bug#21031: 25.0.50; emacs_backtrace.txt

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 11 Jul 2015 00:47:48 +0200
> From: Dani Moncayo <dmoncayo@gmail.com>
> Cc: Drew Adams <drew.adams@oracle.com>, 21031@debbugs.gnu.org
> 
> On Fri, Jul 10, 2015 at 10:00 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> >> Date: Fri, 10 Jul 2015 12:14:03 -0700 (PDT)
> >> From: Drew Adams <drew.adams@oracle.com>
> >>
> >> Crash from emacs -Q.  This is the contents of emacs_backtrace.txt:
> >>
> >>
> >> Exception 0xc0000005 at this address:
> >> 01174719
> >>
> >> Backtrace:
> >> 011ae147
> >>
> >>
> >> In GNU Emacs 25.0.50.1 (i686-pc-mingw32)
> >>  of 2015-07-03 on LEG570
> >> Repository revision: 2b848fadd51e805b2f46da64c5958ea7f009048a
> >
> > Thanks, but I cannot do anything with this data, because the binary
> > you downloaded was stripped of all symbols (something I won't expect
> > to see in snapshots).
> >
> > Perhaps Dani can provide the output of addr2line for this backtrace.
> > Failing that, this data is useless.
> 
> ??
> ??:0
> Fbackward_prefix_chars at syntax.c:3047

Thanks.  This is here:

  while (!char_quoted (pos, pos_byte)
	 /* Previous statement updates syntax table.  */
	 && ((c = FETCH_CHAR_AS_MULTIBYTE (pos_byte), SYNTAX (c) == Squote)
	     || syntax_prefix_flag_p (c)))
    {
      opoint = pos;
      opoint_byte = pos_byte;

      if (pos + 1 > beg)
	DEC_BOTH (pos, pos_byte);  <<<<<<<<<<<<<<<<<<<<<
    }

I don't see how could that crash.  Anyone?