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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=unavailable 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 0B5D9C433C1 for ; Tue, 30 Mar 2021 07:32:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AAE9C61953 for ; Tue, 30 Mar 2021 07:32:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230243AbhC3Hb2 (ORCPT ); Tue, 30 Mar 2021 03:31:28 -0400 Received: from mga07.intel.com ([134.134.136.100]:24226 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231133AbhC3HbZ (ORCPT ); Tue, 30 Mar 2021 03:31:25 -0400 IronPort-SDR: KWqsCyN/90bAP5BNkm4Jmscn4o3JGQsraffZ6MYHlxxwPAjzxD3lJcZnE0lGlflqWj3BiOojeb TtY17eMkB/Hg== X-IronPort-AV: E=McAfee;i="6000,8403,9938"; a="255703138" X-IronPort-AV: E=Sophos;i="5.81,290,1610438400"; d="scan'208";a="255703138" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Mar 2021 00:31:24 -0700 IronPort-SDR: c7x/pcWzvq34dYDlYvECbGrDbjnhbf9hSYAEqk3fSTk7qhunnERbK/71WLnzFAGkwgTmXbiO6x 8Smkuo2gSr7g== X-IronPort-AV: E=Sophos;i="5.81,290,1610438400"; d="scan'208";a="418045968" Received: from xguo30-mobl.ccr.corp.intel.com ([10.249.174.220]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Mar 2021 00:31:22 -0700 Message-ID: Subject: Re: [PATCH v2 04/15] ACPI: table: replace __attribute__((packed)) by __packed From: Zhang Rui To: Xiaofei Tan , David Laight , "rjw@rjwysocki.net" , "lenb@kernel.org" , "bhelgaas@google.com" Cc: "linux-acpi@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-pci@vger.kernel.org" , "linuxarm@openeuler.org" Date: Tue, 30 Mar 2021 15:31:19 +0800 In-Reply-To: <34dd3de8-644d-6e44-965a-0991b7027cae@huawei.com> References: <1616831193-17920-1-git-send-email-tanxiaofei@huawei.com> <1616831193-17920-5-git-send-email-tanxiaofei@huawei.com> <6df04be78e544e17b3b57f159312541f@AcuMS.aculab.com> <34dd3de8-644d-6e44-965a-0991b7027cae@huawei.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Tue, 2021-03-30 at 10:23 +0800, Xiaofei Tan wrote: > Hi David, > > On 2021/3/29 18:09, David Laight wrote: > > From: Xiaofei Tan > > > Sent: 27 March 2021 07:46 > > > > > > Replace __attribute__((packed)) by __packed following the > > > advice of checkpatch.pl. > > > > > > Signed-off-by: Xiaofei Tan > > > --- > > > drivers/acpi/acpi_fpdt.c | 6 +++--- > > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > > > diff --git a/drivers/acpi/acpi_fpdt.c b/drivers/acpi/acpi_fpdt.c > > > index a89a806..690a88a 100644 > > > --- a/drivers/acpi/acpi_fpdt.c > > > +++ b/drivers/acpi/acpi_fpdt.c > > > @@ -53,7 +53,7 @@ struct resume_performance_record { > > > u32 resume_count; > > > u64 resume_prev; > > > u64 resume_avg; > > > -} __attribute__((packed)); > > > +} __packed; > > > > > > struct boot_performance_record { > > > struct fpdt_record_header header; > > > @@ -63,13 +63,13 @@ struct boot_performance_record { > > > u64 bootloader_launch; > > > u64 exitbootservice_start; > > > u64 exitbootservice_end; > > > -} __attribute__((packed)); > > > +} __packed; > > > > > > struct suspend_performance_record { > > > struct fpdt_record_header header; > > > u64 suspend_start; > > > u64 suspend_end; > > > -} __attribute__((packed)); > > > +} __packed; > > > > My standard question about 'packed' is whether it is actually > > needed. > > It should only be used if the structures might be misaligned in > > memory. > > If the only problem is that a 64bit item needs to be 32bit aligned > > then a suitable type should be used for those specific fields. > > > > Those all look very dubious - the standard header isn't packed > > so everything must eb assumed to be at least 32bit aligned. > > > > There are also other sub-structures that contain 64bit values. > > These don't contain padding - but that requires 64bit alignement. > > > > The only problematic structure is the last one - which would have > > a 32bit pad after the header. > > Is this even right given than there are explicit alignment pads > > in some of the other structures. > > > > If 64bit alignment isn't guaranteed then a '64bit aligned to 32bit' > > type should be used for the u64 fields. > > > > Yes, some of them has been aligned already, then nothing changed > when > add this "packed ". Maybe the purpose of the original author is for > extension, and can tell others that this struct need be packed. > The patch is upstreamed recently but it was made long time ago. I think the original problem is that one of the address, probably the suspend_performance record, is not 64bit aligned, thus we can not read the proper content of suspend_start and suspend_end, mapped from physical memory. I will try to find a machine to reproduce the problem with all __attribute__((packed)) removed to double confirm this. thanks, rui > > David > > > > - > > Registered Address Lakeside, Bramley Road, Mount Farm, Milton > > Keynes, MK1 1PT, UK > > Registration No: 1397386 (Wales) > > > > > > . > > > >