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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$ @3 [: n ^, J
猜测4 z% F2 ]5 z; T. Y$ t5 c
指针变量应该存储两方面的信息：地址，类型信息2 E9 k4 C8 {% W
+ W# @6 s. ]- m/ P9 t实证
' J% [4 o7 j4 Y$ w8 }用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息5 _9 s' w4 z* h. B8 ~
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 & P. |" Y' U/ c
: Z) ]+ n) a; z, Y3 d( k实例2：
2 v7 g8 m- N* g# @. h6 ?#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } 8 J. H: l! G0 v( f$ q0 o' u4 `* I( G
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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4 A/ @1 u( S5 ]( X" X实例3：& l+ ~6 y O6 m' z k8 F
#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; } + V0 Y+ b/ U- {* O) k) r
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 2 R: n8 A% f# U+ t" E& @- a# o+ e1 Q
3 v& j; {# d$ s7 H% P! r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 }: ]- b& y4 W1 B1 M7 N/ O; c
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。2 o$ |/ @) h+ X( A& j
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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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