Hi,
following mrg's advices I got a 32bit kernel compiled. But it doens't
boot on my ultra/1:
Rebooting with command: boot net netbsd32 -s                          
Boot device: /sbus/ledma@e,8400010/le@e,8c00000  File and args: netbsd32 -s
15400 >> NetBSD/sparc64 OpenFirmware Boot, Revision 
>> (bouyer@java, Sat Nov 10 22:15:45 MET 2001)
Using BOOTPARAMS protocol: ip address: 132.227.63.55, hostname: metal
root addr=132.227.63.44 path=/home/NetBSD/sparc
loadfile: reading header
elf32_exec: Booting /sbus@1f,0/ledma@e,8400010/le@e,8c00000/netbsd32
1878320@0x1000000+63668@0x1800000+4130636@0x180f8b4 
symbols @ 0xfff501ec 74+109504+86012 start=0x1000000
chain: calling OF_chain(800000, eef0, 1000000, fffb5a80, 18)
console is /sbus@1f,0/zs@f,1100000:a
Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001
    The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
    The Regents of the University of California.  All rights reserved.


RED State Exception

TL=0000.0000.0000.0005 TT=0000.0000.0000.0030
   TPC=0000.0000.0100.8958 TnPC=0000.0000.0100.895c TSTATE=0000.0044.5800.0d00
TL=0000.0000.0000.0004 TT=0000.0000.0000.0030
   TPC=0000.0000.0100.8958 TnPC=0000.0000.0100.895c TSTATE=0000.0044.5800.0d00
TL=0000.0000.0000.0003 TT=0000.0000.0000.0030
   TPC=0000.0000.0100.8958 TnPC=0000.0000.0100.895c TSTATE=0000.0044.5800.0d00
TL=0000.0000.0000.0002 TT=0000.0000.0000.0030
   TPC=0000.0000.0100.8958 TnPC=0000.0000.0100.895c TSTATE=0000.0044.5800.0d00
TL=0000.0000.0000.0001 TT=0000.0000.0000.0030
   TPC=0000.0000.0115.5ebc TnPC=0000.0000.0115.5ec0 TSTATE=0000.0099.8200.0c00


Watchdog Reset
Externally Initiated Reset

This is with both GENERIC32 and a custom kernel. The 64bit kernel derived from
the same config file boots fine.

What can I do to help debug this ?

Related note: I tried booting a GENERIC 64bit kernel on this machine with
a 32bit userland, hoping that compat_netbsd32 would do it. It fails when
trying to exec /bin/sh:
Rebooting with command: boot disk netbsd -s                           
Boot device: /sbus/espdma@e,8400000/esp@e,8800000/sd@0,0  File and args: netbsd -s
NetBSD IEEE 1275 Bootblock
..>> NetBSD/sparc64 OpenFirmware Boot, Revision 1.5
>> (bouyer@java, Sat Nov 10 22:14:35 MET 2001)
loadfile: reading header
elf64_exec: Booting /sbus@1f,0/espdma@e,8400000/esp@e,8800000/sd@0,0:a/netbsd
4759286@0x1000000+133944@0x1800000+4060360@0x1820b38 
symbols @ 0xfef86300 74+322704+172151 start=0x1000000
chain: calling OF_chain(800000, ee08, 1000000, fffb5a80, 18)
[ using 495704 bytes of netbsd ELF symbol table ]
console is /sbus@1f,0/zs@f,1100000:a
Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001
    The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
    The Regents of the University of California.  All rights reserved.

NetBSD 1.5Y (GENERIC) #0: Fri Nov  9 10:31:56 MET 2001
    bouyer@java:/home/cvs.netbsd.org/sys/arch/sparc64/compile/GENERIC
total memory = 128 MB
avail memory = 108 MB
using 832 buffers containing 6656 KB of memory
bootpath: /sbus@1f,0/espdma@e,8400000/esp@e,8800000/sd@0,0
mainbus0 (root): SUNW,Ultra-1
cpu0 at mainbus0: SUNW,UltraSPARC @ 142.993 MHz, version 0 FPU
cpu0: physical 4K instruction (32 b/l), 4K data (32 b/l), 2048K external (64 b/l) 
[...]
root on sd0a dumps on sd0b
root file system type: ffs
Enter pathname of shell or RETURN for sh: 
text_access_fault: pc=0 va=0
kernel trap 64: +fast instruction access MMU miss
Stopped in pid 7 (sh) at                 0:     undefined
db> tr
netbsd32_execve(8f530e0, 8f83dd0, 8f83dc0, 134bd6c, 0, 0) at netbsd32_execve+0x5
4
syscall(8f83ed0, 3b, 0, 176cc, 400, 2) at syscall+0x304
syscall_setup(4dfe0, ffffda88, 7a170, 7a170, 0, 0) at syscall_setup+0x12c
db> 

--
Manuel Bouyer, LIP6, Universite Paris VI.           Manuel.Bouyer@lip6.fr
--