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SubjectRe: 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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