2 * Mach Operating System
3 * Copyright (c) 1992, 1991 Carnegie Mellon University
6 * Permission to use, copy, modify and distribute this software and its
7 * documentation is hereby granted, provided that both the copyright
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9 * software, derivative works or modified versions, and any portions
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12 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
13 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
14 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
16 * Carnegie Mellon requests users of this software to return to
18 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
19 * School of Computer Science
20 * Carnegie Mellon University
21 * Pittsburgh PA 15213-3890
23 * any improvements or extensions that they make and grant Carnegie Mellon
24 * the rights to redistribute these changes.
26 * from: Mach, Revision 2.2 92/04/04 11:36:29 rpd
27 * $FreeBSD: src/sys/i386/boot/biosboot/start.S,v 1.13 1999/08/28 00:43:14 peter Exp $
31 Copyright 1988, 1989, 1990, 1991, 1992
32 by Intel Corporation, Santa Clara, California.
36 Permission to use, copy, modify, and distribute this software and
37 its documentation for any purpose and without fee is hereby
38 granted, provided that the above copyright notice appears in all
39 copies and that both the copyright notice and this permission notice
40 appear in supporting documentation, and that the name of Intel
41 not be used in advertising or publicity pertaining to distribution
42 of the software without specific, written prior permission.
44 INTEL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
45 INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
46 IN NO EVENT SHALL INTEL BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
47 CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
48 LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
49 NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
50 WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
57 LOADSZ= 15 /* size of unix boot */
58 PARTSTART= 0x1be /* starting address of partition table */
59 NUMPART= 4 /* number of partitions in partition table */
60 PARTSZ= 16 /* each partition table entry is 16 bytes */
61 BSDPART= 0xA5 /* value of boot_ind, means bootable partition */
62 BOOTABLE= 0x80 /* value of boot_ind, means bootable partition */
63 NAMEBLOCKMAGIC= 0xfadefeed /* value of magicnumebr for block2 */
66 * This DEBUGMSG(msg) macro may be useful for debugging. Its use is
67 * restricted to this file since it only works in real mode.
69 #define DEBUGMSG(msg) \
80 * XXX I have encountered at least one machine (a no-name laptop
81 * with an AMI WinBIOS) that will refuse to run the bootblock
82 * unless this short jump and nop are here. I'm not certain, but
83 * this may be a case of the BIOS performing some kind of simple
86 jmp pacify_braindead_bios
88 pacify_braindead_bios:
91 * start (aka boot1) is loaded at 0x0:0x7c00 but we want 0x7c0:0
92 * ljmp to the next instruction to adjust %cs
102 /* set up %ss and %esp */
107 * make a little room on the stack for
108 * us to save the default bootstring we might find..
109 * effectively, we push the bootstring.
112 mov $BOOTSTACK-64, %esp
114 /* set up %es, (where we will load boot2 to) */
118 /* bootstrap passes us drive number in %dl */
125 * XXX some bootstraps don't pass the drive number in %dl.
126 * This is a problem mainly when we are block 0 on a floppy.
127 * Force drive 0 for floppies.
128 * XXX %dl was assumed valid in the test that led here.
132 /* reset the disk system */
136 mov $0x0001, %ecx /* cyl 0, sector 1 */
137 movb $0, %dh /* head */
141 hd: /**** load sector 0 into the BOOTSEG ****/
144 xor %ebx, %ebx /* %bx = 0 */
149 /*mov $0x0080, %edx*/
154 /* find the first 386BSD partition */
161 movb %es:4(%ebx), %al
176 * BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory
177 * Call with %ah = 0x2
178 * %al = number of sectors
182 * %dl = drive (0x80 for hard disk, 0x0 for floppy disk)
183 * %es:%bx = segment:offset of buffer
185 * %al = 0x0 on success; err code on failure
190 movb %es:1(%ebx), %dh /* head */
192 movl %es:2(%ebx), %ecx /*sect, cyl (+ 2 bytes junk in top word) */
197 * Load the second sector and see if it is a boot instruction block.
198 * If it is then scan the contents for the first valid string and copy it to
199 * the location of the default boot string.. then zero it out.
200 * Finally write the block back to disk with the zero'd out entry..
201 * I hate writing at this stage but we need this to be persistant.
202 * If the boot fails, then the next boot will get the next string.
203 * /etc/rc will regenerate a complete block2 iff the boot succeeds.
205 * Format of block 2 is:
206 * [NAMEBLOCKMAGIC] <--0xdeafc0de
208 * [bootstring]NULL <---e.g. 0:wd(0,a)/kernel.experimental
209 * [bootstring]NULL <---e.g. 0:wd(0,a)/kernel.old
211 * [bootstring]NULL <---e.g. 0:wd(0,f)/kernel
216 * save things we might smash
217 * (that are not smashed immedatly after us anyway.)
220 push %ecx /* preserve 'cyl,sector ' */
224 * Load the second sector
225 * BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory
226 * Call with %ah = 0x2
227 * %al = number of sectors
231 * %dl = drive (0x80 for hard disk, 0x0 for floppy disk)
232 * %es:%bx = segment:offset of buffer
234 * %al = 0x0 on success; err code on failure
237 movl $0x0201, %eax /function 2 (read) 1 sector */
238 xor %ebx, %ebx /* %bx = 0 */ /* buffer address (ES:0) */
240 movl $0x0002, %ecx /* sector 2, cylinder 0 */
242 andl $0x00ff, %edx /* head 0, drive N */
247 * confirm that it is one for us
250 xorl %ebx, %ebx /* magic number at start of buffer */
253 movl %es:(%ebx), %eax
255 cmpl $NAMEBLOCKMAGIC, %eax
257 jne notours /* not ours so return to caller */
259 * scan for a bootstring
260 * Skip the magic number, and scan till we find a non-null,
263 incl %ebx /* quicker and smaller */
269 movb %es:(%ebx), %al /* load the next byte */
270 testb %al, %al /* and if it is null */
271 data32 /* keep scanning (past deleted entries) */
273 incb %al /* now look for -1 */
275 jz notours /* if we reach the 0xFF then we have finished */
278 * save our settings.. we need them twice..
283 * copy it to the default string location
284 * which is just above the stack for 64 bytes.
287 movl $BOOTSTACK-64, %ecx /* 64 bytes at the top of the stack */
290 movb %es:(%ebx), %al /* get the next byte in */
292 movb %al, %es:(%ecx) /* and transfer it to the name buffer */
293 incl %ebx /* get on with the next byte */
294 incl %ecx /* get on with the next byte */
295 testb %al, %al /* if it was 0 then quit this */
297 jnz nxtbyte /* and looop if more to do */
300 * restore the saved settings and
301 * zero it out so next time we don't try it again
304 pop %ebx /* get back our starting location */
305 #ifdef NAMEBLOCK_WRITEBACK
308 movb %es:(%ebx), %al /* get the byte */
310 movb $0, %es:(%ebx) /* zero it out */
312 incl %ebx /* point to the next byte */
313 testb %al, %al /* check if we have finished.. */
317 * Write the second sector back
318 * Load the second sector
319 * BIOS call "INT 0x13 Function 0x3" to write sectors from memory to disk
320 * Call with %ah = 0x3
321 * %al = number of sectors
325 * %dl = drive (0x80 for hard disk, 0x0 for floppy disk)
326 * %es:%bx = segment:offset of buffer
328 * %al = 0x0 on success; err code on failure
331 movl $0x0301, %eax /* write 1 sector */
332 xor %ebx, %ebx /* buffer is at offset 0 */
334 movl $0x0002, %ecx /* block 2 */
336 andl $0xff, %edx /* head 0 */
343 #endif /* NAMEBLOCK_WRITEBACK */
345 * return to the main-line
353 movb $0x2, %ah /* function 2 */
354 movb $LOADSZ, %al /* number of blocks */
355 xor %ebx, %ebx /* %bx = 0, put it at 0 in the BOOTSEG */
361 * ljmp to the second stage boot loader (boot2).
362 * After ljmp, %cs is BOOTSEG and boot1 (512 bytes) will be used
363 * as an internal buffer "intbuf".
367 ljmp $BOOTSEG, $ EXT(boot2)
382 * message: write the error message in %ds:%esi to console
386 * Use BIOS "int 10H Function 0Eh" to write character in teletype mode
387 * %ah = 0xe %al = character
388 * %bh = page %bl = foreground color (graphics modes)
400 lodsb /* load a byte into %al */
405 int $0x10 /* display a byte */
418 jmp stop /* halt doesnt actually halt forever */
429 #ifdef NAMEBLOCK_WRITEBACK
430 ewrite: String "Write error\r\n\0"
431 #endif /* NAMEBLOCK_WRITEBACK */
432 eread: String "Read error\r\n\0"
433 enoboot: String "No bootable partition\r\n\0"
436 * Dummy partition table in case we are block 0. The ending c/h/s values
437 * of the non-null partition are almost arbitary. The length of this
438 * partition is bogus for backwards compatibility and as a signature.
439 * A real partition table shouldn't be as weird and broken as this one,
440 * and the isa slice initialization routine interprets this table as
441 * saying that the whole disk is used for FreeBSD.
443 /* flag, head, sec, cyl, typ, ehead, esect, ecyl, start, len */
444 . = EXT(boot1) + PARTSTART
446 .byte 0x0,0,0,0,0,0,0,0
448 .byte 0x0,0,0,0,0,0,0,0
450 .byte 0x0,0,0,0,0,0,0,0
452 .byte BOOTABLE,0,1,0,BSDPART,255,255,255
454 /* the last 2 bytes in the sector 0 contain the signature */
455 . = EXT(boot1) + 0x1fe
458 . = EXT(boot1) + 0x400