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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C71BC433EF for ; Wed, 2 Feb 2022 11:36:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343943AbiBBLgs (ORCPT ); Wed, 2 Feb 2022 06:36:48 -0500 Received: from mail.efficios.com ([167.114.26.124]:54762 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241292AbiBBLgp (ORCPT ); Wed, 2 Feb 2022 06:36:45 -0500 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id B785434EB03; Wed, 2 Feb 2022 06:36:44 -0500 (EST) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id BcjIfy6EbqW3; Wed, 2 Feb 2022 06:36:44 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 3A12B34E92B; Wed, 2 Feb 2022 06:36:44 -0500 (EST) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 3A12B34E92B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1643801804; bh=rxS2P9dAZNsnpQt9S56KVrnhmEyCUB0/0QQLFiwcG4M=; h=Date:From:To:Message-ID:MIME-Version; b=fU+aRFidh/q56dL5ZhXWz9i50Q3f6eIBNxRcr3WK9Jv5AmwjHV9KdcZvACpBUgDQ6 ROejxUBkXZnK1hLCtXcFkwFmPaQtAAVy1jegehFEA3PfyqATvXss380XGsiO1pGP+z JsOj5JNv0TOibk/uJUazbrLVf8g55CwQaRWGitHXMt5DKcGDm5clEUsf76Y6G4MwkD bV13tgHVBhJeaWlUiOVitS6ZSYZLZWbGa5rnWuuZVZDinU2luTsOW8VtBHJm9wkl+1 3SqzkIiOaccx1Hd0eRmbnEm5A5OwFmGHgZ2fVn1K5JNNX2+oTHrb6jo88fg1x3FclO HGc2FH+NLd5CQ== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 2orB1KVM8yug; Wed, 2 Feb 2022 06:36:44 -0500 (EST) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id 2BAFA34E9AD; Wed, 2 Feb 2022 06:36:44 -0500 (EST) Date: Wed, 2 Feb 2022 06:36:44 -0500 (EST) From: Mathieu Desnoyers To: Florian Weimer Cc: Chris Kennelly , Paul Turner , Peter Oskolkov , libc-alpha , linux-kernel , Peter Zijlstra Message-ID: <1375227765.27051.1643801804042.JavaMail.zimbra@efficios.com> In-Reply-To: <875ypx1x0d.fsf@oldenburg.str.redhat.com> References: <432231420.24682.1643727496135.JavaMail.zimbra@efficios.com> <87mtja1fuz.fsf@oldenburg.str.redhat.com> <875ypx1x0d.fsf@oldenburg.str.redhat.com> Subject: Re: Aligning tcmalloc with glibc 2.35 rseq ABI MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_4203 (ZimbraWebClient - FF96 (Linux)/8.8.15_GA_4203) Thread-Topic: Aligning tcmalloc with glibc 2.35 rseq ABI Thread-Index: bfYiCaJUUsTdq41BtJE3Fb9JJIH1YA== Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Feb 2, 2022, at 3:41 AM, Florian Weimer fweimer@redhat.com wrote: > * Florian Weimer: > >> * Chris Kennelly: >> >>> Thanks for the heads up. >>> >>> I did have a question about whether the new protocol would introduce >>> an extra memory reference while initializing a critical section. >>> >>> * With initial-exec TLS, I can directly reference __rseq_abi. >>> * With the new ABI, I might need to ask glibc for the address of the >>> registered rseq structure in its thread data. >> >> You can write __rseq_offset to a static/hidden variable in an ELF >> constructor, and then use pretty much the same assembler sequences as >> for initial-exec TLS on most architectures. > > And now I'm kind of worried that we should be using ptrdiff_t for > __rseq_offset because that's what the initial-exec relocations use. 8-/ I suspect the underlying question here is: how likely is it that a libc requires an offset of more than 2GB either way from the thread pointer to allocate its rseq thread area on a 64-bit architecture ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com