[Vm-dev] 64bit FFI?
bert at freudenbergs.de
Thu Feb 12 19:58:25 UTC 2009
On 12.02.2009, at 20:40, Eliot Miranda wrote:
>> 1) a 32-bit VM compiled to run 32-bit images
>> 2) a 32-bit VM compiled to run 64-bit images
>> 3) a 64-bit VM compiled to run 32-bit images
>> 4) a 64-bit VM compiled to run 64-bit images
> Speaking through a self-imposed gag let me suggest the FAQ
> distinguish clearly between a 64-bit VM (meaning a VM that runs 64-
> bit images that necessarly is compiled as a 64-bit executable) and a
> 32-bit VM compiled to run as a 64-bit executable. The latter
> doesn't count as a 64-bit VM for me. 64-bit clean perhaps.
It may not count for you but that's how we have been calling it. Since
nobody expects 64 bit images to work "64-bit" VM refers to the host
architecture. I'm not quite sure how we could phase out that
> Let me further suggest that 2) is pointless, in that it can't scale
> beyond the 32-bit address space but uses about 1.5 times the space
> of a 32-bit image as it tries to do so. i.e. it'll fail a lot
> earlier than a 32-bit image. Further, if a 64-bit image is larger
> than will fit in a 32-bit address space one *cant* run it on 2
> because it won't fit.
The point of this was not to be used in production but to *create* VM
for running a 64 bit image without having to use a 64 bit host.
> So I would suggest the FAQ explain tat there are really three
> different VMs, two 32-bit ones and one 64-bit one. One of the 32-
> bit VMs is compiled to run as a 64-bit executable on 64-bit systems
> but only runs a 32-bit image. That at least accords with the planet
> I grew up on :)
Only if you want to use 64 bit images. Which nobody wants. Yet.
- Bert -
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