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

[Pip Cet]

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. In
particular, I believe 0x170cb040 is a pointer to a valid marker.

>   (gdb) p $28->next
>   $30 = (struct Lisp_Overlay *) 0x13050320
>   (gdb) p $28->next->start
>   $31 = XIL(0xa000000016172310)
>   (gdb) xtype
>   Lisp_Vectorlike
>   Cannot access memory at address 0x18ac04f8

Same here.

If you could disassemble signal_before_change, we'd know whether
start_marker and end_marker live in callee-saved registers, and thus
whether this is likely to be Andrea's bug.