backtrace(3) - Linux manual page (original) (raw)
backtrace(3) Library Functions Manual backtrace(3)
NAME top
backtrace, backtrace_symbols, backtrace_symbols_fd - support for
application self-debuggingLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#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 top
**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)](../man3/malloc.3.html)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)](../man3/malloc.3.html),
and so can be employed in situations where the latter function
might fail, but see NOTES.RETURN VALUE top
**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)](../man3/malloc.3.html)ed by the call; on error, NULL is returned.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────────────────┼───────────────┼─────────┤
│ **backtrace**(), **backtrace_symbols**(), │ Thread safety │ MT-Safe │
│ **backtrace_symbols_fd**() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘STANDARDS top
GNU.HISTORY top
glibc 2.1.NOTES top
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)](../man1/gcc.1.html)'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)](../man3/malloc.3.html). 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 top
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 top
[addr2line(1)](../man1/addr2line.1.html), [gcc(1)](../man1/gcc.1.html), [gdb(1)](../man1/gdb.1.html), [ld(1)](../man1/ld.1.html), [dlopen(3)](../man3/dlopen.3.html), [malloc(3)](../man3/malloc.3.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 backtrace(3)
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