Re: Building the GNU/Hurd glibc with GCC 4.1, problem with `__builtin_frame_address'

[Joe Buck]

On Mon, Nov 20, 2006 at 11:50:44AM +0100, Thomas Schwinge wrote:
> There is a problem when building glibc for GNU/Hurd with GCC 4.1, see
> <http://savannah.gnu.org/bugs/?17647>.  This is due to a change in the
> behavior of `__builtin_frame_address' in GCC 4.1:

The example you give is a test that the argc argument to main lives in the
third 32-bit word of the frame as returned by __builtin_frame_address;
evidently (according to your test) this is true for 3.3, 3.4, and 4.0 but
not 4.1.  But there is no standard that specifies this position for argc.

I did a little looking and found

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8335

since the fix is a change to __builtin_frame_address behavior that
appeared in 4.1.  I wonder if you are relying on undocumented behavior
that turned out to be a bug that has since been fixed.