linux上一个经典的segmentation fault

废话不多说，请看下面代码：

#include<string>
#include<stdio.h>
#include<unistd.h>
#include<string.h>
int version=1;

int main()
{
	char *testarry[3]={"a","b","c"};
	strcpy(testarry[2],"C");
	printf("%c",testarry[2][0]);
	printf("%s\n",testarry[2]);
	if(testarry[2][0])
	{
	printf("version:%d",1);
	}
	return 0;
}
           

编译运行，segmentation fault 出现了。分析以上代码，一眼看上去，似乎没毛病，尝试把下面语句去掉

strcpy(testarry[2],“C”);

竟然运行通过，也就说使用testarry[2][0]作为if判断的标准，作为%c输出都没有问题。

那么奇怪了啊，为什么strcopy语句一加上就挂呢。搞出gdb来分析。

使用g++ main.cpp -g编译得到a.out -g是为了得到符号表

过程如下：

[email protected]:~/testcplus$ gdb a.out

GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.5) 7.11.1

Copyright © 2016 Free Software Foundation, Inc.

License GPLv3+: GNU GPL version 3 or later http://gnu.org/licenses/gpl.html

This is free software: you are free to change and redistribute it.

There is NO WARRANTY, to the extent permitted by law. Type “show copying”

and “show warranty” for details.

This GDB was configured as “x86_64-linux-gnu”.

Type “show configuration” for configuration details.

For bug reporting instructions, please see:

http://www.gnu.org/software/gdb/bugs/.

Find the GDB manual and other documentation resources online at:

http://www.gnu.org/software/gdb/documentation/.

For help, type “help”.

Type “apropos word” to search for commands related to “word”…

Reading symbols from a.out…done.

(gdb) list

1 #include

2 #include<stdio.h>

3 #include<unistd.h>

4 #include<string.h>

5

6 //#include “dervied.h”

7 int version=1;

8

9 int main()

10 {

(gdb) list

11 char *testarry[3]={“a”,“b”,“c”};

12 strcpy(testarry[2],“C”);

13 printf("%c",testarry[2][0]);

14 printf("%s\n",testarry[2]);

15 if(testarry[2][0])

16 {

17 printf(“version:%d”,1);

18 }

19 return 0;

20 }

(gdb) break 11

Breakpoint 1 at 0x40063d: file main.cpp, line 11.

(gdb) r

Starting program: /home/yuneec01/testcplus/a.out

Breakpoint 1, main () at main.cpp:11

11 char *testarry[3]={“a”,“b”,“c”};

(gdb) n

12 strcpy(testarry[2],“C”);

(gdb) n

Program received signal SIGSEGV, Segmentation fault.//这里就挂了

0x0000000000400659 in main () at main.cpp:12

12 strcpy(,“C”);

(gdb) p testarry //果断把testarry的打出来看看，看到testarry[2]的地址是0x400748

$1 = {0x400744 “a”, 0x400746 “b”, 0x400748 “c”}

也就是操作这个地址挂了

我们去read以下a.out看看

使用readelf -S a.out

找0x400748所在的段，如下：

[16] .rodata PROGBITS 0000000000400740 00000740

0000000000000015 0000000000000000 A 0 0 4

问题出现，此段为.rodata

strcpy把rodata当作目标字符串操作，setmentation fault是必然出现了。

以上给大家班门弄斧的展示了一次寻找segmentation fault根源的方法。水平有限，还望赐教。

谢谢