Reload selector registers and print OKAY

src/arch/x86_64/boot.asm

@@ -13,6 +13,7 @@
 ; limitations under the License.
 
 global start
+extern long_mode_start
 
 section .text
 bits 32
@@ -29,9 +30,13 @@ start:
     ; load the 64-bit GDT
     lgdt [gdt64.pointer]
 
-    ; print `OK` to screen
-    mov dword [0xb8000], 0x2f4b2f4f
-    hlt
+    ; update selectors
+    mov ax, gdt64.data
+    mov ss, ax
+    mov ds, ax
+    mov es, ax
+
+    jmp gdt64.code:long_mode_start
 
 setup_page_tables:
     ; map first P4 entry to P3 table

src/arch/x86_64/long_mode_init.asm

@@ -0,0 +1,23 @@
+; Copyright 2015 Philipp Oppermann
+;
+; Licensed under the Apache License, Version 2.0 (the "License");
+; you may not use this file except in compliance with the License.
+; You may obtain a copy of the License at
+;
+;    http://www.apache.org/licenses/LICENSE-2.0
+;
+; Unless required by applicable law or agreed to in writing, software
+; distributed under the License is distributed on an "AS IS" BASIS,
+; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+; See the License for the specific language governing permissions and
+; limitations under the License.
+
+global long_mode_start
+
+section .text
+bits 64
+long_mode_start:
+    ; print `OKAY` to screen
+    mov rax, 0x2f592f412f4b2f4f
+    mov qword [0xb8000], rax
+    hlt