NetBSD domU ksyms issue under xen 4.1.6.1 and 4.2.3, not under 4.1.2

[Jeff Rizzo <riz%tastylime.net@localhost>]

I ran into a weird problem today that I'm still not 100% sure the root 
cause of, and can use some additional ideas for what might be happening.

I'm setting up a new dom0 host, a lovely 12-core box with 72G RAM; it's 
running NetBSD 6.1.2/amd64 in dom0.  I launched a NetBSD 6.1.2/amd64 
domU, and noticed vmstat wasn't working:

domU14# vmstat 1
vmstat: undefined symbols: _allevents
domU14#

After some poking around, it looks like the symbol table as returned by 
/dev/ksyms is slightly corrupted - some symbols (but not a lot!) are 
missing.  Weird.

I have another system (dom0 - the one I'm replacing with the new box) 
with the same 6.1.2 domU image (I verified the md5), and the domU run on 
this system does NOT exhibit the problem.

Since the new box was running Xen 4.2.3 (binary pkg from 
ftp.netbsd.org), and the old box Xen 4.1.2 (package I built myself a 
year or two ago), I tried backing out to the Xen 4.1.6.1 package on 
ftp.netbsd.org on the new box, and I got the same result.

If, however, I tar up the xenkernel41 and xentools41 package from the 
working system and install on the new box, the domU starts working as 
expected!

Does anyone know what might be going on here?  Any suggestions for 
further testing?  I'd really like to move to a newer Xen package...

Working Xen kernel:

Loading /netbsd-XEN3_DOM0.gz
 __  __            _  _    _   ____
 \ \/ /___ _ __   | || |  / | |___ \
  \  // _ \ '_ \  | || |_ | |   __) |
  /  \  __/ | | | |__   _|| |_ / __/
 /_/\_\___|_| |_|    |_|(_)_(_)_____|
                                     xen4.1)
(XEN) Xen version 4.1.2 (riz@) (gcc version 4.5.3 (NetBSD nb2 20110806) 
) Tue Dec 27 23:41:48 PST 2011


Non-working:
 __  __            _  _    _   __    _
 \ \/ /___ _ __   | || |  / | / /_  / |
  \  // _ \ '_ \  | || |_ | || '_ \ | |
  /  \  __/ | | | |__   _|| || (_) || |
 /_/\_\___|_| |_|    |_|(_)_(_)___(_)_|

(XEN) Xen version 4.1.6.1 (pbulk@) (gcc version 4.5.3 (NetBSD nb2 
20110806) ) Thu Oct  3 00:12:36 UTC 2013


Note that the NetBSD install (in the dom0 or the domU) didn't change in 
any other way...

+j