sf@neox:~$ gdb gnome-shell
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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 1400)]
[New Thread 0x7fffd8334700 (LWP 1404)]

(gnome-shell:1390): 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) backtrace full
#0  0x00007ffff6d18580 in meta_monitor_manager_tiled_monitor_removed (manager=0x0, monitor=0xaa0790)
    at backends/meta-monitor-manager.c:1695
Python Exception <class 'gdb.MemoryError'> Cannot access memory at address 0x0: 
        manager_class = #1  0x00007ffff5865c7a in g_object_unref () at /usr/lib/libgobject-2.0.so.0
#2  0x00007ffff5583a6d in g_list_foreach () at /usr/lib/libglib-2.0.so.0
#3  0x00007ffff5583a8b in g_list_free_full () at /usr/lib/libglib-2.0.so.0
#4  0x00007ffff6d18601 in rebuild_monitors (manager=0x6641d0) at backends/meta-monitor-manager.c:1647
        i = <optimized out>
        old_outputs = 0xaa4400
        old_crtcs = 0xaa6710
        old_modes = 0xaa5dd0
        n_old_outputs = 4
        n_old_crtcs = 4
        n_old_modes = 49
#5  0x00007ffff6d18601 in meta_monitor_manager_read_current_state (manager=0x6641d0)
    at backends/meta-monitor-manager.c:1731
        old_outputs = 0xaa4400
        old_crtcs = 0xaa6710
        old_modes = 0xaa5dd0
        n_old_outputs = 4
---Type <return> to continue, or q <return> to quit---
        n_old_crtcs = 4
        n_old_modes = 49
#6  0x00007ffff6d208f1 in meta_monitor_manager_xrandr_ensure_initial_config (manager=0x6641d0)
    at backends/x11/meta-monitor-manager-xrandr.c:1293
#7  0x00007ffff6d1880c in meta_monitor_manager_ensure_initial_config (manager=0x6641d0)
    at backends/meta-monitor-manager.c:281
        manager = 0x6641d0
        manager_class = <optimized out>
#8  0x00007ffff6d1880c in meta_monitor_manager_constructed (object=<optimized out>)
    at backends/meta-monitor-manager.c:445
        manager = 0x6641d0
        manager_class = <optimized out>
#9  0x00007ffff5866777 in  () at /usr/lib/libgobject-2.0.so.0
#10 0x00007ffff5867c0d in g_object_newv () at /usr/lib/libgobject-2.0.so.0
#11 0x00007ffff58683c4 in g_object_new () at /usr/lib/libgobject-2.0.so.0
#12 0x00007ffff6d093a5 in create_monitor_manager (backend=0x6370d0) at backends/meta-backend.c:308
#13 0x00007ffff6d093a5 in meta_backend_real_post_init (backend=0x6370d0) at backends/meta-backend.c:320
#14 0x00007ffff6d1cba6 in meta_backend_x11_post_init (backend=0x6370d0)
    at backends/x11/meta-backend-x11.c:432
---Type <return> to continue, or q <return> to quit---
        monitor_manager = <optimized out>
        major = 2
        minor = 3
#15 0x00007ffff6d1dbd9 in meta_backend_x11_cm_post_init (backend=0x6370d0)
    at backends/x11/cm/meta-backend-x11-cm.c:83
#16 0x00007ffff6d477bc in meta_init () at core/main.c:567
        act = 
          {__sigaction_handler = {sa_handler = 0x1, sa_sigaction = 0x1}, sa_mask = {__val = {0 <repeats 16 times>}}, sa_flags = 0, sa_restorer = 0x1}
        empty_mask = {__val = {0 <repeats 16 times>}}
        compositor_type = <optimized out>
        backend_gtype = 6508768
#17 0x0000000000401d52 in main (argc=<optimized out>, argv=<optimized out>) at main.c:427
        ctx = 0x633b60
        error = 0x0
        ecode = <optimized out>
(gdb) 

