linux-kernel - Re: Fix empty macros in acpi.

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Message-ID: <20070613002631.GL21478@ftp.linux.org.uk>
Date:	Wed, 13 Jun 2007 01:26:31 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Fix empty macros in acpi.

On Tue, Jun 12, 2007 at 08:21:15PM -0400, Dave Jones wrote:
> On Wed, Jun 13, 2007 at 01:00:29AM +0100, Al Viro wrote:
>  > On Tue, Jun 12, 2007 at 07:33:09PM -0400, Dave Jones wrote:
>  > > +#define DBG(x...) do { } while(0)
>  > 
>  > Eh...  Please, stop it - if you want a function-call-like no-op returning void,
>  > use ((void)0).  At least that way one can say DBG(....),foo(), etc.
> 
> They both end up compiled to nothing anyway, so I'm not bothered
> either way..   I'm not sure I follow why the syntax of that last part
> is a good thing.  It looks like something we'd want to avoid rather
> than promote?

If on one side of ifdef it's a void-valued expression, so it should be
on another; the reason is that we don't get surprise differences between
the builds...

IOW, if it doesn't build in some context, it should consistently fail to
build in that context.
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