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

From: WANG Chao <chao.wang@ucloud.cn>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	artem.savkov@gmail.com, joe.lawrence@redhat.com
Subject: Re: [PATCH] kbuild: add extra-y to targets-for-modules
Date: Tue, 8 Dec 2020 17:20:35 +0800	[thread overview]
Message-ID: <20201208092035.GA96434@MacBook-Pro-2.local> (raw)
In-Reply-To: <CAK7LNASH7Pj9eUdxF-sp1_Ap+uA9jEtsXa--pUDDw_pNVLtviA@mail.gmail.com>

Sorry for the late reply.

On 11/25/20 at 10:42P, Masahiro Yamada wrote:
> On Tue, Nov 24, 2020 at 12:05 AM WANG Chao <chao.wang@ucloud.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@ucloud.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@ucloud.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're right. I missed that.

> 
> 
> 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

I don't have a clean fix to kpatch right now.

I'm looping kpatch forks in. They're also looking at this right now:

https://github.com/dynup/kpatch/pull/1149

Thanks
WANG Chao

> 
> 
> > 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
> 