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=-2.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 340A4C5CFFE for ; Tue, 11 Dec 2018 15:29:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E70D520849 for ; Tue, 11 Dec 2018 15:29:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E70D520849 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 S1727051AbeLKP35 (ORCPT ); Tue, 11 Dec 2018 10:29:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39235 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726839AbeLKP35 (ORCPT ); Tue, 11 Dec 2018 10:29:57 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 04DAB3001582; Tue, 11 Dec 2018 15:29:57 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.131]) by smtp.corp.redhat.com (Postfix) with SMTP id 0FA15608F7; Tue, 11 Dec 2018 15:29:54 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 11 Dec 2018 16:29:56 +0100 (CET) Date: Tue, 11 Dec 2018 16:29:54 +0100 From: Oleg Nesterov To: "Dmitry V. Levin" Cc: Andy Lutomirski , Elvira Khabirova , Eugene Syromyatnikov , Kees Cook , Jann Horn , linux-api@vger.kernel.org, strace-devel@lists.strace.io, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 24/25] ptrace: add PTRACE_GET_SYSCALL_INFO request Message-ID: <20181211152953.GA8504@redhat.com> References: <20181210042352.GA6092@altlinux.org> <20181210043126.GX6131@altlinux.org> <20181210141107.GB4177@redhat.com> <20181210162131.GG14149@altlinux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181210162131.GG14149@altlinux.org> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Tue, 11 Dec 2018 15:29:57 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/10, Dmitry V. Levin wrote: > > On Mon, Dec 10, 2018 at 03:11:07PM +0100, Oleg Nesterov wrote: > > On 12/10, Dmitry V. Levin wrote: > > > > > > +struct ptrace_syscall_info { > > > + __u8 op; /* PTRACE_SYSCALL_INFO_* */ > > > + __u8 __pad0[3]; > > > + __u32 arch; > > > + __u64 instruction_pointer; > > > + __u64 stack_pointer; > > > + __u64 frame_pointer; > > > + union { > > > + struct { > > > + __u64 nr; > > > + __u64 args[6]; > > > + } entry; > > > + struct { > > > + __s64 rval; > > > + __u8 is_error; > > > + __u8 __pad1[7]; > > > + } exit; > > > + struct { > > > + __u64 nr; > > > + __u64 args[6]; > > > + __u32 ret_data; > > > + __u8 __pad2[4]; > > > + } seccomp; > > > + }; > > > +}; > > > > Could you explain why ptrace_syscall_info needs __pad{0,1,2} ? I simply can't > > understand why... > > I suppose the idea behind the use of these pads was to make the structure > arch-independent. Still can't understand... are you saying that without (say) __pad2[4] sizeof(ptrace_syscall_info) or offsetofend(ptrace_syscall_info, seccomp) will depend on arch? Or what? I am just curious. > I don't think we really need to keep it exactly the same on all > architectures - the only practical requirement is to avoid any compat > issues, but I don't mind keeping the structure arch-independent. OK, but may be you can add a short comment to explain these pads. Oleg.