Michael Hitch writes:

>  Here's a start - I can now execute a dhrystone program compiled on
>Ultrix with the -mips3 option.  All it does is recognize the mips3 binary
>as a valid ECOFF binary.  I'm not sure what to do to verify that it's
>only valid on mips3 cpus.

I'm just guessing, but I think the right thing to do is to add code to
mips/mips/cpu_exec.c:cpu_ecoff_exec_hook(), to check the required
cputype from the ECOFF binary against the current CPU type.

(I think there are already macro hooks to handle a similar test for
native execs, I don't know about ECOFF.)

That would work for executing the additional mips3 instructions in
32-bit mode.

Of course the kernel also needs to save and restore all 64 bits of
register contents (either FP or integer) before user code can safely
use 64-bit registers.