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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-Disposition: inline In-Reply-To: <20210713063053.qqttzxlopvpnadj3@pengutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210713_022004_871065_559B5BBE X-CRM114-Status: GOOD ( 24.78 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jul 13, 2021 at 08:30:53AM +0200, Uwe Kleine-K=F6nig 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_breakinp= ut > > 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 =3D nb; > > - array_size =3D nb * sizeof(struct stm32_breakinput) / sizeof(u32); > > + array_size =3D nb * sizeof(struct stm32_breakinput) / (3 * sizeof(u32= )); > > ret =3D 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) =3D=3D 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! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel