MdePkg/Library/BaseLib/Ia32/EnablePaging32.c

   1 /** @file
   2   AsmEnablePaging32 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   Enables the 32-bit paging mode on the CPU.
  13
  14   Enables the 32-bit paging mode on the CPU. CR0, CR3, CR4, and the page tables
  15   must be properly initialized prior to calling this service. This function
  16   assumes the current execution mode is 32-bit protected mode. This function is
  17   only available on IA-32. After the 32-bit paging mode is enabled, control is
  18   transferred to the function specified by EntryPoint using the new stack
  19   specified by NewStack and passing in the parameters specified by Context1 and
  20   Context2. Context1 and Context2 are optional and may be NULL. The function
  21   EntryPoint must never return.
  22
  23   There are a number of constraints that must be followed before calling this
  24   function:
  25   1)  Interrupts must be disabled.
  26   2)  The caller must be in 32-bit protected mode with flat descriptors. This
  27       means all descriptors must have a base of 0 and a limit of 4GB.
  28   3)  CR0 and CR4 must be compatible with 32-bit protected mode with flat
  29       descriptors.
  30   4)  CR3 must point to valid page tables that will be used once the transition
  31       is complete, and those page tables must guarantee that the pages for this
  32       function and the stack are identity mapped.
  33
  34   @param  EntryPoint  A pointer to function to call with the new stack after
  35                       paging is enabled.
  36   @param  Context1    A pointer to the context to pass into the EntryPoint
  37                       function as the first parameter after paging is enabled.
  38   @param  Context2    A pointer to the context to pass into the EntryPoint
  39                       function as the second parameter after paging is enabled.
  40   @param  NewStack    A pointer to the new stack to use for the EntryPoint
  41                       function after paging is enabled.
  42
  43 **/
  44 __declspec(naked)
  45 VOID
  46 EFIAPI
  47 InternalX86EnablePaging32 (
  48   IN      SWITCH_STACK_ENTRY_POINT  EntryPoint,
  49   IN      VOID                      *Context1     OPTIONAL,
  50   IN      VOID                      *Context2     OPTIONAL,
  51   IN      VOID                      *NewStack
  52   )
  53 {
  54   _asm {
  55     push    ebp
  56     mov     ebp, esp
  57     mov     ebx, EntryPoint
  58     mov     ecx, Context1
  59     mov     edx, Context2
  60     pushfd
  61     pop     edi
  62     cli
  63     mov     eax, cr0
  64     bts     eax, 31
  65     mov     esp, NewStack
  66     mov     cr0, eax
  67     push    edi
  68     popfd
  69     push    edx
  70     push    ecx
  71     call    ebx
  72     jmp     $
  73   }
  74 }