When using coredump in gdb, how do I know exactly which thread called SIGSEGV?

When you use gdb

a core dump file to parse, it gdb

will stop at the function that calls the core dump of the program. And the current thread will be murder. Take the following program as an example:

#include <stdio.h>
#include <pthread.h>
void *thread_func(void *p_arg)
{
        while (1)
        {
                printf("%s\n", (char*)p_arg);
                sleep(10);
        }
}
int main(void)
{
        pthread_t t1, t2;

        pthread_create(&t1, NULL, thread_func, "Thread 1");
        pthread_create(&t2, NULL, thread_func, NULL);

        sleep(1000);
        return;
}

      

        
        
        
      

    

The thread t2

will cause the program to terminate as it refers to a pointer NULL

. After the program finishes, use the following gdb

to parse the kernel dump file:

[root@localhost nan]# gdb -q a core.32794
Reading symbols from a...done.
[New LWP 32796]
[New LWP 32795]
[New LWP 32794]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Core was generated by `./a'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00000034e4281451 in __strlen_sse2 () from /lib64/libc.so.6
(gdb)

      

        
        
        
      

    

The function gdb

stops at __strlen_sse2

, it means that this function will disable the program. Then use the command bt

to see how it is called on which thread:

(gdb) bt
#0  0x00000034e4281451 in __strlen_sse2 () from /lib64/libc.so.6
#1  0x00000034e4268cdb in puts () from /lib64/libc.so.6
#2  0x00000000004005cc in thread_func (p_arg=0x0) at a.c:7
#3  0x00000034e4a079d1 in start_thread () from /lib64/libpthread.so.0
#4  0x00000034e42e8b6d in clone () from /lib64/libc.so.6
(gdb) i threads
  Id   Target Id         Frame
  3    Thread 0x7ff6104c1700 (LWP 32794) 0x00000034e42accdd in nanosleep () from /lib64/libc.so.6
  2    Thread 0x7ff6104bf700 (LWP 32795) 0x00000034e42accdd in nanosleep () from /lib64/libc.so.6
* 1    Thread 0x7ff60fabe700 (LWP 32796) 0x00000034e4281451 in __strlen_sse2 () from /lib64/libc.so.6

      

        
        
        
      

    

The command bt

shows the stack frame of the current thread (which is a kill). The " i threads

" commands show all threads, the thread number starting with *

is the current thread.

As for " How are the threads numbered?

", it depends on the OS. you can refer to the gdb manual for more information.