linux-kernel - Re: [PATCH net-next 08/11] ath9k: work around false-positive gcc warning

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Date:   Mon, 02 Nov 2020 18:26:51 +0200
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     QCA ath9k Development <ath9k-devel@....qualcomm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 08/11] ath9k: work around false-positive gcc warning

Arnd Bergmann <arnd@...nel.org> writes:

> From: Arnd Bergmann <arnd@...db.de>
>
> gcc-10 shows a false-positive warning with CONFIG_KASAN:
>
> drivers/net/wireless/ath/ath9k/dynack.c: In function 'ath_dynack_sample_tx_ts':
> include/linux/etherdevice.h:290:14: warning: writing 4 bytes into a region of size 0 [-Wstringop-overflow=]
>   290 |  *(u32 *)dst = *(const u32 *)src;
>       |  ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
>
> Until gcc is fixed, work around this by using memcpy() in place
> of ether_addr_copy(). Hopefully gcc-11 will not have this problem.
>
> Link: https://godbolt.org/z/sab1MK
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97490
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/net/wireless/ath/ath9k/dynack.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/net/wireless/ath/ath9k/dynack.c b/drivers/net/wireless/ath/ath9k/dynack.c
> index fbeb4a739d32..e4eb96b26ca4 100644
> --- a/drivers/net/wireless/ath/ath9k/dynack.c
> +++ b/drivers/net/wireless/ath/ath9k/dynack.c
> @@ -247,8 +247,14 @@ void ath_dynack_sample_tx_ts(struct ath_hw *ah, struct sk_buff *skb,
>  	ridx = ts->ts_rateindex;
>  
>  	da->st_rbf.ts[da->st_rbf.t_rb].tstamp = ts->ts_tstamp;
> +#if defined(CONFIG_KASAN) && (CONFIG_GCC_VERSION >= 100000) && (CONFIG_GCC_VERSION < 110000)
> +	/* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97490 */
> +	memcpy(da->st_rbf.addr[da->st_rbf.t_rb].h_dest, hdr->addr1, ETH_ALEN);
> +	memcpy(da->st_rbf.addr[da->st_rbf.t_rb].h_src, hdr->addr2, ETH_ALEN);
> +#else
>  	ether_addr_copy(da->st_rbf.addr[da->st_rbf.t_rb].h_dest, hdr->addr1);
>  	ether_addr_copy(da->st_rbf.addr[da->st_rbf.t_rb].h_src, hdr->addr2);
> +#endif

Isn't there a better way to handle this? I really would not want
checking for GCC versions become a common approach in drivers.

I even think that using memcpy() always is better than the ugly ifdef.

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