netbsd-5 diskless xdm pam failures?

["John D. Baker" <jdbaker%mylinuxisp.com@localhost>]

Shortly before the 5.2 release cycle, I started having problems with
a machine I run diskless.  It runs the native in-tree Xorg X11R7 in
the netbsd-5 branch.  If it makes any difference, it's a Dell Optiplex
GX110.

In particular, one can no-longer log in via 'xdm'.  The server is
immediately reset and the login widget redrawn.  At first, I thought
I had botched my custom ".xsession" script, but I copied the one that
is known to work on other systems and the problem remained.  I added
logging statements to verify, but it never got even that far.

The system's "/var/log/xdm.log" reads as follows:

--------------------
X.Org X Server 1.6.3
Release Date: 2009-7-7
X Protocol Version 11, Revision 0
Build Operating System: NetBSD/i386  - 
Current Operating System: NetBSD plextwo 5.2_STABLE NetBSD 5.2_STABLE (PLEXOR) #2: Thu Dec 20 01:08:04 CST 2012  sysop%verthandi.technoskunk.fur@localhost:/d0/build/netbsd-5/obj/i386/sys/arch/i386/compile/PLEXOR i386
Build Date: 09 July 2009  12:14:03AM

        Before reporting problems, check http://wiki.X.Org
        to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
        (++) from command line, (!!) notice, (II) informational,
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Thu Dec 20 12:29:44 2012
(==) Using config file: "/etc/X11/xorg.conf"
(EE) intel(0): Unknown EDID version 2
chown: Undefined PLT symbol "_libc_init" (symnum = 17)
X connection to :0.0 broken (explicit kill or server shutdown).
(EE) XKB: No components provided for device Virtual core keyboard
xdm error (pid 824): pam_authenticate failure: conversation failure
X connection to :0.0 broken (explicit kill or server shutdown).
--------------------

I'm puzzled by the error from "chown", but that part seems to be
working nonetheless.

I've seen the "conversation failure" in other contexts (SIGINT in
response to 'sudo' password prompt) but I'm lost as to what's going
on to elicit it from 'xdm'.

X-Windows otherwise works fine (via 'startx', etc).  I used to not have
any problems with 'xdm' graphical login on this diskless machine.

Unfortunately, I only have this one data point as it's the only machine
I have running netbsd-5 diskless.  The only other netbsd-5 system boots
from local disk (which built the release for itself and which populates
the NFS root for the diskless client).  Said disk-based machine has no
problems with 'xdm' authentication.

(I'd like to move to netbsd-6 on the diskless system, but Xorg is
broken on the i810e graphics hardware in this Dell Optiplex GX110
although it works fine on other i810e-based systems I have.  That's
a topic for another message.)

Hints for what to check or test are appreciated.

Thanks.

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