Function error_to_trap_cause

crates/virtual-machine/src/cpu/traps.rs:128–139

Map a `VmError` to a trap cause/tval pair. Returns `Some((cause, tval))` if the error should trigger a trap, or `None` if it is a fatal error that cannot be trapped.

(e: &VmError)

    let prev_priv = match mpp {
        0 => PrivilegeMode::User,
        1 => PrivilegeMode::Supervisor,
        3 => PrivilegeMode::Machine,
        _ => PrivilegeMode::Machine, // reserved value; treat as Machine
    };
    regs.priv_mode = prev_priv;
    csrs.mstatus &= !(0x3u64 << 11); // MPP = User

    // Clear MPRV if returning below M-mode.
    if prev_priv != PrivilegeMode::Machine {
        csrs.mstatus &= !(1u64 << 17);
    }

    csrs.mepc
}