linux-kernel - Re: [PATCH v5 9/9] bug.h, compiler.h: Introduce compiletime_assert & BUILD_BUG_ON

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Date:	Fri, 16 Nov 2012 17:25:09 -0600
From:	Daniel Santos <danielfsantos@....net>
To:	Borislav Petkov <bp@...en8.de>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christopher Li <sparse@...isli.org>,
	David Daney <david.daney@...ium.com>,
	David Howells <dhowells@...hat.com>,
	Joe Perches <joe@...ches.com>,
	Josh Triplett <josh@...htriplett.org>,
	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>
Subject: Re: [PATCH v5 9/9] bug.h, compiler.h: Introduce compiletime_assert
 & BUILD_BUG_ON_MSG

On 11/13/2012 04:13 PM, danielfsantos@....net wrote:
> +#define __compiletime_assert(condition, msg, __func)			\
> +	do {								\
> +		bool __cond = !(condition);				\
> +		extern void __func(void) __compiletime_error(msg);	\
> +		if (__cond)						\
> +			__func();					\
> +		__compiletime_error_fallback(__cond);			\
> +	} while (0)
> +
> +#define _compiletime_assert(condition, msg, __func) \
> +	__compiletime_assert(condition, msg, __func)
> +
> +/**
> + * compiletime_assert - break build and emit msg if condition is false
> + * @condition: a compile-time constant condition to check
> + * @msg:       a message to emit if condition is false
> + *
> + * In tradition of POSIX assert, this macro will break the build if the
> + * supplied condition is *false*, emitting the supplied error message if the
> + * compiler has support to do so.
> + */
> +#define compiletime_assert(condition, msg) \
> +	_compiletime_assert(condition, msg, __compiletime_assert_ ## __LINE__)
> +

Whoops, this implementation pastes the tokens before allowing them to
expand, it should be something like this:

#define __compiletime_assert(condition, msg, __func) .... stuff
#define _compiletime_assert(condition, msg, prefix, suffix) \
        __compiletime_assert(condition, msg, prefix ## suffix)
#define compiletime_assert(condition, msg) \
        _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)

I'll fix that as well.

Daniel
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