gdb多进程/多线程调试实战

时间：2022-01-01 16:43:31

gdb多进程调试

  • set follow-fork-mode [parent|child] set detach-on-fork [on|off]
follow-fork-mode detach-on-fork 说明
parent on 只调试主进程（GDB默认）
child on 只调试子进程
parent off 同时调试两个进程，gdb跟主进程，子进程block在fork位置
child off 同时调试两个进程，gdb跟子进程，主进程block在fork位置
  • 查询正在调试的进程：info inferiors
  • 切换调试的进程： inferior +inferior number
  • catch fork命令可以捕获进程的创建
  • attach + pid ， 可以附到一个正在运行的进程上进行调试

gdb多线程调试

  • show scheduler-locking //显示当前scheduler-locking
  • set scheduler-locking [on/off/step] //设置scheduler-locking
    • on：只有当前调试线程运行，其他线程处于暂停状态。
    • off：当前调试线程外的其他线程一直在正常运行。
    • step：其他线程跟随当前调试线程运行，但具体怎么协同运行，测试中无法体现。
    • 注意：set scheduler-locking要处于线程运行环境下才能生效，也就是程序已经运行并且暂停在某个断点处，否则会出现“Target ‘exec’ cannot support this command.”这样的错误；而且经过测试，设置后的scheduler-locking值在整个进程内有效，不属于某个线程。

gdb多进程/多线程调试实战例子

b@b-VirtualBox:~/Documents/temp_test$ sudo gdb ./o_multi_thread_process 
[sudo] password for b: 
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
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<http://www.gnu.org/software/gdb/bugs/>.
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<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./o_multi_thread_process...done.
(gdb) attach 3027
Attaching to program: /home/b/Documents/temp_test/o_multi_thread_process, process 3027
Reading symbols from /lib/x86_64-linux-gnu/libpthread.so.0...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libpthread-2.19.so...done.
done.
[New LWP 3029]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Loaded symbols for /lib/x86_64-linux-gnu/libpthread.so.0
Reading symbols from /lib/x86_64-linux-gnu/libc.so.6...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.19.so...done.
done.
Loaded symbols for /lib/x86_64-linux-gnu/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/ld-2.19.so...done.
done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
0x00007f5c9acb8dfd in nanosleep () at ../sysdeps/unix/syscall-template.S:81
81  ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) set follow-fork-mode parent 
(gdb) set detach-on-fork off
(gdb) catch fork
Catchpoint 1 (fork)
(gdb) r
Starting program: /home/b/Documents/temp_test/o_multi_thread_process 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Catchpoint 1 (forked process 3002), 0x00007ffff78b7ee4 in __libc_fork ()
    at ../nptl/sysdeps/unix/sysv/linux/x86_64/../fork.c:130
130 ../nptl/sysdeps/unix/sysv/linux/x86_64/../fork.c: No such file or directory.
(gdb) info inferiors 
  Num  Description       Executable        
* 1    process 2998      /home/b/Documents/temp_test/o_multi_thread_process 
(gdb) b 14
Breakpoint 2 at 0x7ffff78b7f5b: file ../nptl/sysdeps/unix/sysv/linux/x86_64/../fork.c, line 14.
(gdb) info breakpoints 
Num     Type           Disp Enb Address            What
1       catchpoint     keep y                      fork, process 3002 
    catchpoint already hit 1 time
2       breakpoint     keep y   0x00007ffff78b7f5b in __libc_fork 
                                                   at ../nptl/sysdeps/unix/sysv/linux/x86_64/../fork.c:14
(gdb) d 2
(gdb) info breakpoints 
Num     Type           Disp Enb Address            What
1       catchpoint     keep y                      fork, process 3002 
    catchpoint already hit 1 time
(gdb) b multi_thread_process.cpp : 14
Breakpoint 3 at 0x4007f4: file ./multi_thread_process.cpp, line 14.
(gdb) c
Continuing.
[New process 3002]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Reading symbols from /usr/lib/debug/lib/x86_64-linux-gnu/libpthread-2.19.so...done.
Reading symbols from /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.19.so...done.
Reading symbols from /usr/lib/debug/lib/x86_64-linux-gnu/ld-2.19.so...done.

Breakpoint 3, main (argc=1, argv=0x7fffffffe598) at ./multi_thread_process.cpp:15
15    if(pid != 0)
(gdb) info inferiors 
  Num  Description       Executable        
2    process 3002      /home/b/Documents/temp_test/o_multi_thread_process 
* 1    process 2998      /home/b/Documents/temp_test/o_multi_thread_process 
(gdb) inferior 2
[Switching to inferior 2 [process 3002] (/home/b/Documents/temp_test/o_multi_thread_process)]
[Switching to thread 2 (Thread 0x7ffff7fdf740 (LWP 3002))] 
0  0x00007ffff78b7ee4 in __libc_fork () at ../nptl/sysdeps/unix/sysv/linux/x86_64/../fork.c:130
130 ../nptl/sysdeps/unix/sysv/linux/x86_64/../fork.c: No such file or directory.
(gdb) set scheduler-locking on
(gdb) b multi_thread_process.cpp : 50
Breakpoint 4 at 0x400916: multi_thread_process.cpp:50. (2 locations)
(gdb) info threads 
  Id   Target Id         Frame 
* 2    Thread 0x7ffff7fdf740 (LWP 3002) "o_multi_thread_" 0x00007ffff78b7ee4 in __libc_fork ()
    at ../nptl/sysdeps/unix/sysv/linux/x86_64/../fork.c:130
1    Thread 0x7ffff7fdf740 (LWP 2998) "o_multi_thread_" main (argc=1, argv=0x7fffffffe598)
    at ./multi_thread_process.cpp:15
(gdb) c
Continuing.

Breakpoint 3, main (argc=1, argv=0x7fffffffe598) at ./multi_thread_process.cpp:15
15    if(pid != 0)
(gdb) info threads 
  Id   Target Id         Frame 
* 2    Thread 0x7ffff7fdf740 (LWP 3002) "o_multi_thread_" main (argc=1, argv=0x7fffffffe598)
    at ./multi_thread_process.cpp:15
1    Thread 0x7ffff7fdf740 (LWP 2998) "o_multi_thread_" main (argc=1, argv=0x7fffffffe598)
    at ./multi_thread_process.cpp:15
(gdb) c
Continuing.
ProcessB: 3002 step1
ProcessB: 3002 step2
ProcessB: 3002 step3
^C
Program received signal SIGINT, Interrupt.
0x00007ffff78b7de0 in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:81
81  ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) info threads 
  Id   Target Id         Frame 
* 2    Thread 0x7ffff7fdf740 (LWP 3002) "o_multi_thread_" 0x00007ffff78b7de0 in __nanosleep_nocancel ()
    at ../sysdeps/unix/syscall-template.S:81
1    Thread 0x7ffff7fdf740 (LWP 2998) "o_multi_thread_" main (argc=1, argv=0x7fffffffe598)
    at ./multi_thread_process.cpp:15
(gdb) info inferiors 
  Num  Description       Executable        
* 2    process 3002      /home/b/Documents/temp_test/o_multi_thread_process 
1    process 2998      /home/b/Documents/temp_test/o_multi_thread_process 
(gdb) inferior 1
[Switching to inferior 1 [process 2998] (/home/b/Documents/temp_test/o_multi_thread_process)]
[Switching to thread 1 (Thread 0x7ffff7fdf740 (LWP 2998))] 
0  main (argc=1, argv=0x7fffffffe598) at ./multi_thread_process.cpp:15
15    if(pid != 0)
(gdb) list
10    {
11    int pid;
12  
13    pid = fork();
14  
15    if(pid != 0)
16      processA();
17    else
18      processB();
19  
(gdb) r
The program being debugged has been started already.
Start it from the beginning? (y or n) n
Program not restarted.
(gdb) c
Continuing.
ProcessA: 2998 step1
[New Thread 0x7ffff77f6700 (LWP 3017)]
^C
Program received signal SIGINT, Interrupt.
0x00007ffff78b7dfd in nanosleep () at ../sysdeps/unix/syscall-template.S:81
81  ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) info threads 
  Id   Target Id         Frame 
3    Thread 0x7ffff77f6700 (LWP 3017) "o_multi_thread_" clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:81
2    Thread 0x7ffff7fdf740 (LWP 3002) "o_multi_thread_" 0x00007ffff78b7de0 in __nanosleep_nocancel ()
    at ../sysdeps/unix/syscall-template.S:81
* 1    Thread 0x7ffff7fdf740 (LWP 2998) "o_multi_thread_" 0x00007ffff78b7dfd in nanosleep ()
    at ../sysdeps/unix/syscall-template.S:81
(gdb)
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