I am using Kubuntu 13.10 and since my upgrade to this version I see a reproducable crash during the start of the X-server. I am using the free Radeon driver, not the propietary fglrx one.

Adding "nomodeset" to the grub boot manager suppress the crash.

I have already opened a bug in Ubuntu launchpad and added a lot of information, but was unable to get any feedback about my problem:
https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/1241973

Xorg version:
-------------

X.Org X Server 1.14.3
Release Date: 2013-09-12
X Protocol Version 11, Revision 0
Build Operating System: Linux 3.2.0-37-generic x86_64 Ubuntu
Current Operating System: Linux henning-desktop 3.11.0-13-generic #20-Ubuntu SMP Wed Oct 23 07:38:26 UTC 2013 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.11.0-13-generic root=UUID=05496ac7-b628-444e-b652-e4f5b08ce1a9 ro quiet nomodeset
Build Date: 15 October 2013  09:23:37AM
xorg-server 2:1.14.3-3ubuntu2 (For technical support please see http://www.ubuntu.com/support) 
Current version of pixman: 0.30.2

Crash Backtrace:
----------------

[    33.092] (II) glamor: EGL version 1.4 (DRI2):
[    33.093] (EE) 
[    33.093] (EE) Backtrace:
[    33.093] (EE) 0: /usr/bin/X (xorg_backtrace+0x3d) [0x7f0060e2502d]
[    33.093] (EE) 1: /usr/bin/X (0x7f0060c83000+0x1a5d99) [0x7f0060e28d99]
[    33.093] (EE) 2: /lib/x86_64-linux-gnu/libpthread.so.0 (0x7f005fd83000+0xfbb0) [0x7f005fd92bb0]
[    33.094] (EE) 3: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZNK4llvm3EVT21getExtendedSizeInBitsEv+0x4) [0x7f0057e5ff44]
[    33.094] (EE) 4: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZN4llvm12SelectionDAG7getLoadENS_3ISD14MemIndexedModeENS1_11LoadExtTypeENS_3EVTENS_8DebugLocENS_7SDValueES6_S6_NS_18MachinePointerInfoES4_bbbjPKNS_6MDNodeESA_+0x297) [0x7f0058358c17]
[    33.094] (EE) 5: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZN4llvm12SelectionDAG10getExtLoadENS_3ISD11LoadExtTypeENS_8DebugLocENS_3EVTENS_7SDValueES5_NS_18MachinePointerInfoES4_bbjPKNS_6MDNodeE+0x12a) [0x7f0058359e1a]
[    33.094] (EE) 6: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZNK4llvm18R600TargetLowering20LowerFormalArgumentsENS_7SDValueENS_11CallingConv2IDEbRKNS_15SmallVectorImplINS_3ISD8InputArgEEENS_8DebugLocERNS_12SelectionDAGERNS4_IS1_EE+0x24a) [0x7f00581971aa]
[    33.094] (EE) 7: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZN4llvm16SelectionDAGISel14LowerArgumentsERKNS_8FunctionE+0x683) [0x7f0058383453]
[    33.095] (EE) 8: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZN4llvm16SelectionDAGISel20SelectAllBasicBlocksERKNS_8FunctionE+0xa0a) [0x7f005839924a]
[    33.095] (EE) 9: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZN4llvm16SelectionDAGISel20runOnMachineFunctionERNS_15MachineFunctionE+0x361) [0x7f005839a061]
[    33.095] (EE) 10: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZN4llvm13FPPassManager13runOnFunctionERNS_8FunctionE+0x1d7) [0x7f0057e4da67]
[    33.095] (EE) 11: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZN4llvm13FPPassManager11runOnModuleERNS_6ModuleE+0x2b) [0x7f0057e4dafb]
[    33.095] (EE) 12: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZN4llvm13MPPassManager11runOnModuleERNS_6ModuleE+0x20b) [0x7f0057e4dd2b]
[    33.096] (EE) 13: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (_ZN4llvm15PassManagerImpl3runERNS_6ModuleE+0xac) [0x7f0057e4febc]
[    33.096] (EE) 14: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (0x7f00575d8000+0xe6ed70) [0x7f0058446d70]
[    33.096] (EE) 15: /usr/lib/x86_64-linux-gnu/libLLVM-3.3.so.1 (LLVMTargetMachineEmitToMemoryBuffer+0x155) [0x7f00584470b5]
[    33.096] (EE) 16: /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so (radeon_llvm_compile+0x1a6) [0x7f0059c8a3c6]
[    33.096] (EE) 17: /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so (si_compile_llvm+0x75) [0x7f0059c7fac5]
[    33.096] (EE) 18: /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so (si_pipe_shader_create+0x4c1) [0x7f0059c80241]
[    33.096] (EE) 19: /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so (si_shader_select+0x28e) [0x7f0059c8641e]
[    33.096] (EE) 20: /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so (0x7f0059c6c000+0x1a6ba) [0x7f0059c866ba]
[    33.096] (EE) 21: /usr/lib/x86_64-linux-gnu/libgallium.so.0 (ureg_create_shader+0x4f) [0x7f00591022ff]
[    33.096] (EE) 22: /usr/lib/x86_64-linux-gnu/libgallium.so.0 (util_make_empty_fragment_shader+0x6d) [0x7f005912e78d]
[    33.096] (EE) 23: /usr/lib/x86_64-linux-gnu/libgallium.so.0 (util_blitter_create+0x42d) [0x7f005911001d]
[    33.096] (EE) 24: /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so (0x7f0059c6c000+0x1083f) [0x7f0059c7c83f]
[    33.096] (EE) 25: /usr/lib/x86_64-linux-gnu/libgallium.so.0 (0x7f0059086000+0x164772) [0x7f00591ea772]
[    33.096] (EE) 26: /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so (dri_create_context+0x197) [0x7f0059c8d1e7]
[    33.096] (EE) 27: /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so (0x7f0059c6c000+0xa600) [0x7f0059c76600]
[    33.096] (EE) 28: /usr/lib/x86_64-linux-gnu/mesa-egl/libEGL.so.1 (0x7f005d441000+0x11ce8) [0x7f005d452ce8]
[    33.096] (EE) 29: /usr/lib/x86_64-linux-gnu/mesa-egl/libEGL.so.1 (eglCreateContext+0x90) [0x7f005d449310]
[    33.096] (EE) 30: /usr/lib/xorg/modules/libglamoregl.so (glamor_egl_init+0x19c) [0x7f005d665e6c]
[    33.096] (EE) 31: /usr/lib/xorg/modules/drivers/radeon_drv.so (0x7f005a8e6000+0x4c3f1) [0x7f005a9323f1]
[    33.096] (EE) 32: /usr/lib/xorg/modules/drivers/radeon_drv.so (0x7f005a8e6000+0x45abf) [0x7f005a92babf]
[    33.096] (EE) 33: /usr/bin/X (InitOutput+0xadd) [0x7f0060d1907d]
[    33.096] (EE) 34: /usr/bin/X (0x7f0060c83000+0x4437b) [0x7f0060cc737b]
[    33.096] (EE) 35: /lib/x86_64-linux-gnu/libc.so.6 (__libc_start_main+0xf5) [0x7f005e9bede5]
[    33.096] (EE) 36: /usr/bin/X (0x7f0060c83000+0x448af) [0x7f0060cc78af]
[    33.096] (EE) 
[    33.096] (EE) Segmentation fault at address 0x8
[    33.096] (EE) 
Fatal server error:
[    33.096] (EE) Caught signal 11 (Segmentation fault). Server aborting