%include "inc.asm"
PageDirBase0 equ 0x200000
PageTblBase0 equ 0x201000
PageDirBase1 equ 0x300000
PageTblBase1 equ 0x301000
org 0x9000
jmp ENTRY_SEGMENT
[section .gdt]
; GDT definition
; 段基址， 段界限， 段属性
GDT_ENTRY : Descriptor 0, 0, 0
CODE32_DESC : Descriptor 0, Code32SegLen - 1, DA_C + DA_32
VIDEO_DESC : Descriptor 0xB8000, 0x07FFF, DA_DRWA + DA_32
DATA32_DESC : Descriptor 0, Data32SegLen - 1, DA_DRW + DA_32
STACK32_DESC : Descriptor 0, TopOfStack32, DA_DRW + DA_32
PAGE_DIR_DESC0 : Descriptor PageDirBase0, 4095, DA_DRW + DA_32
PAGE_TBL_DESC0 : Descriptor PageTblBase0, 1023, DA_DRW + DA_LIMIT_4K + DA_32
PAGE_DIR_DESC1 : Descriptor PageDirBase1, 4095, DA_DRW + DA_32
PAGE_TBL_DESC1 : Descriptor PageTblBase1, 1023, DA_DRW + DA_LIMIT_4K + DA_32
; GDT end
GdtLen equ $ - GDT_ENTRY
GdtPtr:
dw GdtLen - 1
dd 0
; GDT Selector
Code32Selector equ (0x0001 << 3) + SA_TIG + SA_RPL0
VideoSelector equ (0x0002 << 3) + SA_TIG + SA_RPL0
Data32Selector equ (0x0003 << 3) + SA_TIG + SA_RPL0
Stack32Selector equ (0x0004 << 3) + SA_TIG + SA_RPL0
PageDirSelector0 equ (0x0005 << 3) + SA_TIG + SA_RPL0
PageTblSelector0 equ (0x0006 << 3) + SA_TIG + SA_RPL0
PageDirSelector1 equ (0x0007 << 3) + SA_TIG + SA_RPL0
PageTblSelector1 equ (0x0008 << 3) + SA_TIG + SA_RPL0
; end of [section .gdt]
TopOfStack16 equ 0x7c00
[section .dat]
[bits 32]
DATA32_SEGMENT:
DTOS db "D.T.OS!", 0
DTOS_OFFSET equ DTOS - $$
HELLO_WORLD db "Hello World!", 0
HELLO_WORLD_OFFSET equ HELLO_WORLD - $$
Data32SegLen equ $ - DATA32_SEGMENT
[section .s16]
[bits 16]
ENTRY_SEGMENT:
mov ax, cs
mov ds, ax
mov es, ax
mov ss, ax
mov sp, TopOfStack16
; initialize GDT for 32 bits code segment
mov esi, CODE32_SEGMENT
mov edi, CODE32_DESC
call InitDescItem
mov esi, DATA32_SEGMENT
mov edi, DATA32_DESC
call InitDescItem
mov esi, STACK32_SEGMENT
mov edi, STACK32_DESC
call InitDescItem
; initialize GDT pointer struct
mov eax, 0
mov ax, ds
shl eax, 4
add eax, GDT_ENTRY
mov dword [GdtPtr + 2], eax
; 1. load GDT
lgdt [GdtPtr]
; 2. close interrupt
cli
; 3. open A20
in al, 0x92
or al, 00000010b
out 0x92, al
; 4. enter protect mode
mov eax, cr0
or eax, 0x01
mov cr0, eax
; 5. jump to 32 bits code
jmp dword Code32Selector : 0
; esi --> code segment label
; edi --> descriptor label
InitDescItem:
push eax
mov eax, 0
mov ax, cs
shl eax, 4
add eax, esi
mov word [edi + 2], ax
shr eax, 16
mov byte [edi + 4], al
mov byte [edi + 7], ah
pop eax
ret
[section .s32]
[bits 32]
CODE32_SEGMENT:
mov ax, VideoSelector
mov gs, ax
mov ax, Stack32Selector
mov ss, ax
mov eax, TopOfStack32
mov esp, eax
mov ax, Data32Selector
mov ds, ax
mov ebp, DTOS_OFFSET
mov bx, 0x0C
mov dh, 12
mov dl, 33
call PrintString
mov ebp, HELLO_WORLD_OFFSET
mov bx, 0x0C
mov dh, 13
mov dl, 31
call PrintString
mov eax, PageDirSelector0
mov ebx, PageTblSelector0
mov ecx, PageTblBase0
call InitPageTable
mov eax, PageDirSelector1
mov ebx, PageTblSelector1
mov ecx, PageTblBase1
call InitPageTable
mov eax, PageDirBase0
call SwitchPageTable
mov eax, PageDirBase1
call SwitchPageTable
jmp $
; eax --> page dir base selector
; ebx --> page table base selector
; ecx --> page table base
InitPageTable:
push es
push eax ; [esp + 12]
push ebx ; [esp + 8]
push ecx ; [esp + 4]
push edi ; [esp]
mov es, ax
mov ecx, 1024 ; 1K sub page tables
mov edi, 0
mov eax, [esp + 4]
or eax, PG_P | PG_USU | PG_RWW
cld
stdir:
stosd
add eax, 4096
loop stdir
mov ax, [esp + 8]
mov es, ax
mov ecx, 1024 * 1024 ; 1M pages
mov edi, 0
mov eax, PG_P | PG_USU | PG_RWW
cld
sttbl:
stosd
add eax, 4096
loop sttbl
pop edi
pop ecx
pop ebx
pop eax
pop es
ret
; eax --> page directory base
SwitchPageTable:
push eax
mov eax, cr0
and eax, 0x7FFFFFFF
mov cr0, eax ；cr0最高位置0，暂时关闭分页机制
mov eax, [esp]
mov cr3, eax
mov eax, cr0
or eax, 0x80000000
mov cr0, eax
pop eax
ret
; ds:ebp --> string address
; bx --> attribute
; dx --> dh : row, dl : col
PrintString:
push ebp
push eax
push edi
push cx
push dx
print:
mov cl, [ds:ebp]
cmp cl, 0
je end
mov eax, 80
mul dh
add al, dl
shl eax, 1
mov edi, eax
mov ah, bl
mov al, cl
mov [gs:edi], ax
inc ebp
inc dl
jmp print
end:
pop dx
pop cx
pop edi
pop eax
pop ebp
ret
Code32SegLen equ $ - CODE32_SEGMENT
[section .gs]
[bits 32]
STACK32_SEGMENT:
times 1024 * 4 db 0
Stack32SegLen equ $ - STACK32_SEGMENT
TopOfStack32 equ Stack32SegLen - 1页表切换实现
在Bochs下运行的结果为
可知，运行成功
原文：https://blog.51cto.com/13475106/2520729