Linux笔记程序调试gdb

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本文介绍如何使用GDB进行基本的程序调试，包括设置断点、查看变量、跟踪函数调用等操作，并通过一个示例程序详细展示了GDB的使用过程。

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1 调试准备
首先新建test1.c文件。

  1 #include <stdio.h>                                                                                 
  2 #include <stdlib.h>
  3 #include <unistd.h>
  4 
  5 int myfun(int a){
  6         int i = 0;
  7         int* buff = (int*)malloc(sizeof(int)*100);
  8         while(i<100){
  9                 buff[i] = a;
 10                 a+=i;
 11                 i++;
 12         }
 13         free(buff);
 14         return a/2;
 15 }
 16 
 17 void main(){
 18         printf("begin...\n");
 19         int num = 0;
 20         if(num > 10){
 21              printf("%d>10\n",num);
 22         }else{
 23                  printf("%d<=10\n",num);
 24         }
 25 
 26         int i;
 27         for(i=0;i<5;i++){
 28                 printf("i:%d\n",i);
 29                 num+=i;
 30         }
 31         myfun(&num);
 32 
 33         printf("end...\n");
 34 }

然后使用命令

gcc test1.c -g -o test1

将会看到生成了可执行文件test1

root@iZ2zea2ti45wm5djtomfm5Z:/usr/yeliang/linux# ls
core  test1  test1.c  test2  test2.c

使用gdb调试test1
gdb test1

root@iZ2zea2ti45wm5djtomfm5Z:/usr/yeliang/linux# gdb test1
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
Copyright (C) 2014 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 test1...done.

开始调试
start

(gdb) start
Temporary breakpoint 1 at 0x40067a: file test1.c, line 18.
Starting program: /usr/yeliang/linux/test1 

Temporary breakpoint 1, main () at test1.c:18
18      printf("begin...\n");

2 list命令显示代码
list简写l
显示main()前后的代码

(gdb) list
13      free(buff);
14      return a/2;
15  }
16  
17  void main(){
18      printf("begin...\n");
19      int num = 0;
20      if(num > 10){
21           printf("%d>10\n",num);
22      }else{

可以继续向下查看

(gdb) list
19        int num = 0;
20        if(num > 10){
21             printf("%d>10\n",num);
22        }else{
23             printf("%d<=10\n",num);
24        }
25   
26        int i;
27        for(i=0;i<5;i++){
28            printf("i:%d\n",i);
(gdb) l
29            num+=i;
30        }
31        myfun(&num);
32   
33        printf("end...\n");
34    }

3 执行下一步 next
next 简写是n 。可以直接按回车，执行上一次命令

(gdb) n
begin...
19      int num = 0;
(gdb) 
20      if(num > 10){
(gdb) n
23           printf("%d<=10\n",num);
(gdb) n
0<=10
27      for(i=0;i<5;i++){

4 查看某一个函数内容list+函数名称

(gdb) list myfun
1   #include <stdio.h>
2   #include <stdlib.h>
3   #include <unistd.h>
4   
5   int myfun(int a){
6       int i = 0;
7       int* buff = (int*)malloc(sizeof(int)*100);
8       while(i<100){
9           buff[i] = a;
10          a+=i;

5 查看某一行地代码list+行数

(gdb) list 10
5   int myfun(int a){
6       int i = 0;
7       int* buff = (int*)malloc(sizeof(int)*100);
8       while(i<100){
9           buff[i] = a;
10          a+=i;
11          i++;
12      }
13      free(buff);
14      return a/2;

6 查看变量 print+变量名字

27        for(i=0;i<5;i++){
(gdb)
28            printf("i:%d\n",i);
(gdb)
i:1
29            num+=i;
(gdb)
27        for(i=0;i<5;i++){
(gdb)
28            printf("i:%d\n",i);
(gdb) print i
$1 = 2

7 step进入某个函数简写s

31        myfun(&num);
(gdb) step
myfun (a=-6776) at test1.c:6
6        int i = 0;

第六行是函数的的第一行

5    int myfun(int a){
6        int i = 0;
7        int* buff = (int*)malloc(sizeof(int)*100);
8        while(i<100){

8 设置断点 break+行号（gdb中的行号）- 简写b

(gdb) break 31
Breakpoint 6 at 0x4006ef: file test1.c, line 31.

9 查看有哪些断点 info breakpoint

(gdb) info breakpoint
Num     Type           Disp Enb Address            What
6       breakpoint     keep y   0x00000000004006ef in main at test1.c:31

10 跳转到下个断点 continue简写c

(gdb) continue
Continuing.
i:1
i:2
i:3
i:4

Breakpoint 6, main () at test1.c:31
31        myfun(&num);

11 删除断点 delete breakpoints+行号

31        myfun(&num);
(gdb) i breakpoint
Num     Type           Disp Enb Address            What
2       breakpoint     keep y   0x00000000004006ef in main at test1.c:31
    breakpoint already hit 1 time
3       breakpoint     keep y   0x00000000004006fa in main at test1.c:33
(gdb) delete breakpoints 3
(gdb) c
Continuing.
end...

12 修改变量的值 set var 变量 = 值

(gdb) n
begin...
19        int num = 0;
(gdb)  set var num = 20
(gdb) p num
$1 = 20

13 程序调用堆栈
当前函数之前所有函数的列表打印出来 backtrace简写bt 每一个函数都会分配一个“帧” 最近的在0号帧

31        myfun(&num);
(gdb) step
myfun (a=-6776) at test1.c:6
6        int i = 0;
(gdb) bt
#0  myfun (a=-6776) at test1.c:6
#1  0x00000000004006fa in main () at test1.c:31

可以看到myfun（）方法在0帧 main()方法在第一帧

14 切换栈帧 frame 1 查看指定栈帧的变量

(gdb) frame 1
#1  0x00000000004006fa in main () at test1.c:31
31        myfun(&num);
(gdb) list
26        int i;
27        for(i=0;i<5;i++){
28            printf("i:%d\n",i);
29            num+=i;
30        }
31        myfun(&num);
32   
33        printf("end...\n");
34    }
(gdb) p num
$2 = 10

15 自动显示 display+变量名称

(gdb) display a
2: a = -6776
(gdb)
(gdb)
(gdb) n
11            i++;
2: a = -6775
1: i = 1

每次执行下一步都会显示变量a的值，也可以自动显示多个值。display a然后在display b。

16 取消自动显示 undisplay+行号

2: a = -6773
1: i = 3
(gdb) undisplay 8
No display number 8.
(gdb) undisplay 2
(gdb) n
9            buff[i] = a;
1: i = 3
(gdb)
10            a+=i;
1: i = 3
(gdb)
11            i++;
1: i = 3
(gdb)

17 查看内存布局
x /20+地址 x/20 buff查看buff数组的前20个元素
首先切换到myfun方法中

(gdb) step
myfun (a=-6776) at test1.c:6
6       int i = 0;
(gdb) n
7       int* buff = (int*)malloc(sizeof(int)*100);
(gdb) 
8       while(i<100){
(gdb) 
9           buff[i] = a;
(gdb) 
10          a+=i;
(gdb) 
11          i++;

buff数组已经被赋值，然后查看buff数组的前20个元素

(gdb) x/20 buff
0x602010:   -6776   0   0   0
0x602020:   0   0   0   0
0x602030:   0   0   0   0
0x602040:   0   0   0   0
0x602050:   0   0   0   0

Linux笔记 程序调试gdb

Linux笔记程序调试gdb