1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
|
#------------------------------------------------------------------------------
#
# Copyright (c) 2006 - 2008, 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:
#
# Thunk16.S
#
# Abstract:
#
# Real mode thunk
#
#------------------------------------------------------------------------------
#include <Library/BaseLib.h>
ASM_GLOBAL ASM_PFX(m16Start), ASM_PFX(m16Size), ASM_PFX(mThunk16Attr), ASM_PFX(m16Gdt), ASM_PFX(m16GdtrBase), ASM_PFX(mTransition)
ASM_GLOBAL ASM_PFX(InternalAsmThunk16)
ASM_PFX(m16Start):
SavedGdt: .space 6
ASM_PFX(BackFromUserCode):
push %ss
push %cs
.byte 0x66
call L_Base1 # push eip
L_Base1:
pushfw # pushfd actually
cli # disable interrupts
push %gs
push %fs
push %es
push %ds
pushaw # pushad actually
.byte 0x66, 0xba # mov edx, imm32
ASM_PFX(ThunkAttr): .space 4
testb $THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15, %dl
jz 1f
movl $0x15cd2401, %eax # mov ax, 2401h & int 15h
cli # disable interrupts
jnc 2f
1:
testb $THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL, %dl
jz 2f
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 ASM_PFX(ToUserCode) - ASM_PFX(m16Start)
.word 0x8
_16Idtr: .word 0x3ff
.long 0
_16Gdtr: .word GdtEnd - _NullSegDesc - 1
_16GdtrBase: .long _NullSegDesc
ASM_PFX(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 L_Base # push eip
L_Base:
popw %bp # ebp <- offset L_Base
.byte 0x67; # address size override
push 54(%esp)
lea 0xc(%esi), %eax
push %eax
lret
L_RealMode:
mov %edx, %cs:0xffffffc5(%esi)
mov %bx, %cs:0xffffffcb(%esi)
lidtw %cs:0xffffffd7(%esi)
popaw # popad actually
pop %ds
pop %es
pop %fs
pop %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
#
ASM_PFX(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
pop %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
pop %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:
ASM_PFX(m16Size): .word ASM_PFX(InternalAsmThunk16) - ASM_PFX(m16Start)
ASM_PFX(mThunk16Attr): .word ASM_PFX(ThunkAttr) - ASM_PFX(m16Start)
ASM_PFX(m16Gdt): .word _NullSegDesc - ASM_PFX(m16Start)
ASM_PFX(m16GdtrBase): .word _16GdtrBase - ASM_PFX(m16Start)
ASM_PFX(mTransition): .word _EntryPoint - ASM_PFX(m16Start)
|