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 ' ?- d! p$ ]" A& n
/ L) l! f" \! X- u) n3 S# }
丢失的类型信息3 X9 w, }/ C! a9 l: o' C& ?
猜测/ h# A& @, ]7 A$ c8 R( u \% k
指针变量应该存储两方面的信息：地址，类型信息
w3 W* V. [* M6 j$ f4 \7 t) U7 h( Q. K8 d9 M3 q
实证8 `( z8 s. n5 F$ S( q; o
用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息
$ I8 u' t: x; ?反汇编一段代码来看看: b: E0 C1 r+ V4 k5 t$ f6 ?6 B( s
实例1：
( i; F) P, Q& u B; o#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 " ]5 @8 A/ U" b- G
) K3 Y5 R: f4 p8 X* L- _
实例2： C6 K' c: y9 F- B' Q& K7 B# z
#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; }
6 j$ O) X. |9 W# 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
6 z; ]5 s C7 X2 |8 _6 n$ \' X0 a4 D, I7 M0 }/ u
实例3：
( A$ L4 p5 P5 n! ?, y: N#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; }
/ }: m F3 z8 I! E( 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 7 C2 M3 P( V# e5 `- X
) ~* r r: h% k, D2 r4 P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。
: u p8 W8 }3 P% c' t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% e X4 B( w* S
| 
( 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