ArmPkg/ArmDisassemblerLib: fix check for MSR instruction

[mirror_edk2.git] / MdePkg / Library / BaseLib / Ia32 / WriteDr5.asm

diff --git a/MdePkg/Library/BaseLib/Ia32/WriteDr5.asm b/MdePkg/Library/BaseLib/Ia32/WriteDr5.asm
index c6def6820cde14de5ddfef07199a90ac3bcf217e..0df817529b43b688a1addc59365d18767c0109ae 100644 (file)
--- a/MdePkg/Library/BaseLib/Ia32/WriteDr5.asm
+++ b/MdePkg/Library/BaseLib/Ia32/WriteDr5.asm
@@ -1,10 +1,10 @@
 ;------------------------------------------------------------------------------\r
 ;\r
-; Copyright (c) 2006, Intel Corporation\r
-; All rights reserved. This program and the accompanying materials\r
+; Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>\r
+; This program and the accompanying materials\r
 ; are licensed and made available under the terms and conditions of the BSD License\r
 ; which accompanies this distribution.  The full text of the license may be found at\r
-; http://opensource.org/licenses/bsd-license.php\r
+; http://opensource.org/licenses/bsd-license.php.\r
 ;\r
 ; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
 ; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
@@ -34,6 +34,13 @@
 ;------------------------------------------------------------------------------\r
 AsmWriteDr5 PROC\r
     mov     eax, [esp + 4]\r
+    ;\r
+    ; DR5 is alias to DR7 only if DE (in CR4) is cleared. Otherwise, writing to\r
+    ; this register will cause a #UD exception.\r
+    ;\r
+    ; MS assembler doesn't support this instruction since no one would use it\r
+    ; under normal circustances. Here opcode is used.\r
+    ;\r
     DB      0fh, 23h, 0e8h\r
     ret\r
 AsmWriteDr5 ENDP\r