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

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Date:	Thu, 10 Mar 2011 10:04:44 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Michal Marek <mmarek@...e.cz>, Borislav Petkov <bp@...en8.de>,
	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

* 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

Although i'm not sure if it is wise to mix build details into the object build tree 
hierarchy like that ...

Maybe we can live with some multi-line definition after all - until all of the 
kernel is covered by such a mechanism. But the per object file rule would still be 
important, for multi-maintainenace-boundaries directories like kernel/*.o.

Thanks,

	Ingo
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