gdb调试coredump

程序异常终止时，将会产生core文件，其包含了程序崩溃时的信息，比如调用栈等，可使用gdb来调试core文件。

1. main测试

实例：主函数创建一个子线程，子线程内部未正确使用指针，引发Segmentation fault (core dumped)

(1). 源文件

x
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>

void* running(void* arg)
{
    printf("At child thread: %ld\n", pthread_self());
    int *tmp;
    *tmp = 1;   //引发段错误
}
int main()
{
    printf("At parent thread: %ld\n", pthread_self());

    pthread_t tid;
    int ret = pthread_create(&tid, NULL, running, NULL);
    if(ret != 0)
    {
        return -1;
    }
    pthread_join(tid, NULL);
    return 0;
}

(2). gdb调试

x
# 编译：需要加-g
xxx# gcc -g main.c -lpthread
xxx# ./a.out
At parent thread: 140656779855680
At child thread: 140656779851328
Segmentation fault (core dumped)    # 产生段错误
xxx# ls
a.out  core-a.out-348574-1731476560-11  main.c  # 生成了core文件

# gdb调试
xxx# gdb a.out core-a.out-348574-1731476560-11
...
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from a.out...
[New LWP 348575]
[New LWP 348574]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `./a.out'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00005647e54711f9 in running (arg=0x0) at main.c:12  ####找到程序崩溃处
12          *tmp = 1;   //引发段错误                                     
[Current thread is 1 (Thread 0x7fed3565f640 (LWP 348575))]

# 查看段错误前后文
(gdb) l main.c:12
7
8       void* running(void* arg)
9       {
10          printf("At child thread: %ld\n", pthread_self());
11          int *tmp;
12          *tmp = 1;
13      }
14      int main()
15      {
16          printf("At parent thread: %ld\n", pthread_self());

#查看栈
(gdb) bt
#0  0x00005647e54711f9 in running (arg=0x0) at main.c:12
#1  0x00007fed356f7ac3 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
#2  0x00007fed35789850 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

# 查看局部变量
(gdb) info locals
tmp = 0x0

# 查看参数
(gdb) info args
arg = 0x0

# 查看线程
(gdb) info threads
  Id   Target Id                          Frame
* 1    Thread 0x7fed3565f640 (LWP 348575) 0x00005647e54711f9 in running (arg=0x0) at main.c:12
  2    Thread 0x7fed35660740 (LWP 348574) 0x00007fed357487f8 in __GI___clock_nanosleep (clock_id=clock_id@entry=0, flags=flags@entry=0, req=req@entry=0x7fff7a2a22e0, rem=rem@entry=0x7fff7a2a22e0)
    at ../sysdeps/unix/sysv/linux/clock_nanosleep.c:78
(gdb)

2. core文件生成

大小：默认情况下,core核心转储文件文件生成大小为0，表示核心转储功能被禁用。

x
# 临时生成大小为无限制
xxx# ulimit -c unlimited
xxx# ulimit -c
unlimited

# 临时生成位置，说明:
# %e: 程序文件的完整路径
# %p: 进程ID
# %t: 进程崩溃的时间戳
# %s: 哪个信号让程序崩溃
xxx# echo "/root/coredoc/core-%e-%p-%t-%s" > /proc/sys/kernel/core_pattern
xxx# cat /proc/sys/kernel/core_pattern
/root/coredoc/core-%e-%p-%t-%s