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include vmm.inc
 
VMMcall _GetGlblRng0V86IntBase
 
mov     [Address], eax      ; address for ring-0 V86 interrupt handlers
 
The _GetGlblRng0V86IntBase service returns the linear address used to manage
ring-0 global V86 interrupt handlers.
 
This service is only available during initialization, and only available for
Windows version 3.1 or later.
 
This service has no parameters.
 
Return Value
 
The EAX register contains the linear address of the ring-0 handler.
 
Comments
 
Ring-0 global V86 interrupt handlers require segment selectors that permit
execution in protected mode at ring 0. Furthermore, the selectors must
represent memory that is not subject to page faults. Page faults are a
potential problem because part of the global code or data for a ring-0 V86
interrupt handler may overlap with the noninstanced part of an instance data
page.
 
This service returns the linear address of the start of a V86 address space
in which instance data pages are always present. The linear address is a
duplicate of the V86 address 0:0 in the system virtual machine. The size of
this duplicate mapping is 1 megabyte plus 64 kilobytes. This address space
includes the xMS HMA (pages 100h-10Fh). The system sets up the duplicate
mapping after all virtual devices have processed the Sys_Critical_Init
message. The A20 state of the system virtual machine, or any other virtual
machine, has no effect on the mapping used for this address space. The
physical (global) HMA is always mapped in this address space. Thus, A20 is
effectively always on (HMA always enabled).
 
Virtual devices that use this address space must wait until the Device_Init
or Init_Complete message to request the address. This service returns zero
if a virtual device attempts to retrieve the address while processing the
Sys_Critical_Init message. If a virtual device needs the address sooner than
receipt of the Device_Init message, the virtual device can use a base
address of 0 to build the selectors. It can then edit the selectors when it
processes the Device_Init message, changing the base address to the correct
location by adding in the return value from this service.
 
Ring-0 global V86 interrupt handlers may only access global memory.
 
Instance data does not work properly in this address space. The local part
of this address space is mapped with the system nul page.
 
Uses
 
EAX
 
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