[Vm-dev] 64 bits

[Eliot Miranda]

On Fri, May 4, 2012 at 12:31 PM, Igor Stasenko <siguctua at gmail.com> wrote:

>
> On 4 May 2012 18:27, Eliot Miranda <eliot.miranda at gmail.com> wrote:
> >
> >
> >
> > On Fri, May 4, 2012 at 7:44 AM, Bert Freudenberg <bert at freudenbergs.de>
> wrote:
> >>
> >>
> >> On 04.05.2012, at 16:33, David T. Lewis wrote:
> >>
> >> > On Fri, May 04, 2012 at 02:36:28PM +0200, Bert Freudenberg wrote:
> >> >>
> >> >> The OP's question was about a Cog VM compiled for x86_64 - is that
> easily available?
> >> >>
> >> >> - Bert -
> >> >
> >> > No, that would be a larger project. Eliot could speak to this better
> >> > than I can, but in general terms I expect that this would involve
> first
> >> > building a 64-bit StackVM (i.e. the current StackVM compiled in 64-bit
> >> > mode), and then developing the code generation for Cog. Both of these
> >> > would involve work above and beyond what I described above for the
> >> > interpreter VM. My assumption would be that these are large enough
> >> > chunks of work that we should not expect them to happen on a strictly
> >> > volunteer basis.
> >> >
> >> > Dave
> >>
> >> I thought that x86-64 was a strict extension of the 32 bit x86 model.
> So Cog's generated 32 bit code should work just fine even under x86-64.
> >
> >
> > That's not quite true.  x86-64 is actually a different ISA that adds 8
> registers and a pc-relative addressing mode drops some instructions (inc
> dec, others?).  IIRC one has to go through a mode switch to But the
> processor can execute both ISAs. On x86-64, x86 is a "sub-mode" and is
> entered via interrupts or "gate descriptors" (?). See e.g.
> http://wiki.osdev.org/X86-64#Entering_Long_Mode_directly.  So executing
> 32-bit code inside a 64-bit process isn't trivial.  Instead most x86-64
> platforms do provide support for running x86 binaries in the x86 submode.
> >
> > I wish it was easy, but I fear not.  At the very least we would want a
> 32-bit to 64-bit transition on calling the FFI.    Alternatively we could
> look at extending the Cog glue so that generated code is x86 but the glue
> calls x86-64 code in the rest of the VM.  I don't have cycles for this, and
> personally would rather see work on a real x86-64 code generator with a
> full 64-bit image.
> >
>
> Yes, 64bit mode is similar but not the same as 32bit. And of course
> you cannot run binary compiled
> for 32bits and expect that it will work correctly.
>
> [a little OT] FWIW recently Camillo (with a bit of my help) added
> support for 64bit assembler in AsmJit project.
> So, actually we can produce 64-bit compatible code using smalltalk :)
> But of course it is too far from having JIT compiler in VM.
>

Woot!  Why not now apply that expertise to creating a CogIA64Compiler
subclass of CogAbstractInstruction?  Bochs is easily reconfigurable as an
x86-64.


>
> >>
> >>
> >> Cog would have to be cleaned up for pointer operations of course, just
> as you did for the interpreter.
> >>
> >> - Bert -
> >>
> >>
> >
> >
> >
> > --
> > best,
> > Eliot
> >
> >
>
>
>
> --
> Best regards,
> Igor Stasenko.
>



-- 
best,
Eliot
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