backtrace(3) — Linux manual page


BACKTRACE(3)              Linux Programmer's Manual             BACKTRACE(3)

NAME         top

       backtrace,  backtrace_symbols,  backtrace_symbols_fd  -  support  for
       application self-debugging

SYNOPSIS         top

       #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);

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)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

       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         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)ed by the call; on error, NULL is returned.

VERSIONS         top

       backtrace(), backtrace_symbols(), and backtrace_symbols_fd() are
       provided in glibc since version 2.1.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface              Attribute     Value   │
       │backtrace(),           │ Thread safety │ MT-Safe │
       │backtrace_symbols(),   │               │         │
       │backtrace_symbols_fd() │               │         │

CONFORMING TO         top

       These functions are GNU extensions.

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)'s
          nonzero optimization levels) may cause these assumptions to be

       *  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         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/ [0xb7e38f9c]
           ./prog [0x8048711]

   Program source

       #include <execinfo.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       #define BT_BUF_SIZE 100

           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) {

           for (j = 0; j < nptrs; j++)
               printf("%s\n", strings[j]);


       static void   /* "static" means don't export the symbol... */

       myfunc(int ncalls)
           if (ncalls > 1)
               myfunc(ncalls - 1);

       main(int argc, char *argv[])
           if (argc != 2) {
               fprintf(stderr, "%s num-calls\n", argv[0]);


SEE ALSO         top

       addr2line(1), gcc(1), gdb(1), ld(1), dlopen(3), malloc(3)

COLOPHON         top

       This page is part of release 5.08 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

GNU                              2020-06-09                     BACKTRACE(3)

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