Re: PATCH: PR target/40838: gcc shouldn't assume that the stack is aligned

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Oct 15, 2009 at 12:32:12PM -0700, H.J. Lu wrote:
> > Then we should do realignment the other way around: instead of using
> > -mstackrealing for all the code (including where it has no effect), let's
> > use -mstackrealign to activate realignment functionality that is introduced
> > by your patch.
> 
> That defeats the whole purpose of my patch, which automatically
> realigns the stack when there is a hard alignment requirement. If it
> isn't turned on by default, it is not very useful.
> 
> > IOW, lightweight -mstackrealign, firing up only when there is the
> > possibility of unaligned access in the code it precedes.
> >
> 
> That is what my patch does, but turned it on by default.

I agree with Uros, I have nothing against a lightweight -mstackrealign,
but forcing this upon everybody just because a few people insist on compiling
code with -mpreferred-stack-boundary=2 is IMHO a very bad idea and I object
against it.  -mpreferred-stack-boundary=2 is fine for the kernel where you
basically define your own ABI, like many other ABI changing options, and for
people who know what they are doing and bear the consequences (e.g. that
they need to -mstackrealign when calling outside code), but we shouldn't
penalize because of that rare option all the code by default.  At least not
on Linux.

	Jakub