Wrap syscalls in user_lib && change xstate to exit_code

user/src/console.rs

@@ -1,11 +1,13 @@
 use core::fmt::{self, Write};
-use crate::syscall::{STDOUT, sys_write};
+use super::write;
 
 struct Stdout;
 
+const STDOUT: usize = 1;
+
 impl Write for Stdout {
     fn write_str(&mut self, s: &str) -> fmt::Result {
-        sys_write(STDOUT, s.as_bytes());
+        write(STDOUT, s.as_bytes());
         Ok(())
     }
 }