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 43622C10F25 for ; Tue, 10 Mar 2020 01:07:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1D07124649 for ; Tue, 10 Mar 2020 01:07:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726557AbgCJBHx (ORCPT ); Mon, 9 Mar 2020 21:07:53 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:57727 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726115AbgCJBHx (ORCPT ); Mon, 9 Mar 2020 21:07:53 -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=e01e04400;MF=joseph.qi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0Ts9xOdL_1583802470; Received: from JosephdeMacBook-Pro.local(mailfrom:joseph.qi@linux.alibaba.com fp:SMTPD_---0Ts9xOdL_1583802470) by smtp.aliyun-inc.com(127.0.0.1); Tue, 10 Mar 2020 09:07:50 +0800 Subject: Re: [PATCH][next] ocfs2: ocfs2_fs.h: 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: <20200309202155.GA8432@embeddedor> From: Joseph Qi Message-ID: Date: Tue, 10 Mar 2020 09:07:50 +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: <20200309202155.GA8432@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 04:21, 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/ocfs2_fs.h | 18 +++++++++--------- > 1 file changed, 9 insertions(+), 9 deletions(-) > > diff --git a/fs/ocfs2/ocfs2_fs.h b/fs/ocfs2/ocfs2_fs.h > index 0db4a7ec58a2..0dd8c41bafd4 100644 > --- a/fs/ocfs2/ocfs2_fs.h > +++ b/fs/ocfs2/ocfs2_fs.h > @@ -470,7 +470,7 @@ struct ocfs2_extent_list { > __le16 l_reserved1; > __le64 l_reserved2; /* Pad to > sizeof(ocfs2_extent_rec) */ > -/*10*/ struct ocfs2_extent_rec l_recs[0]; /* Extent records */ > +/*10*/ struct ocfs2_extent_rec l_recs[]; /* Extent records */ > }; > > /* > @@ -484,7 +484,7 @@ struct ocfs2_chain_list { > __le16 cl_count; /* Total chains in this list */ > __le16 cl_next_free_rec; /* Next unused chain slot */ > __le64 cl_reserved1; > -/*10*/ struct ocfs2_chain_rec cl_recs[0]; /* Chain records */ > +/*10*/ struct ocfs2_chain_rec cl_recs[]; /* Chain records */ > }; > > /* > @@ -496,7 +496,7 @@ struct ocfs2_truncate_log { > /*00*/ __le16 tl_count; /* Total records in this log */ > __le16 tl_used; /* Number of records in use */ > __le32 tl_reserved1; > -/*08*/ struct ocfs2_truncate_rec tl_recs[0]; /* Truncate records */ > +/*08*/ struct ocfs2_truncate_rec tl_recs[]; /* Truncate records */ > }; > > /* > @@ -640,7 +640,7 @@ struct ocfs2_local_alloc > __le16 la_size; /* Size of included bitmap, in bytes */ > __le16 la_reserved1; > __le64 la_reserved2; > -/*10*/ __u8 la_bitmap[0]; > +/*10*/ __u8 la_bitmap[]; > }; > > /* > @@ -653,7 +653,7 @@ struct ocfs2_inline_data > * for data, starting at id_data */ > __le16 id_reserved0; > __le32 id_reserved1; > - __u8 id_data[0]; /* Start of user data */ > + __u8 id_data[]; /* Start of user data */ > }; > > /* > @@ -798,7 +798,7 @@ struct ocfs2_dx_entry_list { > * possible in de_entries */ > __le16 de_num_used; /* Current number of > * de_entries entries */ > - struct ocfs2_dx_entry de_entries[0]; /* Indexed dir entries > + struct ocfs2_dx_entry de_entries[]; /* Indexed dir entries > * in a packed array of > * length de_num_used */ > }; > @@ -935,7 +935,7 @@ struct ocfs2_refcount_list { > __le16 rl_used; /* Current number of used records */ > __le32 rl_reserved2; > __le64 rl_reserved1; /* Pad to sizeof(ocfs2_refcount_record) */ > -/*10*/ struct ocfs2_refcount_rec rl_recs[0]; /* Refcount records */ > +/*10*/ struct ocfs2_refcount_rec rl_recs[]; /* Refcount records */ > }; > > > @@ -1021,7 +1021,7 @@ struct ocfs2_xattr_header { > buckets. A block uses > xb_check and sets > this field to zero.) */ > - struct ocfs2_xattr_entry xh_entries[0]; /* xattr entry list. */ > + struct ocfs2_xattr_entry xh_entries[]; /* xattr entry list. */ > }; > > /* > @@ -1207,7 +1207,7 @@ struct ocfs2_local_disk_dqinfo { > /* Header of one chunk of a quota file */ > struct ocfs2_local_disk_chunk { > __le32 dqc_free; /* Number of free entries in the bitmap */ > - __u8 dqc_bitmap[0]; /* Bitmap of entries in the corresponding > + __u8 dqc_bitmap[]; /* Bitmap of entries in the corresponding > * chunk of quota file */ > }; > >