cdboot.S revision 1.3
1 /* $NetBSD: cdboot.S,v 1.3 2005/07/06 18:12:31 junyoung Exp $ */ 2 3 /*- 4 * Copyright (c) 2005 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Bang Jun-Young. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the NetBSD 21 * Foundation, Inc. and its contributors. 22 * 4. Neither the name of The NetBSD Foundation nor the names of its 23 * contributors may be used to endorse or promote products derived 24 * from this software without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 29 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 36 * POSSIBILITY OF SUCH DAMAGE. 37 */ 38 39 /* 40 * This is a primary boot loader that loads a secondary boot loader 41 * directly from CD without performing floppy/hard disk emulation as 42 * described by the El Torito specification. 43 * 44 * TODO: 45 * - Support for loading secondary boot loader > 64kB 46 */ 47 48 #include <machine/asm.h> 49 50 #define BOOT_ADDR 0x7c00 51 #define BLOCK_SIZE 2048 /* Default for ISO 9660 */ 52 #define VD_LBA 16 /* LBA of Volume Descriptor (VD) */ 53 #define PVD_ADDR 0x1000 /* Where Primary VD is loaded */ 54 #define ROOTDIR_ADDR 0x1800 /* Where Root Directory is loaded */ 55 #define LOADER_ADDR SECONDARY_LOAD_ADDRESS 56 57 /* 58 * See src/sys/sys/bootblock.h for details. 59 */ 60 #define MBR_PART_COUNT 4 61 #define MBR_PART_OFFSET 446 62 #define MBR_PART_SIZE 16 /* sizeof(struct mbr_partition) */ 63 64 /* 65 * Disk error codes 66 */ 67 #define ERROR_TIMEOUT 0x80 68 69 /* 70 * Volume Descriptor types. 71 */ 72 #define VD_PRIMARY 1 73 #define VD_SUPPLEMENTARY 2 74 #define VD_TERMINATOR 255 75 76 /* Only actually used entries are listed below */ 77 78 /* 79 * Format of Primary Volume Descriptor (8.4) 80 */ 81 #define PVD_ROOT_DR 156 /* Offset of Root Directory Record */ 82 83 /* 84 * Format of Directory Record (9.1) 85 */ 86 #define DR_LEN 0 87 #define DR_EXTENT 2 88 #define DR_DATA_LEN 10 89 #define DR_NAME_LEN 32 90 #define DR_NAME 33 91 92 .text 93 .code16 94 ENTRY(start) 95 xorw %ax, %ax 96 movw %ax, %ds 97 movw %ax, %es 98 movw %ax, %ss 99 movw $BOOT_ADDR, %sp 100 movw %sp, %si 101 movw $start, %di 102 movw $BLOCK_SIZE/2, %cx 103 rep 104 movsw 105 ljmp $0, $real_start 106 107 real_start: 108 movb %dl, boot_drive /* Save boot drive number */ 109 110 /* 111 * We can skip boot wait when: 112 * - there's no hard disk present. 113 * - there's no active partition in the MBR of the 1st hard disk. 114 */ 115 116 /* 117 * Check presence of hard disks. 118 */ 119 movw $0x475, %si 120 movb (%si), %al 121 testb %al, %al 122 jz boot_cdrom 123 124 /* 125 * Find the active partition from the MBR. 126 */ 127 movw $0x0201, %ax /* %al = number of sectors to read */ 128 movw $BOOT_ADDR, %bx /* %es:%bx = data buffer */ 129 movw $0x0001, %cx /* %ch = low 8 bits of cylinder no */ 130 /* %cl = high 2 bits of cyl no & */ 131 /* sector number */ 132 movw $0x0080, %dx /* %dh = head number */ 133 /* %dl = disk number */ 134 int $0x13 /* Read MBR into memory */ 135 jc boot_cdrom /* CF set on error */ 136 137 movb $1, mbr_loaded 138 movb $MBR_PART_COUNT, %cl 139 movw $BOOT_ADDR+MBR_PART_OFFSET, %si 140 1: 141 movb (%si), %al 142 testb $0x80, %al 143 jnz found_active 144 addw $MBR_PART_SIZE, %si 145 decb %cl 146 testb %cl, %cl 147 jnz 1b /* If 0, no active partition found */ 148 jmp boot_cdrom 149 150 found_active: 151 movw $str_press_key, %si 152 call message 153 next_second: 154 movw $str_dot, %si 155 call message 156 decb wait_count 157 jz boot_hard_disk 158 xorb %ah, %ah /* Get system time */ 159 int $0x1a 160 movw %dx, %di /* %cx:%dx = number of clock ticks */ 161 addw $19, %di /* 19 ~= 18.2 Hz */ 162 wait_key: 163 movb $1, %ah /* Check for keystroke */ 164 int $0x16 165 jz not_avail /* ZF clear if keystroke available */ 166 xorb %ah, %ah /* Read key to flush keyboard buf */ 167 int $0x16 168 jmp boot_cdrom 169 not_avail: 170 xorb %ah, %ah /* Get system time */ 171 int $0x1a 172 cmpw %dx, %di /* Compare with saved time */ 173 jnz wait_key 174 jmp next_second 175 176 boot_hard_disk: 177 movw $str_crlf, %si 178 call message 179 cmpb $1, mbr_loaded 180 jz 1f 181 movw $0x0201, %ax /* %al = number of sectors to read */ 182 movw $BOOT_ADDR, %bx /* %es:%bx = data buffer */ 183 movw $0x0001, %cx /* %ch = low 8 bits of cylinder no */ 184 /* %cl = high 2 bits of cyl no & */ 185 /* sector number */ 186 movw $0x0080, %dx /* %dh = head number */ 187 /* %dl = disk number */ 188 int $0x13 /* Read MBR into memory */ 189 jc panic /* CF set on error */ 190 1: 191 movw %cs, %ax /* Restore initial state */ 192 movw %ax, %ds 193 movw %ax, %es 194 movw $0x0080, %dx /* %dl = boot drive number */ 195 jmp $0, $BOOT_ADDR /* Jump to MBR! */ 196 197 panic: 198 hlt 199 jmp panic 200 201 boot_cdrom: 202 movw $str_banner, %si 203 call message 204 movl $VD_LBA, %eax 205 next_block: 206 movb $1, %dh /* Number of sectors to read */ 207 movl $PVD_ADDR, %ebx 208 call read_sectors 209 cmpb $VD_PRIMARY, (%bx) /* Is it Primary Volume Descriptor? */ 210 jz pvd_found 211 incl %eax 212 cmpb $VD_TERMINATOR, (%bx) 213 jnz next_block 214 movw $str_no_pvd, %si 215 call message 216 jmp panic 217 218 pvd_found: 219 movw $PVD_ADDR+PVD_ROOT_DR, %bx 220 movl DR_EXTENT(%bx), %eax /* LBA of the root directory */ 221 movl DR_DATA_LEN(%bx), %edx 222 shrl $11, %edx /* Convert to number of sectors */ 223 movb %dl, %dh /* ... and load it to %dh */ 224 movl $ROOTDIR_ADDR, %ebx 225 call read_sectors 226 next_entry: 227 cmpb $0, DR_LEN(%bx) 228 jz last_entry 229 movw %bx, %si 230 addw $DR_NAME, %si 231 movb DR_NAME_LEN(%bx), %cl 232 movw $str_loader, %di 233 1: 234 movb (%si), %al 235 cmpb %al, (%di) 236 jnz fail 237 incw %si 238 incw %di 239 decb %cl 240 jnz 1b 241 jmp load_loader 242 fail: 243 addw DR_LEN(%bx), %bx 244 jmp next_entry 245 last_entry: 246 movw $str_no_loader, %si 247 call message 248 jmp panic 249 250 load_loader: 251 movl DR_EXTENT(%bx), %eax 252 movl DR_DATA_LEN(%bx), %edx 253 addl $(BLOCK_SIZE-1), %edx /* Convert file length to */ 254 shrl $11, %edx /* ... number of sectors */ 255 movb %dl, %dh 256 movl $LOADER_ADDR, %ebx 257 call read_sectors 258 xorl %esi, %esi /* Don't provide boot_params */ 259 xorl %edx, %edx 260 movb boot_drive, %dl 261 xorl %ebx, %ebx /* Zero sector number */ 262 lcall $LOADER_ADDR/16, $0 263 jmp panic 264 265 /* 266 * Read disk sector(s) into memory 267 * 268 * %eax = LBA of starting sector 269 * %ebx = buffer to store sectors 270 * %dh = number of sectors to read 271 */ 272 read_sectors: 273 pusha 274 movl %eax, edd_lba /* Convert LBA to segment */ 275 shrl $4, %ebx 276 movw %bx, edd_segment 277 movb %dh, edd_nsecs 278 movb boot_drive, %dl 279 movw $edd_packet, %si 280 read_again: 281 movb $0x42, %ah 282 int $0x13 283 jc read_fail 284 popa 285 ret 286 read_fail: 287 cmpb $ERROR_TIMEOUT, %ah 288 jz read_again 289 movw $str_read_error, %si 290 call message 291 jmp panic 292 293 /* 294 * For debugging purpose 295 */ 296 put_char: 297 pusha 298 movb $0x0e, %ah 299 movw $0x0001, %bx 300 int $0x10 301 popa 302 ret 303 304 #include <message.S> 305 306 edd_packet: 307 edd_len: .word 16 308 edd_nsecs: .word 0 /* Number of sectors to transfer */ 309 edd_offset: .word 0 310 edd_segment: .word 0 311 edd_lba: .quad 0 312 313 wait_count: .byte 6 314 boot_drive: .byte 0 315 mbr_loaded: .byte 0 316 317 str_banner: .ascii "\r\nNetBSD/i386 cd9660 Primary Bootstrap" 318 str_crlf: .asciz "\r\n" 319 str_press_key: .asciz "\r\nPress any key to boot from CD" 320 str_dot: .asciz "." 321 str_read_error: .asciz "Can't read CD" 322 str_no_pvd: .asciz "Can't find Primary Volume Descriptor" 323 str_no_loader: .asciz "Can't find /boot" 324 str_loader: .asciz "BOOT.;1" 325 326 /* Used to calculate free bytes */ 327 free_space = end - . 328 329 . = start + BLOCK_SIZE 330 end: 331
Indexes created Thu Oct 02 10:09:58 GMT 2025