Bug#165992: gcc: __builtin_return_address doesn't work properly

[Greg Stark <gsstark@mit.edu>]

Daniel Jacobowitz <dan@debian.org> writes:

> > The following program illustrates that __builtin_return_address seg faults when
> > you reach the top of the stack rather than returning 0 as it is specified in
> > the gcc manual. 
> > 
> > I see the same behaviour with both gcc 2.95 and gcc 3.0.
> 
> GCC 3.2 says:
>      On some machines it may be impossible to determine the return
>      address of any function other than the current one; in such cases,
>      or when the top of the stack has been reached, this function will
>      return `0' or a random value. In addition,
>      `__builtin_frame_address' may be used to determine if the top of
>      the stack has been reached.

Well, that's not what my documentation from GCC 2.95 says:

     On some machines it may be impossible to determine the return
     address of any function other than the current one; in such cases,
     or when the top of the stack has been reached, this function will
     return `0'.

I'm puzzled why I can use __builtin_frame_address to determine if the top of
the stack has been reached but gcc's builtin can't do the same for me. I must
be missing something, how do gdb and other tools happily decode stack traces
all the time without crashing?

-- 
greg