1. Added comments to ASM files

[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 ca9a839f7028f8a053348640221f8d373e5f89dd..9c10305b4da7079c6124977395a4d9c0388754b0 100644 (file)
--- a/MdePkg/Library/BaseLib/Ia32/WriteDr4.asm
+++ b/MdePkg/Library/BaseLib/Ia32/WriteDr4.asm
@@ -34,6 +34,13 @@
 ;------------------------------------------------------------------------------\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