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From: "Rod Pemberton" <do_not_have AT bitfoad DOT cmm>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: 64 bit access under DOS?
Date: Wed, 13 Sep 2006 05:21:54 -0400
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"Martin Str|mberg" <ams AT speedy DOT ludd DOT ltu DOT se> wrote in message
news:4506ff21$0$486$cc7c7865 AT news DOT luth DOT se...
> Ivor Bowden <ivorlist AT peritek DOT com> wrote:
> > I could use something like _farpeekll / _farpokell (long long). I'm not
> > sure what else I would need to do to set up the system for these kind of
> > accesses.
>
> I'm not sure if there are any 64-bit wide x86 instructions but the
> cmpxchg8.
>
> > The other thought I had was to set up some assembly routines to use the
> > AMD64 instructions.
>
> Unfortunately AMD64 instructions are only available in long 64-bit
> (non-compatibility) mode and in long mode vm86 mode isn't supported,
> so this won't happen.
>

Ah, good, someone who is familiar with 64-bit mode.

What you're saying it that there are no override prefixes to access the
64-bit instructions in 32-bit mode.  Correct?

Is there a method to switch into and out of 64-bit mode safely while running
under 32-bit protected mode (DPMI or Windows)?


Rod Pemberton