Function wait

user/src/task.rs:21–31

(exit_code: &mut i32)

    sys_exec(path, args)
}
pub fn wait(exit_code: &mut i32) -> isize {
    loop {
        match sys_waitpid(-1, exit_code as *mut _) {
            -2 => {
                yield_();
            }
            // -1 or a real pid
            exit_pid => return exit_pid,
        }
    }
}

pub fn waitpid(pid: usize, exit_code: &mut i32) -> isize {
    loop {