#-
# Copyright (c) 2007 Yahoo!, Inc.
# All rights reserved.
# Written by: John Baldwin <jhb@FreeBSD.org>
#
# 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.
# 3. Neither the name of the author nor the names of any co-contributors
# may be used to endorse or promote products derived from this software
# without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``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 AUTHOR 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.
#
# $FreeBSD$
#
# Partly from: src/sys/boot/i386/mbr/mbr.s 1.7
# A 512 byte PMBR boot manager to read a boot program and run it.
# The embedded MBR is set up for PMBR and default bootblock sector
# is hardcoded to 256 and size 1. The actual values are supposed to be
# updated by installboot.
.set LOAD,0x7c00 # Load address
.set EXEC,0x600 # Execution address
.set MAGIC,0xaa55 # Magic: bootable
.set SECSIZE,0x200 # Size of a single disk sector
.set DISKSIG,440 # Disk signature offset
.set STACK,EXEC+SECSIZE*4 # Stack address
.set DPBUF,STACK
.set NHRDRV,0x475 # Number of hard drives
.globl start # Entry point
.code16
.text
start: jmp real_code
.fill 0x3c,0x1,0x90 # fill with nop to ease disasm
#
# BIOS Parameter Block. Reserved space from 0xb to 0x3e, the FAT32 BPB
# is 60 (3Ch) bytes.
#
. = start + 0x3e
#
# Setup the segment registers for flat addressing and setup the stack.
#
real_code: cld # String ops inc
xorw %ax,%ax # Zero
movw %ax,%es # Address
movw %ax,%ds # data
movw %ax,%ss # Set up
movw $STACK,%sp # stack
#
# Relocate ourself to a lower address so that we have more room to load
# other sectors.
#
movw $main-EXEC+LOAD,%si # Source
movw $main,%di # Destination
movw $SECSIZE-(main-start),%cx # Byte count
rep # Relocate
movsb # code
#
# Jump to the relocated code.
#
jmp main-LOAD+EXEC # To relocated code
#
# Validate drive number in %dl.
#
main: cmpb $0x80,%dl # Drive valid?
jb main.1 # No
movb NHRDRV,%dh # Calculate the highest
addb $0x80,%dh # drive number available
cmpb %dh,%dl # Within range?
jb main.2 # Yes
main.1: movb $0x80,%dl # Assume drive 0x80
#
# Load stage2 and start it. location and size is written by installboot
# and if size is 0, we can not do anything...
#
main.2: movw stage2_size, %ax
cmpw $0, %ax
je err_noboot # the stage2 size is not set
pushw %dx # save drive
movb $0x41, %ah # check extensions
movw $0x55aa, %bx
int $0x13
popw %dx # restore drive
jc err_rd # need lba mode for now
cmpw $0xaa55, %bx # chs support is not
jne err_rd # implemented.
movw $stage2_sector, %si # pointer to lba
movw $LOAD/16,%bx # set buffer segment
movw %bx,%es
xorw %bx,%bx # and offset
load_boot: push %si # Save %si
call read
pop %si # Restore
decw stage2_size # stage2_size--
jnz next_boot
boot: mov %bx,%es # Reset %es to zero
jmp LOAD # Jump to boot code
next_boot: incl (%si) # Next LBA
adcl $0,4(%si)
mov %es,%ax # Adjust segment for next
addw $SECSIZE/16,%ax # sector
mov %ax,%es #
jmp load_boot
#
# Load a sector (64-bit LBA at %si) from disk %dl into %es:%bx by creating
# a EDD packet on the stack and passing it to the BIOS. Trashes %ax and %si.
#
read: pushl 0x4(%si) # Set the LBA
pushl 0x0(%si) # address
pushw %es # Set the address of
pushw %bx # the transfer buffer
pushw $0x1 # Read 1 sector
pushw $0x10 # Packet length
movw %sp,%si # Packer pointer
movw $0x4200,%ax # BIOS: LBA Read from disk
int $0x13 # Call the BIOS
add $0x10,%sp # Restore stack
jc err_rd # If error
ret
#
# Various error message entry points.
#
err_rd: movw $msg_rd,%si # "I/O error loading
jmp putstr # boot loader"
err_noboot: movw $msg_noboot,%si # "Missing boot
jmp putstr # loader"
#
# Output an ASCIZ string to the console via the BIOS.
#
putstr.0: movw $0x7,%bx # Page:attribute
movb $0xe,%ah # BIOS: Display
int $0x10 # character
putstr: lodsb # Get character
testb %al,%al # End of string?
jnz putstr.0 # No
putstr.1: jmp putstr.1 # Await reset
msg_rd: .asciz "I/O error"
msg_noboot: .asciz "No boot loader"
nop
mbr_version: .byte 1, 1 # 1.1
.align 4
stage2_size: .word 1 # bootblock size in sectors
stage2_sector: .quad 256 # lba of bootblock
disk_uuid: .quad 0 # uuid
.quad 0
# this is the end of the code block we can use, next is space for
# signature, partition table 4 entries and signature.
.org DISKSIG,0x1b8 #
sig: .long 0 # OS Disk Signature
.word 0 # "Unknown" in PMBR
partbl: .byte 0x00 # non-bootable
.byte 0x00 # head 0
.byte 0x02 # sector
.byte 0x00 # cylinder
.byte 0xEE # ID
.byte 0xFF # ending head
.byte 0xFF # ending sector
.byte 0xFF # ending cylinder
.long 0x00000001 # starting LBA
.long 0xFFFFFFFF # size
.fill 0x10,0x3,0x0 # other 3 entries
.word MAGIC # Magic number