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 19527C433E0 for ; Wed, 20 May 2020 19:11:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CF3E9207D4 for ; Wed, 20 May 2020 19:11:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590001886; bh=xy+F+Xk6Eh27TpQwycM8KVFcBwkkldw7VDh+CKoRc4U=; h=Date:From:To:Cc:Subject:List-ID:From; b=m0RFfyo7DFOzfhW0F6p8IEB29DgZC7VFCYRf8QoEE7/bKIwA4lvHjA3Hvlxp3bT15 ZlHLCZr9oAanEKQriWSpZ95Y6ez1H9w8gok3tMFUi92EGusYa5MqHqkfPy4v5b4Y3W Z4ciZft3BMjngHpPbDCfrtBqRlTRiWl1Nqvd1gAI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726833AbgETTL0 (ORCPT ); Wed, 20 May 2020 15:11:26 -0400 Received: from mail.kernel.org ([198.145.29.99]:33630 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726548AbgETTLZ (ORCPT ); Wed, 20 May 2020 15:11:25 -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 CEB1D206B6; Wed, 20 May 2020 19:11:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590001885; bh=xy+F+Xk6Eh27TpQwycM8KVFcBwkkldw7VDh+CKoRc4U=; h=Date:From:To:Cc:Subject:From; b=KeoSit7FEot91Av1rOcj3Y6AZne6zDmV1+pKSeffKQzno+1EiIAnhhGWSISar8/Pa iyW9G2sGEdej30zDTh+qWDjG+s1ZHjb0qpaBvJb5JrGH6zvJFw3U556+wlYe3qWca+ qTTiWm7UY5NJeeWD2hRKxSRFH0Yxz5Zt5AaXvxys= Date: Wed, 20 May 2020 14:16:13 -0500 From: "Gustavo A. R. Silva" To: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim Cc: linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH perf/core] perf branch: Replace zero-length array with flexible-array Message-ID: <20200520191613.GA26869@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 and audited _manually_. [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 --- tools/perf/util/branch.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/perf/util/branch.h b/tools/perf/util/branch.h index 4d3f02fa223df..17b2ccc61094b 100644 --- a/tools/perf/util/branch.h +++ b/tools/perf/util/branch.h @@ -46,7 +46,7 @@ struct branch_entry { struct branch_stack { u64 nr; u64 hw_idx; - struct branch_entry entries[0]; + struct branch_entry entries[]; }; /* -- 2.26.2