linux-kernel - [PATCH] kbuild: add $(CLANG_CFLAGS) to KBUILD

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Date:   Sun,  9 Apr 2023 23:53:57 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Tom Rini <trini@...sulko.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>, Tom Rix <trix@...hat.com>,
        llvm@...ts.linux.dev
Subject: [PATCH] kbuild: add $(CLANG_CFLAGS) to KBUILD_CPPFLAGS

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

Reported-by: Tom Rini <trini@...sulko.com>
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 scripts/Makefile.clang | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
index 70b354fa1cb4..93ca059cc3b8 100644
--- a/scripts/Makefile.clang
+++ b/scripts/Makefile.clang
@@ -38,6 +38,5 @@ CLANG_FLAGS	+= -Werror=unknown-warning-option
 CLANG_FLAGS	+= -Werror=ignored-optimization-argument
 CLANG_FLAGS	+= -Werror=option-ignored
 CLANG_FLAGS	+= -Werror=unused-command-line-argument
-KBUILD_CFLAGS	+= $(CLANG_FLAGS)
-KBUILD_AFLAGS	+= $(CLANG_FLAGS)
+KBUILD_CPPFLAGS	+= $(CLANG_FLAGS)
 export CLANG_FLAGS
-- 
2.37.2