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

[Masami Hiramatsu <mhiramat@kernel.org>]

On Thu, 14 Sep 2017 12:08:07 +0530
"Naveen N. Rao" <naveen.n.rao@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@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?

Thank you,

> 
> Thanks for the review!
> - Naveen
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>