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Re: BUG: GCC-4.4.x changes the function frame on some functions
- From: "H. Peter Anvin" <hpa at zytor dot com>
- To: rostedt at goodmis dot org
- Cc: David Daney <ddaney at caviumnetworks dot com>, Linus Torvalds <torvalds at linux-foundation dot org>, Andrew Haley <aph at redhat dot com>, Richard Guenther <richard dot guenther at gmail dot com>, Thomas Gleixner <tglx at linutronix dot de>, Ingo Molnar <mingo at elte dot hu>, LKML <linux-kernel at vger dot kernel dot org>, Andrew Morton <akpm at linux-foundation dot org>, Heiko Carstens <heiko dot carstens at de dot ibm dot com>, feng dot tang at intel dot com, Fr??d??ric Weisbecker <fweisbec at gmail dot com>, Peter Zijlstra <peterz at infradead dot org>, jakub at redhat dot com, gcc at gcc dot gnu dot org
- Date: Thu, 19 Nov 2009 11:50:05 -0800
- Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions
- References: <alpine.LFD.2.00.0911181933540.24119@localhost.localdomain> <tip-887a29f59b93cf54e21814869a4ab6e80b6fa623@git.kernel.org> <20091119072040.GA23579@elte.hu> <alpine.LFD.2.00.0911191053390.24119@localhost.localdomain> <alpine.LFD.2.00.0911191423190.24119@localhost.localdomain> <alpine.LFD.2.00.0911191607440.24119@localhost.localdomain> <alpine.LFD.2.00.0911190934070.2793@localhost.localdomain> <1258653562.22249.682.camel@gandalf.stny.rr.com> <84fc9c000911191003t244eb864o3d5b355ab5485f@mail.gmail.com> <4B058CCD.8050605@redhat.com> <alpine.LFD.2.00.0911191039470.2793@localhost.localdomain> <alpine.LFD.2.00.0911191041471.2793@localhost.localdomain> <alpine.LFD.2.00.0911191047350.2793@localhost.localdomain> <4B05982B.6060200@caviumnetworks.com> <1258658886.22249.874.camel@gandalf.stny.rr.com>
On 11/19/2009 11:28 AM, Steven Rostedt wrote:
>
> Hehe, scratch register on i686 ;-)
>
> i686 has no extra regs. It just has:
>
> %eax, %ebx, %ecx, %edx - as the general purpose regs
> %esp - stack
> %ebp - frame pointer
> %edi, %esi - counter regs
>
> That's just 8 regs, and half of those are special.
>
For a modern ABI it is better described as:
%eax, %edx, %ecx - argument/return/scratch registers
%ebx, %esi, %edi - saved registers
%esp - stack pointer
%ebp - frame pointer (saved)
> Perhaps we could create another profiler? Instead of calling mcount,
> call a new function: __fentry__ or something. Have it activated with
> another switch. This could make the performance of the function tracer
> even better without all these exceptions.
>
> <function>:
> call __fentry__
> [...]
>
Calling the profiler immediately at the entry point is clearly the more
sane option. It means the ABI is well-defined, stable, and independent
of what the actual function contents are. It means that ABI isn't the
normal C ABI (the __fentry__ function would have to preserve all
registers), but that's fine...
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.