Re: [MirageOS-devel] Mirage on Xen/ARM status

[Thomas Leonard <talex5@xxxxxxxxx>]

On 13 June 2014 10:21, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
> On 13 Jun 2014, at 10:15, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>
>> On 13 June 2014 10:09, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
>>> On 12 Jun 2014, at 15:46, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>>>>>
>>>>> The next step is to get networking working on ARM.
>>>>
>>>> This seems to be working now (I can telnet to port 80 and send it a
>>>> message), which it displays on the console.
>>>
>>> Fantastic!!
>>>
>>>> The main problem turned out to be ones_complement_checksum_bigarray,
>>>> which was doing unaligned double-word (64-bit) memory access. This
>>>> faults on ARM. For testing, I replaced it with the version in the unix
>>>> directory.
>>>
>>> Interesting -- they were meant to be exactly the same if I remember.
>>> Is there an actual code difference between the two aside from include
>>> headers?
>>
>> They are very different. Looks like one got optimised without the other here:
>>
>> https://github.com/mirage/mirage-platform/commit/6fc97d77d0846bc7f17bd0702832ea1faa8a7e71
>>
>
> Ah yes, istr the reasoning behind this was that the Unix one would never
> be used in a high-performance context, so portability was more useful than
> performance.
>
> Still, being able to unify these is very desirable, as being able to test
> the stack independently of Xen (and expecting similar behavioural 
> characteristics)
> is extremely important.

Perhaps the ones complement stuff should be moved out of
mirage-platform anyway? It seems to be specific to networking, rather
than to any particular platform. I see there's also a third version in
the ns3 directory, which always returns zero.


-- 
Dr Thomas Leonard        http://0install.net/
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