linux-kernel - Re: [PATCH v2 1/2] kernel.h: Add BUILD

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Date:	Wed, 23 Nov 2011 11:11:20 +0000
From:	David Howells <dhowells@...hat.com>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	dhowells@...hat.com, ralf@...ux-mips.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>, DM <dm.n9107@...il.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH v2 1/2] kernel.h: Add BUILD_BUG() macro.

David Daney <ddaney.cavm@...il.com> wrote:

> From: David Daney <david.daney@...ium.com>
> 
> We can place this in definitions that we expect the compiler to remove
> by dead code elimination.  If this assertion fails, we get a nice
> error message at build time.
> 
> The GCC function attribute error("message") was added in version 4.3,
> so we define a new macro __linktime_error(message) to expand to this
> for GCC-4.3 and later.  This will give us an error diagnostic from the
> compiler on the line that fails.  For other compilers
> __linktime_error(message) expands to nothing, and we have to be
> content with a link time error, but at least we will still get a build
> error.
> 
> BUILD_BUG() expands to the undefined function __build_bug_failed() and
> will fail at link time if the compiler ever emits code for it.  On
> GCC-4.3 and later, attribute((error())) is used so that the failure
> will be noted at compile time instead.
> 
> Signed-off-by: David Daney <david.daney@...ium.com>

Acked-by: David Howells <dhowells@...hat.com>
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