linux-kernel - Re: [PATCH] kbuild: add extra-y to targets-for-modules

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Message-ID: <CAK7LNASH7Pj9eUdxF-sp1_Ap+uA9jEtsXa--pUDDw_pNVLtviA@mail.gmail.com>
Date:   Wed, 25 Nov 2020 22:42:28 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     WANG Chao <chao.wang@...oud.cn>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH] kbuild: add extra-y to targets-for-modules

On Tue, Nov 24, 2020 at 12:05 AM WANG Chao <chao.wang@...oud.cn> wrote:
>
> On 11/23/20 at 02:23P, Masahiro Yamada wrote:
> > On Tue, Nov 3, 2020 at 3:23 PM WANG Chao <chao.wang@...oud.cn> wrote:
> > >
> > > extra-y target doesn't build for 'make M=...' since commit 6212804f2d78
> > > ("kbuild: do not create built-in objects for external module builds").
> > >
> > > This especially breaks kpatch, which is using 'extra-y := kpatch.lds'
> > > and 'make M=...' to build livepatch patch module.
> > >
> > > Add extra-y to targets-for-modules so that such kind of build works
> > > properly.
> > >
> > > Signed-off-by: WANG Chao <chao.wang@...oud.cn>
> > > ---
> > >  scripts/Makefile.build | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> > > index ae647379b579..0113a042d643 100644
> > > --- a/scripts/Makefile.build
> > > +++ b/scripts/Makefile.build
> > > @@ -86,7 +86,7 @@ ifdef need-builtin
> > >  targets-for-builtin += $(obj)/built-in.a
> > >  endif
> > >
> > > -targets-for-modules := $(patsubst %.o, %.mod, $(filter %.o, $(obj-m)))
> > > +targets-for-modules := $(extra-y) $(patsubst %.o, %.mod, $(filter %.o, $(obj-m)))
> > >
> > >  ifdef need-modorder
> > >  targets-for-modules += $(obj)/modules.order
> > > --
> > > 2.29.1
> > >
> >
> > NACK.
> >
> > Please fix your Makefile.
> >
> > Hint:
> > https://patchwork.kernel.org/project/linux-kbuild/patch/20201123045403.63402-6-masahiroy@kernel.org/
> >
> >
> > Probably what you should use is 'targets'.
>
> I tried with 'targets' and 'always-y'. Both doesn't work for me.
>
> I narraw it down to the following example:
>
> cat > Makefile << _EOF_
> obj-m += foo.o
>
> ldflags-y += -T $(src)/kpatch.lds
> always-y += kpatch.lds
>
> foo-objs += bar.o
>
> all:
>         make -C /lib/modules/$(shell uname -r)/build M=$(PWD)
> clean:
>         make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
> _EOF_
>
> Take a look into scripts/Makefile.build:488:
>
> __build: $(if $(KBUILD_BUILTIN), $(targets-for-builtin)) \
>          $(if $(KBUILD_MODULES), $(targets-for-modules)) \
>          $(subdir-ym) $(always-y)
>         @:
>
> 'always-y' is built after 'targets-for-modules'. This makes
> 'targets-for-modules' fails because kpatch.lds isn't there.


Heh, you rely on the targets built from left to right,
and you have never thought Make supports the parallel option -j.


You need to specify the dependency if you expect objects
are built in the particular order.

However, in this case, using ldflags-y looks wrong
in the first place.

The linker script is used when combining the object
as well as the final link of *.ko


> For 'targets', in case of OOT, does not seem to be useful.
>
> What change do you suggest to make to fix this kind of Makefile?
>
> Thanks,
> WANG Chao



-- 
Best Regards
Masahiro Yamada