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 BEDE8C38A24 for ; Thu, 7 May 2020 18:53:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 98EBB215A4 for ; Thu, 7 May 2020 18:53:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877619; bh=a3q7EVtRZYdws6ttRdc7CqZlAg4XEZKPq6gzkh3v70E=; h=Date:From:To:Cc:Subject:List-ID:From; b=Kc4iPx/lyXOnBsCnXuXgzGc9HvCwoYBIw5IG0QPRp9Tix8yBZsiV18nceyI4Iw2iU dmf5PHMAUXC+ExVGV9LQH6xDnpkW7l+/6gBAczXYgdoBB++KNAy/bR89QNPylOpbK3 +4Kk0ipF/Hyg29+CgB4v5dwFK/cDEHrswA4BQdXA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728781AbgEGSxj (ORCPT ); Thu, 7 May 2020 14:53:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:55528 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727826AbgEGSxi (ORCPT ); Thu, 7 May 2020 14:53:38 -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 4040920870; Thu, 7 May 2020 18:53:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877617; bh=a3q7EVtRZYdws6ttRdc7CqZlAg4XEZKPq6gzkh3v70E=; h=Date:From:To:Cc:Subject:From; b=pZFh6Bvivm/9yt4HEz1VmtQOTA0kAk4gl8f++6RwXmbw3ebMigsp5bxH3Ktj2+m+S Mvf9iMdh7xyfZHQETabnvLUgG2S1XKmjxuJ6XGf/tzEMTsghq7ggwvttufRps1M9G5 Qqplf8sBda1op/dTYkK57zl8YNq7/bDs6gTIGxxY= Date: Thu, 7 May 2020 13:58:04 -0500 From: "Gustavo A. R. Silva" To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: linux-kernel@vger.kernel.org Subject: [PATCH] locking/lockdep: Replace zero-length array with flexible-array Message-ID: <20200507185804.GA15036@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/locking/lockdep.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index ac10db66cc63..cfdff122905b 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))