cdboot.S revision 1.4
1 /* $NetBSD: cdboot.S,v 1.4 2005/07/20 03:27:51 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 #ifndef DISABLE_KEYPRESS 111 /* 112 * We can skip boot wait when: 113 * - there's no hard disk present. 114 * - there's no active partition in the MBR of the 1st hard disk. 115 */ 116 117 /* 118 * Check presence of hard disks. 119 */ 120 movw $0x475, %si 121 movb (%si), %al 122 testb %al, %al 123 jz boot_cdrom 124 125 /* 126 * Find the active partition from the MBR. 127 */ 128 movw $0x0201, %ax /* %al = number of sectors to read */ 129 movw $BOOT_ADDR, %bx /* %es:%bx = data buffer */ 130 movw $0x0001, %cx /* %ch = low 8 bits of cylinder no */ 131 /* %cl = high 2 bits of cyl no & */ 132 /* sector number */ 133 movw $0x0080, %dx /* %dh = head number */ 134 /* %dl = disk number */ 135 int $0x13 /* Read MBR into memory */ 136 jc boot_cdrom /* CF set on error */ 137 138 movb $1, mbr_loaded 139 movb $MBR_PART_COUNT, %cl 140 movw $BOOT_ADDR+MBR_PART_OFFSET, %si 141 1: 142 movb (%si), %al 143 testb $0x80, %al 144 jnz found_active 145 addw $MBR_PART_SIZE, %si 146 decb %cl 147 testb %cl, %cl 148 jnz 1b /* If 0, no active partition found */ 149 jmp boot_cdrom 150 151 found_active: 152 movw $str_press_key, %si 153 call message 154 next_second: 155 movw $str_dot, %si 156 call message 157 decb wait_count 158 jz boot_hard_disk 159 xorb %ah, %ah /* Get system time */ 160 int $0x1a 161 movw %dx, %di /* %cx:%dx = number of clock ticks */ 162 addw $19, %di /* 19 ~= 18.2 Hz */ 163 wait_key: 164 movb $1, %ah /* Check for keystroke */ 165 int $0x16 166 jz not_avail /* ZF clear if keystroke available */ 167 xorb %ah, %ah /* Read key to flush keyboard buf */ 168 int $0x16 169 jmp boot_cdrom 170 not_avail: 171 xorb %ah, %ah /* Get system time */ 172 int $0x1a 173 cmpw %dx, %di /* Compare with saved time */ 174 jnz wait_key 175 jmp next_second 176 177 boot_hard_disk: 178 movw $str_crlf, %si 179 call message 180 cmpb $1, mbr_loaded 181 jz 1f 182 movw $0x0201, %ax /* %al = number of sectors to read */ 183 movw $BOOT_ADDR, %bx /* %es:%bx = data buffer */ 184 movw $0x0001, %cx /* %ch = low 8 bits of cylinder no */ 185 /* %cl = high 2 bits of cyl no & */ 186 /* sector number */ 187 movw $0x0080, %dx /* %dh = head number */ 188 /* %dl = disk number */ 189 int $0x13 /* Read MBR into memory */ 190 jc panic /* CF set on error */ 191 1: 192 movw %cs, %ax /* Restore initial state */ 193 movw %ax, %ds 194 movw %ax, %es 195 movw $0x0080, %dx /* %dl = boot drive number */ 196 jmp $0, $BOOT_ADDR /* Jump to MBR! */ 197 jmp panic /* This should be never executed */ 198 #endif /* !DISABLE_KEYPRESS */ 199 200 boot_cdrom: 201 movw $str_banner, %si 202 call message 203 movl $VD_LBA, %eax 204 next_block: 205 movb $1, %dh /* Number of sectors to read */ 206 movl $PVD_ADDR, %ebx 207 call read_sectors 208 cmpb $VD_PRIMARY, (%bx) /* Is it Primary Volume Descriptor? */ 209 jz pvd_found 210 incl %eax 211 cmpb $VD_TERMINATOR, (%bx) 212 jnz next_block 213 movw $str_no_pvd, %si 214 call message 215 jmp panic 216 217 pvd_found: 218 movw $PVD_ADDR+PVD_ROOT_DR, %bx 219 movl DR_EXTENT(%bx), %eax /* LBA of the root directory */ 220 movl DR_DATA_LEN(%bx), %edx 221 shrl $11, %edx /* Convert to number of sectors */ 222 movb %dl, %dh /* ... and load it to %dh */ 223 movl $ROOTDIR_ADDR, %ebx 224 call read_sectors 225 next_entry: 226 cmpb $0, DR_LEN(%bx) 227 jz last_entry 228 movw %bx, %si 229 addw $DR_NAME, %si 230 movb DR_NAME_LEN(%bx), %cl 231 movw $str_loader, %di 232 1: 233 movb (%si), %al 234 cmpb %al, (%di) 235 jnz fail 236 incw %si 237 incw %di 238 decb %cl 239 jnz 1b 240 jmp load_loader 241 fail: 242 addw DR_LEN(%bx), %bx 243 jmp next_entry 244 last_entry: 245 movw $str_no_loader, %si 246 call message 247 jmp panic 248 249 load_loader: 250 movl DR_EXTENT(%bx), %eax 251 movl DR_DATA_LEN(%bx), %edx 252 addl $(BLOCK_SIZE-1), %edx /* Convert file length to */ 253 shrl $11, %edx /* ... number of sectors */ 254 movb %dl, %dh 255 movl $LOADER_ADDR, %ebx 256 call read_sectors 257 xorl %esi, %esi /* Don't provide boot_params */ 258 xorl %edx, %edx 259 movb boot_drive, %dl 260 xorl %ebx, %ebx /* Zero sector number */ 261 lcall $LOADER_ADDR/16, $0 262 /* fall through on load failure */ 263 panic: 264 hlt 265 jmp panic 266 267 /* 268 * Read disk sector(s) into memory 269 * 270 * %eax = LBA of starting sector 271 * %ebx = buffer to store sectors 272 * %dh = number of sectors to read 273 */ 274 read_sectors: 275 pusha 276 movl %eax, edd_lba /* Convert LBA to segment */ 277 shrl $4, %ebx 278 movw %bx, edd_segment 279 movb %dh, edd_nsecs 280 movb boot_drive, %dl 281 movw $edd_packet, %si 282 read_again: 283 movb $0x42, %ah 284 int $0x13 285 jc read_fail 286 popa 287 ret 288 read_fail: 289 cmpb $ERROR_TIMEOUT, %ah 290 jz read_again 291 movw $str_read_error, %si 292 call message 293 jmp panic 294 295 /* 296 * For debugging purpose 297 */ 298 put_char: 299 pusha 300 movb $0x0e, %ah 301 movw $0x0001, %bx 302 int $0x10 303 popa 304 ret 305 306 #include <message.S> 307 308 edd_packet: 309 edd_len: .word 16 310 edd_nsecs: .word 0 /* Number of sectors to transfer */ 311 edd_offset: .word 0 312 edd_segment: .word 0 313 edd_lba: .quad 0 314 315 wait_count: .byte 6 316 boot_drive: .byte 0 317 mbr_loaded: .byte 0 318 319 str_banner: .ascii "\r\nNetBSD/i386 cd9660 Primary Bootstrap" 320 str_crlf: .asciz "\r\n" 321 str_press_key: .asciz "\r\nPress any key to boot from CD" 322 str_dot: .asciz "." 323 str_read_error: .asciz "Can't read CD" 324 str_no_pvd: .asciz "Can't find Primary Volume Descriptor" 325 str_no_loader: .asciz "Can't find /boot" 326 str_loader: .asciz "BOOT.;1" 327 328 /* Used to calculate free bytes */ 329 free_space = end - . 330 331 . = start + BLOCK_SIZE 332 end: 333
Indexes created Thu Oct 02 07:10:07 GMT 2025