DOS: fix int08 stack for DPMI mode.#27
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The DPMI spec requires a DPMI host to provide a locked protected mode stack for hardware interrupts. So after the interrupt handler changing DS/ES, DS equals ES, but SS is not. but the compiled code assume SS also equals DS (flat/small model). The crashed disassembly for timer_poll_proc_ptr looks like this:
Here EBP by default is using SS, but stos uses ES, thus cause a incorrect address.
This problem does not exist when no DPMI present, as the GO32v2 extender will provide a interrupt stack that uses program current DS. But it won't work with CWSDPMI.
After the fix, it should work with CWSDPMI and probably Windows too. And works with SBEMU. FYI SBEMU provides OPL3 emulation using modern sound cards (AC97, Intel HDA etc.).