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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,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 5C9AEC38A2A for ; Thu, 7 May 2020 18:47:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3430420870 for ; Thu, 7 May 2020 18:47:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877261; bh=Q87e/4coWysbUm2Zo1Y28X2901o7xCuO/CduL7ySatE=; h=Date:From:To:Cc:Subject:List-ID:From; b=eIxmlCtnBYJXlFiLX77yFMm8HT73BArhOp+s+YAMaikzoR2Mvx1h1PayCh7Shx1W5 FGHjkAdUgqqSfOxwBtEri6CUr/PQqmziPn0Jv6n/EQKGFJoLmm0wrQ/kcTm9qeuAvv 62wQNjogeX3WT0dSaojCmrqO22BsyyMwM6N8xzsc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728329AbgEGSrk (ORCPT ); Thu, 7 May 2020 14:47:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:48236 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726467AbgEGSrj (ORCPT ); Thu, 7 May 2020 14:47:39 -0400 Received: from embeddedor (unknown [189.207.59.248]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CAC12221F7; Thu, 7 May 2020 18:47:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877259; bh=Q87e/4coWysbUm2Zo1Y28X2901o7xCuO/CduL7ySatE=; h=Date:From:To:Cc:Subject:From; b=TKflrXuGzDcOT9OuYsvV4mzUc3IDYcsfR6UjVJ0RBjwsTw0euPU8Yos0Cn8m4Pyzt qomcqLn7oqZvZldpyglWjVsuXZGoHG14rME6VkhBnT4ZnBZcr36toO9/xby0Pl0g6U iRBjJ3tozPrS1zkA2jshtMs6CkZIEN4w02Lcilr8= Date: Thu, 7 May 2020 13:52:05 -0500 From: "Gustavo A. R. Silva" To: Christine Caulfield , David Teigland Cc: cluster-devel@redhat.com, linux-kernel@vger.kernel.org Subject: [PATCH] dlm: Replace zero-length array with flexible-array Message-ID: <20200507185205.GA14139@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. 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/dlm/dlm_internal.h | 6 +++--- fs/dlm/user.c | 2 +- 2 files changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/dlm/dlm_internal.h b/fs/dlm/dlm_internal.h index 416d9de35679..d231ae5d2c65 100644 --- a/fs/dlm/dlm_internal.h +++ b/fs/dlm/dlm_internal.h @@ -421,7 +421,7 @@ struct dlm_message { int m_bastmode; int m_asts; int m_result; /* 0 or -EXXX */ - char m_extra[0]; /* name or lvb */ + char m_extra[]; /* name or lvb */ }; @@ -450,7 +450,7 @@ struct dlm_rcom { uint64_t rc_id; /* match reply with request */ uint64_t rc_seq; /* sender's ls_recover_seq */ uint64_t rc_seq_reply; /* remote ls_recover_seq */ - char rc_buf[0]; + char rc_buf[]; }; union dlm_packet { @@ -506,7 +506,7 @@ struct rcom_lock { __le16 rl_wait_type; __le16 rl_namelen; char rl_name[DLM_RESNAME_MAXLEN]; - char rl_lvb[0]; + char rl_lvb[]; }; /* diff --git a/fs/dlm/user.c b/fs/dlm/user.c index 5264bac75115..e5cefa90b1ce 100644 --- a/fs/dlm/user.c +++ b/fs/dlm/user.c @@ -46,7 +46,7 @@ struct dlm_lock_params32 { __u32 bastaddr; __u32 lksb; char lvb[DLM_USER_LVB_LEN]; - char name[0]; + char name[]; }; struct dlm_write_request32 { From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gustavo A. R. Silva Date: Thu, 7 May 2020 13:52:05 -0500 Subject: [Cluster-devel] [PATCH] dlm: Replace zero-length array with flexible-array Message-ID: <20200507185205.GA14139@embeddedor> List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. 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/dlm/dlm_internal.h | 6 +++--- fs/dlm/user.c | 2 +- 2 files changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/dlm/dlm_internal.h b/fs/dlm/dlm_internal.h index 416d9de35679..d231ae5d2c65 100644 --- a/fs/dlm/dlm_internal.h +++ b/fs/dlm/dlm_internal.h @@ -421,7 +421,7 @@ struct dlm_message { int m_bastmode; int m_asts; int m_result; /* 0 or -EXXX */ - char m_extra[0]; /* name or lvb */ + char m_extra[]; /* name or lvb */ }; @@ -450,7 +450,7 @@ struct dlm_rcom { uint64_t rc_id; /* match reply with request */ uint64_t rc_seq; /* sender's ls_recover_seq */ uint64_t rc_seq_reply; /* remote ls_recover_seq */ - char rc_buf[0]; + char rc_buf[]; }; union dlm_packet { @@ -506,7 +506,7 @@ struct rcom_lock { __le16 rl_wait_type; __le16 rl_namelen; char rl_name[DLM_RESNAME_MAXLEN]; - char rl_lvb[0]; + char rl_lvb[]; }; /* diff --git a/fs/dlm/user.c b/fs/dlm/user.c index 5264bac75115..e5cefa90b1ce 100644 --- a/fs/dlm/user.c +++ b/fs/dlm/user.c @@ -46,7 +46,7 @@ struct dlm_lock_params32 { __u32 bastaddr; __u32 lksb; char lvb[DLM_USER_LVB_LEN]; - char name[0]; + char name[]; }; struct dlm_write_request32 {