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Subject: Re: [mac80211-next:cfg80211-mac80211-multi-bssid 8/20] ERROR:
 "__umoddi3" [net/wireless/cfg80211.ko] undefined!
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Jouni Malinen <j@w1.fi>
Cc:     kbuild test robot <lkp@intel.com>, Peng Xu <pxu@codeaurora.org>,
        kbuild-all@01.org, linux-wireless@vger.kernel.org,
        Sara Sharon <sara.sharon@intel.com>,
        Jouni Malinen <jouni@codeaurora.org>
Date:   Mon, 11 Feb 2019 15:58:48 +0100
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On Mon, 2019-02-11 at 16:57 +0200, Jouni Malinen wrote:
> On Sat, Feb 09, 2019 at 09:08:20AM +0100, Johannes Berg wrote:
> 
> > but maybe the whole thing is more readable as
> > 
> > static inline void cfg80211_gen_new_bssid(const u8 *bssid_addr, u8 max_bssid,
> >                                           u8 mbssid_index, u8 *new_bssid_addr)
> > {
> >         u64 bssid = ether_addr_to_u64(bssid_addr);
> >         u64 mask = GENMASK_ULL(max_bssid - 1, 0);
> >         u64 new_bssid;
> > 
> >         new_bssid &= bssid & ~mask;
> 
> That should be "=" not "&="..

Yes, good point.

> > However, isn't it true that 0 <= mbssid_index < max_bssid? Then the
> > whole masking isn't really needed at all?
> 
> 0 <= mbssid_index < 2^max_bssid. 

True, sorry.

> The transmitted BSSID (i.e., that
> bssid_addr argument) is not required to be the first BSSID in the range,
> so the masking is needed to cover wraparound for addition modulo
> 2^mbssid_index when max_bssid LSBs of bssid are not zeros.

Ah ok.

Alright, I'll send out a proper patch.

Thanks!

johannes