From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi1-x241.google.com (mail-oi1-x241.google.com [IPv6:2607:f8b0:4864:20::241]) by sourceware.org (Postfix) with ESMTPS id 2A5E73858010 for ; Fri, 27 Nov 2020 18:42:20 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 2A5E73858010 Received: by mail-oi1-x241.google.com with SMTP id c80so6846755oib.2 for ; Fri, 27 Nov 2020 10:42:20 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=PP9vrSXsDnr7ZEVNv85rpt/R/61+lCcTjRlxezxE2E0=; b=ebio1adYEMZy/poJTK9MD5blZ+BMzhz7vmuLnoYSxqi2xLdQCARETtEZFofyIAXpSr Z0hfic3yBSr0huh/MZtDCtLNx6Lb+AMKgadtPzeAeqTchWLxEhcbTP1YCpUlNtBanEeV mBzxexav8JPzeOmE7W/FVMPe3erfr5OfPqOq0F0PY5PP4LCN2zZsR87fceeJg3UdPk0M R6lvU4RvtY0bvNpHnyO3trl3oa4a/e51g2G8UXV8Xuykk9+t4C+5J0Mw0w9WIkhr9d5Y TgSNCFkn0qitvs70ww3RK3EHrmHQ+6zxpQF3YZ/4ZG95cDdwTFfwRm0MU4bUXCnQT0+g JbOw== X-Gm-Message-State: AOAM530RXp1FTaUs+p/LejRoOKNZVFnoqV7SoVvVf/TzXQBzhFzqaj4J 1AwL9OWCRcwsE5hU8yULPOwRewtzHBuundHO6D4= X-Google-Smtp-Source: ABdhPJyrsnm41EzrE1TTcDXnzIhATDmiswJoObwEYqlPdriJv/7t+LvqciuNhdzRo/3Ez5tJmuA4YclxLZYwOKKOCeU= X-Received: by 2002:aca:4304:: with SMTP id q4mr4785149oia.25.1606502539602; Fri, 27 Nov 2020 10:42:19 -0800 (PST) MIME-Version: 1.0 References: <6173c59d-ee67-9499-ac61-c2dd37b56c67@foss.arm.com> <1938dee9-f8e5-ca9a-8f28-efb3ac91bf61@gotplt.org> <23462613-48c0-9fdf-aa89-18c98d9c6656@gotplt.org> <70937aae-cb56-50ad-dd1d-7e6b335ac927@gotplt.org> <605f0816-8a64-1d64-044a-beb5c5ca37bd@foss.arm.com> <74b5295e-2c12-adc1-d27f-342b9b20d84e@gotplt.org> <20201127170216.GU20578@arm.com> In-Reply-To: <20201127170216.GU20578@arm.com> From: "H.J. Lu" Date: Fri, 27 Nov 2020 10:41:43 -0800 Message-ID: Subject: Re: [PATCH v3 2/8] elf: Add a tunable to control use of tagged memory To: Szabolcs Nagy Cc: Richard Earnshaw , GNU C Library , Richard Earnshaw Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3029.6 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 27 Nov 2020 18:42:21 -0000 On Fri, Nov 27, 2020 at 9:02 AM Szabolcs Nagy wrote: > > The 11/27/2020 06:54, H.J. Lu via Libc-alpha wrote: > > On Fri, Nov 27, 2020 at 4:24 AM Richard Earnshaw > > wrote: > > > On 27/11/2020 11:27, Siddhesh Poyarekar wrote: > > > > From a distribution perspective, this could be done in two phases: > > > > > > > > 1. Phase 1 where you ave the tunable which is disabled by default and no > > > > marker present. This makes tagging available to those who want to opt-in > > > > > > > > 2. Phase 2 is where the tunable is now enabled by default and can be > > > > overridden with an opt-out marker. Running this opt-out binary on the > > > > older version is safe (and shouldn't need an ABI bump) since tunables > > > > are disabled by default. > > > > > > > > Does that make sense? If not then I'd really like to see a more > > > > detailed description of how you intend to roll this out. > > > > > > > > Siddhesh > > > > > > Yes, you've captured my thoughts and summarised it better that I was > > > doing myself. Thank you. > > > > > > > We need a plan for binary marker first. > > if we enable heap tagging in those two phases then the first > phase has no abi commitment (tunables are not abi stable). > > heap tagging will not be very useful in phase 1 but at least > users can start testing it and report back issues. (assuming > they have hardware or emulator.) > > i was hoping we can have an abi stable env var ui, but i'm > fine with tunables only since that sounds the safest. > (if we wait for the marking design and binutils etc support > then we have less chance to see deployment problems early.) We should try to get it right if it will be installed as the system glibc. -- H.J.