DTrace SDT Provider not working?

Hi John, all!

I tried to add the SDT Hooks for callout(9), see attached patch.
> # dtrace -l -f callout
>    ID   PROVIDER            MODULE                          FUNCTION NAME
>     6        sdt            kernel                           callout entry
>     7        sdt            kernel                           callout return

however, a simple

> # dtrace -n 'sdt:kernel:callout:entry{printf("1");}'

prints that a probe is matched but nothing else, same for
sdt:kernel:linker_load_module:entry and kldload'ing a module.

I use the snapshot code you provided.

Any idea where to look next?

Thank you very much for your work!
regards
Marius