GDB調試——啟動調試程序
一、啟動
>>gdb啟動
gdb 調試之前加載調試符號，即編譯時候加 –g選項，如 gcc file.c –g –o target
啟用gdb的方法種有3種，一種是啟動core，還有是attach一個已經運行的進程。
1. gdb <program>
2. gdb <program> core
用gdb同時調試一個運行程序和core文件，core是程序非法執行後core dump後產生的文件。
3. gdb <program> <PID>
如果你的程序是一個服務程序，那麽你可以指定這個服務程序運行時的進程ID。gdb會自動attach上去，並調試他。 program應該在PATH環境變量中搜索得到。
>>運行調試程序
1. run argv1 argv2
gdb帶參數運行
2. run
不帶參數運行
3. set args argv_a argv_b
gdb啟動程序執行後可重新設置參數
4. run > ./output
gdb啟動程序時進行重定向
二、gdb調試多進程（attach）
運行gdb:
gdb
(gdb) attach xxxxx --- xxxxx為利用ps命令獲得的子進程process id
(gdb) stop --- 這點很重要，你需要先暫停那個子進程，然後設置一些斷點和一些Watch
(gdb) break 37
Breakpoint 1 at 0x10808: file eg1.c, line 37.
(gdb) continue
Continuing.
三、gdb調試多線程
1、使用gdb調試的時候，gdb只能跟蹤一個進程。
可以在fork函數調用之前，通過指令設置gdb調試工具跟蹤父進程或子進程。
默認情況下gdb是跟蹤父進程的。
set follow-fork-mode child 命令設置gdb在fork之後跟蹤子進程。
set follow-fork-mode parent設置跟蹤父進程。
默認設置下，在調試多進程程序時GDB只會調試主進程。但是GDB（>V7.0）支持多進程的分別以及同時調試，換句話說，GDB可以同時調試多個程序。只需要設置follow-fork-mode(默認值：parent)和detach-on-fork（默認值：on）即可。
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
設置方法：set follow-fork-mode [parent|child] set detach-on-fork [on|off]
查詢正在調試的進程：info inferiors
切換調試的進程： inferior <infer number>
添加新的調試進程： add-inferior [-copies n] [-exec executable] ,可以用file executable來分配給inferior可執行文件。
其他：remove-inferiors infno， detach inferior
2. GDB默認支持調試多線程，跟主線程，子線程block在create thread。
查詢線程：info threads
切換調試線程：thread <thread number>
例程：
#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");
}
輸出：
[[email protected] c-lab]$ ./test ProcessA: 802 step1ProcessB: 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
調試：
1. 調試主進程，block子進程。
(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. 切換到子進程：
(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. 設斷點繼續調試主進程，主進程產生兩個子線程：
(gdb) break test.c:50Breakpoint 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. 切換到主進程中的子線程，註意：線程2為前面產生的子進程
(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
GDB調試——啟動調試程序