RISC-V 特权架构中的 mstatus.SIE/SPIE/SPP 是否有实际作用？

[yuanix]

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？

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

[elechi]

不懂