linux-kernel - Re: [PATCH 1/2] function-graph: disable when both x86

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Message-ID: <20090621104527.GA22961@elte.hu>
Date:	Sun, 21 Jun 2009 12:45:27 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 1/2] function-graph: disable when both x86_32 and
	optimize for size are configured


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Sat, 20 Jun 2009, Ingo Molnar wrote:
> 
> > 
> > * Steven Rostedt <rostedt@...dmis.org> wrote:
> > 
> > > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> > > index 4a13e5a..1eac852 100644
> > > --- a/kernel/trace/Kconfig
> > > +++ b/kernel/trace/Kconfig
> > > @@ -121,6 +121,7 @@ config FUNCTION_GRAPH_TRACER
> > >  	bool "Kernel Function Graph Tracer"
> > >  	depends on HAVE_FUNCTION_GRAPH_TRACER
> > >  	depends on FUNCTION_TRACER
> > > +	depends on !X86_32 || !CC_OPTIMIZE_FOR_SIZE
> > >  	default y
> > 
> > Hm, nice fix, but this is a quite nasty constraint - distros like to 
> > enable CC_OPTIMIZE_FOR_SIZE as it neatly trims the kernel's size by 
> > about 30%.
> > 
> > Just in case you have not checked yet: is there no way to turn off 
> > the specific gcc optimization that causes this? Or is it -Os itself 
> > that does this optimization?
> 
> It seems to me that -Os causes it for i386. I did a make V=1 to 
> capture how the files in question were being compiled, and tried 
> various disabling of flags. -Os was the only one to make a 
> difference. :-(

oh well. I think GCC should be fixed/improved to not do this 
particular (rather narrow looking) optimization if -pg is specified 
too.

	Ingo
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