KDE crash dialog does not produce useful backtraces even when dbg packages are installed

[Alan Jenkins]

Environment: Kubuntu 9.04 i386 install
KDE version: 4.2.2-ubuntu4

Today I had a crash in krunner. The KDE crash dialogue appeared, and said that no useful backtrace could be generated. But I *have* installed the dbg packages.

E.g. I can run gdb against the running krunner, and resolve all symbols. So the crash handler should be able to as well!

$ gdb -p `pgrep krunner`
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
Attaching to process 4845
Reading symbols from /usr/bin/krunner...Reading symbols from /usr/lib/debug/usr/bin/krunner...done.
done.
...
(gdb) where
#0 0xb800a430 in __kernel_vsyscall ()
#1 0xb6795ae7 in *__GI___poll (fds=0x8920140, nfds=6, timeout=4995) at ../sysdeps/unix/sysv/linux/poll.c:87
#2 0xb507574b in g_poll () from /usr/lib/libglib-2.0.so.0
#3 0xb5067f82 in ?? () from /usr/lib/libglib-2.0.so.0
#4 0xb5068268 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#5 0xb6c05438 in QEventDispatcherGlib::processEvents (this=0x85bbf58, flags={i = -1074628040}) at kernel/qeventdispatcher_glib.cpp:323
#6 0xb714d3f5 in QGuiEventDispatcherGlib::processEvents (this=0x85bbf58, flags={i = -1074627992}) at kernel/qguieventdispatcher_glib.cpp:202
#7 0xb6bd806a in QEventLoop::processEvents (this=0xbff27ae0, flags={i = -1074627928}) at kernel/qeventloop.cpp:149
#8 0xb6bd84aa in QEventLoop::exec (this=0xbff27ae0, flags={i = -1074627864}) at kernel/qeventloop.cpp:200
#9 0xb6bda959 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:880
#10 0xb70abda7 in QApplication::exec () at kernel/qapplication.cpp:3553
#11 0xb7fcd916 in kdemain (argc=1, argv=0xbff27c64) at /build/buildd/kdebase-workspace-4.2.2/krunner/main.cpp:59
#12 0x08048712 in main (argc=Cannot access memory at address 0x6
) at /build/buildd/kdebase-workspace-4.2.2/obj-i486-linux-gnu/krunner/krunner_dummy.cpp:3
(gdb)

And here are the dbg packages I have installed:

$ dpkg-query -l "*dbg*" | grep ii
ii amarok-dbg 2:2.0.2mysql5.1.30-0ubuntu3 debugging symbols for Amarok
ii kdebase-dbg 4:4.2.2-0ubuntu4 debugging symbols for the KDE 4 base applica
ii kdebase-runtime-dbg 4:4.2.2-0ubuntu1 debugging symbols for KDE 4 base runtime mod
ii kdebase-workspace-dbg 4:4.2.2-0ubuntu2 debugging symbols for the KDE 4 base workspa
ii kdelibs-dbg 4:3.5.10.dfsg.1-1ubuntu8 debugging symbols for kdelibs
ii kdelibs5-dbg 4:4.2.2-0ubuntu5 debugging symbols for the KDE 4 libraries mo
ii lib64gcc1-dbg 1:4.3.3-5ubuntu4 GCC support library (debug symbols)
ii lib64stdc++6-4.2-dbg 4.2.4-5ubuntu1 The GNU Standard C++ Library v3 (debugging f
ii libc6-dbg 2.9-4ubuntu6 GNU C Library: detached debugging symbols
ii libqt4-dbg 4.5.0-0ubuntu4 Qt 4 library debugging symbols
ii pkg-create-dbgsym 0.26 automatically build debug symbol ddeb packag
ii qt-x11-free-dbg 3:3.3.8-b-5ubuntu1 debugging symbols for qt-x11-free binaries

[Jonathan Thomas (echidnaman)]

Could you show the backtrace from the KDE crash handler please?

[Alan Jenkins (aj504)]

Jonathan Thomas wrote:
> Could you show the backtrace from the KDE crash handler please?
>
> ** Package changed: kdelibs (Ubuntu) => kde4libs (Ubuntu)
>
> ** Changed in: kde4libs (Ubuntu)
> Status: New => Incomplete
>

(I don't have a _reproducable_ crash, so for testing I've been
triggering one with "kill -SIGSEGV").

Hmm, it works fine now. Confusing. Maybe KDE only picked up the dbg
packages when I logged out or rebooted. Since it works for me now, I'm
happy to close the bug.

Do you think it's worth pursuing? I could have another go with the
LiveCD, and experiment with installing the dbg packages from my apt
cache. That would show whether it was necessary to log out or not.
Obviously I couldn't test rebooting :-).

My expectation is that installing the dbg packages should have an
immediate effect. It should be possible since the debug symbols are
only loaded when the crash happens. I think it makes sense from the
user POV. Also it should make it easier to report crashes without
having to worry about losing the state that causes the bug.

Ta
Alan

[Jonathan Thomas (echidnaman)]

Sometimes even when you have -dbg packages installed, gdb (what the KDE crash handler uses) can't get a good backtrace. Not having the symbols is not the only way for a backtrace to be incomplete, though most times when users get useless backtraces, it is due to them not having the symbols.

Anways, without the backtrace KDE was claiming was invalid, it's pretty much impossible to diagnose the issue. Thanks for the report anyways.