I have an Ultra Sparc Enterprise E250, which can boot and work fine with an UP kernel (kernel-image-2.4.26-sparc64) but not with the SMP one (kernel-image-2.4.26-sparc64-smp):
Sun (TM) Enterprise 250 (2 X UltraSPARC-II 400MHz), No Keyboard OpenBoot 3.26, 2048 MB memory installed, Serial #10943764. Ethernet address 8:0:20:a6:fd:14, Host ID: 80a6fd14. Rebooting with command: boot Boot device: disk File and args: SILO Version 1.4.5 boot: Allocated 8 Megs of memory at 0x40000000 for kernel Uncompressing image... Loaded kernel version 2.4.26 Remapping the kernel... Booting Linux... Starting CPU 1... Illegal Instruction {1} ok