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=-0.9 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 722C7C65BAE for ; Thu, 13 Dec 2018 16:05:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3FB8920870 for ; Thu, 13 Dec 2018 16:05:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3FB8920870 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729516AbeLMQFJ (ORCPT ); Thu, 13 Dec 2018 11:05:09 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57552 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728682AbeLMQFJ (ORCPT ); Thu, 13 Dec 2018 11:05:09 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 23C1081DFA; Thu, 13 Dec 2018 16:05:08 +0000 (UTC) Received: from oldenburg2.str.redhat.com (ovpn-116-82.ams2.redhat.com [10.36.116.82]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 211536012B; Thu, 13 Dec 2018 16:05:01 +0000 (UTC) From: Florian Weimer To: Rich Felker Cc: Catalin Marinas , Andy Lutomirski , tg@mirbsd.de, Linus Torvalds , X86 ML , LKML , Linux API , "H. Peter Anvin" , Peter Zijlstra , Borislav Petkov , Mike Frysinger , "H. J. Lu" , x32@buildd.debian.org, Arnd Bergmann , Will Deacon Subject: Re: Can we drop upstream Linux x32 support? References: <20181212165237.GT23599@brightrain.aerifal.cx> <20181213124025.bczxzj6ez34joo6v@localhost> <20181213155744.GU23599@brightrain.aerifal.cx> Date: Thu, 13 Dec 2018 17:04:59 +0100 In-Reply-To: <20181213155744.GU23599@brightrain.aerifal.cx> (Rich Felker's message of "Thu, 13 Dec 2018 10:57:44 -0500") Message-ID: <87o99pl8es.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Thu, 13 Dec 2018 16:05:08 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Rich Felker: >> If the compiler can handle the zeroing, that would be great, though not >> sure how (some __attribute__((zero)) which generates a type constructor >> for such structure; it kind of departs from what the C language offers). > > The compiler fundamentally can't. At the very least it would require > effective type tracking, which requires shadow memory and is even more > controversial than -fstrict-aliasing (because in a sense it's a > stronger version thereof). It's possible to do it with the right types. See _Bool on 32-bit Darwin PowerPC for an example, which is four bytes instead of the usual one. Similarly, we could have integer types with trap representations. Whether it is a good idea is a different matter, but the amount of compiler magic required is actually limited. Thanks, Florian