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#------------------------------------------------------------------------------
#
# Copyright (c) 2006, 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:
#
# Thunk16.S
#
# Abstract:
#
# Real mode thunk
#
#------------------------------------------------------------------------------
.global _m16Start, _m16Size, _mThunk16Attr, _m16GdtrBase, _m16Gdt, _m16GdtrBase, _mTransition
.global _InternalAsmThunk16
#THUNK_ATTRIBUTE_BIG_REAL_MODE EQU 1
#THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 EQU 2
#THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL EQU 4
.code:
_m16Start:
SavedGdt: .space 6
_BackFromUserCode:
push %ss
push %cs
.byte 0x66
call @Base1 # push eip
@Base1:
pushfw # pushfd actually
cli # disable interrupts
push %gs
push %fs
push %es
push %ds
pushaw # pushad actually
.byte 0x66,0xba # mov edx, imm32
_ThunkAttr: .space 4
testb $THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15, %dl
jz @1
movl $0x15cd2401, %eax # mov ax, 2401h & int 15h
cli # disable interrupts
jnc @2
@1:
testb $THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL, %dl
jz @2
inb $0x92, %al
orb $2, %al
outb %al, $0x92 # deactivate A20M#
@2:
movl %ss, %eax
.byte 0x67, 0x66, 0x8d, 0x6c, 0x24, 0x34, 0x66
mov %ebp,0xffffffd8(%esi)
mov 0xfffffff8(%esi),%ebx
shlw $4, %ax # shl eax, 4
addw %ax, %bp # add ebp, eax
.byte 0x66,0xb8 # mov eax, imm32
SavedCr4: .space 4
movl %eax, %cr4
lgdtw %cs:0xfffffff2(%edi)
.byte 0x66,0xb8 # mov eax, imm32
SavedCr0: .space 4
movl %eax, %cr0
.byte 0xb8 # mov ax, imm16
SavedSs: .space 2
movl %eax, %ss
.byte 0x66,0xbc # mov esp, imm32
SavedEsp: .space 4
.byte 0x66
lret # return to protected mode
_EntryPoint: .long _ToUserCode - _m16Start
.word 0x8
_16Idtr: .word 0x3ff
.long 0
_16Gdtr: .word GdtEnd - _NullSegDesc - 1
_16GdtrBase: .long _NullSegDesc
_ToUserCode:
movl %ss, %edx
movl %ecx, %ss # set new segment selectors
movl %ecx, %ds
movl %ecx, %es
movl %ecx, %fs
movl %ecx, %gs
movl %eax, %cr0
movl %ebp, %cr4 # real mode starts at next instruction
movl %esi, %ss # set up 16-bit stack segment
xchgw %bx, %sp # set up 16-bit stack pointer
.byte 0x66
call @Base # push eip
@Base:
popw %bp # ebp <- offset @Base
addr16 pushl 36(%si)
.byte 0x36
lea 0xc(%esi),%eax
pushl %eax
lret
@RealMode:
mov %edx,%cs:0xffffffc5(%esi)
mov %bx,%cs:0xffffffcb(%esi)
lidtw %cs:0xffffffd7(%esi)
popaw # popad actually
popl %ds
popl %es
popl %fs
popl %gs
popfw # popfd
lretw # transfer control to user code
_NullSegDesc: .quad 0
_16CsDesc:
.word -1
.word 0
.byte 0
.byte 0x9b
.byte 0x8f # 16-bit segment, 4GB limit
.byte 0
_16DsDesc:
.word -1
.word 0
.byte 0
.byte 0x93
.byte 0x8f # 16-bit segment, 4GB limit
.byte 0
GdtEnd:
#
# @param RegSet Pointer to a IA32_DWORD_REGS structure
# @param Transition Pointer to the transition code
# @return The address of the 16-bit stack after returning from user code
#
_InternalAsmThunk16:
push %ebp
push %ebx
push %esi
push %edi
push %ds
push %es
push %fs
push %gs
movl 36(%esp), %esi # esi <- RegSet
movzwl 0x32(%esi),%edx
mov 0xc(%esi),%edi
add $0xffffffc8,%edi
movl %edi, %ebx # ebx <- stack offset
imul $0x10,%edx,%eax
push $0xd
addl %eax, %edi # edi <- linear address of 16-bit stack
popl %ecx
rep
movsl # copy RegSet
movl 40(%esp), %eax # eax <- address of transition code
movl %edx, %esi # esi <- 16-bit stack segment
lea 0x5e(%eax),%edx
movl %eax, %ecx
andl $0xf, %ecx
shll $12, %eax
lea 0x6(%ecx),%ecx
movw %cx, %ax
stosl # [edi] <- return address of user code
sgdtl 0xffffffa2(%edx)
sidtl 0x24(%esp)
movl %cr0, %eax
movl %eax, (%edx) # save CR0 in SavedCr0
andl $0x7ffffffe, %eax # clear PE, PG bits
movl %cr4, %ebp
mov %ebp,0xfffffff1(%edx)
andl $0x300, %ebp # clear all but PCE and OSFXSR bits
pushl $0x10
popl %ecx # ecx <- selector for data segments
lgdtl 0x20(%edx)
pushfl
lcall *0x14(%edx)
popfl
lidtl 0x24(%esp)
lea 0xffffffcc(%ebp),%eax
pop %gs
pop %fs
pop %es
pop %ds
pop %edi
pop %esi
pop %ebx
pop %ebp
ret
.const:
_m16Size: .word _InternalAsmThunk16 - _m16Start
_mThunk16Attr: .word _ThunkAttr - _m16Start
_m16Gdt: .word _NullSegDesc - _m16Start
_m16GdtrBase: .word _16GdtrBase - _m16Start
_mTransition: .word _EntryPoint - _m16Start
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