SEGV Signal 발생합니다. 도움 부탁드려요

#define MAX_LINE_NUM	20
 
struct test_stat
{
        int     pid;                            /* process pid           */
        int     stat;                           /* 0:전송불가 1:전송가능 */
        int     fifocnt;                        /* fifo cnt */
        char    usrid           [8];            /* user id               */
};
struct  test_stat    *op;
 
void main(int argc, char *argv[])
{
	int	line_num = 1;
        int     shmid;
        int     shmsize = sizeof(struct test_stat) * MAX_LINE_NUM;
 
        shmid = ShmGet(shmkey);
        if(shmid < 0)
        {
                shmid = ShmCreate(shmkey, shmsize, SHM_PERM | IPC_CREAT);
                if(shmid < 0)
                {
                        Log("Shared Memory Create fail (%d)\n", errno);
                        return -9;
                }
                Log("shm create OK\n");
 
                op = (struct test_stat *)ShmAttach(shmid);
                if(op == (void *)-1)
                {
                        Log("Shared Memory Attach fail (%d)\n", errno);
                        return -10;
                }
 
                memset((char*)op, 0x00, shmsize);
		Log("Initialize\n");
        }
        else
        {
                op = (struct test_stat *)ShmAttach(shmid);
                if(op == (void *)-1)
                {
                        Log("Shared Memory Attach fail (%d)\n", errno);
                        return -11;
                }
        }
        Log("Shared Memory Attach OK\n");
 
        (op+line_num-1)->pid = getpid();
        Log("test1111\n");
 
 
	return 0;
}
 
int ShmGet(key_t key)
{
        return shmget(key, 0, 0);
}
 
int ShmCreate(key_t key, size_t size, int flag)
{
    return shmget(key, size, flag);
}
 
void *ShmAttach(int shmid)
{
    return (void *)shmat(shmid, (char *)0, 0);
}