linux-kernel - Re: [PATCH v2 07/10] compiler.h, bug.h: Prevent double error messages with BUILD_BUG{,

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Message-ID: <20121005205922.GA7362@jtriplet-mobl1>
Date:	Fri, 5 Oct 2012 13:59:22 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	danielfsantos@....net
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Christopher Li <sparse@...isli.org>,
	David Daney <david.daney@...ium.com>,
	David Howells <dhowells@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Joe Perches <joe@...ches.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-sparse@...r.kernel.org,
	Michel Lespinasse <walken@...gle.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Pavel Pisa <pisa@....felk.cvut.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Santos <daniel.santos@...ox.com>
Subject: Re: [PATCH v2 07/10] compiler.h, bug.h: Prevent double error
 messages with BUILD_BUG{,_ON}

On Fri, Oct 05, 2012 at 02:42:46PM -0500, danielfsantos@....net wrote:
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -296,6 +296,11 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
>  #endif
>  #ifndef __compiletime_error
>  # define __compiletime_error(message)
> +# define __compiletime_error_fallback(condition) \
> +	 ((void)sizeof(char[1 - 2*!!(condition)]))
> +#endif
> +#ifndef __compiletime_error_fallback
> +# define __compiletime_error_fallback(condition) (void)(0)

Might want to use do { } while (0) here, to force the use of a
semicolon and avoid the use of __compiletime_error_fallback in an
expression.

- Josh Triplett
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