Reverse Assembly _ dowhile statement Disassembly

Reverse Assembly _ dowhile statement Disassembly

By: for example

The sample code is as follows:

 1  #include"stdio.h" 2  int function(int a,int b) 3  { 4       int c=a+b; 5       int i=0; 6       do 7       { 8           c=c+i; 9       }while(i<50);10       return c;11  }12  void main()13  {14       function(1,2);15  }

 

Disassembly code

1 #include "stdio.h"2 3 4 int function(int a,int b)5 6 {

012e1a40 push EBP 012e1a41 mov EBP, ESP 012e1a43 sub ESP, 0d8h  012e1a49 push EBX; save the environment 012e1a4a push ESI 012e1a4b push EDI  012e1a4c Lea EDI, [ebp-0D8h]; initialized to 0xcc 012e1a52 mov ECx, 36 h 012e1a57 mov eax, 0 cccccccch 012e1a5c rep STOs dword ptr es: [EDI] 

1     int c=a+b;

012e1a5e mov eax, dword ptr [A] 012e1a61 add eax, dword ptr [B] 012e1a64 mov dword ptr [c], eax

1     int i=0;

012e1a67 mov dword ptr [I], 0

 

 

  do    {        c=c+i;

012e1a6e mov eax, dword ptr [c]; in the previous two chapters, I am familiar with this structure. 012e1a71 add eax, dword ptr [I] 012e1a74 mov dword ptr [c], eax

1    }while(i<50);

012e1a77 cmp dword ptr [I], 32 h; compare whether it is greater than 50; if it is smaller than it, jump up 012e1a7b JL Function + 2EH (12e1a6eh)
 

1     return c;

012e1a7d mov eax, dword ptr [c]} 012e1a80 pop EDI 012e1a81 pop ESI 012e1a82 pop EBX  012e1a83 mov ESP, EBP 012e1a85 pop EBP

012e1a86 RET

Conclusion: The do while loop is relatively easy to recognize. Do_begin  .. ...  Jxx Do_beginHere is a jump-up process; execute the statement block first, and then compare it. When the condition is set, the statement will continue to be executed quickly,