Added the Global Descriptor Table.

kernel/io.s

@@ -16,6 +16,25 @@ global inb
 ; stack: [esp + 4] The address of the I/O port
 ;		 [esp    ] The return address
 inb:
-	mov dx, [esp + 4] 	; Move the address of the I/O port to the dx register.
+	mov dx, [esp + 4] 	; Move the address of the I/O port to the dx register
 	in al, dx 			; Read a byte from the I/O port and store it in the al register
 	ret
+	
+global load_gdt
+
+; load_gdt - Installs a new GDT
+; stack: [esp + 4] The address of the GDT
+;		 [esp    ] The return addess
+load_gdt:
+	mov eax, [esp + 4]
+	lgdt [eax]
+	mov ax, 0x10
+	mov ds, ax
+	mov es, ax
+	mov fs, ax
+	mov gs, ax
+	mov ss, ax
+	jmp 0x08:return		; Perform a "far jump" to load 0x08 in the CS register
+	
+return:
+	ret					; Now we've changed CS to 0x08