linux-kernel - Re: [PATCH v4 1/2] Makefile: infer --target from ARCH for CC=clang

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Date:   Fri, 30 Jul 2021 14:54:15 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     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 v4 1/2] Makefile: infer --target from ARCH for CC=clang

On Fri, Jul 30, 2021 at 1:17 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> +ifeq ($(SRCARCH),arm)
> +CLANG_FLAGS    += --target=arm-linux-gnueabi
..,.

Ugh.

A wise man once said: "All problems in computer science can be solved
with another level of indirection".

Just do it like this:

   CLANG_TARGET_FLAGS_arm = arm-linux-gnueabi
   CLANG_TARGET_FLAGS_hexagon = hexagon-linux-gnu
   ..
   CLANG_TARGET_FLAGS = $(CLANG_TARGET_FLAGS_$(ARCH))

Which is a lot denser and simpler.

And then the only if-statement can be something along the lines of

   ifeq ($(CLANG_TARGET_FLAGS),)
   $(error Specify clang target flags)
   else
   CLANG_FLAGS    += --target=$(CLANG_TARGET_FLAGS)
   endif

Plus add *random handwaving* about all the details for CROSS_COMPILE
and friends.

            Linus