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 548B4C38A24 for ; Thu, 7 May 2020 18:51:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 277B42495B for ; Thu, 7 May 2020 18:51:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877492; bh=jpe2+TjrMnwu2H2dyg8faPNc4w8u0PpZiuofrEf/xT4=; h=Date:From:To:Cc:Subject:List-ID:From; b=o0S2y+jTeEmLzdClu6flngUTWaP7BolOPflQIPpQncD5gEIzA9mEhhLMoa9xIRF0l ko3xKzqdloAzT9m4YcLnRo0hFo7XJt2kP7i/YUHVVj8VQOPlGcvfwvUPUxD7YN3KW8 s2GDw//Lsm5DCxZZ1idrp/+aVMIDYFCbmGxJ0mF8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728731AbgEGSvb (ORCPT ); Thu, 7 May 2020 14:51:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:52246 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727964AbgEGSva (ORCPT ); Thu, 7 May 2020 14:51:30 -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 09BEA24957; Thu, 7 May 2020 18:51:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877489; bh=jpe2+TjrMnwu2H2dyg8faPNc4w8u0PpZiuofrEf/xT4=; h=Date:From:To:Cc:Subject:From; b=hz8cQChXh4vf4srecpx8AKf9ARB4tro3ux3p9bC04rzou9lBEqxu5pkbcV3YwAtr2 XUwYFhyS8iTI6CUN6Q+S9Uc74jYWdfW+65avnCLWTDVyt3HsikQ5A5dw0XkdBBQl+x oPrZRUZlVP/L2sy9TBxninEpu8ywVfKmb8NKsai0= Date: Thu, 7 May 2020 13:55:55 -0500 From: "Gustavo A. R. Silva" To: David Woodhouse , Richard Weinberger Cc: linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH] jffs2: Replace zero-length array with flexible-array Message-ID: <20200507185555.GA14739@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 --- fs/jffs2/nodelist.h | 2 +- fs/jffs2/summary.h | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/jffs2/nodelist.h b/fs/jffs2/nodelist.h index 0637271f3770..8ff4d1a1e774 100644 --- a/fs/jffs2/nodelist.h +++ b/fs/jffs2/nodelist.h @@ -259,7 +259,7 @@ struct jffs2_full_dirent uint32_t ino; /* == zero for unlink */ unsigned int nhash; unsigned char type; - unsigned char name[0]; + unsigned char name[]; }; /* diff --git a/fs/jffs2/summary.h b/fs/jffs2/summary.h index 60207a2ae952..e4131cb1f1d4 100644 --- a/fs/jffs2/summary.h +++ b/fs/jffs2/summary.h @@ -61,7 +61,7 @@ struct jffs2_sum_dirent_flash jint32_t ino; /* == zero for unlink */ uint8_t nsize; /* dirent name size */ uint8_t type; /* dirent type */ - uint8_t name[0]; /* dirent name */ + uint8_t name[]; /* dirent name */ } __attribute__((packed)); struct jffs2_sum_xattr_flash @@ -117,7 +117,7 @@ struct jffs2_sum_dirent_mem jint32_t ino; /* == zero for unlink */ uint8_t nsize; /* dirent name size */ uint8_t type; /* dirent type */ - uint8_t name[0]; /* dirent name */ + uint8_t name[]; /* dirent name */ } __attribute__((packed)); struct jffs2_sum_xattr_mem