BUG_ON and gcc don't mix

[David Laight]

> On Tue, Aug 20, 2013 at 02:02:11PM +0930, Alan Modra wrote:
> > On Tue, Aug 20, 2013 at 12:37:50PM +1000, Anton Blanchard wrote:
> > > address of the trap instruction for our bug exception table. Maybe
> > > we need a gcc builtin in which we can get a label on the trap
> > > instruction. Would that be possible?
> >
> > Not your actual _EMIT_BUG_ENTRY, but something like this ought to work.
> > The only trick here is not putting anything after __builtin_trap()..
>
> Doh!  I guess the whole point was to get the condition folded into the
> trap, which is foiled by emitting an asm between the condition and
> buildin_trap().

I was thinking that you could add the label after the trap and
then use '.long 1b-4'. But you'd have to put the asm outside the
conditional - so that wouldn't work if the condition was more
complicated and the trap had to be out of line.

If the trap is out of line, then it could be a long way from
the surrounding code block - so a label 'nearby' in the C isn't
any use.

With fix sized instructions the .text segment of the object files
could be scanned for trap instructions.

	David