Merge branch 'post-06' into post-07

src/lib.rs

@@ -72,7 +72,7 @@ pub fn hlt_loop() -> ! {
 
 /// Entry point for `cargo xtest`
 #[cfg(test)]
-#[no_mangle]
+#[unsafe(no_mangle)]
 pub extern "C" fn _start() -> ! {
     init();
     test_main();