[PATCH] Properly check stack alignment [BZ #27901]

[H.J. Lu]

On Mon, May 24, 2021 at 3:56 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu via Libc-alpha:
>
> > 1. Replace
> >
> > if ((((uintptr_t) &_d) & (__alignof (double) - 1)) != 0)
> >
> > which may be optimized by compiler, with
> >
> > static int
> > __attribute__ ((noclone, noinline))
> > aligned (void *p, int align)
> > {
> >   return (((uintptr_t) p) & (align - 1)) != 0;
> > }
>
> I think you need to use __attribute__ ((weak)) (and drop the static) for
> a fully effective compiler barrier.  Due to the new global nature of the
> symbol, you probably should switch to a different identifier less prone
> to collisions.

I changed it to

int
__attribute__ ((weak, noclone, noinline))
is_aligned (void *p, int align)
{
  return (((uintptr_t) p) & (align - 1)) != 0;
}

> GCC 8 also supports the noipa attribute, but that's too recent for us.
>
> Thanks,
> Florian
>

I sent out the v2 patch.

-- 
H.J.