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    SECTION .text
25
26;------------------------------------------------------------------------------
27; UINTN
28; EFIAPI
29; AsmReadDr4 (
30;   VOID
31;   );
32;------------------------------------------------------------------------------
33global ASM_PFX(AsmReadDr4)
34ASM_PFX(AsmReadDr4):
35    ;
36    ; DR4 is alias to DR6 only if DE (in CR4) is cleared. Otherwise, reading
37    ; this register will cause a #UD exception.
38    ;
39    ; MS assembler doesn't support this instruction since no one would use it
40    ; under normal circustances. Here opcode is used.
41    ;
42    DB      0xf, 0x21, 0xe0
43    ret
44
45