DTrace cannot reference the external kernel variable `ticks` on FreeBSD

Question

I've come across the following DTrace one-liner on https://wiki.freebsd.org/DTrace/One-Liners:

# Summarize TCP life span in seconds:
dtrace -n 'fbt::tcp_close:entry { 
    @["TCP life span (seconds):"] = quantize((uint32_t)(`ticks - args[0]->t_starttime) / `hz); 
}'

It does not work on latest FreeBSD 15.0-CURRENT anymore. It errors out with:

dtrace: invalid probe specifier fbt::tcp_close:entry {
 @["TCP life span (seconds):"] = 
    quantize((uint32_t)(`ticks - args[0]->t_starttime) / `hz); 
}:
  in action list: no symbolic type information is available for kernel`ticks:
    No type information available for symbol

^{error text above manually wrapped/indented}

Any ideas why DTrace cannot find `ticks? It finds `hz just fine.

According to the wiki page, all the one liners were tested in the past so that is not a typo. Also, I tried including sys/kernel.h as it seems to be where ticks is declared, but that did not help (it ends up needing sys/queue.h as well and even then it does not work).

Answer 1

It turns out this might be a bug.

All the other symbols I tested resolve just fine.

The reason why ticks (and interestingly enough ticksl as well) are not understood by DTrace could be due to the change in the implementation of ticks earlier this year.

Essentially, on my FreeBSD 15.0-CURRENT ticks is defined in an assembly file sys/kern/subr_ticks.s. As a result, ticks might not have any type info that ctfconvert could consume.

Refer to the PR in FreeBSD Bugzilla for more details: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=287752