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本帖最后由 kangels 于 2013-3-19 10:23 编辑 ) P! |* s% c7 e' W r
, a# Z! X8 r, d- h8 e丢失的类型信息
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指针变量应该存储两方面的信息：地址，类型信息% p. ^- ], J7 [$ R! Z
$ ^( q6 D6 L( ]0 W实证* C8 h K% M1 c0 n/ 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
0 k0 p, o/ z5 e反汇编一段代码来看看
" }) f }4 l4 H1 d实例1：: W C0 b! \# x" N1 v( x- J% I
#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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+ B4 X4 j" s- _" l实例2：
! k) \# t6 N7 R" K3 z& q% K#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } + q) U0 X, e$ ]2 u( }+ e
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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7 a9 E: g/ K @- I- [7 o1 ?' ~实例3：9 I+ N1 `, u5 i% a6 [/ v# z) _
#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; } % u5 R. X+ X& l3 j; O
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 7 C! D) k B/ a% }- a- S+ D
$ Y" x4 q2 {* x4 x, r% O# K$ G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。
! z* B* \. O4 s, |% k) J9 k: U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。
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发表于 2013-3-12 20:59:39
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貌似很高深的反汇编
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