bug#22526: 25.0.90; Crash starting gnus

[Eli Zaretskii]

> From: Andy Moreton <andrewjmoreton@gmail.com>
> Date: Fri, 12 Feb 2016 22:26:02 +0000
> 
> On Fri 12 Feb 2016, Eli Zaretskii wrote:
> 
> >> From: Andy Moreton <andrewjmoreton@gmail.com>
> >> Date: Fri, 12 Feb 2016 13:34:37 +0000
> >> 
> >> I have managed to reproduce the crash again, and kept the gdb
> >> session running.
> >
> > Thanks.  Now that you've succeeded, I'm going to ask you to terminate
> > the debug session and try applying a patch ;-)
> 
> No obvious problems after applying the patch, but it may take a while to
> find the right circumstances to trigger any issues.

Thanks, let's wait.

FWIW, I'm not really sure that patch will fix the problem, for 2
reasons: (1) the code it fixes should only get executed very rarely,
if ever; and (2) according to my reading of gap_left, it should have
touched these addresses just before hitting the segfault.  So I
believe there's some other factor at work here I cannot figure out.

Maybe Fabrice will have some ideas.

Btw, can you attach GDB to Emacs _before_ the problem happens?  It
could be that the backtrace we see is not entirely reliable when
attaching GDB after the segfault.

Also, is this an optimized build?  I don't think I've seen all the
basic data collected by report-emacs-bug about your build; can you
post it?

Thanks.