linux-kernel - Re: [PATCH -v5] kbuild: Add extra gcc checks

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Message-ID: <20110309151134.GA15730@elte.hu>
Date:	Wed, 9 Mar 2011 16:11:34 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Michal Marek <mmarek@...e.cz>
Cc:	Borislav Petkov <bp@...en8.de>, Arnd Bergmann <arnd@...db.de>,
	Sam Ravnborg <sam@...nborg.org>, torvalds@...ux-foundation.org,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-kbuild@...r.kernel.org, bp@...64.org
Subject: Re: [PATCH -v5] kbuild: Add extra gcc checks


* Michal Marek <mmarek@...e.cz> wrote:

> On Tue, Mar 01, 2011 at 09:35:29AM +0100, Borislav Petkov wrote:
> > Add a 'W=1' Makefile switch which adds additional checking per build
> > object.
> > 
> > The idea behind this option is targeted at developers who, in the
> > process of writing their code, want to do the occasional
> > 
> > make W=1 [target.o]
> > 
> > and let gcc do more extensive code checking for them. Then, they
> > could eyeball the output for valid gcc warnings about various
> > bugs/discrepancies which are not reported during the normal build
> > process.
> > 
> > For more background information and a use case, read through this
> > thread: http://marc.info/?l=kernel-janitors&m=129802065918147&w=2
> > 
> > -v5: Document internal kbuild variable which is introduced by this.
> > Simplify assignment.
> 
> Thanks, applied to kbuild-2.6.git#packaging. If someone comes up with a
> good selection of warnings for W=1 and W=2, we can change it later.

Another, related, very nice kbuild feature would be to allow for arch maintainers to 
mark certain files as "should only build fine without warnings" - i.e. -Werror 
should be the default. There would be a Kconfig feature to opt out of this, 
CONFIG_CC_IGNORE_WARNINGS=y or so. This would allow for people to still build the 
kernel with old (or buggy) versions of GCC.

arch/x86/ would start using this by gradually marking more and more files as -Werror 
by default. Some architectures like arch/sparc/ and arch/powerpc/ already build with 
-Werror enabled - but for arch/x86/ we cannot force this (we cannot break the build 
for who knows how many people) so we want to do it gradually and with a way out for 
users with buggy compilers.

Thanks,

	Ingo
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