bug#48843: pos_visible_p segfault

[Eli Zaretskii <eliz@gnu.org>]

> From: Christopher Howard <christopher@librehacker.com>
> Date: Fri, 04 Jun 2021 21:05:52 -0800
> 
> Hello, I am able to consistently reproduce a segfault under rather
> precise conditions, when I am doing a search while comparing two files
> using emacs-vdiff. The segfault seems to be happening in pos_visible_p.
> 
> GNU Emacs 27.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.24,
> cairo version 1.16.0)
> 
> christopher@nightshade ~$ guix describe
> Generation 7	Jun 04 2021 15:20:58	(current)
>   guix 7382aa0
>     repository URL: https://git.savannah.gnu.org/git/guix.git
>     branch: master
>     commit: 7382aa00b82860762bc326dec6b45f8cd2161327
> 
> christopher@nightshade ~$ guix show emacs-vdiff | grep version
> version: 0.2.4
> 
> christopher@nightshade ~$ neofetch --stdout | grep CPU
> CPU: AMD Athlon II X3 455 (3) @ 3.300GHz
> 
> Steps to reproduce:
> 
> - Starts Emacs (in Gnome or in virtual console)
> - M-x vdiff-file
> - for file 1: my.dump (attached)
> - for file 2: upstream.dump (attached)
> - while in file 1 buffer: C-s 1 e 2 d
> 
> I figured out how to get a backtrace in gdb:
> 
> Thread 1 ".emacs-27.2-rea" received signal SIGSEGV, Segmentation fault.
> 0x000000000045c447 in pos_visible_p ()
> (gdb) bt
> #0  0x000000000045c447 in pos_visible_p ()
> #1  0x000000000047ddab in Fpos_visible_in_window_p ()

Thanks.  This is a known bug in Emacs 27.2 (see bug#45156), which is
already fixed on the master branch.

So I'm closing this bug.