Re: extern��ָ��ָ��

Article View: cn.comp.security

Article #13

#13

From: nukq
Date: Thu, 20 Nov 2003 08:36

174 lines
9063 bytes

���岻ͬ�ˡ�*table[]��table�����飬��table������û�д洢�ռ�ģ���Ȼ���ʾ��
���׵�ַ��talbe[0] table[1] ..�Ÿ�����4byte�Ŀռ䡣

����Ҫ����
o.c�����Ϊ

void *__table[]={"0","1","2","3",NULL};
void **table=__table;


"Qing, Quan" <skipme@263.net> д���ʼ� news:bpfrjc$17uo$1@mail.cn99.com...
> > 804841e:       a1 18 95 04 08          mov    0x8049518,%eax <-----��
> 0x8049518��ַ�е�ֵ�ŵ�eax��
> > 8048423:       83 c0 04                add    $0x4,%eax      <-----�ٰ�
��
> ��ֵ��4������Ȼ�����ǵı����г���
>
> > table 8049518
> > &table[1] 8048507 <-----������Ȼ����������Ҫ��
> > table[1] (null)   <-----������ǳ�����
>
> 0x8049518+0x04=0x804951c����ʹ�ӡ������զ��ϵ�ϵ��أ�:(
> ��ô����û�д?��
>
> -- 
> ------
> Qing, Quan
> Center for Nanoscale Science and Technology
> Peking University
> Beijing, P.R. China
> http://www.chem.pku.edu.cn/nanochemistry
> "NewBlue" <NewBlue@yaako.com> д���ʼ� news:uad84zjij.fsf@yaako.com...
> > [tips] extern��ָ���ָ�����
> >
> > alert7  �����ڣ�2003-09-08 13:02
> >
> >  extern��ָ���ָ�����
> >
> > by alert7
> >
> >   gcc��һ��С����,�������Ѿ�֪�����ȽϷ�ǳ�����ǲ�֪���Ŀ��ܻ����ƺü���
С
> ʱ��
> >
> >   һֱ���������Ƕ���Ϊchar *argv[]��char **argv�ǵȼ۵ġ���������
> > Ҳһֱû�г��?���Խ��ҵ���Ϊchar *argv[]��char **argv�ǵȼ۵ģ�ԭ��
> > ��һ��������ͨ�õġ�
> >   ���ǣ������һ��BUG������һ�죬���ƾ���֮�������Ƕ���ָ���ָ���
��
> > �ǵĻ�������ԭ�ͣ�Ӧ�ö����ָ�����顣���������ְѾ���д�ɱ��ģ���ʹ��
��
> ��
> > ��һЩ��·��
> >
> >   ���µ��������ҳ�������ģ�table�������ָ�����飬��ʵ����ʵ��o.c������
��
> ��
> > ���ṩ�������û��Դ���룬����ܲݲݵİ�table����Ϊextern void ** ;
> >
> > [root@redhat73 root]# cat o.c
> > #include <stdio.h>
> > void * table[]={"0","1","2","3",NULL};
> >
> > int test(void )
> > {
> >
> >         return 0;
> > }
> >
> > [root@redhat73 root]# cat t.c
> > #include <stdio.h>
> > int main(int argc, char *argv[])
> > {
> >         extern void **table;
> >         int t;
> >
> >         printf("table %x\n",&table);
> >         printf("&table[1] %x\n",&table[1]);
> >         printf("table[1] %s\n",table[1]);
> >
> >         return 0;
> > }
> > [root@redhat73 root]# gcc -c t.c
> > [root@redhat73 root]# gcc -o t t.o o.o
> > [root@redhat73 root]# ./t
> > table 8049518
> > &table[1] 8048507 <-----������Ȼ����������Ҫ��
> > table[1] (null)   <-----������ǳ�����
> >
> > ���������»�����
> > 08048400 <main>:
> > 8048400:       55                      push   %ebp
> > 8048401:       89 e5                   mov    %esp,%ebp
> > 8048403:       83 ec 08                sub    $0x8,%esp
> > 8048406:       83 ec 08                sub    $0x8,%esp
> > 8048409:       68 18 95 04 08          push   $0x8049518  <------table��
ַ
> > 804840e:       68 d8 84 04 08          push   $0x80484d8
> > 8048413:       e8 d8 fe ff ff          call   80482f0 <_init+0x58>
> > 8048418:       83 c4 10                add    $0x10,%esp
> > 804841b:       83 ec 08                sub    $0x8,%esp
> > 804841e:       a1 18 95 04 08          mov    0x8049518,%eax <-----��
> 0x8049518��ַ�е�ֵ�ŵ�eax��
> > 8048423:       83 c0 04                add    $0x4,%eax      <-----�ٰ�
��
> ��ֵ��4������Ȼ�����ǵı����г���
> > 8048426:       50                      push   %eax
> > 8048427:       68 e2 84 04 08          push   $0x80484e2
> > 804842c:       e8 bf fe ff ff          call   80482f0 <_init+0x58>
> > 8048431:       83 c4 10                add    $0x10,%esp
> > 8048434:       83 ec 08                sub    $0x8,%esp
> > 8048437:       a1 18 95 04 08          mov    0x8049518,%eax
> > 804843c:       83 c0 04                add    $0x4,%eax
> > 804843f:       ff 30                   pushl  (%eax)
> > 8048441:       68 f0 84 04 08          push   $0x80484f0
> > 8048446:       e8 a5 fe ff ff          call   80482f0 <_init+0x58>
> > 804844b:       83 c4 10                add    $0x10,%esp
> > 804844e:       b8 00 00 00 00          mov    $0x0,%eax
> > 8048453:       c9                      leave
> > 8048454:       c3                      ret
> >
> > �������°���ԭ�Ͷ����extern void *table[];
> > #include <stdio.h>
> > int main(int argc, char *argv[])
> > {
> >         extern void *table[];
> >         int t;
> >
> >         printf("table %x\n",&table);
> >         printf("&table[1] %x\n",&table[1]);
> >         printf("table[1] %s\n",table[1]);
> >
> >         return 0;
> > }
> > [root@redhat73 root]# gcc -c t.c
> > [root@redhat73 root]# gcc -o t t.o o.o
> > [root@redhat73 root]# ./t
> > table 8049508
> > &table[1] 804950c
> > table[1] 1
> > 08048400 <main>:
> > 8048400:       55                      push   %ebp
> > 8048401:       89 e5                   mov    %esp,%ebp
> > 8048403:       83 ec 08                sub    $0x8,%esp
> > 8048406:       83 ec 08                sub    $0x8,%esp
> > 8048409:       68 08 95 04 08          push   $0x8049508
> > 804840e:       68 c8 84 04 08          push   $0x80484c8
> > 8048413:       e8 d8 fe ff ff          call   80482f0 <_init+0x58>
> > 8048418:       83 c4 10                add    $0x10,%esp
> > 804841b:       83 ec 08                sub    $0x8,%esp
> > 804841e:       68 0c 95 04 08          push   $0x804950c  <--------����
��
> ����
> > 8048423:       68 d2 84 04 08          push   $0x80484d2
> > 8048428:       e8 c3 fe ff ff          call   80482f0 <_init+0x58>
> > 804842d:       83 c4 10                add    $0x10,%esp
> > 8048430:       83 ec 08                sub    $0x8,%esp
> > 8048433:       ff 35 0c 95 04 08       pushl  0x804950c
> > 8048439:       68 e0 84 04 08          push   $0x80484e0
> > 804843e:       e8 ad fe ff ff          call   80482f0 <_init+0x58>
> > 8048443:       83 c4 10                add    $0x10,%esp
> > 8048446:       b8 00 00 00 00          mov    $0x0,%eax
> > 804844b:       c9                      leave
> > 804844c:       c3                      ret
> >
> > ���ԣ����ǻ���Ҫ�ϸ��պ����ԭ�������塣
> >
> > ����һЩʵ�飬ָ���ָ���������extern����������Ҫע���ˣ�
> > ��ʱ��ָ���ָ�������ָ������Ͳ���ͨ���ˡ�
> > -- 
> > NewBlue
> > �Դ����뿪���Ժ���һֱ�ȴ��������
>
>

Technical Details

Message-ID: <bphude$p0f$1@news.yaako.com>

Path:

arc1-ca.pugleaf.net!archiver1.google.com!news2.google.com!news.maxwell.syr.edu!newsfeed.media.kyoto-u.ac.jp!news.cn99.com!news.yaako.com!not-for-mail

References: <uad84zjij.fsf@yaako.com> <bpfrjc$17uo$1@mail.cn99.com>

Show Full Headers

Complete Article Headers

X-Google-Language: Chinese,GB
X-Google-Thread: 1009e6,a15f179b39aafe37
X-Google-Attributes: gid1009e6,public
X-Google-Thread: 1098a9,a15f179b39aafe37
X-Google-Attributes: gid1098a9,public
X-Google-Thread: 11047e,a15f179b39aafe37
X-Google-Attributes: gid11047e,public
X-Google-Thread: 10b277,a15f179b39aafe37
X-Google-Attributes: gid10b277,public
X-Google-Thread: 113009,a15f179b39aafe37
X-Google-Attributes: gid113009,public
X-Google-Thread: f5fb9,a15f179b39aafe37
X-Google-Attributes: gidf5fb9,public
X-Google-ArrivalTime: 2003-11-20 00:37:35 PST
Path: arc1-ca.pugleaf.net!archiver1.google.com!news2.google.com!news.maxwell.syr.edu!newsfeed.media.kyoto-u.ac.jp!news.cn99.com!news.yaako.com!not-for-mail
From: "nukq" <simenking@sohu.com>
Newsgroups: cn.comp.security,cn.comp.programm,cn.comp.lang.c,cn.comp.os.linux,cn.comp.os.freebsd,cn.comp.hacker
Subject: Re: extern��ָ���ָ�����
Date: Thu, 20 Nov 2003 16:36:13 +0800
Organization: Bentium Ltd. (CN99)
Lines: 176
Message-ID: <bphude$p0f$1@news.yaako.com>
References: <uad84zjij.fsf@yaako.com> <bpfrjc$17uo$1@mail.cn99.com>
Reply-To: "nukq" <simenking@sohu.com>
NNTP-Posting-Host: 218.72.8.119
X-Trace: news.yaako.com 1069317358 25615 218.72.8.119 (20 Nov 2003 08:35:58 GMT)
X-Complaints-To: usenet@news.yaako.com
NNTP-Posting-Date: Thu, 20 Nov 2003 08:35:58 +0000 (UTC)
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 6.00.2800.1158
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165

Reply to Parent Message

Article View: cn.comp.security

Re: extern��ָ���ָ�����

Re: extern��ָ��ָ��