GDB Debug Multi-process and multithreaded commandsSource: http://blog.csdn.net/pbymw8iwm/article/details/78767971. By default, GDB will only debug the main process when debugging a multi-process program. But GDB (>v7.0) supports multi-process and simultaneous debugging, in other words, GDB can debug multiple programs at the same time. You only need to set Follow-fork-mode (default: Parent) and Detach-on-fork (default: On).
Follow-fork-mode detach-on-fork Description Parent on only debugging main process (GDB default)
Child on only debugging sub-processes
Parent off simultaneously debug two processes, GDB with main process, sub-process block at fork position
Child off simultaneously debug two processes, GDB and subprocess, main process block at Fork position Set method: Set Follow-fork-mode [Parent|child] s ET detach-on-fork [On|off]
Querying the process being debugged: info inferiors
Switch Debug process: inferior <infer number>
Add a new debug process: Add-inferior [-copies n] [-exec executable], you can use the file executable to assign to the inferior executable.
Others: Remove-inferiors infno, detach inferior
2. GDB supports debugging multi-threading by default, with the main thread, the child thread block in the Create thread.
Query Thread: INFO threads
Toggle Debug Thread: Thread <thread number>
Routines:
#include <stdio.h>
#include <pthread.h>
void Processa ();
void Processb ();
void * Processaworker (void *arg);
int main (int argc, const char *argv[])
{
int pid;
PID = fork ();
if (pid! = 0)
Processa ();
Else
PROCESSB ();
return 0;
}
void Processa ()
{
pid_t pid = Getpid ();
Char prefix[] = "Processa:";
Char tprefix[] = "thread";
int tstatus;
pthread_t pt;
printf ("%s%lu%s\n", prefix, PID, "Step1");
Tstatus = pthread_create (&pt, NULL, processaworker, NULL);
if (tstatus! = 0)
{
printf ("Processa:can not create new thread.");
}
Processaworker (NULL);
Sleep (1);
}
void * Processaworker (void *arg)
{
pid_t pid = Getpid ();
pthread_t tid = pthread_self ();
Char prefix[] = "Processa:";
Char tprefix[] = "thread";
printf ("%s%lu%s%lu%s\n", prefix, PID, Tprefix, Tid, "Step2");
printf ("%s%lu%s%lu%s\n", prefix, PID, Tprefix, Tid, "step3");
return NULL;
}
void Processb ()
{
pid_t pid = Getpid ();
Char prefix[] = "PROCESSB:";
printf ("%s%lu%s\n", prefix, PID, "Step1");
printf ("%s%lu%s\n", prefix, PID, "Step2");
printf ("%s%lu%s\n", prefix, PID, "Step3");
}
Output:
[Email protected] c-lab]$/testprocessa: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
Debugging:
1. Debug the main process, block child process.
(GDB) Set Detach-on-fork off
(GDB) Show detach-on-fork
Whether GDB would 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. Switch to Child process:
(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. Set a breakpoint to continue debugging the main process, and the main process to produce two sub-threads:
(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. Switch to the child thread in the main process, note: Thread 2 is the child process that was created earlier
(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
GDB Debug Multi-process and multithreaded commands
