马上注册，结交更多好友，享用更多功能^_^
您需要 登录 才可以下载或查看，没有账号？立即注册
x
本帖最后由 kangels 于 2013-3-19 10:23 编辑
4 Z2 m4 `( n$ i8 n' I* r0 @+ E* x5 @5 l) a. d
丢失的类型信息4 t0 {! n, y5 a
猜测
7 r' j8 v5 `6 z3 U6 S指针变量应该存储两方面的信息：地址，类型信息, Q$ M9 t+ s$ \
* o& ^, Q# `0 H实证1 }: i% o4 `7 N( w" e: y; p
用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息4 }5 }4 H; n! m& E
反汇编一段代码来看看
) E' I6 `0 j/ n1 X7 b3 w# J8 N5 |实例1：/ K& D8 K) Q$ O7 N! f4 w
#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 / Y% m6 @, A0 L2 m' h) y
$ z. h7 N5 {9 o) ^ q. T1 M
实例2：9 w3 s9 T' D, ]" V9 V
#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } # m. o/ I" G4 l6 h. [1 L$ j
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 6 L3 z1 u/ h. \/ i3 ^
' z& V" Y8 \( u+ _6 Q, Y; M
实例3：8 N" ?9 o, x" G& f7 l1 ~/ W) e
#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; } 4 D/ o0 m+ ^+ ?% |- }
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 1 W# H+ w% e+ W4 p
8 b6 z) ?! F8 t
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。
, `- ~$ h+ Q9 ^9 h4 e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。: `/ G( E* _1 J) q( D
| 
( 粤ICP备18085999号-1 | 粤公网安备 44051102000585号)
狗仔卡
发表于 2013-3-12 20:59:39
置顶卡
千斤顶
显身卡
貌似很高深的反汇编
楼主