Re: [PATCH 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS

Nick Desaulniers
2021-08-25T22:27:44Z

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