linux-kernel - Re: How to link a .o with all modules

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Message-Id: <D346E2E4-26C3-482E-ABBF-AF1EE97E91CD@kernel.crashing.org>
Date:	Mon, 5 May 2008 09:46:08 -0500
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	lkml List <linux-kernel@...r.kernel.org>,
	"linuxppc-dev@...abs.org list" <linuxppc-dev@...abs.org>
Subject: Re: How to link a .o with all modules


On May 4, 2008, at 2:24 PM, Sam Ravnborg wrote:

> On Sun, May 04, 2008 at 01:22:38PM -0500, Kumar Gala wrote:
>> Sam,
>>
>> We have a case in powerpc in which we want to link some library
>> routines with all module objects.  The routines are intended for
>> handling out-of-line function call register save/restore so having
>> them as EXPORT_SYMBOL() is counter productive (we do also need to  
>> link
>> the same "library" code into the kernel).
>>
>> Any suggestions on how to handle this?
>
> I assume you have the .o file build somewhere as part of the
> normal kernel build.
>
> Then you in
> arch/powerpc/Makefile adds the following assignment:
>
> LDFLAGS_MODULE += arch/powerpc/lib/my_magic_file.o
>
> kbuild will then during the modpost stage link this
> file on all modules.
> To add the same file to the kernel just include it
> in a obj-y += my_magic_file.o
>
> One trap is that my_magic_file.o needs to be built
> for a modules build too.
> I think you need to assign it to always:
>
>   always := my_magic_file.o
>
> to accomplish this.
>
> So in the end we will have:
>
> arch/powerpc/Makefile:
> LDFLAGS_MODULE += arch/powerpc/lib/my_magic_file.o
>
> arch/powerpc/lib/Makefile:
> always := my_magic_file.o
> obj-y += my_magic_file.o
>
>
> Let me know if this does address your question.

The problem is MODPOST complains about undefined symbols:

   MODPOST 24 modules
ERROR: "_restgpr_20_x" [net/key/af_key.ko] undefined!
ERROR: "_restgpr_25_x" [net/key/af_key.ko] undefined!
ERROR: "_restgpr_30_x" [net/key/af_key.ko] undefined!

...

Any ideas on that?

- k
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