MdePkg/Library/BaseLib/x86EnablePaging32.c

   1 /** @file
   2   IA-32/x64 AsmEnablePaging32()
   3
   4   Copyright (c) 2006, Intel Corporation<BR>
   5   All rights reserved. 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   Module Name:  x86EnablePaging32.c
  14
  15 **/
  16
  17 #include "BaseLibInternals.h"
  18
  19 /**
  20   Enables the 32-bit paging mode on the CPU.
  21
  22   Enables the 32-bit paging mode on the CPU. CR0, CR3, CR4, and the page tables
  23   must be properly initialized prior to calling this service. This function
  24   assumes the current execution mode is 32-bit protected mode. This function is
  25   only available on IA-32. After the 32-bit paging mode is enabled, control is
  26   transferred to the function specified by EntryPoint using the new stack
  27   specified by NewStack and passing in the parameters specified by Context1 and
  28   Context2. Context1 and Context2 are optional and may be NULL. The function
  29   EntryPoint must never return.
  30
  31   If the current execution mode is not 32-bit protected mode, then ASSERT().
  32   If EntryPoint is NULL, then ASSERT().
  33   If NewStack is NULL, then ASSERT().
  34
  35   There are a number of constraints that must be followed before calling this
  36   function:
  37   1)  Interrupts must be disabled.
  38   2)  The caller must be in 32-bit protected mode with flat descriptors. This
  39       means all descriptors must have a base of 0 and a limit of 4GB.
  40   3)  CR0 and CR4 must be compatible with 32-bit protected mode with flat
  41       descriptors.
  42   4)  CR3 must point to valid page tables that will be used once the transition
  43       is complete, and those page tables must guarantee that the pages for this
  44       function and the stack are identity mapped.
  45
  46   @param  EntryPoint  A pointer to function to call with the new stack after
  47                       paging is enabled.
  48   @param  Context1    A pointer to the context to pass into the EntryPoint
  49                       function as the first parameter after paging is enabled.
  50   @param  Context2    A pointer to the context to pass into the EntryPoint
  51                       function as the second parameter after paging is enabled.
  52   @param  NewStack    A pointer to the new stack to use for the EntryPoint
  53                       function after paging is enabled.
  54
  55 **/
  56 VOID
  57 EFIAPI
  58 AsmEnablePaging32 (
  59   IN      SWITCH_STACK_ENTRY_POINT  EntryPoint,
  60   IN      VOID                      *Context1,  OPTIONAL
  61   IN      VOID                      *Context2,  OPTIONAL
  62   IN      VOID                      *NewStack
  63   )
  64 {
  65   ASSERT (EntryPoint != NULL);
  66   ASSERT (NewStack != NULL);
  67   InternalX86EnablePaging32 (EntryPoint, Context1, Context2, NewStack);
  68 }