MdePkg/BaseSynchronizationLib: Add InterlockedCompareExchange16

This implements the function InterlockedCompareExchange16 () for all
architectures, using architecture and toolchain specific intrinsics
or primitive assembler instructions.

Contributed-under: TianoCore Contribution Agreement 1.0
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
Acked-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Michael Kinney <michael.d.kinney@intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16966 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/Include/Library/SynchronizationLib.h

@@ -183,6 +183,32 @@ InterlockedDecrement (
   );
 
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+  If Value is NULL, then ASSERT().
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+**/
+UINT16
+EFIAPI
+InterlockedCompareExchange16 (
+  IN OUT  UINT16                    *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  );
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.
 

MdePkg/Library/BaseSynchronizationLib/AArch64/Synchronization.S

@@ -16,11 +16,55 @@
 .text
 .align 3
 
+GCC_ASM_EXPORT(InternalSyncCompareExchange16)
 GCC_ASM_EXPORT(InternalSyncCompareExchange32)
 GCC_ASM_EXPORT(InternalSyncCompareExchange64)
 GCC_ASM_EXPORT(InternalSyncIncrement)
 GCC_ASM_EXPORT(InternalSyncDecrement)
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+//UINT16
+//EFIAPI
+//InternalSyncCompareExchange16 (
+//  IN      volatile UINT16           *Value,
+//  IN      UINT16                    CompareValue,
+//  IN      UINT16                    ExchangeValue
+//  )
+ASM_PFX(InternalSyncCompareExchange16):
+  uxth    w1, w1
+  uxth    w2, w2
+  dmb     sy
+
+InternalSyncCompareExchange16Again:
+  ldxrh   w3, [x0]
+  cmp     w3, w1
+  bne     InternalSyncCompareExchange16Fail
+
+InternalSyncCompareExchange16Exchange:
+  stxrh   w4, w2, [x0]
+  cbnz    w4, InternalSyncCompareExchange16Again
+
+InternalSyncCompareExchange16Fail:
+  dmb     sy
+  mov     w0, w3
+  ret
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.
 

MdePkg/Library/BaseSynchronizationLib/Arm/Synchronization.S

@@ -1,6 +1,7 @@
 //  Implementation of synchronization functions for ARM architecture
 //
 //  Copyright (c) 2012-2015, ARM Limited. All rights reserved.
+//  Copyright (c) 2015, Linaro Limited. All rights reserved.
 //
 //  This program and the accompanying materials
 //  are licensed and made available under the terms and conditions of the BSD License
@@ -15,11 +16,54 @@
 .text
 .align 3
 
+GCC_ASM_EXPORT(InternalSyncCompareExchange16)
 GCC_ASM_EXPORT(InternalSyncCompareExchange32)
 GCC_ASM_EXPORT(InternalSyncCompareExchange64)
 GCC_ASM_EXPORT(InternalSyncIncrement)
 GCC_ASM_EXPORT(InternalSyncDecrement)
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+//UINT16
+//EFIAPI
+//InternalSyncCompareExchange16 (
+//  IN      volatile UINT16           *Value,
+//  IN      UINT16                    CompareValue,
+//  IN      UINT16                    ExchangeValue
+//  )
+ASM_PFX(InternalSyncCompareExchange16):
+  dmb
+
+InternalSyncCompareExchange16Again:
+  ldrexh  r3, [r0]
+  cmp     r3, r1
+  bne     InternalSyncCompareExchange16Fail
+
+InternalSyncCompareExchange16Exchange:
+  strexh  ip, r2, [r0]
+  cmp     ip, #0
+  bne     InternalSyncCompareExchange16Again
+
+InternalSyncCompareExchange16Fail:
+  dmb
+  mov     r0, r3
+  bx      lr
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.
 

MdePkg/Library/BaseSynchronizationLib/Arm/Synchronization.asm

@@ -1,6 +1,7 @@
 //  Implementation of synchronization functions for ARM architecture
 //
 //  Copyright (c) 2012-2015, ARM Limited. All rights reserved.
+//  Copyright (c) 2015, Linaro Limited. All rights reserved.
 //
 //  This program and the accompanying materials
 //  are licensed and made available under the terms and conditions of the BSD License
@@ -12,6 +13,7 @@
 //
 //
 
+    EXPORT  InternalSyncCompareExchange16
     EXPORT  InternalSyncCompareExchange32
     EXPORT  InternalSyncCompareExchange64
     EXPORT  InternalSyncIncrement
@@ -19,6 +21,48 @@
 
     AREA   ArmSynchronization, CODE, READONLY
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+//UINT16
+//EFIAPI
+//InternalSyncCompareExchange16 (
+//  IN      volatile UINT16           *Value,
+//  IN      UINT16                    CompareValue,
+//  IN      UINT16                    ExchangeValue
+//  )
+InternalSyncCompareExchange16
+  dmb
+
+InternalSyncCompareExchange16Again
+  ldrexh  r3, [r0]
+  cmp     r3, r1
+  bne     InternalSyncCompareExchange16Fail
+
+InternalSyncCompareExchange16Exchange
+  strexh  ip, r2, [r0]
+  cmp     ip, #0
+  bne     InternalSyncCompareExchange16Again
+
+InternalSyncCompareExchange16Fail
+  dmb
+  mov     r0, r3
+  bx      lr
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.
 

MdePkg/Library/BaseSynchronizationLib/BaseSynchronizationLib.inf

@@ -32,12 +32,14 @@
 [Sources.IA32]
   Ia32/InterlockedCompareExchange64.c | MSFT 
   Ia32/InterlockedCompareExchange32.c | MSFT 
+  Ia32/InterlockedCompareExchange16.c | MSFT
   Ia32/InterlockedDecrement.c | MSFT 
   Ia32/InterlockedIncrement.c | MSFT 
   SynchronizationMsc.c  | MSFT
 
   Ia32/InterlockedCompareExchange64.asm | INTEL 
   Ia32/InterlockedCompareExchange32.asm | INTEL 
+  Ia32/InterlockedCompareExchange16.asm | INTEL
   Ia32/InterlockedDecrement.asm | INTEL 
   Ia32/InterlockedIncrement.asm | INTEL 
   Synchronization.c | INTEL
@@ -48,9 +50,11 @@
 [Sources.X64]
   X64/InterlockedCompareExchange64.c | MSFT
   X64/InterlockedCompareExchange32.c | MSFT
+  X64/InterlockedCompareExchange16.c | MSFT
   
   X64/InterlockedCompareExchange64.asm | INTEL
   X64/InterlockedCompareExchange32.asm | INTEL
+  X64/InterlockedCompareExchange16.asm | INTEL
   
   X64/InterlockedDecrement.c | MSFT 
   X64/InterlockedIncrement.c | MSFT 
@@ -67,6 +71,7 @@
   Ipf/Synchronization.c
   Ipf/InterlockedCompareExchange64.s
   Ipf/InterlockedCompareExchange32.s
+  Ipf/InterlockedCompareExchange16.s
 
   Synchronization.c     | INTEL 
   SynchronizationMsc.c  | MSFT 

MdePkg/Library/BaseSynchronizationLib/BaseSynchronizationLibInternals.h

@@ -62,6 +62,32 @@ InternalSyncDecrement (
   );
 
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  A 16-bit value used in compare operation.
+  @param  ExchangeValue A 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+UINT16
+EFIAPI
+InternalSyncCompareExchange16 (
+  IN      volatile UINT16           *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  );
+
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.
 

MdePkg/Library/BaseSynchronizationLib/Ebc/Synchronization.c

@@ -12,6 +12,37 @@
 
 **/
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit
+  unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit
+  unsigned integer specified by Value.  If Value is equal to
+  CompareValue, then Value is set to ExchangeValue and
+  CompareValue is returned.  If Value is not equal to
+  CompareValue, then Value is returned. The compare exchange
+  operation must be performed using MP safe mechanisms.
+
+  @param  Value         A pointer to the 16-bit value for the
+                        compare exchange operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+UINT16
+EFIAPI
+InternalSyncCompareExchange16 (
+  IN      volatile UINT16           *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  )
+{
+  return *Value != CompareValue ? *Value :
+           ((*Value = ExchangeValue), CompareValue);
+}
+
 /**
   Performs an atomic compare exchange operation on a 32-bit
   unsigned integer.

MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c

@@ -87,6 +87,48 @@ InternalSyncDecrement (
   return Result;
 }
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+UINT16
+EFIAPI
+InternalSyncCompareExchange16 (
+  IN OUT volatile  UINT16           *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  )
+{
+
+  __asm__ __volatile__ (
+    "                     \n\t"
+    "lock                 \n\t"
+    "cmpxchgw    %1, %2   \n\t"
+    : "=a" (CompareValue)
+    : "q"  (ExchangeValue),
+      "m"  (*Value),
+      "0"  (CompareValue)
+    : "memory",
+      "cc"
+    );
+
+  return CompareValue;
+}
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.
 

MdePkg/Library/BaseSynchronizationLib/Ia32/InterlockedCompareExchange16.asm

@@ -0,0 +1,46 @@
+;------------------------------------------------------------------------------
+;
+; Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
+; Copyright (c) 2015, Linaro Ltd. 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
+
+;------------------------------------------------------------------------------
+; UINT16
+; EFIAPI
+; InternalSyncCompareExchange16 (
+;   IN      UINT16                    *Value,
+;   IN      UINT16                    CompareValue,
+;   IN      UINT16                    ExchangeValue
+;   );
+;------------------------------------------------------------------------------
+InternalSyncCompareExchange16   PROC
+    mov     ecx, [esp + 4]
+    mov     ax, [esp + 8]
+    mov     dx, [esp + 12]
+    lock    cmpxchg [ecx], dx
+    ret
+InternalSyncCompareExchange16   ENDP
+
+    END

MdePkg/Library/BaseSynchronizationLib/Ia32/InterlockedCompareExchange16.c

@@ -0,0 +1,51 @@
+/** @file
+  InterlockedCompareExchange16 function
+
+  Copyright (c) 2006 - 2010, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2015, Linaro Ltd. 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.
+
+**/
+
+
+
+
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+UINT16
+EFIAPI
+InternalSyncCompareExchange16 (
+  IN      UINT16                    *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  )
+{
+  _asm {
+    mov     ecx, Value
+    mov     ax, CompareValue
+    mov     dx, ExchangeValue
+    lock    cmpxchg [ecx], dx
+  }
+}
+

MdePkg/Library/BaseSynchronizationLib/Ipf/InterlockedCompareExchange16.s

@@ -0,0 +1,30 @@
+/// @file
+///   Contains an implementation of InterlockedCompareExchange16 on Itanium-
+///   based architecture.
+///
+/// Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
+/// Copyright (c) 2015, Linaro Ltd. 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.s
+///
+///
+
+.auto
+.text
+
+.proc   InternalSyncCompareExchange16
+.type   InternalSyncCompareExchange16, @function
+InternalSyncCompareExchange16::
+        zxt2                r33 = r33
+        mov                 ar.ccv = r33
+        cmpxchg2.rel        r8  = [r32], r34
+        mf
+        br.ret.sptk.many    b0
+.endp   InternalSyncCompareExchange16

MdePkg/Library/BaseSynchronizationLib/Synchronization.c

@@ -276,6 +276,37 @@ InterlockedDecrement (
   return InternalSyncDecrement (Value);
 }
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+  If Value is NULL, then ASSERT().
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+UINT16
+EFIAPI
+InterlockedCompareExchange16 (
+  IN OUT  UINT16                    *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  )
+{
+  ASSERT (Value != NULL);
+  return InternalSyncCompareExchange16 (Value, CompareValue, ExchangeValue);
+}
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.
 

MdePkg/Library/BaseSynchronizationLib/SynchronizationGcc.c

@@ -292,6 +292,37 @@ InterlockedDecrement (
   return InternalSyncDecrement (Value);
 }
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+  If Value is NULL, then ASSERT().
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  A 16-bit value used in compare operation.
+  @param  ExchangeValue A 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+UINT16
+EFIAPI
+InterlockedCompareExchange16 (
+  IN OUT  UINT16                    *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  )
+{
+  ASSERT (Value != NULL);
+  return InternalSyncCompareExchange16 (Value, CompareValue, ExchangeValue);
+}
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.
 

MdePkg/Library/BaseSynchronizationLib/SynchronizationMsc.c

@@ -294,6 +294,37 @@ InterlockedDecrement (
   return InternalSyncDecrement (Value);
 }
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+  If Value is NULL, then ASSERT().
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  A 16-bit value used in a compare operation.
+  @param  ExchangeValue A 16-bit value used in an exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+UINT16
+EFIAPI
+InterlockedCompareExchange16 (
+  IN OUT  UINT16                    *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  )
+{
+  ASSERT (Value != NULL);
+  return InternalSyncCompareExchange16 (Value, CompareValue, ExchangeValue);
+}
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.
 

MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c

@@ -88,6 +88,50 @@ InternalSyncDecrement (
 }
 
 
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer
+  specified by Value.  If Value is equal to CompareValue, then Value is set to
+  ExchangeValue and CompareValue is returned.  If Value is not equal to CompareValue,
+  then Value is returned.  The compare exchange operation must be performed using
+  MP safe mechanisms.
+
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+UINT16
+EFIAPI
+InternalSyncCompareExchange16 (
+  IN OUT volatile  UINT16           *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  )
+{
+
+
+  __asm__ __volatile__ (
+    "lock                 \n\t"
+    "cmpxchgw    %3, %1       "
+    : "=a" (CompareValue),
+      "=m" (*Value)
+    : "a"  (CompareValue),
+      "r"  (ExchangeValue),
+      "m"  (*Value)
+    : "memory",
+      "cc"
+    );
+
+  return CompareValue;
+}
+
+
 /**
   Performs an atomic compare exchange operation on a 32-bit unsigned integer.
 

MdePkg/Library/BaseSynchronizationLib/X64/InterlockedCompareExchange16.asm

@@ -0,0 +1,42 @@
+;------------------------------------------------------------------------------
+;
+; Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
+; Copyright (c) 2015, Linaro Ltd. 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:
+;
+;------------------------------------------------------------------------------
+
+    .code
+
+;------------------------------------------------------------------------------
+; UINT16
+; EFIAPI
+; InterlockedCompareExchange16 (
+;   IN      UINT16                    *Value,
+;   IN      UINT16                    CompareValue,
+;   IN      UINT16                    ExchangeValue
+;   );
+;------------------------------------------------------------------------------
+InternalSyncCompareExchange16   PROC
+    mov     ax, dx
+    lock    cmpxchg [rcx], r8w
+    ret
+InternalSyncCompareExchange16   ENDP
+
+    END

MdePkg/Library/BaseSynchronizationLib/X64/InterlockedCompareExchange16.c

@@ -0,0 +1,54 @@
+/** @file
+  InterlockedCompareExchange16 function
+
+  Copyright (c) 2006 - 2010, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2015, Linaro Ltd. 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.
+
+**/
+
+/**
+  Microsoft Visual Studio 7.1 Function Prototypes for I/O Intrinsics.
+**/
+
+__int16 _InterlockedCompareExchange16(
+   __int16 volatile * Destination,
+   __int16 Exchange,
+   __int16 Comperand
+);
+
+#pragma intrinsic(_InterlockedCompareExchange16)
+
+/**
+  Performs an atomic compare exchange operation on a 16-bit unsigned integer.
+
+  Performs an atomic compare exchange operation on the 16-bit unsigned integer specified
+  by Value.  If Value is equal to CompareValue, then Value is set to ExchangeValue and
+  CompareValue is returned.  If Value is not equal to CompareValue, then Value is returned.
+  The compare exchange operation must be performed using MP safe mechanisms.
+
+  @param  Value         A pointer to the 16-bit value for the compare exchange
+                        operation.
+  @param  CompareValue  16-bit value used in compare operation.
+  @param  ExchangeValue 16-bit value used in exchange operation.
+
+  @return The original *Value before exchange.
+
+**/
+UINT16
+EFIAPI
+InternalSyncCompareExchange16 (
+  IN      UINT16                    *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  )
+{
+  return _InterlockedCompareExchange16 (Value, ExchangeValue, CompareValue);
+}
+