#-
# 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