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
|
/* $OpenBSD: srt0.S,v 1.3 2012/10/31 14:31:30 jsing Exp $ */
/*
* Copyright (c) 1997 Michael Shalayeff
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
*/
#include <machine/asm.h>
#include <assym.h>
#define BOOTSTACK 0xfffc
.globl _C_LABEL(end)
.globl _C_LABEL(edata)
.globl _C_LABEL(boot)
.globl _C_LABEL(_rtt)
.globl _C_LABEL(bios_bootdev)
.globl _ASM_LABEL(pmm_init)
.globl Gdtr
.text
.code16
.globl _start
_start:
#ifdef DEBUG
movl $0xb80a0, %ebx
addr32 movl $0x07420742, (%ebx)
#endif
/* Clobbers %ax, maybe more */
#define putc(c) movb $c, %al; call Lchr
/*
* We operate as a no emulation boot image, as defined by the
* El Torito Bootable CD-ROM Format Specification v1.0. We use
* a load segment of 0x07C0 (physical load address of 0x7C00).
* Like the standard /boot, we are linked to run at 0x40120
* (load address 0x40000), so we relocate to there.
*
* From 0x7C00 to 0x40000 is 0x38400 (230400) bytes, so we don't
* have to worry about an overlapping copy until cdboot is
* over 225 KB.
*
* Our cdbr CD-ROM boot sector passes us the drive number to use
* in %dl.
*/
#define CDBOOTADDR 0x7c00 /* Address where BIOS loads up */
xorw %ax, %ax
movw %ax, %ss /* CPU disables interrupts till... */
movl $CDBOOTADDR-4, %esp /* after this instruction */
pushl %edx /* Preserve the drive number. */
movw $(CDBOOTADDR >> 4), %ax /* Reloc from %ds = 0x7c0. */
movw $(LINKADDR >> 4), %bx /* Reloc to %es = 0x4012. */
movl $_C_LABEL(end), %edx
subl $_C_LABEL(_start), %edx /* How big are we? */
/*
* Relocate in blocks that are a maximum of 32KB in size, incrementing
* the segment registers after each block. The 'rep; movsb' instruction
* uses %cx, which limits us to a maximum block size of 0xfff0, even
* though we can address the full 64KB within a single segment.
*/
#define RELOC_BLOCK_SIZE 0x8000
reloc_loop:
movl %edx, %ecx
jcxz reloc_done
cmpl $RELOC_BLOCK_SIZE, %ecx
jbe reloc_notrunc
movl $RELOC_BLOCK_SIZE, %ecx
reloc_notrunc:
subl %ecx, %edx
movw %ax, %ds /* Where we're coming from */
xorw %si, %si
movw %bx, %es /* Where we're going to */
xorw %di, %di
cld
rep; movsb /* Copy into place */
addw $(RELOC_BLOCK_SIZE >> 4), %ax
addw $(RELOC_BLOCK_SIZE >> 4), %bx
jmp reloc_loop
reloc_done:
popl %edx
jmpl $(LINKADDR >> 4), $(relocated-_start) /* Now relocate */
relocated:
/*
* In 16-bit mode, we have segment registers == 0x4012, and
* offsets work from here, with offset(_start) == 0.
*
* In 32-bit mode, we have a flat memory model, where
* offset(_start) == 0x40120. This is how we're linked.
*
* Now transition to protected mode.
*
* First, initialise the global descriptor table.
*/
cli
push %cs
pop %ds
addr32 data32 lgdt (Gdtr - LINKADDR)
movl %cr0, %eax
orl $CR0_PE, %eax
data32 movl %eax, %cr0
data32 ljmp $8, $1f /* Seg sel 0x08 is flat 32-bit code */
1:
.code32
movl $0x10, %eax /* Seg sel 0x10 is flat 32-bit data */
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %ax, %ss
movl $BOOTSTACK, %esp
#ifdef DEBUG
movl $0xb8000, %ebx
movl $0x07420742, (%ebx)
#endif
movzbl %dl, %eax
orl $0x100, %eax /* Indicate that it's a cd device */
pushl %eax /* boot() takes this as a parameter */
#ifdef DEBUG
movl $0xb80a4, %ebx
movl $0x07520752, (%ebx)
#endif
/* Zero .bss */
xorl %eax, %eax
movl $_C_LABEL(end), %ecx
subl $_C_LABEL(edata), %ecx
movl $_C_LABEL(edata), %edi
cld
rep; stosb
/* Set up an interrupt descriptor table for protected mode. */
call _ASM_LABEL(pmm_init)
/* Set our program name ("CDBOOT", not "BOOT"). */
movl $cd_progname, %eax
movl %eax, progname
/* Put the boot device number into the globals that need it */
popl %eax /* Get this back from the stack */
pushl %eax /* boot() takes this as a parameter */
movl %eax, _C_LABEL(bios_bootdev)
movl %eax, _C_LABEL(bios_cddev)
/*
* Now call "main()".
*
* We run in flat 32-bit protected mode, with no address mapping.
*/
#ifdef DEBUG
movl $0xb8004, %ebx
movl $0x07410741, (%ebx)
#endif
call _C_LABEL(boot)
/* boot() should not return. If it does, reset computer. */
jmp _C_LABEL(_rtt)
ENTRY(debugchar)
pushl %ebx
movl 8(%esp), %ebx
addl %ebx, %ebx
addl $0xb8000, %ebx
xorl %eax, %eax
movb 12(%esp), %al
andl $0xfffffffe, %ebx
movb %al, (%ebx)
popl %ebx
ret
.code16
/*
* Display ASCIZ string at %si. Trashes %si.
*/
Lstr:
pushw %ax
cld
1:
lodsb /* %al = *%si++ */
testb %al, %al
jz 1f
call Lchr
jmp 1b
1: popw %ax
ret
/*
* Write out value in %ax in hex
*/
hex_word:
pushw %ax
mov %ah, %al
call hex_byte
popw %ax
/* fall thru */
/*
* Write out value in %al in hex
*/
hex_byte:
pushw %ax
shrb $4, %al
call hex_nibble
popw %ax
/* fall thru */
/* Write out nibble in %al */
hex_nibble:
and $0x0F, %al
add $'0', %al
cmpb $'9', %al
jbe Lchr
addb $'A'-'9'-1, %al
/* fall thru to Lchr */
/*
* Lchr: write the character in %al to console
*/
Lchr:
pushw %bx
movb $0x0e, %ah
xorw %bx, %bx
incw %bx /* movw $0x01, %bx */
int $0x10
popw %bx
ret
cd_progname:
.asciz "CDBOOT"
.end
|
