linux-kernel - [PATCH v3 1/2] kbuild: replace AS=clang with LLVM

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Message-Id: <20200408013623.31974-1-masahiroy@kernel.org>
Date:   Wed,  8 Apr 2020 10:36:22 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     clang-built-linux@...glegroups.com,
        Fangrui Song <maskray@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 1/2] kbuild: replace AS=clang with LLVM_IAS=1

The 'AS' variable is unused for building the kernel. Only the remaining
usage is to turn on the integrated assembler. A boolean flag is a better
fit for this purpose.

AS=clang was added for experts. So, I replaced it with LLVM_IAS=1,
breaking the backward compatibility.

Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
---

Changes in v3:
  - rename LLVM_IA to LLVM_IAS (per Fangrui Song)

Changes in v2:
  - new patch

 Documentation/kbuild/llvm.rst | 5 ++++-
 Makefile                      | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
index eefbdfa3e4d9..0fefdf1737e9 100644
--- a/Documentation/kbuild/llvm.rst
+++ b/Documentation/kbuild/llvm.rst
@@ -50,11 +50,14 @@ LLVM Utilities
 LLVM has substitutes for GNU binutils utilities. These can be invoked as
 additional parameters to `make`.
 
-	make CC=clang AS=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
+	make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \\
 	  OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump OBJSIZE=llvm-size \\
 	  READELF=llvm-readelf HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar \\
 	  HOSTLD=ld.lld
 
+Currently, the integrated assembler is disabled by default. You can pass
+LLVM_IAS=1 to enable it.
+
 Getting Help
 ------------
 
diff --git a/Makefile b/Makefile
index 1b2691057cb5..a2aadcf8a36c 100644
--- a/Makefile
+++ b/Makefile
@@ -538,7 +538,7 @@ endif
 ifneq ($(GCC_TOOLCHAIN),)
 CLANG_FLAGS	+= --gcc-toolchain=$(GCC_TOOLCHAIN)
 endif
-ifeq ($(if $(AS),$(shell $(AS) --version 2>&1 | head -n 1 | grep clang)),)
+ifneq ($(LLVM_IAS),1)
 CLANG_FLAGS	+= -no-integrated-as
 endif
 CLANG_FLAGS	+= -Werror=unknown-warning-option
-- 
2.17.1