interruption and exception handling

1.         hardware’s assistance: every time before executing an instruction, it checks whether a exception or interruption happens

2.         based on the irq number, it finds out the corresponding interruption descriptor

3.         exception handler or interruption handler is invoked

4.         if it’s exception, generally a signal is sent to the current process; else if it’s interruption, the registered irq_action is invoked

5.         handles pending soft interruption if any, and this is only for interruption

6.         schedules to other processes if needed

7.         when back from schedule, handles pending signal if any

8.         restore the context from kernel stack