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From: Nathan Chancellor <nathan@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, Masahiro Yamada <masahiroy@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
	clang-built-linux@googlegroups.com, llvm@lists.linux.dev,
	Nathan Chancellor <nathan@kernel.org>
Subject: [PATCH 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS
Date: Mon, 23 Aug 2021 19:26:40 -0700	[thread overview]
Message-ID: <20210824022640.2170859-3-nathan@kernel.org> (raw)
In-Reply-To: <20210824022640.2170859-1-nathan@kernel.org>

Similar to commit 589834b3a009 ("kbuild: Add
-Werror=unknown-warning-option to CLANG_FLAGS").

Clang ignores certain GCC flags that it has not implemented, only
emitting a warning:

$ echo | clang -fsyntax-only -falign-jumps -x c -
clang-14: warning: optimization flag '-falign-jumps' is not supported
[-Wignored-optimization-argument]

When one of these flags gets added to KBUILD_CFLAGS unconditionally, all
subsequent cc-{disable-warning,option} calls fail because -Werror was
added to these invocations to turn the above warning and the equivalent
-W flag warning into errors.

To catch the presence of these flags earlier, turn
-Wignored-optimization-argument into an error so that the flags can
either be implemented or ignored via cc-option and there are no more
weird errors.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 scripts/Makefile.clang | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
index 4cce8fd0779c..2fe38a9fdc11 100644
--- a/scripts/Makefile.clang
+++ b/scripts/Makefile.clang
@@ -29,7 +29,11 @@ CLANG_FLAGS	+= --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
 else
 CLANG_FLAGS	+= -fintegrated-as
 endif
+# By default, clang only warns on unknown warning or optimization flags
+# Make it behave more like gcc by erroring when these flags are encountered
+# so they can be implemented or wrapped in cc-option.
 CLANG_FLAGS	+= -Werror=unknown-warning-option
+CLANG_FLAGS	+= -Werror=ignored-optimization-argument
 KBUILD_CFLAGS	+= $(CLANG_FLAGS)
 KBUILD_AFLAGS	+= $(CLANG_FLAGS)
 export CLANG_FLAGS
-- 
2.33.0


  parent reply	other threads:[~2021-08-24  2:27 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-24  2:26 [PATCH 0/2] Harden clang against unknown flag options Nathan Chancellor
2021-08-24  2:26 ` [PATCH 1/2] x86: Do not add -falign flags unconditionally for clang Nathan Chancellor
2021-08-24  2:56   ` Fangrui Song
2021-08-24 21:53     ` Nathan Chancellor
2021-08-25 22:32   ` Nick Desaulniers
2021-09-16 17:18   ` Borislav Petkov
2021-09-16 18:42     ` Nathan Chancellor
2021-09-16 19:05       ` Borislav Petkov
2021-08-24  2:26 ` Nathan Chancellor [this message]
2021-08-25 22:27   ` [PATCH 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS Nick Desaulniers
2021-09-13 18:08 ` [PATCH 0/2] Harden clang against unknown flag options Nathan Chancellor

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