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

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Message-ID: <f6ffa0d0-8214-8fc0-4fe9-4b70a1581d3e@gmail.com>
Date:   Tue, 28 Jan 2020 07:37:58 -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 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
>

Thanks,

I'll see if I can get that to work.

- Greg


>
>> Make sure to include the external kernel module's Kbuild so that the
>> necessary command line flags from the external module are set.
>>
>> Reported-by: David Ahern <dsahern@...il.com>
>> CC: Masahiro Yamada <yamada.masahiro@...ionext.com>
>> Signed-off-by: Greg Rose <gvrose8192@...il.com>
>> ---
>>   scripts/Makefile.modfinal | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
>> index 411c1e60..a645ba6 100644
>> --- a/scripts/Makefile.modfinal
>> +++ b/scripts/Makefile.modfinal
>> @@ -21,6 +21,10 @@ __modfinal: $(modules)
>>   modname = $(notdir $(@:.mod.o=))
>>   part-of-module = y
>>
>> +# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
>> +include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
>> +             $(KBUILD_EXTMOD)/Kbuild)
>> +
>>   quiet_cmd_cc_o_c = CC [M]  $@
>>         cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
>>
>> --
>> 1.8.3.1
>>
>