jump macro selector,offsetv
db 0eah
dw offsetv
dw selector
endm
echoch macro ascii
mov ah,2
mov dl,ascii
int 21h
endm
descriptor struc
limitl dw 0
basel dw 0
basem db 0
attributes dw 0
baseh db 0
descriptor ends
pdesc struc
limit dw 0
base dd 0
pdesc ends
.386p
data segment use16
gdt label byte
dummy descriptor <>
code_des descriptor <0ffffh,0,0,98h,0>
code_sel = code_des - gdt
datad_des descriptor <0ffffh,0,0,92h,0>
datad_sel = datad_des - gdt
datas_des descriptor <0ffffh,0,11h,92h,0>
datas_sel = datas_des - gdt
gdtlen = $-gdt
vgdtr pdesc
bufferlen = 256
buffer db bufferlen dup(0)
data ends
code segment use16
assume cs:code,ds:data
start:
mov ax,data
mov ds,ax
mov bx,16
mul bx
add ax,offset gdt
adc dx,0
mov word ptr vgdtr.base,ax
mov word ptr vgdtr.base+2,dx
mov ax,cs
mul bx
mov code_des.basel,ax
mov code_des.basem,dl
mov code_des.baseh,dh
mov ax,ds
mul bx
add ax,offset buffer
adc dx,0
mov datad_des.basel,ax
mov datad_des.basem,dl
mov datad_des.baseh,dh
lgdt qword ptr vgdtr
clicall ea20
mov eax,cr0
or eax,1
mov cr0,eax
jump ,
virtual:
mov ax,datas_sel
mov ds,ax
mov ax,datad_sel
mov es,ax
cldxor si,si
xor di,di
mov cx,bufferlen/4
repz movsd
mov eax,cr0
and eax,0fffffffeh
mov cr0,eax
jump ,
real:
call da20
stimov ax,data
mov ds,ax
mov si,offset buffer
cldmov bp,bufferlen/16
nextline:
mov cx,16
nextch:
lodsb
push ax
shr al,4
call toascii
echoch al
pop ax
call toascii
echoch al
echoch ' '
loop nextch
echoch 0dh
echoch 0ah
dec bp
jnz nextline
mov ah,4ch
int 21h
toascii proc
and al,0fh
add al,90h
daaadc al,40h
daaret
toascii endp
ea20 proc
push ax
in al,92h
or al,2
out 92h,al
pop ax
ret
ea20 endp
da20 proc
push ax
in al,92h
and al,0fdh
out 92h,ax
pop ax
retda20 endp
code ends
end start
楊季文 80x86組合語言程式設計 例項二
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