/// <summary>
/// Steps back a single instruction. Throws a HistoryEmptyRuntimeException
/// if the history of the VM is empty.
/// </summary>
public void StepBack()
{
if (!VirtualMachine.Data.Uncommit())
{
throw new HistoryEmptyRuntimeException(new ushort[] { 0 }, VirtualMachine.Data.DirectPC);
}
DataDelta uncommited = VirtualMachine.Data.Delta;
VirtualMachine.Data.Rollback();
// The breakpoint checker executes an instruction in advance to determine
// whether it will trigger any breakpoints.
// Since we are undoing an instruction, we already know its effect,
// so we are informing the checker here.
BreakpointChecker.SetNextDelta(uncommited, VirtualMachine.Data.DirectPC);
}
/// <summary>
/// Calculates the effects of the next instruction.
/// </summary>
/// <remarks>
/// This calculation in advance allows breakpoints to be hit BEFORE the
/// actual execution.
/// </remarks>
/// <returns>A value holding the effects of the instruction.</returns>
protected DataDelta CalculateNextDelta()
{
Data data = Target.VirtualMachine.Data;
if (_processor == null || _processor.Data != data)
{
_processor = new Processor(data, _nullDevice);
}
data.Commit(); // Commits any previous changes
try { _processor.Step(); } // Execute next instruction (breakpoint probe).
catch (Exception) { }
DataDelta result = data.Delta; // Delta object holds the changes made by the probe
if (!data.Uncommit()) // Uncommit restores previous Delta object from history and discards the probe changes.
{
// If uncommit fails, we need to manually discard probe changes by calling Rollback().
data.Rollback();
}
return(result);
}
/// <summary>
/// Sets the NextDelta and the corresponding PC.
/// </summary>
/// <remarks>
/// This method should be used when stepping back to avoid
/// reexecuting the undone instruction in CalculateNextDelta.
/// </remarks>
/// <param name="nextDelta">The Delta of the next instruction</param>
/// <param name="pc">The address of the instruction</param>
public void SetNextDelta(DataDelta nextDelta, ushort pc)
{
_nextDelta = nextDelta;
_nextDeltaPC = pc;
}
