#-
# 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.
#
#
# Partly from: src/sys/boot/i386/mbr/mbr.s 1.7

# A 512 byte PMBR boot manager that looks for a FreeBSD boot GPT partition
# and boots it.

                .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 GPT_ADDR,STACK             # GPT header address
                .set GPT_SIG,0
                .set GPT_SIG_0,0x20494645       # "EFI "
                .set GPT_SIG_1,0x54524150       # "PART"
                .set GPT_MYLBA,24
                .set GPT_PART_LBA,72
                .set GPT_NPART,80
                .set GPT_PART_SIZE,84
                .set PART_ADDR,GPT_ADDR+SECSIZE # GPT partition array address
                .set PART_TYPE,0
                .set PART_START_LBA,32
                .set PART_END_LBA,40
                .set DPBUF,PART_ADDR+SECSIZE
                .set DPBUF_SEC,0x10             # Number of sectors

                .set NHRDRV,0x475               # Number of hard drives

                .globl start                    # Entry point
                .code16

#
# Setup the segment registers for flat addressing and setup the stack.
#
start:          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 the GPT header and verify signature.  Try LBA 1 for the primary one and
# the last LBA for the backup if it is broken.
#
main.2:         call getdrvparams               # Read drive parameters
                movb $1,%dh                     # %dh := 1 (reading primary)
main.2a:        movw $GPT_ADDR,%bx
                movw $lba,%si
                call read                       # Read header and check GPT sig
                cmpl $GPT_SIG_0,GPT_ADDR+GPT_SIG
                jnz main.2b
                cmpl $GPT_SIG_1,GPT_ADDR+GPT_SIG+4
                jnz main.2b
                jmp load_part
main.2b:        cmpb $1,%dh                     # Reading primary?
                jne err_pt                      # If no - invalid table found
#
# Try alternative LBAs from the last sector for the GPT header.
#
main.3:         movb $0,%dh                     # %dh := 0 (reading backup)
                movw $DPBUF+DPBUF_SEC,%si       # %si = last sector + 1
                movw $lba,%di                   # %di = $lba
main.3a:        subl $1, (%si)                  # 0x0(%si) = last sec (0-31)
                sbbl $0, 4(%si)
                movw $4,%cx
                rep
                movsw                           # $lastsec--, copy it to $lba
                jmp main.2a                     # Read the next sector
#
# Load a partition table sector from disk and look for a FreeBSD boot
# partition.
#
load_part:      movw $GPT_ADDR+GPT_PART_LBA,%si
                movw $PART_ADDR,%bx
                call read
scan:           movw %bx,%si                    # Compare partition UUID
                movw $boot_uuid,%di             #  with FreeBSD boot UUID 
                movw $0x10,%cx
                repe cmpsb
                jnz next_part                   # Didn't match, next partition
#
# We found a boot partition.  Load it into RAM starting at 0x7c00.
#
                movw %bx,%di                    # Save partition pointer in %di
                leaw PART_START_LBA(%di),%si
                movw $LOAD/16,%bx
                movw %bx,%es
                xorw %bx,%bx
load_boot:      push %si                        # Save %si
                call read
                pop %si                         # Restore
                movl PART_END_LBA(%di),%eax     # See if this was the last LBA
                cmpl (%si),%eax
                jnz next_boot
                movl PART_END_LBA+4(%di),%eax
                cmpl 4(%si),%eax
                jnz next_boot
                mov %bx,%es                     # Reset %es to zero 
                jmp LOAD                        # Jump to boot code
next_boot:      addl $1,(%si)                   # Next LBA
                adcl $0,4(%si)
                mov %es,%ax                     # Adjust segment for next
                addw $SECSIZE/16,%ax            #  sector
                cmp $0x9000,%ax                 # Don't load past 0x90000,
                jb sz_ok                        #  545k should be enough for
                call err_big                    #  any boot code, but warn
                mov $0x9000-SECSIZE/16,%ax      #  and truncate
sz_ok:          mov %ax,%es
                jmp load_boot
#
# Move to the next partition.  If we walk off the end of the sector, load
# the next sector.  We assume that partition entries are smaller than 64k
# and that they won't span a sector boundary.
#
# XXX: Should we int 0x18 instead of err_noboot if we hit the end of the table?
#
next_part:      decl GPT_ADDR+GPT_NPART         # Was this the last partition?
                jz err_noboot
                movw GPT_ADDR+GPT_PART_SIZE,%ax
                addw %ax,%bx                    # Next partition
                cmpw $PART_ADDR+0x200,%bx       # Still in sector?
                jb scan
                addl $1, GPT_ADDR+GPT_PART_LBA  # Next sector
                adcl $0,GPT_ADDR+GPT_PART_LBA+4
                jmp load_part
#
# 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
#
# Check the number of LBAs on the drive index %dx.  Trashes %ax and %si.
#
getdrvparams:
                movw $DPBUF,%si                 # Set the address of result buf
                movw $0x001e,(%si)              # len
                movw $0x4800,%ax                # BIOS: Read Drive Parameters
                int $0x13                       # Call the BIOS
                jc err_rd                       # "I/O error" if error
                ret
#
# Various error message entry points.
#
err_big:        movw $msg_big,%si               # "Truncated
                call putstr                     #  to 545k"
                ret

err_pt:         movw $msg_pt,%si                # "Invalid partition
                call putstr                     #  table"
err_pt.1:       jmp err_pt.1                    # Await reset

err_rd:         movw $msg_rd,%si                # "I/O error loading
                call putstr                     #  boot loader"
                jmp err_pt.1

err_noboot:     movw $msg_noboot,%si            # "Missing boot
                call putstr                     #  loader"
                jmp err_pt.1
#
# 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
                ret

msg_big:        .asciz "Loaded only 545k"
msg_pt:         .asciz "Invalid partition table"
msg_rd:         .asciz "I/O error loading boot loader"
msg_noboot:     .asciz "Missing boot loader"

lba:            .quad 1                         # LBA of GPT header 

boot_uuid:      .long 0x83bd6b9d
                .word 0x7f41
                .word 0x11dc
                .byte 0xbe
                .byte 0x0b
                .byte 0x00
                .byte 0x15
                .byte 0x60
                .byte 0xb8
                .byte 0x4f
                .byte 0x0f

                .org DISKSIG,0x90
sig:            .long 0                         # OS Disk Signature
                .word 0                         # "Unknown" in PMBR

partbl:         .fill 0x10,0x4,0x0              # Partition table
                .word MAGIC                     # Magic number