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Date: Fri, 20 Nov 2009 12:06:00 -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
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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.

Andrew.