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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
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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, 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 │
├───────────────────────┼───────────────┼─────────┤
│backtrace(), │ Thread safety │ MT-Safe │
│backtrace_symbols(), │ │ │
│backtrace_symbols_fd() │ │ │
└───────────────────────┴───────────────┴─────────┘
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
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 j, 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 (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)
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2017-09-15 BACKTRACE(3)
Pages that refer to this page: mallopt(3)
Copyright and license for this manual page
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