linux-kernel - Re: [PATCH] hwmon: (ibmaem) Replace zero-length array with flexible-array member

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Date:   Wed, 12 Feb 2020 12:45:43 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (ibmaem) Replace zero-length array with
 flexible-array member

On Tue, Feb 11, 2020 at 05:42:37PM -0600, Gustavo A. R. Silva wrote:
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array member[1][2],
> introduced in C99:
> 
> struct foo {
>         int stuff;
>         struct boo array[];
> };
> 
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertenly introduced[3] to the codebase from now on.
> 
> This issue was found with the help of Coccinelle.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>

Applied to hwmon-next.

Thanks,
Guenter

> ---
>  drivers/hwmon/ibmaem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/ibmaem.c b/drivers/hwmon/ibmaem.c
> index db63c1295cb2..fb052c2d9c34 100644
> --- a/drivers/hwmon/ibmaem.c
> +++ b/drivers/hwmon/ibmaem.c
> @@ -232,7 +232,7 @@ struct aem_read_sensor_req {
>  
>  struct aem_read_sensor_resp {
>  	struct aem_iana_id	id;
> -	u8			bytes[0];
> +	u8			bytes[];
>  } __packed;
>  
>  /* Data structures to talk to the IPMI layer */