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Date: Thu, 19 Nov 2009 15:46:00 -0000
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,         Andrew Morton <akpm@linux-foundation.org>,         Heiko Carstens <heiko.carstens@de.ibm.com>, feng.tang@intel.com,         Fr??d??ric Weisbecker <fweisbec@gmail.com>,         Steven Rostedt <rostedt@goodmis.org>,         Peter Zijlstra <peterz@infradead.org>, jakub@redhat.com,         gcc@gcc.gnu.org
Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions
References: <alpine.LFD.2.00.0911181933540.24119@localhost.localdomain> <tip-887a29f59b93cf54e21814869a4ab6e80b6fa623@git.kernel.org> <20091119072040.GA23579@elte.hu> <alpine.LFD.2.00.0911191053390.24119@localhost.localdomain> <alpine.LFD.2.00.0911191423190.24119@localhost.localdomain> <alpine.LFD.2.00.0911191607440.24119@localhost.localdomain>
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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.