1 /** @file 2 AsmDisablePaging32 function. 3 4 Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR> 5 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 } 78
