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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY autolearn=unavailable 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 0F04CC11F69 for ; Thu, 1 Jul 2021 16:41:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE6C8613D9 for ; Thu, 1 Jul 2021 16:41:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229974AbhGAQnc (ORCPT ); Thu, 1 Jul 2021 12:43:32 -0400 Received: from smtprelay0194.hostedemail.com ([216.40.44.194]:57082 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S229764AbhGAQnb (ORCPT ); Thu, 1 Jul 2021 12:43:31 -0400 Received: from omf05.hostedemail.com (clb03-v110.bra.tucows.net [216.40.38.60]) by smtprelay01.hostedemail.com (Postfix) with ESMTP id 6A3B5100E472A; Thu, 1 Jul 2021 16:40:59 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: joe@perches.com) by omf05.hostedemail.com (Postfix) with ESMTPA id 37C34B2793; Thu, 1 Jul 2021 16:40:58 +0000 (UTC) Message-ID: <6ddc71efad6cd45e45991028a7656eab203df12d.camel@perches.com> Subject: Re: [PATCH] scsi: aic94xx: Fix fall-through warning for Clang From: Joe Perches To: "Gustavo A. R. Silva" , "James E.J. Bottomley" , "Martin K. Petersen" Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, Kees Cook Date: Thu, 01 Jul 2021 09:40:56 -0700 In-Reply-To: <20210701010433.GA57746@embeddedor> References: <20210701010433.GA57746@embeddedor> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.40.0-1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspamout02 X-Rspamd-Queue-Id: 37C34B2793 X-Stat-Signature: gznc799dteu3m8s9wumnqrhepq5map57 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Session-ID: U2FsdGVkX19DwiLC1MjWGtvuepLMBtmJQwGEjJXxw9w= X-HE-Tag: 1625157658-948689 Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On Wed, 2021-06-30 at 20:04 -0500, Gustavo A. R. Silva wrote: > In preparation to enable -Wimplicit-fallthrough for Clang, fix a > warning by explicitly adding a fallthrough; statement. > > Notice that this seems to be a Duff device for performance[1]. So, > although the code looks a bit _funny_, I didn't want to refactor > or modify it beyond merely adding a fallthrough marking, which > might be the least disruptive way to fix this issue. If you read the surrounding calling code, it appears it's not performant. * @start has to be the _base_ element start, since the * linked list entries's offset is from this pointer. * Some linked list entries use only the first id, in which case * you can pass 0xFF for the second. > diff --git a/drivers/scsi/aic94xx/aic94xx_sds.c b/drivers/scsi/aic94xx/aic94xx_sds.c [] > @@ -718,10 +718,12 @@ static void *asd_find_ll_by_id(void * const start, const u8 id0, const u8 id1) >   do { >   switch (id1) { >   default: > - if (el->id1 == id1) > + if (el->id1 == id1) { > + fallthrough; >   case 0xFF: >   if (el->id0 == id0) >   return el; > + } >   } >   el = start + le16_to_cpu(el->next); >   } while (el != start); And this is still horrible code to read. I think the below is rather more sensible and it doesn't change the defconfig with aic94xx object size. $ size drivers/scsi/aic94xx/aic94xx_sds.o* text data bss dec hex filename 10010 192 0 10202 27da drivers/scsi/aic94xx/aic94xx_sds.o.new 10010 192 0 10202 27da drivers/scsi/aic94xx/aic94xx_sds.o.old --- drivers/scsi/aic94xx/aic94xx_sds.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/drivers/scsi/aic94xx/aic94xx_sds.c b/drivers/scsi/aic94xx/aic94xx_sds.c index 297a66770260c..069278f6d6cea 100644 --- a/drivers/scsi/aic94xx/aic94xx_sds.c +++ b/drivers/scsi/aic94xx/aic94xx_sds.c @@ -717,11 +717,14 @@ static void *asd_find_ll_by_id(void * const start, const u8 id0, const u8 id1) do { switch (id1) { - default: - if (el->id1 == id1) case 0xFF: - if (el->id0 == id0) - return el; + if (el->id0 == id0) + return el; + break; + default: + if (el->id0 == id0 && el->id1 == id1) + return el; + break; } el = start + le16_to_cpu(el->next); } while (el != start);