gdb多進程/多線程調試實戰

gdb多進程調試

• set follow-fork-mode [parent|child] set detach-on-fork [on|off]

follow-fork-mode	detach-on-fork	說明
parent	on	只調試主進程（GDB默認）
child	on	只調試子進程
parent	off	同時調試兩個進程，gdb跟主進程，子進程block在fork位置
child	off	同時調試兩個進程，gdb跟子進程，主進程block在fork位置

• 查詢正在調試的進程：info inferiors
• 切換調試的進程： inferior +inferior number
• catch fork命令可以捕獲進程的創建
• attach + pid ， 可以附到一個正在運行的進程上進行調試

gdb多線程調試

• show scheduler-locking //顯示當前scheduler-locking
• set scheduler-locking [on/off/step] //設置scheduler-locking
  
  • on：只有當前調試線程運行，其他線程處於暫停狀態。
  • off：當前調試線程外的其他線程一直在正常運行。
  • step：其他線程跟隨當前調試線程運行，但具體怎麼協同運行，測試中無法體現。
  • 注意：set scheduler-locking要處於線程運行環境下才能生效，也就是程序已經運行並且暫停在某個斷點處，否則會出現“Target ‘exec’ cannot support this command.”這樣的錯誤；而且經過測試，設置後的scheduler-locking值在整個進程內有效，不屬於某個線程。

gdb多進程/多線程調試實戰例子

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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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)