cdboot.S revision 1.9
1 /* $NetBSD: cdboot.S,v 1.9 2009/10/24 10:28:30 dsl 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 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 /* 33 * This is a primary boot loader that loads a secondary boot loader 34 * directly from CD without performing floppy/hard disk emulation as 35 * described by the El Torito specification. 36 * 37 * TODO: 38 * - Support for loading secondary boot loader > 64kB 39 */ 40 41 #include <machine/asm.h> 42 #include <sys/bootblock.h> 43 44 #define BOOT_ADDR 0x7c00 45 #define BLOCK_SIZE 2048 /* Default for ISO 9660 */ 46 #define VD_LBA 16 /* LBA of Volume Descriptor (VD) */ 47 #define PVD_ADDR 0x1000 /* Where Primary VD is loaded */ 48 #define ROOTDIR_ADDR 0x1800 /* Where Root Directory is loaded */ 49 #define LOADER_ADDR SECONDARY_LOAD_ADDRESS 50 51 #ifdef BOOT_FROM_FAT 52 #define MBR_AFTERBPB 90 /* BPB size in FAT32 partition BR */ 53 #else 54 #define MBR_AFTERBPB 62 /* BPB size in floppy master BR */ 55 #endif 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 jmp start1 96 97 . = start + MBR_AFTERBPB /* skip BPB */ 98 . = start + MBR_DSN_OFFSET 99 .long 0 100 101 /* mbr_bootsel_magic (not used here) */ 102 . = start + MBR_BS_MAGIC_OFFSET 103 .word 0 104 105 . = start + MBR_PART_OFFSET 106 . = start + MBR_MAGIC_OFFSET 107 pbr_magic: 108 .word MBR_MAGIC 109 .fill 512 /* reserve space for disklabel */ 110 start1: 111 jmp 1f 112 .balign 4 113 .long X86_BOOT_MAGIC_1 /* checked by installboot & pbr code */ 114 boot_params: /* space for patchable variables */ 115 .long 1f - boot_params /* length of this data area */ 116 #include <boot_params.S> 117 . = start1 + 0x80 /* Space for patching unknown params */ 118 119 1: xorw %ax, %ax 120 movw %ax, %ds 121 movw %ax, %es 122 movw %ax, %ss 123 movw $BOOT_ADDR, %sp 124 movw %sp, %si 125 movw $start, %di 126 movw $BLOCK_SIZE/2, %cx 127 rep 128 movsw 129 ljmp $0, $real_start 130 131 real_start: 132 movb %dl, boot_drive /* Save boot drive number */ 133 134 #ifndef DISABLE_KEYPRESS 135 /* 136 * We can skip boot wait when: 137 * - there's no hard disk present. 138 * - there's no active partition in the MBR of the 1st hard disk. 139 */ 140 141 /* 142 * Check presence of hard disks. 143 */ 144 movw $0x475, %si 145 movb (%si), %al 146 testb %al, %al 147 jz boot_cdrom 148 149 /* 150 * Find the active partition from the MBR. 151 */ 152 movw $0x0201, %ax /* %al = number of sectors to read */ 153 movw $BOOT_ADDR, %bx /* %es:%bx = data buffer */ 154 movw $0x0001, %cx /* %ch = low 8 bits of cylinder no */ 155 /* %cl = high 2 bits of cyl no & */ 156 /* sector number */ 157 movw $0x0080, %dx /* %dh = head number */ 158 /* %dl = disk number */ 159 int $0x13 /* Read MBR into memory */ 160 jc boot_cdrom /* CF set on error */ 161 162 movb $1, mbr_loaded 163 movb $MBR_PART_COUNT, %cl 164 movw $BOOT_ADDR+MBR_PART_OFFSET, %si 165 1: 166 movb (%si), %al 167 testb $0x80, %al 168 jnz found_active 169 addw $MBR_PART_SIZE, %si 170 decb %cl 171 testb %cl, %cl 172 jnz 1b /* If 0, no active partition found */ 173 jmp boot_cdrom 174 175 found_active: 176 movw $str_press_key, %si 177 call message 178 next_second: 179 movw $str_dot, %si 180 call message 181 decb wait_count 182 jz boot_hard_disk 183 xorb %ah, %ah /* Get system time */ 184 int $0x1a 185 movw %dx, %di /* %cx:%dx = number of clock ticks */ 186 addw $19, %di /* 19 ~= 18.2 Hz */ 187 wait_key: 188 movb $1, %ah /* Check for keystroke */ 189 int $0x16 190 jz not_avail /* ZF clear if keystroke available */ 191 xorb %ah, %ah /* Read key to flush keyboard buf */ 192 int $0x16 193 jmp boot_cdrom 194 not_avail: 195 xorb %ah, %ah /* Get system time */ 196 int $0x1a 197 cmpw %dx, %di /* Compare with saved time */ 198 jnz wait_key 199 jmp next_second 200 201 boot_hard_disk: 202 movw $str_crlf, %si 203 call message 204 cmpb $1, mbr_loaded 205 jz 1f 206 movw $0x0201, %ax /* %al = number of sectors to read */ 207 movw $BOOT_ADDR, %bx /* %es:%bx = data buffer */ 208 movw $0x0001, %cx /* %ch = low 8 bits of cylinder no */ 209 /* %cl = high 2 bits of cyl no & */ 210 /* sector number */ 211 movw $0x0080, %dx /* %dh = head number */ 212 /* %dl = disk number */ 213 int $0x13 /* Read MBR into memory */ 214 jc panic /* CF set on error */ 215 1: 216 movw %cs, %ax /* Restore initial state */ 217 movw %ax, %ds 218 movw %ax, %es 219 movw $0x0080, %dx /* %dl = boot drive number */ 220 jmp $0, $BOOT_ADDR /* Jump to MBR! */ 221 jmp panic /* This should be never executed */ 222 #endif /* !DISABLE_KEYPRESS */ 223 224 boot_cdrom: 225 movw $str_banner, %si 226 call message 227 228 /* Read volume descriptor sectors until Primary decriptor found */ 229 movl $VD_LBA, %eax 230 next_block: 231 movb $1, %dh /* Number of sectors to read */ 232 movl $PVD_ADDR, %ebx 233 call read_sectors 234 cmpb $VD_PRIMARY, (%bx) /* Is it Primary Volume Descriptor? */ 235 jz pvd_found 236 incl %eax 237 cmpb $VD_TERMINATOR, (%bx) 238 jnz next_block 239 movw $str_no_pvd, %si 240 call message 241 jmp panic 242 243 /* Read all of root directory */ 244 pvd_found: 245 movw $PVD_ADDR+PVD_ROOT_DR, %bx 246 movl DR_EXTENT(%bx), %eax /* LBA of the root directory */ 247 movl DR_DATA_LEN(%bx), %edx 248 shrl $11, %edx /* Convert to number of sectors */ 249 movb %dl, %dh /* ... and load it to %dh */ 250 movl $ROOTDIR_ADDR, %ebx 251 call read_sectors 252 253 /* Scan directory entries searching for /boot */ 254 next_entry: 255 cmpb $0, DR_LEN(%bx) 256 jz last_entry 257 movw %bx, %si 258 addw $DR_NAME, %si 259 movb DR_NAME_LEN(%bx), %cl 260 movw $str_loader, %di 261 1: 262 movb (%si), %al 263 cmpb %al, (%di) 264 jnz fail 265 incw %si 266 incw %di 267 decb %cl 268 jnz 1b 269 jmp load_loader 270 fail: 271 addw DR_LEN(%bx), %bx 272 jmp next_entry 273 last_entry: 274 movw $str_no_loader, %si 275 call message 276 jmp panic 277 278 /* Found /boot, read contents to 0x1000:0 */ 279 load_loader: 280 movl DR_EXTENT(%bx), %eax 281 movl DR_DATA_LEN(%bx), %edx 282 addl $(BLOCK_SIZE-1), %edx /* Convert file length to */ 283 shrl $11, %edx /* ... number of sectors */ 284 movb %dl, %dh 285 movl $LOADER_ADDR, %ebx 286 call read_sectors 287 288 /* Finally call into code of /boot */ 289 movl $boot_params, %esi /* Provide boot_params */ 290 xorl %edx, %edx 291 movb boot_drive, %dl 292 xorl %ebx, %ebx /* Zero sector number */ 293 lcall $LOADER_ADDR/16, $0 294 /* fall through on load failure */ 295 panic: 296 hlt 297 jmp panic 298 299 /* 300 * Read disk sector(s) into memory 301 * 302 * %eax = LBA of starting sector 303 * %ebx = buffer to store sectors 304 * %dh = number of sectors to read 305 */ 306 read_sectors: 307 pusha 308 movl %eax, edd_lba 309 shrl $4, %ebx /* Convert buffer addr to seg:0 */ 310 movw %bx, edd_segment 311 movb %dh, edd_nsecs 312 movb boot_drive, %dl 313 movw $edd_packet, %si 314 read_again: 315 movb $0x42, %ah 316 int $0x13 317 jc read_fail 318 popa 319 ret 320 read_fail: 321 cmpb $ERROR_TIMEOUT, %ah 322 jz read_again 323 movw $str_read_error, %si 324 call message 325 jmp panic 326 327 /* 328 * For debugging purpose 329 */ 330 put_char: 331 pusha 332 movb $0x0e, %ah 333 movw $0x0001, %bx 334 int $0x10 335 popa 336 ret 337 338 #include <message.S> 339 340 edd_packet: 341 edd_len: .word 16 342 edd_nsecs: .word 0 /* Number of sectors to transfer */ 343 edd_offset: .word 0 344 edd_segment: .word 0 345 edd_lba: .quad 0 346 347 wait_count: .byte 6 348 boot_drive: .byte 0 349 mbr_loaded: .byte 0 350 351 str_banner: .ascii "\r\nNetBSD/x86 cd9660 Primary Bootstrap" 352 str_crlf: .asciz "\r\n" 353 str_press_key: .asciz "\r\nPress any key to boot from CD" 354 str_dot: .asciz "." 355 str_read_error: .asciz "Can't read CD" 356 str_no_pvd: .asciz "Can't find Primary Volume Descriptor" 357 str_no_loader: .asciz "Can't find /boot" 358 str_loader: .asciz "BOOT.;1" 359 360 /* Used to calculate free bytes */ 361 free_space = end - . 362 363 . = start + BLOCK_SIZE 364 end: 365
Indexes created Thu Oct 02 10:09:58 GMT 2025