gdb调试多进程和多线程命令（转）

1. 默认设置下，在调试多进程程序时GDB只会调试主进程。但是GDB（>V7.0）支持多进程的分别以及同时调试，换句话说，GDB可以同时调试多个程序。只需要设置follow-fork-mode(默认值：parent)和detach-on-fork（默认值：on）即可。

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

   设置方法：set follow-fork-mode [parent|child]   set detach-on-fork [on|off]

   查询正在调试的进程：info inferiors
   切换调试的进程： inferior <infer number>
   添加新的调试进程： add-inferior [-copies n] [-exec executable] ,可以用file executable来分配给inferior可执行文件。
   其他：remove-inferiors infno， detach inferior

2. GDB默认支持调试多线程，跟主线程，子线程block在create thread。
   查询线程：info threads
   切换调试线程：thread <thread number>

例程：

 1 #include <stdio.h>
 2 #include <pthread.h>
 3 
 4 void processA();
 5 void processB();
 6 void * processAworker(void *arg);
 7 
 8 int main(int argc, const char *argv[])
 9   {
10   int pid;
11 
12   pid = fork();
13 
14   if(pid != 0)
15     processA();
16   else
17     processB();
18 
19   return 0;
20   }
21 
22 void processA()
23   {
24   pid_t pid = getpid();
25   char prefix[] = "ProcessA: ";
26   char tprefix[] = "thread ";
27   int tstatus;
28   pthread_t pt;
29 
30   printf("%s%lu %s\n", prefix, pid, "step1");
31 
32   tstatus = pthread_create(&pt, NULL, processAworker, NULL);
33   if( tstatus != 0 )
34     {
35     printf("ProcessA: Can not create new thread.");
36     }
37  
38   processAworker(NULL);
39   sleep(1);
40   }
41 
42 void * processAworker(void *arg)
43   {
44   pid_t pid = getpid();
45   pthread_t tid = pthread_self();
46   char prefix[] = "ProcessA: ";
47   char tprefix[] = "thread ";
48 
49   printf("%s%lu %s%lu %s\n", prefix, pid, tprefix, tid, "step2");
50   printf("%s%lu %s%lu %s\n", prefix, pid, tprefix, tid, "step3");
51 
52   return NULL;
53   }
54 
55 void processB()
56   {
57   pid_t pid = getpid();
58   char prefix[] = "ProcessB: ";
59   printf("%s%lu %s\n", prefix, pid, "step1");
60   printf("%s%lu %s\n", prefix, pid, "step2");
61   printf("%s%lu %s\n", prefix, pid, "step3");
62 
63   }

输出：

[cnwuwil@centos c-lab]$ ./test
ProcessA: 802 step1
ProcessB: 803 step1
ProcessB: 803 step2
ProcessB: 803 step3
ProcessA: 802 thread 3077555904 step2
ProcessA: 802 thread 3077555904 step3
ProcessA: 802 thread 3077553008 step2
ProcessA: 802 thread 3077553008 step3

调试：
1. 调试主进程，block子进程。

(gdb) set detach-on-fork off
(gdb) show detach-on-fork
Whether gdb will detach the child of a fork is off.
(gdb) catch fork
Catchpoint 1 (fork)
(gdb) r
[Thread debugging using libthread_db enabled]

Catchpoint 1 (forked process 3475), 0x00110424 in __kernel_vsyscall ()
Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.47.el6.i686
(gdb) break test.c:14
Breakpoint 2 at 0x8048546: file test.c, line 14.
(gdb) cont
[New process 3475]
[Thread debugging using libthread_db enabled]

Breakpoint 2, main (argc=1, argv=0xbffff364) at test.c:14
Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.47.el6.i686
(gdb) info inferiors
  Num  Description       Executable       
  2    process 3475      /home/cnwuwil/labs/c-lab/test
* 1    process 3472      /home/cnwuwil/labs/c-lab/test

2. 切换到子进程：

(gdb) inferior 2
[Switching to inferior 2 [process 3475] (/home/cnwuwil/labs/c-lab/test)]
[Switching to thread 2 (Thread 0xb7fe86c0 (LWP 3475))]
#0  0x00110424 in ?? ()
(gdb) info inferiors
  Num  Description       Executable       
* 2    process 3475      /home/cnwuwil/labs/c-lab/test
  1    process 3472      /home/cnwuwil/labs/c-lab/test
(gdb) inferior 1
[Switching to inferior 1 [process 3472] (/home/cnwuwil/labs/c-lab/test)]
[Switching to thread 1 (Thread 0xb7fe86c0 (LWP 3472))]
#0  main (argc=1, argv=0xbffff364) at test.c:14
(gdb) info inferiors
  Num  Description       Executable       
  2    process 3475      /home/cnwuwil/labs/c-lab/test
* 1    process 3472      /home/cnwuwil/labs/c-lab/test

3. 设断点继续调试主进程，主进程产生两个子线程：

(gdb) break test.c:50
Breakpoint 3 at 0x804867d: file test.c, line 50. (2 locations)
(gdb) cont
ProcessA: 3472 step1
[New Thread 0xb7fe7b70 (LWP 3562)]
ProcessA: 3472 thread 3086911168 step2

Breakpoint 3, processAworker (arg=0x0) at test.c:50
(gdb) info inferiors
  Num  Description       Executable       
  2    process 3475      /home/cnwuwil/labs/c-lab/test
* 1    process 3472      /home/cnwuwil/labs/c-lab/test
(gdb) info threads
  3 Thread 0xb7fe7b70 (LWP 3562)  0x00110424 in __kernel_vsyscall ()
  2 Thread 0xb7fe86c0 (LWP 3475)  0x00110424 in ?? ()
* 1 Thread 0xb7fe86c0 (LWP 3472)  processAworker (arg=0x0) at test.c:50

4. 切换到主进程中的子线程，注意：线程2为前面产生的子进程

(gdb) thread 3
[Switching to thread 3 (Thread 0xb7fe7b70 (LWP 3562))]#0  0x00110424 in __kernel_vsyscall ()
(gdb) cont
ProcessA: 3472 thread 3086911168 step3
ProcessA: 3472 thread 3086908272 step2
[Switching to Thread 0xb7fe7b70 (LWP 3562)]

Breakpoint 3, processAworker (arg=0x0) at test.c:50
(gdb) info threads
* 3 Thread 0xb7fe7b70 (LWP 3562)  processAworker (arg=0x0) at test.c:50
  2 Thread 0xb7fe86c0 (LWP 3475)  0x00110424 in ?? ()
  1 Thread 0xb7fe86c0 (LWP 3472)  0x00110424 in __kernel_vsyscall ()
(gdb) thread 1