Re: [PATCH v3 2/2] Makefile: infer CROSS_COMPILE from SRCARCH for CC=clang LLVM_IAS=1

[Arnd Bergmann]

On Thu, Jul 29, 2021 at 6:50 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
>
> We get constant feedback that the command line invocation of make is too
> long. CROSS_COMPILE is helpful when a toolchain has a prefix of the
> target triple, or is an absolute path outside of $PATH, but it's mostly
> redundant for a given SRCARCH. SRCARCH itself is derived from ARCH
> (normalized for a few different targets).
>
> If CROSS_COMPILE is not set, simply set --target= for CLANG_FLAGS,
> KBUILD_CFLAGS, and KBUILD_AFLAGS based on $SRCARCH.
>
> Previously, we'd cross compile via:
> $ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make LLVM=1 LLVM_IAS=1
> Now:
> $ ARCH=arm64 make LLVM=1 LLVM_IAS=1
>
> For native builds (not involving cross compilation) we now explicitly
> specify a target triple rather than rely on the implicit host triple.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1399
> Suggested-by: Arnd Bergmann <arnd@xxxxxxxxxx>
> Suggested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Suggested-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

Looks good to me,

Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

> +else
> +$(error Specify CROSS_COMPILE or add '--target=' option to scripts/Makefile.clang)
> +endif # SRCARCH
> +endif # LLVM_IAS

Now in theory I suppose we could just have the fallback use
--target="$(SRCARCH)-linux-gnu"
to avoid having to change this for every new architecture. I think in
most cases, this
would just work, even though a lot of the one you listed have
different patterns.

       Arnd