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

[Joe Lawrence]

On 12/16/20 1:14 AM, Masahiro Yamada wrote:
> On Tue, Dec 8, 2020 at 11:31 PM Artem Savkov <artem.savkov@xxxxxxxxx> wrote:
> > On Tue, Dec 08, 2020 at 05:20:35PM +0800, WANG Chao wrote:
> > > 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@xxxxxxxxx> wrote:
> > > > > On 11/23/20 at 02:23P, Masahiro Yamada wrote:
> > > > > > On Tue, Nov 3, 2020 at 3:23 PM WANG Chao <chao.wang@xxxxxxxxx> 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@xxxxxxxxx>
> > > > > > > ---
> > > > > > >   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@xxxxxxxxxx/
> > > > > >
> > > > > >
> > > > > > 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
> >
> > We want linker script to be used on both those steps, otherwise modpost
> > fails.
>
>
> In that case, does the following work?
> (untested)
>
>
>
> diff --git a/kmod/patch/Makefile b/kmod/patch/Makefile
> index e017b17..02d4c66 100644
> --- a/kmod/patch/Makefile
> +++ b/kmod/patch/Makefile
> @@ -12,7 +12,9 @@ endif
>
>   obj-m += $(KPATCH_NAME).o
>   ldflags-y += -T $(src)/kpatch.lds
> -extra-y := kpatch.lds
> +targets += kpatch.lds
> +
> +$(obj)/$(KPATCH_NAME).o: $(obj)/kpatch.lds
>
>   $(KPATCH_NAME)-objs += patch-hook.o output.o

Hi Masahiro,

Yeah this is more or less what Artem came up with:
https://github.com/dynup/kpatch/pull/1149

though we hadn't added kpatch.lds to targets.  Is there documentation 
somewhere on what effect "targets" has for out-of-tree builds?

Thanks,

-- Joe