linux-kernel - Re: [PATCH 04/10] ARM: ftrace: allow building without frame pointers

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Message-ID: <20100223184104.GA6325@debian>
Date:	Wed, 24 Feb 2010 00:11:04 +0530
From:	Rabin Vincent <rabin@....in>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Ingo Molnar <mingo@...hat.com>,
	Abhishek Sagar <sagar.abhishek@...il.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH 04/10] ARM: ftrace: allow building without frame
 pointers

On Tue, Feb 23, 2010 at 01:03:05PM -0500, Steven Rostedt wrote:
> On Tue, 2010-02-23 at 23:28 +0530, Rabin Vincent wrote:
> > The easiest option to have a more obvious message than a linker error
> > would be to add something like this in entry-common.S:
> > 
> >   #if (__GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 4)) \
> > 	&& !defined(OLD_MCOUNT)
> >   #warning Ftrace on GCC < 4.4 requires frame pointers
> >   #endif
> > 
> > Messages like this are also present in other places in ARM (for example
> > arch/arm/kernel/unwind.c), so this wouldn't be this first.
> > 
> > Note that the above message would help in all cases except the one where
> > someone builds the kernel with !fp and GCC 4.4+, and then builds a
> > module with an older GCC.  That would still be only a linker error.
> 
> I was going to recommend the #if above. But shouldn't it be a #error
> instead of a #warning?

Yes, I'll make it a #error.

(I had it at #warning in case some one had a custom compiler that had
the new mcount patch backported, and chose to ignore the warning.  But
it's probably better to leave it at #error and see if someone actually
complains about it, rather than have someone miss the message with it as
a #warning.)

Rabin
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