linux-kernel - Re: [PATCH v2 09/21] kconfig: add 'macro' keyword to support user-defined function

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Message-ID: <CAGXu5jJkqgAYexAq27fK75cLRaWaHwac9oTMWqgqbDVZxApVFA@mail.gmail.com>
Date:   Tue, 27 Mar 2018 20:45:08 -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 09/21] kconfig: add 'macro' keyword to support
 user-defined function

On Mon, Mar 26, 2018 at 10:29 PM, Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> Now, we got a basic ability to test compiler capability in Kconfig.
>
> config CC_HAS_STACKPROTECTOR
>         def_bool $(shell (($CC -Werror -fstack-protector -c -x c /dev/null -o /dev/null) && echo y) || echo n)
>
> This works, but it is ugly to repeat this long boilerplate.
>
> We want to describe like this:
>
> config CC_HAS_STACKPROTECTOR
>         bool
>         default $(cc-option -fstack-protector)
>
> It is straight-forward to add a new function, but I do not like to
> hard-code specialized functions like this.  Hence, here is another
> feature to add functions from Kconfig files.
>
> A user-defined function is defined with a special keyword 'macro'.
> It can be referenced in the same way as built-in functions.  This
> feature was also inspired by Makefile where user-defined functions
> are referenced by $(call func-name, args...), but I omitted the 'call'
> to makes it shorter.
>
> The macro definition can contain $(1), $(2), ... which will be replaced
> with arguments from the caller.  The macro works just as a textual
> shorthand, which is also expanded in the lexer phase.
>
> [Example Code]
>
>   macro success $(shell ($(1) && echo y) || echo n)
>
>   config TRUE
>           bool "true"
>           default $(success true)
>
>   config FALSE
>           bool "false"
>           default $(success false)
>
> [Result]
>
>   $ make -s alldefconfig
>   $ tail -n 2 .config
>   CONFIG_TRUE=y
>   # CONFIG_FALSE is not set
>
> [Example Code]
>
>   macro success $(shell ($(1) && echo y) || echo n)
>
>   macro cc-option $(success $CC -Werror $(1) -c -x c /dev/null -o /dev/null)
>
>   config CC_HAS_STACKPROTECTOR
>           def_bool $(cc-option -fstack-protector)
>
> [Result]
>   $ make -s alldefconfig
>   $ tail -n 1 .config
>   CONFIG_CC_HAS_STACKPROTECTOR=y
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

Cool, I like this "macro" idea for keeping this clean.

> ---
>
> Reminder for myself:
> Update Documentation/kbuild/kconfig-language.txt

Yes please. :)

Otherwise, looks good!

-Kees

-- 
Kees Cook
Pixel Security