linux-kernel - Re: [PATCH 2/2] Makefile: drop CROSS_COMPILE for LLVM=1 LLVM

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Date:   Thu, 8 Jul 2021 13:44:52 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     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>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH 2/2] Makefile: drop CROSS_COMPILE for LLVM=1 LLVM_IAS=1

On Thu, Jul 8, 2021 at 12:23 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> On Thu, Jul 8, 2021 at 7:43 AM 'Nick Desaulniers' via Clang Built
>
> We must rely on this behavior of Clang because
> --target (which is contained in CLANG_FLAGS)
> must be specified before the Kconfig time.
> Then, a user can toggle CONFIG_64BIT any time
> from menuconfig etc.
>
> With this in mind, using $(ARCH) as if-else
> switches is pointless.
> $(SRCARCH) is the only meaningful input.
>
>
>   else ifeq ($(ARCH),i386)
>   CLANG_FLAGS    += --target=i686-linux-gnu
>   else ifeq ($(ARCH),x86)
>   CLANG_FLAGS    += --target=x86_64-linux-gnu
>   else ifeq ($(ARCH),x86_64)
>   CLANG_FLAGS    += --target=x86_64-linux-gnu
>
> should be replaced with:
>
>   else ifeq ($(SRCARCH),x86_64)
>   CLANG_FLAGS    += --target=x86_64-linux-gnu

I think we usually only have to provide the architecture
name, as in "--target=x86_64", though for arm I get a
warning "clang: warning: unknown platform, assuming
-mfloat-abi=soft" unless I provide the full triple.

> For example for ARCH=arm, which is better
> --target=arm-linux-gnueabi or
> --target=arm-lnux-gnueabihf or something we don't care about?

The kernel is always soft-float itself, so it does not matter either way.

       Arnd