2007-06-22 05:21:45 +02:00
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//
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// Include common header file for this module.
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//
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2007-06-30 01:22:13 +02:00
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#include <BaseLibInternals.h>
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2007-06-22 05:21:45 +02:00
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;------------------------------------------------------------------------------
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;
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; Copyright (c) 2006, Intel Corporation
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; All rights reserved. This program and the accompanying materials
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; are licensed and made available under the terms and conditions of the BSD License
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; which accompanies this distribution. The full text of the license may be found at
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; http://opensource.org/licenses/bsd-license.php
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;
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; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
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; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
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;
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; Module Name:
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;
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; Thunk.asm
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;
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; Abstract:
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;
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; Real mode thunk
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;
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;------------------------------------------------------------------------------
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.686p
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.model flat,C
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EXTERNDEF C m16Start:BYTE
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EXTERNDEF C m16Size:WORD
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EXTERNDEF C mThunk16Attr:WORD
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EXTERNDEF C m16Gdt:WORD
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EXTERNDEF C m16GdtrBase:WORD
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EXTERNDEF C mTransition:WORD
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;
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; Here is the layout of the real mode stack. _ToUserCode() is responsible for
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; loading all these registers from real mode stack.
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;
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IA32_REGS STRUC 4t
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_EDI DD ?
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_ESI DD ?
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_EBP DD ?
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_ESP DD ?
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_EBX DD ?
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_EDX DD ?
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_ECX DD ?
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_EAX DD ?
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_DS DW ?
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_ES DW ?
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_FS DW ?
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_GS DW ?
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_EFLAGS DD ?
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_EIP DD ?
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_CS DW ?
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_SS DW ?
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IA32_REGS ENDS
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.const
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;
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; These are global constant to convey information to C code.
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;
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m16Size DW InternalAsmThunk16 - m16Start
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mThunk16Attr DW _ThunkAttr - m16Start
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m16Gdt DW _NullSegDesc - m16Start
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m16GdtrBase DW _16GdtrBase - m16Start
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mTransition DW _EntryPoint - m16Start
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.code
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m16Start LABEL BYTE
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SavedGdt LABEL FWORD
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DW ?
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DD ?
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;------------------------------------------------------------------------------
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; _BackFromUserCode() takes control in real mode after 'retf' has been executed
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; by user code. It will be shadowed to somewhere in memory below 1MB.
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;------------------------------------------------------------------------------
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_BackFromUserCode PROC
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;
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; The order of saved registers on the stack matches the order they appears
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; in IA32_REGS structure. This facilitates wrapper function to extract them
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; into that structure.
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;
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push ss
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push cs
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DB 66h
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call @Base ; push eip
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@Base:
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pushf ; pushfd actually
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cli ; disable interrupts
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push gs
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push fs
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push es
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push ds
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pushaw ; pushad actually
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DB 66h, 0bah ; mov edx, imm32
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_ThunkAttr DD ?
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test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
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jz @1
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mov eax, 15cd2401h ; mov ax, 2401h & int 15h
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cli ; disable interrupts
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jnc @2
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@1:
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test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
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jz @2
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in al, 92h
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or al, 2
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out 92h, al ; deactivate A20M#
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@2:
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mov eax, ss
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DB 67h
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lea bp, [esp + sizeof (IA32_REGS)]
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;
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; esi's in the following 2 instructions are indeed bp in 16-bit code. Fact
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; is "esi" in 32-bit addressing mode has the same encoding of "bp" in 16-
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; bit addressing mode.
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;
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mov word ptr (IA32_REGS ptr [esi - sizeof (IA32_REGS)])._ESP, bp
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mov ebx, (IA32_REGS ptr [esi - sizeof (IA32_REGS)])._EIP
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shl ax, 4 ; shl eax, 4
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add bp, ax ; add ebp, eax
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DB 66h, 0b8h ; mov eax, imm32
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SavedCr4 DD ?
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mov cr4, eax
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DB 66h
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lgdt fword ptr cs:[edi + (SavedGdt - @Base)]
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DB 66h, 0b8h ; mov eax, imm32
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SavedCr0 DD ?
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mov cr0, eax
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DB 0b8h ; mov ax, imm16
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SavedSs DW ?
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mov ss, eax
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DB 66h, 0bch ; mov esp, imm32
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SavedEsp DD ?
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DB 66h
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retf ; return to protected mode
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_BackFromUserCode ENDP
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_EntryPoint DD _ToUserCode - m16Start
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DW 8h
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_16Idtr FWORD (1 SHL 10) - 1
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_16Gdtr LABEL FWORD
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DW GdtEnd - _NullSegDesc - 1
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_16GdtrBase DD _NullSegDesc
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;------------------------------------------------------------------------------
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; _ToUserCode() takes control in real mode before passing control to user code.
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; It will be shadowed to somewhere in memory below 1MB.
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;------------------------------------------------------------------------------
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_ToUserCode PROC
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mov edx, ss
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mov ss, ecx ; set new segment selectors
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mov ds, ecx
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mov es, ecx
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mov fs, ecx
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mov gs, ecx
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mov cr0, eax
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mov cr4, ebp ; real mode starts at next instruction
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mov ss, esi ; set up 16-bit stack segment
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xchg sp, bx ; set up 16-bit stack pointer
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DB 66h
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call @Base ; push eip
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@Base:
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pop bp ; ebp <- address of @Base
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DB 67h ; address size override
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push [esp + sizeof (IA32_REGS) + 2]
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lea eax, [esi + (@RealMode - @Base)]
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push eax
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retf
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@RealMode:
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mov cs:[esi + (SavedSs - @Base)], edx
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mov cs:[esi + (SavedEsp - @Base)], bx
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DB 66h
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lidt fword ptr cs:[esi + (_16Idtr - @Base)]
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popaw ; popad actually
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pop ds
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pop es
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pop fs
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pop gs
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popf ; popfd
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DB 66h ; Use 32-bit addressing for "retf" below
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retf ; transfer control to user code
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_ToUserCode ENDP
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_NullSegDesc DQ 0
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_16CsDesc LABEL QWORD
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DW -1
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DW 0
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DB 0
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DB 9bh
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DB 8fh ; 16-bit segment, 4GB limit
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DB 0
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_16DsDesc LABEL QWORD
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DW -1
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DW 0
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DB 0
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DB 93h
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DB 8fh ; 16-bit segment, 4GB limit
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DB 0
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GdtEnd LABEL QWORD
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;------------------------------------------------------------------------------
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; IA32_REGISTER_SET *
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; EFIAPI
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; InternalAsmThunk16 (
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; IN IA32_REGISTER_SET *RegisterSet,
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; IN OUT VOID *Transition
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; );
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;------------------------------------------------------------------------------
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InternalAsmThunk16 PROC USES ebp ebx esi edi ds es fs gs
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mov esi, [esp + 36] ; esi <- RegSet, the 1st parameter
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movzx edx, (IA32_REGS ptr [esi])._SS
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mov edi, (IA32_REGS ptr [esi])._ESP
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add edi, - (sizeof (IA32_REGS) + 4) ; reserve stack space
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mov ebx, edi ; ebx <- stack offset
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imul eax, edx, 16 ; eax <- edx * 16
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push sizeof (IA32_REGS) / 4
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add edi, eax ; edi <- linear address of 16-bit stack
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pop ecx
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rep movsd ; copy RegSet
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mov eax, [esp + 40] ; eax <- address of transition code
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mov esi, edx ; esi <- 16-bit stack segment
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lea edx, [eax + (SavedCr0 - m16Start)]
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mov ecx, eax
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and ecx, 0fh
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shl eax, 12
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lea ecx, [ecx + (_BackFromUserCode - m16Start)]
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mov ax, cx
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stosd ; [edi] <- return address of user code
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sgdt fword ptr [edx + (SavedGdt - SavedCr0)]
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sidt fword ptr [esp + 36] ; save IDT stack in argument space
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mov eax, cr0
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mov [edx], eax ; save CR0 in SavedCr0
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and eax, 7ffffffeh ; clear PE, PG bits
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mov ebp, cr4
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mov [edx + (SavedCr4 - SavedCr0)], ebp
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and ebp, 300h ; clear all but PCE and OSFXSR bits
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push 10h
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pop ecx ; ecx <- selector for data segments
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lgdt fword ptr [edx + (_16Gdtr - SavedCr0)]
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pushfd ; Save df/if indeed
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call fword ptr [edx + (_EntryPoint - SavedCr0)]
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popfd
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lidt fword ptr [esp + 36] ; restore protected mode IDTR
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lea eax, [ebp - sizeof (IA32_REGS)] ; eax <- the address of IA32_REGS
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ret
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InternalAsmThunk16 ENDP
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END
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