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//asm source code note 1.10 union 和 enum 的访问

//************************************************************ //* original c code //************************************************************ #include "stdafx.h" #include <windows.h> #include <stdlib.h> #include <stdio.h> typedef enum {     enum_1 = 0x111, //搞个特殊的数, 容易看     enum_2,     enum_3, }myenum; typedef struct  {     int a;     int b;     int c; }mystruct; typedef union {     mystruct s;     myenum e[3]; }myunion; int fn(int a, int b); int main(int argc, char* argv[]) {     fn(1, 2);         return 0; } int fn(int a, int b) {     int i = 0;     UCHAR buf[100] = {0};     myunion * uns = NULL;     for(i = 0; i < 5; i++)     {         uns = (myunion *)(buf + sizeof(myunion) * i);         uns->s.a = 0x666;         uns->s.b = 0x777;         uns->s.c = 0x888;         uns->e[0] = enum_1;         uns->e[1] = enum_2;         uns->e[2] = enum_3;     }     return 0; } //************************************************************ //* asm code //************************************************************ /*     memory image:         addr(uns) = ebp - 0x6c;         addr(buf[100]) = ebp - 0x68;         addr(i) = ebp - 4; */ 37: 38:   int fn(int a, int b) 39:   { 00401070   push        ebp 00401071   mov         ebp,esp 00401073   sub         esp,0ACh 00401079   push        ebx 0040107A   push        esi 0040107B   push        edi 0040107C   lea         edi,[ebp-0ACh] 00401082   mov         ecx,2Bh 00401087   mov         eax,0CCCCCCCCh 0040108C   rep stos    dword ptr [edi] 40:       int i = 0; 0040108E   mov         dword ptr [ebp-4],0 41:       UCHAR buf[100] = {0}; //由于对Buf[0]赋值的原因(1Byte), 填充buf[100]的过程分成了3次(96Bytes, 2Bytes, 1Byte) 00401095   mov         byte ptr [ebp-68h],0 00401099   mov         ecx,18h 0040109E   xor         eax,eax 004010A0   lea         edi,[ebp-67h] 004010A3   rep stos    dword ptr [edi] 004010A5   stos        word ptr [edi] 004010A7   stos        byte ptr [edi] 42:       myunion * uns = NULL; 004010A8   mov         dword ptr [ebp-6Ch],0 43: 44:       for(i = 0; i < 5; i++) 004010AF   mov         dword ptr [ebp-4],0 //i = 0; 004010B6   jmp         fn+51h (004010c1) 004010B8   mov         eax,dword ptr [ebp-4] 004010BB   add         eax,1 004010BE   mov         dword ptr [ebp-4],eax 004010C1   cmp         dword ptr [ebp-4],5 004010C5   jge         fn+0A0h (00401110) //if(i >= 5) break; 45:       { 46:           uns = (myunion *)(buf + sizeof(myunion) * i); 004010C7   mov         ecx,dword ptr [ebp-4] 004010CA   imul        ecx,ecx,0Ch //ecx = i * 0xc;//算出在buf中union的偏移 004010CD   lea         edx,[ebp+ecx-68h] //当前union总偏移 = buf + ecx; 004010D1   mov         dword ptr [ebp-6Ch],edx //更新当前uns 47: 48:           uns->s.a = 0x666; 004010D4   mov         eax,dword ptr [ebp-6Ch] 004010D7   mov         dword ptr [eax],666h //给结构成员1赋值, 结构内偏移(ebp-6Ch + 0) 49:           uns->s.b = 0x777; 004010DD   mov         ecx,dword ptr [ebp-6Ch] 004010E0   mov         dword ptr [ecx+4],777h //给结构成员2赋值, 结构内偏移(ebp-6Ch + 4) 50:           uns->s.c = 0x888; 004010E7   mov         edx,dword ptr [ebp-6Ch] 004010EA   mov         dword ptr [edx+8],888h //给结构成员3赋值, 结构内偏移(ebp-6Ch + 8) 51: 52:           uns->e[0] = enum_1; 004010F1   mov         eax,dword ptr [ebp-6Ch] 004010F4   mov         dword ptr [eax],111h //给结构成员1赋值, 结构内偏移(ebp-6Ch + 0) 53:           uns->e[1] = enum_2; 004010FA   mov         ecx,dword ptr [ebp-6Ch] 004010FD   mov         dword ptr [ecx+4],112h //给结构成员2赋值, 结构内偏移(ebp-6Ch + 4) 54:           uns->e[2] = enum_3; 00401104   mov         edx,dword ptr [ebp-6Ch] 00401107   mov         dword ptr [edx+8],113h //给结构成员3赋值, 结构内偏移(ebp-6Ch + 8) 55:       } 0040110E   jmp         fn+48h (004010b8) 56: 57:       return 0; 00401110   xor         eax,eax 58:   } 00401112   pop         edi 00401113   pop         esi 00401114   pop         ebx 00401115   mov         esp,ebp 00401117   pop         ebp 00401118   ret //************************************************************ //* note //************************************************************ 指令功能说明: rep stos    dword ptr [edi]; //[eax] copy to [edi], move counter is [ecx], operand is DWORD stos        word ptr [edi]; //[eax] copy to [edi], move one time, operand is WORD stos        byte ptr [edi]; //[eax] copy to [edi], move one time, operand is BYTE 单从asm代码无法看出是struct还是union, 在asm代码中都是操作的struct

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