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 C9D8EC38A2A for ; Thu, 7 May 2020 19:15:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A6A46208E4 for ; Thu, 7 May 2020 19:15:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588878910; bh=G6KMEamY18fl3fWqdUXZEPHjZzA7lN73yyBEGPKoCPg=; h=Date:From:To:Cc:Subject:List-ID:From; b=tsGNRnO/U5fNCP6E5c5KdHJyqzrUhBWP1kbm93Pr/mTQCwnaTDxq+oBI618p6VGam +la/QLLcCjOcS8qMuIg8666+JOtWsOLxroymSu+UjMDkZ2yjZ8SKPj2putYkgH7AFB 1Iw9vcDWrOX9GF5OPSWxYlnCfIRaXcM4vjwC/fk0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728556AbgEGTPJ (ORCPT ); Thu, 7 May 2020 15:15:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:38614 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726320AbgEGTPG (ORCPT ); Thu, 7 May 2020 15:15:06 -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 C6B74208D6; Thu, 7 May 2020 19:15:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588878906; bh=G6KMEamY18fl3fWqdUXZEPHjZzA7lN73yyBEGPKoCPg=; h=Date:From:To:Cc:Subject:From; b=eF6nDo0Kauty1qyvRId7Y4Z4Y2qmkPQHPx6M4S3vF4q3FklYUyhJg/jAkPzXchXkN wCMK7Ltw8VN3iGt5jOrO0pEllR9K0gqoANqIlUL1PeWjHqYoew1Fy/fPm0cjRdOPVT w2cIloaxI+FsLyj6daG9Ohzu5Q/IyP5K2y/lKHzY= Date: Thu, 7 May 2020 14:19:32 -0500 From: "Gustavo A. R. Silva" To: Ilya Dryomov , Sage Weil Cc: Dongsheng Yang , ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] rbd: Replace zero-length array with flexible-array Message-ID: <20200507191932.GA15991@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 --- drivers/block/rbd_types.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/block/rbd_types.h b/drivers/block/rbd_types.h index ac98ab6ccd3b..a600e0eb6b6f 100644 --- a/drivers/block/rbd_types.h +++ b/drivers/block/rbd_types.h @@ -93,7 +93,7 @@ struct rbd_image_header_ondisk { __le32 snap_count; __le32 reserved; __le64 snap_names_len; - struct rbd_image_snap_ondisk snaps[0]; + struct rbd_image_snap_ondisk snaps[]; } __attribute__((packed));