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本帖最后由 kangels 于 2013-3-19 10:23 编辑
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丢失的类型信息; x0 I: E! j4 v' m$ C# Y, t
猜测
, c" b3 u' e K7 U y7 I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
) q* x! g5 ?) N. C# Y用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息
( J8 {# S$ H5 A- `4 b; T C反汇编一段代码来看看5 Y/ h* X+ e( u# E0 x' r2 a, ~
实例1： f2 S) ~; Z; H8 }! e& R# K6 @3 G
#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
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9 q, Z' \# d# i) j0 x( h! ~实例2：
4 p# e7 `# y( M#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } * f9 O0 w: {4 r
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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6 |0 v. _. T( O: F4 k! V+ t. S* w" B实例3：
7 X4 D8 V! [7 }) }# B' u" T#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; } 3 r" w7 U6 u1 s& v0 {# u
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 8 g( G: w w9 S7 O) N2 H
3 d% e! N, Z3 y; O% m/ l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。' q2 ~& H; |! v4 v! r
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。. k% B0 {" N# `# V# o
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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