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
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
|
/*
* From coreboot x86_asm.S, cleaned up substantially
*
* Copyright (C) 2009-2010 coresystems GmbH
*
* SPDX-License-Identifier: GPL-2.0
*/
#include <asm/processor.h>
#include <asm/processor-flags.h>
#include "bios.h"
#define SEG(segment) $segment * X86_GDT_ENTRY_SIZE
/*
* This is the interrupt handler stub code. It gets copied to the IDT and
* to some fixed addresses in the F segment. Before the code can used,
* it gets patched up by the C function copying it: byte 3 (the $0 in
* movb $0, %al) is overwritten with the interrupt numbers.
*/
.code16
.globl __idt_handler
__idt_handler:
pushal
movb $0, %al /* This instruction gets modified */
ljmp $0, $__interrupt_handler_16bit
.globl __idt_handler_size
__idt_handler_size:
.long . - __idt_handler
.macro setup_registers
/* initial register values */
movl 44(%ebp), %eax
movl %eax, __registers + 0 /* eax */
movl 48(%ebp), %eax
movl %eax, __registers + 4 /* ebx */
movl 52(%ebp), %eax
movl %eax, __registers + 8 /* ecx */
movl 56(%ebp), %eax
movl %eax, __registers + 12 /* edx */
movl 60(%ebp), %eax
movl %eax, __registers + 16 /* esi */
movl 64(%ebp), %eax
movl %eax, __registers + 20 /* edi */
.endm
.macro enter_real_mode
/* Activate the right segment descriptor real mode. */
ljmp SEG(X86_GDT_ENTRY_16BIT_CS), $PTR_TO_REAL_MODE(1f)
1:
.code16
/*
* Load the segment registers with properly configured segment
* descriptors. They will retain these configurations (limits,
* writability, etc.) once protected mode is turned off.
*/
mov SEG(X86_GDT_ENTRY_16BIT_DS), %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %ax, %ss
/* Turn off protection */
movl %cr0, %eax
andl $~X86_CR0_PE, %eax
movl %eax, %cr0
/* Now really going into real mode */
ljmp $0, $PTR_TO_REAL_MODE(1f)
1:
/*
* Set up a stack: Put the stack at the end of page zero. That way
* we can easily share it between real and protected, since the
* 16-bit ESP at segment 0 will work for any case.
*/
mov $0x0, %ax
mov %ax, %ss
/* Load 16 bit IDT */
xor %ax, %ax
mov %ax, %ds
lidt __realmode_idt
.endm
.macro prepare_for_irom
movl $0x1000, %eax
movl %eax, %esp
/* Initialise registers for option rom lcall */
movl __registers + 0, %eax
movl __registers + 4, %ebx
movl __registers + 8, %ecx
movl __registers + 12, %edx
movl __registers + 16, %esi
movl __registers + 20, %edi
/* Set all segments to 0x0000, ds to 0x0040 */
push %ax
xor %ax, %ax
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov SEG(X86_GDT_ENTRY_16BIT_FLAT_DS), %ax
mov %ax, %ds
pop %ax
.endm
.macro enter_protected_mode
/* Go back to protected mode */
movl %cr0, %eax
orl $X86_CR0_PE, %eax
movl %eax, %cr0
/* Now that we are in protected mode jump to a 32 bit code segment */
data32 ljmp SEG(X86_GDT_ENTRY_32BIT_CS), $PTR_TO_REAL_MODE(1f)
1:
.code32
mov SEG(X86_GDT_ENTRY_32BIT_DS), %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %gs
mov %ax, %ss
mov SEG(X86_GDT_ENTRY_32BIT_FS), %ax
mov %ax, %fs
/* restore proper idt */
lidt idt_ptr
.endm
/*
* In order to be independent of U-Boot's position in RAM we relocate a part
* of the code to the first megabyte of RAM, so the CPU can use it in
* real-mode. This code lives at asm_realmode_code.
*/
.globl asm_realmode_code
asm_realmode_code:
/* Realmode IDT pointer structure. */
__realmode_idt = PTR_TO_REAL_MODE(.)
.word 1023 /* 16 bit limit */
.long 0 /* 24 bit base */
.word 0
/* Preserve old stack */
__stack = PTR_TO_REAL_MODE(.)
.long 0
/* Register store for realmode_call and realmode_interrupt */
__registers = PTR_TO_REAL_MODE(.)
.long 0 /* 0 - EAX */
.long 0 /* 4 - EBX */
.long 0 /* 8 - ECX */
.long 0 /* 12 - EDX */
.long 0 /* 16 - ESI */
.long 0 /* 20 - EDI */
/* 256 byte buffer, used by int10 */
.globl asm_realmode_buffer
asm_realmode_buffer:
.skip 256
.code32
.globl asm_realmode_call
asm_realmode_call:
/* save all registers to the stack */
pusha
pushf
movl %esp, __stack
movl %esp, %ebp
/*
* This function is called with regparm=0 and we have to skip the
* 36 bytes from pushf+pusha. Hence start at 40.
* Set up our call instruction.
*/
movl 40(%ebp), %eax
mov %ax, __lcall_instr + 1
andl $0xffff0000, %eax
shrl $4, %eax
mov %ax, __lcall_instr + 3
wbinvd
setup_registers
enter_real_mode
prepare_for_irom
__lcall_instr = PTR_TO_REAL_MODE(.)
.byte 0x9a
.word 0x0000, 0x0000
enter_protected_mode
/* restore stack pointer, eflags and register values and exit */
movl __stack, %esp
popf
popa
ret
.globl __realmode_interrupt
__realmode_interrupt:
/* save all registers to the stack and store the stack pointer */
pusha
pushf
movl %esp, __stack
movl %esp, %ebp
/*
* This function is called with regparm=0 and we have to skip the
* 36 bytes from pushf+pusha. Hence start at 40.
* Prepare interrupt calling code.
*/
movl 40(%ebp), %eax
movb %al, __intXX_instr + 1 /* intno */
setup_registers
enter_real_mode
prepare_for_irom
__intXX_instr = PTR_TO_REAL_MODE(.)
.byte 0xcd, 0x00 /* This becomes intXX */
enter_protected_mode
/* restore stack pointer, eflags and register values and exit */
movl __stack, %esp
popf
popa
ret
/*
* This is the 16-bit interrupt entry point called by the IDT stub code.
*
* Before this code code is called, %eax is pushed to the stack, and the
* interrupt number is loaded into %al. On return this function cleans up
* for its caller.
*/
.code16
__interrupt_handler_16bit = PTR_TO_REAL_MODE(.)
push %ds
push %es
push %fs
push %gs
/* Clear DF to not break ABI assumptions */
cld
/*
* Clean up the interrupt number. We could do this in the stub, but
* it would cost two more bytes per stub entry.
*/
andl $0xff, %eax
pushl %eax /* ... and make it the first parameter */
enter_protected_mode
/* Call the C interrupt handler */
movl $interrupt_handler, %eax
call *%eax
enter_real_mode
/*
* Restore all registers, including those manipulated by the C
* handler
*/
popl %eax
pop %gs
pop %fs
pop %es
pop %ds
popal
iret
.globl asm_realmode_code_size
asm_realmode_code_size:
.long . - asm_realmode_code
|
