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

[Ingo Molnar <mingo@elte.hu>]

* Sam Ravnborg <sam@ravnborg.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