From: Paul Mackerras <paulus@samba.org>

This patch fixes a whole pile of problems in the xmon kernel debugger for
ppc64.  This basically makes xmon SMP-safe.  Now, when we enter xmon it
sends an IPI to the other CPUs to get them into xmon too.  It also changes
the way we do single-stepping and breakpoints so that we don't have to
remove a breakpoint to proceed from it (instead we either emulate the
instruction where the breakpoint was, or execute it out of place).  With
this patch, if we get an exception inside xmon, it will just return to the
xmon command loop instead of hanging the system as at present.

The patch is quite large because it updates the disassembler to the latest
version from binutils (trimmed a bit), which is why I didn't cc lkml.