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Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Andrew Haley <aph at redhat dot com>
- Cc: Thomas Gleixner <tglx at linutronix dot de>, "H.J. Lu" <hjl dot tools at gmail dot com>, rostedt at goodmis dot org, Ingo Molnar <mingo at elte dot hu>, "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: Tue, 24 Nov 2009 10:36:34 -0500
- Subject: Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue
- References: <1258694593.22249.1012.camel@gandalf.stny.rr.com> <1258736456.22249.1032.camel@gandalf.stny.rr.com> <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> <4B0BFC84.7070806@redhat.com>
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Tue, Nov 24, 2009 at 03:32:20PM +0000, Andrew Haley wrote:
> 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.
>
> Does it affect code size when we don't have to realign the stack pointer?
Yes, a lot. The difference is that -maccumulate-outgoing-args allocates
space for arguments of the callee with most arguments in the prologue, using
subtraction from sp, then to pass arguments uses movl XXX, 4(%esp) etc.
and the stack pointer doesn't usually change within the function (except for
alloca/VLAs).
With -mno-accumulate-outgoing-args args are pushed using push instructions
and stack pointer is constantly changing.
Jakub