Created attachment 68982 [details]
xorg.0.log

System Environment:
--------------------------
Arch:           i386
Platform:       Sandybridge
Libdrm:		(master)libdrm-2.4.39-20-ga4cb7233a8da171e53b48b376be5c1265c29a612
Mesa:		(master)ab7188e1992e655031550d611178c55abe33d5c5
Xserver:(master)xorg-server-1.13.0-55-ga69429a17bf4630f6e26f61630a1c2b287202627
Xf86_video_intel:(master)2.20.12-8-g4dfc83359d006a4e410e3280003b49683309afc3
Libva:		(staging)86484495155e65fd8ac33ed3ede43fb42defd966 Libva_intel_driver:(staging)f557dd6ad06c31bcf787468e804c948ecc4cf39b
Kernel:	(drm-intel-nightly) e47b4a11cc3e3c5bd83509e91886f3353508352e

Bug detailed description:
-------------------------
Run: xinit, X fails to start with headless.
It passes if connect a monitor.
It happens on sandybridge with mesa master branch.It doesn't happen on 9.0 branch.
The last known good commit: 9aa8bac98b823e8783bc3a06a6e5b23fbf8d87fb
The last known bad commit: 328961d95586931a17fe81ba816d362e8389c105

output:
(EE) module ABI major version (7) doesn't match the server's version (14)
Loading extension GLX

Fatal server error:
no screens found
(EE)
Please consult the The X.Org Foundation support
         at http://wiki.x.org
 for help.
(EE) Please also check the log file at "/opt/X11R7/var/log/Xorg.0.log" for additional information.
(EE)
Server terminated with error (1). Closing log file.
giving up.
xinit:  Connection refused (errno 111):  unable to connect to X server
xinit:  No such process (errno 3):  Server error.

[1]+  Exit 1                  xinit

Reproduce steps:
----------------
1. Disconnect monitor
2. xinit