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=-13.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 83476C4332B for ; Thu, 19 Mar 2020 23:47:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5A4D720740 for ; Thu, 19 Mar 2020 23:47:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727207AbgCSXrq (ORCPT ); Thu, 19 Mar 2020 19:47:46 -0400 Received: from mga04.intel.com ([192.55.52.120]:23507 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726663AbgCSXrq (ORCPT ); Thu, 19 Mar 2020 19:47:46 -0400 IronPort-SDR: 9dD2uojPZvTES1JeE4uKY8crjQ//qthW79N8IbYrDZjW2g2W3rv7VzHHTqZIBeGdTrcjYmQx7F c3DYXtX0jLog== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Mar 2020 16:47:45 -0700 IronPort-SDR: bHiYt5HDMIE9YwlgXNYceQMPMy1leuD0nyfCae+QpsBK3aDPbY2OM/ttnZi/gQiGEcEYRWqsQy /wmgw4ygKKLA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,573,1574150400"; d="scan'208";a="263895304" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by orsmga002.jf.intel.com with ESMTP; 19 Mar 2020 16:47:45 -0700 Date: Thu, 19 Mar 2020 16:47:44 -0700 From: Ira Weiny To: "Gustavo A. R. Silva" Cc: Dan Williams , Vishal Verma , Dave Jiang , linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH][next] nvdimm: nd.h: Replace zero-length array with flexible-array member Message-ID: <20200319234744.GA1688758@iweiny-DESK2.sc.intel.com> References: <20200319230937.GA16648@embeddedor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200319230937.GA16648@embeddedor.com> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 19, 2020 at 06:09:37PM -0500, Gustavo A. R. Silva wrote: > The current codebase makes use of the zero-length array language > extension to the C90 standard, but the preferred mechanism to declare > variable-length types such as these ones is a flexible array member[1][2], > introduced in C99: > > struct foo { > int stuff; > struct boo array[]; > }; > > By making use of the mechanism above, we will get a compiler warning > in case the flexible array does not occur last in the structure, which > will help us prevent some kind of undefined behavior bugs from being > inadvertently introduced[3] to the codebase from now on. > > Also, notice that, dynamic memory allocations won't be affected by > this change: "won't" be affected? My reading of [1] indicates that this change will break the allocation in nd_region_activate() because sizeof() can no longer be used on the base structure? What am I missing? Ira > > "Flexible array members have incomplete type, and so the sizeof operator > may not be applied. As a quirk of the original implementation of > zero-length arrays, sizeof evaluates to zero."[1] > > This issue was found with the help of Coccinelle. > > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > [2] https://github.com/KSPP/linux/issues/21 > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva > --- > drivers/nvdimm/nd.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/nvdimm/nd.h b/drivers/nvdimm/nd.h > index c4d69c1cce55..85dbb2a322b9 100644 > --- a/drivers/nvdimm/nd.h > +++ b/drivers/nvdimm/nd.h > @@ -39,7 +39,7 @@ struct nd_region_data { > int ns_count; > int ns_active; > unsigned int hints_shift; > - void __iomem *flush_wpq[0]; > + void __iomem *flush_wpq[]; > }; > > static inline void __iomem *ndrd_get_flush_wpq(struct nd_region_data *ndrd, > @@ -157,7 +157,7 @@ struct nd_region { > struct nd_interleave_set *nd_set; > struct nd_percpu_lane __percpu *lane; > int (*flush)(struct nd_region *nd_region, struct bio *bio); > - struct nd_mapping mapping[0]; > + struct nd_mapping mapping[]; > }; > > struct nd_blk_region { > -- > 2.23.0 >