From: Nathan Chancellor <natechancellor@xxxxxxxxx> [ 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@xxxxxxxxxx> Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx> Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- Makefile | 1 + 1 file changed, 1 insertion(+) diff --git a/Makefile b/Makefile index c80dad45334e..60b562dbd97f 100644 --- a/Makefile +++ b/Makefile @@ -515,6 +515,7 @@ 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) endif -- 2.20.1