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,
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.
backtrace(), backtrace_symbols(), and backtrace_symbols_fd() are provided in
glibc since version 2.1.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
|
|
Thread safety | MT-Safe |
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]
#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 (int 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);
}