bug#17753: Cygwin emacs-X11 core dump

[Eli Zaretskii]

> Date: Thu, 09 Oct 2014 12:44:44 +0200
> From: Markus Hoenicka <markus.hoenicka@mhoenicka.de>
> Cc: kbrown@cornell.edu, 17753@debbugs.gnu.org
> 
> (gdb) print (it->f)->face_cache->used
> $4 = 31

??? That's unexpected.  What about this one:

  (gdb) print (it->f)->face_cache->faces_by_id[it->face_id]

(The above is the expansion of the call to the FACE_FROM_ID macro,
which, judging by your backtrace, yielded a NULL pointer.)