Date: Tue, 2 Sep 2014 16:44:13 -0400 From: Mark Johnston <markj@freebsd.org> To: Shrikanth Kamath <shrikanth07@gmail.com> Cc: freebsd-hackers@freebsd.org, freebsd-dtrace@freebsd.org Subject: Re: Usage of DTRACE_PROBE macro from sdt.h in kernel modules Message-ID: <20140902204413.GC59246@charmander.home> In-Reply-To: <CAEOAkMWw07D-XTx8JXvVjU%2BOjUQbKcOZmYoLvzSGA=80B8q-tw@mail.gmail.com> References: <CAEOAkMWw07D-XTx8JXvVjU%2BOjUQbKcOZmYoLvzSGA=80B8q-tw@mail.gmail.com>
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On Tue, Sep 02, 2014 at 01:24:47PM -0700, Shrikanth Kamath wrote:
> Adding a DTRACE_PROBE(name) in a kernel module does not create the SDT
> probe. I added
> the following to the module file before using DTRACE_PROBE.
Somewhat confusingly, DTRACE_PROBE* shouldn't be used in the kernel. It's
there for compatibility with the DTrace probes in ZFS, which use the SDT
interfaces in illumos. The SDT_PROBE* macros should be used instead. If
you grep the kernel sources, you'll find lots of examples of SDT providers
and probes.
> #include "opt_kdtrace.h"
> #include <sys/sdt.h>
>
> function_foo() {
> ...
> + DTRACE_PROBE(name);
> ...
> }
>
> I figured the sdt.h does declare SDT_PROVIDER_DECLARE(set); but that
> is not helping. Was expecting a sdt probe added under provider 'set'.
SDT_PROVIDER_DEFINE() is used to define a provider.
SDT_PROVIDER_DECLARE() just adds a declaration, so it won't result in
anything being added to the SDT provider linker set in the corresponding
kld.
So SDT_PROVIDER_DEFINE() should be used once to define a new provider,
and the provider can be made visible across multiple files using
SDT_PROVIDER_DECLARE().
>
> The SDT probe creation returns from sdt_kld_load from here
>
> if (linker_file_lookup_set(lf, "sdt_providers_set", &begin, &end, NULL))
> return;
>
> I did a nm on the kernel module and did not find anything matching
> "sdt_providers_set"
>
> nm -a module.ko | grep sdt
>
> 00000000 r __set_sdt_probes_set_sym_sdt_sdt______func____LINE__.103790
>
> U __start_set_sdt_probes_set
>
> U __stop_set_sdt_probes_set
>
> U sdt_probe_func
>
> U sdt_provider_sdt
>
> 000006c0 d sdt_sdt______func____LINE__.103789
>
> Can't seem to figure how to get the SDT probe created by using
> DTRACE_PROBE macro in a kernel module.
In addition to the comments above, I suggest taking a look at the SDT(9)
man page, which has a few examples.
Thanks,
-Mark
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