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

[Lucas De Marchi]

On Wed, Sep 11, 2024 at 09:10:09AM GMT, Jing Leng wrote:
> > -----Original Messages-----
> > From: "Lucas De Marchi" <lucas.demarchi@xxxxxxxxx>
> > Send time:Tuesday, 09/10/2024 22:00:29
> > To: "Masahiro Yamada" <masahiroy@xxxxxxxxxx>
> > Cc: 3090101217@xxxxxxxxxx, "Michal Marek" <michal.lkml@xxxxxxxxxxx>, "Nick
> >  Desaulniers" <ndesaulniers@xxxxxxxxxx>, "Linux Kbuild mailing list" <linux-kbuild@xxxxxxxxxxxxxxx>, "Linux Kernel Mailing List" <linux-kernel@xxxxxxxxxxxxxxx>, "Jing Leng" <jleng@xxxxxxxxxxxxx>
> > 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@xxxxxxxxxx> wrote:
> > >>
> > >> From: Jing Leng <jleng@xxxxxxxxxxxxx>
> > >>
> > >> 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@xxxxxxxxxxxxx>
> > >> ---
> > >>  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