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 $
28 * $DragonFly: src/sys/i386/boot/biosboot/Attic/start.S,v 1.2 2003/06/17 04:28:34 dillon Exp $
32 Copyright 1988, 1989, 1990, 1991, 1992
33 by Intel Corporation, Santa Clara, California.
37 Permission to use, copy, modify, and distribute this software and
38 its documentation for any purpose and without fee is hereby
39 granted, provided that the above copyright notice appears in all
40 copies and that both the copyright notice and this permission notice
41 appear in supporting documentation, and that the name of Intel
42 not be used in advertising or publicity pertaining to distribution
43 of the software without specific, written prior permission.
45 INTEL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
46 INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
47 IN NO EVENT SHALL INTEL BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
48 CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
49 LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
50 NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
51 WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
58 LOADSZ= 15 /* size of unix boot */
59 PARTSTART= 0x1be /* starting address of partition table */
60 NUMPART= 4 /* number of partitions in partition table */
61 PARTSZ= 16 /* each partition table entry is 16 bytes */
62 BSDPART= 0xA5 /* value of boot_ind, means bootable partition */
63 BOOTABLE= 0x80 /* value of boot_ind, means bootable partition */
64 NAMEBLOCKMAGIC= 0xfadefeed /* value of magicnumebr for block2 */
67 * This DEBUGMSG(msg) macro may be useful for debugging. Its use is
68 * restricted to this file since it only works in real mode.
70 #define DEBUGMSG(msg) \
81 * XXX I have encountered at least one machine (a no-name laptop
82 * with an AMI WinBIOS) that will refuse to run the bootblock
83 * unless this short jump and nop are here. I'm not certain, but
84 * this may be a case of the BIOS performing some kind of simple
87 jmp pacify_braindead_bios
89 pacify_braindead_bios:
92 * start (aka boot1) is loaded at 0x0:0x7c00 but we want 0x7c0:0
93 * ljmp to the next instruction to adjust %cs
103 /* set up %ss and %esp */
108 * make a little room on the stack for
109 * us to save the default bootstring we might find..
110 * effectively, we push the bootstring.
113 mov $BOOTSTACK-64, %esp
115 /* set up %es, (where we will load boot2 to) */
119 /* bootstrap passes us drive number in %dl */
126 * XXX some bootstraps don't pass the drive number in %dl.
127 * This is a problem mainly when we are block 0 on a floppy.
128 * Force drive 0 for floppies.
129 * XXX %dl was assumed valid in the test that led here.
133 /* reset the disk system */
137 mov $0x0001, %ecx /* cyl 0, sector 1 */
138 movb $0, %dh /* head */
142 hd: /**** load sector 0 into the BOOTSEG ****/
145 xor %ebx, %ebx /* %bx = 0 */
150 /*mov $0x0080, %edx*/
155 /* find the first 386BSD partition */
162 movb %es:4(%ebx), %al
177 * BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory
178 * Call with %ah = 0x2
179 * %al = number of sectors
183 * %dl = drive (0x80 for hard disk, 0x0 for floppy disk)
184 * %es:%bx = segment:offset of buffer
186 * %al = 0x0 on success; err code on failure
191 movb %es:1(%ebx), %dh /* head */
193 movl %es:2(%ebx), %ecx /*sect, cyl (+ 2 bytes junk in top word) */
198 * Load the second sector and see if it is a boot instruction block.
199 * If it is then scan the contents for the first valid string and copy it to
200 * the location of the default boot string.. then zero it out.
201 * Finally write the block back to disk with the zero'd out entry..
202 * I hate writing at this stage but we need this to be persistant.
203 * If the boot fails, then the next boot will get the next string.
204 * /etc/rc will regenerate a complete block2 iff the boot succeeds.
206 * Format of block 2 is:
207 * [NAMEBLOCKMAGIC] <--0xdeafc0de
209 * [bootstring]NULL <---e.g. 0:wd(0,a)/kernel.experimental
210 * [bootstring]NULL <---e.g. 0:wd(0,a)/kernel.old
212 * [bootstring]NULL <---e.g. 0:wd(0,f)/kernel
217 * save things we might smash
218 * (that are not smashed immedatly after us anyway.)
221 push %ecx /* preserve 'cyl,sector ' */
225 * Load the second sector
226 * BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory
227 * Call with %ah = 0x2
228 * %al = number of sectors
232 * %dl = drive (0x80 for hard disk, 0x0 for floppy disk)
233 * %es:%bx = segment:offset of buffer
235 * %al = 0x0 on success; err code on failure
238 movl $0x0201, %eax /function 2 (read) 1 sector */
239 xor %ebx, %ebx /* %bx = 0 */ /* buffer address (ES:0) */
241 movl $0x0002, %ecx /* sector 2, cylinder 0 */
243 andl $0x00ff, %edx /* head 0, drive N */
248 * confirm that it is one for us
251 xorl %ebx, %ebx /* magic number at start of buffer */
254 movl %es:(%ebx), %eax
256 cmpl $NAMEBLOCKMAGIC, %eax
258 jne notours /* not ours so return to caller */
260 * scan for a bootstring
261 * Skip the magic number, and scan till we find a non-null,
264 incl %ebx /* quicker and smaller */
270 movb %es:(%ebx), %al /* load the next byte */
271 testb %al, %al /* and if it is null */
272 data32 /* keep scanning (past deleted entries) */
274 incb %al /* now look for -1 */
276 jz notours /* if we reach the 0xFF then we have finished */
279 * save our settings.. we need them twice..
284 * copy it to the default string location
285 * which is just above the stack for 64 bytes.
288 movl $BOOTSTACK-64, %ecx /* 64 bytes at the top of the stack */
291 movb %es:(%ebx), %al /* get the next byte in */
293 movb %al, %es:(%ecx) /* and transfer it to the name buffer */
294 incl %ebx /* get on with the next byte */
295 incl %ecx /* get on with the next byte */
296 testb %al, %al /* if it was 0 then quit this */
298 jnz nxtbyte /* and looop if more to do */
301 * restore the saved settings and
302 * zero it out so next time we don't try it again
305 pop %ebx /* get back our starting location */
306 #ifdef NAMEBLOCK_WRITEBACK
309 movb %es:(%ebx), %al /* get the byte */
311 movb $0, %es:(%ebx) /* zero it out */
313 incl %ebx /* point to the next byte */
314 testb %al, %al /* check if we have finished.. */
318 * Write the second sector back
319 * Load the second sector
320 * BIOS call "INT 0x13 Function 0x3" to write sectors from memory to disk
321 * Call with %ah = 0x3
322 * %al = number of sectors
326 * %dl = drive (0x80 for hard disk, 0x0 for floppy disk)
327 * %es:%bx = segment:offset of buffer
329 * %al = 0x0 on success; err code on failure
332 movl $0x0301, %eax /* write 1 sector */
333 xor %ebx, %ebx /* buffer is at offset 0 */
335 movl $0x0002, %ecx /* block 2 */
337 andl $0xff, %edx /* head 0 */
344 #endif /* NAMEBLOCK_WRITEBACK */
346 * return to the main-line
354 movb $0x2, %ah /* function 2 */
355 movb $LOADSZ, %al /* number of blocks */
356 xor %ebx, %ebx /* %bx = 0, put it at 0 in the BOOTSEG */
362 * ljmp to the second stage boot loader (boot2).
363 * After ljmp, %cs is BOOTSEG and boot1 (512 bytes) will be used
364 * as an internal buffer "intbuf".
368 ljmp $BOOTSEG, $ EXT(boot2)
383 * message: write the error message in %ds:%esi to console
387 * Use BIOS "int 10H Function 0Eh" to write character in teletype mode
388 * %ah = 0xe %al = character
389 * %bh = page %bl = foreground color (graphics modes)
401 lodsb /* load a byte into %al */
406 int $0x10 /* display a byte */
419 jmp stop /* halt doesnt actually halt forever */
430 #ifdef NAMEBLOCK_WRITEBACK
431 ewrite: String "Write error\r\n\0"
432 #endif /* NAMEBLOCK_WRITEBACK */
433 eread: String "Read error\r\n\0"
434 enoboot: String "No bootable partition\r\n\0"
437 * Dummy partition table in case we are block 0. The ending c/h/s values
438 * of the non-null partition are almost arbitary. The length of this
439 * partition is bogus for backwards compatibility and as a signature.
440 * A real partition table shouldn't be as weird and broken as this one,
441 * and the isa slice initialization routine interprets this table as
442 * saying that the whole disk is used for FreeBSD.
444 /* flag, head, sec, cyl, typ, ehead, esect, ecyl, start, len */
445 . = EXT(boot1) + PARTSTART
447 .byte 0x0,0,0,0,0,0,0,0
449 .byte 0x0,0,0,0,0,0,0,0
451 .byte 0x0,0,0,0,0,0,0,0
453 .byte BOOTABLE,0,1,0,BSDPART,255,255,255
455 /* the last 2 bytes in the sector 0 contain the signature */
456 . = EXT(boot1) + 0x1fe
459 . = EXT(boot1) + 0x400