MdePkg/Library/BaseLib/Ia32/DisablePaging32.c

   1 /** @file
   2   AsmDisablePaging32 function.
   3
   4   Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
   5   SPDX-License-Identifier: BSD-2-Clause-Patent
   6
   7 **/
   8
   9 #include "BaseLibInternals.h"
  10
  11 /**
  12   Disables the 32-bit paging mode on the CPU.
  13
  14   Disables the 32-bit paging mode on the CPU and returns to 32-bit protected
  15   mode. This function assumes the current execution mode is 32-paged protected
  16   mode. This function is only available on IA-32. After the 32-bit paging mode
  17   is disabled, control is transferred to the function specified by EntryPoint
  18   using the new stack specified by NewStack and passing in the parameters
  19   specified by Context1 and Context2. Context1 and Context2 are optional and
  20   may be NULL. The function EntryPoint must never return.
  21
  22   There are a number of constraints that must be followed before calling this
  23   function:
  24   1)  Interrupts must be disabled.
  25   2)  The caller must be in 32-bit paged mode.
  26   3)  CR0, CR3, and CR4 must be compatible with 32-bit paged mode.
  27   4)  CR3 must point to valid page tables that guarantee that the pages for
  28       this function and the stack are identity mapped.
  29
  30   @param  EntryPoint  A pointer to function to call with the new stack after
  31                       paging is disabled.
  32   @param  Context1    A pointer to the context to pass into the EntryPoint
  33                       function as the first parameter after paging is disabled.
  34   @param  Context2    A pointer to the context to pass into the EntryPoint
  35                       function as the second parameter after paging is
  36                       disabled.
  37   @param  NewStack    A pointer to the new stack to use for the EntryPoint
  38                       function after paging is disabled.
  39
  40 **/
  41 __declspec (naked)
  42 VOID
  43 EFIAPI
  44 InternalX86DisablePaging32 (
  45   IN      SWITCH_STACK_ENTRY_POINT  EntryPoint,
  46   IN      VOID                      *Context1,    OPTIONAL
  47   IN      VOID                      *Context2,    OPTIONAL
  48   IN      VOID                      *NewStack
  49   )
  50 {
  51   _asm {
  52     push    ebp
  53     mov     ebp, esp
  54     mov     ebx, EntryPoint
  55     mov     ecx, Context1
  56     mov     edx, Context2
  57     pushfd
  58     pop     edi                         // save EFLAGS to edi
  59     cli
  60     mov     eax, cr0
  61     btr     eax, 31
  62     mov     esp, NewStack
  63     mov     cr0, eax
  64     push    edi
  65     popfd                               // restore EFLAGS from edi
  66     push    edx
  67     push    ecx
  68     call    ebx
  69     jmp     $                           // EntryPoint() should not return
  70   }
  71 }