1 files changed, 44 insertions, 0 deletions
diff --git a/MdePkg/Library/BaseLib/Ia32/ReadDr4.nasm b/MdePkg/Library/BaseLib/Ia32/ReadDr4.nasm
new file mode 100644
index 0000000000..478c50e47b
--- /dev/null
+++ b/MdePkg/Library/BaseLib/Ia32/ReadDr4.nasm
@@ -0,0 +1,44 @@
+;------------------------------------------------------------------------------
+;
+; 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:
+;
+;   ReadDr4.Asm
+;
+; Abstract:
+;
+;   AsmReadDr4 function
+;
+; Notes:
+;
+;------------------------------------------------------------------------------
+
+    SECTION .text
+
+;------------------------------------------------------------------------------
+; UINTN
+; EFIAPI
+; AsmReadDr4 (
+;   VOID
+;   );
+;------------------------------------------------------------------------------
+global ASM_PFX(AsmReadDr4)
+ASM_PFX(AsmReadDr4):
+    ;
+    ; DR4 is alias to DR6 only if DE (in CR4) is cleared. Otherwise, reading
+    ; 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      0xf, 0x21, 0xe0
+    ret
+