LinuxLists.cc - [PATCH] kbuild: add extra-y to targets-for-modules

2020-11-03 11:50:29

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

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 <[email protected]>
---
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

2020-11-23 06:22:41

by Masahiro Yamada

[permalink] [raw]

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

On Tue, Nov 3, 2020 at 3:23 PM WANG Chao <[email protected]> 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 <[email protected]>
> ---
> 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/[email protected]/

Probably what you should use is 'targets'.

--
Best Regards
Masahiro Yamada

2020-11-24 00:32:23

by WANG Chao

[permalink] [raw]

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

On 11/23/20 at 02:23P, Masahiro Yamada wrote:
> On Tue, Nov 3, 2020 at 3:23 PM WANG Chao <[email protected]> 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 <[email protected]>
> > ---
> > 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/[email protected]/
>
>
> 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.

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

2020-11-25 13:45:20

by Masahiro Yamada

[permalink] [raw]

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

On Tue, Nov 24, 2020 at 12:05 AM WANG Chao <[email protected]> wrote:
>
> On 11/23/20 at 02:23P, Masahiro Yamada wrote:
> > On Tue, Nov 3, 2020 at 3:23 PM WANG Chao <[email protected]> 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 <[email protected]>
> > > ---
> > > 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/[email protected]/
> >
> >
> > 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

2020-12-08 09:26:13

by WANG Chao

[permalink] [raw]

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

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 <[email protected]> wrote:
> >
> > On 11/23/20 at 02:23P, Masahiro Yamada wrote:
> > > On Tue, Nov 3, 2020 at 3:23 PM WANG Chao <[email protected]> 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 <[email protected]>
> > > > ---
> > > > 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/[email protected]/
> > >
> > >
> > > 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
>

2020-12-08 14:36:22

by Artem Savkov

[permalink] [raw]

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

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 <[email protected]> wrote:
> > >
> > > On 11/23/20 at 02:23P, Masahiro Yamada wrote:
> > > > On Tue, Nov 3, 2020 at 3:23 PM WANG Chao <[email protected]> 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 <[email protected]>
> > > > > ---
> > > > > 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/[email protected]/
> > > >
> > > >
> > > > 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.

It looks like the right thing to do here is leave ldflags-y in, get rid
of always-y/extra-y altogether and specify our linker script as a
dependency for the object.

> 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
> >
>

--
Regards,
Artem Savkov

2020-12-17 08:30:55

by Masahiro Yamada

[permalink] [raw]

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

On Thu, Dec 17, 2020 at 8:04 AM Joe Lawrence <[email protected]> wrote:
>
> On 12/16/20 1:14 AM, Masahiro Yamada wrote:
> > On Tue, Dec 8, 2020 at 11:31 PM Artem Savkov <[email protected]> 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 <[email protected]> wrote:
> >>>>>
> >>>>> On 11/23/20 at 02:23P, Masahiro Yamada wrote:
> >>>>>> On Tue, Nov 3, 2020 at 3:23 PM WANG Chao <[email protected]> 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 <[email protected]>
> >>>>>>> ---
> >>>>>>> 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/[email protected]/
> >>>>>>
> >>>>>>
> >>>>>> 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
>

Please try the rebuild without changing any source code.

If kpatch.lds is needlessly rebuilt, you need to add
it to 'targets'.

In linux-next, this is documented.

Documentation/kbuild/makefile.rst:

Any target that utilizes if_changed must be listed in $(targets),
otherwise the command line check will fail, and the target will
always be built.

--
Best Regards
Masahiro Yamada

2020-12-17 12:06:53

by Artem Savkov

[permalink] [raw]

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

On Thu, Dec 17, 2020 at 05:26:07PM +0900, Masahiro Yamada wrote:
> On Thu, Dec 17, 2020 at 8:04 AM Joe Lawrence <[email protected]> wrote:
> >
> > On 12/16/20 1:14 AM, Masahiro Yamada wrote:
> > > On Tue, Dec 8, 2020 at 11:31 PM Artem Savkov <[email protected]> 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 <[email protected]> wrote:
> > >>>>>
> > >>>>> On 11/23/20 at 02:23P, Masahiro Yamada wrote:
> > >>>>>> On Tue, Nov 3, 2020 at 3:23 PM WANG Chao <[email protected]> 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 <[email protected]>
> > >>>>>>> ---
> > >>>>>>> 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/[email protected]/
> > >>>>>>
> > >>>>>>
> > >>>>>> 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
> >
>
>
> Please try the rebuild without changing any source code.
>
> If kpatch.lds is needlessly rebuilt, you need to add
> it to 'targets'.
>
>
> In linux-next, this is documented.
>
> Documentation/kbuild/makefile.rst:
>
> Any target that utilizes if_changed must be listed in $(targets),
> otherwise the command line check will fail, and the target will
> always be built.

Ah yes, it did rebuild every time. Thank you for the pointer.

--
Artem

2022-01-18 02:28:08

by Artem Savkov

[permalink] [raw]