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

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Message-ID: <4B056820.1050104@zytor.com>
Date:	Thu, 19 Nov 2009 07:45:36 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Ingo Molnar <mingo@...e.hu>, 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>,
	Steven Rostedt <rostedt@...dmis.org>,
	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 11/19/2009 07:37 AM, Thomas Gleixner wrote:
> 
> modified function start on a handful of functions only seen with gcc
> 4.4.x on x86 32 bit:
> 
> 	push   %edi
> 	lea    0x8(%esp),%edi
> 	and    $0xfffffff0,%esp
> 	pushl  -0x4(%edi)
> 	push   %ebp
> 	mov    %esp,%ebp
> 	...
> 	call   mcount
> 

The real questions is why we're aligning the stack in the kernel.  It is
probably not what we want -- we don't use SSE for anything but a handful
of special cases in the kernel, and we don't want the overhead.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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