From patchwork Thu May 7 19:00:38 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: 11534735 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id F099514B4 for ; Thu, 7 May 2020 18:56:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D95D32184D for ; Thu, 7 May 2020 18:56:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877773; bh=4Vs8QxaVwzsgCZC7VZqciOtD1Lflpg1/+iLS46dpZGM=; h=Date:From:To:Cc:Subject:List-ID:From; b=Z+c6W2AtcjM+MTaLu2JpOLPzUkGFlf3wVsLxyl57DJ2Lu+mgjtwTbeJrdFzjULpxz +Ak3tDLrrR2YEk/hbnJY1QgakFzgs8elGqY0FuDMXiqrtpKq2V1uWiVfrR2xtX4h7H oEqaNAiyyikN6e0X9bRxANd8jEtTNzSijEmazurY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726367AbgEGS4N (ORCPT ); Thu, 7 May 2020 14:56:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:57670 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727799AbgEGS4N (ORCPT ); Thu, 7 May 2020 14:56:13 -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 24E0220575; Thu, 7 May 2020 18:56:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877772; bh=4Vs8QxaVwzsgCZC7VZqciOtD1Lflpg1/+iLS46dpZGM=; h=Date:From:To:Cc:Subject:From; b=O9847wy6gQrf3ooNlVPFe+hHKH/0f/mytZcFG+j+BNZBaXoQrvTeAEhKECvvx/DBf VGlMP6sU4ne/8Ma9PawMSCVC4QG6ES2Ga9zJqGc0R671Oedp+xMhGTxiSsrKIDyibR 7XTe4/2TKtN2z4P6CdP26AEUsvIx7mznlhQJ1Fyc= Date: Thu, 7 May 2020 14:00:38 -0500 From: "Gustavo A. R. Silva" To: Ludovic Desroches Cc: linux-arm-kernel@lists.infradead.org, dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] dmaengine: at_hdmac: Replace zero-length array with flexible-array Message-ID: <20200507190038.GA15272@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@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 Acked-by: Ludovic Desroches --- drivers/dma/at_hdmac_regs.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/dma/at_hdmac_regs.h b/drivers/dma/at_hdmac_regs.h index 397692e937b3..80fc2fe8c77e 100644 --- a/drivers/dma/at_hdmac_regs.h +++ b/drivers/dma/at_hdmac_regs.h @@ -331,7 +331,7 @@ struct at_dma { struct dma_pool *dma_desc_pool; struct dma_pool *memset_pool; /* AT THE END channels table */ - struct at_dma_chan chan[0]; + struct at_dma_chan chan[]; }; #define dma_readl(atdma, name) \