Date: Wed, 3 Sep 2014 14:09:48 -0700 From: Shrikanth Kamath <shrikanth07@gmail.com> To: avg@freebsd.org, markj@freebsd.org, freebsd-hackers@freebsd.org, freebsd-dtrace@freebsd.org Subject: Re: Usage of DTRACE_PROBE macro from sdt.h in kernel modules Message-ID: <CAEOAkMXbn_jeLru4THvtnpj4EsEDLutgK=gOkAciYkgWCYBEJg@mail.gmail.com> In-Reply-To: <540711ED.2050909@FreeBSD.org> References: <CAEOAkMWw07D-XTx8JXvVjU%2BOjUQbKcOZmYoLvzSGA=80B8q-tw@mail.gmail.com> <20140902204413.GC59246@charmander.home> <540711ED.2050909@FreeBSD.org>
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Thanks Mark/Andriy for helping with this query. I checked the define
KDTRACE_HOOKS define that is set. Rather I tried this, I defined a
fake provider just to check if that prompts sdt_kld_load to create the
SDT probes from my kernel module.
+ SDT_PROVIDER_DEFINE(fake);
And it does help load the SDT probes I created, even though I am not
using the fake provider I defined. I feel that sdt_kld_load is flawed
when it is looking for sdt_providers_set in the module. It expects at
least a provider define and cannot use one of the defined ones in
kernel by just declaring it.
if (linker_file_lookup_set(lf, "sdt_providers_set", &begin,
&end, NULL))
return;
I intended to use DTRACE_PROBE() instead of the conventional
SDT_PROBE_DEFINE/SDT_PROBE usage because I wanted to create probes
which have probe names based on __LINE__ macro...disclaimer...this was
just for experiment sakes...
E.g
func_foo()
{
....
if ()
return EINVAL;
...
if ()
return EINVAL;
...
if ()
return EINVAL;
}
which I replaced with
func_foo()
{
...
if ()
RETSDT(func_foo, EINVAL);
...
if ()
RETSDT(func_foo, EINVAL);
...
if ()
RETSDT(func_foo, EINVAL);
}
where RETSDT macro and other macros are defined as
#define PROBENAME1(func, __LINE__) func ## __LINE__
#define PROBENAME(func, line) PROBENAME1(func, line)
#define RETSDT(func, error_code) \
do { \
DTRACE_PROBE(PROBENAME(func, __LINE__));\
return (error_code); \
} while (0)
With the fake provider I defined I get to see and execute my SDT probes
% dtrace -l | grep func_foo
56455 sdt netstack func_foo1592
Here netstack is my module, and I have a probe name based on __LINE__
which is 1592.
Don't know if that is good way to do it but using SDT_PROBE_DEFINE
looks like a problem because of the presence of __LINE__ in the
probename.
Thanks for reaching out...
--
Shrikanth R K
On Wed, Sep 3, 2014 at 6:04 AM, Andriy Gapon <avg@freebsd.org> wrote:
> on 02/09/2014 23:44 Mark Johnston said the following:
>> Somewhat confusingly, DTRACE_PROBE* shouldn't be used in the kernel.
>
> But it can be used.
>
> Shrikanth, please double check that KDTRACE_HOOKS is defined when you compile
> your module.
>
> --
> Andriy Gapon
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