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=-21.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS 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 95507C2B9F4 for ; Fri, 25 Jun 2021 20:08:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F32961973 for ; Fri, 25 Jun 2021 20:08:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229864AbhFYUKZ (ORCPT ); Fri, 25 Jun 2021 16:10:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:39114 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229712AbhFYUKY (ORCPT ); Fri, 25 Jun 2021 16:10:24 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7A69761960; Fri, 25 Jun 2021 20:08:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1624651683; bh=NlrfNtc194UlEd/q110C08hY9M4sajBezN97jjTWyY0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=i1Qf5Nyvau5r1xhbMEMCySZ+xdDEQAEVe/I9EQYmz1aGUxT9Zs4a9bj3PAa+5h3T7 XGmgELeyxdj+RJK5ERNBChniycSKC7UIyE7y0VYk+eVuAUE7OMU6M9Ji4Wqnyk0brk 670xDGSHV+dnjBclobYlkImMCCfGta1JGVKHTCZQrgqhvqJ+hT4vPN6KMCOLUb9mvK GKedY5RA90OA41ZNb7KcCGr2+aKFrQNJWIKdqxoF7RS6NAl5Z9orNcDRSweB+xSjrz +2K9OkKfM2cfyjEj/ZFeAh9uMmdDnm+SAMgGfQAx5Ve/TF1KawhLzygZ3mLfO4USat uLJ2sb6CwkjSg== Date: Fri, 25 Jun 2021 13:08:00 -0700 From: Nathan Chancellor To: "Geoffrey D. Bennett" Cc: alsa-devel@alsa-project.org, Nick Desaulniers , linux-kernel@vger.kernel.org, Takashi Iwai , clang-built-linux@googlegroups.com Subject: Re: [PATCH v2] ALSA: usb-audio: scarlett2: Fix for loop increment in scarlett2_usb_get_config Message-ID: References: <20210625175418.2019892-1-nathan@kernel.org> <20210625184342.GA23780@m.b4.vu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210625184342.GA23780@m.b4.vu> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jun 26, 2021 at 04:13:42AM +0930, Geoffrey D. Bennett wrote: > On Fri, Jun 25, 2021 at 10:54:19AM -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. This is not a bug in practice > > because count is not greater than one at the moment but this could > > change in the future so this should be fixed. > > > > Replace the cast with a temporary variable of the proper type, which is > > less error prone and fixes the iteration. Do the same thing for the > > 'u8 *' below this if block. > > > > 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 > > --- > > > > v1 -> v2: > > > > * Use temporary variables of proper type rather than casting, as > > requested by Takashi. I did not include Geoffrey's ack for this > > reason. > > > > * Mention that there is not a bug at the moment per Geoffrey's comment. > > > > sound/usb/mixer_scarlett_gen2.c | 14 ++++++++++---- > > 1 file changed, 10 insertions(+), 4 deletions(-) > > > > diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c > > index fcba682cd422..b13903bed330 100644 > > --- a/sound/usb/mixer_scarlett_gen2.c > > +++ b/sound/usb/mixer_scarlett_gen2.c > > @@ -1177,17 +1177,22 @@ static int scarlett2_usb_get_config( > > const struct scarlett2_config *config_item = > > &scarlett2_config_items[info->has_mixer][config_item_num]; > > int size, err, i; > > + u8 *buf_8; > > u8 value; > > > > /* For byte-sized parameters, retrieve directly into buf */ > > if (config_item->size >= 8) { > > + u16 *buf_16; > > + > > I would prefer that the u16 *buf_16 declaration above be removed from > there... > > > size = config_item->size / 8 * count; > > err = scarlett2_usb_get(mixer, config_item->offset, buf, size); > > if (err < 0) > > return err; > > - if (size == 2) > > - for (i = 0; i < count; i++, (u16 *)buf++) > > - *(u16 *)buf = le16_to_cpu(*(__le16 *)buf); > > + if (size == 2) { > > + buf_16 = buf; > > ...and combined with the assignment here, like: u16 *buf_16 = buf; Thanks for pointing it out, I was not paying enough attention to realize that the scope could be reduced. v3 sent with your Ack added, thank you for taking a look in a quick manner! Cheers, Nathan > Regardless: > > Acked-by: Geoffrey D. Bennett > > And, thanks again! > > > + for (i = 0; i < count; i++, buf_16++) > > + *buf_16 = le16_to_cpu(*(__le16 *)buf_16); > > + } > > return 0; > > } > > > > @@ -1197,8 +1202,9 @@ static int scarlett2_usb_get_config( > > return err; > > > > /* then unpack from value into buf[] */ > > + buf_8 = buf; > > for (i = 0; i < 8 && i < count; i++, value >>= 1) > > - *(u8 *)buf++ = value & 1; > > + *buf_8++ = value & 1; > > > > return 0; > > } > > > > base-commit: 0cbbeaf370221fc469c95945dd3c1198865c5fe4 > > -- > > 2.32.0.93.g670b81a890 > >