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

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Message-ID: <20110310092034.GA21454@liondog.tnic>
Date:	Thu, 10 Mar 2011 10:20:34 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Sam Ravnborg <sam@...nborg.org>, Michal Marek <mmarek@...e.cz>,
	Arnd Bergmann <arnd@...db.de>, 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

On Thu, Mar 10, 2011 at 10:04:44AM +0100, Ingo Molnar wrote:
> 
> * Sam Ravnborg <sam@...nborg.org> wrote:
> 
> > > 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.
> > 
> > To add -Werror for all files conditionally you can do:
> > 
> >     ccflags-$(CONFIG_WERROR) += -Werror
> > 
> > For individual files we can then drop -Werror like this:
> > 
> >     CFLAGS_REMOVE_foobar.o := -Werror
> > 
> > So it should be doable with the existing infrastructure.
> 
> Stupid question: is there an existing kbuild rule that i could use to enable -Werror 
> for a single .o file, such as kernel/sched.o - without affecting other files in 
> kernel/ that i do not maintain?
> 
> Also, adding 3 lines per object file is pretty ugly - would it be possible to create 
> a nicer, compact, single-line way to someone condense a CONFIG_ERROR opt-out 
> mechanism, the -Werror default and the single-object-file into a single rule?
> 
> Something like:
> 
>   obj-werror-y += sched.o

I believe you can do

CFLAGS_sched.o = -Werror

or similar but you'll have to try it out. I remember doing a more
involved per-object flags fumbling with the popcnt stuff, i.e. you might
want to take a look at d61931d89be506372d01a90d1755f6d0a9fafe2d where
we pass it an arch-specific config option so you can have per-object,
per-arch build flags :).

HTH.

-- 
Regards/Gruss,
    Boris.
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