MdePkg/Library/BaseLib/Ia32/ReadDr4.asm

   1 ;------------------------------------------------------------------------------
   2 ;
   3 ; Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
   4 ; This program and the accompanying materials
   5 ; are licensed and made available under the terms and conditions of the BSD License
   6 ; which accompanies this distribution.  The full text of the license may be found at
   7 ; http://opensource.org/licenses/bsd-license.php.
   8 ;
   9 ; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  10 ; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  11 ;
  12 ; Module Name:
  13 ;
  14 ;   ReadDr4.Asm
  15 ;
  16 ; Abstract:
  17 ;
  18 ;   AsmReadDr4 function
  19 ;
  20 ; Notes:
  21 ;
  22 ;------------------------------------------------------------------------------
  23
  24     .586p
  25     .model  flat,C
  26     .code
  27
  28 ;------------------------------------------------------------------------------
  29 ; UINTN
  30 ; EFIAPI
  31 ; AsmReadDr4 (
  32 ;   VOID
  33 ;   );
  34 ;------------------------------------------------------------------------------
  35 AsmReadDr4  PROC
  36     ;
  37     ; DR4 is alias to DR6 only if DE (in CR4) is cleared. Otherwise, reading
  38     ; this register will cause a #UD exception.
  39     ;
  40     ; MS assembler doesn't support this instruction since no one would use it
  41     ; under normal circustances. Here opcode is used.
  42     ;
  43     DB      0fh, 21h, 0e0h
  44     ret
  45 AsmReadDr4  ENDP
  46
  47     END