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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 709C4C433FE for ; Sat, 19 Nov 2022 10:28:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232754AbiKSKXm (ORCPT ); Sat, 19 Nov 2022 05:23:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50660 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232670AbiKSKXd (ORCPT ); Sat, 19 Nov 2022 05:23:33 -0500 Received: from smtp.smtpout.orange.fr (smtp-18.smtpout.orange.fr [80.12.242.18]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A2571AE77 for ; Sat, 19 Nov 2022 02:23:29 -0800 (PST) Received: from [192.168.1.18] ([86.243.100.34]) by smtp.orange.fr with ESMTPA id wL0PovmdsCoWhwL0PornL6; Sat, 19 Nov 2022 11:23:27 +0100 X-ME-Helo: [192.168.1.18] X-ME-Auth: Y2hyaXN0b3BoZS5qYWlsbGV0QHdhbmFkb28uZnI= X-ME-Date: Sat, 19 Nov 2022 11:23:27 +0100 X-ME-IP: 86.243.100.34 Message-ID: <629bac45-32c2-9eac-6fed-f2f9e39d2740@wanadoo.fr> Date: Sat, 19 Nov 2022 11:23:25 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: [PATCH 1/2][next] scsi: qla2xxx: Replace one-element array with DECLARE_FLEX_ARRAY() helper Content-Language: fr To: "Gustavo A. R. Silva" Cc: "Martin K. Petersen" , "James E.J. Bottomley" , GR-QLogic-Storage-Upstream@marvell.com, Nilesh Javali , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org References: From: Christophe JAILLET In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 19/11/2022 à 09:56, Gustavo A. R. Silva a écrit : > On Sat, Nov 19, 2022 at 09:44:02AM +0100, Christophe JAILLET wrote: >> Le 19/11/2022 à 00:47, Gustavo A. R. Silva a écrit : >>> One-element arrays as fake flex arrays are deprecated and we are moving >>> towards adopting C99 flexible-array members, instead. So, replace >>> one-element array declaration in struct ct_sns_gpnft_rsp, which is >>> ultimately being used inside a union: >>> >>> drivers/scsi/qla2xxx/qla_def.h: >>> 3240 struct ct_sns_gpnft_pkt { >>> 3241 union { >>> 3242 struct ct_sns_req req; >>> 3243 struct ct_sns_gpnft_rsp rsp; >>> 3244 } p; >>> 3245 }; >>> >>> Important to mention is that doing a build before/after this patch results >>> in no binary differences. >> >> Hi, >> >> even with the: >> >>> rspsz = sizeof(struct ct_sns_gpnft_rsp) + >>> - ((vha->hw->max_fibre_devices - 1) * >>> + (vha->hw->max_fibre_devices * >>> sizeof(struct ct_sns_gpn_ft_data)); >> >> change ? > > Yep; that change compensates for the removal of the 1 in the declaration > of entries[]. > > The above piece of code is a common idiom to calculate the size for an > allocation when a one-element array is involved. In the original code > (vha->hw->max_fibre_devices - 1) compensates for the _extra_ size of one > element of type struct ct_sns_gpn_ft_data in sizeof(struct ct_sns_gpnft_rsp). > Yes, I do agree, that the code is equivalent. I was surprised that a compiler was smart enough to generate the same binary code. With gcc 11.3.0 (x86_64), I do get some differences when I do: make drivers/scsi/qla2xxx/qla_gs.o objdump -D drivers/scsi/qla2xxx/qla_gs.o > before.asm patch -p1 < patch.diff make drivers/scsi/qla2xxx/qla_gs.o objdump -D drivers/scsi/qla2xxx/qla_gs.o > after.asm diff -u before.asm after.asm Mostly some slight ordering of instruction changes, but the binary are not the same. CJ > -- > Gustavo > >> >> CJ >> >>> >>> This help us make progress towards globally enabling >>> -fstrict-flex-arrays=3 [1]. >>> >>> Link: https://github.com/KSPP/linux/issues/245 >>> Link: https://github.com/KSPP/linux/issues/193 >>> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1] >>> Signed-off-by: Gustavo A. R. Silva >>> --- >>> drivers/scsi/qla2xxx/qla_def.h | 4 ++-- >>> drivers/scsi/qla2xxx/qla_gs.c | 2 +- >>> 2 files changed, 3 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/scsi/qla2xxx/qla_def.h b/drivers/scsi/qla2xxx/qla_def.h >>> index a26a373be9da..1eea977ef426 100644 >>> --- a/drivers/scsi/qla2xxx/qla_def.h >>> +++ b/drivers/scsi/qla2xxx/qla_def.h >>> @@ -3151,12 +3151,12 @@ struct ct_sns_gpnft_rsp { >>> uint8_t vendor_unique; >>> }; >>> /* Assume the largest number of targets for the union */ >>> - struct ct_sns_gpn_ft_data { >>> + DECLARE_FLEX_ARRAY(struct ct_sns_gpn_ft_data { >>> u8 control_byte; >>> u8 port_id[3]; >>> u32 reserved; >>> u8 port_name[8]; >>> - } entries[1]; >>> + }, entries); >>> }; >>> /* CT command response */ >>> diff --git a/drivers/scsi/qla2xxx/qla_gs.c b/drivers/scsi/qla2xxx/qla_gs.c >>> index 64ab070b8716..69d3bc795f90 100644 >>> --- a/drivers/scsi/qla2xxx/qla_gs.c >>> +++ b/drivers/scsi/qla2xxx/qla_gs.c >>> @@ -4073,7 +4073,7 @@ int qla24xx_async_gpnft(scsi_qla_host_t *vha, u8 fc4_type, srb_t *sp) >>> sp->u.iocb_cmd.u.ctarg.req_size = GPN_FT_REQ_SIZE; >>> rspsz = sizeof(struct ct_sns_gpnft_rsp) + >>> - ((vha->hw->max_fibre_devices - 1) * >>> + (vha->hw->max_fibre_devices * >>> sizeof(struct ct_sns_gpn_ft_data)); >>> sp->u.iocb_cmd.u.ctarg.rsp = dma_alloc_coherent(&vha->hw->pdev->dev, >> >