From patchwork Thu May 7 18:53:29 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Gustavo A. R. Silva" X-Patchwork-Id: 207638 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 1B7D3C38A24 for ; Thu, 7 May 2020 18:49:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E36F224957 for ; Thu, 7 May 2020 18:49:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877344; bh=9FfT5ytYuVZhMpl5DmSdFr17qoYPHAktygqL1MmAtH4=; h=Date:From:To:Cc:Subject:List-ID:From; b=oCVihR4Isd1WEe8BE4MmEV5nNEbOTXPGX1xWRTGOU+AWkDZmaHJpNmUL8YTcGJjkJ 5Ih5nf9L7Ql7XgmLanrIk/QrEy/EHUsui400PuYLEAic2TwT8B47l+1FsT18d95Tz3 TDmdCRujXKLreZYBwXM1jNFd6Su1viX8yaZCy4TI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728166AbgEGStD (ORCPT ); Thu, 7 May 2020 14:49:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:50214 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728018AbgEGStD (ORCPT ); Thu, 7 May 2020 14:49:03 -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 43CC124955; Thu, 7 May 2020 18:49:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877342; bh=9FfT5ytYuVZhMpl5DmSdFr17qoYPHAktygqL1MmAtH4=; h=Date:From:To:Cc:Subject:From; b=g9Axh4DeD69j75cW+0/OJiqkixbSS1yIGuftScR6tclyt8KYgScdUTPi3sssCN6Si OnFwHCWNx6jwnHpgXs585yBwRRlnAS/bMgY8xmtCvrmRQQvfQOzz3oho020afb3CXD +LXcsXZFFLf06bVY/eWUP/6TJXmgweZQddN3jXQc= Date: Thu, 7 May 2020 13:53:29 -0500 From: "Gustavo A. R. Silva" To: Peter Rosin Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] i2c: mux: Replace zero-length array with flexible-array Message-ID: <20200507185329.GA14436@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-i2c-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-i2c@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/i2c-mux.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/i2c-mux.h b/include/linux/i2c-mux.h index c5a977320f82..98ef73b7c8fd 100644 --- a/include/linux/i2c-mux.h +++ b/include/linux/i2c-mux.h @@ -29,7 +29,7 @@ struct i2c_mux_core { int num_adapters; int max_adapters; - struct i2c_adapter *adapter[0]; + struct i2c_adapter *adapter[]; }; struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,