Re: [PATCH 1/4] sim: Allow an overdue event to be descheduled

Sebastian Huber <[email protected]> writes:

> sim_events_deschedule() asserted that a non-empty event queue implies a
> non-negative time from event.  That is not an invariant.
> sim_events_slip() decrements the time from event unconditionally, so the
> time can pass an event which is still queued.  update_time_from_event()
> then computes a negative time from event for the head of the queue,
> which is overdue rather than pending.  The next tick raises the pending
> work flag and sim_events_process() consumes it, so nothing is lost.
>
> An event handler which deschedules another overdue event triggers the
> assertion.  The MIPS jmr3904 board reaches this with two timers running:
> they queue events for the same time, a branch delay slot slips the time
> past both, and the handler of the first deschedules the second.
>
> Assert only the direction which holds: an empty queue gives a negative
> time from event.
>
> Signed-off-by: Sebastian Huber <[email protected]>
> ---
>  sim/common/sim-events.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/sim/common/sim-events.c b/sim/common/sim-events.c
> index f87f133efc3..e908c40f764 100644
> --- a/sim/common/sim-events.c
> +++ b/sim/common/sim-events.c
> @@ -852,7 +852,11 @@ sim_events_deschedule (SIM_DESC sd,
>  		       (dead->trace != NULL) ? dead->trace : ""));
>  	      sim_events_free (sd, dead);
>  	      update_time_from_event (sd);
> -	      SIM_ASSERT ((events->time_from_event >= 0) == (events->queue != NULL));
> +	      /* sim_events_slip() advances the time past an event
> +		 which is still queued. The head of the queue is then

Two spaces after the period please.  With that fixed:

Approved-By: Andrew Burgess <[email protected]>

Thanks,
Andrew


> +		 overdue rather than pending.  */
> +	      SIM_ASSERT (events->queue != NULL
> +			  || events->time_from_event < 0);
>  	      return;
>  	    }
>  	}
> -- 
> 2.51.0