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Date: Wed, 25 Jul 2007 18:19:56 +0100
From: Al Viro <viro@ftp.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Miller <davem@davemloft.net>, jeremy@goop.org, hpa@zytor.com,
       kaos@ocs.com.au, xyzzy@speakeasy.org, linux-kernel@vger.kernel.org,
       linux-arch@vger.kernel.org
Subject: Re: [PATCH][RFC] getting rid of stupid loop in BUG()
Message-ID: <20070725171956.GF27237@ftp.linux.org.uk>
References: <21803.1185331847@ocs10w.ocs.com.au> <46A6DB04.3000003@zytor.com> <46A6ECB7.7090208@goop.org> <20070724.232914.56812376.davem@davemloft.net> <alpine.LFD.0.999.0707250954400.3607@woody.linux-foundation.org>
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On Wed, Jul 25, 2007 at 09:56:12AM -0700, Linus Torvalds wrote:
> 
> 
> On Tue, 24 Jul 2007, David Miller wrote:
> >
> > From: Jeremy Fitzhardinge <jeremy@goop.org>
> > Date: Tue, 24 Jul 2007 23:24:55 -0700
> > 
> > > H. Peter Anvin wrote:
> > > > How far back was __builtin_trap() supported?
> > > 
> > > I think its relatively recent, but it might be within our supported
> > > compiler window.
> > 
> > I'm pretty sure it is.
> 
> .. and I'm pretty sure it's immaterial.
> 
> 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.

Umm...  Actually, we might be able to do something like
{
	l: __builtin_trap();
	static struct ... v __attribute__((section(...))) = { &&l, n, file };
}

except that it would need block-local labels and those are ugly (so's
&&<label>, while we are at it)...