sf@neox:~$ gdb gnome-shell
GNU gdb (GDB) 7.12.1
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Reading symbols from gnome-shell...done.
(gdb) run
Starting program: /usr/bin/gnome-shell 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
[New Thread 0x7fffe0c18700 (LWP 18217)]
[New Thread 0x7fffd8334700 (LWP 18218)]

(gnome-shell:18213): mutter-WARNING **: (backends/meta-monitor.c:560):create_tiled_monitor_mode: runtime check failed: (mode->spec.refresh_rate == 0.0f || (mode->spec.refresh_rate == preferred_crtc_mode->refresh_rate))

Thread 1 "gnome-shell" received signal SIGSEGV, Segmentation fault.
meta_monitor_manager_tiled_monitor_removed (manager=0x0, monitor=0xaa0790)
    at backends/meta-monitor-manager.c:1695
1695	  if (manager_class->tiled_monitor_removed)
(gdb) 

