From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, Masahiro Yamada <masahiroy@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
clang-built-linux@googlegroups.com, llvm@lists.linux.dev
Subject: Re: [PATCH 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS
Date: Wed, 25 Aug 2021 15:27:29 -0700 [thread overview]
Message-ID: <CAKwvOdk8nj6Yu=+k+cDx_rKh=ug6+VyYRzzFGDiZjrQQ8q7eCw@mail.gmail.com> (raw)
In-Reply-To: <20210824022640.2170859-3-nathan@kernel.org>
On Mon, Aug 23, 2021 at 7:27 PM Nathan Chancellor <nathan@kernel.org> wrote:
>
> 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>
Good idea.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> 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
>
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2021-08-25 22:27 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 ` [PATCH 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS Nathan Chancellor
2021-08-25 22:27 ` Nick Desaulniers [this message]
2021-09-13 18:08 ` [PATCH 0/2] Harden clang against unknown flag options Nathan Chancellor
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