From patchwork Thu May 7 18:51:38 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Gustavo A. R. Silva" X-Patchwork-Id: 11534685 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2498E14B4 for ; Thu, 7 May 2020 18:47:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0D6AE2184D for ; Thu, 7 May 2020 18:47:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877236; bh=f+LUv1Y7A4BpaBDHCwe6DTNBpqkkYTWihjXsRz71OLM=; h=Date:From:To:Cc:Subject:List-ID:From; b=k6uzSWgX4aUHstR19UmzF7f4DKWTrQCkydCnIu0kIkxIjqKNlyi7cf5PJxJMrv+2q rPCWpDCu+MAj1lY4lvwHL1mtwmgQ5EKGbZk4MqunmV9grKFXre7E0HUn3Zz3p79rb5 U0N3EeYCRJWgb8fiU6iYU+V//TGN7JRPZTX8f6nA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728485AbgEGSrN (ORCPT ); Thu, 7 May 2020 14:47:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:47650 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726467AbgEGSrN (ORCPT ); Thu, 7 May 2020 14:47:13 -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 05D1421835; Thu, 7 May 2020 18:47:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877232; bh=f+LUv1Y7A4BpaBDHCwe6DTNBpqkkYTWihjXsRz71OLM=; h=Date:From:To:Cc:Subject:From; b=e54Ef6Dxw35dosckI9n+IIoNelf/NcaMvUZzlp44lRwX+kmktdYylj9TVGR1o1h0Q bVAPouqFdqyNXBnlCsTWz9Mu1+aA3bIYB5j2uqIi0J8ABL9wRepsAL9owWSFcnLI+i EEU3kC5WCWnCyBmMQ5VykK/HzqNbmiSMImUslmgM= Date: Thu, 7 May 2020 13:51:38 -0500 From: "Gustavo A. R. Silva" To: Ilya Dryomov , Jeff Layton , Sage Weil Cc: ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] libceph: Replace zero-length array with flexible-array Message-ID: <20200507185138.GA14076@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: ceph-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: ceph-devel@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 --- include/linux/ceph/mon_client.h | 2 +- include/linux/crush/crush.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/ceph/mon_client.h b/include/linux/ceph/mon_client.h index dbb8a6959a73..ce4ffeb384d7 100644 --- a/include/linux/ceph/mon_client.h +++ b/include/linux/ceph/mon_client.h @@ -19,7 +19,7 @@ struct ceph_monmap { struct ceph_fsid fsid; u32 epoch; u32 num_mon; - struct ceph_entity_inst mon_inst[0]; + struct ceph_entity_inst mon_inst[]; }; struct ceph_mon_client; diff --git a/include/linux/crush/crush.h b/include/linux/crush/crush.h index 54741295c70b..38b0e4d50ed9 100644 --- a/include/linux/crush/crush.h +++ b/include/linux/crush/crush.h @@ -87,7 +87,7 @@ struct crush_rule_mask { struct crush_rule { __u32 len; struct crush_rule_mask mask; - struct crush_rule_step steps[0]; + struct crush_rule_step steps[]; }; #define crush_rule_size(len) (sizeof(struct crush_rule) + \