Return from assembly

Show calling an assembly fn and returning a value

rust_experiments/src/lib.rs

@@ -5,7 +5,7 @@
 extern crate rlibc;
 
 extern {
-    fn asm_printchar();
+    fn asm_printchar() -> u32;
 }
 
 
@@ -13,11 +13,12 @@ extern {
 pub extern fn rust_main() {
     clear();
 
-
-
     checkerboard(vga_buffer::Color::Red);
     unsafe {
-        asm_printchar();
+        let a = asm_printchar();
+        if a == 1 {
+            checkerboard(vga_buffer::Color::Blue);
+        }
     }
 
     loop {}

rust_experiments/src/long_mode_init.asm

@@ -50,6 +50,7 @@ setup_SSE:
 
 asm_printchar:
     mov rax, 0xf056
-    mov [0xb8000], rax
+    mov [0xb8000], ax
+    mov rax, 0x1
     ret