1 files changed, 77 insertions, 0 deletions
diff --git a/MdePkg/Library/BaseLib/Ia32/DisablePaging32.c b/MdePkg/Library/BaseLib/Ia32/DisablePaging32.c
new file mode 100644
index 0000000000000..eb7556652d452
--- /dev/null
+++ b/MdePkg/Library/BaseLib/Ia32/DisablePaging32.c
@@ -0,0 +1,77 @@
+/** @file
+  AsmDisablePaging32 function.
+
+  Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
+  This program and the accompanying materials
+  are licensed and made available under the terms and conditions of the BSD License
+  which accompanies this distribution.  The full text of the license may be found at
+  http://opensource.org/licenses/bsd-license.php.
+
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+
+#include "BaseLibInternals.h"
+
+/**
+  Disables the 32-bit paging mode on the CPU.
+
+  Disables the 32-bit paging mode on the CPU and returns to 32-bit protected
+  mode. This function assumes the current execution mode is 32-paged protected
+  mode. This function is only available on IA-32. After the 32-bit paging mode
+  is disabled, control is transferred to the function specified by EntryPoint
+  using the new stack specified by NewStack and passing in the parameters
+  specified by Context1 and Context2. Context1 and Context2 are optional and
+  may be NULL. The function EntryPoint must never return.
+
+  There are a number of constraints that must be followed before calling this
+  function:
+  1)  Interrupts must be disabled.
+  2)  The caller must be in 32-bit paged mode.
+  3)  CR0, CR3, and CR4 must be compatible with 32-bit paged mode.
+  4)  CR3 must point to valid page tables that guarantee that the pages for
+      this function and the stack are identity mapped.
+
+  @param  EntryPoint  A pointer to function to call with the new stack after
+                      paging is disabled.
+  @param  Context1    A pointer to the context to pass into the EntryPoint
+                      function as the first parameter after paging is disabled.
+  @param  Context2    A pointer to the context to pass into the EntryPoint
+                      function as the second parameter after paging is
+                      disabled.
+  @param  NewStack    A pointer to the new stack to use for the EntryPoint
+                      function after paging is disabled.
+
+**/
+__declspec (naked)
+VOID
+EFIAPI
+InternalX86DisablePaging32 (
+  IN      SWITCH_STACK_ENTRY_POINT  EntryPoint,
+  IN      VOID                      *Context1,    OPTIONAL
+  IN      VOID                      *Context2,    OPTIONAL
+  IN      VOID                      *NewStack
+  )
+{
+  _asm {
+    push    ebp
+    mov     ebp, esp
+    mov     ebx, EntryPoint
+    mov     ecx, Context1
+    mov     edx, Context2
+    pushfd
+    pop     edi                         // save EFLAGS to edi
+    cli
+    mov     eax, cr0
+    btr     eax, 31
+    mov     esp, NewStack
+    mov     cr0, eax
+    push    edi
+    popfd                               // restore EFLAGS from edi
+    push    edx
+    push    ecx
+    call    ebx
+    jmp     $                           // EntryPoint() should not return
+  }
+}