Call assembly from rust

All this does is print a V to the screen, but it means caling asm from
rust works. Remember that if this were in boot.asm, it'd be now-invalid
32 bit code and calling it would cause a page fault.

rust_experiments/src/lib.rs

@@ -4,10 +4,21 @@
 
 extern crate rlibc;
 
+extern {
+    fn asm_printchar();
+}
+
+
 #[no_mangle]
 pub extern fn rust_main() {
     clear();
+
+
+
     checkerboard(vga_buffer::Color::Red);
+    unsafe {
+        asm_printchar();
+    }
 
     loop {}
 }

rust_experiments/src/long_mode_init.asm

@@ -1,4 +1,5 @@
 global long_mode_start
+global asm_printchar
 
 section .text
 bits 64
@@ -46,3 +47,9 @@ setup_SSE:
     .no_SSE:
     mov al, "a"
     jmp error
+
+asm_printchar:
+    mov rax, 0xf056
+    mov [0xb8000], rax
+    ret
+