linux-kernel - Re: External modules with O=... (was: Re: [PATCH] kbuild: Fix include path in scripts/Makefile.modpost)

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Message-ID: <lnizw6jklneisxkhah7ezy4tcrn2wpm52ibh5euz7ipyfansde@kc4onuvrrmxr>
Date: Tue, 10 Sep 2024 21:43:14 -0500
From: Lucas De Marchi <lucas.demarchi@...el.com>
To: Jing Leng <3090101217@....edu.cn>
CC: Masahiro Yamada <masahiroy@...nel.org>, Michal Marek
	<michal.lkml@...kovi.net>, Nick Desaulniers <ndesaulniers@...gle.com>, "Linux
 Kbuild mailing list" <linux-kbuild@...r.kernel.org>, Linux Kernel Mailing
 List <linux-kernel@...r.kernel.org>, Jing Leng <jleng@...arella.com>
Subject: Re: External modules with O=... (was: Re: [PATCH] kbuild: Fix
 include path in scripts/Makefile.modpost)

On Wed, Sep 11, 2024 at 09:10:09AM GMT, Jing Leng wrote:
>> -----Original Messages-----
>> From: "Lucas De Marchi" <lucas.demarchi@...el.com>
>> Send time:Tuesday, 09/10/2024 22:00:29
>> To: "Masahiro Yamada" <masahiroy@...nel.org>
>> Cc: 3090101217@....edu.cn, "Michal Marek" <michal.lkml@...kovi.net>, "Nick
>>  Desaulniers" <ndesaulniers@...gle.com>, "Linux Kbuild mailing list" <linux-kbuild@...r.kernel.org>, "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>, "Jing Leng" <jleng@...arella.com>
>> Subject: External modules with O=... (was: Re: [PATCH] kbuild: Fix include path in scripts/Makefile.modpost)
>>
>> Hi, I was pointed to this thread since I'm trying something similar
>> in kmod's testsuite. See below.
>>
>> On Tue, May 24, 2022 at 02:52:45AM GMT, Masahiro Yamada wrote:
>> >On Tue, May 17, 2022 at 7:51 PM <3090101217@....edu.cn> wrote:
>> >>
>> >> From: Jing Leng <jleng@...arella.com>
>> >>
>> >> When building an external module, if users don't need to separate the
>> >> compilation output and source code, they run the following command:
>> >> "make -C $(LINUX_SRC_DIR) M=$(PWD)". At this point, "$(KBUILD_EXTMOD)"
>> >> and "$(src)" are the same.
>> >>
>> >> If they need to separate them, they run "make -C $(KERNEL_SRC_DIR)
>> >> O=$(KERNEL_OUT_DIR) M=$(OUT_DIR) src=$(PWD)". Before running the
>> >> command, they need to copy "Kbuild" or "Makefile" to "$(OUT_DIR)" to
>> >> prevent compilation failure.
>> >>
>> >> So the kernel should change the included path to avoid the copy operation.
>> >>
>> >> Signed-off-by: Jing Leng <jleng@...arella.com>
>> >> ---
>> >>  scripts/Makefile.modpost | 3 +--
>> >>  1 file changed, 1 insertion(+), 2 deletions(-)
>> >>
>> >> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
>> >> index 48585c4d04ad..0273bf7375e2 100644
>> >> --- a/scripts/Makefile.modpost
>> >> +++ b/scripts/Makefile.modpost
>> >> @@ -87,8 +87,7 @@ obj := $(KBUILD_EXTMOD)
>> >>  src := $(obj)
>> >>
>> >>  # Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
>> >> -include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
>> >> -             $(KBUILD_EXTMOD)/Kbuild, $(KBUILD_EXTMOD)/Makefile)
>> >> +include $(if $(wildcard $(src)/Kbuild), $(src)/Kbuild, $(src)/Makefile)
>> >>
>> >>  # modpost option for external modules
>> >>  MODPOST += -e
>> >> --
>> >> 2.17.1
>> >>
>> >
>> >
>> >I do not think "M=$(OUT_DIR) src=$(PWD)" is the official way,
>> >but this patch is a clean up.
>>
>> I tried what is in this patch and also tried to find an official way in
>> the docs.
>>
>> In kmod's testsuite we build dummy kernel modules to exercise the API.
>> https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/tree/testsuite/module-playground
>>
>> This works:
>> 	make -C /lib/modules/$(uname -r)/build M=$PWD
>>
>> This doesn't:
>> 	make -C /lib/modules/$(uname -r)/build M=$PWD O=/tmp/kmod_test_modules
>>
>> I also tried the variants above with setting src, but all of them give
>> me errors - I used 6.10 and 6.11-rc7 for these tests.
>>
>> Is there a way to do this?
>>
>> thanks
>> Lucas De Marchi
>>
>> >
>> >Applied to linux-kbuild. Thanks.
>> >
>> >
>> >--
>> >Best Regards
>> >Masahiro Yamada
>
>Hi Masahiro,

I guess you meant Lucas :)

>
>I think your intention is to separate the source code from the compiled output.
>The correct command should be:
>    make -C /lib/modules/$(uname -r)/build src=$PWD M=/tmp/kmod_test_modules

oh, looks like this works. Apparently my mistake was trying to set O=
like I normally do for in-tree modules.

Thanks
Lucas De Marchi

>
>You also can refer to:
>    https://github.com/lengjingzju/cbuild-ng/blob/main/scripts/core/inc.mod.mk
>1. The complete command is as follows:
>    make -C <Linux kernel source code directory> O=<Linux kernel compilation output directory> src=<Current driver module source code directory> M=<Current driver module compilation output directory>
>2. If the <Linux kernel source code directory> and the <Linux kernel compilation output directory> are the same, <O=xxx> can be omitted:
>    make -C <Linux kernel source code directory> src=<Current driver module source code directory> M=<Current driver module compilation output directory>
>2. If the <Current driver module source code directory> and the <Current driver module compilation output directory> are the same, <src=xxx> can be omitted:
>    make -C <Linux kernel source code directory> O=<Linux kernel compilation output directory> M=<Current driver module source code directory>
>
>Best Regards!
>Jing Leng