Re: Minutes 20070516

[Andrew Cagney <cagney at redhat dot com>]

Mark Wielaard wrote:
> I don't believe anything changed here since it was implemented. Which
> doesn't mean it cannot/shouldn't be improved (now that it is implemented
> I see why you want to have it setup differently, isn't that always the
> case...). Here is how it currently works:
>
>   

> - Given a Task you call requestAddCodeObserver(TaskObserver.Code, long)
> where the address is given as a long and the Code observer is the
> listener that you want to be called whenever the Task hits the given
> address.
>   

The call is task specific, that is task.requestAddCodeObserver 
(TaskObserver.Code, <address>) adds an observer to just that task and 
hence the observer is only notified when that code address is reached 
for that specific task.  This is consistent with the other task-specific 
observers where, unless an observer is explicitly attached to a task, it 
isn't notified of that task's events.  Doing this opens the way for a 
low-level efficient filtering of these events (eventually embedded in 
the kernel even); and to allow find-grained selection of ISA specific 
methods.

Perhaps this isn't the most suitable initial model though?  For 
instance, instead we could implement a global breakpoint mechanism, 
proc.addCodeObserver(..., <addr>) say, bound to the process, that 
assumes that the process has a single ISA, and thread-global so any 
thread encountering the code-address will do a notification.

Andrew

> - This inserts a breakpoint at the given address in the Proc associated
> with the Task (the breakpoint is global since the address space is
> shared between Tasks).
> - Whenever the breakpoint is hit in the process by a Task that task is
> temporarily suspended and frysk-core is notified about the event.
> - frysk-core calls the given Code observer is called with updateHit
> (Task, long) indicating the Task that tripped over the breakpoint at a
> given address. Returning Action.BLOCK from that method will permanently
> block that Task, returning Action.CONTINUE the Task will be resumed
> (given that no other listener returned BLOCK).
>
>