page    ,132
  title   VM ASSEMBLY LANGUAGE ROUTINES
;****************************************************************************
;*                                                                         
;*  Copyright (c) 2006, Intel Corporation                                                         
;*  All rights reserved. This program and the accompanying materials                          
;*  are licensed and made available under the terms and conditions of the BSD License         
;*  which accompanies this distribution.  The full text of the license may be found at        
;*  http://opensource.org/licenses/bsd-license.php                                            
;*                                                                                            
;*  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,                     
;*  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.             
;*                                                                          
;****************************************************************************
;****************************************************************************
;                                   REV 1.0
;****************************************************************************
;
; Rev  Date      Description
; ---  --------  ------------------------------------------------------------
; 1.0  05/09/12  Initial creation of file.
;
;****************************************************************************
                             
;* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
; This code provides low level routines that support the Virtual Machine
; for option ROMs. 
;* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

;---------------------------------------------------------------------------
; Equate files needed.
;---------------------------------------------------------------------------

text SEGMENT

;---------------------------------------------------------------------------
;;GenericPostSegment      SEGMENT USE16
;---------------------------------------------------------------------------

;****************************************************************************
; EbcLLCALLEX
;
; This function is called to execute an EBC CALLEX instruction. 
; This instruction requires that we thunk out to external native
; code. For x64, we switch stacks, copy the arguments to the stack
; and jump to the specified function. 
; On return, we restore the stack pointer to its original location.
;
; Destroys no working registers.
;****************************************************************************
; VOID EbcLLCALLEXNative(UINTN FuncAddr, UINTN NewStackPointer, VOID *FramePtr)
EbcLLCALLEXNative        PROC
      push   rbp
      push   rbx
      mov    rbp, rsp
      ; Function prolog
      
      ; Copy FuncAddr to a preserved register.
      mov    rbx, rcx

      ; Set stack pointer to new value
      mov    rsp, rdx      
      
      ; Considering the worst case, load 4 potiential arguments
      ; into registers.
      mov    rcx, qword ptr [rsp]
      mov    rdx, qword ptr [rsp+8h]
      mov    r8,  qword ptr [rsp+10h]
      mov    r9,  qword ptr [rsp+18h]

      ; Now call the external routine
      call  rbx
      
      ; Function epilog
      mov      rsp, rbp
      pop      rbx
      pop      rbp
      ret
EbcLLCALLEXNative    ENDP


; UINTN EbcLLGetEbcEntryPoint(VOID);
; Routine Description:
;   The VM thunk code stuffs an EBC entry point into a processor
;   register. Since we can't use inline assembly to get it from
;   the interpreter C code, stuff it into the return value 
;   register and return.
;
; Arguments:
;     None.
;
; Returns:
;     The contents of the register in which the entry point is passed.
;
EbcLLGetEbcEntryPoint        PROC
    ret
EbcLLGetEbcEntryPoint    ENDP

;/*++
;
;Routine Description:
;  
;  Return the caller's value of the stack pointer.
;
;Arguments:
;
;  None.
;
;Returns:
;
;  The current value of the stack pointer for the caller. We
;  adjust it by 4 here because when they called us, the return address
;  is put on the stack, thereby lowering it by 4 bytes.
;
;--*/

; UINTN EbcLLGetStackPointer()            
EbcLLGetStackPointer        PROC
    mov    rax, rsp      ; get current stack pointer
    ; Stack adjusted by this much when we were called,
    ; For this function, it's 4.
    add   rax, 4
    ret
EbcLLGetStackPointer    ENDP

; UINT64 EbcLLGetReturnValue(VOID);
; Routine Description:
;   When EBC calls native, on return the VM has to stuff the return
;   value into a VM register. It's assumed here that the value is still
;    in the register, so simply return and the caller should get the
;   return result properly.
;
; Arguments:
;     None.
;
; Returns:
;     The unmodified value returned by the native code.
;
EbcLLGetReturnValue   PROC
    ret
EbcLLGetReturnValue    ENDP

text  ENDS
END