[Qemu-devel] Re: Qemu PPC ethernet checksum bug

["J. Mayer" <l_indien@magic.fr>]

On Sat, 2007-03-17 at 07:53 -0700, Wessel, Jason wrote:
> Hi Jocelyn,
> 
> Previously it was mentioned that there is a regression that was
> introduced by your original merge on March 8, 2007.  I tested this
> latest code and it is still there.  The nature of the problem is that
> the networking does not work when booting QEMU and using the built in
> slirp networking.  A dhcp packet will work but the udp and tcp packets
> do not appear to send.

> It appears that the packet check sum computed by the Linux network stack
> is incorrect.  When the code in slirp/ip_input.c checks the checksum of
> the udp or tcp packet it throws the packet away because the checksum was
> invalid.  I took the code from March 7, 2007 in cvs for target-ppc/* and
> used it with the latest of everything else and the packet checksums are
> computed correct and the target boots with networking.  
> 
> This points to the problem being what ever instructions the kernel is
> using to compute the checksum are not being translated correctly by your
> latest changes.  The next step will be to take a closer look at which
> instructions are used to compute the checksum.  I thought I might send
> out some further analysis of the original stated problem in case you had
> an idea of where to look to fix the problem off the top of your head.
> If you have any ideas, please drop me some e-mail.
> 
> Also with regard to the 2.6.21 kernel and the ppc-prep machine, I
> patched the kernel to make it send PCI interrupts the same way the prior
> kernels did.  It seems there is a regression there inside the kernel in
> the way that the IRQ acknowledgements are handled.  It could be that the
> emulation is not right in QEMU, but I figure that mystery is one for
> another day.  If you need a kernel that boots on the ppc-prep please let
> me know.  I also patched the prep loader in the linux kernel so I could
> boot an image that was larger than 4 megs.

Hi,

My concern is I cannot reproduce your problem for the following reasons:
- the PREP machine (and the heathrow too...) is broken and cannot even
boot. PCI and/or IRQ are broken, so the Linux kernel hangs.
- when using the "known to work" Linux distributions on the mac99
machine (please take a look at the STATUS file), I am able to download a
kernel from www.kernel.org, which makes me think TCP packets are sent
and received correctly, with valid checksums.

Then, it would be a great thing if you could isolate the failing routine
and, for example, make a test case usable with linux-user emulation.
This would be a great help to solve this issue.

Thanks by advance.

-- 
J. Mayer <l_indien@magic.fr>
Never organized