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Re: BUG: GCC-4.4.x changes the function frame on some functions
- From: Linus Torvalds <torvalds at linux-foundation dot org>
- To: "H. Peter Anvin" <hpa at zytor dot com>
- Cc: rostedt at goodmis dot org, David Daney <ddaney at caviumnetworks dot com>, 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 12:06:32 -0800 (PST)
- 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> <4B05A16D.1050807@zytor.com>
On Thu, 19 Nov 2009, H. Peter Anvin wrote:
>
> 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...
As far as I know, that's true of _mcount already: it's not a normal ABI
and is rather a highly architecture-specific special case to begin with.
At least ARM has some (several?) special mcount calling conventions,
afaik.
(And then ARM people use __attribute__((naked)) and insert the code by
inline asm, or something. That seems to be "standard" in the embedded
world, where they often do even stranger things than we do in the
kernel. At least our low-level system call and interrupt handlers are
written as assembly language - the embedded world seems to commonly
write them as C functions with magic attributes and inline asm).
Linus