[Vm-dev] 64bit FFI?

Eliot Miranda eliot.miranda at gmail.com
Thu Feb 12 19:30:30 UTC 2009

On Thu, Feb 12, 2009 at 11:24 AM, Andreas Raab <andreas.raab at gmx.de> wrote:

> Eliot Miranda wrote:
>> So I don't see how this allows one to have a 64-bit VM that can run true
>> 64-bit images.  What am I missing?
> You are mostly confused about the various combinations ;-) Let's start from
> first principles: You can run 32bit images on top of 64 bit VMs. This is
> achieved by using oopForPointer/pointerForOop.
> In order to run 64 bit images you need a 64 bit image to begin with. The 64
> bit VM doesn't auto-magically convert your 32bit image into a 64 bit one.
> This is done by SystemTracer and friends.
> Does that help?

No.  Read my description of how I think oopForPointer/pointerForOop has to
work and point out to me how one has code that can do both 64-bit and 32-bit
oops and I'll be happy.  AFAICT the only way to run 32-bit images above
64-bit VMs is to swizzle and I don;t see swizzling code in the VMs but do
know there is a swizzling SystemTracer.  So yes, I see that one can start
with a 32-bit image and derive a 64-bit one
 (been  there, done that) and see how (but not why) one would swizzle a
32-bit image to a 64-bit image on start-up (its a slow load).  But I don;t
see how (efficiently) onecreates a 64-bit VM that will run 32-bit and 64-bit
images without swizzling.

There's a dearth of comment from Dan and Ian and David who ave actually
worked with the 64-bit VM.  I'm going to keep quiet on this topic from now
on.  I've clearly antagonized more than enough people this a.m.

Apologies for the noise.

> Cheers,
>  - Andreas
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