On Thu, 07 Mar 2002 10:49:22 -0800 Terry Lambert <[EMAIL PROTECTED]> wrote:
> Simon 'corecode' Schubert wrote: > > to everybody who doesn't believe that: it really generates bad code. > > i've been having severe problems with my tcp and udp stack lately (on a > > i586/mmx machine). guess what, -O2 resulted in code which >>sometimes<< > > generated bad tcp and/or udp checksums (depending on ip). i didn't > > investigate any further, but believe me: not being able to access some > > dns servers is a pain in the ass. > > Are you using NAT? yep. > The libalias incremental checksum calculation is incorrect; > it assumes that a two's complement network order underflow > will result in the same value as a one's complement host > order underflow. This results in off-by-one errors. so is this an optimisation issue or not? when compiling with -O it works again. furthermore i don't know if my bind uses the internal address or the external one for queries. > This is actually a *different* problem than the RFC 1624 > correction of RFC 1141 (also an off-by-one error). > > Have you used a recent version of ethereal? It's an incredible > bugger to get installed correctly for 4.5 or above, since you > have to come from packages (the dependencies for the ports are > incorrect), but it will tell you the correct checksum vs. the > one that it got. > > There's also printing it out in tcp_input when you get a bad > checksum. If you see a lot of "0xfffe", then you'll know it's > an off-by-one error. yah, got lots of them, seen in tcpdump -vvvxXlei gif0 ;] > If the problem is only on ACK packets... I can tell you that > the tcp_respond() code path is not really throughly exercised. tho i've seen these problems recently on UDP DNS lookups, too. then i switched back to -O cheerz corecode -- /"\ http://corecode.ath.cx/ \ / \ ASCII Ribbon Campaign / \ Against HTML Mail and News
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