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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 16599C76188 for ; Mon, 22 Jul 2019 12:24:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EA4A420665 for ; Mon, 22 Jul 2019 12:24:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727594AbfGVMYn (ORCPT ); Mon, 22 Jul 2019 08:24:43 -0400 Received: from relay11.mail.gandi.net ([217.70.178.231]:50447 "EHLO relay11.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727040AbfGVMYn (ORCPT ); Mon, 22 Jul 2019 08:24:43 -0400 Received: from aptenodytes (lfbn-1-17395-211.w86-250.abo.wanadoo.fr [86.250.200.211]) (Authenticated sender: paul.kocialkowski@bootlin.com) by relay11.mail.gandi.net (Postfix) with ESMTPSA id C6615100005; Mon, 22 Jul 2019 12:24:38 +0000 (UTC) Date: Mon, 22 Jul 2019 14:24:38 +0200 From: Paul Kocialkowski To: Jeremy Sowden Cc: Nishka Dasgupta , maxime.ripard@bootlin.com, mchehab@kernel.org, gregkh@linuxfoundation.org, wens@csie.org, linux-media@vger.kernel.org, devel@driverdev.osuosl.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2] staging: media: sunxi: Add bool cast to value Message-ID: <20190722122438.GA1908@aptenodytes> References: <20190722060651.6538-1-nishkadg.linux@gmail.com> <20190722111225.GA2695@azazel.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190722111225.GA2695@azazel.net> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Hi, On Mon 22 Jul 19, 12:12, Jeremy Sowden wrote: > On 2019-07-22, at 11:36:51 +0530, Nishka Dasgupta wrote: > > Typecast as bool the return value of cedrus_find_format in > > cedrus_check_format as the return value of cedrus_check_format is > > always treated like a boolean value. > > > > Signed-off-by: Nishka Dasgupta > > --- > > Changes in v2: > > - Add !! to the returned pointer to ensure that the return value is > > always either true or false, and never a non-zero value other than > > true. > > > > drivers/staging/media/sunxi/cedrus/cedrus_video.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_video.c b/drivers/staging/media/sunxi/cedrus/cedrus_video.c > > index e2b530b1a956..b731745f21f8 100644 > > --- a/drivers/staging/media/sunxi/cedrus/cedrus_video.c > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_video.c > > @@ -86,7 +86,7 @@ static struct cedrus_format *cedrus_find_format(u32 pixelformat, u32 directions, > > static bool cedrus_check_format(u32 pixelformat, u32 directions, > > unsigned int capabilities) > > { > > - return cedrus_find_format(pixelformat, directions, capabilities); > > + return !!(bool)cedrus_find_format(pixelformat, directions, capabilities); > > } > > I think the original was fine. The return value of cedrus_find_format > will be automatically converted to bool before being returned from > cedrus_check_format since that is the return-type of the function, and > the result of converting any non-zero value to bool is 1. Okay I was a bit unsure about that and wanted to play it on the safe side without really looking it up, but that gave me the occasion to verify. >From what I could find (from my GNU system's /usr/include/unistring/stdbool.h): Limitations of this substitute, when used in a C89 environment: - In C99, casts and automatic conversions to '_Bool' or 'bool' are performed in such a way that every nonzero value gets converted to 'true', and zero gets converted to 'false'. This doesn't work with this substitute. With this substitute, only the values 0 and 1 give the expected result when converted to _Bool' or 'bool'. So since the kernel is built for C89 (unless I'm mistaken), I don't think the compiler provides any guarantee about bool values being converted to 1 when they are non-zero. As a result, I think it's best to be careful. However, I'm not sure I really see what cocinelle was unhappy about. You mentionned single-line functions, but I don't see how that can be a problem. So in the end, I think we should keep the !! and drop the (bool) cast if there's no particular warning about it. What do you think? Cheers, Paul > > static void cedrus_prepare_format(struct v4l2_pix_format *pix_fmt) > > -- > > 2.19.1 -- Paul Kocialkowski, Bootlin Embedded Linux and kernel engineering https://bootlin.com