Re: perf probe and bitfields

[Masami Hiramatsu <masami.hiramatsu@gmail.com>]

On Fri, 26 Jan 2018 09:28:49 -0700
David Ahern <dsahern@gmail.com> wrote:

> On 1/25/18 11:56 PM, Namhyung Kim wrote:
> > Hi David,
> > 
> > On Fri, Jan 19, 2018 at 08:43:50AM -0800, David Ahern wrote:
> >> 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'
> > 
> > Bitfield type takes 3 parameters according to the Doc/perf-probe.txt.
> > Maybe it's like 'ptype=skb->pkt_type:b3@0/8' ?
> 
> missed that. Thanks, Namyhung.



Hmm, if you have debuginfo, it must be automatically translated.
E.g.

$ sudo perf probe -D "arp_rcv ptype=skb->pkt_type dev=dev->name:string"
p:probe/arp_rcv _text+8135904 ptype=+144(%di):b3@5/8 dev=+0(%si):string

So as you can see the ptype automatically has ":b3@5/8" types.

Thanks,

-- 
Masami Hiramatsu