Network booting issues

[Nils Ackermann <Nils.Ackermann@math.uni-giessen.de>]

Linux klio 2.2.18pre21 #1 Wed Nov 22 17:12:06 EST 2000 sparc64 unknown

Server: Ultra1 (sun4u)
Clients: SparcStation4 (sun4m)

Scenario: Let SS4s be diskless X-terminals for Ultra Server, using
`diskless' package.

I have working potato installations on the server and on one of the
clients (local, the disk is not removed yet).  I compiled a kernel
with root nfs, DHCP, BOOTP and rarp on the client, for sun4m
architecture.  I have mknbi from `netboot' v.  0.8.1-4 (potato).

1. On client and server, 

mknbi-linux -k zImage -o netboot-img

(where zImage is the sun4m kernel) gives

mknbi-linux: Could not find magic number in kernel image

(same with pertinent options `-d rom -i rom').

2. How can I compile a kernel for sun4m on the sun4u architecture?  Do
   I need a cross compiler for this?

Thanks for any help or pointers.

Nils