linux-kernel - RE: [PATCH] regulator: da9062: Replace zero-length array with flexible-array member

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Date:   Wed, 12 Feb 2020 11:12:22 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Support Opensource <Support.Opensource@...semi.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] regulator: da9062: Replace zero-length array with
 flexible-array member

On 11 February 2020 23:46, 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>
> ---
>  drivers/regulator/da9062-regulator.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/regulator/da9062-regulator.c b/drivers/regulator/da9062-
> regulator.c
> index b064d8a19d4c..c3b6ba9bafdf 100644
> --- a/drivers/regulator/da9062-regulator.c
> +++ b/drivers/regulator/da9062-regulator.c
> @@ -86,7 +86,7 @@ struct da9062_regulators {
>  	int					irq_ldo_lim;
>  	unsigned				n_regulators;
>  	/* Array size to be defined during init. Keep at end. */
> -	struct da9062_regulator			regulator[0];
> +	struct da9062_regulator			regulator[];

I don't think is the correct change here for this driver. In the probe
'struct_size()' is used to determine the actual size requested from 'malloc()'
when allocating memory for this structure. It's not statically initialised.
Your change will break that code I believe.

>  };
> 
>  /* BUCK modes */
> --
> 2.25.0