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
  16 #include <BaseLibInternals.h>
  17
  18 #if _MSC_EXTENSIONS
  19
  20 /**
  21   Disables the 32-bit paging mode on the CPU.
  22
  23   Disables the 32-bit paging mode on the CPU and returns to 32-bit protected
  24   mode. This function assumes the current execution mode is 32-paged protected
  25   mode. This function is only available on IA-32. After the 32-bit paging mode
  26   is disabled, control is transferred to the function specified by EntryPoint
  27   using the new stack specified by NewStack and passing in the parameters
  28   specified by Context1 and Context2. Context1 and Context2 are optional and
  29   may be NULL. The function EntryPoint must never return.
  30
  31   There are a number of constraints that must be followed before calling this
  32   function:
  33   1)  Interrupts must be disabled.
  34   2)  The caller must be in 32-bit paged mode.
  35   3)  CR0, CR3, and CR4 must be compatible with 32-bit paged mode.
  36   4)  CR3 must point to valid page tables that guarantee that the pages for
  37       this function and the stack are identity mapped.
  38
  39   @param  EntryPoint  A pointer to function to call with the new stack after
  40                       paging is disabled.
  41   @param  Context1    A pointer to the context to pass into the EntryPoint
  42                       function as the first parameter after paging is disabled.
  43   @param  Context2    A pointer to the context to pass into the EntryPoint
  44                       function as the second parameter after paging is
  45                       disabled.
  46   @param  NewStack    A pointer to the new stack to use for the EntryPoint
  47                       function after paging is disabled.
  48
  49 **/
  50 __declspec (naked)
  51 VOID
  52 EFIAPI
  53 InternalX86DisablePaging32 (
  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                         // save EFLAGS to edi
  68     cli
  69     mov     eax, cr0
  70     btr     eax, 31
  71     mov     esp, NewStack
  72     mov     cr0, eax
  73     push    edi
  74     popfd                               // restore EFLAGS from edi
  75     push    edx
  76     push    ecx
  77     call    ebx
  78     jmp     $                           // EntryPoint() should not return
  79   }
  80 }
  81
  82 #endif