linux-kernel - Re: [tip:core/urgent] WARN_ON_SMP(): Add comment to explain ({0;})

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Message-ID: <4D90A08D.707@zytor.com>
Date:	Mon, 28 Mar 2011 07:51:57 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	torvalds@...ux-foundation.org, rostedt@...dmis.org,
	srostedt@...hat.com, tglx@...utronix.de, adobriyan@...il.com
CC:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/urgent] WARN_ON_SMP(): Add comment to explain ({0;})

On 03/28/2011 07:45 AM, tip-bot for Steven Rostedt wrote:
> 
> WARN_ON_SMP(): Add comment to explain ({0;})
> 
> The define to use ({0;}) for the !CONFIG_SMP case of WARN_ON_SMP()
> can be confusing. As the WARN_ON_SMP() needs to be a nop when
> CONFIG_SMP is not set, including all its parameters must not be
> evaluated, and that it must work as both a stand alone statement
> and inside an if condition, we define it to a funky ({0;}).
> 
> A simple "0" will not work as it causes gcc to give the warning that
> the statement has no effect.
> 
> As this strange definition has raised a few eyebrows from some
> major kernel developers, it is wise to document why we create such
> a work of art.
> 

What the heck is wrong with the idiomatic and non-gcc-extension-using:

	((void)0)

?

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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