pub fn get_num_app() -> usize {
    extern "C" { fn _num_app(); }
    unsafe { (_num_app as usize as *const usize).read_volatile() }
}

pub fn get_app_data(app_id: usize) -> &'static [u8] {
    extern "C" { fn _num_app(); }
    let num_app_ptr = _num_app as usize as *const usize;
    let num_app = get_num_app();
    let app_start = unsafe {
        core::slice::from_raw_parts(num_app_ptr.add(1), num_app + 1)
    };
    assert!(app_id < num_app);
    unsafe {
        core::slice::from_raw_parts(
            app_start[app_id] as *const u8,
            app_start[app_id + 1] - app_start[app_id]
        )
    }
}