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=-11.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 A1EDAC433E0 for ; Tue, 19 May 2020 18:44:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 90E9B207D3 for ; Tue, 19 May 2020 18:44:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728162AbgESSoo (ORCPT ); Tue, 19 May 2020 14:44:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727995AbgESSo2 (ORCPT ); Tue, 19 May 2020 14:44:28 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F0E76C08C5C0; Tue, 19 May 2020 11:44:27 -0700 (PDT) Received: from [5.158.153.53] (helo=tip-bot2.lab.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jb7E0-0006gA-MP; Tue, 19 May 2020 20:44:24 +0200 Received: from [127.0.1.1] (localhost [IPv6:::1]) by tip-bot2.lab.linutronix.de (Postfix) with ESMTP id 5AFC01C0178; Tue, 19 May 2020 20:44:24 +0200 (CEST) Date: Tue, 19 May 2020 18:44:24 -0000 From: "tip-bot2 for Gustavo A. R. Silva" Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/core] locking/lockdep: Replace zero-length array with flexible-array Cc: "Gustavo A. R. Silva" , "Peter Zijlstra (Intel)" , x86 , LKML In-Reply-To: <20200507185804.GA15036@embeddedor> References: <20200507185804.GA15036@embeddedor> MIME-Version: 1.0 Message-ID: <158991386428.17951.3540978557111480073.tip-bot2@tip-bot2> X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the locking/core branch of tip: Commit-ID: db78538c75e49c09b002a2cd96a19ae0c39be771 Gitweb: https://git.kernel.org/tip/db78538c75e49c09b002a2cd96a19ae0c39be771 Author: Gustavo A. R. Silva AuthorDate: Thu, 07 May 2020 13:58:04 -05:00 Committer: Peter Zijlstra CommitterDate: Tue, 19 May 2020 20:34:18 +02:00 locking/lockdep: Replace zero-length array with flexible-array 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 Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200507185804.GA15036@embeddedor --- kernel/locking/lockdep.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index ac10db6..cfdff12 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -489,7 +489,7 @@ struct lock_trace { struct hlist_node hash_entry; u32 hash; u32 nr_entries; - unsigned long entries[0] __aligned(sizeof(unsigned long)); + unsigned long entries[] __aligned(sizeof(unsigned long)); }; #define LOCK_TRACE_SIZE_IN_LONGS \ (sizeof(struct lock_trace) / sizeof(unsigned long))