linux-kernel - Re: VirtualBox module build breakage since commit 39808e451fdf

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Message-ID: <6a0f3245-eaaf-ebff-1122-89d56baf4b1d@lwfinger.net>
Date:   Tue, 17 Dec 2019 09:19:51 -0600
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: VirtualBox module build breakage since commit 39808e451fdf

On 12/15/19 11:11 PM, Masahiro Yamada wrote:
> Hi.
> 
> On Mon, Dec 16, 2019 at 11:48 AM Larry Finger <Larry.Finger@...inger.net> wrote:
>>
>> Hi,
>>
>> Since commit 39808e451fdf ("kbuild: do not read
>> $(KBUILD_EXTMOD)/Module.symvers"), some of the modules for VirtualBox have
>> failed to build. There are at least 3 such modules, namely vboxdrv, vboxnetflt,
>> and vboxnetadp.
> 
> As the section 6.3 of Documentation/kbuild/modules.rst says,
> the best practice is to put the related modules into the same source
> tree, and then do like this:
> 
>    obj-m := vboxdrv/  vboxnetfit/  vboxnetadp/
> 
> 
> 
> If you want to maintain the three separately,
> as 39808e451fdf mentions, you can useKBUILD_EXTRA_SYMBOLS.
> KBUILD_EXTRA_SYMBOLS was added more than a decade.
> So, you should be able to use it for your modules.
> 
> I think it is a cleaner solution than
> copying around Module.symvers in your build tree.

Masahiro,

Thank you for your prompt reply. Once I got it right, the KBUILD_EXTRA_SYMBOLS 
method works. The debugging was slow due to the problem area happening near the 
end of a 45-minute build, but I now have a solution that works for all kernels.

Thanks again,

Larry