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BACKTRACE(3) Library Functions Manual BACKTRACE(3)

backtrace, backtrace_symbols, backtrace_symbols_fd, backtrace_symbols_fmt, backtrace_symbols_fd_fmt — fill in the backtrace of the currently executing thread

#include <execinfo.h>

size_t
backtrace(void **addrlist, size_t len);

char **
backtrace_symbols(void * const *addrlist, size_t len);

int
backtrace_symbols_fd(void * const *addrlist, size_t len, int fd);

char **
backtrace_symbols_fmt(void * const *addrlist, size_t len, const char *fmt);

int
backtrace_symbols_fd_fmt(void * const *addrlist, size_t len, int fd, const char *fmt);

The () function places into the array pointed by addrlist the array of the values of the program counter for each frame called up to len frames. The number of frames found (which can be fewer than len) is returned.

The () function takes an array of previously filled addresses from backtrace() in addrlist of len elements, and uses fmt to format them. The formatting characters available are:

The numeric address of each element as would be printed using %p.
The name of the nearest function symbol (smaller than the address element) as determined by dladdr(3)
The difference of the symbol address and the address element printed using 0x%tx.
The difference of the symbol address and the address element printed using +0x%tx if non-zero, or nothing if zero.
The filename of the symbol as determined by dladdr(3).

The array of formatted strings is returned as a contiguous memory address which can be freed by a single free(3).

The () function is equivalent of calling backtrace_symbols_fmt() with a format argument of “%a <%n%D> at %f”

The () and () are similar to the non _fd named functions, only instead of returning an array of strings, they print a new-line separated array of strings in fd, and return 0 on success and -1 on failure.

The backtrace() function returns the number of elements that were filled in the backtrace. The backtrace_symbols() and backtrace_symbols_fmt() return a string array on success, and NULL on failure, setting errno.

dladdr(3)

The backtrace() library of functions first appeared in NetBSD 7.0 and was imported into OpenBSD 7.0.

  1. Only unwinding with libunwind is supported. On architectures without libunwind the backtrace() function simply returns 0.
  2. Since dladdr(3) only deals with dynamic symbols, local symbols from the main portion of the program are not printed.
June 11, 2021 openbsd