linux-kernel - [PATCH] kbuild: check CONFIG_AS_IS_LLVM instead of LLVM

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Message-Id: <20210805150102.131008-1-masahiroy@kernel.org>
Date:   Fri,  6 Aug 2021 00:01:02 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: [PATCH] kbuild: check CONFIG_AS_IS_LLVM instead of LLVM_IAS

LLVM_IAS is the user interface to set the -(no-)integrated-as flag,
and it should be used only for that purpose.

LLVM_IAS is checked in some places to determine the assembler type,
but it is not precise.

 $ make CC=gcc LLVM_IAS=1

... will use the GNU assembler since LLVM_IAS=1 is effective only when
$(CC) is clang.

Of course, the combination of CC=gcc and LLVM_IAS=1 does not make
sense, but the build system can be more robust against such insane
input.

Commit ba64beb17493a ("kbuild: check the minimum assembler version in
Kconfig") introduced CONFIG_AS_IS_GNU/LLVM, which is more precise
because Kconfig checks the version string from the assembler in use.

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 Makefile            | 2 +-
 arch/riscv/Makefile | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 4ab151060931..8b56c9692c3c 100644
--- a/Makefile
+++ b/Makefile
@@ -844,7 +844,7 @@ else
 DEBUG_CFLAGS	+= -g
 endif
 
-ifneq ($(LLVM_IAS),1)
+ifndef CONFIG_AS_IS_LLVM
 KBUILD_AFLAGS	+= -Wa,-gdwarf-2
 endif
 
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index bc74afdbf31e..dcfbd2a87d41 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -41,7 +41,7 @@ endif
 ifeq ($(CONFIG_LD_IS_LLD),y)
 	KBUILD_CFLAGS += -mno-relax
 	KBUILD_AFLAGS += -mno-relax
-ifneq ($(LLVM_IAS),1)
+ifndef CONFIG_AS_IS_LLVM
 	KBUILD_CFLAGS += -Wa,-mno-relax
 	KBUILD_AFLAGS += -Wa,-mno-relax
 endif
-- 
2.30.2