RE: IPv4 checksum oddness (gcc compiler bug?)

	I ran into a checksum problem and filed the following bug
report.
	See if it's related.

http://www.freebsd.org/cgi/query-pr.cgi?pr=69257

>Category:       i386
>Responsible:    freebsd-i386
>Synopsis:       in_cksum_hdr is non-functional without -O compiler flag
>Arrival-Date:   Sun Jul 18 23:10:10 GMT 2004



	-- Qing




> -----Original Message-----
> From: owner-freebsd-current_at_freebsd.org 
> [mailto:owner-freebsd-current_at_freebsd.org] On Behalf Of Mike Bristow
> Sent: Tuesday, August 24, 2004 2:53 PM
> To: freebsd-current_at_freebsd.org
> Subject: IPv4 checksum oddness (gcc compiler bug?)
> 
> 
> Hi,
> 
> I've been suffering from really horrid (~60-70%) packet loss 
> for a while, but only with IPv4.
> 
> I've spent some time thinking I had a hardware problem, as it 
> started at the same time as changed some networking bits but 
> it doesn't appear to be the case:  older (5.2.1) version of 
> FreeBSD don't have this problem.
> 
> I've just cvsuped to RELENG_5 box (cvsup'ed with tag=RELENG_5 
> date=2004.08.24.00.00.00), and with the attached patch I see 
> many entries like in my logs:
> 
> csum calc discrepancy: 
> 45:10:00:64:b0:22:40:00:40:06:98:95:50:b1:28:36:50:b1:28:34
> csum calc discrepancy: 
> 45:10:00:84:b0:23:40:00:40:06:98:74:50:b1:28:36:50:b1:28:34
> 
> However, my patch is obviously wrong.  
> 
> The only thing that I can think of that might possibly be the 
> cause is a compiler optimization bug - but I'm not sure that 
> that's the case, either.  My make.conf is boring 
> (http://www.urgle.com/~mike/make.conf
> if you want to see its dullness).    I can't believe that this is
> a real problem, rather than an artifact of my stupidity, 
> because if it was a real problem everyone with old PIIs would 
> be screaming
> the place down.   
> 
> Has anyone any ideas as to how to debug this?  
> 
> The kernel is GENERIC; possibly interesting other facts include:
> 
> hw.model: Pentium II/Pentium II Xeon/Celeron
> hw.ncpu: 2
> vr0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         inet 80.177.40.52 netmask 0xfffffff0 broadcast 80.177.40.63
>         inet6 fe80::280:c8ff:feea:8041%vr0 prefixlen 64 scopeid 0x1
>         inet6 2002:50b1:2836:1:280:c8ff:feea:8041 prefixlen 
> 64 autoconf
>         ether 00:80:c8:ea:80:41
>         media: Ethernet autoselect (100baseTX <full-duplex>)
>         status: active
> 
> 
> --- ip_input.c.orig     Tue Aug 24 22:24:45 2004
> +++ ip_input.c  Tue Aug 24 22:24:45 2004
> _at__at_ -366,6 +366,14 _at__at_
>         } else {
>                 if (hlen == sizeof(struct ip)) {
>                         sum = in_cksum_hdr(ip);
> +                       if (sum) {
> +                               u_short sumchk;
> +                               sumchk = in_cksum(m, hlen);
> +                               if (!sumchk) {
> +                                       printf("csum calc 
> discrepancy: %20D\n", (u_char *)ip, ":");
> +                                       sum = 0;
> +                               }
> +                       }
>                 } else {
>                         sum = in_cksum(m, hlen);
>                 }
> 
> 
> -- 
> You dont have to be illiterate to use the Internet, but it 
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