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 6C9F5C10F25 for ; Tue, 10 Mar 2020 01:06:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 44B7D24649 for ; Tue, 10 Mar 2020 01:06:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726402AbgCJBGg (ORCPT ); Mon, 9 Mar 2020 21:06:36 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:59064 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726115AbgCJBGg (ORCPT ); Mon, 9 Mar 2020 21:06:36 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R211e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04407;MF=joseph.qi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0Ts9yW7e_1583802391; Received: from JosephdeMacBook-Pro.local(mailfrom:joseph.qi@linux.alibaba.com fp:SMTPD_---0Ts9yW7e_1583802391) by smtp.aliyun-inc.com(127.0.0.1); Tue, 10 Mar 2020 09:06:32 +0800 Subject: Re: [PATCH][next] ocfs2: cluster: 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: <20200309201907.GA8005@embeddedor> From: Joseph Qi Message-ID: <3509c78c-4387-f248-ee66-6218c1264fcf@linux.alibaba.com> Date: Tue, 10 Mar 2020 09:06:31 +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: <20200309201907.GA8005@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 04:19, 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/cluster/tcp.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/ocfs2/cluster/tcp.h b/fs/ocfs2/cluster/tcp.h > index de87cbffd175..736338f45c59 100644 > --- a/fs/ocfs2/cluster/tcp.h > +++ b/fs/ocfs2/cluster/tcp.h > @@ -32,7 +32,7 @@ struct o2net_msg > __be32 status; > __be32 key; > __be32 msg_num; > - __u8 buf[0]; > + __u8 buf[]; > }; > > typedef int (o2net_msg_handler_func)(struct o2net_msg *msg, u32 len, void *data, > From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joseph Qi Date: Tue, 10 Mar 2020 09:06:31 +0800 Subject: [Ocfs2-devel] [PATCH][next] ocfs2: cluster: Replace zero-length array with flexible-array member In-Reply-To: <20200309201907.GA8005@embeddedor> References: <20200309201907.GA8005@embeddedor> Message-ID: <3509c78c-4387-f248-ee66-6218c1264fcf@linux.alibaba.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Gustavo A. R. Silva" , Mark Fasheh , Joel Becker , Andrew Morton Cc: ocfs2-devel@oss.oracle.com, linux-kernel@vger.kernel.org On 2020/3/10 04:19, 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://urldefense.com/v3/__https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html__;!!GqivPVa7Brio!INdYafacLMiUgRrK-HDy3FhbqtTkRakuBQtEmPbN6cZAHCDBAvGOTj194lmB8udIjmmjqw$ > [2] https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/21__;!!GqivPVa7Brio!INdYafacLMiUgRrK-HDy3FhbqtTkRakuBQtEmPbN6cZAHCDBAvGOTj194lmB8ufEoscJWg$ > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva Acked-by: Joseph Qi > --- > fs/ocfs2/cluster/tcp.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/ocfs2/cluster/tcp.h b/fs/ocfs2/cluster/tcp.h > index de87cbffd175..736338f45c59 100644 > --- a/fs/ocfs2/cluster/tcp.h > +++ b/fs/ocfs2/cluster/tcp.h > @@ -32,7 +32,7 @@ struct o2net_msg > __be32 status; > __be32 key; > __be32 msg_num; > - __u8 buf[0]; > + __u8 buf[]; > }; > > typedef int (o2net_msg_handler_func)(struct o2net_msg *msg, u32 len, void *data, >