linux-kernel - Re: BUG: GCC-4.4.x changes the function frame on some functions

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Date:	Thu, 19 Nov 2009 21:36:25 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Richard Guenther <richard.guenther@...il.com>, rostedt@...dmis.org,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	feng.tang@...el.com, Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>, jakub@...hat.com,
	gcc@....gnu.org
Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions

On Thu, 19 Nov 2009, Linus Torvalds wrote:
> On Thu, 19 Nov 2009, Richard Guenther wrote:
> > 
> > Note that I only can reproduce the issue with
> > -mincoming-stack-boundary=2, not with -mpreferred-stack-boundary=2.
> 
> Since you can reproduce it with -mincoming-stack-boundary=2, I woul 
> suggest just fixing mcount handling that way regardless of anything else. 
> The current code generated by gcc is just insane - even for the case where 
> you _want_ 16-byte stack alignment.
> 
> Instead crazy code like
> 
> >       push   %edi
> >       lea    0x8(%esp),%edi
> >       and    $0xfffffff0,%esp
> >       pushl  -0x4(%edi)
> >       push   %ebp
> >       mov    %esp,%ebp
> >       ...
> >       call   mcount
> 
> the sane thing to do would be to just do it as
> 
> 	push   %ebp
> 	mov    %esp,%ebp
> 	call   mcount
> 	and    $0xfffffff0,%esp

which is what the 64bit compile does except that the mcount call
happens a bit later which is fine.

ffffffff8107cd34 <timer_stats_update_stats>:
ffffffff8107cd34:       55                      push   %rbp
ffffffff8107cd35:       48 89 e5                mov    %rsp,%rbp
ffffffff8107cd38:       48 83 e4 c0             and    $0xffffffffffffffc0,%rsp

Thanks,

	tglx
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