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Message-ID: <oli5wymvdxrk4ds54yh65s4cewztn4daxujgjfprzw2f2ozqqi@35kdsvivgrzw>
Date: Wed, 11 Sep 2024 10:38:58 -0500
From: Lucas De Marchi <lucas.demarchi@...el.com>
To: Masahiro Yamada <masahiroy@...nel.org>
CC: Jing Leng <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: Re: External modules with O=... (was: Re: [PATCH] kbuild: Fix
include path in scripts/Makefile.modpost)
On Wed, Sep 11, 2024 at 04:28:30PM GMT, Masahiro Yamada wrote:
>On Wed, Sep 11, 2024 at 1:36 PM Lucas De Marchi
><lucas.demarchi@...el.com> wrote:
>>
>> On Tue, Sep 10, 2024 at 09:43:14PM GMT, Lucas De Marchi wrote:
>> >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=$(PWD)" is the official way,
>> >>>>but this patch is a clean up.
>> >>>
>> >>>I tried what is in this patch and also tried to find an official way in
>> >>>the docs.
>
>
>There is no official way.
>
>> >>>
>> >>>In kmod's testsuite we build dummy kernel modules to exercise the API.
>> >>>https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/tree/testsuite/module-playground
>> >>>
>> >>>This works:
>> >>> make -C /lib/modules/$(uname -r)/build M=$PWD
>> >>>
>> >>>This doesn't:
>> >>> make -C /lib/modules/$(uname -r)/build M=$PWD O=/tmp/kmod_test_modules
>
>
>
>O= points the output directory of the kernel,
>not the output directory of the external modules.
>
>
>/lib/modules/$(uname -r)/build
>is the clean source tree.
>
>/tmp/kmod_test_modules
>contains the build artifacts of vmlinux and
>in-tree modules.
>
>Then, the command you gave would work.
>
>
>
>
>
>
>> >>>
>> >>>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.
>>
>> spoke too early... It worked because I was in another machine pointing
>> to a 6.8 kernel. It seems like something broke between 6.9 and 6.10.
>>
>> Running a quick bisect, it's pointing to this commit:
>> 9a0ebe5011f4 ("kbuild: use $(obj)/ instead of $(src)/ for common pattern rules")
>
>
>Overriding 'src' from the command is not allowed. That's why.
>
>
>> Error like below:
>>
>> $ make -j$(nproc) -C ~/p/linux-dim/src MddPWD/build srcx=$PWD
>> make: Entering directory '/home/ldmartin/p/linux-dim/src'
>> make[2]: *** No rule to make target '/home/ldmartin/p/kmod/testsuite/module-playground/build/mod-simple.o', needed by '/home/ldmartin/p/kmod/testsuite/module-playground/build/'. Stop.
>> make[1]: *** [/home/ldmartin/p/linux-dim/src/Makefile:1922: /home/ldmartin/p/kmod/testsuite/module-playground/build] Error 2
>> make: *** [Makefile:240: __sub-make] Error 2
>> make: Leaving directory '/home/ldmartin/p/linux-dim/src'
>
>
>I suggested M=relative-path + VPATH=
>but I do not know what you want to achieve.
>
>https://lore.kernel.org/linux-kbuild/CAK7LNATGGibmjZzYX_A2SkJthmOPbKw2K3R7JYuHTWzgGL2Zjg@mail.gmail.com/
but that is only for in-tree modules, not external modules, right?
Quick reproducer on what I expected would work:
git clone https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git
cd kmod/testsuite/module-playground
make -C $KDIR M=$PWD O=$PWD/build
So... did I get the below statement right?
There never was an official way to build external modules with
source and build in different directories. Up until 6.9 we
could pass `-C <kernel_srcdir> M=<mod_builddir> src=<mod_srcdir>`
for unofficial way. After that there's no alternative.
thanks
Lucas De Marchi
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