From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olivier Dion via lttng-dev Subject: Re: [PATCH lttng-ust] Add ctor/dtor priorities for tracepoints/events Date: Mon, 13 Jul 2020 14:46:16 -0400 Message-ID: <87lfjnxngn.fsf@clara> References: <20200711152907.676582-1-olivier.dion@polymtl.ca> <756801034.9565.1594561774215.JavaMail.zimbra@efficios.com> <87tuycybqx.fsf@clara> <1851244021.9798.1594646692671.JavaMail.zimbra@efficios.com> <87r1tfxx1l.fsf@clara> <2029726158.10046.1594654110710.JavaMail.zimbra@efficios.com> Reply-To: Olivier Dion Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from smtp.polymtl.ca (smtp.polymtl.ca [132.207.4.11]) by lists.lttng.org (Postfix) with ESMTPS id 4B5CHw41fmz1VvC for ; Mon, 13 Jul 2020 14:45:00 -0400 (EDT) In-Reply-To: <2029726158.10046.1594654110710.JavaMail.zimbra@efficios.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" To: Mathieu Desnoyers Cc: lttng-dev List-Id: lttng-dev@lists.lttng.org On Mon, 13 Jul 2020, Mathieu Desnoyers wrote: > ----- On Jul 13, 2020, at 11:19 AM, Olivier Dion olivier.dion@polymtl.ca wrote: > >> On Mon, 13 Jul 2020, Mathieu Desnoyers wrote: > [...] >> >>>>> Also, we should compare two approaches to fulfill your goal: >>>>> one alternative would be to have application/library constructors >>>>> explicitly call tracepoint constructors if they wish to use them. >>>> >>>> I would prefer this way. The former solution might not work in some >>>> cases (e.g. with LD_PRELOAD and priority =101) and I prefer explicit >>>> initialization in that case. >>>> >>>> I don't see any cons for the second approach, except making the symbols >>>> table a few bytes larger. I'll post a patch soon so we can compare and >>>> try to find more documentation on ctor priority. >>> >>> And users will have to explicitly call the constructor on which they >>> depend, but I don't see it as a huge burden. >> >> The burden is small indeed. But users should pay close attention to >> release the references in a destructor too. >> >>> Beware though that there are a few configurations which can be used for >>> probe providers (see lttng-ust(3)). >> >> I'm not following you here. I don't see any configuration for provider >> except TRACEPOINT_LOGLEVEL. What should I be aware of? > > See sections "Statically linking the tracepoint provider" and > "Dynamically loading the tracepoint provider" from lttng-ust(3). It's > especially the dynamic loading I am concerned about, because then it > becomes tricky for an instrumented .so (or app) to call the probe provider's > constructor without dlopening it beforehand, because there are no dependencies > from the instrumented module on probe symbols. And given you plan to call > this from a constructor, it means the dynamic loader lock is already held, > so even if we dlopen the probe provider from the instrumented constructor, > I am not sure the dlopen'd .so's constructor will be allowed to run > immediately. > > Maybe one thing that could work for the dynamic loading case would be to: > > - let the instrumented constructor dlopen its probe, > - from the instrumented constructor, use dlsym to get the probe's constructor > symbols. > - call those constructors. > > If this is common enough, maybe we would want to provide helpers for > this. Okay so to be clear. __tracepoints__init() should be call first, then __tracepoints__ptrs_init() and then dlsym(3) on __lttng_events_init__provider() _if_ TRACEPOINT_PROBE_DYNAMIC_LINKAGE. Reverse the steps in destructor. And so would something along these lines work? -------------------------------------------------------------------------------- #ifdef TRACEPOINT_PROBE_DYNAMIC_LINKAGE # define tracepoint_acquire(provider) \ do { \ void (*init)(void); \ __tracepoints__init(); \ __tracepoints__ptrs_init(); \ init = dlsym(RTLD_DEFAULT, \ "__lttng_events_init__" #provider); \ if (init) { \ init(); \ } \ } while(0) #else # define tracepoint_acquire(provider) \ do { \ __tracepoint__init(); \ __tracepoints_ptrs_init(); \ _TP_COMBINE_TOKENS(__lttng_events_init__, provider)(); \ } while(0) #endif -------------------------------------------------------------------------------- And then: ---------------------------------------------------------------------- #include "my-trace.h" __attribute__((constructor)) static void my_ctor(void) { tracepoint_acquire(my_provider); tracepoint(my_provider, my_event, my_state); } __attribute__((destructor)) static void my_ctor(void) { tracepoint_release(my_provider) } ---------------------------------------------------------------------- Of course, this requires making __tracepoints__* externally visibile. -- Olivier Dion PolyMtl From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35BDDC433E3 for ; Mon, 13 Jul 2020 18:45:04 +0000 (UTC) Received: from lists.lttng.org (lists.lttng.org [167.114.26.123]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B03DA20657 for ; Mon, 13 Jul 2020 18:45:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.lttng.org header.i=@lists.lttng.org header.b="disSnGTH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B03DA20657 Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=lists.lttng.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lttng-dev-bounces@lists.lttng.org Received: from lists-lttng01.efficios.com (localhost [IPv6:::1]) by lists.lttng.org (Postfix) with ESMTP id 4B5CHx1dglz1VxK; Mon, 13 Jul 2020 14:45:01 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lists.lttng.org; s=default; t=1594665902; bh=h0PRtt9jc4+TmCPp3YVcBQ1nmWE81uI/WUHcclysxZQ=; h=To:Cc:In-Reply-To:References:Date:Subject:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From:Reply-To:From; b=disSnGTHgjxkCdpB7ohmMCJYhe68vaMg/FUi6bgbrJQPh5/2DHETTlg8TN/H8M/b+ XMnfuSyiCGBp3ojv4xE99iIVXmCBlsAOoZvqyeHHhY19ZAzkKk0uXIZsx34lJ3kheW 3x1+ErLZUoS8qYMZo7mwiM5t5qcc1b75Jpune6a+3ocqXUO7227A/268Z6JRBKxQ1R NyuZobUh+Vqwdf0AEfCs8EWgWZX9uZoBAzF9ASGOKhh4KXysK6eoIFolG9vzYiVsny vjNlhHnYEFhi/FQMsmZvOG+4MSRpkYaxwOYgbNq59hKKx7nxocwCJVHH+Nhilpgrsl RSlB3JFXoeSRg== Received: from smtp.polymtl.ca (smtp.polymtl.ca [132.207.4.11]) by lists.lttng.org (Postfix) with ESMTPS id 4B5CHw41fmz1VvC for ; Mon, 13 Jul 2020 14:45:00 -0400 (EDT) Received: from localhost (modemcable059.101-200-24.mc.videotron.ca [24.200.101.59]) by smtp.polymtl.ca (8.14.7/8.14.7) with ESMTP id 06DIis6Y014941 (version=TLSv1/SSLv3 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 13 Jul 2020 14:44:59 -0400 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp.polymtl.ca 06DIis6Y014941 To: Mathieu Desnoyers Cc: lttng-dev In-Reply-To: <2029726158.10046.1594654110710.JavaMail.zimbra@efficios.com> References: <20200711152907.676582-1-olivier.dion@polymtl.ca> <756801034.9565.1594561774215.JavaMail.zimbra@efficios.com> <87tuycybqx.fsf@clara> <1851244021.9798.1594646692671.JavaMail.zimbra@efficios.com> <87r1tfxx1l.fsf@clara> <2029726158.10046.1594654110710.JavaMail.zimbra@efficios.com> Date: Mon, 13 Jul 2020 14:46:16 -0400 Message-ID: <87lfjnxngn.fsf@clara> MIME-Version: 1.0 X-Poly-FromMTA: (modemcable059.101-200-24.mc.videotron.ca [24.200.101.59]) at Mon, 13 Jul 2020 18:44:54 +0000 Subject: Re: [lttng-dev] [PATCH lttng-ust] Add ctor/dtor priorities for tracepoints/events X-BeenThere: lttng-dev@lists.lttng.org X-Mailman-Version: 2.1.31 Precedence: list List-Id: LTTng development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Olivier Dion via lttng-dev Reply-To: Olivier Dion Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" Message-ID: <20200713184616.O6EHBlYpO7CyzKchYg9FVXHVoMjkSj0piSkT8ro3S88@z> On Mon, 13 Jul 2020, Mathieu Desnoyers wrote: > ----- On Jul 13, 2020, at 11:19 AM, Olivier Dion olivier.dion@polymtl.ca wrote: > >> On Mon, 13 Jul 2020, Mathieu Desnoyers wrote: > [...] >> >>>>> Also, we should compare two approaches to fulfill your goal: >>>>> one alternative would be to have application/library constructors >>>>> explicitly call tracepoint constructors if they wish to use them. >>>> >>>> I would prefer this way. The former solution might not work in some >>>> cases (e.g. with LD_PRELOAD and priority =101) and I prefer explicit >>>> initialization in that case. >>>> >>>> I don't see any cons for the second approach, except making the symbols >>>> table a few bytes larger. I'll post a patch soon so we can compare and >>>> try to find more documentation on ctor priority. >>> >>> And users will have to explicitly call the constructor on which they >>> depend, but I don't see it as a huge burden. >> >> The burden is small indeed. But users should pay close attention to >> release the references in a destructor too. >> >>> Beware though that there are a few configurations which can be used for >>> probe providers (see lttng-ust(3)). >> >> I'm not following you here. I don't see any configuration for provider >> except TRACEPOINT_LOGLEVEL. What should I be aware of? > > See sections "Statically linking the tracepoint provider" and > "Dynamically loading the tracepoint provider" from lttng-ust(3). It's > especially the dynamic loading I am concerned about, because then it > becomes tricky for an instrumented .so (or app) to call the probe provider's > constructor without dlopening it beforehand, because there are no dependencies > from the instrumented module on probe symbols. And given you plan to call > this from a constructor, it means the dynamic loader lock is already held, > so even if we dlopen the probe provider from the instrumented constructor, > I am not sure the dlopen'd .so's constructor will be allowed to run > immediately. > > Maybe one thing that could work for the dynamic loading case would be to: > > - let the instrumented constructor dlopen its probe, > - from the instrumented constructor, use dlsym to get the probe's constructor > symbols. > - call those constructors. > > If this is common enough, maybe we would want to provide helpers for > this. Okay so to be clear. __tracepoints__init() should be call first, then __tracepoints__ptrs_init() and then dlsym(3) on __lttng_events_init__provider() _if_ TRACEPOINT_PROBE_DYNAMIC_LINKAGE. Reverse the steps in destructor. And so would something along these lines work? -------------------------------------------------------------------------------- #ifdef TRACEPOINT_PROBE_DYNAMIC_LINKAGE # define tracepoint_acquire(provider) \ do { \ void (*init)(void); \ __tracepoints__init(); \ __tracepoints__ptrs_init(); \ init = dlsym(RTLD_DEFAULT, \ "__lttng_events_init__" #provider); \ if (init) { \ init(); \ } \ } while(0) #else # define tracepoint_acquire(provider) \ do { \ __tracepoint__init(); \ __tracepoints_ptrs_init(); \ _TP_COMBINE_TOKENS(__lttng_events_init__, provider)(); \ } while(0) #endif -------------------------------------------------------------------------------- And then: ---------------------------------------------------------------------- #include "my-trace.h" __attribute__((constructor)) static void my_ctor(void) { tracepoint_acquire(my_provider); tracepoint(my_provider, my_event, my_state); } __attribute__((destructor)) static void my_ctor(void) { tracepoint_release(my_provider) } ---------------------------------------------------------------------- Of course, this requires making __tracepoints__* externally visibile. -- Olivier Dion PolyMtl _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev