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Date: Thu, 19 Nov 2009 16:52:24 +0100
Message-ID: <84fc9c000911190752o27afbc31o8a6196ebdfc68d39@mail.gmail.com>
Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions
From: Richard Guenther <richard.guenther@gmail.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, 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
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On Thu, Nov 19, 2009 at 4:49 PM, Richard Guenther
<richard.guenther@gmail.com> wrote:
> On Thu, Nov 19, 2009 at 4:45 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> 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.
>
> It's likely because you have long long vars on the stack which is
> faster when they are aligned. ?-mno-stackrealign may do what you
> want (or may not, I have not checked). ?I assume you already
> use -mpreferred-stack-boundary=2.

Just checking it seems you must be using -mincoming-stack-boundary=2
instead but keep the preferred stack boundary at 4.

Richard.
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