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本帖最后由 kangels 于 2013-3-19 10:23 编辑 4 i' U* M& i7 {8 p Q! i. F
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丢失的类型信息( {: ~7 P3 ^4 z6 G5 f6 w! t* {
猜测$ l+ s7 \1 P- ~+ T
指针变量应该存储两方面的信息：地址，类型信息
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实证; ^( T% V2 y/ |9 G ?
用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息
1 n5 m* K2 j5 l8 ^; k- S反汇编一段代码来看看
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#include <stdio.h> int gi; int * pi; void main(int argc, char **argv) { pi = &gi; *pi = 12; } 1: #include <stdio.h> 2: int gi; 3: int * pi; 4: void main(int argc, char **argv) 5: { 00411370 push ebp 00411371 mov ebp,esp 00411373 sub esp,0C0h 00411379 push ebx 0041137A push esi 0041137B push edi 0041137C lea edi,[ebp+FFFFFF40h] 00411382 mov ecx,30h 00411387 mov eax,0CCCCCCCCh 0041138C rep stos dword ptr es:[edi] 6: pi = &gi; 0041138E mov dword ptr ds:[00417140h],417144h 7: *pi = 12; 00411398 mov eax,dword ptr ds:[00417140h] 0041139D mov dword ptr [eax],0Ch 8: } 004113A3 xor eax,eax 004113A5 pop edi 004113A6 pop esi 004113A7 pop ebx 004113A8 mov esp,ebp 004113AA pop ebp 004113AB ret 5 d# g! q4 q( A, J& \8 O) M! i
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实例2：' R# P4 X' e' p6 L9 j, ^, j7 u' i# v& O5 l
#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } 2 K+ Z$ ]1 i, Z, g* O6 I
1: #include <stdio.h> 2: short gs; 3: short * ps; 4: void main(int argc, char **argv) 5: { 00411370 push ebp 00411371 mov ebp,esp 00411373 sub esp,0C0h 00411379 push ebx 0041137A push esi 0041137B push edi 0041137C lea edi,[ebp+FFFFFF40h] 00411382 mov ecx,30h 00411387 mov eax,0CCCCCCCCh 0041138C rep stos dword ptr es:[edi] 6: ps = &gs; 0041138E mov dword ptr ds:[00417140h],417144h 7: *ps = 12; 00411398 mov eax,0Ch 0041139D mov ecx,dword ptr ds:[00417140h] 004113A3 mov word ptr [ecx],ax 8: } 004113A6 xor eax,eax 004113A8 pop edi 004113A9 pop esi 004113AA pop ebx 004113AB mov esp,ebp 004113AD pop ebp 004113AE ret
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3 E! g6 Z! \* o; d3 D. x. q实例3：0 h' Y! s+ e- b: w5 \, f
#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; }
" ~9 R: S* \7 Z3 I, L 1: #include <stdio.h> 2: char gc; 3: char * pc; 4: void main(int argc, char **argv) 5: { 00411370 push ebp 00411371 mov ebp,esp 00411373 sub esp,0C0h 00411379 push ebx 0041137A push esi 0041137B push edi 0041137C lea edi,[ebp+FFFFFF40h] 00411382 mov ecx,30h 00411387 mov eax,0CCCCCCCCh 0041138C rep stos dword ptr es:[edi] 6: pc = &gc; 0041138E mov dword ptr ds:[00417140h],417144h 7: *pc = 12; 00411398 mov eax,dword ptr ds:[00417140h] 0041139D mov byte ptr [eax],0Ch 8: } 004113A0 xor eax,eax 004113A2 pop edi 004113A3 pop esi 004113A4 pop ebx 004113A5 mov esp,ebp 004113A7 pop ebp 004113A8 ret ) U, F8 J+ _$ a9 G5 P/ v H
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可以看出指针的类型信息决定了赋值/读取时读/写多少个字节。! }6 H" E; K, V2 p- }
读/写多少字节的信息不是存放在指针变量中，而是放到了与该地址相关的赋值指令中。6 V/ v) p+ b6 v$ V" h7 g1 E
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狗仔卡
发表于 2013-3-12 20:59:39
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貌似很高深的反汇编
楼主
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