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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,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 9DB57C31E46 for ; Wed, 12 Jun 2019 14:23:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7D00F208CA for ; Wed, 12 Jun 2019 14:23:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2409341AbfFLOXF (ORCPT ); Wed, 12 Jun 2019 10:23:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36884 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726533AbfFLOXF (ORCPT ); Wed, 12 Jun 2019 10:23:05 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E8AA23003AEC; Wed, 12 Jun 2019 14:23:04 +0000 (UTC) Received: from oldenburg2.str.redhat.com (unknown [10.36.118.125]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 77A8C5D9CA; Wed, 12 Jun 2019 14:22:57 +0000 (UTC) From: Florian Weimer To: Mathieu Desnoyers 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 Subject: Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup and thread creation (v10) References: <20190503184219.19266-1-mathieu.desnoyers@efficios.com> <875zprm4jo.fsf@oldenburg2.str.redhat.com> <732661684.21584.1559314109886.JavaMail.zimbra@efficios.com> <87muj2k4ov.fsf@oldenburg2.str.redhat.com> <1528929896.22217.1559326257155.JavaMail.zimbra@efficios.com> <87o93d4lqb.fsf@oldenburg2.str.redhat.com> <117220011.27079.1559663870037.JavaMail.zimbra@efficios.com> <87wohzorj0.fsf@oldenburg2.str.redhat.com> <1329439108.43041.1560348962006.JavaMail.zimbra@efficios.com> Date: Wed, 12 Jun 2019 16:22:55 +0200 In-Reply-To: <1329439108.43041.1560348962006.JavaMail.zimbra@efficios.com> (Mathieu Desnoyers's message of "Wed, 12 Jun 2019 10:16:02 -0400 (EDT)") Message-ID: <87blz27uio.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Wed, 12 Jun 2019 14:23:05 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Mathieu Desnoyers: >> It's the registration from libc.so which needs some care. In >> particular, we must not override an existing registration. > > OK, so it could check if __rseq_abi.cpu_id is -1, and only > perform registration if it is the case. Or do you have another > approach in mind ? No, __rseq_abi will not be shared with the outer libc, so the inner libc will always see -1 there, even if the outer libc has performed registration. libio/vtables.c has some example what you can do: /* In case this libc copy is in a non-default namespace, we always need to accept foreign vtables because there is always a possibility that FILE * objects are passed across the linking boundary. */ { Dl_info di; struct link_map *l; if (!rtld_active () || (_dl_addr (_IO_vtable_check, &di, &l, NULL) != 0 && l->l_ns != LM_ID_BASE)) return; } _IO_vtable_check would have to be replaced with your own function; the actual function doesn't really matter. The rtld_active check covers the static dlopen case, where rtld_active () is false in the inner libc. Thanks, Florian