From owner-freebsd-alpha@FreeBSD.ORG  Mon Nov 15 21:42:06 2004
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Date: Mon, 15 Nov 2004 22:42:03 +0100 (CET)
From: Sten Spans <sten@blinkenlights.nl>
To: John Baldwin <jhb@FreeBSD.org>
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cc: Robert Watson <rwatson@FreeBSD.org>
cc: freebsd-alpha@FreeBSD.org
Subject: Re: alpha and em mtu
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On Mon, 15 Nov 2004, John Baldwin wrote:

> On Monday 15 November 2004 04:07 pm, Sten Spans wrote:
>> On Mon, 15 Nov 2004, John Baldwin wrote:
>>
>> changed to ((off0 & 0x3) != 0), didn't seem to print anything.
>
> Ok, try this one then instead:
>
> Index: netinet/tcp_input.c
> ===================================================================
> RCS file: /usr/cvs/src/sys/netinet/tcp_input.c,v
> retrieving revision 1.255
> diff -u -r1.255 tcp_input.c
> --- netinet/tcp_input.c	7 Nov 2004 19:19:35 -0000	1.255
> +++ netinet/tcp_input.c	15 Nov 2004 21:19:50 -0000
> @@ -504,6 +504,8 @@
> 			}
> 		}
> 		ip = mtod(m, struct ip *);
> +		if (((uintptr_t)ip & 0x3) != 0)
> +			printf("%s: ip %p is misaligned\n", __func__, ip);
> 		ipov = (struct ipovly *)ip;
> 		th = (struct tcphdr *)((caddr_t)ip + off0);
> 		tlen = ip->ip_len;
>

This does print something:
deepthought# ifconfig em0 mtu 1501
deepthought# tcp_input: ip 0xfffffc001817f00e is misaligned

fatal kernel trap:

     trap entry     = 0x4 (unaligned access fault)
     faulting va    = 0xfffffc001817f02e
     opcode         = 0x28
     register       = 0x1
     pc             = 0xfffffc00004cd134
     ra             = 0xfffffc00004ccf94
     sp             = 0xfffffe00187a9af0
     curthread      = 0xfffffc001f3a70e0
         pid = 14, comm = swi1: net

[thread 100006]
Stopped at      tcp_input+0x3a4:        srl     t0,#0x2,t0      <t0=0x45>


The ip's used are 192.168.1.3 and 192.168.1.4.

-- 
Sten Spans

"There is a crack in everything, that's how the light gets in."
Leonard Cohen - Anthem