From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 014/155] ocfs2: replace zero-length array with flexible-array member Date: Wed, 01 Apr 2020 21:03:48 -0700 Message-ID: <20200402040348.OyJel4HK9%akpm@linux-foundation.org> References: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:48300 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726136AbgDBEDu (ORCPT ); Thu, 2 Apr 2020 00:03:50 -0400 In-Reply-To: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, gechangwei@live.cn, ghe@suse.com, gustavo@embeddedor.com, jlbec@evilplan.org, joseph.qi@linux.alibaba.com, junxiao.bi@oracle.com, linux-mm@kvack.org, mark@fasheh.com, mm-commits@vger.kernel.org, piaojun@huawei.com, torvalds@linux-foundation.org From: "Gustavo A. R. Silva" Subject: ocfs2: replace zero-length array with flexible-array member 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") Link: http://lkml.kernel.org/r/20200213160244.GA6088@embeddedor Signed-off-by: Gustavo A. R. Silva Acked-by: Joseph Qi Cc: Mark Fasheh Cc: Joel Becker Cc: Junxiao Bi Cc: Changwei Ge Cc: Gang He Cc: Jun Piao Signed-off-by: Andrew Morton --- fs/ocfs2/journal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/fs/ocfs2/journal.c~ocfs2-replace-zero-length-array-with-flexible-array-member +++ a/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) _