MdePkg/Library/BaseLib/Ia32/DisablePaging32.c

   1 /** @file
   2   AsmDisablePaging32 function.
   3
   4   Copyright (c) 2006 - 2007, 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 **/
  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
  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 }