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=-5.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 7ED88C31E44 for ; Fri, 14 Jun 2019 10:14:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 38D832084E for ; Fri, 14 Jun 2019 10:14:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="hitN2muT" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727283AbfFNKOM (ORCPT ); Fri, 14 Jun 2019 06:14:12 -0400 Received: from mail.efficios.com ([167.114.142.138]:37836 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726951AbfFNKOM (ORCPT ); Fri, 14 Jun 2019 06:14:12 -0400 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 8698325156E; Fri, 14 Jun 2019 06:14:10 -0400 (EDT) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id nA8w-lK6TlPi; Fri, 14 Jun 2019 06:14:10 -0400 (EDT) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id F4175251563; Fri, 14 Jun 2019 06:14:09 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com F4175251563 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1560507250; bh=Mf1RtqNecFmDuZIOTCNNi4jRodfbuTrPr7L+AaQPg5w=; h=Date:From:To:Message-ID:MIME-Version; b=hitN2muTkDmoGrBacLuoX6vzik6K4AZ0zwjjihSkuuftRsx/VQ9Uyk28KA8+kAZ+E A2O0LVlgq1tfifc74u/BgLBunHHEJiZiWi0KRbW0Md24GX8jbfHI2Bx40z0VgxJOcT /mbl3exRUeBF+lTIcnjuOzDQt7aOUkuLRX8vtj2yT9yZYs2Lw8ePz+X7j386V6xBfd 4/ui8urMQ8o+tNtZFE8p5eo6jA6BesW9x2AqfopI+Wb+NCtLZ8PlnVs2sMb24a9b2D I/1fCMZIHkxSixqdWS8rmEtSj4PGzyCiIMDhUesCzWSEZ3PGYQPPqXDIEXynGT0434 ++peFSjmP4knw== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id 3Hs2xVKoMsEa; Fri, 14 Jun 2019 06:14:09 -0400 (EDT) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id D755B25155D; Fri, 14 Jun 2019 06:14:09 -0400 (EDT) Date: Fri, 14 Jun 2019 06:14:09 -0400 (EDT) From: Mathieu Desnoyers To: Florian Weimer Cc: carlos , Joseph Myers , Szabolcs Nagy , libc-alpha , Thomas Gleixner , Ben Maurer , Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , Will Deacon , Dave Watson , Paul Turner , Rich Felker , linux-kernel , linux-api Message-ID: <1635690189.3049.1560507249693.JavaMail.zimbra@efficios.com> In-Reply-To: <87ftocwkei.fsf@oldenburg2.str.redhat.com> References: <20190503184219.19266-1-mathieu.desnoyers@efficios.com> <87o93d4lqb.fsf@oldenburg2.str.redhat.com> <117220011.27079.1559663870037.JavaMail.zimbra@efficios.com> <87wohzorj0.fsf@oldenburg2.str.redhat.com> <914051741.43025.1560348011775.JavaMail.zimbra@efficios.com> <802638054.3032.1560506584705.JavaMail.zimbra@efficios.com> <87ftocwkei.fsf@oldenburg2.str.redhat.com> Subject: Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup and thread creation (v10) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.12_GA_3803 (ZimbraWebClient - FF67 (Linux)/8.8.12_GA_3794) Thread-Topic: glibc: Perform rseq(2) registration at C startup and thread creation (v10) Thread-Index: kYRcFH9aozKT8hkvRfqxQ+J8ADLHgA== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Jun 14, 2019, at 12:06 PM, Florian Weimer fweimer@redhat.com wrote: > * Mathieu Desnoyers: > >> ----- On Jun 12, 2019, at 4:00 PM, Mathieu Desnoyers >> mathieu.desnoyers@efficios.com wrote: >> >>> ----- On Jun 10, 2019, at 4:43 PM, carlos carlos@redhat.com wrote: >>> >>>> On 6/6/19 7:57 AM, Florian Weimer wrote: >>>>> Let me ask the key question again: Does it matter if code observes the >>>>> rseq area first without kernel support, and then with kernel support? >>>>> If we don't expect any problems immediately, we do not need to worry >>>>> much about the constructor ordering right now. I expect that over time, >>>>> fixing this properly will become easier. >>>> >>>> I just wanted to chime in and say that splitting this into: >>>> >>>> * Ownership (__rseq_handled) >>>> >>>> * Initialization (__rseq_abi) >>>> >>>> Makes sense to me. >>>> >>>> I agree we need an answer to this question of ownership but not yet >>>> initialized, to owned and initialized. >>>> >>>> I like the idea of having __rseq_handled in ld.so. >>> >>> Very good, so I'll implement this approach. Sorry for the delayed >>> feedback, I am traveling this week. >> >> I had issues with cases where application or LD_PRELOAD library also >> define the __rseq_handled symbol. They appear not to see the same >> address as the one initialized by ld.so. > > What exactly did you do? How did you determine the addresses? How is > __rseq_handled defined in ld.so? The easiest way to answer these questions is through links to my github dev branch: https://github.com/compudj/glibc-dev/tree/glibc-rseq specifically this commit: https://github.com/compudj/glibc-dev/commit/c49a286497d065a7fc00aafd846e6edce14f97fc and this attempt at using GL(): https://github.com/compudj/glibc-dev/commit/8a02acfbb6943672bfa36b4fc6f61905ee4fa180 My test programs are: * a.c: #include #include extern __thread struct rseq __rseq_abi __attribute__ ((tls_model ("initial-exec")));/* = { .cpu_id = -1, };*/ extern int __rseq_handled; int main() { fprintf(stderr, "__rseq_handled main: %d %p\n", __rseq_handled, &__rseq_handled); fprintf(stderr, "__rseq_abi.cpu_id main: %d %p\n", __rseq_abi.cpu_id, &__rseq_abi); return 0; } * s.c: #include #include #if 0 __thread struct rseq __rseq_abi __attribute__ ((tls_model ("initial-exec"))) = { .cpu_id = -1, }; int __rseq_handled; #else extern __thread struct rseq __rseq_abi __attribute__ ((tls_model ("initial-exec"))); extern int __rseq_handled; #endif void __attribute__((constructor)) myinit(void) { fprintf(stderr, "__rseq_handled s.so: %d %p\n", __rseq_handled, &__rseq_handled); fprintf(stderr, "__rseq_abi.cpu_id s.so: %d %p\n", __rseq_abi.cpu_id, &__rseq_abi); } * Makefile: LIBCPATH=/home/efficios/glibc-test/lib KERNEL_HEADERS=/home/efficios/git/linux-percpu-dev/usr/include CFLAGS=-I${KERNEL_HEADERS} -L${LIBCPATH} -Wl,--rpath=${LIBCPATH} -Wl,--dynamic-linker=${LIBCPATH}/ld-linux-x86-64.so.2 all: gcc ${CFLAGS} -o a a.c gcc ${CFLAGS} -shared -fPIC -o s.so s.c Thanks, Mathieu > > Thanks, > Florian -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com