From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754866AbeCGXL2 (ORCPT ); Wed, 7 Mar 2018 18:11:28 -0500 Received: from gateway23.websitewelcome.com ([192.185.48.104]:29972 "EHLO gateway23.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754052AbeCGXL1 (ORCPT ); Wed, 7 Mar 2018 18:11:27 -0500 Subject: Re: [PATCH] rtc: remove VLA usage To: Alexandre Belloni Cc: "Gustavo A. R. Silva" , Alessandro Zummo , linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20180307201133.GA5860@embeddedgus> <20180307212506.GO3035@piout.net> <3e8e1515-0f0e-73d4-72eb-3a2a2fbf04e9@embeddedor.com> <20180307230136.GB20370@piout.net> From: "Gustavo A. R. Silva" Message-ID: Date: Wed, 7 Mar 2018 17:09:22 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180307230136.GB20370@piout.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator4166.hostgator.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - embeddedor.com X-BWhitelist: no X-Source-IP: 187.162.24.133 X-Source-L: No X-Exim-ID: 1etiBY-001F3W-Vp X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: 187-162-24-133.static.axtel.net ([192.168.3.98]) [187.162.24.133]:20646 X-Source-Auth: garsilva@embeddedor.com X-Email-Count: 4 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/07/2018 05:01 PM, Alexandre Belloni wrote: > 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. > I see... I was looking into this piece of code drivers/rtc/rtc-mcp795.c:302:         tmp[0] = (tmp[0] & 0x80) | bin2bcd(alm->time.tm_sec);         tmp[1] = (tmp[1] & 0x80) | bin2bcd(alm->time.tm_min);         tmp[2] = (tmp[2] & 0xE0) | bin2bcd(alm->time.tm_hour);         tmp[3] = (tmp[3] & 0x80) | bin2bcd(alm->time.tm_wday + 1);         /* set alarm match: seconds, minutes, hour, day, date and month */         tmp[3] |= (MCP795_ALM0C2_BIT | MCP795_ALM0C1_BIT | MCP795_ALM0C0_BIT);         tmp[4] = (tmp[4] & 0xC0) | bin2bcd(alm->time.tm_mday);         tmp[5] = (tmp[5] & 0xE0) | bin2bcd(alm->time.tm_mon + 1);         ret = mcp795_rtcc_write(dev, MCP795_REG_ALM0_SECONDS, tmp, sizeof(tmp)); OK. I'll work on v2 of this patch. I'll send it shortly. Thanks -- Gustavo