[PATCH 2/5] powerpc/kprobes: Do not suppress instruction emulation if a single run failed

[Naveen N. Rao]

On 2017/09/14 02:45AM, Masami Hiramatsu wrote:
> On Thu, 14 Sep 2017 12:08:07 +0530
> "Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com> wrote:
> 
> > On 2017/09/13 04:53PM, Masami Hiramatsu wrote:
> > > On Thu, 14 Sep 2017 02:50:33 +0530
> > > "Naveen N. Rao" <naveen.n.rao at linux.vnet.ibm.com> wrote:
> > > 
> > > > Currently, we disable instruction emulation if emulate_step() fails for
> > > > any reason. However, such failures could be transient and specific to a
> > > > particular run. Instead, only disable instruction emulation if we have
> > > > never been able to emulate this. If we had emulated this instruction
> > > > successfully at least once, then we single step only this probe hit and
> > > > continue to try emulating the instruction in subsequent probe hits.
> > > 
> > > Hmm, would this mean that the instruction is emulatable or not depends
> > > on context? What kind of situation is considerable?
> > 
> > Yes, as an example, a load/store instruction can cause exceptions 
> > depending on the address. In some of those cases, we will have to single 
> > step the instruction, but we will be able to emulate in most scenarios.
> 
> OK, I got it.
> Could you add this example as comment in the code so that readers can
> easily understand?

Sure.

Thanks,
Naveen