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32-bit MSDOS (Announce)

posted by kerravon E-mail, Ligao, Free World North, 30.06.2021, 22:42

> > I think the test is - any application executable
> > that demands that a segment register be set a
> > certain way, or an interrupt vector be set a
> > certain way, precludes the ability of the caller
> > to be unprivileged.
>
> I appreciate that PDOS is your personal project --- but what you said is
> simply not true.
>
> I do not know where you get the idea that DPMI applications demand "that a
> segment register be set a certain way",
http://dos32a.narechk.net/manual/index.html

ES = 32-bit data selector with base=PSP and limit=256 bytes


That's what DOS32A executables require. The
caller needs the privilege requires to set the
ES register. In some environments I am interested
in, that is not possible.

Win32 executables do not have such a requirement.
I have no idea why DOS32A (and thus DOS/4GW) didn't
just pass that on the stack.

> or that they cannot run unprivileged.
It is the caller who needs to be privileged in
order to set segment registers and interrupt
vectors. In an environment I am interested in
(interested in running Win32 executables), I
will not be privileged.

I can't think of any reason to require a
privileged caller when the stack can be used.

Note that Win32 executables don't use the stack
for this purpose, they have DLL references
resolved at load time instead. I think (I'm not
sure) the stack would have been better, but the
important thing is that the loader doesn't need
to be privileged in either design.

BFN. Paul.

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