By compiling a simple C program, analyze the assembly code to understand how the computer works

Name: Ma Qiyang No.: 20135234

(* Original works reproduced please specify the source *)

(Study course: "Linux kernel Analysis" MOOC course http://mooc.study.163.com/course/USTC-1000029000)

Experimental requirements:

Experimental content:

(The following commands apply to the lab building 64-bit Linux virtual machine environment, 32-bit Linux environments may be slightly different) using gcc –S –o main.s main.c -m32  commands to compile the assembly code,

The code is as follows (to prevent the similarity of others, change the code):

 int  G (int x) {return x + 1;} int f (int x) {return g (x);} int main  (void) {return F (6" + 1;} 
 
   experimental process and:   
 1. Enter the lab building, enter the code folder,         Create mqy.c file using VI 
 
  

  2. Complete code Write, save exit 
 
 
 3. Use Gcc-s-o mqy.s mqy.c-m32 to compile mqy.c into assembly code MQY.S and use        vi open MQY.S  

 4. will be "." The beginning of the line is deleted, get clean assembly code 
 
 
   Experimental Analysis: Stack changes (the orange underline of the code represents the current EIP execution position)  
  1. Start with EIP pointing at 19 lines, EBP esp in 0 position (01234 on the right is set for convenient analysis) 
 
 2.PUSHL%ebp, the EBP value stack 
 
 
 3.movl%esp,%ebp, Assign ESP value to EBP 
 
 4.subl $4,%esp, move esp down one grid 
 
 5.movl $33, (%ESP), save 33 at the point where ESP refers to 
 
 6.call F, call the F function, and the EIP 24 press stack, at which point the EIP points to the F function 
 
 7.pushl%ebp, and the EBP value is stacked at this time 
 
 8.          movl %esp,%ebp,将esp值赋给ebp

9.subl $4,%esp,esp向下移一格

10.movl 8(%ebp),%eax,将ebp向上两格装的值赋给eax

11.movl %eax,(%esp),将eax的值赋给esp此时指向的格

12.call g,调用g函数,eip 16压栈,此时eip指向g函数

13.pushl %ebp,将此时ebp值压栈

14.movl %esp,%ebp,将esp值赋给ebp

15.movl 8(%ebp),%eax,将ebp上两格的装的值赋给eax

16.addl $5,%eax,给eax加5

17.popl %ebp，弹栈，此时ebp赋值为栈中所存的ebp 4，esp缩进退一格

18.ret,弹栈,此时eip赋值为栈中所存eip 16，esp缩进一格

19.leave(leave指令为如下步骤)

故先 movl %ebp,%esp,将ebp赋值给esp

然后弹栈，此时ebp指向弹栈的ebp 1，esp缩进一格

20.ret,弹栈，此时eip指向弹栈的eip 24.

21.addl $1,%eax,将eax加1

22.leave操作（先 movl %ebp,%esp,将ebp赋值给esp）

然后弹栈，此时ebp指向弹栈的ebp 0,esp缩进一格

By compiling a simple C program, analyze the assembly code to understand how the computer works