如何在 Linux 下调试动态链接库 2

下面我们就开始调试上面命令生成的 app程序吧。如果已经把上面生成的 libggg.so放到了库文件搜索路径指定的文件目录，比如/lib或/usr/lib之类的，调试就顺利完成，如下

：

QUOTE:
linux#gdb">zhoulifa@linux#gdb ./app
GNU gdb 6.4-debian
Copyright 2005 Free Software Foundation,Inc.
GDB is free software, covered by the GNU

General Public License, and you are
welcome to change it and/or distribute

copies of it under certain conditions.
Type "show copying" to see theconditions.


There is absolutely no warranty for GDB.

Type "show warranty"for details.This GDB was configured as"i486-linux-

gnu"...Using host libthread_db library"/lib/tls/i686/cmov/libthread_db.so.1".

(gdb) b main   /* 这是在程序的 main 处设置断点 */
Breakpoint 1 at0x804853c: file pk.cpp,line7.
(gdb) b set     /* 这是在程序的 set 处设置断点 */
Function "set" not defined.
Make breakpoint pending on future shared

library load?(y or[n]) y/* 这里必须选择 y 调试程序才会跟踪到动态链接库内部去

*/Breakpoint 2(set) pending.
(gdb) run/* 开始运行我们的程序，直到遇见断点时暂停 */
Starting program:/data/example/c/app
Breakpoint 3 at0xb7f665f8: file get.cpp,line11.
Pending breakpoint "set" resolved

Breakpoint 1, main(argc=1,argv=0xbf990504) at pk.cpp:7
7               int a=100;
(gdb) n    /* 继续执行程序的下一行代码

*/
8              int b= get();
(gdb) n     /* 程序执行到了我们断点所在的动态链接库了 */
get x=0
9               int c= set(a);(gdb) n

Breakpoint 3, set(a=100) at get.cpp:11
11              printf ("set a=%d\n", a);

(gdb) list  /* 查看当前代码行周围的代码，证明我们已经跟踪到动态链接库的源代码里面了 */
6               printf("get x=%d\n", x);
7              return x;
8      }
9      int set(int a)
10     {
11              printf("set a=%d\n", a);
12              x= a;
13             return x;
14     }
(gdb) n
set a=100
12              x = a;(gdb) n
13             return x;(gdb) n
14     }
(gdb) n
main (argc=1, argv=0xbf990504) at

pk.cpp:10
10              int d= get();
(gdb) n
get x=100
11              printf ("a=%d,b=%d,c=%

d,d=%d\n",a,b,c,d);
(gdb) n
a=100,b=0,c=100,d=100
12              return0;
(gdb) c
Continuing.

Program exited normally.
(gdb) quit/* 程序顺利执行结束 */zhoulifa@linux#

如果我们没有把动态链接库放到指定目录，比如/lib里面，调试就会失败，过程如下：

QUOTE:
zhoulifa@linux# gdb ./app
GNU gdb 6.4-debian
Copyright 2005 Free Software Foundation,

Inc.
GDB is free software, covered by the GNU

General Public License, and you arewelcome to change it and/or distribute

copies of it under certain conditions.


Type "show copying" to see theconditions.
There is absolutely no warranty for GDB.

Type "show warranty"for details.
This GDB was configured as "i486-linux-

gnu"...Using host libthread_db library

"/lib/tls/i686/cmov/libthread_db.so.1".

(gdb) b main
Breakpoint 1 at0x804853c: file pk.cpp,

line 7.
(gdb) b set
Function "set" not defined.
Make breakpoint pending on future shared

library load?(y or[n]) y
Breakpoint 2(set) pending.
(gdb) run/* 虽然调试操作都一样，但程序执行失败 */
Starting program:/data/example/c/app
/data/example/c/app: error while loading

shared libraries: libggg.so: cannot open

shared object file: No such file or

directory

Program exited with code 0177.
(gdb) quit