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/** @file
AsmDisablePaging32 function.
Copyright (c) 2006 - 2008, Intel Corporation<BR>
All rights reserved. This program and the accompanying materials
are licensed and made available under the terms and conditions of the BSD License
which accompanies this distribution. The full text of the license may be found at
http://opensource.org/licenses/bsd-license.php
THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
**/
#include "BaseLibInternals.h"
/**
Disables the 32-bit paging mode on the CPU.
Disables the 32-bit paging mode on the CPU and returns to 32-bit protected
mode. This function assumes the current execution mode is 32-paged protected
mode. This function is only available on IA-32. After the 32-bit paging mode
is disabled, control is transferred to the function specified by EntryPoint
using the new stack specified by NewStack and passing in the parameters
specified by Context1 and Context2. Context1 and Context2 are optional and
may be NULL. The function EntryPoint must never return.
There are a number of constraints that must be followed before calling this
function:
1) Interrupts must be disabled.
2) The caller must be in 32-bit paged mode.
3) CR0, CR3, and CR4 must be compatible with 32-bit paged mode.
4) CR3 must point to valid page tables that guarantee that the pages for
this function and the stack are identity mapped.
@param EntryPoint A pointer to function to call with the new stack after
paging is disabled.
@param Context1 A pointer to the context to pass into the EntryPoint
function as the first parameter after paging is disabled.
@param Context2 A pointer to the context to pass into the EntryPoint
function as the second parameter after paging is
disabled.
@param NewStack A pointer to the new stack to use for the EntryPoint
function after paging is disabled.
**/
__declspec (naked)
VOID
EFIAPI
InternalX86DisablePaging32 (
IN SWITCH_STACK_ENTRY_POINT EntryPoint,
IN VOID *Context1, OPTIONAL
IN VOID *Context2, OPTIONAL
IN VOID *NewStack
)
{
_asm {
push ebp
mov ebp, esp
mov ebx, EntryPoint
mov ecx, Context1
mov edx, Context2
pushfd
pop edi // save EFLAGS to edi
cli
mov eax, cr0
btr eax, 31
mov esp, NewStack
mov cr0, eax
push edi
popfd // restore EFLAGS from edi
push edx
push ecx
call ebx
jmp $ // EntryPoint() should not return
}
}
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