Chapter 6 Programs Containing Multiple Segments

"Assembly Language Third Edition" by Wang Shuang ------Reading Notes 

6.1 Use data in code snippets

       From a specification point of view, the system should allocate memory space for us.

 

Pseudo assembly instructions (recognized by the compiler)

db : define byte type variable

dw : define word type variable

dd : define double word type variable

program

assume cs:code

code segment
dw 0123h,0456h,0789h,0abch,0defh,0fedh,0cbah,0987h'

start: mov bx,0
       mov ax,0
  
       mov cx,8
     s:add ax,cs:[bx]
       add bx,2
       loop s

       mov 4c00h
       int 21h

code ends

end start

Executable program

     It consists of  description information and  procedures  ,

    Descriptive information: It is mainly the information obtained by compiling and linking the program to process the relevant pseudo-instructions in the source program

     Program: assembly instructions and defined data from the source program;

 

The role of pseudo-instruction end

      In addition to notifying the compiler of the end of the program, end can also notify the compiler where the entry of the program is

      Example: end start indicates that the entry of the program is at the label start, and the label start is an address

      After compiling and linking, the program entry specified by "end start" is converted into an entry address,

       Stored in the description information of the executable file

    When the program is loaded into the memory, the loader reads the program’s entry address from the description information of the program’s executable file,

    Set CS:IP

After all: we can arrange Framework Program

assume cs:code

code segment

      ...数据...

start:

      ...代码...

code ends

end start

 

6.2 Use the stack in the code segment

          Review the knowledge points of the third chapter stack

 

6.3 Put data, code, and stack into different segments

the reason:

     1) Putting it in the same segment makes the program appear chaotic

     2) In the 8086 mode, the capacity of a segment cannot be greater than the 64KB program frame:

assume cs:code

data segment
   dw 0123h,0456h
data ends

stack segment
   dw 0,0,0,0
stack ends

code segment

start: 第一条命令

code ends

end start