From patchwork Fri May 8 21:07:07 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: 11537595 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 463C0139F for ; Fri, 8 May 2020 21:02:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2DCB1218AC for ; Fri, 8 May 2020 21:02:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588971762; bh=y3FP7YDdmJObHtYuLlASoDfQ6AYJiXDdMFXW8X469gU=; h=Date:From:To:Cc:Subject:List-ID:From; b=UFQ7elYQbqcMn2puVWYGgk3Z2/ZestKuVwSuVlU/pmV+E6ilMK+7sM9hbMzv83mSY ZaL5eB1AokMz9KeHU3+tNrn02NyoQ9iFayvh9ybpee2078HpSlVr0zWi1gRSbhxxQb aS7xx946eeDKk0/1YrSm/h+f7pufAOcRns1hTnf8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727095AbgEHVCl (ORCPT ); Fri, 8 May 2020 17:02:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:59968 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726817AbgEHVCl (ORCPT ); Fri, 8 May 2020 17:02:41 -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 2361E2173E; Fri, 8 May 2020 21:02:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588971760; bh=y3FP7YDdmJObHtYuLlASoDfQ6AYJiXDdMFXW8X469gU=; h=Date:From:To:Cc:Subject:From; b=ICO4guylj57FjvVLT+yGfZuLeZo88/jGrEjq1XnHFgVJ9EH7tg/kK00lvAwmK8a2f J0szkaa+NY9Qi7TTpM+QkYYrDc4NzdYGxCoxoJ0L7YAxcjydZ4KHd3olXdIV3HXgAQ D6U5gDWY8VE6fQkwxbyNbBVY3WTqkSclf58EAV+g= Date: Fri, 8 May 2020 16:07:07 -0500 From: "Gustavo A. R. Silva" To: Andy Gross , Bjorn Andersson , Dan Williams , Vinod Koul , Jeffrey Hugo Cc: linux-arm-msm@vger.kernel.org, dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH] dmaengine: qcom: bam_dma: Replace zero-length array with flexible-array Message-ID: <20200508210707.GA24136@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") Reviewed-by: Jeffrey Hugo Signed-off-by: Gustavo A. R. Silva --- drivers/dma/qcom/bam_dma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c index ef73f65224b1..5a08dd0d3388 100644 --- a/drivers/dma/qcom/bam_dma.c +++ b/drivers/dma/qcom/bam_dma.c @@ -74,7 +74,7 @@ struct bam_async_desc { struct list_head desc_node; enum dma_transfer_direction dir; size_t length; - struct bam_desc_hw desc[0]; + struct bam_desc_hw desc[]; }; enum bam_reg {