Tracing dropped UDP packets

[bazzoola]

Greetings,

I would like to know where (in the kernel) UDP packets are dropped.

I looked at udp_usrreq.c but is overwhelming for the 1st time. Is it
possible to use DTrace to locate where the packets are being dropped? or
is there a tool similar to 'dropwatch' which can tell me where in the
kernel my packets are getting dropped?

On Linux, I used dropwatch and they were dropped packets were at
udp_queue_rcv_skb().

Thanks!