From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Ahern <dsahern@gmail.com>
Subject: perf probe and bitfields
Date: Fri, 19 Jan 2018 08:43:50 -0800
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To: Arnaldo Carvalho de Melo <acme@kernel.org>, Masami Hiramatsu <mhiramat@kernel.org>, Perf Users <linux-perf-users@vger.kernel.org>

Hi Arnaldo / Masami:

Are there known issues / limitations with perf probe and bitfields?

Here's an example: pkt_type is a bitfield in sk_buff. When I put a probe
in arp_rcv to examine the pkt_type value:

$ perf probe 'arp_rcv ptype=skb->pkt_type dev=dev->name:string'

I only get '0' output:

$ perf script
     vhost-27472 27483 [013] 4313207.619714: probe:arp_rcv:
(ffffffff815653b0) ptype=0 dev="br1"
     vhost-27472 27483 [013] 4313207.619763: probe:arp_rcv:
(ffffffff815653b0) ptype=0 dev="br1"
     vhost-27472 27483 [013] 4313210.588990: probe:arp_rcv:
(ffffffff815653b0) ptype=0 dev="br1"

when I know broadcast packet are getting handled (pkt_type ==
PACKET_BROADCAST). This is confirmed by adding a printk to arp_rcv.

Thanks,
David