Trace from the core dump (with qt enabled with dbg symbols):

root@ubuntu-desktop:/home/ubuntu/qt5/snowshoe-1.0~git+20120608# gdb ./snowshoe core 
GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2) 7.4-2012.04
Copyright (C) 2012 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 "arm-linux-gnueabihf".
For bug reporting instructions, please see:
<http://bugs.launchpad.net/gdb-linaro/>...
Reading symbols from /home/ubuntu/qt5/snowshoe-1.0~git+20120608/snowshoe...done.
[New LWP 8591]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".
Core was generated by `./snowshoe'.
Program terminated with signal 11, Segmentation fault.
#0  0xb2453698 in QXcbConnection::initializeXFixes (this=0x210bc70) at qxcbconnection.cpp:1045
1045	    xfixes_first_event = reply->first_event;
(gdb) l
1040	
1041	void QXcbConnection::initializeXFixes()
1042	{
1043	    xcb_generic_error_t *error = 0;
1044	    const xcb_query_extension_reply_t *reply = xcb_get_extension_data(m_connection, &xcb_xfixes_id);
1045	    xfixes_first_event = reply->first_event;
1046	
1047	    xcb_xfixes_query_version_cookie_t xfixes_query_cookie = xcb_xfixes_query_version(m_connection,
1048	                                                                                     XCB_XFIXES_MAJOR_VERSION,
1049	                                                                                     XCB_XFIXES_MINOR_VERSION);
(gdb) bt full
#0  0xb2453698 in QXcbConnection::initializeXFixes (this=0x210bc70) at qxcbconnection.cpp:1045
        xfixes_query_cookie = {sequence = 0}
        xfixes_query = 0xffffffff
        __PRETTY_FUNCTION__ = "void QXcbConnection::initializeXFixes()"
        error = 0x0
        reply = 0x0
#1  0xb2451d70 in QXcbConnection::QXcbConnection (this=0x210bc70, nativeInterface=0x210bc08, displayName=0x0) at qxcbconnection.cpp:180
        dpy = 0x210bf38
        it = {data = 0x211286c, rem = 0, index = 1632}
        screenNumber = 2
#2  0xb24558ac in QXcbIntegration::QXcbIntegration (this=0x21047e8, parameters=...) at qxcbintegration.cpp:101
No locals.
#3  0xb24663be in QXcbIntegrationPlugin::create (this=0x21005e8, system=..., parameters=...) at main.cpp:66
No locals.
#4  0xb49db386 in qLoadPlugin1<QPlatformIntegration, QPlatformIntegrationFactoryInterface, QStringList> (loader=0x2100408, key=..., parameter1=...)
    at ../../include/QtCore/5.0.0/QtCore/private/../../../../../src/corelib/plugin/qfactoryloader_p.h:118
        result = 0xbecd8650
        factory = 0x21005f0
        factoryObject = 0x21005e8
        index = 3
#5  0xb49dac0e in QPlatformIntegrationFactory::create (key=..., platformPluginPath=...) at kernel/qplatformintegrationfactory_qpa.cpp:72
        ret = 0xbecd8464
        paramList = {<QList<QString>> = {{p = {static shared_null = {ref = {atomic = {_q_value = -1}}, alloc = 0, begin = 0, end = 0, array = {0x0}}, 
                d = 0x21003b0}, d = 0x21003b0}}, <No data fields>}
        platform = {static null = {<No data fields>}, d = 0x2100390}
#6  0xb49e0570 in init_platform (pluginArgument=..., platformPluginPath=...) at kernel/qguiapplication.cpp:629
        name = {static null = {<No data fields>}, d = 0x2100390}
        arguments = {<QList<QString>> = {{p = {static shared_null = {ref = {atomic = {_q_value = -1}}, alloc = 0, begin = 0, end = 0, array = {0x0}}, 
                d = 0xb478ece8}, d = 0xb478ece8}}, <No data fields>}
        __PRETTY_FUNCTION__ = "void init_platform(const QString&, const QString&)"
        themeNames = {<QList<QString>> = {{p = {static shared_null = {ref = {atomic = {_q_value = -1}}, alloc = 0, begin = 0, end = 0, array = {0x0}}, 
                d = 0xbecd84e8}, d = 0xbecd84e8}}, <No data fields>}
#7  0xb49e110a in QGuiApplicationPrivate::createPlatformIntegration (this=0x20ff968) at kernel/qguiapplication.cpp:753
        platformPluginPath = {static null = {<No data fields>}, d = 0xb478d16c}
        platformName = {d = 0x20ff898}
        platformNameEnv = {d = 0xb478d0b4}
        j = 1
#8  0xb49e11b8 in QGuiApplicationPrivate::createEventDispatcher (this=0x20ff968) at kernel/qguiapplication.cpp:760
No locals.
#9  0xb4eadb40 in QApplicationPrivate::createEventDispatcher (this=0x20ff968) at kernel/qapplication_qpa.cpp:90
No locals.
#10 0xb46de0d0 in QCoreApplication::init (this=0xbecd8650) at kernel/qcoreapplication.cpp:567
        d = 0x20ff968
#11 0xb46ddf40 in QCoreApplication::QCoreApplication (this=0xbecd8650, p=...) at kernel/qcoreapplication.cpp:508
No locals.
#12 0xb49dfb12 in QGuiApplication::QGuiApplication (this=0xbecd8650, p=...) at kernel/qguiapplication.cpp:342
No locals.
#13 0xb4e427c4 in QApplication::QApplication (this=0xbecd8650, argc=@0xbecd864c: 1, argv=0xbecd8824, _internal=327680) at kernel/qapplication.cpp:554
No locals.
#14 0x00011380 in main (argc=1, argv=0xbecd8824) at main.cpp:35
        app = {<QGuiApplication> = {<QCoreApplication> = {<QObject> = {_vptr.QObject = 0xb493ca88, static staticMetaObject = {d = {superdata = 0x0, 
                    stringdata = 0xb4816e28, data = 0xb4816f00, 
                    static_metacall = 0xb47125c5 <QObject::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, 
                    extradata = 0x0}}, d_ptr = {d = 0x20ff968}, static staticQtMetaObject = {d = {superdata = 0x0, stringdata = 0xb4890300, 
                    data = 0xb4897bb8, static_metacall = 0, relatedMetaObjects = 0x0, extradata = 0x0}}}, static staticMetaObject = {d = {
                  superdata = 0x1e6780, stringdata = 0xb4813c98, data = 0xb4813dec, 
                  static_metacall = 0xb46e0ffd <QCoreApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, relatedMetaObjects = 0x0, 
                  extradata = 0x0}}, static self = 0xbecd8650}, static staticMetaObject = {d = {superdata = 0xb493ca48, stringdata = 0xb4c738b4, 
                data = 0xb4c73a7c, static_metacall = 0xb49e5395 <QGuiApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, 
                relatedMetaObjects = 0x0, extradata = 0x0}}}, static staticMetaObject = {d = {superdata = 0xb4d112d8, stringdata = 0xb521013c, 
              data = 0xb5210418, static_metacall = 0xb4e4ae3d <QApplication::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)>, 
              relatedMetaObjects = 0x0, extradata = 0x0}}}
        arguments = {<QList<QString>> = {{p = {static shared_null = {ref = {atomic = {_q_value = -1}}, alloc = 0, begin = 0, end = 0, array = {0x0}}, 
                d = 0x3}, d = 0x3}}, <No data fields>}
        window = <optimized out>
        fullScreen = <optimized out>

And output from X11:

Backtrace:
Segmentation fault at address 0x68

Caught signal 11 (Segmentation fault). Server aborting

Please consult the The X.Org Foundation support 
	 at http://wiki.x.org
 for help. 
Please also check the log file at "/var/log/Xorg.0.log" for additional information.