linux-kernel - Re: [PATCH] kbuild: use -S instead of -E for precise cc-option test in Kconfig

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Message-ID: <CAK7LNAQ-jkwUT3qcuqZeKUhiDjTP_XuEK1qgjTwEoL00v+c07g@mail.gmail.com>
Date:   Wed, 22 Jan 2020 00:47:54 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: use -S instead of -E for precise cc-option test
 in Kconfig

On Sat, Jan 18, 2020 at 2:16 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> Currently, -E (stop after the preprocessing stage) is used to check
> whether the given compiler flag is supported.
>
> While it is faster than -S (or -c), it can be false-positive. You need
> to run the compilation proper to check the flag more precisely.
>
> For example, when testing "--param asan-instrument-allocas=1", my gcc
> gives a different result for -E vs -S.
>
> $ gcc -Werror --param asan-instrument-allocas=1 -E -x c /dev/null -o /dev/null
> $ echo $?
> 0
>
> $ gcc -Werror --param asan-instrument-allocas=1 -S -x c /dev/null -o /dev/null
> cc1: error: invalid --param name ‘asan-instrument-allocas’; did you mean ‘asan-instrument-writes’?
> $ echo $?
> 1
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---

Applied to linux-kbuild.


>  scripts/Kconfig.include | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
> index d4adfbe42690..bfb44b265a94 100644
> --- a/scripts/Kconfig.include
> +++ b/scripts/Kconfig.include
> @@ -25,7 +25,7 @@ failure = $(if-success,$(1),n,y)
>
>  # $(cc-option,<flag>)
>  # Return y if the compiler supports <flag>, n otherwise
> -cc-option = $(success,$(CC) -Werror $(CLANG_FLAGS) $(1) -E -x c /dev/null -o /dev/null)
> +cc-option = $(success,$(CC) -Werror $(CLANG_FLAGS) $(1) -S -x c /dev/null -o /dev/null)
>
>  # $(ld-option,<flag>)
>  # Return y if the linker supports <flag>, n otherwise
> --
> 2.17.1
>


-- 
Best Regards
Masahiro Yamada