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
* ^! e; ~3 v. c0 C
4 e9 A @4 e4 A% J- t丢失的类型信息 {9 f5 {# r" M( g2 H5 N) B
猜测
& P6 p, o" Q6 q$ U) L( L指针变量应该存储两方面的信息：地址，类型信息' w0 e {( v* t/ b
! z0 F, v! R# p+ j( F& W: l. F; p
实证: [/ E3 ^0 I0 J* u+ ?$ d
用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息
, f x# D6 d$ Q5 X: c+ C+ K反汇编一段代码来看看
+ P) a& o+ q# D/ o% H) o实例1：9 C4 C/ v) I* r# K
#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
+ D* G8 Y( w1 y, @8 j4 p' K6 Y4 j1 ]" v
实例2：3 L6 X7 B& J( M, g( u
#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; }
2 a1 l7 t8 P% l; j! G+ w/ X 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
& ~+ y; ^# W: R- {; m2 _ n; K2 t2 ?3 |" Z4 l0 ~! p
实例3：
) D) m: @3 @6 h8 I#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; }
& } {+ l6 E' [ N7 N. E8 l! y9 P 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
# S) |" B1 t3 z0 g6 s C G: \; C7 r) R, i% B$ {
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。8 q- J( M) i. e6 Q6 r
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。# f. t/ ^6 J4 T& \1 b/ w# L8 Y5 E
| 
( 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
7 L% O! f. f1 \+ P3 C7 l4 M, Q