We absolutely ran into these issues.

A couple notes that help quite a bit:

1. Always build the eBPF programs in a container - this is great for reproducibility of course, but also makes DevX on MacOS better for those who prefer to use that.

2. You actually can do a full checksum! You need to limit the MTU but you can:

  static __always_inline void tcp_checksum(const struct iphdr *ip_header, struct tcphdr *tcp_header, const __u16 tcp_len, const void *data_end) {
    __u32 sum = 0;
    __u16 *buf = (void *)tcp_header;
    ip_header_pseudo_checksum(ip_header, tcp_len, &sum);
    tcp_header->check = 0;
    __u16 max_packet_size = tcp_len;
    if (max_packet_size > MAX_TCP_PACKET_SIZE) {
        max_packet_size = MAX_TCP_PACKET_SIZE;
    }
    for (int i = 0; i < max_packet_size / 2; i++) {
        if ((void *)(buf + 1) > data_end) {
            break;
        }
        sum += *buf;
        buf++;
    }
    if ((void *)buf + 1 <= data_end && ((__u8 *)buf - (__u8 *)tcp_header) < max_packet_size) {
        sum += *(__u8 *)buf;
    }
    tcp_header->check = csum_fold_helper(sum);
  }

With that being said, it's not lost on me that XDP in general is something you should only reach for once you hit some sort of bottleneck. The original version of our network migration was actually implemented in userspace for this exact reason!