netdev - Re: wireless extensions vs. 64-bit architectures

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Message-ID: <20070308184954.GA24485@bougret.hpl.hp.com>
Date:	Thu, 8 Mar 2007 10:49:54 -0800
From:	Jean Tourrilhes <jt@....hp.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Michael Buesch <mb@...sch.de>, linux-wireless@...r.kernel.org,
	netdev <netdev@...r.kernel.org>, Jeff Garzik <jgarzik@...ox.com>,
	Dan Williams <dcbw@...hat.com>,
	Jouni Malinen <jkm@...icescape.com>
Subject: Re: wireless extensions vs. 64-bit architectures

On Thu, Mar 08, 2007 at 03:39:07PM +0100, Johannes Berg wrote:
> On Tue, 2007-03-06 at 18:03 -0800, Jean Tourrilhes wrote:
> 
> > 	Ok, please check the patch attached. I don't have a box to
> > test that on, and on my 32 bit kernel it is not even compiled, but I
> > believe I got everything all right.
> 
> Don't I wish it was that easy... Granted, that does seem to fix the
> issue with iw_point but that's not the only thing that's broken. Here's
> the next thing, I think this only happens after applying that patch,
> without it probably just craps out earlier. Same thing happens with
> iwevent (and maybe other things too.)
> 
> Enabling debugging in wireless tools yields (on my 64-bit kernel with
> 32-bit userland):
> # LD_LIBRARY_PATH=.  ./iwlist wlan0 scan
> Scan result 4096
> [00:18:8B:15:50:8A:35:E0:00:01:00:C0:02:E1:B8:0E:C0:00:00:00:50:8A:35:F0:00:19:8B:1B:50:8A:35:E0:00:09:00:01:50:8A:35:F0:47:6F:6C:6F:73:4E:65:74:7A:00:18:8B:01:50:8A:35:E0:49:45:45:45:20:38:30:32:2E:31:31:62:67:00:35:F0:00:0C:8B:07:50:8A:35:E0:00:00:00:03:00:10:8B:05:50:8A:35:E0:00:00:00:07:00:00:00:32:00:10:8B:2B:50:8A:35:E0:00:00:08:00:67:00:35:F0:00:70:8B:21:50:8A:35:E0:00:0F:42:40:00:00:00:32:00:1E:84:80:00:00:00:32:00:53:EC:60:00:00:00:32:00:5B:8D:80:00:00:00:32:00:89:54:40:00:00:00:32:00:A7:D8:C0:00:00:00:<lots more zeroes>
> wlan0     Scan completed : 
> DBG - stream->current = 0x10019008, stream->value = (nil), stream->end = 0x1001a008
> DBG - iwe->cmd = 0x8B15, iwe->len = 24
> 
>                          ^^^^^^^^^^^^^ that's already bogus

	Ok, now I get it. It's an alignement issue, the kernel align
struct to 64 bit boundary, whereas the userspace expect it to 32 bit
boundary. Pretty nasty.
	A proper fix would involve forcing the alignement in the
kernel. Unfortunately, that would break 64bit->64bit configs. I think
I can build a workaround for this in iwlib.

	Thanks for the detailed bug report !

	Jean
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