Message-ID: <4B068A10.2090608@redhat.com>
Date: Fri, 20 Nov 2009 12:22:40 +0000
From: Andrew Haley <aph@redhat.com>
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To: Thomas Gleixner <tglx@linutronix.de>
CC: Jeff Law <law@redhat.com>, rostedt@goodmis.org,
       "H. Peter Anvin" <hpa@zytor.com>,
       David Daney <ddaney@caviumnetworks.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Richard Guenther <richard.guenther@gmail.com>,
       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>,
       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: <viy9pk4xossnb6m2v041qu00.1258665258503@email.android.com>   <4B05B7AD.20500@redhat.com> <1258670580.22249.1002.camel@gandalf.stny.rr.com> <4B05DBBF.5000804@redhat.com> <alpine.LFD.2.00.0911200122190.24119@localhost.localdomain> <4B0685B7.4060601@redhat.com>
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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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