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 356C8C38A2A for ; Thu, 7 May 2020 18:47:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0B36324956 for ; Thu, 7 May 2020 18:47:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877268; bh=L19SLkkQXKcOuzW3RL8LtzKlqMiQPoyoesq3zLXKhnA=; h=Date:From:To:Cc:Subject:List-ID:From; b=x81Ojog/ydAdiswDrUPwq/D0kAMadE+MqAx2fthOtifddX8+Rfs1BrSxQblvswsuq Baws4ilxQimnQKs+hKGMMKN+ljcugeuUyVc5CkMPepmU3v7dZ0RYWUgmlRYjg6cdPL 1VX3VOijQ+Bq/LNPODfAJuDQjwISNfs8yQAnT+Rs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728536AbgEGSrr (ORCPT ); Thu, 7 May 2020 14:47:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:48436 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726467AbgEGSrq (ORCPT ); Thu, 7 May 2020 14:47:46 -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 908C124954; Thu, 7 May 2020 18:47:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877266; bh=L19SLkkQXKcOuzW3RL8LtzKlqMiQPoyoesq3zLXKhnA=; h=Date:From:To:Cc:Subject:From; b=Z65uFmK9tBSaSMi50NVL8iZ9JUxFnlgm4iHolyTl8/eZ9jcErJOhoUHk31un83xOW 7K9w4V79TCedl3epr+ZSOZqyenRt7cNlIiDY4i2KjckpxL7tKYNAcWYSJBQfulHb5j rs0z8eA/uaI7I0yqfUppDH/u4ElRzXnctijFPdmU= Date: Thu, 7 May 2020 13:52:12 -0500 From: "Gustavo A. R. Silva" To: Philipp Reisner , Lars Ellenberg Cc: drbd-dev@lists.linbit.com, linux-kernel@vger.kernel.org Subject: [PATCH] drbd: Replace zero-length array with flexible-array Message-ID: <20200507185212.GA14165@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/drbd/drbd_int.h | 2 +- drivers/block/drbd/drbd_protocol.h | 8 ++++---- 2 files changed, 5 insertions(+), 5 deletions(-) diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h index aae99a2d7bd4..a3314dd781a7 100644 --- a/drivers/block/drbd/drbd_int.h +++ b/drivers/block/drbd/drbd_int.h @@ -620,7 +620,7 @@ struct fifo_buffer { unsigned int head_index; unsigned int size; int total; /* sum of all values */ - int values[0]; + int values[]; }; extern struct fifo_buffer *fifo_alloc(unsigned int fifo_size); diff --git a/drivers/block/drbd/drbd_protocol.h b/drivers/block/drbd/drbd_protocol.h index e6fc5ad72501..dea59c92ecc1 100644 --- a/drivers/block/drbd/drbd_protocol.h +++ b/drivers/block/drbd/drbd_protocol.h @@ -271,7 +271,7 @@ struct p_rs_param { u32 resync_rate; /* Since protocol version 88 and higher. */ - char verify_alg[0]; + char verify_alg[]; } __packed; struct p_rs_param_89 { @@ -305,7 +305,7 @@ struct p_protocol { u32 two_primaries; /* Since protocol version 87 and higher. */ - char integrity_alg[0]; + char integrity_alg[]; } __packed; @@ -360,7 +360,7 @@ struct p_sizes { u16 dds_flags; /* use enum dds_flags here. */ /* optional queue_limits if (agreed_features & DRBD_FF_WSAME) */ - struct o_qlim qlim[0]; + struct o_qlim qlim[]; } __packed; struct p_state { @@ -409,7 +409,7 @@ struct p_compressed_bm { */ u8 encoding; - u8 code[0]; + u8 code[]; } __packed; struct p_delay_probe93 {