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
S3 _1 |* w8 J# @7 T
; x% r x8 y0 L; K9 c8 h' ]丢失的类型信息
9 Q% [2 f. n0 @; G猜测) J0 e/ {0 X! w7 @% n% P
指针变量应该存储两方面的信息：地址，类型信息! m- s8 P4 Z$ a: }: u
1 K$ `3 b6 U; c2 f2 i5 s; F; L
实证& o- h+ f0 g( O9 n: e
用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息, d8 X/ L, H+ [/ y% q* {0 ^; ~
反汇编一段代码来看看: u( i0 W' g4 i" I
实例1：( Z5 z! B+ V/ w; h) s8 W1 u
#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
+ V$ D6 b& P7 ]5 \+ p4 J( s. e( G( w% ~* E% V
实例2：
- Y' @8 O" r. {7 ^! j#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } & o6 d f$ l3 z: R \0 N
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 c( U% s# K' P6 u( L
* z. @# _7 @( }; B实例3：
$ X9 u/ ~- f! M" T+ V, D#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; }
8 p, t% I/ L) W) f/ n6 J 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 * K0 j4 `0 M: y' _, m1 `. T5 G- o
_( x- q1 B; W8 o4 V; B5 o
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。
# \# I. P& E5 b% T! v$ K& u" Y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。8 a5 V# V* ^ F" ~. ^
| 
( 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