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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,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 1282EC2D0DB for ; Tue, 21 Jan 2020 15:34:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D265B20882 for ; Tue, 21 Jan 2020 15:34:38 +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="fvEOfJkZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729147AbgAUPei (ORCPT ); Tue, 21 Jan 2020 10:34:38 -0500 Received: from gateway23.websitewelcome.com ([192.185.49.124]:21679 "EHLO gateway23.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727508AbgAUPeh (ORCPT ); Tue, 21 Jan 2020 10:34:37 -0500 X-Greylist: delayed 1360 seconds by postgrey-1.27 at vger.kernel.org; Tue, 21 Jan 2020 10:34:37 EST Received: from cm16.websitewelcome.com (cm16.websitewelcome.com [100.42.49.19]) by gateway23.websitewelcome.com (Postfix) with ESMTP id B8901B6F8 for ; Tue, 21 Jan 2020 09:11:56 -0600 (CST) Received: from gator4166.hostgator.com ([108.167.133.22]) by cmsmtp with SMTP id tvC8ij98O32AdtvC8isvap; Tue, 21 Jan 2020 09:11:56 -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=gjlJV5wKgFb1He4YAJ98M6BrY00AixE+NrUX1UsbNIw=; b=fvEOfJkZ8t80xXesNrBzteOmSm dLK86Al1z7aBZr5QuSzw5E2Sd56HwP5EWlOQvYY2GGI3vx1CV9NOiaCzNxXukQTZfxZ+1fBMnX7Bc VQm47yQKAqiAY4NFI4ZSCQ29j15BAJJfxBxkWRYC/YQ0TyCdGSUY7w+eJWX2pRxIBwb265VdoVuRd 9jXnEzXB0/0w4qvRuCsbvW75vRUWWkSCkyoXkB1/JtJziAbIYGz6RTzvd26RTIllyMHJxlcTxTIrS yKxYura7kOSXPR+6j2oWaVtqdvsq634pvp38TMIpukwy6jR97FZX2pCFC92z8M3HWFOUQPWhkZADg Af+1Lg8w==; Received: from [189.152.234.38] (port=52988 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 1itvC8-000TSh-CI; Tue, 21 Jan 2020 09:11:56 -0600 To: Mikael Magnusson Cc: gregkh@linuxfoundation.org, jslaby@suse.com, linux-kernel@vger.kernel.org References: <957960eb-118f-21c7-8901-50f54d65d7cb@embeddedor.com> <20200121150053.31457-1-mikachu@gmail.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: <995ff17c-81e2-15ad-c776-f07c8d61385b@embeddedor.com> Date: Tue, 21 Jan 2020 09:14:15 -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: <20200121150053.31457-1-mikachu@gmail.com> Content-Type: text/plain; charset=utf-8 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: 1itvC8-000TSh-CI X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: ([192.168.43.131]) [189.152.234.38]:52988 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 4 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 1/21/20 09:00, Mikael Magnusson wrote: > Gustavo Silva wrote: >> On 1/20/20 23:54, Jiri Slaby wrote: >>> On 21. 01. 20, 0:45, Gustavo A. R. Silva wrote: >>>> 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. > > This is not true, but maybe it's still not necessary in this particular code, I didn't examine it. > I should have said _in terms of dynamic memory allocation_. Your example is correct: "... a one-element array always occupies at least as much space as a single object of the type."[1] But the above does not affect on the current code. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html Thanks -- Gustavo > Consider the following: > #include > > struct flex { > int count; > char buf[PRE]; > char flex[]; > }; > > struct one { > int count; > char buf[PRE]; > char one[1]; > }; > > void main() { > printf("%ld %ld\n", sizeof(struct flex), sizeof(struct one)); > } > > --snip-- > > % gcc -o siz siz.c -std=c99 -DPRE=7 && ./siz > 12 12 > % gcc -o siz siz.c -std=c99 -DPRE=8 && ./siz > 12 16 > > Since all the preceding stuff in the struct in the patch is aligned, then the [1] will definitely add something to the sizeof count. >