[PATCH 5.4 5/6] kbuild: add $(CLANG_FLAGS) to KBUILD_CPPFLAGS

[Nathan Chancellor <nathan@kernel.org>]

From: Masahiro Yamada <masahiroy@kernel.org>

commit feb843a469fb0ab00d2d23cfb9bcc379791011bb upstream.

When preprocessing arch/*/kernel/vmlinux.lds.S, the target triple is
not passed to $(CPP) because we add it only to KBUILD_{C,A}FLAGS.

As a result, the linker script is preprocessed with predefined macros
for the build host instead of the target.

Assuming you use an x86 build machine, compare the following:

 $ clang -dM -E -x c /dev/null
 $ clang -dM -E -x c /dev/null -target aarch64-linux-gnu

There is no actual problem presumably because our linker scripts do not
rely on such predefined macros, but it is better to define correct ones.

Move $(CLANG_FLAGS) to KBUILD_CPPFLAGS, so that all *.c, *.S, *.lds.S
will be processed with the proper target triple.

[Note]
After the patch submission, we got an actual problem that needs this
commit. (CBL issue 1859)

Link: https://github.com/ClangBuiltLinux/linux/issues/1859
Reported-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 Makefile | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index f65e282f4a3f..16a23aaaa547 100644
--- a/Makefile
+++ b/Makefile
@@ -568,8 +568,7 @@ ifneq ($(LLVM_IAS),1)
 CLANG_FLAGS	+= -no-integrated-as
 endif
 CLANG_FLAGS	+= -Werror=unknown-warning-option
-KBUILD_CFLAGS	+= $(CLANG_FLAGS)
-KBUILD_AFLAGS	+= $(CLANG_FLAGS)
+KBUILD_CPPFLAGS	+= $(CLANG_FLAGS)
 export CLANG_FLAGS
 endif
 
-- 
2.50.1