23.1; json-read-string crashes emacs with long string
Carl Worth
cworth at cworth.org
Tue May 18 09:08:17 PDT 2010
> Please describe exactly what actions triggered the bug
> and the precise symptoms of the bug:
A user of the emacs-based mail client, Notmuch [*], found that
attempting to display a particular message would consistently
causes a segmentation fault in emacs.
I tracked this down to calling `json-read-string' with a very long
string, (roughly 1 million characters). Rather than including that
enormous string in this message, here's a little snippet of emacs lisp
that creates and reads such a string. So, if evaluated, this code should
trigger the segmentation fault, (assuming a copy of GPLv3 exists at
/usr/share/emacs/23.1/etc/COPYING---adjust the filename if necessary).
;; Caution: Evaluating the block below has been known to crash emacs
(with-temp-buffer
(require 'json)
;; First we just need a lot of text. 32 copies of GPLv3 seems to do it
(dotimes (i 32)
(insert-file "/usr/share/emacs/23.1/etc/COPYING"))
;; Now create a buffer with a json-encoded version of the text
(let ((json-string (json-encode-string (buffer-string))))
(with-temp-buffer
(insert json-string)
(goto-char (point-min))
;; And try to read the string. This triggers the segfault.
(json-read-string))))
> If Emacs crashed, and you have the Emacs process in the gdb debugger,
> please include the output from the following gdb commands:
> `bt full' and `xbacktrace'.
I haven't attempted to debug this within gdb yet, (I'll have to get my
hands on a build of emacs with debugging symbols first). But I wanted to
share things right away, so that perhaps someone else could do further
debugging and follow up.
In the meantime, notmuch folks, if you've got a good idea for modifying
notmuch to avoid this bug I'd be glad to hear it. Adjust followups to
include the notmuch list and not the gnu.org bug address as appropriate.
-Carl
[*] http://notmuchmail.org
PS. Here are some of the details provided by `report-emacs-bug':
In GNU Emacs 23.1.1 (i486-pc-linux-gnu, GTK+ Version 2.18.2)
of 2010-01-26 on raven, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.10799001
configured using `configure '--build=i486-linux-gnu' '--host=i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' '--localstatedir=/var/lib' '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' '--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.1/leim' '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 'CPPFLAGS=''
Important settings:
value of $LC_ALL: nil
value of $LC_COLLATE: nil
value of $LC_CTYPE: nil
value of $LC_MESSAGES: nil
value of $LC_MONETARY: nil
value of $LC_NUMERIC: nil
value of $LC_TIME: nil
value of $LANG: en_US.UTF-8
value of $XMODIFIERS: nil
locale-coding-system: utf-8-unix
default-enable-multibyte-characters: t
--
carl.d.worth at intel.com
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