fast-trap 0.1.0

use super::{FlowContext, trap_entry};
use core::arch::asm;

macro_rules! exchange {
    () => {
        exchange!(sp)
    };

    ($reg:ident) => {
        concat!("csrrw ", stringify!($reg), ", sscratch, ", stringify!($reg))
    };
}

macro_rules! r#return {
    () => {
        "sret"
    };
}

pub(super) use {exchange, r#return};

impl FlowContext {
    /// 从上下文向硬件加载非调用规范约定的寄存器。
    #[inline]
    pub(crate) unsafe fn load_others(&self) {
        unsafe {
            asm!(
                "   mv         gp, {gp}
                mv         tp, {tp}
                csrw sscratch, {sp}
                csrw     sepc, {pc}
            ",
                gp = in(reg) self.gp,
                tp = in(reg) self.tp,
                sp = in(reg) self.sp,
                pc = in(reg) self.pc,
            );
        }
    }
}

/// 交换突发寄存器。
#[inline]
pub(crate) fn exchange_scratch(mut val: usize) -> usize {
    unsafe { asm!("csrrw {0}, sscratch, {0}", inlateout(reg) val) };
    val
}

/// 模拟一个 `cause` 类的陷入。
///
/// # Safety
///
/// 如同发生一个陷入。
#[inline]
pub unsafe fn soft_trap(cause: usize) {
    unsafe {
        asm!(
            "   la   {0},    1f
            csrw sepc,   {0}
            csrw scause, {cause}
            j    {trap}
         1:
        ",
            out(reg) _,
            cause = in(reg) cause,
            trap  = sym trap_entry,
        );
    }
}

/// 设置全局陷入入口。
///
/// # Safety
///
/// 这个函数操作硬件寄存器，寄存器里原本的值将丢弃。
#[inline]
pub unsafe fn load_direct_trap_entry() {
    unsafe { asm!("csrw stvec, {0}", in(reg) trap_entry, options(nomem)) }
}