; $Id: EMAllA.asm 62478 2016-07-22 18:29:06Z vboxsync $
;; @file
; EM Assembly Routines.
;

;
; Copyright (C) 2006-2016 Oracle Corporation
;
; This file is part of VirtualBox Open Source Edition (OSE), as
; available from http://www.virtualbox.org. This file is free software;
; you can redistribute it and/or modify it under the terms of the GNU
; General Public License (GPL) as published by the Free Software
; Foundation, in version 2 as it comes in the "COPYING" file of the
; VirtualBox OSE distribution. VirtualBox OSE is distributed in the
; hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
;

;*******************************************************************************
;* Header Files                                                                *
;*******************************************************************************
%include "VBox/asmdefs.mac"
%include "VBox/err.mac"
%include "iprt/x86.mac"

;; @def MY_PTR_REG
; The register we use for value pointers (And,Or,Dec,Inc,XAdd).
%ifdef RT_ARCH_AMD64
 %define MY_PTR_REG     rcx
%else
 %define MY_PTR_REG     ecx
%endif

;; @def MY_RET_REG
; The register we return the result in.
%ifdef RT_ARCH_AMD64
 %define MY_RET_REG     rax
%else
 %define MY_RET_REG     eax
%endif

;; @def RT_ARCH_AMD64
; Indicator for whether we can deal with 8 byte operands. (Darwin fun again.)
%ifdef RT_ARCH_AMD64
 %define CAN_DO_8_BYTE_OP  1
%endif


BEGINCODE


;;
; Emulate CMP instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateCmp(uint32_t u32Param1, uint64_t u64Param2, size_t cb);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]  rdi  rcx       Param 1 - First parameter (Dst).
; @param    [esp + 08h]  rsi  edx       Param 2 - Second parameter (Src).
; @param    [esp + 10h]    Param 3 - Size of parameters, only 1/2/4/8 (64 bits host only) is valid.
;
align 16
BEGINPROC   EMEmulateCmp
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 10h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef RT_ARCH_AMD64
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    cmp     rcx, rdx                    ; do 8 bytes CMP
    jmp short .done
%endif

.do_dword:
    cmp     ecx, edx                    ; do 4 bytes CMP
    jmp short .done

.do_word:
    cmp     cx, dx                      ; do 2 bytes CMP
    jmp short .done

.do_byte:
    cmp     cl, dl                      ; do 1 byte CMP

    ; collect flags and return.
.done:
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateCmp


;;
; Emulate AND instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateAnd(void *pvParam1, uint64_t u64Param2, size_t cb);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]    Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]    Param 2 - Second parameter.
; @param    [esp + 10h]    Param 3 - Size of parameters, only 1/2/4/8 (64 bits host only) is valid.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateAnd
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 10h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    and     [MY_PTR_REG], rdx           ; do 8 bytes AND
    jmp short .done
%endif

.do_dword:
    and     [MY_PTR_REG], edx           ; do 4 bytes AND
    jmp short .done

.do_word:
    and     [MY_PTR_REG], dx            ; do 2 bytes AND
    jmp short .done

.do_byte:
    and     [MY_PTR_REG], dl            ; do 1 byte AND

    ; collect flags and return.
.done:
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateAnd


;;
; Emulate LOCK AND instruction.
; VMMDECL(int)      EMEmulateLockAnd(void *pvParam1, uint64_t u64Param2, size_t cbSize, RTGCUINTREG32 *pf);
;
; @returns VINF_SUCCESS on success, VERR_ACCESS_DENIED on \#PF (GC only).
; @param    [esp + 04h]  gcc:rdi  msc:rcx   Param 1 - First parameter - pointer to data item (the real stuff).
; @param    [esp + 08h]  gcc:rsi  msc:rdx   Param 2 - Second parameter- the immediate / register value.
; @param    [esp + 10h]  gcc:rdx  msc:r8    Param 3 - Size of the operation - 1, 2, 4 or 8 bytes.
; @param    [esp + 14h]  gcc:rcx  msc:r9    Param 4 - Where to store the eflags on success.
;                                                     only arithmetic flags are valid.
align 16
BEGINPROC   EMEmulateLockAnd
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     r9, rcx                     ; r9 = eflags result ptr
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 10h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter (MY_PTR_REG)
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    lock and [MY_PTR_REG], rdx           ; do 8 bytes OR
    jmp short .done
%endif

.do_dword:
    lock and [MY_PTR_REG], edx           ; do 4 bytes OR
    jmp short .done

.do_word:
    lock and [MY_PTR_REG], dx            ; do 2 bytes OR
    jmp short .done

.do_byte:
    lock and [MY_PTR_REG], dl            ; do 1 byte OR

    ; collect flags and return.
.done:
    pushf
%ifdef RT_ARCH_AMD64
    pop    rax
    mov    [r9], eax
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 14h + 4]
    pop     dword [eax]
%endif
    mov     eax, VINF_SUCCESS
    retn
ENDPROC     EMEmulateLockAnd

;;
; Emulate OR instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateOr(void *pvParam1, uint64_t u64Param2, size_t cb);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]    Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]    Param 2 - Second parameter.
; @param    [esp + 10h]    Param 3 - Size of parameters, only 1/2/4/8 (64 bits host only) is valid.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateOr
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 10h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    or      [MY_PTR_REG], rdx           ; do 8 bytes OR
    jmp short .done
%endif

.do_dword:
    or      [MY_PTR_REG], edx           ; do 4 bytes OR
    jmp short .done

.do_word:
    or      [MY_PTR_REG], dx            ; do 2 bytes OR
    jmp short .done

.do_byte:
    or      [MY_PTR_REG], dl            ; do 1 byte OR

    ; collect flags and return.
.done:
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateOr


;;
; Emulate LOCK OR instruction.
; VMMDECL(int)      EMEmulateLockOr(void *pvParam1, uint64_t u64Param2, size_t cbSize, RTGCUINTREG32 *pf);
;
; @returns VINF_SUCCESS on success, VERR_ACCESS_DENIED on \#PF (GC only).
; @param    [esp + 04h]  gcc:rdi  msc:rcx   Param 1 - First parameter - pointer to data item (the real stuff).
; @param    [esp + 08h]  gcc:rsi  msc:rdx   Param 2 - Second parameter- the immediate / register value.
; @param    [esp + 10h]  gcc:rdx  msc:r8    Param 3 - Size of the operation - 1, 2, 4 or 8 bytes.
; @param    [esp + 14h]  gcc:rcx  msc:r9    Param 4 - Where to store the eflags on success.
;                                                     only arithmetic flags are valid.
align 16
BEGINPROC   EMEmulateLockOr
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     r9, rcx                     ; r9 = eflags result ptr
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 10h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter (MY_PTR_REG)
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    lock or [MY_PTR_REG], rdx           ; do 8 bytes OR
    jmp short .done
%endif

.do_dword:
    lock or [MY_PTR_REG], edx           ; do 4 bytes OR
    jmp short .done

.do_word:
    lock or [MY_PTR_REG], dx            ; do 2 bytes OR
    jmp short .done

.do_byte:
    lock or [MY_PTR_REG], dl            ; do 1 byte OR

    ; collect flags and return.
.done:
    pushf
%ifdef RT_ARCH_AMD64
    pop    rax
    mov    [r9], eax
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 14h + 4]
    pop     dword [eax]
%endif
    mov     eax, VINF_SUCCESS
    retn
ENDPROC     EMEmulateLockOr


;;
; Emulate XOR instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateXor(void *pvParam1, uint64_t u64Param2, size_t cb);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]    Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]    Param 2 - Second parameter.
; @param    [esp + 10h]    Param 3 - Size of parameters, only 1/2/4/8 (64 bits host only) is valid.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateXor
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 10h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    xor     [MY_PTR_REG], rdx           ; do 8 bytes XOR
    jmp short .done
%endif

.do_dword:
    xor     [MY_PTR_REG], edx           ; do 4 bytes XOR
    jmp short .done

.do_word:
    xor     [MY_PTR_REG], dx            ; do 2 bytes XOR
    jmp short .done

.do_byte:
    xor     [MY_PTR_REG], dl            ; do 1 byte XOR

    ; collect flags and return.
.done:
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateXor

;;
; Emulate LOCK XOR instruction.
; VMMDECL(int)      EMEmulateLockXor(void *pvParam1, uint64_t u64Param2, size_t cbSize, RTGCUINTREG32 *pf);
;
; @returns VINF_SUCCESS on success, VERR_ACCESS_DENIED on \#PF (GC only).
; @param    [esp + 04h]  gcc:rdi  msc:rcx   Param 1 - First parameter - pointer to data item (the real stuff).
; @param    [esp + 08h]  gcc:rsi  msc:rdx   Param 2 - Second parameter- the immediate / register value.
; @param    [esp + 10h]  gcc:rdx  msc:r8    Param 3 - Size of the operation - 1, 2, 4 or 8 bytes.
; @param    [esp + 14h]  gcc:rcx  msc:r9    Param 4 - Where to store the eflags on success.
;                                                     only arithmetic flags are valid.
align 16
BEGINPROC   EMEmulateLockXor
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     r9, rcx                     ; r9 = eflags result ptr
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 10h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter (MY_PTR_REG)
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    lock xor [MY_PTR_REG], rdx           ; do 8 bytes OR
    jmp short .done
%endif

.do_dword:
    lock xor [MY_PTR_REG], edx           ; do 4 bytes OR
    jmp short .done

.do_word:
    lock xor [MY_PTR_REG], dx            ; do 2 bytes OR
    jmp short .done

.do_byte:
    lock xor [MY_PTR_REG], dl            ; do 1 byte OR

    ; collect flags and return.
.done:
    pushf
%ifdef RT_ARCH_AMD64
    pop    rax
    mov    [r9], eax
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 14h + 4]
    pop     dword [eax]
%endif
    mov     eax, VINF_SUCCESS
    retn
ENDPROC     EMEmulateLockXor

;;
; Emulate INC instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateInc(void *pvParam1, size_t cb);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]  rdi  rcx   Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]  rsi  rdx   Param 2 - Size of parameters, only 1/2/4 is valid.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateInc
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, rdx                    ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     rax, rsi                    ; eax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 08h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
%endif

    ; switch on size
%ifdef RT_ARCH_AMD64
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    inc     qword [MY_PTR_REG]          ; do 8 bytes INC
    jmp short .done
%endif

.do_dword:
    inc     dword [MY_PTR_REG]          ; do 4 bytes INC
    jmp short .done

.do_word:
    inc     word [MY_PTR_REG]           ; do 2 bytes INC
    jmp short .done

.do_byte:
    inc     byte [MY_PTR_REG]           ; do 1 byte INC
    jmp short .done

    ; collect flags and return.
.done:
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateInc


;;
; Emulate DEC instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateDec(void *pvParam1, size_t cb);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]    Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]    Param 2 - Size of parameters, only 1/2/4 is valid.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateDec
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, rdx                    ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     rax, rsi                    ; eax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 08h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
%endif

    ; switch on size
%ifdef RT_ARCH_AMD64
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    dec     qword [MY_PTR_REG]          ; do 8 bytes DEC
    jmp short .done
%endif

.do_dword:
    dec     dword [MY_PTR_REG]          ; do 4 bytes DEC
    jmp short .done

.do_word:
    dec     word [MY_PTR_REG]           ; do 2 bytes DEC
    jmp short .done

.do_byte:
    dec     byte [MY_PTR_REG]           ; do 1 byte DEC
    jmp short .done

    ; collect flags and return.
.done:
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateDec


;;
; Emulate ADD instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateAdd(void *pvParam1, uint64_t u64Param2, size_t cb);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]    Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]    Param 2 - Second parameter.
; @param    [esp + 10h]    Param 3 - Size of parameters, only 1/2/4/8 (64 bits host only) is valid.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateAdd
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 10h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    add     [MY_PTR_REG], rdx           ; do 8 bytes ADD
    jmp short .done
%endif

.do_dword:
    add     [MY_PTR_REG], edx           ; do 4 bytes ADD
    jmp short .done

.do_word:
    add     [MY_PTR_REG], dx            ; do 2 bytes ADD
    jmp short .done

.do_byte:
    add     [MY_PTR_REG], dl            ; do 1 byte ADD

    ; collect flags and return.
.done:
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateAdd


;;
; Emulate ADC instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateAdcWithCarrySet(void *pvParam1, uint64_t u64Param2, size_t cb);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]    Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]    Param 2 - Second parameter.
; @param    [esp + 10h]    Param 3 - Size of parameters, only 1/2/4/8 (64 bits host only) is valid.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateAdcWithCarrySet
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 10h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    stc     ; set carry flag
    adc     [MY_PTR_REG], rdx           ; do 8 bytes ADC
    jmp short .done
%endif

.do_dword:
    stc     ; set carry flag
    adc     [MY_PTR_REG], edx           ; do 4 bytes ADC
    jmp short .done

.do_word:
    stc     ; set carry flag
    adc     [MY_PTR_REG], dx            ; do 2 bytes ADC
    jmp short .done

.do_byte:
    stc     ; set carry flag
    adc     [MY_PTR_REG], dl            ; do 1 byte ADC

    ; collect flags and return.
.done:
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateAdcWithCarrySet


;;
; Emulate SUB instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateSub(void *pvParam1, uint64_t u64Param2, size_t cb);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]    Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]    Param 2 - Second parameter.
; @param    [esp + 10h]    Param 3 - Size of parameters, only 1/2/4/8 (64 bits host only) is valid.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateSub
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 10h]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    sub     [MY_PTR_REG], rdx           ; do 8 bytes SUB
    jmp short .done
%endif

.do_dword:
    sub     [MY_PTR_REG], edx           ; do 4 bytes SUB
    jmp short .done

.do_word:
    sub     [MY_PTR_REG], dx            ; do 2 bytes SUB
    jmp short .done

.do_byte:
    sub     [MY_PTR_REG], dl            ; do 1 byte SUB

    ; collect flags and return.
.done:
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateSub


;;
; Emulate BTR instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateBtr(void *pvParam1, uint64_t u64Param2);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]    Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]    Param 2 - Second parameter.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateBtr
%ifdef RT_ARCH_AMD64
%ifndef RT_OS_WINDOWS
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    and     edx, 7
    btr    [MY_PTR_REG], edx

    ; collect flags and return.
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateBtr

;;
; Emulate LOCK BTR instruction.
; VMMDECL(int)      EMEmulateLockBtr(void *pvParam1, uint64_t u64Param2, RTGCUINTREG32 *pf);
;
; @returns VINF_SUCCESS on success, VERR_ACCESS_DENIED on \#PF (GC only).
; @param    [esp + 04h]  gcc:rdi  msc:rcx   Param 1 - First parameter - pointer to data item (the real stuff).
; @param    [esp + 08h]  gcc:rsi  msc:rdx   Param 2 - Second parameter- the immediate / register value. (really an 8 byte value)
; @param    [esp + 10h]  gcc:rdx  msc:r8    Param 3 - Where to store the eflags on success.
;
align 16
BEGINPROC   EMEmulateLockBtr
%ifdef RT_ARCH_AMD64
 %ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; rax = third parameter
 %else  ; !RT_OS_WINDOWS
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rax, rdx                    ; rax = third parameter
    mov     rdx, rsi                    ; rdx = second parameter
 %endif ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
    mov     eax, [esp + 10h]            ; eax = third parameter
%endif

    lock btr [MY_PTR_REG], edx

    ; collect flags and return.
    pushf
    pop     xDX
    mov     [xAX], edx
    mov     eax, VINF_SUCCESS
    retn
ENDPROC     EMEmulateLockBtr


;;
; Emulate BTC instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateBtc(void *pvParam1, uint64_t u64Param2);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]    Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]    Param 2 - Second parameter.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateBtc
%ifdef RT_ARCH_AMD64
%ifndef RT_OS_WINDOWS
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    and     edx, 7
    btc    [MY_PTR_REG], edx

    ; collect flags and return.
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateBtc


;;
; Emulate BTS instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateBts(void *pvParam1, uint64_t u64Param2);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]    Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]    Param 2 - Second parameter.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateBts
%ifdef RT_ARCH_AMD64
%ifndef RT_OS_WINDOWS
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    and     edx, 7
    bts    [MY_PTR_REG], edx

    ; collect flags and return.
    pushf
    pop     MY_RET_REG
    retn
ENDPROC     EMEmulateBts


;;
; Emulate LOCK CMPXCHG instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateLockCmpXchg(void *pvParam1, uint64_t *pu64Param2, uint64_t u64Param3, size_t cbSize);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]  gcc:rdi  msc:rcx   Param 1 - First parameter - pointer to first parameter
; @param    [esp + 08h]  gcc:rsi  msc:rdx   Param 2 - pointer to second parameter (eax)
; @param    [esp + 0ch]  gcc:rdx  msc:r8    Param 3 - third parameter
; @param    [esp + 14h]  gcc:rcx  msc:r9    Param 4 - Size of parameters, only 1/2/4/8 is valid
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateLockCmpXchg
    push    xBX
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    ; rcx contains the first parameter already
    mov     rbx, rdx                    ; rdx = 2nd parameter
    mov     rdx, r8                     ; r8  = 3rd parameter
    mov     rax, r9                     ; r9  = size of parameters
%else
    mov     rax, rcx                    ; rcx = size of parameters (4th)
    mov     rcx, rdi                    ; rdi = 1st parameter
    mov     rbx, rsi                    ; rsi = second parameter
    ;rdx contains the 3rd parameter already
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     ecx, [esp + 04h + 4]        ; ecx = first parameter
    mov     ebx, [esp + 08h + 4]        ; ebx = 2nd parameter (eax)
    mov     edx, [esp + 0ch + 4]        ; edx = third parameter
    mov     eax, [esp + 14h + 4]        ; eax = size of parameters
%endif

%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

%ifdef RT_ARCH_AMD64
.do_qword:
    ; load 2nd parameter's value
    mov     rax, qword [rbx]

    lock cmpxchg qword [rcx], rdx       ; do 8 bytes CMPXCHG
    mov     qword [rbx], rax
    jmp     short .done
%endif

.do_dword:
    ; load 2nd parameter's value
    mov     eax, dword [xBX]

    lock cmpxchg dword [xCX], edx       ; do 4 bytes CMPXCHG
    mov     dword [xBX], eax
    jmp     short .done

.do_word:
    ; load 2nd parameter's value
    mov     eax, dword [xBX]

    lock cmpxchg word [xCX], dx         ; do 2 bytes CMPXCHG
    mov     word [xBX], ax
    jmp     short .done

.do_byte:
    ; load 2nd parameter's value
    mov     eax, dword [xBX]

    lock cmpxchg byte [xCX], dl         ; do 1 byte CMPXCHG
    mov     byte [xBX], al

.done:
    ; collect flags and return.
    pushf
    pop     MY_RET_REG

    pop     xBX
    retn
ENDPROC     EMEmulateLockCmpXchg


;;
; Emulate CMPXCHG instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateCmpXchg(void *pvParam1, uint64_t *pu32Param2, uint64_t u32Param3, size_t cbSize);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]  gcc:rdi  msc:rcx   Param 1 - First parameter - pointer to first parameter
; @param    [esp + 08h]  gcc:rsi  msc:rdx   Param 2 - pointer to second parameter (eax)
; @param    [esp + 0ch]  gcc:rdx  msc:r8    Param 3 - third parameter
; @param    [esp + 14h]  gcc:rcx  msc:r9    Param 4 - Size of parameters, only 1/2/4 is valid.
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateCmpXchg
    push    xBX
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    ; rcx contains the first parameter already
    mov     rbx, rdx                    ; rdx = 2nd parameter
    mov     rdx, r8                     ; r8  = 3rd parameter
    mov     rax, r9                     ; r9  = size of parameters
%else
    mov     rax, rcx                    ; rcx = size of parameters (4th)
    mov     rcx, rdi                    ; rdi = 1st parameter
    mov     rbx, rsi                    ; rsi = second parameter
    ;rdx contains the 3rd parameter already
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     ecx, [esp + 04h + 4]        ; ecx = first parameter
    mov     ebx, [esp + 08h + 4]        ; ebx = 2nd parameter (eax)
    mov     edx, [esp + 0ch + 4]        ; edx = third parameter
    mov     eax, [esp + 14h + 4]        ; eax = size of parameters
%endif

%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

%ifdef RT_ARCH_AMD64
.do_qword:
    ; load 2nd parameter's value
    mov     rax, qword [rbx]

    cmpxchg qword [rcx], rdx            ; do 8 bytes CMPXCHG
    mov     qword [rbx], rax
    jmp     short .done
%endif

.do_dword:
    ; load 2nd parameter's value
    mov     eax, dword [xBX]

    cmpxchg dword [xCX], edx            ; do 4 bytes CMPXCHG
    mov     dword [xBX], eax
    jmp     short .done

.do_word:
    ; load 2nd parameter's value
    mov     eax, dword [xBX]

    cmpxchg word [xCX], dx              ; do 2 bytes CMPXCHG
    mov     word [xBX], ax
    jmp     short .done

.do_byte:
    ; load 2nd parameter's value
    mov     eax, dword [xBX]

    cmpxchg byte [xCX], dl              ; do 1 byte CMPXCHG
    mov     byte [xBX], al

.done:
    ; collect flags and return.
    pushf
    pop     MY_RET_REG

    pop     xBX
    retn
ENDPROC     EMEmulateCmpXchg


;;
; Emulate LOCK CMPXCHG8B instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateLockCmpXchg8b(void *pu32Param1, uint32_t *pEAX, uint32_t *pEDX, uint32_t uEBX, uint32_t uECX);
;
; @returns EFLAGS after the operation, only the ZF flag is valid.
; @param    [esp + 04h]  gcc:rdi  msc:rcx       Param 1 - First parameter - pointer to first parameter
; @param    [esp + 08h]  gcc:rsi  msc:rdx       Param 2 - Address of the eax register
; @param    [esp + 0ch]  gcc:rdx  msc:r8        Param 3 - Address of the edx register
; @param    [esp + 10h]  gcc:rcx  msc:r9        Param 4 - EBX
; @param    [esp + 14h]  gcc:r8   msc:[rsp + 8] Param 5 - ECX
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateLockCmpXchg8b
    push    xBP
    push    xBX
%ifdef RT_ARCH_AMD64
 %ifdef RT_OS_WINDOWS
    mov     rbp, rcx
    mov     r10, rdx
    mov     eax, dword [rdx]
    mov     edx, dword [r8]
    mov     rbx, r9
    mov     ecx, [rsp + 28h + 16]
 %else
    mov     rbp, rdi
    mov     r10, rdx
    mov     eax, dword [rsi]
    mov     edx, dword [rdx]
    mov     rbx, rcx
    mov     rcx, r8
 %endif
%else
    mov     ebp, [esp + 04h + 8]        ; ebp = first parameter
    mov     eax, [esp + 08h + 8]        ; &EAX
    mov     eax, dword [eax]
    mov     edx, [esp + 0ch + 8]        ; &EDX
    mov     edx, dword [edx]
    mov     ebx, [esp + 10h + 8]        ; EBX
    mov     ecx, [esp + 14h + 8]        ; ECX
%endif

%ifdef RT_OS_OS2
    lock    cmpxchg8b [xBP]                ; do CMPXCHG8B
%else
    lock    cmpxchg8b qword [xBP]          ; do CMPXCHG8B
%endif

%ifdef RT_ARCH_AMD64
 %ifdef RT_OS_WINDOWS
    mov     dword [r10], eax
    mov     dword [r8], edx
 %else
    mov     dword [rsi], eax
    mov     dword [r10], edx
 %endif
%else
    mov     ebx, dword [esp + 08h + 8]
    mov     dword [ebx], eax
    mov     ebx, dword [esp + 0ch + 8]
    mov     dword [ebx], edx
%endif
    ; collect flags and return.
    pushf
    pop     MY_RET_REG

    pop     xBX
    pop     xBP
    retn
ENDPROC     EMEmulateLockCmpXchg8b

;;
; Emulate CMPXCHG8B instruction, CDECL calling conv.
; VMMDECL(uint32_t) EMEmulateCmpXchg8b(void *pu32Param1, uint32_t *pEAX, uint32_t *pEDX, uint32_t uEBX, uint32_t uECX);
;
; @returns EFLAGS after the operation, only arithmetic flags are valid.
; @param    [esp + 04h]  gcc:rdi  msc:rcx       Param 1 - First parameter - pointer to first parameter
; @param    [esp + 08h]  gcc:rsi  msc:rdx       Param 2 - Address of the eax register
; @param    [esp + 0ch]  gcc:rdx  msc:r8        Param 3 - Address of the edx register
; @param    [esp + 10h]  gcc:rcx  msc:r9        Param 4 - EBX
; @param    [esp + 14h]  gcc:r8   msc:[rsp + 8] Param 5 - ECX
; @uses     eax, ecx, edx
;
align 16
BEGINPROC   EMEmulateCmpXchg8b
    push    xBP
    push    xBX
%ifdef RT_ARCH_AMD64
 %ifdef RT_OS_WINDOWS
    mov     rbp, rcx
    mov     r10, rdx
    mov     eax, dword [rdx]
    mov     edx, dword [r8]
    mov     rbx, r9
    mov     ecx, [rsp + 28h + 16]
 %else
    mov     rbp, rdi
    mov     r10, rdx
    mov     eax, dword [rsi]
    mov     edx, dword [rdx]
    mov     rbx, rcx
    mov     rcx, r8
 %endif
%else
    mov     ebp, [esp + 04h + 8]        ; ebp = first parameter
    mov     eax, [esp + 08h + 8]        ; &EAX
    mov     eax, dword [eax]
    mov     edx, [esp + 0ch + 8]        ; &EDX
    mov     edx, dword [edx]
    mov     ebx, [esp + 10h + 8]        ; EBX
    mov     ecx, [esp + 14h + 8]        ; ECX
%endif

%ifdef RT_OS_OS2
    cmpxchg8b [xBP]                ; do CMPXCHG8B
%else
    cmpxchg8b qword [xBP]          ; do CMPXCHG8B
%endif

%ifdef RT_ARCH_AMD64
 %ifdef RT_OS_WINDOWS
    mov     dword [r10], eax
    mov     dword [r8], edx
 %else
    mov     dword [rsi], eax
    mov     dword [r10], edx
 %endif
%else
    mov     ebx, dword [esp + 08h + 8]
    mov     dword [ebx], eax
    mov     ebx, dword [esp + 0ch + 8]
    mov     dword [ebx], edx
%endif

    ; collect flags and return.
    pushf
    pop     MY_RET_REG

    pop     xBX
    pop     xBP
    retn
ENDPROC     EMEmulateCmpXchg8b


;;
; Emulate LOCK XADD instruction.
; VMMDECL(uint32_t)   EMEmulateLockXAdd(void *pvParam1, void *pvParam2, size_t cbOp);
;
; @returns (eax=)eflags
; @param    [esp + 04h]  gcc:rdi  msc:rcx  Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]  gcc:rsi  msc:rdx  Param 2 - Second parameter - pointer to second parameter (general register)
; @param    [esp + 0ch]  gcc:rdx  msc:r8   Param 3 - Size of parameters - {1,2,4,8}.
;
align 16
BEGINPROC   EMEmulateLockXAdd
%ifdef RT_ARCH_AMD64
 %ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
 %else  ; !RT_OS_WINDOWS
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
 %endif ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 0ch]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    mov     rax, qword [xDX]            ; load 2nd parameter's value
    lock xadd qword [MY_PTR_REG], rax   ; do 8 bytes XADD
    mov     qword [xDX], rax
    jmp     short .done
%endif

.do_dword:
    mov     eax, dword [xDX]            ; load 2nd parameter's value
    lock xadd dword [MY_PTR_REG], eax   ; do 4 bytes XADD
    mov     dword [xDX], eax
    jmp     short .done

.do_word:
    mov     eax, dword [xDX]            ; load 2nd parameter's value
    lock xadd word [MY_PTR_REG], ax     ; do 2 bytes XADD
    mov     word [xDX], ax
    jmp     short .done

.do_byte:
    mov     eax, dword [xDX]            ; load 2nd parameter's value
    lock xadd byte [MY_PTR_REG], al     ; do 1 bytes XADD
    mov     byte [xDX], al

.done:
    ; collect flags and return.
    pushf
    pop     MY_RET_REG

    retn
ENDPROC     EMEmulateLockXAdd


;;
; Emulate XADD instruction.
; VMMDECL(uint32_t)   EMEmulateXAdd(void *pvParam1, void *pvParam2, size_t cbOp);
;
; @returns eax=eflags
; @param    [esp + 04h]  gcc:rdi  msc:rcx  Param 1 - First parameter - pointer to data item.
; @param    [esp + 08h]  gcc:rsi  msc:rdx  Param 2 - Second parameter - pointer to second parameter (general register)
; @param    [esp + 0ch]  gcc:rdx  msc:r8   Param 3 - Size of parameters - {1,2,4,8}.
align 16
BEGINPROC   EMEmulateXAdd
%ifdef RT_ARCH_AMD64
%ifdef RT_OS_WINDOWS
    mov     rax, r8                     ; eax = size of parameters
%else   ; !RT_OS_WINDOWS
    mov     rax, rdx                    ; rax = size of parameters
    mov     rcx, rdi                    ; rcx = first parameter
    mov     rdx, rsi                    ; rdx = second parameter
%endif  ; !RT_OS_WINDOWS
%else   ; !RT_ARCH_AMD64
    mov     eax, [esp + 0ch]            ; eax = size of parameters
    mov     ecx, [esp + 04h]            ; ecx = first parameter
    mov     edx, [esp + 08h]            ; edx = second parameter
%endif

    ; switch on size
%ifdef CAN_DO_8_BYTE_OP
    cmp     al, 8
    je short .do_qword                  ; 8 bytes variant
%endif
    cmp     al, 4
    je short .do_dword                  ; 4 bytes variant
    cmp     al, 2
    je short .do_word                   ; 2 byte variant
    cmp     al, 1
    je short .do_byte                   ; 1 bytes variant
    int3

    ; workers
%ifdef RT_ARCH_AMD64
.do_qword:
    mov     rax, qword [xDX]            ; load 2nd parameter's value
    xadd    qword [MY_PTR_REG], rax   ; do 8 bytes XADD
    mov     qword [xDX], rax
    jmp     short .done
%endif

.do_dword:
    mov     eax, dword [xDX]            ; load 2nd parameter's value
    xadd    dword [MY_PTR_REG], eax     ; do 4 bytes XADD
    mov     dword [xDX], eax
    jmp     short .done

.do_word:
    mov     eax, dword [xDX]            ; load 2nd parameter's value
    xadd    word [MY_PTR_REG], ax       ; do 2 bytes XADD
    mov     word [xDX], ax
    jmp     short .done

.do_byte:
    mov     eax, dword [xDX]            ; load 2nd parameter's value
    xadd    byte [MY_PTR_REG], al       ; do 1 bytes XADD
    mov     byte [xDX], al

.done:
    ; collect flags and return.
    pushf
    pop     MY_RET_REG

    retn
ENDPROC     EMEmulateXAdd