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;*****************************************************************************
;*
;* Copyright (c) 2006 - 2007, 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.
;*
;* Module Name:
;*
;* Thunk.asm
;*
;* Abstract:
;*
;* Real mode thunk
;*
;*****************************************************************************
.686p
EXTERNDEF C mCode16Size:DWORD
CONST SEGMENT FLAT "DATA" READONLY
mCode16Size DD _TEXT16SIZE
CONST ENDS
_DATA SEGMENT FLAT "DATA"
NullSegSel DQ 0
_16BitCsSel LABEL QWORD
DW -1
DW 0
DB 0
DB 9bh
DB 8fh ; 16-bit segment
DB 0
_16BitSsSel LABEL QWORD
DW -1
DW 0
DB 0
DB 93h
DB 8fh ; 16-bit segment
DB 0
_16Gdtr LABEL FWORD
DW $ - offset NullSegSel - 1
DD offset NullSegSel
_DATA ENDS
_TEXT SEGMENT FLAT "CODE" PARA
IA32_REGS STRUC 4t
_EDI DD ?
_ESI DD ?
_EBP DD ?
_ESP DD ?
_EBX DD ?
_EDX DD ?
_ECX DD ?
_EAX DD ?
_DS DW ?
_ES DW ?
_FS DW ?
_GS DW ?
_EFLAGS DD ?
_EIP DD ?
_CS DW ?
_SS DW ?
IA32_REGS ENDS
_STK16 STRUC 1t
RetEip DD ?
RetCs DW ?
ThunkFlags DW ?
SavedEsp DD ?
SavedSs DW ?
SavedGdtr FWORD ?
SavedCr0 DD ?
SavedCr4 DD ?
_STK16 ENDS
ASSUME ds:_DATA
__Thunk16 PROC USES ebp ebx esi edi ds es fs gs
ASSUME esi:PTR IA32_REGS
mov esi, [esp + 36]
movzx edx, [esi]._SS
mov edi, [esi]._ESP
add edi, - sizeof (_STK16) - sizeof (IA32_REGS)
push edi ; save stack offset
imul eax, edx, 16 ; eax <- edx*16
add edi, eax ; edi <- linear address of 16-bit stack
push sizeof (IA32_REGS) / 4
pop ecx
rep movsd ; copy context to 16-bit stack
pop ebx ; ebx <- 16-bit stack offset
mov eax, offset @F ; return offset
stosd
mov eax, cs ; return segment
stosw
mov eax, [esp + 40] ; THUNK flags
stosw
mov eax, esp
stosd ; save esp
mov eax, ss ; save ss
stosw
sgdt fword ptr [edi] ; save GDTR
sidt fword ptr [esp + 36] ; save IDTR
mov esi, cr0
mov [edi + 6], esi ; save CR0
and esi, NOT 80000001h ; esi <- CR0 to set
mov eax, cr4
mov [edi + 10], eax ; save CR4
and al, NOT 30h ; clear PAE & PSE
mov edi, edx ; edi <- 16-bit stack segment
mov edx, [esp + 44]
shl edx, 16
push edx
pop edx
mov dx, _16BitSsSel - NullSegSel
lgdt _16Gdtr ; load 16-bit GDTR
DB 0eah
DD offset @16Bit
DW _16BitCsSel - NullSegSel ; jmp far 8:@16Bit
@16Bit:
mov ss, dx
mov cr0, esi ; disable protected mode
mov cr4, eax ; disable PAE & PSE
db 67h, 0FFh, 06Ch, 024h, 0FCh ; jmp dword ptr [esp-4]
@@:
mov eax, ss
shl eax, 4
add eax, esp ; eax <- address of 16-bit stack
lss esp, fword ptr (_STK16 ptr [esp + sizeof (IA32_REGS)]).SavedEsp
lidt fword ptr [esp + 36] ; restore IDTR
ret
__Thunk16 ENDP
_TEXT ENDS
_TEXT16 SEGMENT USE16 "CODE" PARA
_Code16Addr PROC C
_Code16Addr ENDP
RealMode PROC
mov ss, di ; set up stack
mov esp, ebx
lidt fword ptr cs:[_16Idtr - _Code16Addr]
popad
pop ds
pop es
pop fs
pop gs
add sp, 4 ; skip EFlags
test (_STK16 ptr [esp + 8]).ThunkFlags, 1
jz @F
pushf
@@:
push cs
; push @FarCallRet - _Code16Addr
DB 68h ; push /iw
DW @FarCallRet - _Code16Addr
jz @F
jmp fword ptr [esp + 6]
@@:
jmp fword ptr [esp + 4]
@FarCallRet:
pushfd
push gs
push fs
push es
push ds
pushad
cli
DB 66h
lgdt (_STK16 ptr [esp + sizeof (IA32_REGS)]).SavedGdtr
mov eax, (_STK16 ptr [esp + sizeof (IA32_REGS)]).SavedCr4
mov cr4, eax
mov eax, (_STK16 ptr [esp + sizeof (IA32_REGS)]).SavedCr0
mov cr0, eax ; restore CR0
jmp fword ptr (_STK16 ptr [esp + sizeof (IA32_REGS)]).RetEip
RealMode ENDP
_16Idtr FWORD (1 SHL 10) - 1
_TEXT16END:
_TEXT16SIZE = _TEXT16END - _Code16Addr
_TEXT16 ENDS
END
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