[Vm-dev] Need a good comment for SystemTracerSpur (was: Tracing a Spur Image from Smalltalk)

[David T. Lewis]

Hi Tim,

The latest version of your system tracer for Spur (on squeaksource) is
in SystemTracing-tfel.41. The SystemTracerSpur class would benefit from
a class comment to explain with it can (and cannot) do. Would you mind
adding a comment to clarify?

My understanding is that SystemTracerSpur traces a 32-bit V3 image to
32-bit Spur, although it is not clear if the traced image can then be
run under a Spur VM (I suspect not, but I am not sure). We also have
64-bit Spur images available, and these will require tracing support
either with SystemTracer, or using the VMMaker tracing that Eliot has
already provided. So I think that this might get confusing soon, and
a class comment will help to explain it.

Thanks!

Dave

On Fri, Feb 26, 2016 at 07:59:04AM -0800, timfelgentreff wrote:
>  
> I've updated the SystemTracer package to trace a Spur-format image.
> 
> This works as far as I can tell, producing a header that looks just like the
> header produced by the VM and the objects written also look good. I can also
> open the image in RSqueak, but not on Spur. It crashes immediately and
> produces a Smalltalk backtrace that looks like it never manages to return
> from the image-saving method (but the names in the Stack-trace all look ok,
> leading me to believe that enough objects got written ok to figure out
> classes, method names, find the right Process to run and so forth).
> 
> Curiously, the old SystemTracer2 class that writes Cog-format images also
> produces images that cannot be opened by Cog VMs, only Interpreter VMs. So I
> assume there are other assumptions that maybe the JIT makes when starting
> up.
> 
> So my question is, what assumptions could there be, and where could I start
> looking.
> 
> Cheers,
> Tim
> 
> (If you're wondering why I'm using the Smalltalk-level tracing at all - in
> our quest to create (with RSqueakVM) a Squeak VM that runs Squeak code fast
> enough that we no longer have to rely on C code from plugins or optional
> primitives, we're trying to see how far we can push this, and e.g. write the
> image from within itself, too.)
> 
> 
> 
> --
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