| __BUILTIN_RETURN_ADDRESS(3) | Library Functions Manual | __BUILTIN_RETURN_ADDRESS(3) | 
__builtin_return_address —
__builtin_return_address(unsigned
  int level);
void *
  
  __builtin_frame_address(unsigned
    int level);
__builtin_return_address() is a GNU extension for
  obtaining the return address of the current function or one of the callers of
  the current function.
The parameter level specifies the number of frames that should be scanned up in the call stack. A value 0 returns the address of the current function, a value 1 requests the address of the caller of the current function, a value 2 asks for the address of the caller's caller, and so forth. If the top of the call stack has been reached, the function will return 0. Note also that on some architectures it is only possible to determine the address of the current function. In such cases a value 0 is returned. Thus, it is usually safe to only use the value 0 for level.
The __builtin_frame_address() behaves
    similarly, but returns the address of the function frame rather than the
    return address of the function.
| December 19, 2010 | NetBSD 9.4 |