[RFC, 1/2] scripts/kconfig/Makefile: Allow KBUILD_DEFCONFIG to be a target

[Michael Ellerman]

On Wed, 2015-10-14 at 09:54 -0700, Olof Johansson wrote:
> On Tue, Oct 13, 2015 at 4:43 PM, Michael Ellerman <mpe at ellerman.id.au> wrote:
> > On Tue, 2015-10-13 at 14:02 -0700, Olof Johansson wrote:
> >> On Fri, Oct 2, 2015 at 12:47 AM, Michael Ellerman <mpe at ellerman.id.au> wrote:
> >> > On Wed, 2015-23-09 at 05:40:34 UTC, Michael Ellerman wrote:
> >> >> Arch Makefiles can set KBUILD_DEFCONFIG to tell kbuild the name of the
> >> >> defconfig that should be built by default.
> >> >>
> >> >> However currently there is an assumption that KBUILD_DEFCONFIG points to
> >> >> a file at arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG).
> >> >>
> >> >> We would like to use a target, using merge_config, as our defconfig, so
> >> >> adapt the logic in scripts/kconfig/Makefile to allow that.
> >> >>
> >> >> To minimise the chance of breaking anything, we first check if
> >> >> KBUILD_DEFCONFIG is a file, and if so we do the old logic. If it's not a
> >> >> file, then we call the top-level Makefile with KBUILD_DEFCONFIG as the
> >> >> target.
> >> >>
> >> >> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> >> >> Acked-by: Michal Marek <mmarek at suse.com>
> >> >
> >> > Applied to powerpc next.
> >> >
> >> > https://git.kernel.org/powerpc/c/d2036f30cfe1daa19e63ce75
> >>
> >> This breaks arm64 defconfig for me:
> >>
> >> mkdir obj-tmp
> >> make -f Makefile O=obj-tmp ARCH=arm64 defconfig
> >> ... watch loop of:
> >> *** Default configuration is based on target 'defconfig'
> >>   GEN     ./Makefile
> >
> > Crap, sorry. I knew I shouldn't have touched that code!
> >
> > Does this fix it for you?
> 
> Yes, it does, however:
> 
> > diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
> > index b2b9c87..3043d6b 100644
> > --- a/scripts/kconfig/Makefile
> > +++ b/scripts/kconfig/Makefile
> > @@ -96,7 +96,7 @@ savedefconfig: $(obj)/conf
> >  defconfig: $(obj)/conf
> >  ifeq ($(KBUILD_DEFCONFIG),)
> >         $< $(silent) --defconfig $(Kconfig)
> > -else ifneq ($(wildcard arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)),)
> > +else ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)),)
> >         @$(kecho) "*** Default configuration is based on '$(KBUILD_DEFCONFIG)'"
> >         $(Q)$< $(silent) --defconfig=arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG) $(Kconfig)
> 
> Do you need a $(srctree) prefix here too? I'm not entirely sure what I
> would do to reproduce a run that goes down this path so I can't
> confirm.

That is the path you're going down, now that it's fixed. That's the path where
KBUILD_DEFCONFIG is a real file, ie. the old behaviour.

I'm not sure why it doesn't have a $(srctree) there, but it's never had one.

It looks like it eventually boils down to zconf_fopen() which looks for the
file in both .  and $(srctree).

So I think we could add a $(srctree) there, it would be more obvious and not
rely on the zconf_fopen() behaviour, but I'd rather leave it as is and let
Michal do that as a cleanup later.

cheers