linux-kernel - Re: [PATCH v4 8/9] bug.h: Add BUILD_BUG_ON_MSG & _BUILD_BUG

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Date:	Tue, 30 Oct 2012 18:17:47 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Daniel Santos <daniel.santos@...ox.com>
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>,
	Daniel Santos <daniel.santos@...ox.com>,
	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>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v4 8/9] bug.h: Add BUILD_BUG_ON_MSG & _BUILD_BUG_INTERNAL

On Sun, Oct 28, 2012 at 03:57:14PM -0500, danielfsantos@....net wrote:
> Add BUILD_BUG_ON_MSG which behaves like BUILD_BUG_ON (with optimizations
> enabled), except that it allows you to specify the error message you
> want emitted as the third parameter.  Under the hood, this relies on
> _BUILD_BUG_INTERNAL, which does the actual work and is pretty-much
> identical to BUILD_BUG_ON.
> 
> Signed-off-by: Daniel Santos <daniel.santos@...ox.com>
> ---
>  include/linux/bug.h |   22 ++++++++++++++++++++++
>  1 files changed, 22 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/bug.h b/include/linux/bug.h
> index 6c38988..3bc1ddf 100644
> --- a/include/linux/bug.h
> +++ b/include/linux/bug.h
> @@ -16,6 +16,7 @@ struct pt_regs;
>  #define BUILD_BUG_ON_NOT_POWER_OF_2(n)
>  #define BUILD_BUG_ON_ZERO(e) (0)
>  #define BUILD_BUG_ON_NULL(e) ((void*)0)
> +#define BUILD_BUG_ON_MSG(cond, msg) (0)
>  #define BUILD_BUG_ON(condition) (0)
>  #define BUILD_BUG() (0)
>  #else /* __CHECKER__ */
> @@ -38,6 +39,27 @@ struct pt_regs;
>   */
>  #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
>  
> +#define __BUILD_BUG_INTERNAL(condition, msg, line)		\
> +	do {							\
> +		extern void __build_bug_on_failed_ ## line	\
> +			(void) __compiletime_error(msg);	\
> +		__compiletime_error_fallback(condition);	\
> +		if (condition)					\
> +			__build_bug_on_failed_ ## line();	\
> +	} while (0)
> +
> +#define _BUILD_BUG_INTERNAL(condition, msg, line) \
> +	__BUILD_BUG_INTERNAL(condition, msg, line)

Stupid question:

can BUILD_BUG_ON and BUILD_BUG_ON_MSG both use __BUILD_BUG_INTERNAL?

In the BUILD_BUG_ON msg will be "BUILD_BUG_ON failed" and line empty.
Can that even work?

Thanks.

-- 
Regards/Gruss,
    Boris.
--
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