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

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Date:	Thu, 10 Mar 2011 10:17:16 +0100
From:	Michal Marek <mmarek@...e.cz>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Sam Ravnborg <sam@...nborg.org>, 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

On 10.3.2011 10:04, 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?

CFLAGS_sched.o := -Werror


> 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 ...

One way without extending the current rules could be:

ifdef CONFIG_CC_WERROR
Werror := -Werror
endif

CFLAGS_sched.o := $(Werror)
CFLAGS_another.o := $(Werror)

What do you think?
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