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

[Jing Leng]

> -----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 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

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