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; Copyright (c) 2004, Intel Corporation
; All rights reserved. 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
;
;------------------------------------------------------------------------------
EXTERNDEF m16Start:BYTE
EXTERNDEF m16Size:WORD
EXTERNDEF mThunk16Attr:WORD
EXTERNDEF m16Gdt:WORD
EXTERNDEF m16GdtrBase:WORD
EXTERNDEF mTransition:WORD
THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 EQU 2
THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL EQU 4
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 DQ ?
_EIP DD ?
_CS DW ?
_SS DW ?
IA32_REGS ENDS
.const
m16Size DW InternalAsmThunk16 - m16Start
mThunk16Attr DW _ThunkAttr - m16Start
m16Gdt DW _NullSegDesc - m16Start
m16GdtrBase DW _16GdtrBase - m16Start
mTransition DW _EntryPoint - m16Start
.code
m16Start LABEL BYTE
SavedGdt LABEL FWORD
DW ?
DQ ?
;------------------------------------------------------------------------------
; _BackFromUserCode() takes control in real mode after 'retf' has been executed
; by user code. It will be shadowed to somewhere in memory below 1MB.
;------------------------------------------------------------------------------
_BackFromUserCode PROC
DB 16h ; push ss
DB 0eh ; push cs
DB 66h
call @Base ; push eip
@Base:
DB 66h
push 0 ; reserved high order 32 bits of EFlags
pushf ; pushfd actually
cli ; disable interrupts
push gs
push fs
DB 6 ; push es
DB 1eh ; push ds
DB 66h, 60h ; pushad
DB 66h, 0bah ; mov edx, imm32
_ThunkAttr DD ?
test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
jz @1
mov eax, 15cd2401h ; mov ax, 2401h & int 15h
cli ; disable interrupts
jnc @2
@1:
test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
jz @2
in al, 92h
or al, 2
out 92h, al ; deactivate A20M#
@2:
xor ax, ax ; xor eax, eax
mov eax, ss
lea bp, [esp + sizeof (IA32_REGS)]
mov word ptr (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._ESP, bp
mov ebx, (IA32_REGS ptr [rsi - sizeof (IA32_REGS)])._EIP
shl ax, 4 ; shl eax, 4
add bp, ax ; add ebp, eax
DB 66h, 0b8h ; mov eax, imm32
SavedCr4 DD ?
mov cr4, rax
DB 66h, 2eh
lgdt fword ptr [rdi + (SavedGdt - @Base)]
DB 66h
mov ecx, 0c0000080h
rdmsr
or ah, 1
wrmsr
DB 66h, 0b8h ; mov eax, imm32
SavedCr0 DD ?
mov cr0, rax
DB 0b8h ; mov ax, imm16
SavedSs DW ?
mov ss, eax
DB 66h, 0bch ; mov esp, imm32
SavedEsp DD ?
DB 66h
retf ; return to protected mode
_BackFromUserCode ENDP
_EntryPoint DD _ToUserCode - m16Start
DW 8h
_16Gdtr LABEL FWORD
DW GdtEnd - _NullSegDesc - 1
_16GdtrBase DQ _NullSegDesc
_16Idtr FWORD (1 SHL 10) - 1
;------------------------------------------------------------------------------
; _ToUserCode() takes control in real mode before passing control to user code.
; It will be shadowed to somewhere in memory below 1MB.
;------------------------------------------------------------------------------
_ToUserCode PROC
mov edi, ss
mov ss, edx ; set new segment selectors
mov ds, edx
mov es, edx
mov fs, edx
mov gs, edx
DB 66h
mov ecx, 0c0000080h
mov cr0, rax ; real mode starts at next instruction
rdmsr
and ah, NOT 1
wrmsr
mov cr4, rbp
mov ss, esi ; set up 16-bit stack segment
xchg sp, bx ; set up 16-bit stack pointer
DB 66h
call @Base ; push eip
@Base:
pop bp ; ebp <- address of @Base
push [esp + sizeof (IA32_REGS) + 2]
lea eax, [rsi + (@RealMode - @Base)]
push rax
retf
@RealMode:
DB 2eh ; cs:
mov [rsi + (SavedSs - @Base)], edi
DB 2eh ; cs:
mov [rsi + (SavedEsp - @Base)], bx
DB 66h, 2eh ; CS and operand size override
lidt fword ptr [rsi + (_16Idtr - @Base)]
DB 66h, 61h ; popad
DB 1fh ; pop ds
DB 07h ; pop es
pop fs
pop gs
popf ; popfd
lea sp, [esp + 4] ; skip high order 32 bits of EFlags
DB 66h
retf ; transfer control to user code
_ToUserCode ENDP
_NullSegDesc DQ 0
_16CsDesc LABEL QWORD
DW -1
DW 0
DB 0
DB 9bh
DB 8fh ; 16-bit segment, 4GB limit
DB 0
_16DsDesc LABEL QWORD
DW -1
DW 0
DB 0
DB 93h
DB 8fh ; 16-bit segment, 4GB limit
DB 0
GdtEnd LABEL QWORD
;------------------------------------------------------------------------------
; IA32_REGISTER_SET *
; EFIAPI
; InternalAsmThunk16 (
; IN IA32_REGISTER_SET *RegisterSet,
; IN OUT VOID *Transition
; );
;------------------------------------------------------------------------------
InternalAsmThunk16 PROC USES rbp rbx rsi rdi
mov r10d, ds
mov r11d, es
push fs
push gs
mov rsi, rcx
movzx r8d, (IA32_REGS ptr [rsi])._SS
mov edi, (IA32_REGS ptr [rsi])._ESP
lea rdi, [edi - (sizeof (IA32_REGS) + 4)]
imul eax, r8d, 16 ; eax <- r8d(stack segment) * 16
mov ebx, edi ; ebx <- stack for 16-bit code
push sizeof (IA32_REGS) / 4
add edi, eax ; edi <- linear address of 16-bit stack
pop rcx
rep movsd ; copy RegSet
lea ecx, [rdx + (SavedCr4 - m16Start)]
mov eax, edx ; eax <- transition code address
and edx, 0fh
shl eax, 12
lea edx, [rdx + (_BackFromUserCode - m16Start)]
mov ax, dx
stosd ; [edi] <- return address of user code
sgdt fword ptr [rcx + (SavedGdt - SavedCr4)]
sidt fword ptr [rsp + 38h] ; save IDT stack in argument space
mov rax, cr0
mov [rcx + (SavedCr0 - SavedCr4)], eax
and eax, 7ffffffeh ; clear PE, PG bits
mov rbp, cr4
mov [rcx], ebp ; save CR4 in SavedCr4
and ebp, 300h ; clear all but PCE and OSFXSR bits
mov esi, r8d ; esi <- 16-bit stack segment
push 10h
pop rdx ; rdx <- selector for data segments
lgdt fword ptr [rcx + (_16Gdtr - SavedCr4)]
pushfq
call fword ptr [rcx + (_EntryPoint - SavedCr4)]
popfq
lidt fword ptr [rsp + 38h] ; restore protected mode IDTR
lea eax, [rbp - sizeof (IA32_REGS)]
pop gs
pop fs
mov es, r11d
mov ds, r10d
ret
InternalAsmThunk16 ENDP
END
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