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bug#23741: 25.0.94; dbus crashes on 32-bit Cygwin
From: |
Ken Brown |
Subject: |
bug#23741: 25.0.94; dbus crashes on 32-bit Cygwin |
Date: |
Fri, 10 Jun 2016 12:12:17 -0400 |
User-agent: |
Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 |
The following elisp file, extracted from dbus-tests.el, causes a crash on
32-bit Cygwin unless emacs is built --with-wide-int.
$ cat dbus-crash.el
(require 'dbus)
(setq output
(shell-command-to-string "dbus-launch --sh-syntax"))
(when (string-match "DBUS_SESSION_BUS_ADDRESS='\\(.+\\)';" output)
(setq bus (match-string 1 output)))
(dbus-init-bus bus)
$ emacs -Q -l dbus-crash.el
Fatal error 11: Segmentation faultSegmentation fault (core dumped)
If there is already a session bus running before starting emacs, simply loading
the dbus library is enough to elicit the crash.
The problem is this line in Fdbus__init_bus in dbusbind.c:
XSETFASTINT (val, (intptr_t) connection);
Here 'connection' is a 32-bit pointer, which may be too big to be treated as an
integer in Emacs. In principle this could happen on any 32-bit platform, but
it is more likely to happen on Cygwin because the heap can be in high memory.
The following gdb session illustrates this.
(Note: For simplicity, I started a session bus before starting emacs, so that I
only had to load dbus to get a crash.)
$ gdb emacs
GNU gdb (GDB) (Cygwin 7.10.1-1) 7.10.1
[...]
Breakpoint 1 at 0x511474: file ../../emacs-25/src/emacs.c, line 354.
Temporary breakpoint 2 at 0x530bc1: file ../../emacs-25/src/sysdep.c, line 915.
(gdb) b Fdbus__init_bus
Breakpoint 3 at 0x50b41d: file ../../emacs-25/src/dbusbind.c, line 1124.
(gdb) r -Q
Starting program: /home/kbrown/src/emacs/32build-emacs-25/src/emacs -Q
[At this point I did M-x load-library RET dbus RET .]
Breakpoint 3, Fdbus__init_bus (bus=816, private=0)
at ../../emacs-25/src/dbusbind.c:1124
1124 XD_DBUS_VALIDATE_BUS_ADDRESS (bus);
(gdb) p bus
$1 = 816
(gdb) pr
:system
(gdb) c
Continuing.
Breakpoint 3, Fdbus__init_bus (bus=792, private=0)
at ../../emacs-25/src/dbusbind.c:1124
1124 XD_DBUS_VALIDATE_BUS_ADDRESS (bus);
(gdb) p bus
$2 = 792
(gdb) pr
:session
(gdb) n
[...]
1151 connection = dbus_bus_get (EQ (bus, QCdbus_system_bus)
(gdb)
1159 if (dbus_error_is_set (&derror))
(gdb) p connection
$3 = (DBusConnection *) 0x2007a960
(gdb) n
[...]
1190 XSETFASTINT (val, (intptr_t) connection);
(gdb)
1191 xd_registered_buses = Fcons (Fcons (bus, val),
xd_registered_buses);
(gdb) p/x val
$5 = 0x801ea582
(gdb) pr
-536368800
[At this point xd_registered_buses contains a bogus connection address for the
session bus.]
(gdb) c
Continuing.
Program received signal SIGSEGV, Segmentation fault.
0x67e2910d in dbus_connection_get_is_connected (connection=0xe007a960)
at /usr/src/debug/dbus-1.10.8-2/dbus/dbus-connection.c:2979
The bogus value 0xe007a960 (instead of 0x2007a960) was retrieved from
xd_registered_buses and caused the crash.
I suspect that there is a simple solution, which involves storing the
connection address in a Lisp Object of type other than integer, but I'll leave
that to the experts.
In GNU Emacs 25.0.94.1 (i686-pc-cygwin, GTK+ Version 3.18.9)
of 2016-06-10 built on desktop-new
Repository revision: 66d556b5187d768bbd233513b54dcb4beaa90c6d
Windowing system distributor 'The Cygwin/X Project', version 11.0.11802000
Configured using:
'configure 'CFLAGS=-g -O0''
Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GCONF GSETTINGS NOTIFY
ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11
Important settings:
value of $LANG: en_US.UTF-8
locale-coding-system: utf-8-unix
- bug#23741: 25.0.94; dbus crashes on 32-bit Cygwin,
Ken Brown <=