测试程序：
// test.c
#include <stdio.h>
#include <pthread.h>
int g_data = 0;
void thread1_func(void *args)
{
int i = 0;
while(i < 2)
{
i++;
g_data += i;
}
}
int main()
{
int i;
int flag = 1;
printf("wait gdb\n");
while(1 == flag);
printf("jump wait gdb\n");
for(i = 1; i <= 100; i ++)
{
g_data += i;
}
printf("g_data[1-100] = %d \n", g_data );
pthread_t t1;
pthread_t t2;
pthread_create(&t1, NULL, (void*)thread1_func, NULL);
pthread_join(t1, NULL);
return 0;
}
编译：
// -g debug 模式
gcc test.c -g -lpthread -o test
1. 程序运行，根据 pid 打开 gdbserver
1.1 ps 查看程序pid进程
ps aux
jony 25651 98.2 0.0 2648 632 pts/0 R+ 21:29 0:07 ./test
jony 25654 0.0 0.0 20324 3672 pts/1 R+ 21:30 0:00 ps -aux
其中， 25651 即为我们想调试的程序pid。
1.2 打开gdbserver
sudo gdbserver --attach localhost:1234 25651
gdbserver：gdb服务器。 嵌入式环境下，需要交叉编译，一般放入/usr/bin目录。
--attach 表示调试正在运行的程序。
localhost:1234 表示gdbserver开放的接入ip和端口。这里也可以使用串口，改为形如/dev/ttyb，具体取决于linux /dev目录下串口名称。
25651 正在运行程序的pid。
至此，gdbserver 服务器已经打开，外部可以根据ip和端口进行远程调试。
2 远程调试
2.1 启动gdb
终端输入gdb，调试目标为嵌入式设备，使用交叉编译器自带的gdb，如arm-linux-gnueabihf-gdb,具体取决于所采用的交叉编译器。
2.2 连接远程gdbserver
(gdb) target remote localhost:1234
target remote：gdb连接远程命令
localhost:1234：远程ip、端口，也可以为串口。
输出结果：
Remote debugging using localhost:1234
Reading /mnt/hgfs/ubuntu20/test_code/gdb_test/test from remote target...
warning: File transfers from remote targets can be slow. Use "set sysroot" to access files locally instead.
Reading /mnt/hgfs/ubuntu20/test_code/gdb_test/test from remote target...
Reading symbols from target:/mnt/hgfs/ubuntu20/test_code/gdb_test/test...
Reading /lib/x86_64-linux-gnu/libpthread.so.0 from remote target...
Reading /lib/x86_64-linux-gnu/libc.so.6 from remote target...
Reading /lib64/ld-linux-x86-64.so.2 from remote target...
Reading symbols from target:/lib/x86_64-linux-gnu/libpthread.so.0...
Reading symbols from /usr/lib/debug/.build-id/e5/4761f7b554d0fcc1562959665d93dffbebdaf0.debug...
Reading symbols from target:/lib/x86_64-linux-gnu/libc.so.6...
Reading /lib/x86_64-linux-gnu/libc-2.31.so from remote target...
Reading /lib/x86_64-linux-gnu/.debug/libc-2.31.so from remote target...
Reading /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.31.so from remote target...
Reading /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.31.so from remote target...
Reading symbols from target:/usr/lib/debug//lib/x86_64-linux-gnu/libc-2.31.so...
Reading symbols from target:/lib64/ld-linux-x86-64.so.2...
Reading /lib64/ld-2.31.so from remote target...
Reading /lib64/.debug/ld-2.31.so from remote target...
Reading /usr/lib/debug//lib64/ld-2.31.so from remote target...
Reading /usr/lib/debug/lib64//ld-2.31.so from remote target...
Reading target:/usr/lib/debug/lib64//ld-2.31.so from remote target...
(No debugging symbols found in target:/lib64/ld-linux-x86-64.so.2)
Reading /lib64/ld-linux-x86-64.so.2 from remote target...
main () at test.c:22
22 while(1 == flag);
可以发现程序停留在 22行死循环。我们可以通过set指令改变变量状态，使程序继续运行调试。
(gdb) set flag=0
(gdb) n
23 printf("jump wait gdb\n");
至此，可以通过gdb命令远程调试程序了。
3. 简单调试
3.1 l 查看查看代码提示
(gdb) l
17 {
18 int i;
19 int flag = 1;
20
21 printf("wait gdb\n");
22 while(1 == flag);
23 printf("jump wait gdb\n");
24
25
26 for(i = 1; i <= 100; i ++)
3.2 b 程序断点
(gdb) b 35
Breakpoint 1 at 0x5574c45e7297: file test.c, line 35.
3.3 watch 放置一个观察点，当变量被读出或写入时程序被暂停
(gdb) watch g_data
Hardware watchpoint 2: g_data
c 程序继续运行， g_data 发生改变，程序暂停。
(gdb) c
Continuing.
Hardware watchpoint 2: g_data
Old value = 105
New value = 120
Hardware watchpoint 3: g_data
Old value = 105
New value = 120
main () at test.c:26
26 for(i = 1; i <= 100; i ++)
3.3 whatis 判断变量类型
(gdb) whatis i
type = int
3.4 查看断点、观测点，删除观测点
(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y 0x00005574c45e7297 in main at test.c:35
2 hw watchpoint keep y g_data
breakpoint already hit 12 times
3 hw watchpoint keep y g_data
breakpoint already hit 12 times
(gdb) delete breakpoints 2
(gdb) delete breakpoints 3
(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y 0x00005574c45e7297 in main at test.c:35
3.5 进入线程
(gdb) b 11 //线程内打断点
Breakpoint 1 at 0x55d837bd11de: file test.c, line 11.
(gdb) info breakpoints // 查看断点
Num Type Disp Enb Address What
1 breakpoint keep y 0x000055d837bd11de in thread1_func at test.c:11
2 breakpoint keep y 0x000055d837bd1297 in main at test.c:35
gdb) c
Continuing.
[New Thread 25911.25926]
Thread 1 "test" hit Breakpoint 2, main () at test.c:35
35 pthread_join(t1, NULL);
(gdb) info threads // 查看线程信息
Id Target Id Frame
* 1 Thread 25911.25911 "test" main () at test.c:35
2 Thread 25911.25926 "test" thread1_func (args=0x0) at test.c:11
(gdb) thread 2 // 进入线程 2
[Switching to thread 2 (Thread 25911.25926)]
#0 thread1_func (args=0x0) at test.c:11
11 i++;
// 线程内调试，查看数据
gdb) p i
$2 = 0
(gdb) p g_data
$3 = 5050
(gdb) n
Thread 2 "test" hit Breakpoint 1, thread1_func (args=0x0) at test.c:11
11 i++;
(gdb) n
12 g_data += i;
(gdb) n
9 while(i < 2)
(gdb) p g_data
$4 = 5051
3.6 捕捉信号
(gdb) catch signal
Display all 149 possibilities? (y or n)
(gdb) catch signal SIGINT
Catchpoint 1 (signal SIGINT)
(gdb) info breakpoints
Num Type Disp Enb Address What
1 catchpoint keep y signal "SIGINT"
(gdb) n
^C
Catchpoint 1 (signal SIGINT), 0x000056160ced322f in main () at test.c:22
22 while(1 == flag);
3.7 until + 行数， 运行到某行
(gdb) u 35
main () at test.c:35
35 pthread_join(t1, NULL);
(gdb) p g_data
$1 = 5053
3.8 多进程调试
代码fork之后，gdb默认进入parent进程，通过如下代码查看fork跟踪进程方式。
(gdb) show follow-fork-mode
Debugger response to a program call of fork or vfork is "parent".
修改为fork跟踪子进程：
(gdb) set follow-fork-mode child
(gdb) show follow-fork-mode
Debugger response to a program call of fork or vfork is "child".
另外，子进程也可通过 gdb attach pid进入。
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