linux-kernel - Re: [PATCH] ARM: Convert BUG() to use unreachable()

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Date:	Thu, 10 Dec 2009 09:55:51 -0800
From:	David Daney <ddaney@...iumnetworks.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: Convert BUG() to use unreachable()

Russell King - ARM Linux wrote:
> On Tue, Dec 08, 2009 at 10:55:38AM +0100, Uwe Kleine-König wrote:
>> Use the new unreachable() macro instead of for(;;);
> 
> Have you investigated what effect this has on generated code?

Yes.

Pre GCC-4.5 the generated code should be identical as 'unreachable()' 
just expands to 'for(;;);' in this case.

Post GCC-4.5 the generated code should be smaller.

I have not tested on ARM, but on x86_64, i686, and mips64 this is the 
case.  The code size reduction is due to not emitting an endless loop 
after the asm() that never returns.

David Daney
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