bug#41321: 27.0.91; Emacs aborts due to invalid pseudovector objects

[Pip Cet]

On Fri, May 22, 2020 at 12:13 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > From: Pip Cet <pipcet@gmail.com>
> > Date: Fri, 22 May 2020 11:47:03 +0000
> > Cc: Stefan Monnier <monnier@iro.umontreal.ca>, 41321@debbugs.gnu.org
> >
> > On Fri, May 22, 2020 at 7:22 AM Eli Zaretskii <eliz@gnu.org> wrote:
> > >   (gdb) p current_buffer->overlays_before
> > >   $28 = (struct Lisp_Overlay *) 0x170cb080
> > >   (gdb) p $28->start
> > >   $29 = XIL(0xa0000000170cb040)
> > >   (gdb) xtype
> > >   Lisp_Vectorlike
> > >   Cannot access memory at address 0x18ac04f8
> >
> > Note that didn't try to print $29, but the original invalid marker.
>
> Sorry, I don't follow.  "xtype" shows the type of the last result,
> AFAIK, in this case the type of $29.  If this changed somehow, either
> we have a bug in .gdbinit or I have been using GDB incorrectly for I
> don't know how many years.

I think it's most likely to be a GDB bug, and I can't reproduce it here.

But it's definitely trying to access memory at address 0x18ac04f8,
which corresponds to start_marker.

  (gdb) p rvoe_arg.location
  $35 = (Lisp_Object *) 0x15c9298 <globals+120>
  (gdb) xtype
  Lisp_Vectorlike
  Cannot access memory at address 0x18ac04f8
  (gdb) p rvoe_arg.errorp
  $36 = false

Surely rvoe_arg.location isn't a vectorlike, so that also points to
GDB not dealing with things correctly.