linux-kernel - Re: [patch 01/10] compiler: define __attribute_unused_

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Date:	Wed, 02 May 2007 16:29:53 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 01/10] compiler: define __attribute_unused__

On Tue, 2007-05-01 at 23:06 -0700, David Rientjes wrote:
> On Wed, 2 May 2007, Rusty Russell wrote:
> 
> > Adding this macro doesn't give us anything that simply saying
> > "__attribute__((unused))" doesn't give.  But it does add a layer of
> > kernel-specific indirection.
> > 
> 
> That's obviously true since we're defining __attribute_unused__ to be 
> __attribute__((unused)).

Hi David,

	I'm horribly familiar with this issue, BTW, so we don't need so many
words 8)

> The patched version makes this:
> 
> 	int type __attribute_unused__ = 0;
>
> which definitely tells you that you're using a compiler attribute that 
> will be attached to that automatic.  In your case:
> 
> 	int type __unneeded = 0;
> 
> doesn't say anything in this case.  It doesn't resemble any attribute that 
> a programmer might be familiar with and begs the question of why we've 
> declared it if it's truly "unneeded"?

Your version makes one wonder why they didn't use
"__attribute__((unused))".  Obviously the __attribute_unused__ macro
exists for a reason, so they wonder what's the difference between that
and the attribute?  The answer: nothing.

OTOH, your point about "__unneeded" is well taken.  "__needed" and
"__optional" perhaps?  But their feature is *exactly* that the don't
look like the gcc attributes, hence avoid their semantic screwage.

> By the way, there are tons of these instances where __attribute__((used)) 
> needs to be added in driver code to suppress unreferenced warnings.

Sure; historically we refactor around it.  But warnings are now so
commonplace few people care 8(

Cheers,
Rusty.


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