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include vmm.inc
 
mov     eax, TimeOut            ; milliseconds until time out
mov     edx, OFFSET32 RefData   ; points to reference data
mov     esi, OFFSET32 Callback  ; points to callback procedure to install
VMMcall Call_When_VM_Returns
 
The Call_When_VM_Returns service installs a callback procedure that receives
control when a virtual machine executes the iret instruction for the current
interrupt.
 
Parameter  Description
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TimeOut    Specifies the number of milliseconds to wait before calling the
           callback procedure. The time-out occurs only if the iret
           instruction is not executed before the specified time elapses. If
           this parameter is positive, the system calls the callback when
           time elapses. If this parameter is negative, the system calls the
           callback when time elapses and calls it again when the iret
           instruction is executed. If this parameter is zero, the system
           ignores the time-out.
 
RefData    Points to reference data to be passed to the callback procedure.
 
Callback   Points to the callback procedure to install. See the Comments
           section for more information about this procedure.
 
Return Value
 
This service has no return value.
 
Comments
 
A virtual device typically uses this service in a callback procedure that it
installed using the Hook_V86_Int_Chain service. This service directs the
system to replace the return address for the interrupt with the address of
the callback procedure. That is, the system pushes the callback procedure
address on the stack when it creates the stack frame for the interrupt. The
system then passes the interrupt to the virtual machine.
 
When the virtual machine executes the iret instruction, the callback
procedure receives control and can carry out tasks. After the callback
procedure returns, the system restores the original interrupt return address
and execution continues as if returning from the interrupt.
 
The system calls this callback procedure as follows:
 
mov     ebx, VM                 ; current VM handle
mov     edx, OFFSET32 RefData   ; points to reference data
mov     ebp, OFFSET32 crs       ; points to a Client_Reg_Struc
call    [Callback]
 
The VM parameter is a handle identifying the current virtual machine. The
RefData parameter points to the reference data supplied when the callback
procedure was installed, and crs points to a Client_Reg_Struc structure
containing the register values for the virtual machine.
 
If the system calls the callback procedure as a result of a time-out, it
sets the carry flag before calling the procedure. If the system calls the
callback a second time (once for a time-out and once for the iret
instruction), the system sets the zero flag before calling the procedure.
 
Uses
 
Client_CS, Client_EIP, Flags
 
See Also
 
Hook_V86_Int_Chain
 
 
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