linux-kernel - Re: [PATCH v2 10/21] kconfig: add 'success' and 'cc-option' macros

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Date:   Tue, 27 Mar 2018 20:46:59 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-kbuild <linux-kbuild@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Ulf Magnusson <ulfalizer@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Nicolas Pitre <nico@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/21] kconfig: add 'success' and 'cc-option' macros

On Mon, Mar 26, 2018 at 10:29 PM, Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> 'cc-option' will be the most frequently used macro.  It evaluates to 'y'
> if the given argument is supported by the compiler, or 'n' otherwise.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

> ---
>
> Changes in v2:
>   - Implement 'success' as a macro
>
>  init/Kconfig | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 0d6fe20..c456030 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -8,6 +8,12 @@ config DEFCONFIG_LIST
>         default ARCH_DEFCONFIG
>         default "arch/$ARCH/defconfig"
>
> +# expanded to y if the command exits with 0, n otherwise
> +macro success $(shell ($(1) && echo y) || echo n)
> +
> +# expanded to y if the given compiler flag is supported, n otherwise
> +macro cc-option $(success $CC -Werror $(1) -c -x c /dev/null -o /dev/null)

This should be fine since most cc-option uses are quite simple. The
specialized per-arch and other-flag-dependency checks can just
continue to live in Makefile if we actually need them.

-Kees

-- 
Kees Cook
Pixel Security