linux-kernel - Re: Anyone working on ftrace function graph support on ARM?

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Date:	Wed, 25 Mar 2009 14:41:16 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Tim Bird <tim.bird@...sony.com>
cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Abhishek Sagar <sagar.abhishek@...il.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.arm.linux.org.uk>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: Anyone working on ftrace function graph support on ARM?


On Wed, 25 Mar 2009, Tim Bird wrote:

> Russell King - ARM Linux wrote:
> > On Wed, Mar 25, 2009 at 06:05:33PM +0100, Uwe Kleine-K???nig wrote:
> >> On Wed, Mar 25, 2009 at 09:34:07AM -0700, Tim Bird wrote:
> >>> Russell King - ARM Linux wrote:
> >>>> As pointed out in my previous mail, identifying where on the stack the
> >>>> return address is stored is only possible for OABI with frame pointers.
> >>>>
> >>>> EABI will probably be possible with the stack unwinding code, but it
> >>>> probably won't be cheap.  The EABI unwinder is scheduled for merging
> >>>> during the present now-open merge window.
> >> EABI with frame pointers should work, too, shouldn't it?
> > 
> > Yes, as I said at the top of my reply dated Wed, 25 Mar 2009 09:57:51 +0000
> 
> It turns out you can't use -pg and -fomit-frame-pointers at the same time.
> At least, my gcc complains about this:
> $ make
> arm-sony-linux-gnueabi-dev-gcc -g -pg -fomit-frame-pointer -o hello hello.c
> arm-sony-linux-gnueabi-dev-gcc: -pg and -fomit-frame-pointer are incompatible
> make: *** [hello] Error 1

Correct, that is because mcount requires (as Russell earlier pointed out) 
the use of frame pointers.

-- Steve

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