一次gdb实战 设置断点 单步调试 打印和修改变量值等操作

本案例总结了gdb的常用用法，详细规则可参考gdb入门教程

总结在前：

1. 编译命令gcc -g gdb_test.c -o gdb_test，通过-g选项添加调试信息，否则使用gdb调试时，会报“No symbol table is loaded. Use the "file" command.”错误。
2. 设置断点：bread(或b) 函数名； bread(或b) -line 行号；例如b main 或 b -line 21。
3. 开始运行：run，该命令会直接运行到断点位置或直至结束。
4. 单步执行：next(n)，该命令将程序执行一行。
5. 打印变量：print 变量名，例如print ret。
6. 修改变量：set 变量名=变量值，例如set ret=1。
7. 多步执行：continue©，继续运行您的程序 (在停止之后，比如在一个断点之后)。

源代码如下：

#include 
#include 
#include 

struct GDB_TEST
{
    
    int gdb_int;
    char gdb_char[64];
};

static struct GDB_TEST my_dgb_test = 
{
    .gdb_int = 5,
    .gdb_char = "This is my test",
};


void main()
{
    printf("main startn");
    int ret = -1;
    struct GDB_TEST *test = &my_dgb_test;

    if (test->gdb_int == 0) 
    {
        ret = 0;
        printf("now ret and gdb_int is 0n");
    }

    if (test->gdb_int == 1)  
    {
        ret = 1;
        printf("now ret and gdb_int is 1n");
    }
    
    printf("returnn");
	return;
} 

实践：

[10283203@zte.intra@127 c_code]$ gcc -g gdb_test.c -o gdb_test


[10283203@zte.intra@127 c_code]$ gdb gdb_test
GNU gdb (GDB) Red Hat Enterprise Linux 8.2-6.el8
……省略gdb版本信息……
Reading symbols from gdb_test...done.


(gdb) b main 
Breakpoint 1 at 0x40058e: file gdb_test.c, line 21.


(gdb) run
Starting program: /media/vdb1/code_test/c_code/gdb_test 
Missing separate debuginfos, use: yum debuginfo-install glibc-2.28-72.el8_1.1.x86_64

Breakpoint 1, main () at gdb_test.c:21
21          printf("main startn");


(gdb) n
main start
22          int ret = -1;
(gdb) n
23          struct GDB_TEST *test = &my_dgb_test;
(gdb) 
25          if (test->gdb_int == 0)


(gdb) print test->gdb_int
$1 = 5


(gdb) set test->gdb_int=0
(gdb) print test->gdb_int
$2 = 0
(gdb) n
27              ret = 0;
(gdb) n
28              printf("now ret and gdb_int is 0n");
(gdb) n
now ret and gdb_int is 0


31          if (test->gdb_int == 1)
(gdb) print test->gdb_int
$3 = 0
(gdb) set test->gdb_int=1
(gdb) print test->gdb_int
$4 = 1
(gdb) n
33              ret = 1;
(gdb) 
34              printf("now ret and gdb_int is 1n");


(gdb) c
Continuing.
now ret and gdb_int is 1
return
[Inferior 1 (process 1297) exited with code 07]
(gdb) quit