Message-ID: <CACqU3MXWH5mq1ycOoqH=1A_87Sn3tgOZU2om+0q=ZrEvnmKVrQ@mail.gmail.com>
Date:	Wed, 13 Jul 2011 11:20:13 -0400
From:	Arnaud Lacombe <lacombar@...il.com>
To:	Michal Marek <mmarek@...e.cz>
Cc:	Sam Ravnborg <sam@...nborg.org>, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Valdis.Kletnieks@...edu
Subject: Re: [PATCH] kconfig: Only generate config_is_xxx for bool and
 tristate options

Hi,

On Wed, Jul 13, 2011 at 9:22 AM, Michal Marek <mmarek@...e.cz> wrote:
> On 18.5.2011 08:23, Arnaud Lacombe wrote:
>>
>> Hi,
>>
>> [added Valdis.Kletnieks@...edu to CC:]
>>
>> On Tue, May 17, 2011 at 3:53 PM, Sam Ravnborg<sam@...nborg.org>  wrote:
>>>
>>> On Tue, May 17, 2011 at 05:35:32PM +0200, Michal Marek wrote:
>>>>
>>>> For strings and integers, the config_is_xxx macros are useless and
>>>> sometimes misleading:
>>>>
>>>>   #define CONFIG_INITRAMFS_SOURCE ""
>>>>   #define config_is_initramfs_source() 1
>>>
>>> I'm late with this comment....
>>> Could we introduce "config_is_foo" using a syntax that
>>> does not break grepability?
>>>
>>> Maybe a syntax like this?
>>>
>>>    #ifdef CONFIG_FOO
>>>
>>> and
>>>
>>>    if (KCONFIG_FOO())
>>>
>>> Grepping for the use of a symbol is a very typical thing,
>>> so we should try to keep this.
>>> And with the suggested syntax above I expect fixdep to
>>> catch up both usage types.
>>>
>> Actually, there is already an issue, on a much smaller scale, in the
>> current tree with NUMA_BUILD and COMPACTION_BUILD. The real way to fix
>> this would be to always defines CONFIG_FOO, its value being 1 or 0
>> depending on whether or not the symbol is selected. This is a
>> +35k/-35k change.
>>
>> Also, I find KCONFIG_FOO() is too specific to be in the kernel source,
>> and redundant with CONFIG_FOO.
>>
>> I've been playing a bit with the preprocessor, and reached that point:
>>
>> #define EXPAND(x)       __ ## x
>> #define CONFIGURED(x)   \
>>         ({  int __1 __maybe_unused = 1;         \
>>             int __ ## x __maybe_unused = 0;     \
>>             EXPAND(x); })
>>
>> I am not specifically proud of that, use case would be:
>>
>> extern func(void);
>> int fn()
>> {
>>         if(CONFIGURED(CONFIG_FOO))
>>                 func();
>> }
>
> I finally got round to revisit this. Your approach inspired me to a much
> simpler scheme: Instead of generating the config_is_xxx macros for direct
> use in the code, name them __enabled_CONFIG_XXX or similar and have a macro
> that expands given CONFIG_XXX symbol to the other form:
>
> /*
>  * Usage: ENABLED(CONFIG_FOO)
>  * Please do not use the __enabled_CONFIG_FOO defines directly to not break
>  * grepability of the code.
>  */
> #define ENABLED(x) __enabled_ ## x
>
> plus a checkpatch.pl check so that people do not use the
> __enabled_CONFIG_FOO macros in their code. git grep -w CONFIG_FOO continues
> to work, fixdep continues to work, it works with -O0 because it expands to a
> if(1) or if(0). Am I missing some obvious problem?
>
not I see immediately. ENABLED() will conflict with existing keyword
in the tree, so it might need tweaking.

Basically, you are taking the approach of always defining CONFIG_FOO
(to 0 or 1), but by introducing a new macro, you avoid to break #ifdef
usage in the tree.

Actually, with this approach, we can even see forward and start replacing:

#ifdef CONFIG_FOO

by

#if ENABLED(CONFIG_FOO)

In a couple of release, we mark the old #ifdef syntax as deprecated,
then after a couple of release, get rid of the duplicated macro
altogether.

You evil ! :-)

 - Arnaud

> Attached is my test program:
> $ gcc -Wall -O0 test.c
> $ ./a.out
> Foo1.0
> Foo1.1
> $ strings ./a.out | grep Foo
> Foo1.0
> Foo1.1
>
> Michal
>
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