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Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue
- From: Ingo Molnar <mingo at elte dot hu>
- To: Thomas Gleixner <tglx at linutronix dot de>
- Cc: Jakub Jelinek <jakub at redhat dot com>, Andrew Haley <aph at redhat dot com>, "H.J. Lu" <hjl dot tools at gmail dot com>, rostedt at goodmis dot org, "H. Peter Anvin" <hpa at zytor dot com>, 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, Peter Zijlstra <peterz at infradead dot org>, Frederic Weisbecker <fweisbec at gmail dot com>, David Daney <ddaney at caviumnetworks dot com>, Richard Guenther <richard dot guenther at gmail dot com>, gcc <gcc at gcc dot gnu dot org>, Linus Torvalds <torvalds at linux-foundation dot org>
- Date: Wed, 25 Nov 2009 17:25:56 +0100
- Subject: Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue
- References: <4B06EF6F.2050507@redhat.com> <6dc9ffc80911220138y15bfa91agccf5c29f1c30e09a@mail.gmail.com> <4B0972C9.302@redhat.com> <6dc9ffc80911221530t38d83cf6je739743c8d756667@mail.gmail.com> <4B0BF119.4070704@redhat.com> <alpine.LFD.2.00.0911241555170.24119@localhost.localdomain> <20091124150604.GJ22813@hs20-bc2-1.build.redhat.com> <alpine.LFD.2.00.0911251604280.24119@localhost.localdomain> <20091125154452.GA9456@elte.hu> <alpine.LFD.2.00.0911251650570.24119@localhost.localdomain>
* Thomas Gleixner <tglx@linutronix.de> wrote:
> On Wed, 25 Nov 2009, Ingo Molnar wrote:
> > * Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > > On Tue, 24 Nov 2009, Jakub Jelinek wrote:
> > >
> > > > On Tue, Nov 24, 2009 at 03:55:49PM +0100, Thomas Gleixner wrote:
> > > > > > you should compile your code with -maccumulate-outgoing-args, and there's
> > > > > > no need to use -mtune=generic. Is that right?
> > > > >
> > > > > Seems to work. What other side effects has that ?
> > > >
> > > > Faster code, significant increase in code size though. Note that on many
> > > > architectures it is the only supported model.
> > >
> > > Just checked on the affected -marchs. The increase in code size is
> > > about 3% which is not that bad and definitely acceptable for the
> > > tracing case. Will zap the -mtune=generic patch and use
> > > -maccumulate-outgoing-args instead.
> >
> > hm, 3% sounds quite large :( dyn-ftrace is enabled in distro configs, so
> > 3% is a big deal IMO.
>
> Distro-configs have -mtune=generic anyway. So it's not changing
> anything for them.
>
> I'm talking about the -march flags which result in that weird code
> (pentium-mmx ....).
ok!
Ingo