From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f67.google.com ([209.85.208.67]:40286 "EHLO mail-ed1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391882AbfFKSnv (ORCPT ); Tue, 11 Jun 2019 14:43:51 -0400 From: Nathan Chancellor Subject: [PATCH] kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS Date: Tue, 11 Jun 2019 11:43:31 -0700 Message-Id: <20190611184331.44242-1-natechancellor@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: Masahiro Yamada , Michal Marek , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org Cc: clang-built-linux@googlegroups.com, Nick Desaulniers , Nathan Chancellor , Peter Smith 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 Signed-off-by: Nathan Chancellor --- 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