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=-13.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED,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 37E10C10F27 for ; Tue, 10 Mar 2020 01:07:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 13F0A24649 for ; Tue, 10 Mar 2020 01:07:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726533AbgCJBH3 (ORCPT ); Mon, 9 Mar 2020 21:07:29 -0400 Received: from out30-45.freemail.mail.aliyun.com ([115.124.30.45]:45939 "EHLO out30-45.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726115AbgCJBHZ (ORCPT ); Mon, 9 Mar 2020 21:07:25 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04420;MF=joseph.qi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0Ts9xOYP_1583802441; Received: from JosephdeMacBook-Pro.local(mailfrom:joseph.qi@linux.alibaba.com fp:SMTPD_---0Ts9xOYP_1583802441) by smtp.aliyun-inc.com(127.0.0.1); Tue, 10 Mar 2020 09:07:21 +0800 Subject: Re: [PATCH][next] ocfs2: dlm: Replace zero-length array with flexible-array member To: "Gustavo A. R. Silva" , Mark Fasheh , Joel Becker , Andrew Morton Cc: ocfs2-devel@oss.oracle.com, linux-kernel@vger.kernel.org References: <20200309202016.GA8210@embeddedor> From: Joseph Qi Message-ID: Date: Tue, 10 Mar 2020 09:07:21 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200309202016.GA8210@embeddedor> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/3/10 04:20, 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: > > "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 Acked-by: Joseph Qi > --- > fs/ocfs2/dlm/dlmcommon.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/fs/ocfs2/dlm/dlmcommon.h b/fs/ocfs2/dlm/dlmcommon.h > index 0463dce65bb2..c8a444622faa 100644 > --- a/fs/ocfs2/dlm/dlmcommon.h > +++ b/fs/ocfs2/dlm/dlmcommon.h > @@ -564,7 +564,7 @@ struct dlm_migratable_lockres > // 48 bytes > u8 lvb[DLM_LVB_LEN]; > // 112 bytes > - struct dlm_migratable_lock ml[0]; // 16 bytes each, begins at byte 112 > + struct dlm_migratable_lock ml[]; // 16 bytes each, begins at byte 112 > }; > #define DLM_MIG_LOCKRES_MAX_LEN \ > (sizeof(struct dlm_migratable_lockres) + \ > @@ -601,7 +601,7 @@ struct dlm_convert_lock > > u8 name[O2NM_MAX_NAME_LEN]; > > - s8 lvb[0]; > + s8 lvb[]; > }; > #define DLM_CONVERT_LOCK_MAX_LEN (sizeof(struct dlm_convert_lock)+DLM_LVB_LEN) > > @@ -616,7 +616,7 @@ struct dlm_unlock_lock > > u8 name[O2NM_MAX_NAME_LEN]; > > - s8 lvb[0]; > + s8 lvb[]; > }; > #define DLM_UNLOCK_LOCK_MAX_LEN (sizeof(struct dlm_unlock_lock)+DLM_LVB_LEN) > > @@ -632,7 +632,7 @@ struct dlm_proxy_ast > > u8 name[O2NM_MAX_NAME_LEN]; > > - s8 lvb[0]; > + s8 lvb[]; > }; > #define DLM_PROXY_AST_MAX_LEN (sizeof(struct dlm_proxy_ast)+DLM_LVB_LEN) > >