Run hello_world/power one by one in batch mode.

os/src/syscall/fs.rs

@@ -0,0 +1,15 @@
+const FD_STDOUT: usize = 1;
+
+pub fn sys_write(fd: usize, buf: *const u8, len: usize) -> isize {
+    match fd {
+        FD_STDOUT => {
+            let slice = unsafe { core::slice::from_raw_parts(buf, len) };
+            let str = core::str::from_utf8(slice).unwrap();
+            print!("{}", str);
+            len as isize
+        },
+        _ => {
+            panic!("Unsupported fd in sys_write!");
+        }
+    }
+}