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Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue
- From: Steven Rostedt <rostedt at goodmis dot org>
- To: Andrew Haley <aph at redhat dot com>
- Cc: Thomas Gleixner <tglx at linutronix dot de>, 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>, jakub at redhat dot com, gcc <gcc at gcc dot gnu dot org>, Linus Torvalds <torvalds at linux-foundation dot org>
- Date: Fri, 20 Nov 2009 14:46:46 -0500
- Subject: Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue
- References: <alpine.LFD.firstname.lastname@example.org> <email@example.com> <20091119072040.GA23579@elte.hu> <alpine.LFD.firstname.lastname@example.org> <alpine.LFD.email@example.com> <firstname.lastname@example.org> <email@example.com> <4B06EF6F.firstname.lastname@example.org>
- Reply-to: rostedt at goodmis dot org
On Fri, 2009-11-20 at 19:35 +0000, Andrew Haley wrote:
> Steven Rostedt wrote:
> > Ingo, Thomas and Linus,
> > I know Thomas did a patch to force the -mtune=generic, but just in case
> > gcc decides to do something crazy again, this patch will catch it.
> > Should we try to get this in now?
> I'm sure this makes sense, but a gcc test case would be even better.
> If this can be detected in the gcc test suite it'll be found and
> fixed long before y'all in kernel land get to see it. That's the
> only way to guarantee this never bothers you again.
> H.J., who wrote the code in question, is hopefully looking at why
> this odd code is being generated. Once he's done I can put a
> suitable test case in the gcc test suite.
Yes a gcc test suite will help new instances of gcc. But we need to
worry about the instances of gcc that people have on their desktops now.
This test case will catch the discrepancy between gcc and the function
graph tracer. I'm not 100% convince that just adding -mtune=generic will
help in all cases. If we miss another instance, then the function graph
tracer may crash someone's kernel.