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To:     Arnd Bergmann <arnd@arndb.de>, linux-kernel@vger.kernel.org,
        Kalle Valo <kvalo@codeaurora.org>,
        "David S. Miller" <davem@davemloft.net>,
        Michal Kazior <michal.kazior@tieto.com>
Cc:     Kalle Valo <kvalo@qca.qualcomm.com>,
        Maharaja Kennadyrajan <mkenna@codeaurora.org>,
        Wen Gong <wgong@codeaurora.org>,
        Erik Stromdahl <erik.stromdahl@gmail.com>,
        ath10k@lists.infradead.org, linux-wireless@vger.kernel.org,
        netdev@vger.kernel.org, Kees Cook <keescook@chromium.org>
References: <20200430213101.135134-1-arnd@arndb.de>
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From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
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Subject: Re: [PATCH 04/15] ath10k: fix gcc-10 zero-length-bounds warnings
Message-ID: <49831bca-b9cf-4b9a-1a60-f4289e9c83c0@embeddedor.com>
Date:   Thu, 30 Apr 2020 16:45:32 -0500
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Sender: linux-kernel-owner@vger.kernel.org
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Hi Arnd,

On 4/30/20 16:30, Arnd Bergmann wrote:
> gcc-10 started warning about out-of-bounds access for zero-length
> arrays:
> 
> In file included from drivers/net/wireless/ath/ath10k/core.h:18,
>                  from drivers/net/wireless/ath/ath10k/htt_rx.c:8:
> drivers/net/wireless/ath/ath10k/htt_rx.c: In function 'ath10k_htt_rx_tx_fetch_ind':
> drivers/net/wireless/ath/ath10k/htt.h:1683:17: warning: array subscript 65535 is outside the bounds of an interior zero-length array 'struct htt_tx_fetch_record[0]' [-Wzero-length-bounds]
>  1683 |  return (void *)&ind->records[le16_to_cpu(ind->num_records)];
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/net/wireless/ath/ath10k/htt.h:1676:29: note: while referencing 'records'
>  1676 |  struct htt_tx_fetch_record records[0];
>       |                             ^~~~~~~
> 
> The structure was already converted to have a flexible-array member in
> the past, but there are two zero-length members in the end and only
> one of them can be a flexible-array member.
> 
> Swap the two around to avoid the warning, as 'resp_ids' is not accessed
> in a way that causes a warning.
> 
> Fixes: 3ba225b506a2 ("treewide: Replace zero-length array with flexible-array member")
> Fixes: 22e6b3bc5d96 ("ath10k: add new htt definitions")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/net/wireless/ath/ath10k/htt.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/ath10k/htt.h b/drivers/net/wireless/ath/ath10k/htt.h
> index e7096a73c6ca..7621f0a3dc77 100644
> --- a/drivers/net/wireless/ath/ath10k/htt.h
> +++ b/drivers/net/wireless/ath/ath10k/htt.h
> @@ -1673,8 +1673,8 @@ struct htt_tx_fetch_ind {
>  	__le32 token;
>  	__le16 num_resp_ids;
>  	__le16 num_records;
> -	struct htt_tx_fetch_record records[0];
> -	__le32 resp_ids[]; /* ath10k_htt_get_tx_fetch_ind_resp_ids() */
> +	__le32 resp_ids[0]; /* ath10k_htt_get_tx_fetch_ind_resp_ids() */
> +	struct htt_tx_fetch_record records[];
>  } __packed;
>  
>  static inline void *
> 

The treewide patch is an experimental change and, as this change only applies
to my -next tree, I will carry this patch in it, so other people don't have
to worry about this at all.

Thank you
--
Gustavo