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Message-Id: <20190729190843.308435390@linuxfoundation.org>
Date: Mon, 29 Jul 2019 21:22:17 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Peter Smith <peter.smith@...aro.org>,
Nathan Chancellor <natechancellor@...il.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 246/293] kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS
[ Upstream commit 589834b3a0097a4908f4112eac0ca2feb486fa32 ]
In commit ebcc5928c5d9 ("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 c3f0d0bc5b01 ("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/517
Suggested-by: Peter Smith <peter.smith@...aro.org>
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
Makefile | 1 +
1 file changed, 1 insertion(+)
diff --git a/Makefile b/Makefile
index 97c744513af0..bbc9b6acb177 100644
--- a/Makefile
+++ b/Makefile
@@ -488,6 +488,7 @@ 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
--
2.20.1
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