1 #-
2 # Copyright (c) 2007 Yahoo!, Inc.
3 # All rights reserved.
4 # Written by: John Baldwin <jhb@FreeBSD.org>
5 #
6 # Redistribution and use in source and binary forms, with or without
7 # modification, are permitted provided that the following conditions
8 # are met:
9 # 1. Redistributions of source code must retain the above copyright
10 # notice, this list of conditions and the following disclaimer.
11 # 2. Redistributions in binary form must reproduce the above copyright
12 # notice, this list of conditions and the following disclaimer in the
13 # documentation and/or other materials provided with the distribution.
14 # 3. Neither the name of the author nor the names of any co-contributors
15 # may be used to endorse or promote products derived from this software
16 # without specific prior written permission.
17 #
18 # THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
19 # ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 # ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
22 # FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 # DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 # OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 # HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 # OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 # SUCH DAMAGE.
29 #
30 # $FreeBSD: releng/8.2/sys/boot/i386/pmbr/pmbr.s 173957 2007-11-26 21:29:59Z jhb $
31 #
32 # Partly from: src/sys/boot/i386/mbr/mbr.s 1.7
33
34 # A 512 byte PMBR boot manager that looks for a FreeBSD boot GPT partition
35 # and boots it.
36
37 .set LOAD,0x7c00 # Load address
38 .set EXEC,0x600 # Execution address
39 .set MAGIC,0xaa55 # Magic: bootable
40 .set SECSIZE,0x200 # Size of a single disk sector
41 .set DISKSIG,440 # Disk signature offset
42 .set STACK,EXEC+SECSIZE*4 # Stack address
43 .set GPT_ADDR,STACK # GPT header address
44 .set GPT_SIG,0
45 .set GPT_SIG_0,0x20494645
46 .set GPT_SIG_1,0x54524150
47 .set GPT_MYLBA,24
48 .set GPT_PART_LBA,72
49 .set GPT_NPART,80
50 .set GPT_PART_SIZE,84
51 .set PART_ADDR,GPT_ADDR+SECSIZE # GPT partition array address
52 .set PART_TYPE,0
53 .set PART_START_LBA,32
54 .set PART_END_LBA,40
55
56 .set NHRDRV,0x475 # Number of hard drives
57
58 .globl start # Entry point
59 .code16
60
61 #
62 # Setup the segment registers for flat addressing and setup the stack.
63 #
64 start: cld # String ops inc
65 xorw %ax,%ax # Zero
66 movw %ax,%es # Address
67 movw %ax,%ds # data
68 movw %ax,%ss # Set up
69 movw $STACK,%sp # stack
70 #
71 # Relocate ourself to a lower address so that we have more room to load
72 # other sectors.
73 #
74 movw $main-EXEC+LOAD,%si # Source
75 movw $main,%di # Destination
76 movw $SECSIZE-(main-start),%cx # Byte count
77 rep # Relocate
78 movsb # code
79 #
80 # Jump to the relocated code.
81 #
82 jmp main-LOAD+EXEC # To relocated code
83 #
84 # Validate drive number in %dl.
85 #
86 main: cmpb $0x80,%dl # Drive valid?
87 jb main.1 # No
88 movb NHRDRV,%dh # Calculate the highest
89 addb $0x80,%dh # drive number available
90 cmpb %dh,%dl # Within range?
91 jb main.2 # Yes
92 main.1: movb $0x80,%dl # Assume drive 0x80
93 #
94 # Load the primary GPT header from LBA 1 and verify signature.
95 #
96 main.2: movw $GPT_ADDR,%bx
97 movw $lba,%si
98 call read
99 cmpl $GPT_SIG_0,GPT_ADDR+GPT_SIG
100 jnz err_pt
101 cmpl $GPT_SIG_1,GPT_ADDR+GPT_SIG+4
102 jnz err_pt
103 #
104 # Load a partition table sector from disk and look for a FreeBSD boot
105 # partition.
106 #
107 load_part: movw $GPT_ADDR+GPT_PART_LBA,%si
108 movw $PART_ADDR,%bx
109 call read
110 scan: movw %bx,%si # Compare partition UUID
111 movw $boot_uuid,%di # with FreeBSD boot UUID
112 movb $0x10,%cl
113 repe cmpsb
114 jnz next_part # Didn't match, next partition
115 #
116 # We found a boot partition. Load it into RAM starting at 0x7c00.
117 #
118 movw %bx,%di # Save partition pointer in %di
119 leaw PART_START_LBA(%di),%si
120 movw $LOAD/16,%bx
121 movw %bx,%es
122 xorw %bx,%bx
123 load_boot: push %si # Save %si
124 call read
125 pop %si # Restore
126 movl PART_END_LBA(%di),%eax # See if this was the last LBA
127 cmpl (%si),%eax
128 jnz next_boot
129 movl PART_END_LBA+4(%di),%eax
130 cmpl 4(%si),%eax
131 jnz next_boot
132 mov %bx,%es # Reset %es to zero
133 jmp LOAD # Jump to boot code
134 next_boot: incl (%si) # Next LBA
135 adcl $0,4(%si)
136 mov %es,%ax # Adjust segment for next
137 addw $SECSIZE/16,%ax # sector
138 cmp $0x9000,%ax # Don't load past 0x90000,
139 jae err_big # 545k should be enough for
140 mov %ax,%es # any boot code. :)
141 jmp load_boot
142 #
143 # Move to the next partition. If we walk off the end of the sector, load
144 # the next sector. We assume that partition entries are smaller than 64k
145 # and that they won't span a sector boundary.
146 #
147 # XXX: Should we int 0x18 instead of err_noboot if we hit the end of the table?
148 #
149 next_part: decl GPT_ADDR+GPT_NPART # Was this the last partition?
150 jz err_noboot
151 movw GPT_ADDR+GPT_PART_SIZE,%ax
152 addw %ax,%bx # Next partition
153 cmpw $PART_ADDR+0x200,%bx # Still in sector?
154 jb scan
155 incl GPT_ADDR+GPT_PART_LBA # Next sector
156 adcl $0,GPT_ADDR+GPT_PART_LBA+4
157 jmp load_part
158 #
159 # Load a sector (64-bit LBA at %si) from disk %dl into %es:%bx by creating
160 # a EDD packet on the stack and passing it to the BIOS. Trashes %ax and %si.
161 #
162 read: pushl 0x4(%si) # Set the LBA
163 pushl 0x0(%si) # address
164 pushw %es # Set the address of
165 pushw %bx # the transfer buffer
166 pushw $0x1 # Read 1 sector
167 pushw $0x10 # Packet length
168 movw %sp,%si # Packer pointer
169 movw $0x4200,%ax # BIOS: LBA Read from disk
170 int $0x13 # Call the BIOS
171 add $0x10,%sp # Restore stack
172 jc err_rd # If error
173 ret
174 #
175 # Various error message entry points.
176 #
177 err_big: movw $msg_big,%si # "Boot loader too
178 jmp putstr # large"
179
180 err_pt: movw $msg_pt,%si # "Invalid partition
181 jmp putstr # table"
182
183 err_rd: movw $msg_rd,%si # "I/O error loading
184 jmp putstr # boot loader"
185
186 err_noboot: movw $msg_noboot,%si # "Missing boot
187 jmp putstr # loader"
188 #
189 # Output an ASCIZ string to the console via the BIOS.
190 #
191 putstr.0: movw $0x7,%bx # Page:attribute
192 movb $0xe,%ah # BIOS: Display
193 int $0x10 # character
194 putstr: lodsb # Get character
195 testb %al,%al # End of string?
196 jnz putstr.0 # No
197 putstr.1: jmp putstr.1 # Await reset
198
199 msg_big: .asciz "Boot loader too large"
200 msg_pt: .asciz "Invalid partition table"
201 msg_rd: .asciz "I/O error loading boot loader"
202 msg_noboot: .asciz "Missing boot loader"
203
204 lba: .quad 1 # LBA of GPT header
205
206 boot_uuid: .long 0x83bd6b9d
207 .word 0x7f41
208 .word 0x11dc
209 .byte 0xbe
210 .byte 0x0b
211 .byte 0x00
212 .byte 0x15
213 .byte 0x60
214 .byte 0xb8
215 .byte 0x4f
216 .byte 0x0f
217
218 .org DISKSIG,0x90
219 sig: .long 0 # OS Disk Signature
220 .word 0 # "Unknown" in PMBR
221
222 partbl: .fill 0x10,0x4,0x0 # Partition table
223 .word MAGIC # Magic number
Cache object: 5fe09b4c4c6e088105b833e65c5e8d9e
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