linux-kernel - Re: Kbuild problem

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Date:	Tue, 20 Feb 2007 14:56:27 +0100
From:	Tilman Schmidt <tilman@...p.cc>
To:	Adrian Bunk <bunk@...sta.de>
CC:	Kai Germaschewski <kai.germaschewski@....edu>,
	Hansjoerg Lipp <hjlipp@....de>, kkeil@...e.de,
	isdn4linux@...tserv.isdn4linux.de, linux-kernel@...r.kernel.org
Subject: Re: Kbuild problem

Adrian Bunk schrieb:
> On Sun, Feb 18, 2007 at 12:22:10AM -0500, Kai Germaschewski wrote:
>> On Sat, 17 Feb 2007, Tilman Schmidt wrote:
>> 
>> > asyncdata.o is only needed for M105 and M101, not for the base
>> > driver. How do I express in Kbuild that asyncdata.o is to be added
>> > to gigaset-y only if CONFIG_GIGASET_M105 and CONFIG_GIGASET_M101
>> > are not both 'n'?
>> 
>> The way this is typically done is via Kconfig. Add a config option 
>> ASYNCDATA (actually something more descriptive/specific would be better), 
>> add a "select ASYNCDATA" to the config options for m101 and m105, and then 
>> you can use CONFIG_ASYNCDATA to decide whether to add asyncdata.o in the 
>> Makefile.
> 
> One disadvantage of this approach is that in a kernel with 
> CONFIG_GIGASET_BASE=y, you can't later compile and load the usb_gigaset 
> or ser_gigaset modules without rebooting since they require a change to 
> the kernel image.

You've got a point there. So linking asyncdata.o into the modules that
need it, as it is currently done, would perhaps be better after all?
The original problem (asyncdata.o linked in twice, causing duplicate
symbol definitions) could be fixed with this (admittedly somewhat
awkward) change to the Makefile (build tested):

--- linux-2.6.20-mm1-work/drivers/isdn/gigaset/Makefile 2007-02-20 13:39:44.000000000 +0100
+++ u/drivers/isdn/gigaset/Makefile     2007-02-20 13:38:58.000000000 +0100
@@ -1,7 +1,10 @@
 gigaset-y := common.o interface.o proc.o ev-layer.o i4l.o
 usb_gigaset-y := usb-gigaset.o asyncdata.o
 bas_gigaset-y := bas-gigaset.o isocdata.o
-ser_gigaset-y := ser-gigaset.o asyncdata.o
+ser_gigaset-y := ser-gigaset.o
+ifneq ($(CONFIG_GIGASET_M101)$(CONFIG_GIGASET_M105),yy)
+ser_gigaset-y += asyncdata.o
+endif

 obj-$(CONFIG_GIGASET_M105) += usb_gigaset.o gigaset.o
 obj-$(CONFIG_GIGASET_BASE) += bas_gigaset.o gigaset.o

The alternative would be to always link asyncdata.o into the gigaset
module whether it's needed or not. "size asyncdata.o" says:
   text    data     bss     dec     hex filename
   4200       0       0    4200    1068 asyncdata.o
which appears tolerable.

Opinions?

-- 
Tilman Schmidt                    E-Mail: tilman@...p.cc
Bonn, Germany
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