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=-10.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,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 36626C47258 for ; Fri, 1 May 2020 20:48:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1C09C216FD for ; Fri, 1 May 2020 20:48:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726626AbgEAUss (ORCPT ); Fri, 1 May 2020 16:48:48 -0400 Received: from mx2.suse.de ([195.135.220.15]:52764 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726045AbgEAUsr (ORCPT ); Fri, 1 May 2020 16:48:47 -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 845B3ABC2; Fri, 1 May 2020 20:48:45 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 4DEE51E129E; Fri, 1 May 2020 22:48:43 +0200 (CEST) Date: Fri, 1 May 2020 22:48:43 +0200 From: Jan Kara To: Arnd Bergmann Cc: Pali =?iso-8859-1?Q?Roh=E1r?= , "linux-kernel@vger.kernel.org" , Jan Kara , Andrew Morton , "Steven J. Magnani" , Al Viro Subject: Re: [PATCH 09/15] udf: avoid gcc-10 zero-length-bounds warnings Message-ID: <20200501204843.GA9544@quack2.suse.cz> References: <20200430213101.135134-1-arnd@arndb.de> <20200430213101.135134-10-arnd@arndb.de> <20200430215450.anfwm4zikvhy2bt5@pali> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 Fri 01-05-20 22:30:27, Arnd Bergmann wrote: > On Thu, Apr 30, 2020 at 11:54 PM Pali Rohár wrote: > > > @@ -360,9 +360,9 @@ struct logicalVolIntegrityDesc { > > > uint8_t logicalVolContentsUse[32]; > > > __le32 numOfPartitions; > > > __le32 lengthOfImpUse; > > > - __le32 freeSpaceTable[0]; > > > __le32 sizeTable[0]; > > > uint8_t impUse[0]; > > > + __le32 freeSpaceTable[]; > > > > Please do not change order of members in these structures. Order is > > strictly defined by ECMA 167 standard and changing them you would just > > confuse reader. In LVID is free space table before size table. > > Ok > > > If you do not like GNU C extension for zero-length arrays then just > > replace it by standard C99 flexible arrays. I think that there is no > > reason to not use standard C99 language constructions, just nobody had > > motivation or time to change (working) code. > > No, the problem is that only the last member can be a flexible array, > so when impUse[] is the last member, freeSpaceTable has to be a zero > length array. > > []> Also this file is semi-synchronized with udftools project in which I > > already replaced all GNU C zero-length arrays by C99 flexible arrays. > > > > You can take inspiration what I did with logicalVolIntegrityDesc: > > https://github.com/pali/udftools/commit/f851d84478ce881d516a76018745fa163f803880#diff-1e1a5b89f620d380f22b973f9449aeaeL381-R384 > > Right, this is likely the best workaround. > > > Anyway, if you have a better idea what to do with such on-disk structure > > and how to represent it in C struct syntax, let me know as it could be > > updated also in udftools project. > > The trick I used for impUse[] would also work for freeSpaceTable[] to avoid > the gcc warning, it's still not great, but maybe you like this better: I like Pali's version somewhat better because whenever I look at several (obviously flexible) arrays in one struct, I start wondering what's going on. So let's not define members of struct whose offset we actually don't know (and thus we cannot sanely use them anyway). Honza > arnd@threadripper:~/arm-soc$ git diff > diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c > index 02f03fadb75b..666d022eb00b 100644 > --- a/fs/udf/balloc.c > +++ b/fs/udf/balloc.c > @@ -98,7 +98,7 @@ static void udf_add_free_space(struct super_block > *sb, u16 partition, u32 cnt) > return; > > lvid = (struct logicalVolIntegrityDesc *)sbi->s_lvid_bh->b_data; > - le32_add_cpu(&lvid->freeSpaceTable[partition], cnt); > + le32_add_cpu(lvid->freeSpaceTable + partition, cnt); > udf_updated_lvid(sb); > } > > diff --git a/fs/udf/ecma_167.h b/fs/udf/ecma_167.h > index 14ffe27342bc..215d97d7edc4 100644 > --- a/fs/udf/ecma_167.h > +++ b/fs/udf/ecma_167.h > @@ -360,9 +360,9 @@ struct logicalVolIntegrityDesc { > uint8_t logicalVolContentsUse[32]; > __le32 numOfPartitions; > __le32 lengthOfImpUse; > __le32 freeSpaceTable[0]; > __le32 sizeTable[0]; > - uint8_t impUse[0]; > + uint8_t impUse[]; > } __packed; > > /* Integrity Type (ECMA 167r3 3/10.10.3) */ > diff --git a/fs/udf/super.c b/fs/udf/super.c > index 379867888c36..a1fc51c2261e 100644 > --- a/fs/udf/super.c > +++ b/fs/udf/super.c > @@ -2517,8 +2517,8 @@ static unsigned int udf_count_free(struct super_block *sb) > (struct logicalVolIntegrityDesc *) > sbi->s_lvid_bh->b_data; > if (le32_to_cpu(lvid->numOfPartitions) > part) { > - accum = le32_to_cpu( > - lvid->freeSpaceTable[part]); > + accum = le32_to_cpup( > + (lvid->freeSpaceTable + part)); > if (accum == 0xFFFFFFFF) > accum = 0; > } > > > > This version could easily be backported to stable kernels to let them be > compiled with gcc-10, and then synchronizing with the udftools version of > the header needs additional changes on top, which do not need to be > backported. > > Arnd -- Jan Kara SUSE Labs, CR