1. Added comments to ASM files

2. Fixed a bug in 64-bit AsmDisablePaging64(), which may cause a #GP exception.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@2206 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/Library/BaseLib/Ia32/WriteDr4.asm

@@ -34,6 +34,13 @@
 ;------------------------------------------------------------------------------
 AsmWriteDr4 PROC
     mov     eax, [esp + 4]
+    ;
+    ; DR4 is alias to DR6 only if DE (in CR4) is cleared. Otherwise, writing to
+    ; 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      0fh, 23h, 0e0h
     ret
 AsmWriteDr4 ENDP