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

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Message-ID: <alpine.DEB.2.00.0906201822320.20813@gandalf.stny.rr.com>
Date:	Sat, 20 Jun 2009 18:24:06 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
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


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. :-(

-- Steve

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