stack_switching.rs

pub unsafe fn swap(arg: usize, new_sp: *mut u8) -> (usize, *mut u8) {
    let ret_val: usize;
    let ret_sp: *mut u8;
    asm!(
        "lea {tmp}, [rip + 10]",
        "push {tmp}",
        "mov rsi, rsp",
        "mov rsp, {new_sp}",
        "pop {tmp}",
        "jmp {tmp}",
        tmp = out(reg) _,
        new_sp = in(reg) new_sp,
        out("rsi") ret_sp,
        inout("rdi") arg => ret_val,
        out("rax") _, out("rcx") _, out("rdx") _,
        out("r8") _, out("r9") _, out("r10") _, out("r11") _,
        out("xmm0") _, out("xmm1") _, out("xmm2") _, out("xmm3") _,
        out("xmm4") _, out("xmm5") _, out("xmm6") _, out("xmm7") _,
        out("xmm8") _, out("xmm9") _, out("xmm10") _, out("xmm11") _,
        out("xmm12") _, out("xmm13") _, out("xmm14") _, out("xmm15") _,
    );

    (ret_val, ret_sp)
}

pub fn resume(&mut self, input: Input) -> Option<Output> {
    let (data_out, stack_ptr) = unsafe { arch::swap(&input as *const Input as usize, self.stack_ptr) };
    self.stack_ptr = stack_ptr;
    std::mem::forget(input);
    unsafe { std::ptr::read(data_out as *const Option<Output>) 
}