size);
char **backtrace_symbols(void *const buffer[.size], int size);
void backtrace_symbols_fd(void *const buffer[.size], 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 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, but see NOTES.
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.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
│ backtrace(), backtrace_symbols(), backtrace_symbols_fd() │ Thread safety │ MT-Safe │
└─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
GNU.
HISTORY
glibc 2.1.
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.
• backtrace() and backtrace_symbols_fd() don't call malloc() explicitly, but they are part of libgcc,
which gets loaded dynamically when first used. Dynamic loading usually triggers a call to malloc(3).
If you need certain calls to these two functions to not allocate memory (in signal handlers, for
example), you need to make sure libgcc is loaded beforehand.
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.
EXAMPLES
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>
#define BT_BUF_SIZE 100
void
myfunc3(void)
{
int nptrs;
void *buffer[BT_BUF_SIZE];
char **strings;
nptrs = backtrace(buffer, BT_BUF_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 (size_t 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);
}
SEE ALSO
addr2line(1), gcc(1), gdb(1), ld(1), dlopen(3), malloc(3)
Linux man-pages 6.9.1 2024-06-15 backtrace(3)