c++ 反汇编 if

1、debug

• if：

10:     if (argc == 0)
0010711E 83 7D 08 00          cmp         dword ptr [argc],0  
00107122 75 11                jne         If+35h (0107135h)  //不相等则跳转（为保持代码顺序，if的比较条件在汇编中相反）
    11:     {
    12:         printf("%d 
", argc);
00107124 8B 45 08             mov         eax,dword ptr [argc]  
···printf00107132 83 C4 08             add         esp,8  
    13:     }
    14:     if (argc > 0)
00107135 83 7D 08 00          cmp         dword ptr [argc],0  
00107139 7E 0D                jle         If+48h (0107148h)  
    15:     {
    16:         printf("argc >= 0");
···printf00107145 83 C4 04             add         esp,4  
    17:     }

总结：debug下，简单的if语句结构为：

cmp

jxx  {if 外语句}

{if 块内语句}

• if···else···

   35:     if (argc == 0)
0010719E 83 7D 08 00          cmp         dword ptr [argc],0  
001071A2 75 09                jne         IfElse+2Dh (01071ADh)  
    36:     {
    37:         argc = 5;
001071A4 C7 45 08 05 00 00 00 mov         dword ptr [argc],5  
    38:     }
    39:     else
001071AB EB 07                jmp         IfElse+34h (01071B4h)  //if块内语句执行结束后，jmp到if-else结束
    40:     {
    41:         argc = 6;
001071AD C7 45 08 06 00 00 00 mov         dword ptr [argc],6  
    42:     }

• if···else if···else

50:     if (argc > 0)
00107215 83 7D 08 00          cmp         dword ptr [argc],0  
00107219 7E 0F                jle         IfElseIf+3Ah (010722Ah)  //if
    51:     {
    52:         printf("argc > 0");
···printf 
00107228 EB 22                jmp         IfElseIf+5Ch (010724Ch)  //if块内结束时jmp出条件结构
    53:     }
    54:     else if (argc == 0)
0010722A 83 7D 08 00          cmp         dword ptr [argc],0  
0010722E 75 0F                jne         IfElseIf+4Fh (010723Fh)  //else if 
    55:     {
    56:         printf("argc == 0");
···printf  
    57:     }
    58:     else
0010723D EB 0D                jmp         IfElseIf+5Ch (010724Ch) //else if块内结束后jmp出条件结构 
    59:     {
    60:         printf("argc <= 0");
···printf  

---

2、release

• if

void If(int argc)
{
    if (argc == 0)
    {
        printf("%d 
", argc);
    }
    if (argc > 0)
    {
        printf("argc >= 0");
    }
    
    return;
}

00351085  | 85C0            | test eax,eax                      | if_else.cpp:73
00351087  | 75 12           | jne if_else.35109B                |
···printf                      |
00351097  | 33C0            | xor eax,eax                       | if_else.cpp:77
00351099  | 5D              | pop ebp                           |
0035109A  | C3              | ret                               |
0035109B  | 7E 0D           | jle if_else.3510AA                | 优化了一条判断语句
···printf                       |
003510AA  | 33C0            | xor eax,eax                       | if_else.cpp:77

• if···else

void IfElse(int argc)
{
    if (argc == 0)
    {
        argc = 5;
    }
    else
    {
        argc = 6;
    }
    printf("%d 
", argc);
}

01381081  | 3945 08         | cmp dword ptr ss:[ebp+0x8],eax    |//类似条件表达式中的优化，
01381084  | 0F95C0          | setne al                          |
01381087  | 83C0 05         | add eax,0x5                       |
···
printf
···
01381098  | 33C0            | xor eax,eax                       | if_else.cpp:76
0138109A  | 5D              | pop ebp                           | if_else.cpp:77
0138109B  | C3              | ret                               |

• if···else if···else

void IfElseIf(int argc)
{
    //argc = 0;
    if (argc > 0)
    {
        printf("argc > 0");
    }
    else if (argc == 0)
    {
        printf("argc == 0");
    }
    else
    {
        printf("argc <= 0");
    }
}

002910A5  | 85C9            | test ecx,ecx             | if_else.cpp:75
002910A7  | 7E 12           | jle if_else.2910BB       |
002910A9  | B8 A4012D00     | mov eax,if_else.2D01A4   | 2D01A4:"argc > 0"
···printf              |
002910B7  | 33C0            | xor eax,eax              |
002910B9  | 5D              | pop ebp                  | if_else.cpp:77
002910BA  | C3              | ret                      |
002910BB  | 85C9            | test ecx,ecx             | if_else.cpp:75
002910BD  | BA BC012D00     | mov edx,if_else.2D01BC   | 2D01BC:"argc <= 0"
002910C2  | B8 B0012D00     | mov eax,if_else.2D01B0   | 2D01B0:"argc == 0"
002910C7  | 0F45C2          | cmovne eax,edx           |//将两条判断优化在一起
···printf