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

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Date:   Wed, 21 Jul 2021 05:52:42 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Fangrui Song <maskray@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Arnd Bergmann <arnd@...nel.org>,
        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 02:54:35PM -0700, Linus Torvalds wrote:
> But there are other things that stick around. In particular, I have
> considered simply using git config variables for that.
> 
> Something like this in the main Makefile:
> 
>     ARCH=$(shell git config build.arch)
>     CC=$(shell git config --default=gcc build.cc)
> 
> would actually be optimal for what _I_ do. Then for my clang build tree, I'd do
> 
>     git config build.cc clang
> 
> and it would stick in that tree. If you don't set the option, it would use gcc.
> 
> Maybe that would be an acceptable model these days? We've used git
> long enough that non-git worries aren't a big deal any more, and I
> guess people could use the old-fashioned

I still this only papers around the fact that the architecture is
fundamentally part of the kernel config and should come from .config,
and the toolchain probably as well.

I for one do have a few different tree for different projects, but
need to try cross compiles in each of them.  And unfortunately sometimes
with clang (nothing against clang itself [1], just that having to deal
with multiple toolchains is a pain)

[1] well, except for the sometimes idiotic diagnostics..