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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 9983AC07E95 for ; Tue, 13 Jul 2021 09:20:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CF3E600D1 for ; Tue, 13 Jul 2021 09:20:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234397AbhGMJWy (ORCPT ); Tue, 13 Jul 2021 05:22:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57794 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234997AbhGMJWu (ORCPT ); Tue, 13 Jul 2021 05:22:50 -0400 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6D4D8C0613DD; Tue, 13 Jul 2021 02:20:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To: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=3U4fXEvYZQ6jKgkN4/AU7jjky/mHZ4e2qC/cN+142q0=; b=ZbjSuQFu6xUZKyZmP35KKaa7h oWMT3hLQ9U1A2HSPpBdszaEgUZ1/9Ac9qHhgTIMIFET76inyqnQZMbTQPGp1ookCogmz/lhU6Iijo EancHG/EMjM0MUzW9zmyJGKlOy3VgtfXFRr8VBW2BDrG/zpZ0f8UgXyOB4jIC+a5Vvr3Vq56vEmvB y1Zc8FLFWBl70qcGOTu3a5/hbbtDY9oi2MFiySCgCTwNpsEcTx887gGRqQ4gOuQzoza3e0PWGUvjt w4FxDaZz6plRmLauHEHixlZvZs2y/ggp17tTlk7HglTPwBXz3qRVqUYSN+02MmxecPpvzpzGOzMRK kygaE7KLw==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:46044) by pandora.armlinux.org.uk with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1m3Ea4-0005pG-7B; Tue, 13 Jul 2021 10:19:56 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1m3Ea2-0000Am-Kx; Tue, 13 Jul 2021 10:19:54 +0100 Date: Tue, 13 Jul 2021 10:19:54 +0100 From: "Russell King (Oracle)" To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Cc: Salah Triki , fabrice.gasnier@foss.st.com, thierry.reding@gmail.com, lee.jones@linaro.org, mcoquelin.stm32@gmail.com, alexandre.torgue@foss.st.com, linux-pwm@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] divide by 3*sizeof(u32) when computing array_size Message-ID: <20210713091954.GG22278@shell.armlinux.org.uk> References: <20210712231910.GA1831270@pc> <20210713063053.qqttzxlopvpnadj3@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210713063053.qqttzxlopvpnadj3@pengutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: Russell King (Oracle) Precedence: bulk List-ID: X-Mailing-List: linux-pwm@vger.kernel.org On Tue, Jul 13, 2021 at 08:30:53AM +0200, Uwe Kleine-König wrote: > Hello Salah, > > On Tue, Jul 13, 2021 at 12:19:10AM +0100, Salah Triki wrote: > > Divide by 3*sizeof(u32) when computing array_size, since stm32_breakinput > > has 3 fields of type u32. > > > > Signed-off-by: Salah Triki > > --- > > drivers/pwm/pwm-stm32.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c > > index 794ca5b02968..fb21bc2b2dd6 100644 > > --- a/drivers/pwm/pwm-stm32.c > > +++ b/drivers/pwm/pwm-stm32.c > > @@ -544,7 +544,7 @@ static int stm32_pwm_probe_breakinputs(struct stm32_pwm *priv, > > return -EINVAL; > > > > priv->num_breakinputs = nb; > > - array_size = nb * sizeof(struct stm32_breakinput) / sizeof(u32); > > + array_size = nb * sizeof(struct stm32_breakinput) / (3 * sizeof(u32)); > > ret = of_property_read_u32_array(np, "st,breakinput", > > (u32 *)priv->breakinputs, array_size); > > if (ret) > > I agree with Philipp here; this looks strange and needs a better > description. > > Looking a bit more in details: > > - priv->breakinputs has type struct stm32_breakinput[MAX_BREAKINPUT] > - nb is in [0 .. MAX_BREAKINPUT] > - sizeof(struct stm32_breakinput) == 3 * sizeof(u32) > - of_property_read_u32_array reads $array_size u32 quantities > > so to read $nb members of type stm32_breakinput array_size must be a > multiple of 3 which isn't given any more after your patch. This makes me > believe your suggested change to be wrong. I concur with your analysis. "array_size" is the number of u32 values to read from DT. It is not the number of entries in priv->breakinputs. I would also note that the code relies on there being no padding in struct stm32_breakinput - it should be noted that a strict interpretation of the C standard allows padding to be added anywhere to a structure - at the start, end or between members. Some further thoughts... DT is effectively an interface (we maintain definitions of what we expect.) The way the code is structured, "struct stm32_breakinput" defines that interface. Maybe this should be commented, and maybe there should be a build time assert that "sizeof(struct stm32_breakinput)" is "3 * sizeof(u32)" since the code is relying on that property? -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!