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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 EB707C43603 for ; Sun, 15 Dec 2019 19:49:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C3B9824676 for ; Sun, 15 Dec 2019 19:49:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726512AbfLOTt0 (ORCPT ); Sun, 15 Dec 2019 14:49:26 -0500 Received: from albireo.enyo.de ([37.24.231.21]:38274 "EHLO albireo.enyo.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726219AbfLOTtZ (ORCPT ); Sun, 15 Dec 2019 14:49:25 -0500 Received: from [172.17.203.2] (helo=deneb.enyo.de) by albireo.enyo.de with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) id 1igZtC-0008Hm-Si; Sun, 15 Dec 2019 19:49:14 +0000 Received: from fw by deneb.enyo.de with local (Exim 4.92) (envelope-from ) id 1igZsO-0002ti-DI; Sun, 15 Dec 2019 20:48:24 +0100 From: Florian Weimer To: Aleksa Sarai Cc: Alexander Viro , Jeff Layton , "J. Bruce Fields" , Shuah Khan , dev@opencontainers.org, containers@lists.linux-foundation.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH] openat2: switch to __attribute__((packed)) for open_how References: <20191213222351.14071-1-cyphar@cyphar.com> Date: Sun, 15 Dec 2019 20:48:24 +0100 In-Reply-To: <20191213222351.14071-1-cyphar@cyphar.com> (Aleksa Sarai's message of "Sat, 14 Dec 2019 09:23:50 +1100") Message-ID: <87o8w9bcaf.fsf@mid.deneb.enyo.de> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Aleksa Sarai: > diff --git a/tools/testing/selftests/openat2/helpers.h b/tools/testing/selftests/openat2/helpers.h > index 43ca5ceab6e3..eb1535c8fa2e 100644 > --- a/tools/testing/selftests/openat2/helpers.h > +++ b/tools/testing/selftests/openat2/helpers.h > @@ -32,17 +32,16 @@ > * O_TMPFILE} are set. > * > * @flags: O_* flags. > - * @mode: O_CREAT/O_TMPFILE file mode. > * @resolve: RESOLVE_* flags. > + * @mode: O_CREAT/O_TMPFILE file mode. > */ > struct open_how { > - __aligned_u64 flags; > + __u64 flags; > + __u64 resolve; > __u16 mode; > - __u16 __padding[3]; /* must be zeroed */ > - __aligned_u64 resolve; > -}; > +} __attribute__((packed)); > > -#define OPEN_HOW_SIZE_VER0 24 /* sizeof first published struct */ > +#define OPEN_HOW_SIZE_VER0 18 /* sizeof first published struct */ > #define OPEN_HOW_SIZE_LATEST OPEN_HOW_SIZE_VER0 A userspace ABI that depends on GCC extensions probably isn't a good idea. Even with GCC, it will not work well with some future extensions because it pretty much rules out having arrays or other members that are access through pointers. Current GCC does not carry over the packed-ness of the struct to addresses of its members.