[PATCH 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS

Nathan Chancellor
2021-08-24T02:27:37Z

Similar to commit 589834b3a009 ("kbuild: Add
-Werror=unknown-warning-option to CLANG_FLAGS").

Clang ignores certain GCC flags that it has not implemented, only
emitting a warning:

$ echo | clang -fsyntax-only -falign-jumps -x c -
clang-14: warning: optimization flag '-falign-jumps' is not supported
[-Wignored-optimization-argument]

When one of these flags gets added to KBUILD_CFLAGS unconditionally, all
subsequent cc-{disable-warning,option} calls fail because -Werror was
added to these invocations to turn the above warning and the equivalent
-W flag warning into errors.

To catch the presence of these flags earlier, turn
-Wignored-optimization-argument into an error so that the flags can
either be implemented or ignored via cc-option and there are no more
weird errors.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
scripts/Makefile.clang | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
index 4cce8fd0779c..2fe38a9fdc11 100644
--- a/scripts/Makefile.clang
+++ b/scripts/Makefile.clang
@@ -29,7 +29,11 @@ CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
else
CLANG_FLAGS += -fintegrated-as
endif
+# By default, clang only warns on unknown warning or optimization flags
+# Make it behave more like gcc by erroring when these flags are encountered
+# so they can be implemented or wrapped in cc-option.
CLANG_FLAGS += -Werror=unknown-warning-option
+CLANG_FLAGS += -Werror=ignored-optimization-argument
KBUILD_CFLAGS += $(CLANG_FLAGS)
KBUILD_AFLAGS += $(CLANG_FLAGS)
export CLANG_FLAGS
--
2.33.0