I have looked through your dmesg and your Xorg log file. Things I have noted:
- You were running 4.7-release/i386.
- You are using your own xorg.conf file. Where did yours come from?
- What happens when you use the OpenBSD default, with no xorg.conf?
- You mentioned xdm as a failure vector. Does X work without xdm?
While I found nothing in the misc@ mailing list archives matching this, I did find an open bug that seems to match it.
See
http://cvs.openbsd.org/cgi-bin/query...s&numbers=6392 -- and note the request for backtrace information from developer Owain Ainsworth. His Email address is in there, too.
Before contacting him....
Here is a link to the README for Xenocara, OpenBSD's packaging of Xorg software. How to get a crash dump is shown at the bottom of the README file:
http://www.openbsd.org/cgi-bin/cvsweb/~checkout~/xenocara/README?rev=1.26;content-type=text%2Fplain;only_with_tag=OPENBSD_4_7_BASE
Working with the crashdump to get the backtrace is discussed in the
crash(8) man page.
If this is too much work, try a 4.8-beta snapshot. It is possible your problem may have been fixed -- this bug does not have enough information to confirm it closed.