[Vm-dev] SystemTracing: SystemTracing-dtl.23.mcz

stephane ducasse stephane.ducasse at gmail.com
Mon Dec 12 14:35:28 UTC 2011

excllent I will add that in the class comments.


On Dec 12, 2011, at 12:43 PM, David T. Lewis wrote:

> On Mon, Dec 12, 2011 at 08:18:41AM +0100, stephane ducasse wrote:
>> Thanks I committed it.
> Thanks, next time I will do it myself :)
>> Now I have a question
>> SystemTracer64 is to run on 64
>> How do I say to SystemTracer or SystemTracer2 that I want to convert or not to 64 bits?
>> Because I thought (stupidly) that SystemTracer2 was for 32->32
> No, you are correct. SystemTracer2 is for 32->32. SystemTracer is
> the original version, which IMO is useful for education to understand
> how these things work, but is not useful with current images.
> SystemTracer64 is for converting an existing (32-bit format) image
> to the experimental 64-bit object format. It is a subclass of
> SystemTracer2 with methods for converting headers, oops, and fields
> from the normal 32-bit format to the 64-bit format.
> This is sometimes confusing, because people may assume that a
> 64-bit image is for 64-bit platforms, but actually it is only
> about the internal data formats. You can run a 32-bit image on
> a 64-bit platform, so for example there is no reason that you
> could not run a 64-bit image on a 32-bit Cog VM (this would
> require some development in the oscog VMMaker but no reason
> it cannot be done). I say this because people may assume that
> 32-bit Cog could not be used for 64-bit images, but this is
> not really true.
> If you invent a new object format (as I expect that Eliot will
> do), then you might create a new subclass of SystemTracer2 that
> would know how to convert to that format.
> Dave

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