From: Nathan Chancellor <natechancellor@gmail.com>
To: Masahiro Yamada <yamada.masahiro@socionext.com>,
Michal Marek <michal.lkml@markovi.net>,
linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: clang-built-linux@googlegroups.com,
Nick Desaulniers <ndesaulniers@google.com>,
Nathan Chancellor <natechancellor@gmail.com>,
Peter Smith <peter.smith@linaro.org>
Subject: [PATCH] kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS
Date: Tue, 11 Jun 2019 11:43:31 -0700 [thread overview]
Message-ID: <20190611184331.44242-1-natechancellor@gmail.com> (raw)
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@linaro.org>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
Makefile | 1 +
1 file changed, 1 insertion(+)
diff --git a/Makefile b/Makefile
index b81e17261250..5f9d09bd2252 100644
--- a/Makefile
+++ b/Makefile
@@ -528,6 +528,7 @@ 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
--
2.22.0
next reply other threads:[~2019-06-11 18:43 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-11 18:43 Nathan Chancellor [this message]
2019-06-11 19:37 ` [PATCH] kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS Nick Desaulniers
2019-06-20 14:23 ` Masahiro Yamada
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