linux-kernel - Re: diet-kconfig: a script to trim unneeded kconfigs

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Message-ID: <s5h3ajsw56j.wl%tiwai@suse.de>
Date:	Mon, 22 Sep 2008 17:50:28 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"Giacomo A. Catenazzi" <cate@...eee.net>,
	Chris Li <lkml@...isli.org>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: diet-kconfig: a script to trim unneeded kconfigs

At Mon, 22 Sep 2008 11:41:36 -0400 (EDT),
Steven Rostedt wrote:
> 
> 
> 
> On Mon, 22 Sep 2008, Giacomo A. Catenazzi wrote:
> > Takashi Iwai wrote:
> > > At Fri, 19 Sep 2008 16:55:51 -0700,
> > > Chris Li wrote:
> > > 
> > > > I avoid arch/ and firmware/ because it is nasty. I figure module in
> > > > arch/ is small enough I don't mind building it. And the firmware
> > > > directory,
> > > > if I don't build the module loads it. Those firmware will automatically
> > > > skipped
> > > > any way.
> > > 
> > > Agreed.
> > > 
> > > > The little tricky part is some thing like this:
> > > > ========================
> > > > ifeq ($(CONFIG_BLK_DEV_CMD640), m)
> > > >         obj-m += cmd640.o
> > > > endif
> > > > ========================
> > > > Internally it get convert it into:
> > > > "obj-$(CONFIG_BLK_DEV_CMD640) += cmd640.o"
> > 
> > Are you sure?
> > I.e. if you set CONFIG_BLK_DEV_CMD640=y, you see that
> > the two constructs gives different results.
> > 
> > If the makefile author did such complex construct, I
> > really think there is a reason ;-)
> > 
> 
> Yes indeed, we should find out what the author meant.
> 
>  ifeq ($(CONFIG_BLK_DEV_CMD640), m)
> 	obj-m += cmd640.o
>  endif
> 
> and
> 
>  obj-$(CONFIG_BLK_DEV_CMD640) += cmd640.o
> 
> mean two different things.
> 
> The former means to compile the cmd640 only if it is set to a module.
> The later means to compile the cmd640 if it is either a module or built 
> into the core kernel code.

FYI, in this particular case, cmd640.o is linked in the upper Makefile
for CONFIG_BLK_DEV_CMD640=y.

> The author needs to make this change or explain why it is like this.

Right.  My guess is the link order, but still there must be a better
way to fix.


thanks,

Takashi
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