__BUILTIN_RETURN_ADDRESS(3) Library Functions Manual
__builtin_return_address -- the return address of a function
__builtin_return_address(unsigned int level);
__builtin_frame_address(unsigned int level);
The __builtin_return_address() is a GNU extension for obtaining the
return address of the current function or one of the callers of the
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.
These are non-standard, compiler-specific extensions.
NetBSD 6.1.5 December 19, 2010 NetBSD 6.1.5