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=-13.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 58049C18E5B for ; Mon, 16 Mar 2020 14:57:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 377CA20719 for ; Mon, 16 Mar 2020 14:57:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731719AbgCPO5w (ORCPT ); Mon, 16 Mar 2020 10:57:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:34096 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731636AbgCPO5v (ORCPT ); Mon, 16 Mar 2020 10:57:51 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 69629B131; Mon, 16 Mar 2020 14:57:47 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 145F11E10DA; Mon, 16 Mar 2020 15:57:47 +0100 (CET) Date: Mon, 16 Mar 2020 15:57:47 +0100 From: Jan Kara To: "Gustavo A. R. Silva" Cc: Jan Kara , linux-kernel@vger.kernel.org Subject: Re: [PATCH][next] udf: udf_sb.h: Replace zero-length array with flexible-array member Message-ID: <20200316145747.GB22684@quack2.suse.cz> References: <20200309202715.GA9428@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200309202715.GA9428@embeddedor> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 09-03-20 15:27:15, 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 Thanks. I've added the patch to my tree. > --- > fs/udf/udf_sb.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/udf/udf_sb.h b/fs/udf/udf_sb.h > index 3d83be54c474..65280ae009e0 100644 > --- a/fs/udf/udf_sb.h > +++ b/fs/udf/udf_sb.h > @@ -83,7 +83,7 @@ struct udf_virtual_data { > struct udf_bitmap { > __u32 s_extPosition; > int s_nr_groups; > - struct buffer_head *s_block_bitmap[0]; > + struct buffer_head *s_block_bitmap[]; > }; > > struct udf_part_map { > -- > 2.25.0 > -- Jan Kara SUSE Labs, CR