RISC-V Vectored-Mode Trap Entry Support?

[Coekjan]

trapframe-rs/src/arch/riscv/trap.rs

Line 44 in 0f27d58

asm!("csrw stvec, {}", in(reg) trap_entry as usize);

This line just sets Direct-Mode and trap.S does not support Vectored-Mode now. I suggest that this library support Vectored-Mode on RISC-V.

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这行直接设置为了 Direct-Mode，而且 trap.S 目前也并不支持 Vectored-Mode。我建议本库支持 RISC-V 上的 Vectored-Mode。