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

[Lucas De Marchi]

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@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.

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