MdePkg/Library/BaseLib/Ia32/EnablePaging32.c

   1 /** @file
   2   AsmEnablePaging32 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   Enables the 32-bit paging mode on the CPU.
  19
  20   Enables the 32-bit paging mode on the CPU. CR0, CR3, CR4, and the page tables
  21   must be properly initialized prior to calling this service. This function
  22   assumes the current execution mode is 32-bit protected mode. This function is
  23   only available on IA-32. After the 32-bit paging mode is enabled, control is
  24   transferred to the function specified by EntryPoint using the new stack
  25   specified by NewStack and passing in the parameters specified by Context1 and
  26   Context2. Context1 and Context2 are optional and may be NULL. The function
  27   EntryPoint must never return.
  28
  29   There are a number of constraints that must be followed before calling this
  30   function:
  31   1)  Interrupts must be disabled.
  32   2)  The caller must be in 32-bit protected mode with flat descriptors. This
  33       means all descriptors must have a base of 0 and a limit of 4GB.
  34   3)  CR0 and CR4 must be compatible with 32-bit protected mode with flat
  35       descriptors.
  36   4)  CR3 must point to valid page tables that will be used once the transition
  37       is complete, and those page tables must guarantee that the pages for this
  38       function and the stack are identity mapped.
  39
  40   @param  EntryPoint  A pointer to function to call with the new stack after
  41                       paging is enabled.
  42   @param  Context1    A pointer to the context to pass into the EntryPoint
  43                       function as the first parameter after paging is enabled.
  44   @param  Context2    A pointer to the context to pass into the EntryPoint
  45                       function as the second parameter after paging is enabled.
  46   @param  NewStack    A pointer to the new stack to use for the EntryPoint
  47                       function after paging is enabled.
  48
  49 **/
  50 __declspec (naked)
  51 VOID
  52 EFIAPI
  53 InternalX86EnablePaging32 (
  54   IN      SWITCH_STACK_ENTRY_POINT  EntryPoint,
  55   IN      VOID                      *Context1,    OPTIONAL
  56   IN      VOID                      *Context2,    OPTIONAL
  57   IN      VOID                      *NewStack
  58   )
  59 {
  60   _asm {
  61     push    ebp
  62     mov     ebp, esp
  63     mov     ebx, EntryPoint
  64     mov     ecx, Context1
  65     mov     edx, Context2
  66     pushfd
  67     pop     edi
  68     cli
  69     mov     eax, cr0
  70     bts     eax, 31
  71     mov     esp, NewStack
  72     mov     cr0, eax
  73     push    edi
  74     popfd
  75     push    edx
  76     push    ecx
  77     call    ebx
  78     jmp     $
  79   }
  80 }
  81