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|
/* $OpenBSD: mbr.S,v 1.18 2003/06/03 20:22:12 mickey Exp $ */
/*
* Copyright (c) 1997 Michael Shalayeff and Tobias Weingartner
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
*/
/* Copyright (c) 1996 VaX#n8 (vax@linkdead.paranoia.com)
* last edited 9 July 1996
* many thanks to Erich Boleyn (erich@uruk.org) for putting up with
* all my questions, and for his work on GRUB
* You may use this code or fragments thereof in a manner consistent
* with the other copyrights as long as you retain my pseudonym and
* this copyright notice in the file.
*/
.file "mbr.S"
#include <machine/asm.h>
#include <assym.h>
#define data32 .byte 0x66
#define addr32 .byte 0x67
#define BOOTBIOS 0x7c0 /* segment where we are loaded */
#define BOOTRELOC 0x7a0 /* segment where to relocate */
#define PARTSZ 16 /* each partition table entry is 16 bytes */
#ifdef DEBUG
#define CHAR_S 'S' /* started */
#define CHAR_R 'R' /* relocated */
#define CHAR_L 'L' /* looking for bootable partition */
#define CHAR_B 'B' /* loading boot */
#define CHAR_G 'G' /* jumping to boot */
#define DBGMSG(msg) \
movb $msg, %al; \
/* call Lchr */; \
.byte 0xe8; \
.word Lchr - . - 2
#else /* !DEBUG */
#define DBGMSG(msg)
#endif /* !DEBUG */
#define puts(s) \
data32; \
movl $s, %esi; \
/* call Lmessage */; \
.byte 0xe8; \
.word Lmessage - . - 2
.text
.globl start
start:
/* Adjust %cs to be right */
data32
ljmp $BOOTBIOS, $1f
1:
/* Set up stack */
movl %cs, %eax
cli
mov %ax, %ss
data32
movl $0xfffc, %esp
sti
/* Set up data segment */
mov %ax, %ds
DBGMSG(CHAR_S)
/* Relocate 512 bytes so we can load PBS here */
data32
movl $BOOTRELOC, %eax
movl %eax, %es
data32
xorl %esi, %esi
data32
xorl %edi, %edi
data32
movl $0x200, %ecx
cld
rep
movsb
/* Jump to relocated self */
data32
ljmp $BOOTRELOC, $reloc
reloc:
DBGMSG(CHAR_R)
/* Set up %es and %ds */
pushl %ds
popl %es /* next boot is at the same place as we were loaded */
pushl %cs
popl %ds /* and %ds is at the %cs */
#ifdef SERIAL
/* Initialize the serial port to 9600 baud, 8N1.
* Do we need to do this? Most things at this level
* do not know or care (on a PC) where the output is
* happening to go. I think if we are headless,
* /boot should figure (as it does now) that out.
*
* If there is a problem with this stage of the boot
* process, connect up a monitor and kbd, and see what
* is going on. Left here for the time being.
*
* --Toby.
*/
xorl %eax, %eax
movb $0xe3, %ax
data32
movl $SERIAL, %dx
int $0x14
#endif
/* bootstrap passes us drive number in %dl
*
* XXX - This is not always true. We currently
* check if %dl points to a HD, and if not we
* complain, and set it to point to the first
* HDD. Note, this is not 100% correct, since
* there is a possibility that you boot of of
* HD #2, and still get (%dl & 0x80) == 0x00,
* these type of systems will loose. I don't
* know of any like this, but I've come to the
* conclusion, that if it can exist, it will,
* someplace in the PC world. If anyone knows
* how to fix this, speak up!
*
* Toby - Thu Jul 31 21:01:00 CDT 1997
*/
testb $0x80, %dl
jnz 1f
/* MBR on floppy or old BIOS
* Note: MBR (this code) should never
* be on a floppy. It does not belong
* there, so %dl should never be 0x00.
*
* Here we simply complain (should we?),
* and then hardcode the boot drive to
* 0x80.
*/
puts(fdmbr)
/* If we are passed bogus data, set it to HD #1.
* We should load the value from a hard coded
* location in this sector. Maybe I'll write
* that next, since my machines seem to be one
* of the weird ones...
*/
movb $0x80, %dl
/* Do we need to check our signature? The BIOS will
* check it for us, I doubt there is a need for us to
* do the same thing over again. If we fail here,
* something terrible is wrong. However, I doubt we
* can recover anyways. The message might be nice
* for the (l)user though.
*/
1: xor %bx, %bx
# cmpw $DOSMBR_SIGNATURE, (%bx)
.byte 0x81, 0xbf
.word signature
.word DOSMBR_SIGNATURE
je sigok
puts(esig)
/* find the first active partition
* Note: this should be the only active
* partition. We currently don't check
* for that, but we really should. If
* and when I feel up to it, I'll add
* that code.
*/
sigok:
data32
movl $pt, %esi
data32
movl $NDOSPART, %ecx
1:
DBGMSG(CHAR_L)
# movb (%si), %al
.byte 0x8a, 0x44, 0x00
cmpb $DOSACTIVE, %al
je found
data32
addl $PARTSZ, %esi
loop 1b
/* No bootable partition */
no_part:
puts(noboot)
err_stop:
cli
hlt
/* Just to make sure */
jmp err_stop
/* Found bootable partition */
found:
DBGMSG(CHAR_B)
pushl %eax
/* Save drive and partition */
movl %edx, %eax
andl $0x0F, %eax
orl $0x30, %eax
#movb %al, adrive
.byte 0xA2
.word adrive
movl %ecx, %eax
decl %eax
xorl $0x03, %eax
andl $0x0F, %eax
orl $0x30, %eax
#movb %al, aprtn
.byte 0xA2
.word aprtn
popl %eax
/* Load values from active partition table entry */
# movb 1(%si), %dh # head
.byte 0x8a, 0x74, 0x01
# movw 2(%si), %cx # sect, cyl
.byte 0x8b, 0x4c, 0x02
# movb 4(%si), %al # partition type
.byte 0x8a, 0x44, 0x04
/*
# BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory
# Call with %ah = 0x2
# %al = number of sectors
# %ch = cylinder
# %cl = sector
# %dh = head
# %dl = drive (0x80 for hard disk, 0x0 for floppy disk)
# %es:%bx = segment:offset of buffer
# Return:
# %al = 0x0 on success; err code on failure
*/
data32
movl $0x200 | 1, %eax /* number of blocks */
xor %bx, %bx /* put it at %es:0 */
int $0x13
jnc 1f
puts(eread)
jmp err_stop
1:
DBGMSG(CHAR_G)
puts(info)
# jump to the new code (%ds:%si is at the right point)
data32
ljmp $0, $BOOTBIOS << 4
/* not reached */
/*
* Display string
*/
Lmessage:
pushl %eax
cld
1:
lodsb # load a byte into %al
testb %al, %al
jz 1f
/* call Lchr */
.byte 0xe8
.word Lchr - . - 2
jmp 1b
#
# Lchr: write the error message in %ds:%si to console
#
Lchr:
pushl %eax
#ifndef SERIAL
pushl %ebx
movb $0x0e, %ah
xor %bx, %bx
inc %bx /* movw $0x01, %bx */
int $0x10
popl %ebx
#else
pushl %edx
movb $0x01, %ah
data32
movl SERIAL, %dx
int $0x14
popl %edx
#endif
1: popl %eax
ret
/* Info messages */
info: .ascii "Using Drive: "
adrive: .byte 'X'
.ascii " Partition: "
aprtn: .byte 'Y'
.asciz "\r\n"
/* Error messages */
fdmbr: .asciz "MBR on floppy or old BIOS\r\n"
eread: .asciz "Read error\r\n"
noboot: .asciz "No active partition\r\n"
esig: .asciz "Invalid Signature\r\n"
endofcode:
nop
/* (MBR) NT registry offset */
. = 0x1b8
.space 4, 0
/* partition table */
/* flag, head, sec, cyl, type, ehead, esect, ecyl, start, len */
. = DOSPARTOFF # starting address of partition table
pt:
.byte 0x0,0,0,0,0,0,0,0
.long 0,0
.byte 0x0,0,0,0,0,0,0,0
.long 0,0
.byte 0x0,0,0,0,0,0,0,0
.long 0,0
.byte DOSACTIVE,0,1,0,DOSPTYP_OPENBSD,255,255,255
.long 0,0x7FFFFFFF
/* the last 2 bytes in the sector 0 contain the signature */
. = 0x1fe
signature:
.short DOSMBR_SIGNATURE
. = 0x200
|
