DOS ain't dead - OS/2 extender

OS/2 extender (Developers)

posted by kerravon , Ligao, Free World North, 11.09.2025, 17:57

> > In the same way that we have 32-bit DOS extenders to allow access to
> memory
> > above 1 MiB - is it technically feasible to have a 64-bit OS/2 extender
> to
> > allow access to memory above 4 GiB?
> >
> > What would that look like?
>
> It would be very difficult, as the kernel would need to be made aware of
> it. In DOS, the extender itself (or the DPMI host, which might be the same
> thing) is the kernel, which can do whatever it wants to. Under OS/2,
> user programs are not allowed to exert this kind of control over the
> machine.

I'm not sure what OS/2 needs to be able to run a privileged program.

Some sort of "administrator command prompt"?

I was considering disabling interrupts, entering 64-bit mode, doing all my work above 4 GiB, and then when I need any service, switching back to 32-bit mode and reenabling interrupts.

Presumably exactly the same as DOS extenders did, especially DOS extenders written prior to DPMI existing (I think that's a thing).

You think the above scheme won't work?

I'm not sure how to find out what memory above 4 GiB I can use - I might need the user to provide address ranges which they can get from some other mechanism. E.g. there is a DOS interrupt that gives you all available memory, including memory above 4 GiB. The output from that interrupt could be put into a flat file when I run my OS/2 extender.

I have a new version of the cc64 compiler to try out - I'm hoping that that is more robust than the one I currently use. So that's a public domain x64 compiler. But it is generated code, so is not a lot different from just having a binary.

So I'm expecting to have a mini-Win64 under OS/2, as there doesn't appear to be such a thing as a 64-bit LX executable.

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Complete thread:

OS/2 extender - kerravon, 10.09.2025, 21:05 (Developers)
- OS/2 extender - Rugxulo, 10.09.2025, 21:30
- OS/2 extender - Ringding, 11.09.2025, 17:44
  - OS/2 extender - kerravon, 11.09.2025, 17:57
    - OS/2 extender - Ringding, 11.09.2025, 20:41
      - OS/2 extender - kerravon, 12.09.2025, 00:08
        OS/2 extender - Rugxulo, 12.09.2025, 04:07
        OS/2 extender - kerravon, 12.09.2025, 16:55
        OS/2 extender - Ringding, 12.09.2025, 17:20
        OS/2 extender - kerravon, 12.09.2025, 18:03