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本帖最后由 kangels 于 2013-3-19 10:23 编辑 % o% W# X) E) ]5 o; Q' x
2 C* N) F7 Z/ F: g3 g+ n: N E6 s丢失的类型信息% @, Q% x2 z+ u8 ?* Y' S- R9 }( n
猜测
7 J4 o8 y: q! n4 M% P3 m指针变量应该存储两方面的信息：地址，类型信息: c2 o' `% r4 t
9 k8 \: B) T/ k, Q实证
, M# @9 ~" I' Q. \% B+ f5 q用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息
: w3 a5 @2 ]+ o% _" w反汇编一段代码来看看$ P" u' T* N3 e
实例1：
, O+ d2 V' I0 @/ r" j% }#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 # E6 q- o; s2 v6 z2 r: p% {, C: b
: S" M+ r! c8 i) A: B实例2：
/ t) _9 f8 ?/ Q5 L m#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } - p4 ]3 W; D& W; b
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 + p" y' @4 Z1 W, n" c
7 @" o5 C5 X2 S7 C实例3：
4 \% r6 @; b7 Q2 G#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; } % B. b# t+ J' X+ t
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 . e# R+ T! ^ Q F! Q; u4 W, c k
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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。
0 p+ o- F" J' k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。- k9 q }( `. Q7 S
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狗仔卡
发表于 2013-3-12 20:59:39
置顶卡
千斤顶
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貌似很高深的反汇编
楼主
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