1. Added comments to ASM files

[mirror_edk2.git] / MdePkg / Library / BaseLib / Ia32 / ReadDr5.asm

diff --git a/MdePkg/Library/BaseLib/Ia32/ReadDr5.asm b/MdePkg/Library/BaseLib/Ia32/ReadDr5.asm
index bba8b602ba196abead08448782f6b1c50564b3ec..091792dab9260688bbb7db048635c6959546f476 100644 (file)
--- a/MdePkg/Library/BaseLib/Ia32/ReadDr5.asm
+++ b/MdePkg/Library/BaseLib/Ia32/ReadDr5.asm
@@ -33,6 +33,13 @@
 ;   );\r
 ;------------------------------------------------------------------------------\r
 AsmReadDr5  PROC\r
+    ;\r
+    ; DR5 is alias to DR7 only if DE (in CR4) is cleared. Otherwise, reading\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, 21h, 0e8h\r
     ret\r
 AsmReadDr5  ENDP\r