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

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Message-ID: <CAKwvOdm6yK3jK45AV2FULQAw614nfJi17RVAESH+wV11i+pMLw@mail.gmail.com>
Date:   Tue, 20 Jul 2021 13:18:02 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        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>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        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 20, 2021 at 12:58 PM Arnd Bergmann <arnd@...nel.org> wrote:
>
> On Tue, Jul 20, 2021 at 7:43 PM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> > On Tue, Jul 20, 2021 at 1:05 AM Masahiro Yamada <masahiroy@...nel.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.

Right, there are many Kconfigs that are predicated on knowing whether
the user is building with gcc vs clang.  We probably could note the
users preference in Kconfig, but we would need to guarantee that we
evaluate that ASAP and before most other Kconfigs were checked.
-- 
Thanks,
~Nick Desaulniers