Index: /trunk/src/VBox/Runtime/Makefile.kmk
===================================================================
--- /trunk/src/VBox/Runtime/Makefile.kmk	(revision 87221)
+++ /trunk/src/VBox/Runtime/Makefile.kmk	(revision 87222)
@@ -833,4 +833,5 @@
 	common/asm/ASMAtomicUoOrU64.asm \
 	common/asm/ASMAtomicUoOrU32.asm \
+	common/asm/ASMAtomicUoXorU32.asm \
 	common/asm/ASMMemFirstMismatchingU8.asm \
 	common/asm/ASMRdMsrEx.asm \
@@ -857,4 +858,5 @@
 	common/asm/ASMAtomicUoOrU64.asm \
 	common/asm/ASMAtomicUoOrU32.asm \
+	common/asm/ASMAtomicUoXorU32.asm \
 	common/asm/ASMMemFirstMismatchingU8.asm \
 	common/asm/ASMRdMsrEx.asm \
@@ -2809,4 +2811,5 @@
 	common/asm/ASMAtomicUoOrU64.asm \
 	common/asm/ASMAtomicUoOrU32.asm \
+	common/asm/ASMAtomicUoXorU32.asm \
 	common/asm/ASMMemFirstMismatchingU8.asm \
 	common/asm/ASMGetXcr0.asm \
@@ -2827,4 +2830,5 @@
 	common/asm/ASMAtomicUoOrU64.asm \
 	common/asm/ASMAtomicUoOrU32.asm \
+	common/asm/ASMAtomicUoXorU32.asm \
 	common/asm/ASMMemFirstMismatchingU8.asm \
 	common/asm/ASMGetXcr0.asm \
Index: /trunk/src/VBox/Runtime/common/asm/ASMAtomicUoXorU32.asm
===================================================================
--- /trunk/src/VBox/Runtime/common/asm/ASMAtomicUoXorU32.asm	(revision 87222)
+++ /trunk/src/VBox/Runtime/common/asm/ASMAtomicUoXorU32.asm	(revision 87222)
@@ -0,0 +1,56 @@
+; $Id$
+;; @file
+; IPRT - ASMAtomicUoXorU32().
+;
+
+;
+; Copyright (C) 2013-2020 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
+
+;;
+; Atomically XOR an unsigned 32-bit value, unordered.
+;
+; @param    pu32     x86:esp+4   gcc:rdi  msc:rcx
+; @param    u32Or    x86:esp+8   gcc:rsi  msc:rdx
+;
+; @returns  void
+;
+BEGINPROC_EXPORTED ASMAtomicUoXorU32
+%ifdef RT_ARCH_AMD64
+ %ifdef ASM_CALL64_MSC
+        xor     [rcx], edx
+ %else
+        xor     [rdi], esi
+ %endif
+%elifdef RT_ARCH_X86
+        mov     ecx, [esp + 04h]
+        mov     edx, [esp + 08h]
+        xor     [ecx], edx
+%endif
+        ret
+ENDPROC ASMAtomicUoXorU32
+