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

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Message-ID: <4B068A10.2090608@redhat.com>
Date:	Fri, 20 Nov 2009 12:22:40 +0000
From:	Andrew Haley <aph@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Jeff Law <law@...hat.com>, rostedt@...dmis.org,
	"H. Peter Anvin" <hpa@...or.com>,
	David Daney <ddaney@...iumnetworks.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Richard Guenther <richard.guenther@...il.com>,
	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>,
	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

Andrew Haley wrote:
> Thomas Gleixner wrote:
> 
>> While testing various kernel configs we found out that the problem
>> comes and goes. Finally I started to compare the gcc command line
>> options and after some fiddling it turned out that the following
>> minimal deltas change the code generator behaviour:
>>
>> Bad:  -march=pentium-mmx                -Wa,-mtune=generic32
>> Good: -march=i686        -mtune=generic -Wa,-mtune=generic32
>> Good: -march=pentium-mmx -mtune-generic -Wa,-mtune=generic32
>>
>> I'm not supposed to understand the logic behind that, right ?
> 
> I don't either.  I'm seeing:
> 
> timer_stats_update_stats:                                       timer_stats_update_stats:
>         pushl   %edi                                          <
>         leal    8(%esp), %edi                                 <
>         andl    $-16, %esp                                    <
>         pushl   -4(%edi)                                      <
>         pushl   %ebp                                                    pushl   %ebp
>         movl    %esp, %ebp                                              movl    %esp, %ebp
>         pushl   %edi                                          |         andl    $-16, %esp
>         pushl   %esi                                          |         subl    $112, %esp
>         pushl   %ebx                                          |         movl    %ebx, 100(%esp)
>         subl    $108, %esp                                    |         movl    %esi, 104(%esp)
>                                                               >         movl    %edi, 108(%esp)
>         call    mcount                                                  call    mcount
> 
> where the only difference is -mtune=generic.  I'm investigating.

Forget that, I see from the gcc-bugs list that hj has tracked it down to
the use of DRAP, and for some reason the mtune options affect that.  He's
the best person to fix this.

Andrew.
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