/** @file
  AsmEnablePaging32 function

  Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
  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"

/**
  Enables the 32-bit paging mode on the CPU.

  Enables the 32-bit paging mode on the CPU. CR0, CR3, CR4, and the page tables
  must be properly initialized prior to calling this service. This function
  assumes the current execution mode is 32-bit protected mode. This function is
  only available on IA-32. After the 32-bit paging mode is enabled, 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 protected mode with flat descriptors. This
      means all descriptors must have a base of 0 and a limit of 4GB.
  3)  CR0 and CR4 must be compatible with 32-bit protected mode with flat
      descriptors.
  4)  CR3 must point to valid page tables that will be used once the transition
      is complete, and those page tables must 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 enabled.
  @param  Context1    A pointer to the context to pass into the EntryPoint
                      function as the first parameter after paging is enabled.
  @param  Context2    A pointer to the context to pass into the EntryPoint
                      function as the second parameter after paging is enabled.
  @param  NewStack    A pointer to the new stack to use for the EntryPoint
                      function after paging is enabled.

**/
__declspec (naked)
VOID
EFIAPI
InternalX86EnablePaging32 (
  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
    cli
    mov     eax, cr0
    bts     eax, 31
    mov     esp, NewStack
    mov     cr0, eax
    push    edi
    popfd
    push    edx
    push    ecx
    call    ebx
    jmp     $
  }
}

