# DF-2253 end-to-end, baseline (stock hexncpy, kernel #1 Sat Oct 17 16:14:33 UTC 2026)
# tap0 created + up; arp_inject writes a 42-byte ethernet frame with ar_hrd=0x1234
# to /dev/tap0 -> tapwrite -> ifp->if_input (ether_input) -> NETISR_ARP -> arpintr
# -> sys/netinet/if_ether.c:643 hexncpy(&ar->ar_hrd, 2, hexstr, 5, NULL)
guest# /root/arp_inject; sleep 2; dmesg | grep -i "arp:" | tail -2
arp_inject: wrote 42 bytes to /dev/tap0 (ar_hrd=0x1234)
arp: unknown hardware address format (0x1)
# NOTE: the logged value is ONE hex digit (0x1); the frame carried 0x1234.
# Reproduced twice (two injections, two identical log lines).