X crashes system?

[Robert Huff]

	[I'm including both graphics and x11 becasue I haven't been able
to narrow it down, and because extra brains might see something.]

Hello:
	1) I have an older and64 system with a Radeon HD 3300/RS780 gpu.
	2) I recently upgraded it from 11-RC2 to

	FreeBSD 13.0-CURRENT r344507  amd64

	and recompiled (from source) _all_ installed ports.
	3) When I originally booted the new system, it was not using any
of the new drm system ... and everything worked fine using the vesa
driver.  (Slowly, but fine.)
	With the oft-tested patience of Niclas Zeising
(zeising+freebsd at daemonic.se) I got drm-legacy-kmod and gpu-firmware-kmod
working.
	Sort of.
	4) With:

	kld_list="/boot/modules/radeonkms.ko"

	in rc.conf, the system boots, recognizes the gpu, comes
successfully to the console with vtys 1-11 enabled. Every that needs
text mode runs correctly and the system is stable.
	5) If I start xdm, the login screen appears and accepts input.
If I don't actually log in, this is also stable (for 24 hours and
counting).
	6) If I _do_ log in, .xsession is processed correctly and the
display accepts input.  However: the system will then panic after a
time ranging from 60 seconds to 30 minutes.  This happens even if the
only two programs running are the window manager (fvwm) and xmessage
(used to end the X session) and there's no activity on mouse or
keyboard.
	And: while the system is up, moving/resizing a window will -
sometimes - leave visual artifacts on the screen.
	7) Superficial examination of the crash dumps appears to show a
variety of memory errors; analysis beyond that is why I'm here.
	8) The last three crash dumps, along with dmesg.boot, xorg.conf
and Xorg.0.log, can be found at: 

	http://209.6.230.48:8888/~huff/crash/

	9) If this is something I caused  - /mea maxima culpa/.  I just
want to find out what's happening and fix it (if possible).


			Respectfully.


				Robert Huff