bug#24417: 25.1; Emacs crashes during gc

[Eli Zaretskii]

> From: Sudarshan Gaikaiwari <sudarshan@acm.org>
> Date: Wed, 28 Sep 2016 19:50:42 -0500
> Cc: 24417@debbugs.gnu.org
> 
> y emacs process crashed again. I was running a debug build as part of
> bug#24417. The back trace indicates that the sefault is in a different
> module. Please let me know if I should file a new bug instead of
> updating this one.
> I was trying to run rgrep when this crash occured. The emacs build is
> of RC2 and not
> the latest release.

This crash looks differently, but I'm not yet sure if it's a separate
problem, so let's keep them together for now.

Is this debugging session still alive?  If so, I'd like to ask you to
report values of some relevant variables.

What seems to have happened here is that Emacs was going to report an
error by starting the Lisp debugger.  Then, while redrawing the
display triggered by that, some font-lock construct caused the display
engine to call a Lisp function, which eventually called
re-search-forward, and that segfaulted because it got an invalid
string pointer.

It would be good to know what was the error Emacs wanted to report,
and what function was invoked from redisplay that caused the crash.