本文出自：http://blog.youkuaiyun.com/edroid1530/article/details/68946136 作为程序员，调试程序是不可避免的，在windows下常用的IDE比如 keil 软件会有集成的debug图形化调试工具，使用起来非常简单易懂。在Linux下虽然没有图形化调试工具，但是gdb作为文本界面的调试工具其功能也是非常强大的，在这里简单介绍gdb的用法。
一.调试准备
1.首先我们编写一个测试程序：
- [lwn@VM_255_164_centos temp2]vim gdbtest.c </span></span></li><li><span><span class="comment">/*********************************************************************************</span> </span></li><li class="alt"><span><span class="comment"> 2 * Copyright: (C) 2017 SCUEC</span> </span></li><li><span><span class="comment"> 3 * All rights reserved.</span> </span></li><li class="alt"><span><span class="comment"> 4 *</span> </span></li><li><span><span class="comment"> 5 * Filename: gdbtest.c</span> </span></li><li class="alt"><span><span class="comment"> 6 * Description: This file</span> </span></li><li><span><span class="comment"> 7 *</span> </span></li><li class="alt"><span><span class="comment"> 8 * Version: 1.0.0(04/01/17)</span> </span></li><li><span><span class="comment"> 9 * Author: LI WJNG <liwjng@gmail.com></span> </span></li><li class="alt"><span><span class="comment"> 10 * ChangeLog: 1, Release initial version on "04/01/17 15:19:12"</span> </span></li><li><span><span class="comment"> 11 *</span> </span></li><li class="alt"><span><span class="comment"> 12 ********************************************************************************/</span><span> </span></span></li><li><span> 13 </span></li><li class="alt"><span> 14 #include <stdio.h> </span></li><li><span> 15 </span></li><li class="alt"><span> 16 <span class="datatypes">int</span><span> func(</span><span class="datatypes">int</span><span> n) </span></span></li><li><span> 17 { </span></li><li class="alt"><span> 18 <span class="datatypes">int</span><span> sum=0,i; </span></span></li><li><span> 19 <span class="keyword">for</span><span>(i=0;i<n;i++) </span></span></li><li class="alt"><span> 20 { </span></li><li><span> 21 sum += i; </span></li><li class="alt"><span> 22 } </span></li><li><span> 23 <span class="keyword">return</span><span> sum; </span></span></li><li class="alt"><span> 24 } </span></li><li><span> 25 </span></li><li class="alt"><span> 26 </span></li><li><span> 27 <span class="comment">/********************************************************************************</span> </span></li><li class="alt"><span><span class="comment"> 28 * Description:</span> </span></li><li><span><span class="comment"> 29 * Input Args:</span> </span></li><li class="alt"><span><span class="comment"> 30 * Output Args:</span> </span></li><li><span><span class="comment"> 31 * Return Value:</span> </span></li><li class="alt"><span><span class="comment"> 32 ********************************************************************************/</span><span> </span></span></li><li><span> 33 <span class="datatypes">int</span><span> main (</span><span class="datatypes">int</span><span> argc, </span><span class="datatypes">char</span><span> **argv) </span></span></li><li class="alt"><span> 34 { </span></li><li><span> 35 <span class="datatypes">int</span><span> i; </span></span></li><li class="alt"><span> 36 <span class="datatypes">long</span><span> result = 0; </span></span></li><li><span> 37 <span class="datatypes">int</span><span> sum = 0; </span></span></li><li class="alt"><span> 38 sum = func(10); </span></li><li><span> 39 <span class="keyword">for</span><span>(i=0;i<100;i++) </span></span></li><li class="alt"><span> 40 { </span></li><li><span> 41 result += i; </span></li><li class="alt"><span> 42 } </span></li><li><span> 43 </span></li><li class="alt"><span> 44 printf(<span class="string">"the result is add 1 to 100 is %d\n"</span><span>,result); </span></span></li><li><span> 45 printf(<span class="string">"the sum is add 1 to %d is %d\n"</span><span>,10,sum); </span></span></li><li class="alt"><span> 46 <span class="keyword">return</span><span> 0; </span></span></li><li><span> 47 } <span class="comment">/* ----- End of main() ----- */</span><span> </span></span></li><li class="alt"><span> 48 </span></li></ol><div class="save_code tracking-ad" style="display: none;" data-mod="popu_249"><a href="javascript:;" target="_blank"><img src="http://static.blog.youkuaiyun.com/images/save_snippets.png"></a></div></div><pre class="cpp" style="display: none;" name="code" snippet_file_name="blog_20170401_1_6673937" code_snippet_id="2306771">[lwn@VM_255_164_centos temp2]vim gdbtest.c /********************************************************************************* 2 * Copyright: (C) 2017 SCUEC 3 * All rights reserved. 4 * 5 * Filename: gdbtest.c 6 * Description: This file 7 * 8 * Version: 1.0.0(04/01/17) 9 * Author: LI WJNG <liwjng@gmail.com> 10 * ChangeLog: 1, Release initial version on “04/01/17 15:19:12” 11 * 12 ********************************************************************************/ 13 14 #include <stdio.h> 15 16 int func(int n) 17 { 18 int sum=0,i; 19 for(i=0;i<n;i++) 20 { 21 sum += i; 22 } 23 return sum; 24 } 25 26 27 /******************************************************************************** 28 * Description: 29 * Input Args: 30 * Output Args: 31 * Return Value: 32 ********************************************************************************/ 33 int main (int argc, char **argv) 34 { 35 int i; 36 long result = 0; 37 int sum = 0; 38 sum = func(10); 39 for(i=0;i<100;i++) 40 { 41 result += i; 42 } 43 44 printf(“the result is add 1 to 100 is %d\n”,result); 45 printf(“the sum is add 1 to %d is %d\n”,10,sum); 46 return 0; 47 } /* —– End of main() —– */ 48
2.编译程序
要使用gdb调试，编译的时候一定要加上 -g 选项，如：gcc -g test.c，否则在gdb命令中l的时候会出现：No symbol table is loaded. Use the “file” command.错误提示；
- [lwn@VM_255_164_centos temp2] gcc -g gdbtest.c -o test </span></span></li><li><span>[lwn@VM_255_164_centos temp2] ls
- gdbtest.c test
[lwn@VM_255_164_centos temp2]$ gcc -g gdbtest.c -o test [lwn@VM_255_164_centos temp2]$ ls gdbtest.c test
3.使用gdb命令进入调试界面
如果直接使用gdb test 会打印gdb的版本信息等，为了显示简洁一点，使用gdb -q可以不显示版本信息- [lwn@VM_255_164_centos temp2] gdb -q test </span></span></li><li><span>Reading symbols from /home/lwn/mysrc/temp2/test...done. </span></li><li class="alt"><span>(gdb) </span></li></ol><div class="save_code tracking-ad" data-mod="popu_249"><a href="javascript:;" target="_blank"><img src="http://static.blog.youkuaiyun.com/images/save_snippets.png"></a></div></div><pre class="cpp" style="display: none;" name="code" snippet_file_name="blog_20170401_3_1036547" code_snippet_id="2306771">[lwn@VM_255_164_centos temp2] gdb -q test Reading symbols from /home/lwn/mysrc/temp2/test…done. (gdb)
二.gdb调试命令：
在gdb调试界面下可以直接使用gdb的调试命令，enter继续执行上条命令。
下面逐条分析：
1.使用list（简写：l） 命令，将看到部分源程序清单。
list： 显示源程序1-10行list +行号： 显示行号前后若干行list +函数名: 显示函数前后若干行这里就不一一列举了，所有有关list的相关操作可以使用 help list 命令进行查看如：- (gdb) l main
- 29 * Input Args:
- 30 * Output Args:
- 31 * Return Value:
- 32 ********************************************************************************/
- 33 int main (int argc, char **argv)
- 34 {
- 35 int i;
- 36 long result = 0;
- 37 int sum = 0;
- 38 sum = func(10);
- (gdb) help list //可以看到有关list的命令说明
- List specified function or line.
- With no argument, lists ten more lines after or around previous listing.
- ”list -“ lists the ten lines before a previous ten-line listing.
- One argument specifies a line, and ten lines are listed around that line.
- Two arguments with comma between specify starting and ending lines to list.
- Lines can be specified in these ways:
- LINENUM, to list around that line in current file,
- FILE:LINENUM, to list around that line in that file,
- FUNCTION, to list around beginning of that function,
- FILE:FUNCTION, to distinguish among like-named static functions.
- *ADDRESS, to list around the line containing that address.
- With two args if one is empty it stands for ten lines away from the other arg.
(gdb) l main 29 * Input Args: 30 * Output Args: 31 * Return Value: 32 ********************************************************************************/ 33 int main (int argc, char **argv) 34 { 35 int i; 36 long result = 0; 37 int sum = 0; 38 sum = func(10); (gdb) help list //可以看到有关list的命令说明 List specified function or line. With no argument, lists ten more lines after or around previous listing. "list -" lists the ten lines before a previous ten-line listing. One argument specifies a line, and ten lines are listed around that line. Two arguments with comma between specify starting and ending lines to list. Lines can be specified in these ways: LINENUM, to list around that line in current file, FILE:LINENUM, to list around that line in that file, FUNCTION, to list around beginning of that function, FILE:FUNCTION, to distinguish among like-named static functions. *ADDRESS, to list around the line containing that address. With two args if one is empty it stands for ten lines away from the other arg.
2.运行程序：run（简写：r），break（简写：b） ，continue（简写：c） ，until（简写：u）
run命令可以让程序全速运行，直到遇到断点处才停下来。如果没有设置断点，那么程序将一直运行到程序结束。break命令用来设置断点，break +行号：将断点设置在固定某行break +函数名：将断点设置在函数开始处info break：列出所有的断点clear +行号：取消某行设置的断点contin命令让程序继续运行到下一处断点，如果后面没有断点将一直运行到程序末尾。until+行号：让程序执行到固定某行，其作用等同于 break+ 行号，再continu；使用until命令的前提是程序已经在运行状态例如：- (gdb) l main
- 29 * Input Args:
- 30 * Output Args:
- 31 * Return Value:
- 32 ********************************************************************************/
- 33 int main (int argc, char **argv)
- 34 {
- 35 int i;
- 36 long result = 0;
- 37 int sum = 0;
- 38 sum = func(10);
- (gdb) b main //在main函数开始出设置断点
- Breakpoint 1 at 0x40056d: file gdbtest.c, line 36.
- (gdb) b 38 //在第38行设置断点
- Breakpoint 2 at 0x40057c: file gdbtest.c, line 38.
- (gdb) i b //命令info break列出所有的断点
- Num Type Disp Enb Address What
- 1 breakpoint keep y 0x000000000040056d in main at gdbtest.c:36
- breakpoint already hit 1 time
- 2 breakpoint keep y 0x000000000040057c in main at gdbtest.c:38
- breakpoint already hit 1 time
- (gdb) r //r命令让程序全速运行
- Starting program: /home/lwn/mysrc/temp2/test
- Breakpoint 1, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:36 //遇到刚刚设置的第一个断点36行停了下来
- 36 long result = 0;
- Missing separate debuginfos, use: debuginfo-install glibc-2.17-106.el7_2.8.x86_64
- (gdb) c //命令contin让程序继续运行
- Continuing.
- Breakpoint 2, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:38 //运行到设置的第二个断点听了下来
- 38 sum = func(10);
- (gdb) u 38//让程序执行到固定某一行
- main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:38
- 38 sum = func(10);
(gdb) l main 29 * Input Args: 30 * Output Args: 31 * Return Value: 32 ********************************************************************************/ 33 int main (int argc, char **argv) 34 { 35 int i; 36 long result = 0; 37 int sum = 0; 38 sum = func(10); (gdb) b main //在main函数开始出设置断点 Breakpoint 1 at 0x40056d: file gdbtest.c, line 36. (gdb) b 38 //在第38行设置断点 Breakpoint 2 at 0x40057c: file gdbtest.c, line 38. (gdb) i b //命令info break列出所有的断点 Num Type Disp Enb Address What 1 breakpoint keep y 0x000000000040056d in main at gdbtest.c:36 breakpoint already hit 1 time 2 breakpoint keep y 0x000000000040057c in main at gdbtest.c:38 breakpoint already hit 1 time (gdb) r //r命令让程序全速运行 Starting program: /home/lwn/mysrc/temp2/test Breakpoint 1, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:36 //遇到刚刚设置的第一个断点36行停了下来 36 long result = 0; Missing separate debuginfos, use: debuginfo-install glibc-2.17-106.el7_2.8.x86_64 (gdb) c //命令contin让程序继续运行 Continuing. Breakpoint 2, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:38 //运行到设置的第二个断点听了下来 38 sum = func(10); (gdb) u 38//让程序执行到固定某一行 main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:38 38 sum = func(10);
3.单步运行next（简写：n） 和step（简写：s）
如果希望程序逐条语句地执行程序，不停地b、c太过于麻烦，gdb提供了更加step 和next命令，其作用是运行当前行。区别在于如果当前行设计函数调用，next命令会把函数当做一条语句整体执行完毕，而step命令会进入到函数内部继续单步运行，下面来看例子：- l (gdb) l //列出相关行的源程序
- 31 * Return Value:
- 32 ********************************************************************************/
- 33 int main (int argc, char **argv)
- 34 {
- 35 int i;
- 36 long result = 0;
- 37 int sum = 0;
- 38 sum = func(10);
- 39 for(i=0;i<100;i++)
- 40 {
- (gdb) b 38 //在调用函数的行设置断点
- Breakpoint 3 at 0x40057c: file gdbtest.c, line 38.
- (gdb) r
- The program being debugged has been started already.
- Start it from the beginning? (y or n) y
- Starting program: /home/lwn/mysrc/temp2/test
- Breakpoint 3, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:38
- 38 sum = func(10);
- (gdb) n //可以看到使用next命令之后程序跳到了39行执行
- 39 for(i=0;i<100;i++)
- ————————————————————————————————————————————————————————————————————————————————————————————————————
- Breakpoint 3, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:38
- 38 sum = func(10);
- (gdb) s //同样使用step命令之后可以看到程序进入到了func函数去执行
- func (n=10) at gdbtest.c:18
- 18 int sum=0,i;
l (gdb) l //列出相关行的源程序 31 * Return Value: 32 ********************************************************************************/ 33 int main (int argc, char **argv) 34 { 35 int i; 36 long result = 0; 37 int sum = 0; 38 sum = func(10); 39 for(i=0;i<100;i++) 40 { (gdb) b 38 //在调用函数的行设置断点 Breakpoint 3 at 0x40057c: file gdbtest.c, line 38. (gdb) r The program being debugged has been started already. Start it from the beginning? (y or n) y Starting program: /home/lwn/mysrc/temp2/test Breakpoint 3, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:38 38 sum = func(10); (gdb) n //可以看到使用next命令之后程序跳到了39行执行 39 for(i=0;i<100;i++) ———————————————————————————————————————————————————————————————————————————————————————————————————— Breakpoint 3, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:38 38 sum = func(10); (gdb) s //同样使用step命令之后可以看到程序进入到了func函数去执行 func (n=10) at gdbtest.c:18 18 int sum=0,i;
4.打印相关信息info（简写：i），print（简写：p），display（简写：disp）
程序运行到某个位置的时候，我们使用info和print命令可以打印出一些变量的值info local：打印局部变量的值p + 变量名：打印该变量的值display +变量名：每次程序停下来都自动打印该变量的值来看例子：- (gdb) r
- Starting program: /home/lwn/mysrc/temp2/test
- Breakpoint 1, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:36
- 36 long result = 0;
- Missing separate debuginfos, use: debuginfo-install glibc-2.17-106.el7_2.8.x86_64
- (gdb) p result //打印result变量的值
- $1 = 140737488348608 //因为第36行语句还没执行，所以现在result还未被初始化，现在是一个垃圾值
- (gdb) i lo //打印所有局部变量的值
- i = 0
- result = 140737488348608
- sum = 0
- (gdb) disp result //每次遇到程序停下来都将显示变量result的值
- 1: result = 140737488348608
- (gdb) c
- Continuing.
- Breakpoint 2, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:38
- 38 sum = func(10);
- 1: result = 0 //result被初始化为0
- (gdb) c
- Continuing.
- Breakpoint 3, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:44
- 44 printf(”the result is add 1 to 100 is %d\n”,result);
- 1: result = 4950 //result为最终的计算值
(gdb) r Starting program: /home/lwn/mysrc/temp2/test Breakpoint 1, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:36 36 long result = 0; Missing separate debuginfos, use: debuginfo-install glibc-2.17-106.el7_2.8.x86_64 (gdb) p result //打印result变量的值 $1 = 140737488348608 //因为第36行语句还没执行，所以现在result还未被初始化，现在是一个垃圾值 (gdb) i lo //打印所有局部变量的值 i = 0 result = 140737488348608 sum = 0 (gdb) disp result //每次遇到程序停下来都将显示变量result的值 1: result = 140737488348608 (gdb) c Continuing. Breakpoint 2, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:38 38 sum = func(10); 1: result = 0 //result被初始化为0 (gdb) c Continuing. Breakpoint 3, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:44 44 printf("the result is add 1 to 100 is %d\n",result); 1: result = 4950 //result为最终的计算值
5.条件控制断点
在for循环中，有时候我们想让循环变量i为某个固定值的时候停下来查看某一变量，如果一直单步运行工作量有可能会很大。gdb提供了一个命令cond命令话不多说，来看例子：39 for(i=0;i<100;i++) 40 { 41 result += i; 42 }在这个循环中，当i=10的时候我想看看result的值怎么办呢？很好办，往下看首先在41行设置断点，然后使用cond 2 i==10- (gdb) b 41 //在41行设置断点
- Breakpoint 1 at 0x400592: file gdbtest.c, line 41.
- (gdb) cond 1 i==10 //当i等于10的时候程序停下来
- (gdb) r
- Starting program: /home/lwn/mysrc/temp2/test
- Breakpoint 1, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:41
- 41 result += i;
- (gdb) p i
- 1 = 10 </span></li><li class="alt"><span>(gdb) p result<span class="comment">//可以看到当i=10的时候 result 的值为45</span><span> </span></span></li><li><span>2 = 45
(gdb) b 41 //在41行设置断点 Breakpoint 1 at 0x400592: file gdbtest.c, line 41. (gdb) cond 1 i==10 //当i等于10的时候程序停下来 (gdb) r Starting program: /home/lwn/mysrc/temp2/test Breakpoint 1, main (argc=1, argv=0x7fffffffe5c8) at gdbtest.c:41 41 result += i; (gdb) p i $1 = 10 (gdb) p result//可以看到当i=10的时候 result 的值为45 $2 = 45
在大多数情况下，灵活使用这些命令已经能够高效的调试程序了，如果对于这些gdb命令还有疑问的可以使用help命令获得详细的帮助信息。
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