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RE: [PATCH] mac80211: fix alignment issue with compare_ether_addr()

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________________________________________
From: John W. Linville [linville@xxxxxxxxxxxxx]
Sent: Wednesday, May 28, 2008 8:46 PM
To: Senthilkumar Balasubramanian
Cc: johannes@xxxxxxxxxxxxxxxx; ron.rindjunsky@xxxxxxxxx; linux-wireless@xxxxxxxxxxxxxxx; Luis Rodriguez
Subject: Re: [PATCH] mac80211: fix alignment issue with compare_ether_addr()

On Wed, May 28, 2008 at 08:20:48PM +0530, Senthil Balasubramanian wrote:
> This addresses an alignment issue with compare_ether_addr().
> The addresses passed to compare_ether_addr should be two bytes aligned.
> It may function properly in x86 platform. However may not work properly
> on IA-64 or ARM processor.

> --- a/net/mac80211/rx.c
> +++ b/net/mac80211/rx.c
> @@ -1116,7 +1116,9 @@ ieee80211_data_to_8023(struct ieee80211_rx_data *rx)
>       u16 fc, hdrlen, ethertype;
>       u8 *payload;
>       u8 dst[ETH_ALEN];
> -     u8 src[ETH_ALEN];
> +     /* Should be aligned on 2 bytes for compare_ether_addr() */
> +     u16 src_aligned[ETH_ALEN >> 1];
> +     u8 *src = (u8 *)src_aligned;
>       struct sk_buff *skb = rx->skb;
>       struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
>       DECLARE_MAC_BUF(mac);

Any reason you couldn't just do this?

I just thought of using the type u16 instead of attribute here. that's all. No specific reason.

@@ -1116,7 +1116,7 @@ ieee80211_data_to_8023(struct ieee80211_rx_data *rx)
        u16 fc, hdrlen, ethertype;
        u8 *payload;
        u8 dst[ETH_ALEN];
-       u8 src[ETH_ALEN];
+       u8 src[ETH_ALEN] __attribute__ ((aligned(2)));
        struct sk_buff *skb = rx->skb;
        struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
        DECLARE_MAC_BUF(mac);

It seems to compile w/o errors on i686, and it seems more clear to me.
Will that not work?

Yes. It should also work. I will re-create the patch and send it to you. I will also include Johannes suggestion of just using __aligned macro.

John
--
John W. Linville
linville@xxxxxxxxxxxxx
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