[Click] [PATCH] EtherAddress needs packing

[Eddie Kohler]

Harald,

Thank you very much for this explanation and for the debugging!!!  I've 
applied a version of this patch, it should be visible soon.

Eddie


Harald Schiöberg wrote:
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> Eddie Kohler wrote:
>> Hi Harald,
>>
>> On which machine is sizeof(EtherAddress) not 6?  Just curious what
>> problem this is solving.
>>
> 
> this is the compiler:
> armeb-linux-g++ -pipe -march=armv5te -mtune=xscale -funit-at-a-time -O2 -g3
> 
> The elements of "uint16_t[3] _data" seem to end up 32-bit aligned.
> 
> here is a bit more detail:
> 
> test config at the bottom of the mail (basically a
> ICMPPingResponder/ARPResponder duo)
> 
> this is the result when pinging the host:
> 
> 01:10:28.822327 00:40:48:b2:3a:c7 > 00:d0:12:09:89:42, ethertype IPv4
> (0x0800), length 98: 172.17.2.12 > 172.17.2.203: ICMP echo request, id
> 31529, seq 1, length 64
> 01:10:28.823319 00:d0:12:09:89:42 > 48:b2:12:09:3a:c7, ethertype IPv4
> (0x0800), length 98: 172.17.2.203 > 172.17.2.12: ICMP echo reply, id
> 31529, seq 1, length 64
> 
> note the src-mac of the echo req. and the dst-mac of the reply, you see
> that the reply contains bytes [3][4][garbage][garbage[5][6] of the mac
> address.
> 
> It all seems to break in arptable.hh:188:
> 
>  *eth = it->_eth;
> 
> (*eth points to the dst_mac field in the packet, "it->_eth" is the
> EtherAddress that was just looked up in the table)
> 
> but that's rather hard to tell since the bug only occurs at -O2 which
> means this piece of code is inlined, and giving a hard time to the
> debugger.
> 
> - ---snip click configuration ---
> ControlSocket(TCP, 9200);
> AddressInfo(eth0 172.17.2.203/24);
> 
> elementclass IPDevice {
> 
> $device |
>         td :: Queue -> ToDevice($device);
> 
>         FromDevice($device, SNIFFER true) ->
> 
>         cl :: Classifier(12/0806 20/0001, 12/0806 20/0002, 3/ffffff,
> 12/0800 30/AC1102CB);
>         cl[1] -> [1]aq :: ARPQuerier($device, $device)  -> td;
> 
>         input[0] -> [0] aq;
> 
>         cl[0] -> ARPResponder($device:ip $device) -> td;
> 
>         cl[2] -> [1]output;
> 
>         cl[3] -> Strip(14) -> CheckIPHeader -> IPPrint (ip-in) -> [0]output;
>         input[1] -> td;
> }
> 
> wired_if :: IPDevice (eth0);
> 
> wired_if[0] -> ICMPPingResponder -> SetIPChecksum -> [0]wired_if ;
> 
> Idle -> [1]wired_if[1] ->  Discard;
> 
> - --
> Harald Schiöberg
> Technische Universität Berlin | T-Laboratories | FG INET
> www: http://www.net.t-labs.tu-berlin.de
> Phone: +49-(0)30-8353-58476 | Fax: +49-(0)391 534 783 47
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