From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934291AbeCGXBk (ORCPT ); Wed, 7 Mar 2018 18:01:40 -0500 Received: from mail.bootlin.com ([62.4.15.54]:56928 "EHLO mail.bootlin.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754500AbeCGXBi (ORCPT ); Wed, 7 Mar 2018 18:01:38 -0500 Date: Thu, 8 Mar 2018 00:01:36 +0100 From: Alexandre Belloni To: "Gustavo A. R. Silva" Cc: "Gustavo A. R. Silva" , Alessandro Zummo , linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] rtc: remove VLA usage Message-ID: <20180307230136.GB20370@piout.net> References: <20180307201133.GA5860@embeddedgus> <20180307212506.GO3035@piout.net> <3e8e1515-0f0e-73d4-72eb-3a2a2fbf04e9@embeddedor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3e8e1515-0f0e-73d4-72eb-3a2a2fbf04e9@embeddedor.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/03/2018 at 16:39:51 -0600, Gustavo A. R. Silva wrote: > Hi Alexandre, > > On 03/07/2018 03:25 PM, Alexandre Belloni wrote: > > On 07/03/2018 at 14:11:33 -0600, Gustavo A. R. Silva wrote: > > > In preparation to enabling -Wvla, remove VLA and replace it > > > with a fixed-length array instead. > > > > > You should probably explain what VLA is and why this is important to do. > > Sure. I can elaborate a little bit more. > > > > Signed-off-by: Gustavo A. R. Silva > > > --- > > > drivers/rtc/rtc-bq32k.c | 2 +- > > > drivers/rtc/rtc-mcp795.c | 2 +- > > > 2 files changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c > > > index e8698e9..e4b234a 100644 > > > --- a/drivers/rtc/rtc-bq32k.c > > > +++ b/drivers/rtc/rtc-bq32k.c > > > @@ -74,7 +74,7 @@ static int bq32k_read(struct device *dev, void *data, uint8_t off, uint8_t len) > > > static int bq32k_write(struct device *dev, void *data, uint8_t off, uint8_t len) > > > { > > > struct i2c_client *client = to_i2c_client(dev); > > > - uint8_t buffer[len + 1]; > > > + uint8_t buffer[256]; > > You chose to change len to 255, probably because this is a uint8_t but > > Correct. > > > this is way too much for this rtc, it only has 10 consecutive registers. > > In that case probably the best solution is to add the following line to the > module: > > #define MAX_LEN 10 > > and update the rest of the code as follows: > > uint8_t buffer[MAX_LEN + 1]; > Seems better, yes. > > > > buffer[0] = off; > > > memcpy(&buffer[1], data, len); > > > diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c > > > index 79e24ea..00e11c1 100644 > > > --- a/drivers/rtc/rtc-mcp795.c > > > +++ b/drivers/rtc/rtc-mcp795.c > > > @@ -82,7 +82,7 @@ static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count) > > > { > > > struct spi_device *spi = to_spi_device(dev); > > > int ret; > > > - u8 tx[2 + count]; > > > + u8 tx[257]; > > For this particular case it seems to me that the following works just fine: > > #define MAX_COUNT 7 > > u8 tx[MAX_COUNT + 2]; > > What do you think? > Nope, that RTC has a section of 255 bytes that could be read at once so 257 is the correct value. -- Alexandre Belloni, Bootlin (formerly Free Electrons) Embedded Linux and Kernel engineering https://bootlin.com