OvmfPkg/XenBusDxe: Add InterlockedCompareExchange16.

This patch is inspired by InterlockedCompareExchange32 from the
BaseSynchronizationLib.

The function will be used in the "OvmfPkg/XenBusDxe: Add Grant Table
functions" patch.

Change in V3:
- Implement both .S and .asm, to get rid of GCC specific asm.
- Implement 32bit part of the assembly

Change in V2:
- Add intel compilation code
  MSFT code is not compied over because I don't know how it works.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16263 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/XenBusDxe/Ia32/InterlockedCompareExchange16.S

@@ -0,0 +1,15 @@
+# UINT16
+# EFIAPI
+# InternalSyncCompareExchange16 (
+#   IN      volatile UINT16           *Value,
+#   IN      UINT16                    CompareValue,
+#   IN      UINT16                    ExchangeValue
+#   );
+ASM_GLOBAL ASM_PFX(InternalSyncCompareExchange16)
+ASM_PFX(InternalSyncCompareExchange16):
+  mov 4(%esp), %ecx
+  mov 8(%esp), %eax
+  mov 12(%esp), %edx
+  lock
+  cmpxchgw %dx, (%ecx)
+  ret

OvmfPkg/XenBusDxe/Ia32/InterlockedCompareExchange16.asm

@@ -0,0 +1,45 @@
+;------------------------------------------------------------------------------
+;
+; Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
+; 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.
+;
+; Module Name:
+;
+;   InterlockedCompareExchange16.Asm
+;
+; Abstract:
+;
+;   InterlockedCompareExchange16 function
+;
+; Notes:
+;
+;------------------------------------------------------------------------------
+
+    .486
+    .model  flat,C
+    .code
+
+;------------------------------------------------------------------------------
+; UINT32
+; EFIAPI
+; InternalSyncCompareExchange16 (
+;   IN      UINT16                    *Value,
+;   IN      UINT16                    CompareValue,
+;   IN      UINT16                    ExchangeValue
+;   );
+;------------------------------------------------------------------------------
+InternalSyncCompareExchange16   PROC
+    mov     ecx, [esp + 4]
+    mov     eax, [esp + 8]
+    mov     edx, [esp + 12]
+    lock    cmpxchg [ecx], dx
+    ret
+InternalSyncCompareExchange16   ENDP
+
+    END