Hi Jonathan!

Thus quoth Jonathan de Boyne Pollard to David Noon:

I doubt if OS/2 would load a PDD with 32-bit code in it.

The kernel *forces* all segments in a PDD to 16-bit on load, ignoring the 32-bit-indicator in the file image. I learned this from my own experiments on this subject.

OS/2 will load a PDD with 32 bit code segments just fine.

Dennis, this is true - but see above.

The "interface" to the rest of the system is still via 16 bit
addressing. The PDD needs to be able to be called via a 16 bit
interface and use 16 bit DevHelp. Just some "assembly glue"
required. <g>

Exactly, very easy indeed!

JdBP> As far as I know, the restriction on I/O instructions applies to
JdBP> application programs running in user mode, not physical device
JdBP> drivers running in kernel mode. So both 16-bit and 32-bit code
JdBP> can perform I/O instructions just fine in a PDD. (This is to be
JdBP> expected, anyway, since PDDs run at ring 0, and the x86
JdBP> architecture doesn't allow IOPL to be set lower than 0!)

This is true, tested by myself.

JdBP> The questions that are raised, however, are:

JdBP> What are the base and limit of the 32-bit selectors in CS/DS/SS
JdBP> for a 32-bit PDD ? Are they based at the same address as the
JdBP> user-mode flat-model CS/DS/SS selectors ?

No.

JdBP> I assume that they are GDT selectors.

Of course, since driver segments must be addressable in every processor context.

JdBP> But who creates the GDT entries ? Does the PDD loader do it,
JdBP> and provide a kernel-mode thunking mechanism that all PDDs can
JdBP> use ?

No, up to now, the kernel has no 32-bit PDD support (see above also). If you like to have a 32-bit PDD, you have to construct it yourself *after load time*.
So your driver itself switches from a 'mini 16-bit PDD' to a full fledged 32-bit PDD by modifying its code segment descriptor in the GDT at any point at init time. The thunking is no problem at all, just 4 instructions in case of the DevHlp calls.

JdBP> If so, what is it ? Or is each 32-bit PDD expected to create its
JdBP> own private selectors ?
JdBP> Anyone know ?

A working example is available on request.

bye, Dani
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