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diff --git a/src/VBox/Runtime/win/amd64/ASMProbeReadByte.asm b/src/VBox/Runtime/win/amd64/ASMProbeReadByte.asm
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+++ b/src/VBox/Runtime/win/amd64/ASMProbeReadByte.asm
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+;; @file
+; IPRT - ASMProbeReadByte().
+;
+
+;
+; Copyright (C) 2006-2019 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.
+;
+; The contents of this file may alternatively be used under the terms
+; of the Common Development and Distribution License Version 1.0
+; (CDDL) only, as it comes in the "COPYING.CDDL" file of the
+; VirtualBox OSE distribution, in which case the provisions of the
+; CDDL are applicable instead of those of the GPL.
+;
+; You may elect to license modified versions of this file under the
+; terms and conditions of either the GPL or the CDDL or both.
+;
+
+;*******************************************************************************
+;* Header Files                                                                *
+;*******************************************************************************
+%include "iprt/asmdefs.mac"
+
+BEGINCODE
+
+;;
+; Probes a byte pointer for read access.
+;
+; While the function will not fault if the byte is not read accessible,
+; the idea is to do this in a safe place like before acquiring locks
+; and such like.
+;
+; Also, this functions guarantees that an eager compiler is not going
+; to optimize the probing away.
+;
+; @param   rcx  pvByte      Pointer to the byte.
+BEGINPROC_EXPORTED ASMProbeReadByte
+        mov     al, [rcx]
+        ret
+ENDPROC ASMProbeReadByte
+