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=-20.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 BD94AC49EA5 for ; Fri, 25 Jun 2021 02:14:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A464A60FE9 for ; Fri, 25 Jun 2021 02:14:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233026AbhFYCQp (ORCPT ); Thu, 24 Jun 2021 22:16:45 -0400 Received: from m.b4.vu ([203.16.231.148]:53408 "EHLO m.b4.vu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232917AbhFYCQn (ORCPT ); Thu, 24 Jun 2021 22:16:43 -0400 X-Greylist: delayed 394 seconds by postgrey-1.27 at vger.kernel.org; Thu, 24 Jun 2021 22:16:43 EDT Received: by m.b4.vu (Postfix, from userid 1000) id 4094561E5F02; Fri, 25 Jun 2021 11:37:48 +0930 (ACST) Date: Fri, 25 Jun 2021 11:37:48 +0930 From: "Geoffrey D. Bennett" To: Nathan Chancellor Cc: Jaroslav Kysela , Takashi Iwai , Nick Desaulniers , alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: [PATCH] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config Message-ID: <20210625020748.GA21766@m.b4.vu> References: <20210624212048.1356136-1-nathan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210624212048.1356136-1-nathan@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 24, 2021 at 02:20:48PM -0700, Nathan Chancellor wrote: > Clang warns: > > sound/usb/mixer_scarlett_gen2.c:1189:32: warning: expression result > unused [-Wunused-value] > for (i = 0; i < count; i++, (u16 *)buf++) > ^ ~~~~~ > 1 warning generated. > > It appears the intention was to cast the void pointer to a u16 pointer > so that the data could be iterated through like an array of u16 values. > However, the cast happens after the increment because a cast is an > rvalue, whereas the post-increment operator only works on lvalues, so > the loop does not iterate as expected. > > Replace the post-increment shorthand with the full expression so the > cast can be added in the right place and the look works as expected. look -> loop > Fixes: ac34df733d2d ("ALSA: usb-audio: scarlett2: Update get_config to do endian conversion") > Link: https://github.com/ClangBuiltLinux/linux/issues/1408 > Signed-off-by: Nathan Chancellor > --- > sound/usb/mixer_scarlett_gen2.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c > index fcba682cd422..c20c7f1ddc50 100644 > --- a/sound/usb/mixer_scarlett_gen2.c > +++ b/sound/usb/mixer_scarlett_gen2.c > @@ -1186,7 +1186,7 @@ static int scarlett2_usb_get_config( > if (err < 0) > return err; > if (size == 2) > - for (i = 0; i < count; i++, (u16 *)buf++) > + for (i = 0; i < count; i++, buf = (u16 *)buf + 1) > *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); > return 0; > } Thanks Nathan! FYI: although incorrect, this caused no bug as there is not yet any case where count > 1. Acked-by: Geoffrey D. Bennett