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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 078DDC76188 for ; Mon, 22 Jul 2019 13:19:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D0A8C217F9 for ; Mon, 22 Jul 2019 13:19:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=azazel.net header.i=@azazel.net header.b="HCEqoqhw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728907AbfGVNTU (ORCPT ); Mon, 22 Jul 2019 09:19:20 -0400 Received: from kadath.azazel.net ([81.187.231.250]:37486 "EHLO kadath.azazel.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728529AbfGVNTU (ORCPT ); Mon, 22 Jul 2019 09:19:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=azazel.net; s=20190108; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=BJZaPv+ZzOIR8B7tw6DrhELBhHNpgCujcs9EdlLvffI=; b=HCEqoqhwpCNV9mX4vPh3vjc+aa o0AmZ8zyOinCSarqcysgs9v+lhMgPR6RX8NrzyDcKekfw6OHHA/cW6IkoaBuJfj8jCrSaPAuM1jvS nmdiEG9FGEMXKMVSTRclxkKl5xVy7qXnofRqccb/QJgrAGmiBw1TwYLNHSVzucbDPWckjj9M47Dy+ erPO4HnEnZg2g+/ucJinCyGpDZSm30IXzn8XVZmNCfhfJey0UcwT8iNNsEsvQixeXnWODNC5jr4zf dDN9Adf9fQeJycJ9CIFFLyC+DGrBQ4l7LwCuucpeFQa8T4E4ejR0DGJyHjRM8gcQhWzodJLnAzO4Q q+nplM8A==; Received: from pnakotus.dreamlands ([192.168.96.5] helo=azazel.net) by kadath.azazel.net with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1hpYDe-0007Bw-TS; Mon, 22 Jul 2019 14:19:10 +0100 Date: Mon, 22 Jul 2019 14:19:11 +0100 From: Jeremy Sowden To: Paul Kocialkowski 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: <20190722131910.GC2695@azazel.net> References: <20190722060651.6538-1-nishkadg.linux@gmail.com> <20190722111225.GA2695@azazel.net> <20190722122438.GA1908@aptenodytes> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="KDt/GgjP6HVcx58l" Content-Disposition: inline In-Reply-To: <20190722122438.GA1908@aptenodytes> User-Agent: Mutt/1.10.1 (2018-07-13) X-SA-Exim-Connect-IP: 192.168.96.5 X-SA-Exim-Mail-From: jeremy@azazel.net X-SA-Exim-Scanned: No (on kadath.azazel.net); SAEximRunCond expanded to false Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org --KDt/GgjP6HVcx58l Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On 2019-07-22, at 14:24:38 +0200, Paul Kocialkowski wrote: > 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. Ick. I checked the C99 standard and assumed that GCC would use the same semantics. I've just tested with "gcc-8 -std=gnu89" and it appears to do the right thing: [azazel@ulthar:/space/azazel/tmp] $ cat test.c #include #include int main (void) { char *p = "test"; bool b = p; fprintf (stderr, "%p, %d\n", (void *) p, b); return 0; } [azazel@ulthar:/space/azazel/tmp] $ gcc-8 -O2 -std=gnu89 -Wall -Wextra test.c -o test [azazel@ulthar:/space/azazel/tmp] $ ./test 0x55d984e0e004, 1 > As a result, I think it's best to be careful. Fair enough. > 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? Seems sensible. 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