bug#43700: 28.0.50; Crash creating a second frame

[Andy Moreton]

On 03/10/2020 13:45, Eli Zaretskii wrote:
> > Cc: 43700@debbugs.gnu.org
> > From: Andy Moreton <andrewjmoreton@gmail.com>
> > Date: Sat, 3 Oct 2020 13:26:09 +0100
> >
> > >     (gdb) watch -l f->face_cache->used if f->face_cache->used == 0
> > >
> > > Then produce a backtrace from any time this watchpoint fires.  That
> > > should show us the culprit.
> >
> > The watchpoint does not fire before the segfault, so there is clearly
> > something wrong with gdb on this platform :-(
>
> Does the watchpoint fire if you remove the condition?  IOW, do this:
>
>      (gdb) watch -l f->face_cache->used
>
> If this works, then you should see also the events where faces are
> added, which will show the 'used' count go up.

As another approach, I have tried building a cygwin 64bit emacs (with 
-O0 and enable_checking) and can reproduce the same problem there.

Unfortunately the watchpoint does not fire in cygwin gdb either, but the 
eassert in FACE_FROM_ID fires before the segfault.

    AndyM