linux-kernel - Re: [PATCH 2/2] Makefile: Only specify '--prefix=' when building with clang + GNU as

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Date:   Wed, 10 Mar 2021 04:55:00 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH 2/2] Makefile: Only specify '--prefix=' when building with
 clang + GNU as

On Wed, Mar 3, 2021 at 6:07 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> When building with LLVM_IAS=1, there is no point to specifying
> '--prefix=' because that flag is only used to find the cross assembler,
> which is clang itself when building with LLVM_IAS=1. All of the other
> tools are invoked directly from PATH or a full path specified via the
> command line, which does not depend on the value of '--prefix='.
>
> Sharing commands to reproduce issues becomes a little bit easier without
> a '--prefix=' value because that '--prefix=' value is specific to a
> user's machine due to it being an absolute path.
>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>


I was tricked by a couple of Reviewed-by/Tested-by tags.

With this patch applied, the code looks as follows:


ifneq ($(CROSS_COMPILE),)
CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
ifneq ($(LLVM_IAS),1)
GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
CLANG_FLAGS += -no-integrated-as
endif
endif


For the native build (empty CROSS_COMPILE),
you cannot add -no-integrated-as.


I dropped this from my tree.



Is the correct code as follows?


ifneq ($(LLVM_IAS),1)
CLANG_FLAGS += -no-integrated-as
ifneq ($(CROSS_COMPILE),)
CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
endif
endif






> ---
>  Makefile | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index c20f0ad8be73..0413b8c594cd 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -566,12 +566,12 @@ CC_VERSION_TEXT = $(shell $(CC) --version 2>/dev/null | head -n 1 | sed 's/\#//g
>  ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
>  ifneq ($(CROSS_COMPILE),)
>  CLANG_FLAGS    += --target=$(notdir $(CROSS_COMPILE:%-=%))
> +ifneq ($(LLVM_IAS),1)
>  GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
>  CLANG_FLAGS    += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
> -endif
> -ifneq ($(LLVM_IAS),1)
>  CLANG_FLAGS    += -no-integrated-as
>  endif
> +endif
>  CLANG_FLAGS    += -Werror=unknown-warning-option
>  KBUILD_CFLAGS  += $(CLANG_FLAGS)
>  KBUILD_AFLAGS  += $(CLANG_FLAGS)
> --
> 2.31.0.rc0.75.gec125d1bc1
>


-- 
Best Regards
Masahiro Yamada