汇编程序44：检测点13.1 (jmp near ptr 标号指令的中断例程)

安装程序：
assume cs:code
//jmp near ptr 标号指令的替代实现,使用iret指令
code segment
    start:
          mov ax,cs
          mov ds,ax
          mov si,offset sub1
          mov ax,0020h
          mov es,ax
          mov di,0
          mov bx,offset sub2 - offset sub1
          cld
          rep movsb
          mov ax,0
          mov es,ax
          mov word ptr es:[7ch*4],200h
          mov word ptr es:[7ch*4+2],0
          mov ax,4c00h
          int 21h
     sub1:
          push bp
          mov bp,sp
          cmp bx,-32768 //近转移最小值偏移
          jl s0 //有符号数小于则转移
          cmp bx,32767 //近转移最大值偏移
          jg s0 //有符号数大于则转移
          add [bp+2],bx //加上两转的偏移即可得到转移目标地址
       s0:
          pop bp
          iret
     sub2:
          nop
code ends

end start

 

测试程序：
assume cs:code
//将数据段的数据显示屏幕上
data segment
    db 'conversation',0
data ends

code segment
    start:
          mov ax,data
          mov ds,ax
          mov si,0
          mov ax,0b800h
          mov es,ax
          mov di,12*160
        s:
          cmp byte ptr [si],0
          je ok
          mov al,[si]
          mov es:[di],al
          inc si
          add di,2
          mov bx,offset s - offset ok
          int 7ch //安装程序
       ok:
          mov ax,4c00h
          int 21h
code ends

end start