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本帖最后由 kangels 于 2013-3-19 10:23 编辑 ! t+ j) g- E$ l3 V- b) R' |
# p6 m w$ W2 h' b' j6 X8 e* `丢失的类型信息6 P5 `; t% X0 ]# l8 G2 k
猜测
* I3 ^; q9 j: j X' C4 [指针变量应该存储两方面的信息：地址，类型信息9 o+ q! c+ V$ h# I
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实证
+ W1 U* J4 u8 S. ~0 h0 |用sizeof()，float *,int*,double *....都是4字节没有存储类型信息只有地址信息/ w' n- T$ ?8 B' Y& p0 O+ J: h& k* o
反汇编一段代码来看看5 d# y, C4 a8 B( P9 r& Y1 A4 }
实例1：
& l0 z2 m) b% f9 ^6 R#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
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实例2：3 M8 r5 M5 q( C" }4 K$ |2 H
#include <stdio.h> short gs; short * ps; void main(int argc, char **argv) { ps = &gs; *ps = 12; } ) @& h5 @3 j/ d3 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 ( V* Z' W# ~' u0 Z2 o" j
* _2 C0 i. ~4 k8 o* G& A! {实例3：
. w# @3 l- Y- t+ a#include <stdio.h> char gc; char * pc; void main(int argc, char **argv) { pc = &gc; *pc = 12; } 4 O4 `, s: l$ z, S* Y- E' d
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
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* y) o/ Q( e/ `; `' r, X( S; J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 p% N# b! N/ K! 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。 \! W7 p1 M( G! W8 k( k
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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
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