Subject: bug#65726: 29.1.50; Crash in regexp engine

From: martin rudalics <[email-masked]>
Date: Mon, 4 Sep 2023 09:46:24 +0200

With emacs -Q load the attached file elinfo.el.  Now type

C-h S split-window RET

C-x o

C-c C-g

This crashes Emacs here with

Thread 1 "emacs" received signal SIGSEGV, Segmentation fault.
0x000000000068810a in skip_noops (p=<error reading variable: Cannot access memory at address 0x7fffff66fff8>, pend=<error reading variable: Cannot access memory at address 0x7fffff66fff0>) at ../../src/regex-emacs.c:3556
3556	{

and an infinite backtrace starting with

Python Exception <class 'gdb.MemoryError'> Cannot access memory at address 0x7fffff66fff8:
#0  0x000000000068810a in skip_noops (p=#1  0x0000000000688823 in mutually_exclusive_p (bufp=0xec9c30 <searchbufs+752>, p1=0x1fcee74 "\004\005", p2=0x1fcee81 "\016\063") at ../../src/regex-emacs.c:3665
#2  0x0000000000688e19 in mutually_exclusive_p (bufp=0xec9c30 <searchbufs+752>, p1=0x1fcee74 "\004\005", p2=0x1fcee81 "\016\063") at ../../src/regex-emacs.c:3838
#3  0x0000000000688e3c in mutually_exclusive_p (bufp=0xec9c30 <searchbufs+752>, p1=0x1fcee74 "\004\005", p2=0x1fceeba "\004\020") at ../../src/regex-emacs.c:3839
#4  0x0000000000688e3c in mutually_exclusive_p (bufp=0xec9c30 <searchbufs+752>, p1=0x1fcee74 "\004\005", p2=0x1fcee84 "\002\001@\004\020") at ../../src/regex-emacs.c:3839
#5  0x0000000000688e19 in mutually_exclusive_p (bufp=0xec9c30 <searchbufs+752>, p1=0x1fcee74 "\004\005", p2=0x1fcee81 "\016\063") at ../../src/regex-emacs.c:3838
...

The same scenario worked well with Emacs 22 through 28.

martin

In GNU Emacs 29.1.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.5,
  cairo version 1.16.0) of 2023-09-03 built on restno
Repository revision: f1e4cbe72aa4da9351cbbcd209d9233c68dd9fbb
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Configured using:
  'configure --with-gif=ifavailable --with-tiff=ifavailable
  --with-gnutls=no --without-pop --enable-gcc-warnings=warn-only
  --enable-checking=yes,glyphs --enable-check-lisp-object-type=yes
  'CFLAGS=-O0 -g3 -no-pie -Wno-missing-braces''

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GSETTINGS HARFBUZZ JPEG LIBSELINUX MODULES
NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND THREADS TOOLKIT_SCROLL_BARS X11
XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
   value of $LANG: de_AT.utf8
   value of $XMODIFIERS: @im=ibus
   locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
   tooltip-mode: t
   global-eldoc-mode: t
   eldoc-mode: t
   show-paren-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   blink-cursor-mode: t
   line-number-mode: t
   indent-tabs-mode: t
   transient-mark-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
cl-loaddefs cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils elinfo texinfo texinfo-loaddefs info rmc
iso-transl tooltip cconv eldoc paren electric uniquify ediff-hook
vc-hooks lisp-float-type elisp-mode mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode lisp-mode prog-mode register
page tab-bar menu-bar rfn-eshadow isearch easymenu timer select
scroll-bar mouse jit-lock font-lock syntax font-core term/tty-colors
frame minibuffer nadvice seq simple cl-generic indonesian philippine
cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese composite emoji-zwj charscript
charprop case-table epa-hook jka-cmpr-hook help abbrev obarray oclosure
cl-preloaded button loaddefs theme-loaddefs faces cus-face macroexp
files window text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget keymap hashtable-print-readable backquote
threads dbusbind inotify dynamic-setting system-font-setting
font-render-setting cairo move-toolbar gtk x-toolkit xinput2 x multi-tty
make-network-process emacs)

Memory information:
((conses 16 45758 8352)
  (symbols 48 5682 0)
  (strings 32 15622 2110)
  (string-bytes 1 431024)
  (vectors 16 10081)
  (vector-slots 8 157669 13073)
  (floats 8 26 23)
  (intervals 56 218 0)
  (buffers 976 10))