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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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backtrace(3) Library Functions Manual backtrace(3)
backtrace, backtrace_symbols, backtrace_symbols_fd - support for
application self-debugging
Standard C library (libc, -lc)
#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);
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.
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.
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼─────────┤
│ backtrace(), backtrace_symbols(), │ Thread safety │ MT-Safe │
│ backtrace_symbols_fd() │ │ │
└─────────────────────────────────────┴───────────────┴─────────┘
GNU.
glibc 2.1.
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.
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);
}
addr2line(1), gcc(1), gdb(1), ld(1), dlopen(3), malloc(3)
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user-space interface documentation) project. Information about
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2024-06-26. If you discover any rendering problems in this HTML
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part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.9.1 2024-06-15 backtrace(3)
Pages that refer to this page: mallopt(3)
Copyright and license for this manual page
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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