1 files changed, 48 insertions, 0 deletions
diff --git a/MdePkg/Library/BaseLib/Ia32/WriteDr4.asm b/MdePkg/Library/BaseLib/Ia32/WriteDr4.asm
new file mode 100644
index 000000000000..4d61dc7c68b8
--- /dev/null
+++ b/MdePkg/Library/BaseLib/Ia32/WriteDr4.asm
@@ -0,0 +1,48 @@
+;------------------------------------------------------------------------------
+;
+; 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:
+;
+;   WriteDr4.Asm
+;
+; Abstract:
+;
+;   AsmWriteDr4 function
+;
+; Notes:
+;
+;------------------------------------------------------------------------------
+
+    .586p
+    .model  flat,C
+    .code
+
+;------------------------------------------------------------------------------
+; UINTN
+; EFIAPI
+; AsmWriteDr4 (
+;   IN UINTN Value
+;   );
+;------------------------------------------------------------------------------
+AsmWriteDr4 PROC
+    mov     eax, [esp + 4]
+    ;
+    ; DR4 is alias to DR6 only if DE (in CR4) is cleared. Otherwise, writing to
+    ; this register will cause a #UD exception.
+    ;
+    ; MS assembler doesn't support this instruction since no one would use it
+    ; under normal circustances. Here opcode is used.
+    ;
+    DB      0fh, 23h, 0e0h
+    ret
+AsmWriteDr4 ENDP
+
+    END