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 B22D6C38A24 for ; Thu, 7 May 2020 18:48:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8074824958 for ; Thu, 7 May 2020 18:48:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877322; bh=0FzK11nGj1WinKh7fS63LIRI8HxfTaRuog1W0ERLTfs=; h=Date:From:To:Cc:Subject:List-ID:From; b=waqG7UvmrY9nk08i2XfChRFI1bYSx+egE7LSsHZyCvkR4lnuk9cBVMhnbOh62+Nkm G5SOgl6g40otw+AX7pgWH7KD3EG52+7/HmgjbsGHTfKlNpyBmmmzpLVgkf+eHbSiRB 2Ty3npgKbOEE5wL08Ag7xs8BVU6PjO9dU+B9Aewo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728624AbgEGSsm (ORCPT ); Thu, 7 May 2020 14:48:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:49710 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728166AbgEGSsl (ORCPT ); Thu, 7 May 2020 14:48:41 -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 7608D21BE5; Thu, 7 May 2020 18:48:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877320; bh=0FzK11nGj1WinKh7fS63LIRI8HxfTaRuog1W0ERLTfs=; h=Date:From:To:Cc:Subject:From; b=bGuqBT6fnSodm0+6QPewScsQbJptYCjrr+i1T9vjHa1tRj0wC+eI0fgcsNxFV0bdt FKCHDjFot3fRPNHsXKMUs41k5WnUZtiTJlLhxAaScl2AIq8VmMA1QfYJzRsClpniN3 Yly1dIEELb172FcW65iiE9Oc220lV91G1NDL0UzI= Date: Thu, 7 May 2020 13:53:07 -0500 From: "Gustavo A. R. Silva" To: David Howells Cc: linux-cachefs@redhat.com, linux-kernel@vger.kernel.org Subject: [PATCH] FS-Cache: Replace zero-length array with flexible-array Message-ID: <20200507185307.GA14353@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 --- include/linux/fscache-cache.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h index d5ba431b5d63..5b6072e4a7ab 100644 --- a/include/linux/fscache-cache.h +++ b/include/linux/fscache-cache.h @@ -46,7 +46,7 @@ struct fscache_cache_tag { unsigned long flags; #define FSCACHE_TAG_RESERVED 0 /* T if tag is reserved for a cache */ atomic_t usage; - char name[0]; /* tag name */ + char name[]; /* tag name */ }; /*