Re: [PATCH v3 0/10] Uprobes v3

["H. Peter Anvin" <hpa@zytor.com>]

On 05/12/2010 07:46 AM, Mathieu Desnoyers wrote:
> 
> Now the tricky case is the sequence: instruction A -> int3 -> instruction B,
> because a core can only see "instruction A -> instruction B" without any
> core synchronization whatsoever, and may not see the int3. That's where the
> djprobes logic (with IPIs to all cores) comes into play. But as long as we stick
> to "insn A -> int3 -> insn A", things can be done very simply.
> 
> By the way, kprobes rely on the assumption that it is OK to put a breakpoint
> atomically and to put back the original instruction afterward.
> 

Keep in mind the following corner case, though:

insnA -> int3@A -> insnA
insnB -> int3@B -> insnB

It is now possible for the core to hit int3@A, without the int3@B being
there.  The int3 handler *has* to be able to handle any of the int3's
put in place, quite possibly out of order, until a core serialization is
performed.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.