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pm.asm
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pm.asm
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;.\nasm2\nasm.exe .\MyOS\pm.asm -o pm.exe
DA_32 equ 4000h ;32位
DA_C equ 98h ;只执行
DA_DRW equ 92h;可读写
DA_DRWA equ 93h;存在的已访问的可读写的
%macro Descriptor 3
dw %2 & 0FFFFh ;段界限1
dw %1 & 0FFFFh ;段基址1
db (%1 >> 16) & 0FFh ;段基址2
dw ((%2 >> 8) & 0F00h) | (%3 & 0F0FFh) ;属性1 + 段界限2 + 属性2
db (%1 >> 24) & 0FFh ;段基址3
%endmacro
org 0100h
jmp PM_BEGIN ;跳入PM_BEGIN
[SECTION .gdt]
;GDT
; 段基址 段界限 属性
PM_GDT: Descriptor 0, 0, 0
PM_DESC_CODE32: Descriptor 0, SegCode32Len - 1, DA_C + DA_32
PM_DESC_DATA: Descriptor 0, DATALen - 1, DA_DRW
PM_DESC_STACK: Descriptor 0, TopOfStack, DA_DRWA + DA_32
PM_DESC_TEST: Descriptor 0200000h,0FFFFh, DA_DRW
PM_DESC_IMAGE: Descriptor 0B8000h,0FFFFh, DA_DRW
GDTLen equ $ - PM_GDT
GDTPtr dw GDTLen - 1
dd 0 ;GDT基地址,在进入保护模式时会填充
;GDT 选择子
SelectorCODE32 equ PM_DESC_CODE32 - PM_GDT
SelectorDATA equ PM_DESC_DATA - PM_GDT
SelectorSTACK equ PM_DESC_STACK - PM_GDT
SelectorTEST equ PM_DESC_TEST - PM_GDT
SelectorIMAGE equ PM_DESC_IMAGE - PM_GDT
;END of [SECTION .gdt]
[SECTION .data]
ALIGN 32
[BITS 32]
PM_DATA:
PMMESSAGE: DB "Protected Mode",0
OFFSETPMMESSAGE equ PMMESSAGE - $$
DATALen equ $ - PM_DATA
;END of [SECTION .data]
;堆栈段
[SECTION .gs]
ALIGN 32
[BITS 32]
PM_STACK:
times 512 db 0
TopOfStack equ $ - PM_STACK - 1
;END Of STACK
[SECTION .s16]
[BITS 16]
PM_BEGIN:
mov ax,cs
mov ds,ax
mov es,ax
mov ss,ax
mov sp,0100h
;初始化GDT内的数据段
xor eax,eax
mov ax,ds
shl eax,4
add eax,PM_DATA
mov word [PM_DESC_DATA + 2],ax ;段基址1
shr eax,16
mov byte [PM_DESC_DATA + 4],al ;段基址2
mov byte [PM_DESC_DATA + 7],ah ;段基址3
;初始化GDT内的代码段
xor eax,eax
mov ax,cs
shl eax,4
add eax,PM_SEG_CODE32
mov word [PM_DESC_CODE32 + 2],ax ;段基址1
shr eax,16
mov byte [PM_DESC_CODE32 + 4],al ;段基址2
mov byte [PM_DESC_CODE32 + 7],ah ;段基址3
;初始化GDT内的堆栈段
xor eax,eax
mov ax,ds
shl eax,4
add eax,PM_STACK
mov word [PM_DESC_STACK + 2],ax ;段基址1
shr eax,16
mov byte [PM_DESC_STACK + 4],al ;段基址2
mov byte [PM_DESC_STACK + 7],ah ;段基址3
;加载GDTR
xor eax,eax
mov ax,ds
shl eax,4
add eax,PM_GDT
mov dword [GDTPtr + 2],eax
lgdt[GDTPtr]
;打开A20地址线
cli
in al,92h
or al,00000010b
out 92h,al
;进入保护模式
mov eax,cr0
or eax,1
mov cr0,eax
jmp dword SelectorCODE32:0
[SECTION .s32]
[BITS 32]
PM_SEG_CODE32:
mov ax,SelectorDATA ;把选择子放入ds寄存器，使用段+偏移进行寻址
mov ds,ax
mov ax,SelectorTEST
mov es,ax
mov ax,SelectorIMAGE
mov gs,ax
mov ax,SelectorSTACK
mov ss,ax
mov esp,TopOfStack
mov ah,0Ch
xor esi,esi
xor edi,edi
mov esi,OFFSETPMMESSAGE ;字符串起始位置
mov edi,(80 * 10 + 30) * 2 ;显示位置
cld
.lo:
lodsb
test al,al
jz .ou
mov [gs:edi],ax
add edi,2
jmp .lo
;显示完毕
.ou:
jmp $
SegCode32Len equ $ - PM_SEG_CODE32
;END Of CODE