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@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

2 files changed, 5 insertions, 2 deletions

diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
index eefbdfa3e4d9..450708534860 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