Date: Thu, 4 Sep 2014 02:23:26 -0700 From: Shrikanth Kamath <shrikanth07@gmail.com> To: Mark Johnston <markj@freebsd.org> Cc: freebsd-hackers@freebsd.org, freebsd-dtrace@freebsd.org, avg@freebsd.org Subject: Re: Usage of DTRACE_PROBE macro from sdt.h in kernel modules Message-ID: <CAEOAkMVnDWwDbgBQ4j%2BNg3z-p1uP6X6NO-EkY94Zm12C9M58yg@mail.gmail.com> In-Reply-To: <20140903234950.GB38016@charmander.home> References: <CAEOAkMWw07D-XTx8JXvVjU%2BOjUQbKcOZmYoLvzSGA=80B8q-tw@mail.gmail.com> <20140902204413.GC59246@charmander.home> <540711ED.2050909@FreeBSD.org> <CAEOAkMXbn_jeLru4THvtnpj4EsEDLutgK=gOkAciYkgWCYBEJg@mail.gmail.com> <20140903234950.GB38016@charmander.home>
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On Wed, Sep 3, 2014 at 4:49 PM, Mark Johnston <markj@freebsd.org> wrote: > On Wed, Sep 03, 2014 at 02:09:48PM -0700, Shrikanth Kamath wrote: >> 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; > > You're completely right; this issue was fixed in > http://svnweb.freebsd.org/base?view=revision&revision=267706 > >> >> 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. > > Why not just use a single probe and make the line number and function > name arguments to the probe? That is, write something like > > #define RETSDT(error_code) do { \ > DTRACE_PROBE2(error__return, __func__, __LINE__) > return (error_code); > } while (0) > Mark, for some reason using a single probe does not seem to fire the probe. -- Shrikanth R K
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