linux-kernel - Re: [PATCH] kbuild: Include external modules compile flags

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Date:   Tue, 4 Feb 2020 14:02:55 -0800
From:   Gregory Rose <gvrose8192@...il.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dev@...nvswitch.org, dsahern@...il.com
Subject: Re: [PATCH] kbuild: Include external modules compile flags


On 2/1/2020 10:07 PM, Masahiro Yamada wrote:
> On Thu, Jan 30, 2020 at 3:09 AM Gregory Rose <gvrose8192@...il.com> wrote:
>>
>> On 1/28/2020 7:37 AM, Gregory Rose wrote:
>>> On 1/27/2020 7:35 PM, Masahiro Yamada wrote:
>>>> On Tue, Jan 28, 2020 at 6:50 AM Greg Rose <gvrose8192@...il.com> wrote:
>>>>> Since this commit:
>>>>> 'commit 9b9a3f20cbe0 ("kbuild: split final module linking out into
>>>>> Makefile.modfinal")'
>>>>> at least one out-of-tree external kernel module build fails
>>>>> during the modfinal make phase because Makefile.modfinal does
>>>>> not include the ccflags-y variable from the exernal module's Kbuild.
>>>> ccflags-y is passed only for compiling C files in that directory.
>>>>
>>>> It is not used for compiling *.mod.c
>>>> This is true for both in-kernel and external modules.
>>>>
>>>> So, ccflags-y is not a good choice
>>>> for passing such flags that should be globally effective.
>>>>
>>>>
>>>> Maybe, KCFLAGS should work.
>>>>
>>>>
>>>> module:
>>>>          $(MAKE) KCFLAGS=...  M=$(PWD) -C /lib/modules/$(uname
>>>> -r)/build modules
>>>>
>> Hi Masahiro,
>>
>> I'm unable to get that to work.  KCFLAGS does not seem to be used in
>> Makefile.modfinal.
>
> I quickly tested it, and confirmed
> KCFLAGS works for external modules, too.
>
>
> Makefile.modfinal includes scripts/Makefile.lib
>
>
> So,  c_flags contains $(KCFLAGS)
>
>   c_flags -> KBUILD_CFLAGS -> KCFLAGS
>

Hi Masahiro,

I must have missed  something then - again, my unfamiliarity with the 
Linux Makefiles is probably tripping me up.  I'll
dig around and see if I can get that working.

Thanks for your help,

- Greg