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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 41D76C4360F for ; Thu, 4 Apr 2019 20:33:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 150AF20855 for ; Thu, 4 Apr 2019 20:33:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731077AbfDDUdB (ORCPT ); Thu, 4 Apr 2019 16:33:01 -0400 Received: from mail-qt1-f194.google.com ([209.85.160.194]:38472 "EHLO mail-qt1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726418AbfDDUdA (ORCPT ); Thu, 4 Apr 2019 16:33:00 -0400 Received: by mail-qt1-f194.google.com with SMTP id d13so4920940qth.5 for ; Thu, 04 Apr 2019 13:32:59 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=Qd5Qz/L4RJIuJje79jaJ+hi5IZTEPZF8lGl4Vo7whcI=; b=jfgeUxgmrbti1Pep2R6RIz4A82sP0TcmXU0ZDhH6c2OH0iYq5rypR4FWdpqeXY4ivj SEAsLptJTAx0ePE47geLqh9z1evX4bFiPqzy5itt4Ibg/tHqAXSUWqKxDO3pNt0FJnne HMJ4mHLUYw0ws4/xIkR/VLU2Sp84AFeovHBaWmTmQaWqCrIeDk4pLrXMzjkSo7zMBMyo y+K1kO4Gf+QGRO3wHPLcc7Zi9ii6GYQ+A62IIZETWP6I9gR7ubUTNSyDVJ+nWsH5U2Cw n24pq3pftgHueFXZA4vgiogSDh2Q18y+5/7LLu3MO39SzUPkKahC4K8r3ydNABC/N1dJ rCHg== X-Gm-Message-State: APjAAAXOqc1nwN9IgTyG5Tq4I57K8V+uwFL8sOJrulPHSmMGK0/TRZ1n ZaOp2SG56elBLcJB6Xz1XyQeTw== X-Google-Smtp-Source: APXvYqxkdWCyIk/+1hwOj5L7QQRjswNBbhZSUIYy6gVZ+4QvcQFEPvbC0UESfqaSKofuVjOY1nQOBw== X-Received: by 2002:ac8:14c:: with SMTP id f12mr7739066qtg.138.1554409979358; Thu, 04 Apr 2019 13:32:59 -0700 (PDT) Received: from [10.150.73.190] (214.sub-174-240-132.myvzw.com. [174.240.132.214]) by smtp.gmail.com with ESMTPSA id o50sm12943268qtc.23.2019.04.04.13.32.55 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 04 Apr 2019 13:32:58 -0700 (PDT) Subject: Re: [PATCH 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v7) To: Florian Weimer , Michael Ellerman Cc: Mathieu Desnoyers , Paul Burton , Will Deacon , Boqun Feng , Heiko Carstens , Vasily Gorbik , Martin Schwidefsky , Russell King , Benjamin Herrenschmidt , Paul Mackerras , carlos , Joseph Myers , Szabolcs Nagy , libc-alpha , Thomas Gleixner , Ben Maurer , Peter Zijlstra , "Paul E. McKenney" , Dave Watson , Paul Turner , Rich Felker , linux-kernel , linux-api References: <20190212194253.1951-1-mathieu.desnoyers@efficios.com> <20190212194253.1951-2-mathieu.desnoyers@efficios.com> <5166fbe9-cfe0-8554-abc7-4fc844cf2765@redhat.com> <1965431879.7576.1553529272844.JavaMail.zimbra@efficios.com> <87lg0tosfz.fsf@concordia.ellerman.id.au> <87pnq4zxyj.fsf@oldenburg2.str.redhat.com> From: Carlos O'Donell Message-ID: Date: Thu, 4 Apr 2019 16:32:53 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <87pnq4zxyj.fsf@oldenburg2.str.redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/2/19 3:08 AM, Florian Weimer wrote: > * Michael Ellerman: > >> I'm a bit vague on what we're trying to do here. >> >> But it seems like you want some sort of "eye catcher" prior to the branch? >> >> That value is a valid instruction on current CPUs (rlwimi. >> r5,r24,6,1,9), and even if it wasn't it could become one in future. >> >> If you change it to 0x8053530 that is both a valid instruction and is a >> nop (conditional trap immediate but with no conditions set). > > I think we need something that is very unlikely to appear in the > instruction stream. It's just a marker. The instruction will never be > executed, and it does not have to be a trap, either (I believe that a > standard trap instruction would be a bad choice). I assume you want to avoid a standard trap instruction because it would be common, and so not meet the intent of the RSEQ_SIG choice as being something that is *uncommon* right? It is valuable that it be a trap, particularly for constant pools because it means that a jump into the constant pool will trap. -- Cheers, Carlos. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Carlos O'Donell Subject: Re: [PATCH 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v7) Date: Thu, 4 Apr 2019 16:32:53 -0400 Message-ID: References: <20190212194253.1951-1-mathieu.desnoyers@efficios.com> <20190212194253.1951-2-mathieu.desnoyers@efficios.com> <5166fbe9-cfe0-8554-abc7-4fc844cf2765@redhat.com> <1965431879.7576.1553529272844.JavaMail.zimbra@efficios.com> <87lg0tosfz.fsf@concordia.ellerman.id.au> <87pnq4zxyj.fsf@oldenburg2.str.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87pnq4zxyj.fsf@oldenburg2.str.redhat.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Florian Weimer , Michael Ellerman Cc: Mathieu Desnoyers , Paul Burton , Will Deacon , Boqun Feng , Heiko Carstens , Vasily Gorbik , Martin Schwidefsky , Russell King , Benjamin Herrenschmidt , Paul Mackerras , carlos , Joseph Myers , Szabolcs Nagy , libc-alpha , Thomas Gleixner , Ben Maurer , Peter Zijlstra , "Paul E. McKenney" , Dave Watson , Paul Turner List-Id: linux-api@vger.kernel.org On 4/2/19 3:08 AM, Florian Weimer wrote: > * Michael Ellerman: > >> I'm a bit vague on what we're trying to do here. >> >> But it seems like you want some sort of "eye catcher" prior to the branch? >> >> That value is a valid instruction on current CPUs (rlwimi. >> r5,r24,6,1,9), and even if it wasn't it could become one in future. >> >> If you change it to 0x8053530 that is both a valid instruction and is a >> nop (conditional trap immediate but with no conditions set). > > I think we need something that is very unlikely to appear in the > instruction stream. It's just a marker. The instruction will never be > executed, and it does not have to be a trap, either (I believe that a > standard trap instruction would be a bad choice). I assume you want to avoid a standard trap instruction because it would be common, and so not meet the intent of the RSEQ_SIG choice as being something that is *uncommon* right? It is valuable that it be a trap, particularly for constant pools because it means that a jump into the constant pool will trap. -- Cheers, Carlos.