Re: [RFC PATCH v3 01/11] plugins: add types for callbacks related to certain discontinuities

[Julian Ganz]

Hi Pierrick,

December 4, 2024 at 11:41 PM, "Pierrick Bouvier" wrote:
> On 12/3/24 00:45, Julian Ganz wrote:
> 
> > 
> > Hi,
> >  December 2, 2024 at 8:26 PM, "Julian Ganz" wrote:
> > 
> > > 
> > > diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
> > >  index 0fba36ae02..9c67374b7e 100644
> > >  --- a/include/qemu/qemu-plugin.h
> > >  +++ b/include/qemu/qemu-plugin.h
> > >  @@ -154,6 +154,49 @@ typedef void 
> > > (*qemu_plugin_vcpu_simple_cb_t)(qemu_plugin_id_t id,
> > > 
> >  <snip>
> > 
> > > 
> > > +/**
> > >  + * typedef qemu_plugin_vcpu_discon_cb_t - vcpu discontinuity callback
> > >  + * @vcpu_index: the current vcpu context
> > >  + * @type: the type of discontinuity
> > >  + * @from_pc: the source of the discontinuity, e.g. the PC before the
> > >  + * transition
> > >  + * @to_pc: the PC pointing to the next instruction to be executed
> > >  + *
> > >  + * The excact semantics of @from_pc depends on @the type of 
> > > discontinuity. For
> > >  + * interrupts, @from_pc will point to the next instruction which would 
> > > have
> > >  + * been executed. For exceptions and host calls, @from_pc will point to 
> > > the
> > >  + * instruction that caused the exception or issued the host call. Note 
> > > that
> > >  + * in the case of exceptions, the instruction is not retired and thus 
> > > not
> > >  + * observable via general instruction exec callbacks. The same may be 
> > > the case
> > >  + * for some host calls such as hypervisor call "exceptions".
> > > 
> >  Some more notes about this bit: I originally tried to make the from_pc
> >  semantics independent from the type of event, i.e. either of the two
> >  cases. I obviously did not succeed in doing so. As, in most cases, the
> >  instruction pointed to by from_pc is not observable via exec callbacks
> >  I could also not test this behaviour in the testing plugin (see patch
> >  11). I am therefore in favor for dropping the from_pc for the next
> >  iteration of this patch series.
> > 
> Does it mean that information returned should be dependent of type of event, 
> as we previously discussed on v1?

Yes, and I don't like it.

Regards,
Julian Ganz