Re: [PATCH v2 2/2] kbuild: Add -Werror=ignored-optimization-argument to CLANG_FLAGS

[Masahiro Yamada]

On Fri, Sep 17, 2021 at 3:42 AM Nathan Chancellor <nathan@xxxxxxxxxx> 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.
>
> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---

Applied to linux-kbuild. Thanks.



>  scripts/Makefile.clang | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang
> index 4cce8fd0779c..51fc23e2e9e5 100644
> --- a/scripts/Makefile.clang
> +++ b/scripts/Makefile.clang
> @@ -29,7 +29,12 @@ CLANG_FLAGS  += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
>  else
>  CLANG_FLAGS    += -fintegrated-as
>  endif
> +# By default, clang only warns when it encounters an unknown warning flag or
> +# certain optimization flags it knows it has not implemented.
> +# 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
>


-- 
Best Regards
Masahiro Yamada