Re: [PATCH v2 2/2] Makefile: infer CROSS_COMPILE from SRCARCH for LLVM=1 LLVM_IAS=1

[Masahiro Yamada <masahiroy@kernel.org>]

On Sat, Jul 24, 2021 at 4:54 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> Hi Yamada-san,
>
> On Wed, Jul 21, 2021 at 6:05 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > On Wed, Jul 21, 2021 at 4:58 AM Arnd Bergmann <arnd@kernel.org> wrote:
> > > On Tue, Jul 20, 2021 at 7:43 PM Linus Torvalds
> > > <torvalds@linux-foundation.org> wrote:
> > > > On Tue, Jul 20, 2021 at 1:05 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > > >
> > > > We do most of the other heavy lifting in this area in Kconfig anyway,
> > > > why not add that compiler choice?
> > > >
> > > > Obviously it would be gated by the tests to see which compilers are
> > > > _installed_ (and that they are valid versions), so that it doesn't ask
> > > > stupid things ("do you want gcc or clang" when only one of them is
> > > > installed and/or viable).
> > >
> > > I don't see a good way of making Kconfig options both select the
> > > compiler and defining variables based on the compiler, since that
> > > would mean teaching Kconfig about re-evaluating all compiler
> > > dependent settings whenever the first option changes.
> > >
> > > I do have another idea that I think would work though.
> > >
> > > > Hmm? So then any "LLVM=1" thing would be about the "make config"
> > > > stage, not the actual build stage.
> > > >
> > > > (It has annoyed me for years that if you want to cross-compile, you
> > > > first have to do "make ARCH=xyz config" and then remember to do "make
> > > > ARCH=xyz" for the build too, but I cross-compile so seldom that I've
> > > > never really cared).
> > >
> > > The best thing that I have come up with is a pre-configure step, where
> > > an object tree gets seeded with a makefile fragment that gets included
> > > for any 'make' invocation. This would set 'ARCH=', 'CROSS_COMPILE',
> > > 'CC=' and possibly any other option that gets passed to 'make' as
> > > a variable and has to exist before calling 'make *config'.
> >
> >
> > There is no need to add a hook to include such makefile fragment(s).
> >
> > Quite opposite, you can put your Makefile (in a different filename)
> > that includes the top Makefile.
> >
> >
> > I think this is what people are already doing:
> >
> >
> > GNU Make looks for 'GNUmakefile', 'makefile', and 'Makefile'
> > in this order.
>
> Exactly. I only have a few source repositories, but lots of build directories
> (I never build in a repo directory). Each build directory has a GNUmakefile:
>
>     build/linux-riscv-starlight$ cat GNUmakefile
>     MAKEARGS = ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-
>
>     include ~/linux/default.mk
>     build/linux-riscv-starlight$ cat ~/linux/default.mk
>     MAKEFLAGS += --no-print-directory
>
>     .PHONY: all $(MAKECMDGOALS)
>
>     all := $(filter-out all Makefile,$(MAKECMDGOALS))
>
>     all:
>             @$(MAKE) $(MAKEARGS) $(all) -f Makefile
>
>     Makefile:;
>
>     $(all): all
>             @:
>
>     %/: all
>             @:
>     build/linux-riscv-starlight$
>
> Perhaps we could have a "make setup ARCH=foo CROSS_COMPILE=bar" target,
> which creates such a GNUmakefile?

No, I do not think so.

Your GNUmakefile is customized in your way.
Other people implement GNUmakefile in their own way.

Upstream is not a place to merge everybody's local tools.








> P.S. I put the extra logic in ~/linux/default.mk, so I don't have to update all
>      GNUmakefiles when I want to make a change to the main logic.
>
>      For build dirs where I want to track a specific config, I have a slightly
>      different version:
>
>          build/linux-m68k-allmodconfig-sun3$ cat GNUmakefile
>          MAKEARGS = ARCH=m68k KCONFIG_ALLCONFIG=1
>          DEFCONFIG = allmodconfig
>
>          include ~/linux/override-oldconfig.mk
>          build/linux-m68k-allmodconfig-sun3$ cat ~/linux/override-oldconfig.mk
>          MAKEFLAGS += --no-print-directory
>
>          .PHONY: all oldconfig realoldconfig $(MAKECMDGOALS)
>
>          all := $(filter-out all oldconfig realoldconfig
> Makefile,$(MAKECMDGOALS))
>
>          all:
>                  @$(MAKE) $(MAKEARGS) $(all) -f Makefile
>
>          # Replace oldconfig by $(DEFCONFIG)
>          oldconfig:
>                  @$(MAKE) $(MAKEARGS) $(DEFCONFIG) -f Makefile
>
>          realoldconfig:
>                  @$(MAKE) $(MAKEARGS) oldconfig -f Makefile
>
>          Makefile:;
>
>          $(all): all
>                  @:
>
>          %/: all
>                  @:
>          build/linux-m68k-allmodconfig-sun3$
>
>      That way I can always just type "make oldconfig", and it will do what
>      I want.
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
>
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-- 
Best Regards
Masahiro Yamada