如果返回
是
个struct对象,
语句会如何做呢?下面是测试代码 #
<iostream> using
std; struct Big
{
char buf[100];
i; long d;
}B,B2;
Big bigfun(Big b)
{
b.i=100;
b; }
{
B2=bigfun(B);
0; }
在
开头和结尾设断点 8:
19: {
004012A0 push ebp
004012A1 mov ebp,esp
004012A3 sub esp,118h
//
开始对这迷惑不解,分析了好久 //原来(118h-40h)剩下
内存块存放了两个Big变量 //低地址放Bigfun
返回值临时变量 //高地址放B2.operator=(Big &)
参数 004012A9 push ebx
004012AA push esi
004012AB push edi
004012AC lea edi,[ebp-118h]
004012B2 mov ecx,46h
004012B7 mov eax,0CCCCCCCCh
004012BC rep stos dword ptr [edi]
20: B2=bigfun(B);
004012BE sub esp,6Ch//b参数入栈
004012C1 mov ecx,1Bh
004012C6 mov esi,off
B (00438490)//B首地址 004012CB mov edi,esp
004012CD rep movs dword ptr [edi],dword ptr [esi]//上面这些指令完成对b
化工作 004012CF lea eax,[ebp-0D8h]//eax存放Big类型
个返回值临时变量首地址 004012D5 push eax//注意
般栈
没有这条指令 004012D6 call @ILT+0(bigfun) (00401005)
/*
004012DB add esp,70h
004012DE mov esi,eax
004012E0 mov ecx,1Bh
004012E5 lea edi,[ebp-6Ch]
004012E8 rep movs dword ptr [edi],dword ptr [esi]
004012EA mov ecx,1Bh
004012EF lea esi,[ebp-6Ch]
004012F2 mov edi,off
B2 (00438500) 004012F7 rep movs dword ptr [edi],dword ptr [esi]
21:
22:
0; 004012F9 xor eax,eax
23:
24: }
004012FB pop edi
004012FC pop esi
004012FD pop ebx
004012FE add esp,118h
00401304 cmp ebp,esp
00401306 call __chkesp (004081e0)
0040130B mov esp,ebp
0040130D pop ebp
0040130E ret
*/
@ILT+0(?bigfun@@YA?AUBig@@U1@@Z):
00401005 jmp bigfun (00401250)
11: Big bigfun(Big b)
12: {
00401250 push ebp
00401251 mov ebp,esp
00401253 sub esp,40h
00401256 push ebx
00401257 push esi
00401258 push edi
00401259 lea edi,[ebp-40h]
0040125C mov ecx,10h
00401261 mov eax,0CCCCCCCCh
00401266 rep stos dword ptr [edi]
13: b.i=100;
00401268 mov dword ptr [ebp+70h],64h
/*
0012FE50 00 00 00 00 64 00 00 00 00 00 00 00
*/
14:
b; 0040126F mov ecx,1Bh
00401274 lea esi,[ebp+0Ch]//esi=b
首地址 00401277 mov edi,dword ptr [ebp+8]//edi=返回值临时变量
首地址 0040127A rep movs dword ptr [edi],dword ptr [esi]
0040127C mov eax,dword ptr [ebp+8]
15: }
0040127F pop edi
00401280 pop esi
00401281 pop ebx
00401282 mov esp,ebp
00401284 pop ebp
00401285 ret
返回到
004012DB add esp,70h//销毁局部参数
004012DE mov esi,eax//bigfunction
返会值临时变量首地址 004012E0 mov ecx,1Bh
004012E5 lea edi,[ebp-6Ch]//B2.operator=(Big &)参数
首地址 004012E8 rep movs dword ptr [edi],dword ptr [esi]
004012EA mov ecx,1Bh
004012EF lea esi,[ebp-6Ch]
004012F2 mov edi,off
B2 (00438500)//B2首地址 004012F7 rep movs dword ptr [edi],dword ptr [esi]
21:
22:
0; 004012F9 xor eax,eax
23:
24: }
004012FB pop edi
004012FC pop esi
004012FD pop ebx
004012FE add esp,118h
00401304 cmp ebp,esp
00401306 call __chkesp (004081e0)
0040130B mov esp,ebp
0040130D pop ebp
0040130E ret
整理总结:
1.
般function frame结构是 内局部变量 ebp
eip
参数 如果返回值是
个struct对象function frame 内局部变量 ebp
eip
返回值临时变量
首地址//特别注意这个 参数 (由于寄存器太小,不可能放
块struct内存,所以保存了临时变量首地址). 2.struct对象
临时变量是在栈上,而不是在堆上.
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