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=-13.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 D0CC9C2D0CE for ; Tue, 21 Jan 2020 14:25:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5C0562070C for ; Tue, 21 Jan 2020 14:25:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=embeddedor.com header.i=@embeddedor.com header.b="osTc3U0a" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729140AbgAUOZ0 (ORCPT ); Tue, 21 Jan 2020 09:25:26 -0500 Received: from gateway31.websitewelcome.com ([192.185.143.4]:26726 "EHLO gateway31.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727255AbgAUOZ0 (ORCPT ); Tue, 21 Jan 2020 09:25:26 -0500 Received: from cm10.websitewelcome.com (cm10.websitewelcome.com [100.42.49.4]) by gateway31.websitewelcome.com (Postfix) with ESMTP id 2C42729157 for ; Tue, 21 Jan 2020 08:25:25 -0600 (CST) Received: from gator4166.hostgator.com ([108.167.133.22]) by cmsmtp with SMTP id tuT6iIPNwkeyDtuT6iLZCP; Tue, 21 Jan 2020 08:25:25 -0600 X-Authority-Reason: nr=8 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=embeddedor.com; s=default; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:Subject:From:References:Cc:To:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Q9f/a3dOUx1ra0gYtY2AlrWZkTvH/SNxvHh3zLiP0O4=; b=osTc3U0aFPpciau3uQa39MMa5R cNJhly5Pw7GDXHG3Yypk8+XLbKXnjhr4/CFsq5NBvVttFQCSk7idouBjmbIwcqtIdvvo6+9yea8Tj yLhcWUODv2F1KduhpYBFLYm46hocoMtjVnM6d0jAz0XMWEU0jD8i9z2eRCCPkIVcYhvRSm6XLYAWS upeduTHD1CF0oJb6QvtktcM9K1yo4NwmRmLLNuoI21M1o0P403Wwb1RGOhCCU71O+mQX9Hvvb9yDr 0pdT/cnnDMdCHncknJuKOTOlH9eFsSw+ACHKhgEEiztPKIIK7aG/dxIk+ZtQmLzkw0+a/kfeJO1+1 XKQXIn8Q==; Received: from [189.152.234.38] (port=47574 helo=[192.168.43.131]) by gator4166.hostgator.com with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.92) (envelope-from ) id 1ituT5-004KmR-SA; Tue, 21 Jan 2020 08:25:23 -0600 To: Jiri Slaby , Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org References: <20200120234528.GA26790@embeddedor.com> From: "Gustavo A. R. Silva" Autocrypt: addr=gustavo@embeddedor.com; keydata= xsFNBFssHAwBEADIy3ZoPq3z5UpsUknd2v+IQud4TMJnJLTeXgTf4biSDSrXn73JQgsISBwG 2Pm4wnOyEgYUyJd5tRWcIbsURAgei918mck3tugT7AQiTUN3/5aAzqe/4ApDUC+uWNkpNnSV tjOx1hBpla0ifywy4bvFobwSh5/I3qohxDx+c1obd8Bp/B/iaOtnq0inli/8rlvKO9hp6Z4e DXL3PlD0QsLSc27AkwzLEc/D3ZaqBq7ItvT9Pyg0z3Q+2dtLF00f9+663HVC2EUgP25J3xDd 496SIeYDTkEgbJ7WYR0HYm9uirSET3lDqOVh1xPqoy+U9zTtuA9NQHVGk+hPcoazSqEtLGBk YE2mm2wzX5q2uoyptseSNceJ+HE9L+z1KlWW63HhddgtRGhbP8pj42bKaUSrrfDUsicfeJf6 m1iJRu0SXYVlMruGUB1PvZQ3O7TsVfAGCv85pFipdgk8KQnlRFkYhUjLft0u7CL1rDGZWDDr NaNj54q2CX9zuSxBn9XDXvGKyzKEZ4NY1Jfw+TAMPCp4buawuOsjONi2X0DfivFY+ZsjAIcx qQMglPtKk/wBs7q2lvJ+pHpgvLhLZyGqzAvKM1sVtRJ5j+ARKA0w4pYs5a5ufqcfT7dN6TBk LXZeD9xlVic93Ju08JSUx2ozlcfxq+BVNyA+dtv7elXUZ2DrYwARAQABzSxHdXN0YXZvIEEu IFIuIFNpbHZhIDxndXN0YXZvQGVtYmVkZGVkb3IuY29tPsLBfQQTAQgAJwUCWywcDAIbIwUJ CWYBgAULCQgHAgYVCAkKCwIEFgIDAQIeAQIXgAAKCRBHBbTLRwbbMZ6tEACk0hmmZ2FWL1Xi l/bPqDGFhzzexrdkXSfTTZjBV3a+4hIOe+jl6Rci/CvRicNW4H9yJHKBrqwwWm9fvKqOBAg9 obq753jydVmLwlXO7xjcfyfcMWyx9QdYLERTeQfDAfRqxir3xMeOiZwgQ6dzX3JjOXs6jHBP cgry90aWbaMpQRRhaAKeAS14EEe9TSIly5JepaHoVdASuxklvOC0VB0OwNblVSR2S5i5hSsh ewbOJtwSlonsYEj4EW1noQNSxnN/vKuvUNegMe+LTtnbbocFQ7dGMsT3kbYNIyIsp42B5eCu JXnyKLih7rSGBtPgJ540CjoPBkw2mCfhj2p5fElRJn1tcX2McsjzLFY5jK9RYFDavez5w3lx JFgFkla6sQHcrxH62gTkb9sUtNfXKucAfjjCMJ0iuQIHRbMYCa9v2YEymc0k0RvYr43GkA3N PJYd/vf9vU7VtZXaY4a/dz1d9dwIpyQARFQpSyvt++R74S78eY/+lX8wEznQdmRQ27kq7BJS R20KI/8knhUNUJR3epJu2YFT/JwHbRYC4BoIqWl+uNvDf+lUlI/D1wP+lCBSGr2LTkQRoU8U 64iK28BmjJh2K3WHmInC1hbUucWT7Swz/+6+FCuHzap/cjuzRN04Z3Fdj084oeUNpP6+b9yW e5YnLxF8ctRAp7K4yVlvA87BTQRbLBwMARAAsHCE31Ffrm6uig1BQplxMV8WnRBiZqbbsVJB H1AAh8tq2ULl7udfQo1bsPLGGQboJSVN9rckQQNahvHAIK8ZGfU4Qj8+CER+fYPp/MDZj+t0 DbnWSOrG7z9HIZo6PR9z4JZza3Hn/35jFggaqBtuydHwwBANZ7A6DVY+W0COEU4of7CAahQo 5NwYiwS0lGisLTqks5R0Vh+QpvDVfuaF6I8LUgQR/cSgLkR//V1uCEQYzhsoiJ3zc1HSRyOP otJTApqGBq80X0aCVj1LOiOF4rrdvQnj6iIlXQssdb+WhSYHeuJj1wD0ZlC7ds5zovXh+FfF l5qH5RFY/qVn3mNIVxeO987WSF0jh+T5ZlvUNdhedGndRmwFTxq2Li6GNMaolgnpO/CPcFpD jKxY/HBUSmaE9rNdAa1fCd4RsKLlhXda+IWpJZMHlmIKY8dlUybP+2qDzP2lY7kdFgPZRU+e zS/pzC/YTzAvCWM3tDgwoSl17vnZCr8wn2/1rKkcLvTDgiJLPCevqpTb6KFtZosQ02EGMuHQ I6Zk91jbx96nrdsSdBLGH3hbvLvjZm3C+fNlVb9uvWbdznObqcJxSH3SGOZ7kCHuVmXUcqoz ol6ioMHMb+InrHPP16aVDTBTPEGwgxXI38f7SUEn+NpbizWdLNz2hc907DvoPm6HEGCanpcA EQEAAcLBZQQYAQgADwUCWywcDAIbDAUJCWYBgAAKCRBHBbTLRwbbMdsZEACUjmsJx2CAY+QS UMebQRFjKavwXB/xE7fTt2ahuhHT8qQ/lWuRQedg4baInw9nhoPE+VenOzhGeGlsJ0Ys52sd XvUjUocKgUQq6ekOHbcw919nO5L9J2ejMf/VC/quN3r3xijgRtmuuwZjmmi8ct24TpGeoBK4 WrZGh/1hAYw4ieARvKvgjXRstcEqM5thUNkOOIheud/VpY+48QcccPKbngy//zNJWKbRbeVn imua0OpqRXhCrEVm/xomeOvl1WK1BVO7z8DjSdEBGzbV76sPDJb/fw+y+VWrkEiddD/9CSfg fBNOb1p1jVnT2mFgGneIWbU0zdDGhleI9UoQTr0e0b/7TU+Jo6TqwosP9nbk5hXw6uR5k5PF 8ieyHVq3qatJ9K1jPkBr8YWtI5uNwJJjTKIA1jHlj8McROroxMdI6qZ/wZ1ImuylpJuJwCDC ORYf5kW61fcrHEDlIvGc371OOvw6ejF8ksX5+L2zwh43l/pKkSVGFpxtMV6d6J3eqwTafL86 YJWH93PN+ZUh6i6Rd2U/i8jH5WvzR57UeWxE4P8bQc0hNGrUsHQH6bpHV2lbuhDdqo+cM9eh GZEO3+gCDFmKrjspZjkJbB5Gadzvts5fcWGOXEvuT8uQSvl+vEL0g6vczsyPBtqoBLa9SNrS VtSixD1uOgytAP7RWS474w== Subject: Re: [PATCH] tty: n_hdlc: Use flexible-array member Message-ID: <957960eb-118f-21c7-8901-50f54d65d7cb@embeddedor.com> Date: Tue, 21 Jan 2020 08:27:41 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=iso-8859-2 Content-Language: en-US Content-Transfer-Encoding: 8bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator4166.hostgator.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - embeddedor.com X-BWhitelist: no X-Source-IP: 189.152.234.38 X-Source-L: No X-Exim-ID: 1ituT5-004KmR-SA X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: ([192.168.43.131]) [189.152.234.38]:47574 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 3 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/20/20 23:54, Jiri Slaby wrote: > On 21. 01. 20, 0:45, Gustavo A. R. Silva wrote: >> Old code in the kernel uses 1-byte and 0-byte arrays to indicate the >> presence of a "variable length array": >> >> struct something { >> int length; >> u8 data[1]; >> }; >> >> struct something *instance; >> >> instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL); >> instance->length = size; >> memcpy(instance->data, source, size); >> >> There is also 0-byte arrays. Both cases pose confusion for things like >> sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism >> to declare variable-length types such as the one above is a flexible array >> member[2] which need to be the last member of a structure and empty-sized: >> >> struct something { >> int stuff; >> u8 data[]; >> }; >> >> Also, 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 >> unadvertenly introduced[3] to the codebase from now on. >> >> [1] https://github.com/KSPP/linux/issues/21 >> [2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html >> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") >> >> Signed-off-by: Gustavo A. R. Silva >> --- >> drivers/tty/n_hdlc.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c >> index 98361acd3053..b5499ca8757e 100644 >> --- a/drivers/tty/n_hdlc.c >> +++ b/drivers/tty/n_hdlc.c >> @@ -115,7 +115,7 @@ >> struct n_hdlc_buf { >> struct list_head list_item; >> int count; >> - char buf[1]; >> + char buf[]; >> }; >> >> #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe) > > Have you checked, that you don't have to "+ 1" here now? > Yep. That's not necessary. _In terms of memory allocation_, zero-length/one-element arrays and flexible-array members work exactly the same way. > Other than that: > Acked-by: Jiri Slaby > Thanks! -- Gustavo