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 AB2C4C38A24 for ; Thu, 7 May 2020 18:53:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CDE12495F for ; Thu, 7 May 2020 18:53:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877611; bh=kWpXTKUl5SLDwdL/OuCFJc8i4rRGOi1NqEX5H1qbazs=; h=Date:From:To:Cc:Subject:List-ID:From; b=i3JU7zy8RKS3gwvYVmb7tbgHoUJnQLrArJWOmy20QXXcRH13wAZslQXpbHefhQAfl g4hS41jCKdA+NTbzdVGH8ROfz6gTqSjTuALAItKevYsfXqGEoF7Z1qAuDPRdzWPr2M Gkpmfjz3D/w+ZgE3VmtI2FyL3boP7rLFdnAPSukw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728698AbgEGSxa (ORCPT ); Thu, 7 May 2020 14:53:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:55126 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728056AbgEGSx3 (ORCPT ); Thu, 7 May 2020 14:53:29 -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 679342495D; Thu, 7 May 2020 18:53:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877609; bh=kWpXTKUl5SLDwdL/OuCFJc8i4rRGOi1NqEX5H1qbazs=; h=Date:From:To:Cc:Subject:From; b=Xk4W14wM9ZxNeT3smEAGC+5SjWJOn6uUrsSZd77MFFQ0JkGXxQboJehLexrDxgU0X gF7QVPpjs8O7MYeLs+0nPdA6bUaYAJAd3MAP5MBZOjBoT/oktNB26hpms+EmtHiUMd C+fjEmsN04syZ/iEEdRVNXOYHARnQJS7I0taq/Cs= Date: Thu, 7 May 2020 13:57:55 -0500 From: "Gustavo A. R. Silva" To: Michael Ellerman Cc: Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: [PATCH] powerpc/mm: Replace zero-length array with flexible-array Message-ID: <20200507185755.GA15014@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/powerpc/mm/hugetlbpage.c | 2 +- tools/testing/selftests/powerpc/pmu/ebb/trace.h | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c index 33b3461d91e8..d06efb946c7d 100644 --- a/arch/powerpc/mm/hugetlbpage.c +++ b/arch/powerpc/mm/hugetlbpage.c @@ -253,7 +253,7 @@ int __init alloc_bootmem_huge_page(struct hstate *h) struct hugepd_freelist { struct rcu_head rcu; unsigned int index; - void *ptes[0]; + void *ptes[]; }; static DEFINE_PER_CPU(struct hugepd_freelist *, hugepd_freelist_cur); diff --git a/tools/testing/selftests/powerpc/pmu/ebb/trace.h b/tools/testing/selftests/powerpc/pmu/ebb/trace.h index 7c0fb5d2bdb1..da2a3be5441f 100644 --- a/tools/testing/selftests/powerpc/pmu/ebb/trace.h +++ b/tools/testing/selftests/powerpc/pmu/ebb/trace.h @@ -18,7 +18,7 @@ struct trace_entry { u8 type; u8 length; - u8 data[0]; + u8 data[]; }; struct trace_buffer @@ -26,7 +26,7 @@ struct trace_buffer u64 size; bool overflow; void *tail; - u8 data[0]; + u8 data[]; }; struct trace_buffer *trace_buffer_allocate(u64 size); -- 2.26.2