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=-13.8 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,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 727E7C47255 for ; Mon, 11 May 2020 20:04:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4D47020720 for ; Mon, 11 May 2020 20:04:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589227481; bh=n63/YfSS2BLXhpW9OHsMu3MiGnyizgEMk8AT2HW5xMs=; h=Date:From:To:Cc:Subject:List-ID:From; b=Q7Rnj+iLKBhFdSO1Nyr4ZoRSyRE5W/z0lvkZODqaptdVgIwr7Mrdv3HMeupGwrebV 6OzAXr+jnY2tNBIfyemMhYbrqnNO3Qiuc8sW867v+bfciZVGMmrMOBqI7BqYvbNQ15 kj6nojxb5vNBqjy3zxOy6GE24cHXBe8I7Q8xHwuU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731514AbgEKUEk (ORCPT ); Mon, 11 May 2020 16:04:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:44394 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727873AbgEKUEk (ORCPT ); Mon, 11 May 2020 16:04:40 -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 7F2E6206F5; Mon, 11 May 2020 20:04:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589227479; bh=n63/YfSS2BLXhpW9OHsMu3MiGnyizgEMk8AT2HW5xMs=; h=Date:From:To:Cc:Subject:From; b=XL4ioT8pz8LypKXDgGNkR5hgGiQk1tQvV5FO7JM0T2Qm+FVPeCTcJlveImKmRYFDE Y+T8oqoS8IqfwI3hU9b1zXUzC5LXq1T8JJz4neAUzrj3m//BZalBJkh88x74nxGrpW KFi8aBMGIa+LYsnUEUu2xdwU71TeZLjAkbVF2OiI= Date: Mon, 11 May 2020 15:09:11 -0500 From: "Gustavo A. R. Silva" To: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Thomas Gleixner , Borislav Petkov , "x86@kernel.org H. Peter Anvin" Cc: linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH] perf/x86: Replace zero-length array with flexible-array Message-ID: <20200511200911.GA13149@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 --- arch/x86/events/intel/bts.c | 2 +- arch/x86/events/intel/uncore.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c index 6a3b599ee0fe..731dd8d0dbb1 100644 --- a/arch/x86/events/intel/bts.c +++ b/arch/x86/events/intel/bts.c @@ -58,7 +58,7 @@ struct bts_buffer { local_t head; unsigned long end; void **data_pages; - struct bts_phys buf[0]; + struct bts_phys buf[]; }; static struct pmu bts_pmu; diff --git a/arch/x86/events/intel/uncore.h b/arch/x86/events/intel/uncore.h index 0da4a4605536..b469ddd45515 100644 --- a/arch/x86/events/intel/uncore.h +++ b/arch/x86/events/intel/uncore.h @@ -130,7 +130,7 @@ struct intel_uncore_box { struct list_head list; struct list_head active_list; void __iomem *io_addr; - struct intel_uncore_extra_reg shared_regs[0]; + struct intel_uncore_extra_reg shared_regs[]; }; /* CFL uncore 8th cbox MSRs */ -- 2.26.2