gdb调试多进程和多线程命令


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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：

#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");

}

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