bug#22739: 25.0.50; Hangs on revertig buffer

[Eli Zaretskii <eliz@gnu.org>]

> From: Óscar Fuentes <ofv@wanadoo.es>
> Cc: 22739@debbugs.gnu.org
> Date: Fri, 19 Feb 2016 14:21:48 +0100
> 
> move_it_vertically_backward (it=it@entry=0x7ffead898b20, dy=dy@entry=500)
>     at ../../emacs/src/xdisp.c:9489
> 9489                   && SREF (it2.string, IT_STRING_BYTEPOS (it2) - 1) == '\n')));
> Value returned is $6 = 812
> (gdb) 
> Run till exit from #0  move_it_vertically_backward (it=it@entry=0x7ffead898b20, 
>     dy=dy@entry=500) at ../../emacs/src/xdisp.c:9489
> 0x000000000054ae08 in internal_condition_case (
>     bfun=bfun@entry=0x4e80d0 <command_loop_1>, handlers=handlers@entry=17856, 
>     hfun=hfun@entry=0x4de9c0 <cmd_error>) at ../../emacs/src/eval.c:1300
> 1300      if (sys_setjmp (c->jmp))
> (gdb) 

This seems to say that the display engine signaled an error.  If so,
the error message should be in *Messages*.  One way of accessing the
error messages is to use the facilities in etc/emacs-buffer.gdb (after
you instruct GDB to load that file with the "source" command) to
access the text of *Messages*.  An alternative is to put a breakpoint
in Fsignal, and look at the error symbol and data when the breakpoint
breaks, using the commands in src/.gdbinit that display Lisp objects.
(But do NOT use "pp", because it invokes a function inside Emacs.)

Can you do any of these?  If you need more detailed instructions, just
ask.

Thanks.