two Xen failures

I have a VPS on RootBSD (freebsd developer's discount).
They use Xen on their vps servers.

yesterday I tried to upgrade my server to -current and came across two 
interesting failure modes.

1/ I somehow wrote a kernel that made the loader crash when loading it 
(not running it).
this was Not Good (TM)  because the loader loads the kernel BEFORE it 
gets to the prompt so there was no way for me to type in the name of 
an alternate kernel. (actually I may have been ab;e to do it from the 
stage 2 loader if I could remember the syntax and hte stage 2 lader 
could load ELF binaries (I remember it could only do a.out .. is that 
still true?))

It's distressing that the loader can be made to crash from loading a 
misformed kernel.
I still have it if anyone is still interested in pulling it apart to 
see what is weird about it.

2/ it is impossible for me to make a -current kernel that can mount root.
it finds the drive, then it tastes it to see if there is a lable it 
wants, fails and then I get an infinite (apparently) set of "waiting 
for root device : usbus0"
(or similar)messages.
a kernel compiled from -current in Jan 1 this year boots just fine
but I hav enot tried bisecting further (it is after all my MAIN server)
I have tried a minimal kernel, a GENERIC kernel, and a XENHVM kernel.
All behave the same.

If I have some time I will try bisect further but I plan on asking 
RootBSD if htey can give me a different VPS to try fdo it on as I 
don't want to screw up my server.. (again).

Julian