Maybe this is useful....
I have just installed x86_64 current on a Dell M3800. It has an Intel chipset but also uses the Nvidia "Optimus" technology. I get this crash and output, but only after restarting X. That is, I boot up fine and can startx no problem. If I then log out of X, and try to startx again, this happens *but not all the time*. Sometimes X will start fine again.
I can provide more output from the logs etc if anyone is interested. I think a few things need ironing out in my system, and I also attempted in install the nvidia proprietary driver before fully understanding the Optimus technology (and added complication). I have disabled the offending nvidia drivers and they no longer appear in the logs.
[ 37059.987] (EE) Backtrace:
[ 37059.987] (EE) 0: /usr/libexec/Xorg (xorg_backtrace+0x49) [0x581b09]
[ 37059.987] (EE) 1: /usr/libexec/Xorg (0x400000+0x1859e9) [0x5859e9]
[ 37059.987] (EE) 2: /lib64/libpthread.so.0 (0x7fbf9f16b000+0x11340) [0x7fbf9f17c340]
[ 37059.987] (EE) 3: /usr/lib64/libpixman-1.so.0 (pixman_region_selfcheck+0x35) [0x7fbf9fbae355]
[ 37059.987] (EE) 4: /usr/lib64/libpixman-1.so.0 (pixman_region_fini+0x9) [0x7fbf9fbae4d9]
[ 37059.987] (EE) 5: /usr/lib64/xorg/modules/drivers/intel_drv.so (0x7fbf99795000+0x5d1e6) [0x7fbf997f21e6]
[ 37059.987] (EE) 6: /usr/lib64/xorg/modules/drivers/intel_drv.so (0x7fbf99795000+0x5afc0) [0x7fbf997effc0]
[ 37059.987] (EE) 7: /usr/libexec/Xorg (0x400000+0x10de4d) [0x50de4d]
[ 37059.987] (EE) 8: /usr/libexec/Xorg (0x400000+0x1048b1) [0x5048b1]
[ 37059.987] (EE) 9: /usr/libexec/Xorg (0x400000+0x37997) [0x437997]
[ 37059.987] (EE) 10: /usr/libexec/Xorg (0x400000+0x3b9cb) [0x43b9cb]
[ 37059.987] (EE) 11: /lib64/libc.so.6 (__libc_start_main+0xf0) [0x7fbf9d7ba870]
[ 37059.987] (EE) 12: /usr/libexec/Xorg (_start+0x29) [0x4270a9]
[ 37059.987] (EE)
[ 37059.987] (EE) Segmentation fault at address 0x0
[ 37059.987] (EE)
Fatal server error:
[ 37059.987] (EE) Caught signal 11 (Segmentation fault). Server aborting
[ 37059.987] (EE)
[ 37059.987] (EE)
Please consult the The X.Org Foundation support
at
http://wiki.x.org
for help.
[ 37059.987] (EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
[ 37059.987] (EE)
[ 37060.023] (EE) Server terminated with error (1). Closing log file.