bug#9436: 24.0.50; Segmentation fault during redisplay

[Eli Zaretskii]

> From: Helmut Eller <eller.helmut@gmail.com>
> Date: Sun, 04 Sep 2011 19:53:06 +0200
> 
> Last week I updated to the trunk version and now Emacs crashes once or
> twice a day.  As far as I can tell, I don't do anything unusual when it
> happens: just reading and moving up and down with the cursor keys.  This
> happened in c-mode, lisp-mode and I think even in man-mode.
> 
> I now start Emacs with (ulimit -c unlimited && emacs)& and have a core
> file.  The output of "bt full" is below. xbacktrace didn't show
> anything, but I'm not sure if I sourced the .gdbinit correctly.

Please try reproducing this in an unoptimized build.  Backtraces from
optimized builds are useless for debugging.  It looks like it->f is
NULL in frames #4 and therefore in frame #3, which is the cause of the
crash.  But I don't believe anything GDB displays in optimized builds,
not even to backtraces.