linux-kernel - Re: [PATCH] rtc: remove VLA usage

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Date:   Wed, 7 Mar 2018 22:25:06 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: Re: [PATCH] rtc: remove VLA usage

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.

> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  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
this is way too much for this rtc, it only has 10 consecutive registers.

>  	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];
>  
>  	tx[0] = MCP795_WRITE;
>  	tx[1] = addr;
> -- 
> 2.7.4
> 

-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com