CallVM.cs

public void CallVM(uint lpfnProc)
{
    // Save the old IP
    var oldCS = cs;
    var oldIP = ip;

    // Setup the new IP
    cs = lpfnProc.Hiword();
    ip = lpfnProc.Loword();

    // Push address of the system return thunk
    this.PushDWord(_sysRetThunk);

    // Handle re-entrancy
    _sysRetDepth++;
    uint sysCallDepthAtCall= _sysRetDepth;

    // Process until the sys return thunk is invoked
    while (_sysRetDepth >= sysCallDepthAtCall)
    {
        Step();
    }

    // Restore instruction pointer
    cs = oldCS;
    ip = oldIP;
}