linux-kernel - Re: [PATCH 0/5] RFC: strip 15,000 lines from a typical autoconf.h

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Date:	Thu, 12 Apr 2012 11:27:02 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, davem@...emloft.net,
	tony@...eyournoodle.com, lacombar@...il.com
Subject: Re: [PATCH 0/5] RFC: strip 15,000 lines from a typical autoconf.h

On 12.4.2012 03:19, Linus Torvalds wrote:
> On Wed, Apr 11, 2012 at 4:58 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> I think we can easily drop IS_ENABLED() if it has been causing
>> problems. And it clearly is.

What is really causing problems is that kconfig has no view of the
entire kernel configuration.


>> And I had never even looked at that generated file. It's disgusting.
>> We need to stop doing that. It must be driving compile-times up too -
>> just parsing that monster is RealWork(tm).

You forgot that it also contributes to global warming.


> Oh, but I have a sick and twisted mind. And I'm incredibly smart and
> photogenic too.
> 
> Here's an implementation of IS_ENABLED() that works in C. Well,
> "gcc-C". It depends on the optimizer DTRT, but gcc really does seem to
> do it.
> 
> Ready? You *will* go blind - blinded by the pure beauty and intellect
> in this thing:
> 
>     #define IS_DEFINED(x) (__stringify(CONFIG_##x)[0]=='1')

Nice. Maybe we could make it simply

#define IS_DEFINED(x) (__stringify(x)[0]=='1')

so that the users are easily grepable and it is obvious that a config
option is being tested, like in the current implementation. The only
thing we lose is the check if 'x' is really a boolean or tristate
option. But it turns out that even now this does not work in all cases.

Michal
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