[Vm-dev] Re: [squeak-dev] A update to SystemTracer for getting back to 32 bits

David T. Lewis lewis at mail.msen.com
Tue Jan 13 16:30:49 UTC 2015

> On 13.01.2015, at 03:29, David T. Lewis <lewis at mail.msen.com> wrote:
>> I was driving home this afternoon and it popped into my head. I am quite
>> sure the the problem is due to the change in floating point word
>> ordering
>> in the Cog image format (6505). If you trace an image that is running
>> under
>> a Cog VM on a little endian host, the Float objects will require special
>> handling to put them back into the original canonical format (which is
>> not
>> the native machine order on a little endian machine).
> But the word accessors in Float handle that I thought? Or don't they, in
> 64 bits?
> - Bert -

This issue would be that the in-memory representation of the float objects
(which contain two 4-byte words of data) have the words reversed (i.e. put
into machine word order) when running on Cog on a little endian machine.
That in-memory representation is the thing being written out to disk
during the trace. The tracer thinks that it is writing objects with fields
in the original (format 6504, non-Cog) format, and it does not know when
it encounters a Float object that it needs to swap the data words. The
reason that it does not know this is that nobody has implemented it yet


More information about the Vm-dev mailing list