Add qemu_aarch64_exit

src/main.rs

@@ -65,5 +65,33 @@ pub fn kmain() -> ! {
     }
 
     writeln!(uart, "Bye, going to sleep now");
-    endless_sleep()
+    qemu_aarch64_exit(); //endless_sleep()
+}
+
+// From https://stackoverflow.com/a/49930361/895245
+// @todo specify exit value depending on tests result?
+fn qemu_aarch64_exit() -> ! {
+    unsafe {
+        asm!("
+            /* 0x20026 == ADP_Stopped_ApplicationExit */
+            mov x1, #0x26
+            movk x1, #2, lsl #16
+            str x1, [sp,#0]
+
+            /* Exit status code. Host QEMU process exits with that status. */
+            mov x0, #0
+            str x0, [sp,#8]
+
+            /* x1 contains the address of parameter block.
+             * Any memory address could be used. */
+            mov x1, sp
+
+            /* SYS_EXIT */
+            mov w0, #0x18
+
+            /* Do the semihosting call on A64. */
+            hlt 0xf000"
+        :::: "volatile");
+    }
+    unreachable!();
 }