Hello,

As far as I can tell PPC registers are unsigned.  At present they are 
signed and this leads to weird problems such as:

(gdb) x/i $sp
0xffff0000: ... error accessing memory at 0xffff0000
(gdb) x/i 0xffff0000
0xffff0000: sc
(gdb)

the attached changes this.

ok, 6.1?

Andrew