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, 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 EED44C3F2D1 for ; Tue, 3 Mar 2020 01:17:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CB7192465E for ; Tue, 3 Mar 2020 01:17:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726915AbgCCBRb (ORCPT ); Mon, 2 Mar 2020 20:17:31 -0500 Received: from out30-54.freemail.mail.aliyun.com ([115.124.30.54]:41784 "EHLO out30-54.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726752AbgCCBRb (ORCPT ); Mon, 2 Mar 2020 20:17:31 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04426;MF=joseph.qi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0TrVMJ8Z_1583198246; Received: from JosephdeMacBook-Pro.local(mailfrom:joseph.qi@linux.alibaba.com fp:SMTPD_---0TrVMJ8Z_1583198246) by smtp.aliyun-inc.com(127.0.0.1); Tue, 03 Mar 2020 09:17:26 +0800 Subject: Re: [PATCH] ocfs2: 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: <20200213160244.GA6088@embeddedor> <1b78acd5-2b5f-55f1-5571-73f45d3c87f7@embeddedor.com> From: Joseph Qi Message-ID: <30493b5f-752d-147f-3d64-95b1c59895ae@linux.alibaba.com> Date: Tue, 3 Mar 2020 09:17:26 +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: <1b78acd5-2b5f-55f1-5571-73f45d3c87f7@embeddedor.com> 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 Sorry for the late replay since I've missed the original mail. This patch looks good to me. Acked-by: Joseph Qi On 2020/3/3 07:57, Gustavo A. R. Silva wrote: > Hi all, > > Friendly ping: Who can take this? > > Thanks > -- > Gustavo > > On 2/13/20 10:02, 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 >> --- >> fs/ocfs2/journal.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c >> index 68ba354cf361..b425f0b01dce 100644 >> --- a/fs/ocfs2/journal.c >> +++ b/fs/ocfs2/journal.c >> @@ -91,7 +91,7 @@ enum ocfs2_replay_state { >> struct ocfs2_replay_map { >> unsigned int rm_slots; >> enum ocfs2_replay_state rm_state; >> - unsigned char rm_replay_slots[0]; >> + unsigned char rm_replay_slots[]; >> }; >> >> static void ocfs2_replay_map_set_state(struct ocfs2_super *osb, int state) >> From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joseph Qi Date: Tue, 3 Mar 2020 09:17:26 +0800 Subject: [Ocfs2-devel] [PATCH] ocfs2: Replace zero-length array with flexible-array member In-Reply-To: <1b78acd5-2b5f-55f1-5571-73f45d3c87f7@embeddedor.com> References: <20200213160244.GA6088@embeddedor> <1b78acd5-2b5f-55f1-5571-73f45d3c87f7@embeddedor.com> Message-ID: <30493b5f-752d-147f-3d64-95b1c59895ae@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 Sorry for the late replay since I've missed the original mail. This patch looks good to me. Acked-by: Joseph Qi On 2020/3/3 07:57, Gustavo A. R. Silva wrote: > Hi all, > > Friendly ping: Who can take this? > > Thanks > -- > Gustavo > > On 2/13/20 10:02, 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!IqIf1kXINaofUdjTQKfUAjzgxIXeGsrvqMv7P5eK_l094j-wNPLRzzZ6U0LKmQmDvBq4SA$ >> [2] https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/21__;!!GqivPVa7Brio!IqIf1kXINaofUdjTQKfUAjzgxIXeGsrvqMv7P5eK_l094j-wNPLRzzZ6U0LKmQmeutI_Bg$ >> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") >> >> Signed-off-by: Gustavo A. R. Silva >> --- >> fs/ocfs2/journal.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c >> index 68ba354cf361..b425f0b01dce 100644 >> --- a/fs/ocfs2/journal.c >> +++ b/fs/ocfs2/journal.c >> @@ -91,7 +91,7 @@ enum ocfs2_replay_state { >> struct ocfs2_replay_map { >> unsigned int rm_slots; >> enum ocfs2_replay_state rm_state; >> - unsigned char rm_replay_slots[0]; >> + unsigned char rm_replay_slots[]; >> }; >> >> static void ocfs2_replay_map_set_state(struct ocfs2_super *osb, int state) >>