1 /** @file
2 AsmDisablePaging32 function.
3
4 Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
5 This program and the accompanying materials
6 are licensed and made available under the terms and conditions of the BSD License
7 which accompanies this distribution. The full text of the license may be found at
8 http://opensource.org/licenses/bsd-license.php.
9
10 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
11 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
12
13 **/
14
15 #include "BaseLibInternals.h"
16
17 /**
18 Disables the 32-bit paging mode on the CPU.
19
20 Disables the 32-bit paging mode on the CPU and returns to 32-bit protected
21 mode. This function assumes the current execution mode is 32-paged protected
22 mode. This function is only available on IA-32. After the 32-bit paging mode
23 is disabled, control is transferred to the function specified by EntryPoint
24 using the new stack specified by NewStack and passing in the parameters
25 specified by Context1 and Context2. Context1 and Context2 are optional and
26 may be NULL. The function EntryPoint must never return.
27
28 There are a number of constraints that must be followed before calling this
29 function:
30 1) Interrupts must be disabled.
31 2) The caller must be in 32-bit paged mode.
32 3) CR0, CR3, and CR4 must be compatible with 32-bit paged mode.
33 4) CR3 must point to valid page tables that guarantee that the pages for
34 this function and the stack are identity mapped.
35
36 @param EntryPoint A pointer to function to call with the new stack after
37 paging is disabled.
38 @param Context1 A pointer to the context to pass into the EntryPoint
39 function as the first parameter after paging is disabled.
40 @param Context2 A pointer to the context to pass into the EntryPoint
41 function as the second parameter after paging is
42 disabled.
43 @param NewStack A pointer to the new stack to use for the EntryPoint
44 function after paging is disabled.
45
46 **/
47 __declspec (naked)
48 VOID
49 EFIAPI
InternalX86DisablePaging32(IN SWITCH_STACK_ENTRY_POINT EntryPoint,IN VOID * Context1,OPTIONAL IN VOID * Context2,OPTIONAL IN VOID * NewStack)50 InternalX86DisablePaging32 (
51 IN SWITCH_STACK_ENTRY_POINT EntryPoint,
52 IN VOID *Context1, OPTIONAL
53 IN VOID *Context2, OPTIONAL
54 IN VOID *NewStack
55 )
56 {
57 _asm {
58 push ebp
59 mov ebp, esp
60 mov ebx, EntryPoint
61 mov ecx, Context1
62 mov edx, Context2
63 pushfd
64 pop edi // save EFLAGS to edi
65 cli
66 mov eax, cr0
67 btr eax, 31
68 mov esp, NewStack
69 mov cr0, eax
70 push edi
71 popfd // restore EFLAGS from edi
72 push edx
73 push ecx
74 call ebx
75 jmp $ // EntryPoint() should not return
76 }
77 }
78