[Xen-devel] [PATCH RFC 07/18] OvmfPkg/XenbusDxe: Add InterlockedCompareExchange16.

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

This is a copy of InterlockedCompareExchange32 from the
BaseSynchronizationLib.

The function will be used in the next patch.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 OvmfPkg/XenbusDxe/InterlockedCompareExchange16.h   |  7 ++++
 .../XenbusDxe/X64/InterlockedCompareExchange16.c   | 41 ++++++++++++++++++++++
 OvmfPkg/XenbusDxe/XenbusDxe.inf                    |  2 ++
 3 files changed, 50 insertions(+)
 create mode 100644 OvmfPkg/XenbusDxe/InterlockedCompareExchange16.h
 create mode 100644 OvmfPkg/XenbusDxe/X64/InterlockedCompareExchange16.c

diff --git a/OvmfPkg/XenbusDxe/InterlockedCompareExchange16.h 
b/OvmfPkg/XenbusDxe/InterlockedCompareExchange16.h
new file mode 100644
index 0000000..55f61a8
--- /dev/null
+++ b/OvmfPkg/XenbusDxe/InterlockedCompareExchange16.h
@@ -0,0 +1,7 @@
+UINT16
+EFIAPI
+InterlockedCompareExchange16 (
+  IN OUT volatile  UINT16           *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  );
diff --git a/OvmfPkg/XenbusDxe/X64/InterlockedCompareExchange16.c 
b/OvmfPkg/XenbusDxe/X64/InterlockedCompareExchange16.c
new file mode 100644
index 0000000..64962ba
--- /dev/null
+++ b/OvmfPkg/XenbusDxe/X64/InterlockedCompareExchange16.c
@@ -0,0 +1,41 @@
+// Took from BaseSynchronizationLib, and replaced 32 by 16
+/**
+  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
+InterlockedCompareExchange16 (
+  IN OUT volatile  UINT16           *Value,
+  IN      UINT16                    CompareValue,
+  IN      UINT16                    ExchangeValue
+  )
+{
+  __asm__ __volatile__ (
+    "lock                 \n\t"
+    "cmpxchgw    %3, %1       "
+    : "=a" (CompareValue),    // %0
+      "=m" (*Value)           // %1
+    : "a"  (CompareValue),    // %2
+      "r"  (ExchangeValue),   // %3 
+      "m"  (*Value)
+    : "memory",
+      "cc"
+    );
+    
+  return CompareValue;
+}
diff --git a/OvmfPkg/XenbusDxe/XenbusDxe.inf b/OvmfPkg/XenbusDxe/XenbusDxe.inf
index 1a6b131..8f58821 100644
--- a/OvmfPkg/XenbusDxe/XenbusDxe.inf
+++ b/OvmfPkg/XenbusDxe/XenbusDxe.inf
@@ -33,10 +33,12 @@
   ComponentName.h
   XenHypercall.c
   XenHypercall.h
+  InterlockedCompareExchange16.h
 
 [Sources.X64]
   X64/hypercall.S
   X64/hypercall.asm
+  X64/InterlockedCompareExchange16.c | GCC
 
 [LibraryClasses]
   UefiDriverEntryPoint
-- 
Anthony PERARD


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