mstatus 真的会用到 SIE/SPIE/SPP 这些位吗？还是只是为了保证 mstatus 作为 sstatus 的超集而保留的？
对于 mstatus ：
- MIE 控制 M-mode 是否启用中断处理
- MPIE 记录进入 trap 之前的 MIE 便于之后 mret 的时候恢复 trap 之前的中断使能状态
- MPP 记录 trap 之前的运行特权级别并用于在 mret 的时候恢复先前特权级
那么 mstatus.SIE/SPIE/SPP 有什么实际作用呢？
This topic created in 1044 days ago, the information mentioned may be changed or developed.
Supplement 1 · Jul 6, 2023
贴一个Reddit上的回答：
They do exactly the same thing when a trap is delegated to S mode for handling.
There is only one physical status register, but different views of it, with M-mode being able to see and change anything and S-mode seeing only a subset.
经过测试发现确实如此：
[firmware_main] Clear MSTATUS_MIE | MSTATUS_SIE for mstatus
[firmware_main] mstatus is 0x0
[firmware_main] sstatus is 0x0
[firmware_main] Set MSTATUS_SIE for mstatus
[firmware_main] mstatus is 0x2
[firmware_main] sstatus is 0x2
[firmware_main] Clear MSTATUS_MIE | MSTATUS_SIE for mstatus
[firmware_main] mstatus is 0x0
[firmware_main] sstatus is 0x0
[firmware_main] Set SSTATUS_SIE for sstatus
[firmware_main] mstatus is 0x2
[firmware_main] sstatus is 0x2
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