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 AF885C07E85 for ; Tue, 11 Dec 2018 11:37:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6F7812081B for ; Tue, 11 Dec 2018 11:37:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6F7812081B 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 S1726375AbeLKLhs (ORCPT ); Tue, 11 Dec 2018 06:37:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39646 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726130AbeLKLhs (ORCPT ); Tue, 11 Dec 2018 06:37:48 -0500 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 989C5308212D; Tue, 11 Dec 2018 11:37:47 +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 01F445D9CC; Tue, 11 Dec 2018 11:37:43 +0000 (UTC) From: Florian Weimer To: Catalin Marinas Cc: Arnd Bergmann , Andy Lutomirski , "H.J. Lu" , the arch/x86 maintainers , Linux Kernel Mailing List , Linux API , "H. Peter Anvin" , Peter Zijlstra , Borislav Petkov , vapier@gentoo.org, Rich Felker , x32@buildd.debian.org, Will Deacon , Linus Torvalds Subject: Re: Can we drop upstream Linux x32 support? References: <20181211113230.GB35824@arrakis.emea.arm.com> Date: Tue, 11 Dec 2018 12:37:42 +0100 In-Reply-To: <20181211113230.GB35824@arrakis.emea.arm.com> (Catalin Marinas's message of "Tue, 11 Dec 2018 11:32:31 +0000") Message-ID: <87efaoxpix.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 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Tue, 11 Dec 2018 11:37:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Catalin Marinas: > On Tue, Dec 11, 2018 at 10:02:45AM +0100, Arnd Bergmann wrote: >> On Tue, Dec 11, 2018 at 6:35 AM Andy Lutomirski wrote: >> > I tried to understand what's going on. As far as I can tell, most of >> > the magic is the fact that __kernel_long_t and __kernel_ulong_t are >> > 64-bit as seen by x32 user code. This means that a decent number of >> > uapi structures are the same on x32 and x86_64. Syscalls that only >> > use structures like this should route to the x86_64 entry points. But >> > the implementation is still highly dubious -- in_compat_syscall() will >> > be *true* in such system calls, >> >> I think the fundamental issue was that the intention had always been >> to use only the 64-bit entry points for system calls, but the most >> complex one we have -- ioctl() -- has to use the compat entry point >> because device drivers define their own data structures using 'long' >> and pointer members and they need translation, as well as >> matching in_compat_syscall() checks. This in turn breaks down >> again whenever a driver defines an ioctl command that takes >> a __kernel_long_t or a derived type like timespec as its argument. > > With arm64 ILP32 we tried to avoid the ioctl() problem by having > __kernel_long_t 32-bit, IOW mimicking the arm32 ABI (compat). The > biggest pain point is signals where the state is completely different > from arm32 (more, wider registers) and can't be dealt with by the compat > layer. I would expect to approach this from the opposite direction: use 64-bit types in places where the 64-bit kernel interface uses 64-bit types. After all, not everyone who is interested in ILP32 has a companion 32-bit architecture which could serve as a model for the application ABI. (If there are conflicts with POSIX, then POSIX needs to be fixed to support this.) Thanks, Florian