; GDT global descriptor table

gdt_start:

; mandatory null entry
gdt_null:
	dd 0x0
	dd 0x0

; code segment
; base=0x0, limit=0xfffff
; flags: present (not paged), ring 0, executable, direction bit
; conforming, writable, not accessed
; granularity: 4kb pages, 32-bit mode, no 64-bit segment, AVL would
; be for our own extensions
gdt_code:
	dw 0xffff	; limit (bits 0-15)
	dw 0x0		; base (bits 0-15)
	db 0x0		; base (bits 16-23)
	db 10011010b	; flags
	db 11001111b	; flags, limit (bits 16-19)
	db 0x0		; base (bit 24-31)
	
; flat model, same as code segment, but flags are
; flags: ring 0, 
gdt_data:
	dw 0xffff	; limit (bits 0-15)
	dw 0x0		; base (bits 0-15)
	db 0x0		; base (bits 16-23)
	db 10010010b	; flags
	db 11001111b	; flags, limit (bits 16-19)
	db 0x0		; base (bit 24-31)

gdt_end:

gdt_descriptor:	
	dw gdt_end -gdt_start - 1	; size
	dd gdt_start			; start address of the GDT
	
; constants representing the segment bases
CODE_SEGMENT equ gdt_code - gdt_start
DATA_SEGMENT equ gdt_data - gdt_start