I figured out what's causing the infinite-SIGSEGVs on the B180 when the
kernel is loaded from disk: the PDC_COPROC call is failing, returning "-3".
the docs describe this as "error of unspecified type".  the kernel then
assumes that no FPU hardware is present, which causes any use of
floating-point instructions to fail because the FP emulation code is
pretty broken.  if I change the kernel to assume that an FPU exists
when this PDC call fails, then everything works fine.

it seems likely that something in the xxboot code is causing this, because
that's the only thing that's different from the netboot case.  I looked at
the xxboot sources but I don't see anything that looks relevant.  does
anyone have any ideas?

if no one has any suggestions then I'll just check in the above hack for now.

-Chuck