结构体的实现机制

在C语言中用结构体定义数据的顺序和它在内存中的数据布局是一致的。

#include <stdio.h>int main(){int i;struct information {int cpu_num;char cpu_name[50];unsigned long cpu_speed;int cpu_price;}Info[3]={{1,"AMD 1.2G 1987",1200,120},{2,"INTEL 2.5G 1998",2500,220},{3,"AMD 2.2G 2008",3000,420}};for (i=0;i<3;i++)printf("%d %s %d %d/n/n",Info[i].cpu_num,Info[i].cpu_name,Info[i].cpu_speed,Info[i].cpu_price);return 0;}

反汇编代码如下所示：

 

int main(){013213A0 push ebp 013213A1 mov ebp,esp 013213A3 sub esp,198h 013213A9 push ebx 013213AA push esi 013213AB push edi 013213AC lea edi,[ebp-198h] 013213B2 mov ecx,66h 013213B7 mov eax,0CCCCCCCCh 013213BC rep stos dword ptr es:[edi] ；以上是初始化工作013213BE mov eax,dword ptr [___security_cookie (1327000h)] ；这是干嘛的呢013213C3 xor eax,ebp 013213C5 mov dword ptr [ebp-4],eax int i;struct information {int cpu_num;char cpu_name[50];unsigned long cpu_speed;int cpu_price;}Info[3]={{1,"AMD 1.2G 1987",1200,120},013213C8 mov dword ptr [ebp-0D4h],1 ；设局部变量[ebp-0D4h]=1013213D2 mov eax,dword ptr [string "AMD 1.2G 1987" (1325770h)] ；将全局变量指针1325770所指的4字节数据放到eax中013213D7 mov dword ptr [ebp-0D0h],eax ；[ebp-0D0h]=[1325770h]013213DD mov ecx,dword ptr ds:[1325774h] ；将全局变量指针1325774所指的4字节数据放到ecx中013213E3 mov dword ptr [ebp-0CCh],ecx ；[ebp-0CCh]=[1325774]013213E9 mov edx,dword ptr ds:[1325778h] ；将全局变量指针1325778所指的4字节数据放到edx中013213EF mov dword ptr [ebp-0C8h],edx ；[ebp-0C8h]=[1325778]013213F5 mov ax,word ptr ds:[0132577Ch] ；将全局变量指针132577c所指的2字节数据放到ax中013213FB mov word ptr [ebp-0C4h],ax ；设局部变量[ebp-0C4h]=[132577c]，占两个字节01321402 xor eax,eax ；清空eax 01321404 mov dword ptr [ebp-0C2h],eax ；剩余的用00000000h填充，补充满50字节，x+4-(ebp-0D0h)=50,得x=ebp-A2，所以直到mov dword ptr [ebp-0A2h],eax0132140A mov dword ptr [ebp-0BEh],eax 01321410 mov dword ptr [ebp-0BAh],eax 01321416 mov dword ptr [ebp-0B6h],eax 0132141C mov dword ptr [ebp-0B2h],eax 01321422 mov dword ptr [ebp-0AEh],eax 01321428 mov dword ptr [ebp-0AAh],eax 0132142E mov dword ptr [ebp-0A6h],eax 01321434 mov dword ptr [ebp-0A2h],eax 0132143A mov dword ptr [ebp-9Ch],4B0h ；设局部变量[ebp-9Ch]=4B0h=1200，此处为什么与上面相隔6个字节？01321444 mov dword ptr [ebp-98h],78h ；设局部变量[ebp-98h]=78h=120{2,"INTEL 2.5G 1998",2500,220},0132144E mov dword ptr [ebp-94h],2 ；过程与上面差不都，但是复制第二个变量时上面第四次是word为什么？为什么在结构体第二个成员变量与第三个成员变量之间隔两个字节，字符”/0”表示字符串结尾？那为什么不写入00h而是保留cch cch呢01321458 mov eax,dword ptr [string "INTEL 2.5G 1998" (132575Ch)] 0132145D mov dword ptr [ebp-90h],eax 01321463 mov ecx,dword ptr ds:[1325760h] 01321469 mov dword ptr [ebp-8Ch],ecx 0132146F mov edx,dword ptr ds:[1325764h] 01321475 mov dword ptr [ebp-88h],edx 0132147B mov eax,dword ptr ds:[01325768h] 01321480 mov dword ptr [ebp-84h],eax 01321486 xor eax,eax 01321488 mov dword ptr [ebp-80h],eax 0132148B mov dword ptr [ebp-7Ch],eax 0132148E mov dword ptr [ebp-78h],eax 01321491 mov dword ptr [ebp-74h],eax 01321494 mov dword ptr [ebp-70h],eax 01321497 mov dword ptr [ebp-6Ch],eax 0132149A mov dword ptr [ebp-68h],eax 0132149D mov dword ptr [ebp-64h],eax 013214A0 mov word ptr [ebp-60h],ax 013214A4 mov dword ptr [ebp-5Ch],9C4h 013214AB mov dword ptr [ebp-58h],0DCh {3,"AMD 2.2G 2008",3000,420}013214B2 mov dword ptr [ebp-54h],3 013214B9 mov eax,dword ptr [string "AMD 2.2G 2008" (132574Ch)] 013214BE mov dword ptr [ebp-50h],eax 013214C1 mov ecx,dword ptr ds:[1325750h] 013214C7 mov dword ptr [ebp-4Ch],ecx 013214CA mov edx,dword ptr ds:[1325754h] 013214D0 mov dword ptr [ebp-48h],edx 013214D3 mov ax,word ptr ds:[01325758h] 013214D9 mov word ptr [ebp-44h],ax 013214DD xor eax,eax 013214DF mov dword ptr [ebp-42h],eax 013214E2 mov dword ptr [ebp-3Eh],eax 013214E5 mov dword ptr [ebp-3Ah],eax 013214E8 mov dword ptr [ebp-36h],eax 013214EB mov dword ptr [ebp-32h],eax 013214EE mov dword ptr [ebp-2Eh],eax 013214F1 mov dword ptr [ebp-2Ah],eax 013214F4 mov dword ptr [ebp-26h],eax 013214F7 mov dword ptr [ebp-22h],eax 013214FA mov dword ptr [ebp-1Ch],0BB8h 01321501 mov dword ptr [ebp-18h],1A4h };for (i=0;i<3;i++)01321508 mov dword ptr [ebp-0Ch],0 ；局部变量[ebp-0Ch]=i=00132150F jmp main+17Ah (132151Ah) ；典型的FOR循环结构无条件跳转到01321511 mov eax,dword ptr [ebp-0Ch] ；eax=i01321514 add eax,1 ；01321517 mov dword ptr [ebp-0Ch],eax ；使i加10132151A cmp dword ptr [ebp-0Ch],3 ；i<3?0132151E jge main+1D1h (1321571h) ；如果i>=3则跳转到printf("%d %s %d %d/n/n",Info[i].cpu_num,Info[i].cpu_name,Info[i].cpu_speed,Info[i].cpu_price);01321520 mov eax,dword ptr [ebp-0Ch] ；eax=i01321523 shl eax,6 ；i=i*2^6=i*64，得到结构体大小01321526 mov esi,esp ；esi指向当前堆栈指针01321528 mov ecx,dword ptr [ebp+eax-98h] ；ecx=局部变量[ebp+eax-98h]，典型的数组或结构体寻址结构0132152F push ecx ；参数入栈01321530 mov edx,dword ptr [ebp-0Ch] ；edx=i01321533 shl edx,6 ；i=i*6401321536 mov eax,dword ptr [ebp+edx-9Ch] ；eax=局部变量[ebp+edx-9Ch]0132153D push eax ；参数入栈0132153E mov ecx,dword ptr [ebp-0Ch] 01321541 shl ecx,6 01321544 lea edx,[ebp+ecx-0D0h] ；edx指向字符串起始位置0132154B push edx ；参数入栈0132154C mov eax,dword ptr [ebp-0Ch] 0132154F shl eax,6 01321552 mov ecx,dword ptr [ebp+eax-0D4h] ；ecx=局部变量[ebp+eax-0D4h]01321559 push ecx ；参数入栈0132155A push offset string "%d %s %d %d/n/n" (132573Ch) ；字符串地址入栈0132155F call dword ptr [__imp__printf (13282BCh)] ；调用printf函数01321565 add esp,14h ；从堆栈中弹出14h字节，14h/4=5个参数01321568 cmp esi,esp ；C_CheckEsp0132156A call @ILT+310(__RTC_CheckEsp) (132113Bh) 0132156F jmp main+171h (1321511h) ；无条件跳转到return 0;01321571 xor eax,eax ；清空eax}01321573 push edx 01321574 mov ecx,ebp 01321576 push eax 01321577 lea edx,[ (13215A4h)] 0132157D call @ILT+130(@_RTC_CheckStackVars@8) (1321087h) 01321582 pop eax 01321583 pop edx 01321584 pop edi 01321585 pop esi 01321586 pop ebx 01321587 mov ecx,dword ptr [ebp-4] 0132158A xor ecx,ebp 0132158C call @ILT+25(@__security_check_cookie@4) (132101Eh) 01321591 add esp,198h ；从堆栈中弹出198h字节01321597 cmp ebp,esp 01321599 call @ILT+310(__RTC_CheckEsp) (132113Bh) 0132159E mov esp,ebp 013215A0 pop ebp 013215A1 ret