Hitachi djprobe mechanism

[Andi Kleen]

Mathieu Desnoyers <compudj@krystal.dyndns.org> writes:
> 
> And as the jmp instruction is 5 bytes, there seems to be no hope to find an
> atomic operation that will write that.

Any 64bit architecture can write 8 bytes mostly atomically (at least towards
readers) and many 32bit architectures (like newer x86 with cmpxchg or sse) 
can too.

An 8 byte read-modify-store is not protected against multiple writers,
but that is no problem for probes which can protect against that
with a different lock.

x86 could actually do it atomically even for writers with cmpxchg8.

-Andi