Using the volatile variable jiffies in a bpftrace program - getting ERROR: Unknown identifier

[tariromukute]

Hi. I am trying to calculate the RTT from an SCTP heartbeat packet on the kprobe sctp_cmd_transport_on. To do so I need to use the jiffies variable but I am getting error ERROR: Unknown identifier: 'jiffies'. See my program below.

bpftrace -e '
#include <net/sctp/structs.h>
#include <linux/jiffies.h>
kprobe:sctp_cmd_transport_on {
    $hbinfo = (struct sctp_sender_hb_info *)arg3->skb->data;
    $rtt = jiffies - $hbinfo->sent_at;
    @[$rtt] = count();
    }'

Is it possible for me to reference the kernel jiffies variable, if so what am I missing, if not, are there any workarounds?

[chengshuyi]

eBPF already has the bpf_jiffies64 helper function, but it seems that bpftrace does not support it yet

[tariromukute]

Thank you @chengshuyi. Does bcc support it? I am guessing my other option is implementing the above as a bcc tool if it supports bpf_jiffies64.

[chengshuyi]

yes, bcc support it.

[viktormalik]

I opened a new issue #2644 for adding the jiffies builtin in case anyone wants to implement it. Thanks for raising this!