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        struct ethhdr *eth = (struct ethhdr *)data;
	struct iphdr *iph = (struct iphdr *)(eth + 1);
	struct tcphdr *tcphdr = (struct tcphdr *)(iph + 1);
        ...
	/* sanity check needed by the eBPF verifier */
	if ((void *)(tcphdr + 1) > data_end)
		return 0;

        void *data_end = (void *)(long)ctx->data_end;
	void *data = (void *)(long)ctx->data;
	struct ethhdr *eth = data;
        ...
       // use the offset
	off = sizeof(struct ethhdr);
        if (data + off > data_end)
		return XDP_PASS;