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

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Message-ID: <CAK8P3a2kb2Zzgd1wvi4m2fJeHWA9aONXUriEVfnsOfYTquJ3eA@mail.gmail.com>
Date:   Tue, 27 Jul 2021 09:49:09 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Fangrui Song <maskray@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Christoph Hellwig <hch@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v2 2/2] Makefile: infer CROSS_COMPILE from SRCARCH for
 LLVM=1 LLVM_IAS=1

On Tue, Jul 27, 2021 at 9:07 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Mon, Jul 26, 2021 at 10:27 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
> > Masahiro Yamada <masahiroy@...nel.org> writes:
> > > On Wed, Jul 21, 2021 at 4:58 AM Arnd Bergmann <arnd@...nel.org> wrote:
> >
> > Does anyone have any ideas?
> >
> > Something so we don't have to specify all of these variables on the make
> > command line would be nice.
>
> Just including the main Makefile does not work.
> That's why I went with the more convoluted solution in
> https://lore.kernel.org/linux-kbuild/CAMuHMdXJBqrpzaSNDJgic14ESiHV6cCcb_5E-st6iniXdmm9_g@mail.gmail.com/

This is roughly what I use as well, but it does have the downside that
it confuses
the inner 'make' when you build multiple targets in parallel, e.g.

make -skj30 kernel/ mm/ init/

works with the normal Makefile, but fails spectacularly with my nested
GNUmakefile because it starts multiple sub-processes that each try to
build the same preparation files (I did not try your version).

What I had in mind was to use something like (but not exactly)

-include $(O)/Makefile.cross

to conditionally include another file from the top-level Makefile before
doing anything else.

          Arnd