Message-ID: <mesi5e46iumhgdbvzl2gfwdamtv34baydb5d4pmud4fu7n4dto@fewx4uzbtjl6>
Date: Tue, 10 Sep 2024 23:23:56 -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 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=$(PWD)" is the official way,
>>>>but this patch is a clean up.
>>>
>>>I tried what is in this patch and also tried to find an official way in
>>>the docs.
>>>
>>>In kmod's testsuite we build dummy kernel modules to exercise the API.
>>>https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/tree/testsuite/module-playground
>>>
>>>This works:
>>>	make -C /lib/modules/$(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.

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")

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'

Lucas De Marchi

>
>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

Powered by blists - more mailing lists