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Subject: Re: [PATCH] arm64: drop CROSS_COMPILE for LLVM=1 LLVM_IAS=1
To:     Nick Desaulniers <ndesaulniers@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Arnd Bergmann <arnd@kernel.org>,
        Fangrui Song <maskray@google.com>,
        Nathan Chancellor <nathan@kernel.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        clang-built-linux@googlegroups.com
References: <20210701235505.1792711-1-ndesaulniers@google.com>
From:   Tom Stellard <tstellar@redhat.com>
Message-ID: <bea79143-b2b8-b7a4-0456-4a593f03907f@redhat.com>
Date:   Thu, 1 Jul 2021 18:05:47 -0700
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On 7/1/21 4:55 PM, 'Nick Desaulniers' via Clang Built Linux 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 ARCH.
> 
> If CROSS_COMPILE is not set, simply set --target=aarch64-linux for
> CLANG_FLAGS, KBUILD_CFLAGS, and KBUILD_AFLAGS.
> 
> Previously, we'd cross compile via:
> $ ARCH=arm64 CROSS_COMPILE=aarch64-linxu-gnu make LLVM=1 LLVM_IAS=1
> Now:
> $ ARCH=arm64 make LLVM=1 LLVM_IAS=1
> 
> We can drop gnu from the triple, but dropping linux from the triple
> produces different .config files for the above invocations for the
> defconfig target.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1399
> Suggested-by: Arnd Bergmann <arnd@kernel.org>
> Suggested-by: Fangrui Song <maskray@google.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
>   arch/arm64/Makefile | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 7bc37d0a1b68..016873fddcc3 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile

Are there plans to do this for other architectures?

-Tom

> @@ -34,6 +34,17 @@ $(warning LSE atomics not supported by binutils)
>     endif
>   endif
>   
> +ifneq ($(LLVM),)
> +ifneq ($(LLVM_IAS),)
> +ifeq ($(CROSS_COMPILE),)
> +CLANG_TARGET	:=--target=aarch64-linux
> +CLANG_FLAGS	+= $(CLANG_TARGET)
> +KBUILD_CFLAGS	+= $(CLANG_TARGET)
> +KBUILD_AFLAGS	+= $(CLANG_TARGET)
> +endif
> +endif
> +endif
> +
>   cc_has_k_constraint := $(call try-run,echo				\
>   	'int main(void) {						\
>   		asm volatile("and w0, w0, %w0" :: "K" (4294967295));	\
>