linux-kernel - Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX

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Date:   Thu, 17 Nov 2022 13:54:49 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Deepak R Varma <drv@...lo.com>
Cc:     linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        gustavoars@...nel.org
Subject: Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with
 DECLARE_FLEX_ARRAY() helper

On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote:
> The code currently uses C90 standard extension based zero length arrays.
> The zero length array member also happens to be the only member of the
> structs. Such zero length array declarations are deprecated and the
> new C99 standard extension of flexible array declarations are to be
> used instead.
> 
> The DECLARE_FLEX_ARRAY() helper allows for a flexible array member as
> the only member in a structure. Refer to these links [1], [2] for
> details.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://lkml.kernel.org/r/YxKY6O2hmdwNh8r8@work
> 
> Issue identified using Coccinelle.
> 
> Signed-off-by: Deepak R Varma <drv@...lo.com>
> ---
> 
> Notes:
>    1. Proposed change is compile tested only.
>    2. Solution feedback from gustavoars@...nel.org
> 
> 
>  drivers/staging/wlan-ng/hfa384x.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/wlan-ng/hfa384x.h b/drivers/staging/wlan-ng/hfa384x.h
> index 0611e37df6ac..3a1edcb43e07 100644
> --- a/drivers/staging/wlan-ng/hfa384x.h
> +++ b/drivers/staging/wlan-ng/hfa384x.h
> @@ -960,15 +960,15 @@ struct hfa384x_pdr_nicid {
>  } __packed;
> 
>  struct hfa384x_pdr_refdac_measurements {
> -	u16 value[0];
> +	DECLARE_FLEX_ARRAY(u16, value);
>  } __packed;

Why?  This structure is never used anywhere, right?  So why is this
needed to be changed and not just removed entirely?  Same for the other
structures in this patch.

thanks,

greg k-h