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

#include <sys/syscall.h>  
#define gettid() syscall(__NR_gettid)

void *hello(void *ptr)
{
	while(1)
	{   
		printf("%lx %ld\n",pthread_self(),gettid());
		sleep(1);   
	}   
}

int main()
{
	pthread_t thread_;
	pthread_create(&thread_, NULL, hello, NULL);  
	while(1)
	{   
		printf("%lx %ld\n",pthread_self(),gettid());
		sleep(1);                                                                                                                          
	}   
	return 0;
}

(gdb) r
Starting program: /root/test/a.out 
[Thread debugging using libthread_db enabled]
[New Thread 0xb7e74b70 (LWP 1188)]
b7e756c0 1185
b7e74b70 1188
b7e756c0 1185
b7e74b70 1188
^C
Program received signal SIGINT, Interrupt.
0xb7fe2424 in __kernel_vsyscall ()
(gdb) info threads 
  2 Thread 0xb7e74b70 (LWP 1188)  0xb7fe2424 in __kernel_vsyscall ()
* 1 Thread 0xb7e756c0 (LWP 1185)  0xb7fe2424 in __kernel_vsyscall ()