Commit 27f2335e authored by Nathan Chancellor's avatar Nathan Chancellor Committed by Greg Kroah-Hartman

kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS

[ Upstream commit 589834b3 ]

In commit ebcc5928 ("arm64: Silence gcc warnings about arch ABI
drift"), the arm64 Makefile added -Wno-psabi to KBUILD_CFLAGS, which is
a GCC only option so clang rightfully complains:

warning: unknown warning option '-Wno-psabi' [-Wunknown-warning-option]

https://clang.llvm.org/docs/DiagnosticsReference.html#wunknown-warning-option

However, by default, this is merely a warning so the build happily goes
on with a slew of these warnings in the process.

Commit c3f0d0bc ("kbuild, LLVMLinux: Add -Werror to cc-option to
support clang") worked around this behavior in cc-option by adding
-Werror so that unknown flags cause an error. However, this all happens
silently and when an unknown flag is added to the build unconditionally
like -Wno-psabi, cc-option will always fail because there is always an
unknown flag in the list of flags. This manifested as link time failures
in the arm64 libstub because -fno-stack-protector didn't get added to
KBUILD_CFLAGS.

To avoid these weird cryptic failures in the future, make clang behave
like gcc and immediately error when it encounters an unknown flag by
adding -Werror=unknown-warning-option to CLANG_FLAGS. This can be added
unconditionally for clang because it is supported by at least 3.0.0,
according to godbolt [1] and 4.0.0, according to its documentation [2],
which is far earlier than we typically support.

[1]: https://godbolt.org/z/7F7rm3
[2]: https://releases.llvm.org/4.0.0/tools/clang/docs/DiagnosticsReference.html#wunknown-warning-option

Link: https://github.com/ClangBuiltLinux/linux/issues/511
Link: https://github.com/ClangBuiltLinux/linux/issues/517Suggested-by: default avatarPeter Smith <peter.smith@linaro.org>
Signed-off-by: default avatarNathan Chancellor <natechancellor@gmail.com>
Tested-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 1fa94381
......@@ -491,6 +491,7 @@ ifneq ($(GCC_TOOLCHAIN),)
CLANG_FLAGS += --gcc-toolchain=$(GCC_TOOLCHAIN)
endif
CLANG_FLAGS += -no-integrated-as
CLANG_FLAGS += -Werror=unknown-warning-option
KBUILD_CFLAGS += $(CLANG_FLAGS)
KBUILD_AFLAGS += $(CLANG_FLAGS)
export CLANG_FLAGS
......
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