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 015CBC433E2 for ; Mon, 13 Jul 2020 15:18:13 +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 9213D2075B for ; Mon, 13 Jul 2020 15:18:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.lttng.org header.i=@lists.lttng.org header.b="AwQ8xinK" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9213D2075B 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 4B56jG6shKz1VRM; Mon, 13 Jul 2020 11:18:10 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lists.lttng.org; s=default; t=1594653491; bh=HMzBfhl+rZuxfR5TQIslTTZi5tneLl+QVcvu513r1Sc=; 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=AwQ8xinKWMoiz23eYDT2I6xUXFG82+ULZlk+uZucixkxNCH+bDlmwvnTXJSH95yKc 6yOCujtJIjkHQKWQji25D6TiQr92/a5aKvAEHBpn2oMdNxIDDcNnkbCArIO5BsSPK/ BLVrGy4LO7MsR3uPMzuI4WauRgoDoUwslYADQs2TitOBgaKfdq3Y/5or9k/Zb7p1wK 5OCj/eBmtCxjTddc0ih5vqJ+PeKUvwjwCTxAf5Rd/YqSW2wAF9SvfzG55OpNb6YX3t bRVAdQu71ENJTzmFFepkgbfWSvVTN8HRGKJI+RAF4y4LoMsEPcE1RlikqzpBFS/Ej1 O/ja3pcDjrK5Q== Received: from smtp.polymtl.ca (smtp.polymtl.ca [132.207.4.11]) by lists.lttng.org (Postfix) with ESMTPS id 4B56jF2pLTz1W7m for ; Mon, 13 Jul 2020 11:18:08 -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 06DFHuXg023821 (version=TLSv1/SSLv3 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 13 Jul 2020 11:18:01 -0400 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp.polymtl.ca 06DFHuXg023821 To: Mathieu Desnoyers Cc: lttng-dev In-Reply-To: <1851244021.9798.1594646692671.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> Date: Mon, 13 Jul 2020 11:19:18 -0400 Message-ID: <87r1tfxx1l.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 15:17:56 +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: <20200713151918.RW68IL5cy6OMyLSW4lUW8oKXyqTqER5ajaZQPNpD6vQ@z> On Mon, 13 Jul 2020, Mathieu Desnoyers wrote: > ----- On Jul 12, 2020, at 11:49 AM, Olivier Dion olivier.dion@polymtl.ca wrote: > >> On Sun, 12 Jul 2020, Mathieu Desnoyers wrote: >>> ----- On Jul 11, 2020, at 11:29 AM, lttng-dev lttng-dev@lists.lttng.org wrote: >>> >>>> Some library might want to generate events in their ctor/dtor. If >>>> LTTng initialize/finalize its tracepoints/events at the wrong time, >>>> events are lost. >>>> >>>> Order of execution of the ctor/dtor is determined by priority. When >>>> some priorities are equal, the order of execution seems to be >>>> determined by: >>>> >>>> a) Order of appearance if in the same compilation unit >>>> >>>> b) Order of link if in different compilation units >>>> >>>> c) Order of load by ld-linux.so or dlopen(3) for >>>> share objects >>> >>> I recall different rules about constructor priorities. Can you provide >>> links to documentation stating the priority order you describe above ? >> >> I haven't found any documentation on that. This is purely empirical. >> Although I'm sure that we can dig something if chatting on GCC's IRC. > > If it is not documented, then I am reluctant on depending on a behavior > which may be what happens today, but may not be the same for past/future > toolchains. Agree. >>> 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? -- Olivier Dion PolyMtl _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev