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 78C26C38A2A for ; Thu, 7 May 2020 19:17:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 49313208E4 for ; Thu, 7 May 2020 19:17:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879037; bh=xbpMeseLUa1F5bWVlyVbWAi8ZUs0iZRWzX8jkygXfNc=; h=Date:From:To:Cc:Subject:List-ID:From; b=1VaFZF5z1ExOIJlYmNz35+J0rn0mJL5El8vjU0O3iVW/+A3L22DaoJV0EfRXBW7xN FISuN/n0gX5pXiFG5htx5swJtri70Jd0V0lHLRvPF0jvKzlwFbp6QHrO8pbKcG2BXM I++35fotx/MkxiHxsls/iYzuH9eyIRatvuRa5iWw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728424AbgEGTRQ (ORCPT ); Thu, 7 May 2020 15:17:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:40230 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726950AbgEGTRQ (ORCPT ); Thu, 7 May 2020 15:17:16 -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 E9650208D6; Thu, 7 May 2020 19:17:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879035; bh=xbpMeseLUa1F5bWVlyVbWAi8ZUs0iZRWzX8jkygXfNc=; h=Date:From:To:Cc:Subject:From; b=mvRSHASPfFqkfHkORLgo1m+YyYGb1LcF/gEQyoL8JEnEGt9A8YcnjI1F/AnSzEcUE efHsTLZRvbaPWRuvXMWDt1j9xQiBoawncw9dBGpur8CV+APrgv97jta/YNYqUpfPB6 va5oMiyAqUQ8k11b/n/n9reMGpAg4VUqCUcsOJpI= Date: Thu, 7 May 2020 14:21:41 -0500 From: "Gustavo A. R. Silva" To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot Cc: Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , linux-kernel@vger.kernel.org Subject: [PATCH] sched/fair: Replace zero-length array with flexible-array Message-ID: <20200507192141.GA16183@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 --- kernel/sched/fair.c | 2 +- kernel/sched/sched.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 02f323b85b6d..b34549708ef4 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1094,7 +1094,7 @@ struct numa_group { * more by CPU use than by memory faults. */ unsigned long *faults_cpu; - unsigned long faults[0]; + unsigned long faults[]; }; /* diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index db3a57675ccf..f504f3ac3967 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1461,7 +1461,7 @@ struct sched_group { * by attaching extra space to the end of the structure, * depending on how many CPUs the kernel has booted up with) */ - unsigned long cpumask[0]; + unsigned long cpumask[]; }; static inline struct cpumask *sched_group_span(struct sched_group *sg)