Hi Stephen, all,
Stephen Berman writes:
Program received signal SIGSEGV, Segmentation fault.
0xb74b88fa in strcmp () from /lib/libc.so.6
(gdb) bt
#0 0xb74b88fa in strcmp () from /lib/libc.so.6
#1 0xb79c1b45 in FcObjectToPtr () from /usr/lib/libfontconfig.so.1
#2 0xb79c5741 in FcPatternAddWithBinding () from /usr/lib/libfontconfig.so.1
[...]
#41 0xb7df2c9c in gtk_widget_size_request ()
from /opt/gnome/lib/libgtk-x11-2.0.so.0
#42 0x080f181c in xg_update_frame_menubar (f=0x8644250)
at /home/steve/emacs-22.0.90/src/gtkutil.c:2924
#43 0x0808bb95 in set_frame_menubar (f=0x8644250, first_time=1, deep_p=1)
at /home/steve/emacs-22.0.90/src/xmenu.c:2098
#44 0x0808bd90 in initialize_frame_menubar (f=0x8644250)
at /home/steve/emacs-22.0.90/src/xmenu.c:2495
#45 0x080d6735 in Fx_create_frame (parms=139409981)
at /home/steve/emacs-22.0.90/src/xfns.c:3368
#46 0x08159461 in Ffuncall (nargs=2, args=0xbfe1dfa8)
at /home/steve/emacs-22.0.90/src/eval.c:2997
I got a crash in the same spot with the latest pretest and I found
this thread in the mail archive.
I analysed it like this:
- The crash occurs because Fontconfig's (libfontconfig.so) data
structures are corrupted, more specifically this involves a linked
list in Fontconfig's fcname.c.
- That linked list is built from data that is passed-in through a
Fontconfig API and used unchecked.
- The caller that registered this particular piece of data is Xft
(libXft.so), called through the QT library linked in by
gtk-qt-engine. gtk-qt-engine seems to be a Gnome theme, probably
used to coordinate settings of Gnome clients with KDE (my main
desktop).
- gtk-qt-engine is loaded during Emacs' call to
gtk_settings_set_string_property() in gtkutil.c:xg_initialize().
- When the crash occurs, gtk-qt-engine is not loaded any more. It
seems to get unloaded after the settings have been determined. Xft
is loaded (through Pango), but it is in a different place now than
it used to be before, because Pango has re-loaded it on-demand long
after it was already unloaded together with gtk-qt-engine.
The root cause seems to be that the Xft shared library is not
unloadable, it doesn't cleanup and unregister the data that it has
passed to fontconfig.
Work-arounds that fix it for me:
- Uninstall gtk-qt-engine.
- Preload Xft using LD_PRELOAD.
Possible work-around in Emacs:
- Link to Xft and call XftInit(0) in gtkutil.c:xg_initialize() or even
before that.
I'm not sure where exactly the problem *should* be fixed.
- Fontconfig could copy the data that comes in.
- Xft could allocate the data on the heap instead of using a static
structure.
- Xft could prevent unloading of itself.
- Xft could provide a cleanup routine for QT and/or gtk-qt-engine to
use.
- gtk-qt-engine could prevent unloading of Xft. It makes things
unusually complicated by combining the two toolkits in one process.
benny
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