Re: [PATCH] powerpc/64: Implement arch_within_stack_frames

On Wed, Dec 14, 2022 at 09:39:25PM +1000, Nicholas Piggin wrote:

What about just copying x86's implementation including using
__builtin_frame_address(1/2)? Are those builtins reliable for all
our targets and compiler versions?

__builtin_frame_address(n) with n > 0 is specifically not supported, not
on any architecture; it does not work in all situations on *any* arch,
and not in *any* situation on some archs.

This is clearly documented:

     Calling this function with a nonzero argument can have
     unpredictable effects, including crashing the calling program.  As
     a result, calls that are considered unsafe are diagnosed when the
     '-Wframe-address' option is in effect.  Such calls should only be
     made in debugging situations.

(and that warning is enabled by -Wall).


Segher