MdePkg/Library/BaseLib/Ia32/ReadDr4.nasm

   1 ;------------------------------------------------------------------------------
   2 ;
   3 ; Copyright (c) 2006 - 2022, Intel Corporation. All rights reserved.<BR>
   4 ; SPDX-License-Identifier: BSD-2-Clause-Patent
   5 ;
   6 ; Module Name:
   7 ;
   8 ;   ReadDr4.Asm
   9 ;
  10 ; Abstract:
  11 ;
  12 ;   AsmReadDr4 function
  13 ;
  14 ; Notes:
  15 ;
  16 ;------------------------------------------------------------------------------
  17
  18     SECTION .text
  19
  20 ;------------------------------------------------------------------------------
  21 ; UINTN
  22 ; EFIAPI
  23 ; AsmReadDr4 (
  24 ;   VOID
  25 ;   );
  26 ;------------------------------------------------------------------------------
  27 global ASM_PFX(AsmReadDr4)
  28 ASM_PFX(AsmReadDr4):
  29     ;
  30     ; DR4 is alias to DR6 only if DE (in CR4) is cleared. Otherwise, reading
  31     ; this register will cause a #UD exception.
  32     ;
  33     ; MS assembler doesn't support this instruction since no one would use it
  34     ; under normal circustances.
  35     ;
  36     mov     eax, dr4
  37     ret
  38