linux-kernel - Re: kbuild - introduce support for subdir-ccflags-y

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Message-ID: <20090419062841.GA17801@uranus.ravnborg.org>
Date:	Sun, 19 Apr 2009 08:28:41 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Kyle Moffett <kyle@...fetthome.net>
Cc:	Ingo Molnar <mingo@...e.hu>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	linux arch <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: kbuild - introduce support for subdir-ccflags-y

On Sat, Apr 18, 2009 at 11:17:44PM -0400, Kyle Moffett wrote:
> On Sat, Apr 18, 2009 at 2:09 PM, Russell King <rmk+lkml@....linux.org.uk> wrote:
> > On Sat, Apr 18, 2009 at 05:07:50PM +0200, Ingo Molnar wrote:
> >> * Russell King <rmk+lkml@....linux.org.uk> wrote:
> >> > On Sat, Apr 18, 2009 at 02:51:59PM +0200, Sam Ravnborg wrote:
> >> > > The typical use cases are an architecture or a subsystem that
> >> > > decide to cover all files with -Werror.
> >> > > Today alpha, mips and sparc uses -Werror in almost all their
> >> > > Makefile - with subdir-ccflag-y it is now simpler to do so
> >> > > as only the top-level directories needs to be covered.
> >> >
> >> > Hmm, this won't make sense for ARM.  We have things like #warning
> >> > and deprecated functions in machine specific headers, and adding
> >> > -Werror to the whole of arch/arm/ will result in these causing
> >> > builds to fail.
> >>
> >> This is optional - if you dont want it, you dont set it.
> >
> > Please read _all_ of my mail, particularly the bit where it talks about
> > it being useful for a certain subset.
> 
> It's my impression that on x86 it's a config option whether or not to
> build with -Werror.  You could do the exact same thing with an
> internal inverted-logic CONFIG_ARM_ALLOW_WARNINGS option and make all
> the boards triggering warnings "select ARM_ALLOW_WARNINGS".  Then have
> a user-visible config option "ARM_USER_ALLOW_WARNINGS" which also
> selects the internal option.  That adds some additional kconfig-level
> documentation on which subarch combos need some love.

Correct - but Russell's original comment was that the subdir-* feature
was of no use for arm. And this is correct with the current way
the individual directories are specified.

If you compare arch/x86/kernel/ and arch/arm/kernel/ you will see
that x86 has 3 subdirectories where arm has none.

Another measure:
Arm has 12 Makefiles outside mach* and plat* where x86 has 24 Makefiles.

Ao unless Russell decide to take the patch that refactor all the core-*
stuff out in a Kbuild file arm has no use of subdir-ccflags-y and
can use the already existing ccflags-y if they decide to cover
most of arm with -Werror.

	Sam
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