linux-kernel - Re: [PATCH 08/23] kconfig: add 'macro' keyword to support user-defined function

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Date:   Fri, 16 Feb 2018 14:49:31 -0500 (EST)
From:   Nicolas Pitre <nico@...xnic.net>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
cc:     linux-kbuild@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ulf Magnusson <ulfalizer@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/23] kconfig: add 'macro' keyword to support user-defined
 function

On Sat, 17 Feb 2018, Masahiro Yamada wrote:

> Now, we got a basic ability to test compiler capability in Kconfig.
> 
> config CC_HAS_STACKPROTECTOR
>         bool
>         default $(shell $CC -Werror -fstack-protector -c -x c /dev/null -o /dev/null)
> 
> 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 implement 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 can be defined as a string type symbol 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.
> 
> Example code:
> 
>   config cc-option
>           string
>           macro $(shell $CC -Werror $(1) -c -x c /dev/null -o /dev/null)

I think this syntax for defining a macro shouldn't start with the 
"config" keyword, unless you want it to be part of the config symbol 
space and land it in .config. And typing it as a "string" while it 
actually returns y/n (hence a bool) is also strange.

What about this instead:

macro cc-option
	bool $(shell $CC -Werror $(1) -c -x c /dev/null -o /dev/null)

This makes it easier to extend as well if need be.


Nicolas