GetProcessNameByReflection.cs

private static Type _processInfoType = null;
private static FieldInfo _processNameField = null;
public static string GetProcessNameByReflection(Process p)
{
    var processInfoField = typeof(System.Diagnostics.Process)
        .GetField("processInfo", BindingFlags.Instance | BindingFlags.NonPublic);
    var processInfo = processInfoField.GetValue(p);

    if (_processInfoType == null)
    {
        _processInfoType = processInfo.GetType();
        _processNameField = _processInfoType.GetField("processName");
    }

    return _processNameField.GetValue(processInfo).ToString();
}