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

David T. Lewis lewis at mail.msen.com
Mon Jan 12 18:20:27 UTC 2015

> On 12.01.2015, at 01:47, David T. Lewis <lewis at mail.msen.com> wrote:
>> I made a minor update to the SystemTracer that allows it to convert a
>> 64-bit
>> image back to 32-bit format, and it worked perfectly with my working
>> Squeak
>> image that has been in 64-bit format for several months now.
> Nice!
>>  The resulting 32-bit image must be opened first using an interpreter
>> VM,
>>  after which it can be run normally with a Cog VM. Tracing should be
>> done
>>  using an interpreter VM.
> Why is that?

I have not yet figured out why it did not work with Cog. One possibility
is that the system is running a jitted method at the time of the trace,
and when the new 64-bit image wakes up in the interpreter VM, it is still
in the middle of that method and the VM does not know what to do with it.

That said, I also tried tracing 64 back to 32 and then running the traced
32-bit image immediately in Cog. That also did not work, so it may be that
there is some other issue involved. I am guessing that it might be related
to the saved start of memory location in the image header, but this is
just a guess.


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