bug#39962: 27.0.90; Crash in Emacs 27.0.90

[Eli Zaretskii]

> From: Pieter van Oostrum <pieter-l@vanoostrum.org>
> Cc: Pieter van Oostrum <pieter@vanoostrum.org>,  39962@debbugs.gnu.org
> Date: Sat, 07 Mar 2020 12:06:50 +0100
> 
> insdel.c:295: Emacs fatal error: assertion failed: m->bytepos >= m->charpos 
> && m->bytepos - m->charpos <= Z_BYTE - Z
> --Type <RET> for more, q to quit, c to continue without paging--
> insdel.c:295: Emacs fatal error: assertion failed: m->bytepos >= m->charpos 
> && m->bytepos - m->charpos <= Z_BYTE - Z

Please show the values of the variables involved in this assertion.

> Lisp Backtrace:
> Cannot access memory at address 0xcfeb5c0

This last bit is highly suspicious.  Something is going on in addition
to the assertion violation, and that something might be the actual
reason for the assertion.

Also note that this is no longer in GC, at least not directly.