1 files changed, 63 insertions, 0 deletions
diff --git a/src/VBox/Runtime/common/asm/ASMAtomicCmpXchgU8.asm b/src/VBox/Runtime/common/asm/ASMAtomicCmpXchgU8.asm
new file mode 100644
index 00000000..c79f143c
--- /dev/null
+++ b/src/VBox/Runtime/common/asm/ASMAtomicCmpXchgU8.asm
@@ -0,0 +1,63 @@
+; $Id: ASMAtomicCmpXchgU8.asm $
+;; @file
+; IPRT - ASMAtomicCmpXchgU8().
+;
+
+;
+; Copyright (C) 2006-2020 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 compares and exchanges an unsigned 8-bit int.
+;
+; @param    pu8     x86:esp+4  msc:rcx  gcc:rdi
+; @param    u8New   x86:esp+8  msc:dl   gcc:sil
+; @param    u8Old   x86:esp+c  msc:r8l  gcc:dl
+;
+; @returns  bool result: true if successfully exchanged, false if not.
+;           x86:al
+;
+BEGINPROC_EXPORTED ASMAtomicCmpXchgU8
+%ifdef RT_ARCH_AMD64
+ %ifdef ASM_CALL64_MSC
+        mov     al, r8b
+        lock cmpxchg [rcx], dl
+ %else
+        mov     al, dl
+        lock cmpxchg [rdi], sil
+ %endif
+%else
+        mov     ecx, [esp + 04h]
+        mov     dl,  [esp + 08h]
+        mov     al,  [esp + 0ch]
+        lock cmpxchg [ecx], dl
+%endif
+        setz    al
+        movzx   eax, al
+        ret
+ENDPROC ASMAtomicCmpXchgU8
+