bug#35429: 27.0.50; Arbitrary xdisp.c related crashes when working with overlay-using packages

[Eli Zaretskii <eliz@gnu.org>]

> From: Kaushal Modi <kaushal.modi@gmail.com>
> Date: Fri, 26 Apr 2019 14:22:51 -0400
> Cc: 35429@debbugs.gnu.org
> 
> (gdb) p current_buffer->name_
> $9 = XIL(0xc35be44)
> (gdb) xstring
> $10 = (struct Lisp_String *) 0xc35be40
> "ascii-art-to-unicode.el"
> (gdb) fr 2
> #2  0x0000000000456b44 in init_iterator (it=it@entry=0x7fffffff3040, w=w@entry=0x89da880, charpos=2874,
>     bytepos=<optimized out>, row=<optimized out>,
> base_face_id=base_face_id@entry=DEFAULT_FACE_ID)
>     at xdisp.c:3047
> 3047          eassert (charpos == BYTE_TO_CHAR (bytepos));
> (gdb) p w->contents
> $11 = XIL(0xc35be95)
> (gdb) xtype
> Lisp_Vectorlike
> PVEC_BUFFER
> (gdb) xbuffer
> $12 = (struct buffer *) 0xc35be90
> (unsigned char *) 0xb6e97a0 "ascii-art-to-unicode.el"
> (gdb) 
> 
> I hope this helps.

It does.

So now what do the following commands tell?

  (gdb) fr 2
  (gdb) p w->start
  (gdb) xmarker
  (gdb) p *$