linux-kernel - Re: [PATCH][RFC] getting rid of stupid loop in BUG()

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Message-ID: <46A78C1B.8070509@goop.org>
Date:	Wed, 25 Jul 2007 10:44:59 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Al Viro <viro@....linux.org.uk>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>, hpa@...or.com,
	kaos@....com.au, xyzzy@...akeasy.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH][RFC] getting rid of stupid loop in BUG()

Al Viro wrote:
> On Wed, Jul 25, 2007 at 09:56:12AM -0700, Linus Torvalds wrote:
>   
>> We don't just do the "ud2" instruction - we also do the file and line 
>> number information after it. Which means that __builtin_trap() is useless.
>>
>> So we might as well keep the loop, since both are two-byte instructions 
>> that tell gcc that it will never continue.
>>     
>
> Actually, the worse problem is that gcc will happily merge these guys.
> And that's a killer.
>   

Merge __builtin_traps()?  Ugh.  But also, there's no real long-term
guarantee that it will keep generating ud2a.  The *only* mention of it
in the manual is a discussion that it will emit a call to abort() on
arches which don't otherwise support it.

    J
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