linux-kernel - Re: Modpost error after changing CONFIG

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Message-ID: <20100712172847.GA17423@merkur.ravnborg.org>
Date:	Mon, 12 Jul 2010 19:28:47 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	Takashi Iwai <tiwai@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: Modpost error after changing CONFIG_SOUND from m to y

On Mon, Jul 12, 2010 at 07:11:47PM +0200, Denys Vlasenko wrote:
> On Mon, Jul 12, 2010 at 7:03 PM, Randy Dunlap <randy.dunlap@...cle.com> wrote:
> > On Mon, 12 Jul 2010 05:54:16 +0200 Denys Vlasenko wrote:
> >> I was using the same .config for my home machine for a long time,
> >> updating it using "make oldconfig" every time I moved to newer kernel.
> >> It worked fine for many kernels.
> >>
> >> In this .config I had CONFIG_SOUND=m.
> >>
> >> Starting witn 2.6.34, build fails with
> >>
> >> sound/core/sound_oss.c:25:2: error: #error "Enable the OSS soundcore multiplexer (CONFIG_SOUND) in the kernel."
> >>
> >> Ok. I changed CONFIG_SOUND to y. Now the build fails at modpost:
> >
> > Hi,
> > I can't get the build to fail (2.6.34 or 2.6.35-rc4-git4).
> > Please provide a full/complete .config file (and that will include a
> > kernel version number :).
> 
> I found out that build only fails if I give empty CFLAGS_KERNEL
> and CFLAGS_MODULE variables to make, like this:
> 
> make CFLAGS_KERNEL="" CFLAGS_MODULE=""

Messing around with kernel internal flags is bound to give
unpredictable bugs.

I this case you loose "-DMODULE" and I guess some sound specificmodules
test on this symbol.
And there may be other subtle side-effects.

What is the intial reason why you assign CFLAGS_KERNEL and CFLAGS_MODULE?

	Sam
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