bug#29031: 25.3; Segmentation fault when starting emacs with my config

[Eli Zaretskii]

> From: Kaushal Modi <kaushal.modi@gmail.com>
> Date: Mon, 30 Oct 2017 14:17:57 +0000
> Cc: Eli Zaretskii <eliz@gnu.org>
> 
> Thread 1 "emacs" received signal SIGSEGV, Segmentation fault.
> 0x000000000043d101 in append_glyph (it=0x7fffffff2390) at xdisp.c:25880

Line 25880 of xdisp.c is this:

      glyph->charpos = CHARPOS (it->position);

So what is the problematic data here?  Is 'glyph' a NULL pointer or
something?  Or is 'it' a garbled pointer?  What do these commands
show:

  (gdb) p glyph
  (gdb) p glyph->charpos
  (gdb) p it->position

Basically, I need you to run this under a debugger and answer several
questions.  Bonus points for reproducing this in an unoptimized build
configured with --enable-checking='yes,glyphs', and then showing the
backtrace from the segfault.

IOW, this problem needs to be debugged, and for that we need data that
explains the crash.  Could you please help in collecting that data?

Thanks.