linux-kernel - Re: build system: no module target ending with slash?

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Message-Id: <200705041056.19286.mail@earthworm.de>
Date:	Fri, 4 May 2007 10:56:14 +0200
From:	Christian Hesse <mail@...thworm.de>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	linux-kernel@...r.kernel.org,
	James Ketrenos <jketreno@...ux.intel.com>
Subject: Re: build system: no module target ending with slash?

On Thursday 03 May 2007, Sam Ravnborg wrote:
> On Thu, May 03, 2007 at 09:17:15AM +0200, Christian Hesse wrote:
> > On Thursday 03 May 2007, Sam Ravnborg wrote:
> > > On Thu, May 03, 2007 at 06:25:11AM +0200, Sam Ravnborg wrote:
> > > > On Thu, May 03, 2007 at 12:43:43AM +0200, Christian Hesse wrote:
> > > > > Hi James, hi everybody,
> > > > >
> > > > > playing with iwlwifi I try to patch it into the kernel and to build
> > > > > it from there. But I have a problem with the build system.
> > > > >
> > > > > The file drivers/net/wireless/mac80211/Makefile contains one single
> > > > > line:
> > > > >
> > > > > obj-$(CONFIG_IWLWIFI)   += iwlwifi/
> > > > >
> > > > > When CONFIG_IWLWIFI=m in scripts/Makefile.lib line 29 the target is
> > > > > filtered as it ends with a slash. That results in
> > > > > drivers/net/wireless/mac80211/built-in.o not being built and the
> > > > > build process breaks with an error. What is the correct way to
> > > > > handle this? Why are targets ending with a slash filtered?
> > > >
> > > > Looks buggy. I will take a look tonight.
> > >
> > > After some coffee...
> > >
> > > Line 29 in Kbuild.include find all modules and a directory is not a
> > > module. In line 26 in same file the directory iwlwifi is included in
> > > the list of directories to visit.
> > > So there is something else going on.
> >
> > In scripts/Kbuild.include line 26 is empty and line 29 is a comment... Do
> > I look at the wrong place?
>
> I looked at lxr.linux.no - so probarly an outdated version.
>
> > I still believe in my version: built-in.o is built if any of $(obj-y)
> > $(obj-m) $(obj-n) $(obj-) $(lib-target) contains anything in
> > scripts/Makefile.build line 77. As scripts/Makefile.lib line 29 filters
> > the only target the object file is not built.
>
> I have applied your patch and tried it out.
> The reason for the problem is the placeholder directory mac80211.
> kbuild will not waste time building built-in.o for a directory where
> it is not necessary. So for mac80211 no built-in.o is created since there
> is no need. The only reference is to a module.

Agreed that it is not really needed. But if you don't build it you should not 
try to link it later...

> The quick-and-dirty workaround is to add a single
> obj-n := xx
> in mac80211/Makefile and kbuild is happy again.
>
> I could teach kbuild to create built-in.o also in the case
> where we refer to a subdirectory only. But then we would end up with a
> built-in.o in all directories where we have a kbuild MAkefile (almost) and
> that is not desireable.

I would prefer to teach it not to link object files that are not built.

> So I recommend the proposed workaround for now with a proper comment.

Ok, thanks for your help.
-- 
Regards,
Chris

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