Update the Guid Value of Ext SCSI Pass Thru Protocol

[mirror_edk2.git] / MdePkg / Library / BaseLib / Ia32 / WriteDr4.asm

diff --git a/MdePkg/Library/BaseLib/Ia32/WriteDr4.asm b/MdePkg/Library/BaseLib/Ia32/WriteDr4.asm
index 2c82512accdebd5ff17cfede1395aa013b54054a..9c10305b4da7079c6124977395a4d9c0388754b0 100644 (file)
--- a/MdePkg/Library/BaseLib/Ia32/WriteDr4.asm
+++ b/MdePkg/Library/BaseLib/Ia32/WriteDr4.asm
@@ -22,20 +22,27 @@
 ;------------------------------------------------------------------------------\r
 \r
     .586p\r
-    .model  flat\r
+    .model  flat,C\r
     .code\r
 \r
 ;------------------------------------------------------------------------------\r
-; VOID\r
+; UINTN\r
 ; EFIAPI\r
 ; AsmWriteDr4 (\r
 ;   IN UINTN Value\r
 ;   );\r
 ;------------------------------------------------------------------------------\r
-_AsmWriteDr4    PROC\r
+AsmWriteDr4 PROC\r
     mov     eax, [esp + 4]\r
+    ;\r
+    ; DR4 is alias to DR6 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, 0e0h\r
     ret\r
-_AsmWriteDr4    ENDP\r
+AsmWriteDr4 ENDP\r
 \r
     END\r