linux-kernel - Re: [PATCH] platform/x86: i2c-multi-instantiate: Replace zero-length array with flexible-array member

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Message-ID: <f8281f16-b47e-41d6-f67b-1300bc5affff@embeddedor.com>
Date:   Thu, 27 Feb 2020 13:03:10 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>
Cc:     platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] platform/x86: i2c-multi-instantiate: Replace zero-length
 array with flexible-array member

Hi all,

Friendly ping: who can take this?

Thanks
--
Gustavo

On 2/12/20 18:55, 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
> inadvertently introduced[3] to the codebase from now on.
> 
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
> 
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
> 
> 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/platform/x86/i2c-multi-instantiate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/x86/i2c-multi-instantiate.c b/drivers/platform/x86/i2c-multi-instantiate.c
> index ffb8d5d1eb5f..6acc8457866e 100644
> --- a/drivers/platform/x86/i2c-multi-instantiate.c
> +++ b/drivers/platform/x86/i2c-multi-instantiate.c
> @@ -28,7 +28,7 @@ struct i2c_inst_data {
>  
>  struct i2c_multi_inst_data {
>  	int num_clients;
> -	struct i2c_client *clients[0];
> +	struct i2c_client *clients[];
>  };
>  
>  static int i2c_multi_inst_count(struct acpi_resource *ares, void *data)
>