part of my codes (Just for learning ProtectMode):
%macro Descriptor 3
dw %2 & 0FFFFh
dw %1 & 0FFFFh
db (%1 >> 16) & 0FFh
dw ((%2 >> 8) & 0F00h) | (%3 & 0F0FFh)
db (%1 >> 24) & 0FFh
%endmacro
DA_32 EQU 4000h
DA_DRW EQU 92h
DA_C EQU 98h
org 0100h
jmp LABEL_BEGIN
[SECTION .gdt]
; GDT
;
LABEL_GDT: Descriptor 0, 0, 0
LABEL_DESC_CODE32: Descriptor 0, SegCode32Len - 1, DA_C + DA_32
LABEL_DESC_VIDEO: Descriptor 0B8000h, 0ffffh, DA_DRW
; GDT END
GdtLen equ $ - LABEL_GDT ; GDT LEN
GdtPtr dw GdtLen - 1
dd 0
; GDT SELECTOR
SelectorCode32 equ LABEL_DESC_CODE32 - LABEL_GDT
SelectorVideo equ LABEL_DESC_VIDEO - LABEL_GDT
; END of [SECTION .gdt]
[SECTION .s16]
[BITS 16]
LABEL_BEGIN:
mov ax, cs
mov ds, ax
mov es, ax
mov ss, ax
mov sp, 0100h
; INITIA
xor eax, eax
mov ax, cs
shl eax, 4
add eax, LABEL_SEG_CODE32
mov word [LABEL_DESC_CODE32 + 2], ax
shr eax, 16
mov byte [LABEL_DESC_CODE32 + 4], al
mov byte [LABEL_DESC_CODE32 + 7], ah
......
I debuger the file with td and get the following codes
1. xor eax,eax
2. mov ax,cs
3. shl eax,0x4
4. add eax,0x180
5. mov [0x10e],ax
6. shr eax,0x10
7. mov [0x110],al
8. mov [0x113],ah
in line 4. I get "LABEL_SEG_CODE32 = 0x180"
and in line 5. get "LABEL_DESC_CODE32 + 2 = 0x10e"
but all know "0x180 + 2 != 0x10e"
why??????
who can explain it.
