The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/boot/i386/pmbr/pmbr.s

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    1 #-
    2 # Copyright (c) 2007 Yahoo!, Inc.
    3 # All rights reserved.
    4 # Written by: John Baldwin <jhb@FreeBSD.org>
    5 #
    6 # Redistribution and use in source and binary forms, with or without
    7 # modification, are permitted provided that the following conditions
    8 # are met:
    9 # 1. Redistributions of source code must retain the above copyright
   10 #    notice, this list of conditions and the following disclaimer.
   11 # 2. Redistributions in binary form must reproduce the above copyright
   12 #    notice, this list of conditions and the following disclaimer in the
   13 #    documentation and/or other materials provided with the distribution.
   14 # 3. Neither the name of the author nor the names of any co-contributors
   15 #    may be used to endorse or promote products derived from this software
   16 #    without specific prior written permission.
   17 #
   18 # THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   19 # ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   20 # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   21 # ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   22 # FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   23 # DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   24 # OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   25 # HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   26 # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   27 # OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   28 # SUCH DAMAGE.
   29 #
   30 # $FreeBSD: releng/8.0/sys/boot/i386/pmbr/pmbr.s 173957 2007-11-26 21:29:59Z jhb $
   31 #
   32 # Partly from: src/sys/boot/i386/mbr/mbr.s 1.7
   33 
   34 # A 512 byte PMBR boot manager that looks for a FreeBSD boot GPT partition
   35 # and boots it.
   36 
   37                 .set LOAD,0x7c00                # Load address
   38                 .set EXEC,0x600                 # Execution address
   39                 .set MAGIC,0xaa55               # Magic: bootable
   40                 .set SECSIZE,0x200              # Size of a single disk sector
   41                 .set DISKSIG,440                # Disk signature offset
   42                 .set STACK,EXEC+SECSIZE*4       # Stack address
   43                 .set GPT_ADDR,STACK             # GPT header address
   44                 .set GPT_SIG,0
   45                 .set GPT_SIG_0,0x20494645
   46                 .set GPT_SIG_1,0x54524150
   47                 .set GPT_MYLBA,24
   48                 .set GPT_PART_LBA,72
   49                 .set GPT_NPART,80
   50                 .set GPT_PART_SIZE,84
   51                 .set PART_ADDR,GPT_ADDR+SECSIZE # GPT partition array address
   52                 .set PART_TYPE,0
   53                 .set PART_START_LBA,32
   54                 .set PART_END_LBA,40
   55 
   56                 .set NHRDRV,0x475               # Number of hard drives
   57 
   58                 .globl start                    # Entry point
   59                 .code16
   60 
   61 #
   62 # Setup the segment registers for flat addressing and setup the stack.
   63 #
   64 start:          cld                             # String ops inc
   65                 xorw %ax,%ax                    # Zero
   66                 movw %ax,%es                    # Address
   67                 movw %ax,%ds                    #  data
   68                 movw %ax,%ss                    # Set up
   69                 movw $STACK,%sp                 #  stack
   70 #
   71 # Relocate ourself to a lower address so that we have more room to load
   72 # other sectors.
   73 # 
   74                 movw $main-EXEC+LOAD,%si        # Source
   75                 movw $main,%di                  # Destination
   76                 movw $SECSIZE-(main-start),%cx  # Byte count
   77                 rep                             # Relocate
   78                 movsb                           #  code
   79 #
   80 # Jump to the relocated code.
   81 #
   82                 jmp main-LOAD+EXEC              # To relocated code
   83 #
   84 # Validate drive number in %dl.
   85 #
   86 main:           cmpb $0x80,%dl                  # Drive valid?
   87                 jb main.1                       # No
   88                 movb NHRDRV,%dh                 # Calculate the highest
   89                 addb $0x80,%dh                  #  drive number available
   90                 cmpb %dh,%dl                    # Within range?
   91                 jb main.2                       # Yes
   92 main.1:         movb $0x80,%dl                  # Assume drive 0x80
   93 #
   94 # Load the primary GPT header from LBA 1 and verify signature.
   95 #
   96 main.2:         movw $GPT_ADDR,%bx
   97                 movw $lba,%si
   98                 call read
   99                 cmpl $GPT_SIG_0,GPT_ADDR+GPT_SIG
  100                 jnz err_pt
  101                 cmpl $GPT_SIG_1,GPT_ADDR+GPT_SIG+4
  102                 jnz err_pt
  103 #
  104 # Load a partition table sector from disk and look for a FreeBSD boot
  105 # partition.
  106 #
  107 load_part:      movw $GPT_ADDR+GPT_PART_LBA,%si
  108                 movw $PART_ADDR,%bx
  109                 call read
  110 scan:           movw %bx,%si                    # Compare partition UUID
  111                 movw $boot_uuid,%di             #  with FreeBSD boot UUID 
  112                 movb $0x10,%cl
  113                 repe cmpsb
  114                 jnz next_part                   # Didn't match, next partition
  115 #
  116 # We found a boot partition.  Load it into RAM starting at 0x7c00.
  117 #
  118                 movw %bx,%di                    # Save partition pointer in %di
  119                 leaw PART_START_LBA(%di),%si
  120                 movw $LOAD/16,%bx
  121                 movw %bx,%es
  122                 xorw %bx,%bx
  123 load_boot:      push %si                        # Save %si
  124                 call read
  125                 pop %si                         # Restore
  126                 movl PART_END_LBA(%di),%eax     # See if this was the last LBA
  127                 cmpl (%si),%eax
  128                 jnz next_boot
  129                 movl PART_END_LBA+4(%di),%eax
  130                 cmpl 4(%si),%eax
  131                 jnz next_boot
  132                 mov %bx,%es                     # Reset %es to zero 
  133                 jmp LOAD                        # Jump to boot code
  134 next_boot:      incl (%si)                      # Next LBA
  135                 adcl $0,4(%si)
  136                 mov %es,%ax                     # Adjust segment for next
  137                 addw $SECSIZE/16,%ax            #  sector
  138                 cmp $0x9000,%ax                 # Don't load past 0x90000,
  139                 jae err_big                     #  545k should be enough for
  140                 mov %ax,%es                     #  any boot code. :)
  141                 jmp load_boot
  142 #
  143 # Move to the next partition.  If we walk off the end of the sector, load
  144 # the next sector.  We assume that partition entries are smaller than 64k
  145 # and that they won't span a sector boundary.
  146 #
  147 # XXX: Should we int 0x18 instead of err_noboot if we hit the end of the table?
  148 #
  149 next_part:      decl GPT_ADDR+GPT_NPART         # Was this the last partition?
  150                 jz err_noboot
  151                 movw GPT_ADDR+GPT_PART_SIZE,%ax
  152                 addw %ax,%bx                    # Next partition
  153                 cmpw $PART_ADDR+0x200,%bx       # Still in sector?
  154                 jb scan
  155                 incl GPT_ADDR+GPT_PART_LBA      # Next sector
  156                 adcl $0,GPT_ADDR+GPT_PART_LBA+4
  157                 jmp load_part
  158 #
  159 # Load a sector (64-bit LBA at %si) from disk %dl into %es:%bx by creating
  160 # a EDD packet on the stack and passing it to the BIOS.  Trashes %ax and %si.
  161 #
  162 read:           pushl 0x4(%si)                  # Set the LBA
  163                 pushl 0x0(%si)                  #  address
  164                 pushw %es                       # Set the address of
  165                 pushw %bx                       #  the transfer buffer
  166                 pushw $0x1                      # Read 1 sector
  167                 pushw $0x10                     # Packet length
  168                 movw %sp,%si                    # Packer pointer
  169                 movw $0x4200,%ax                # BIOS: LBA Read from disk
  170                 int $0x13                       # Call the BIOS
  171                 add $0x10,%sp                   # Restore stack
  172                 jc err_rd                       # If error
  173                 ret
  174 #
  175 # Various error message entry points.
  176 #
  177 err_big:        movw $msg_big,%si               # "Boot loader too
  178                 jmp putstr                      #  large"
  179 
  180 err_pt:         movw $msg_pt,%si                # "Invalid partition
  181                 jmp putstr                      #  table"
  182 
  183 err_rd:         movw $msg_rd,%si                # "I/O error loading
  184                 jmp putstr                      #  boot loader"
  185 
  186 err_noboot:     movw $msg_noboot,%si            # "Missing boot
  187                 jmp putstr                      #  loader"
  188 #
  189 # Output an ASCIZ string to the console via the BIOS.
  190 # 
  191 putstr.0:       movw $0x7,%bx                   # Page:attribute
  192                 movb $0xe,%ah                   # BIOS: Display
  193                 int $0x10                       #  character
  194 putstr:         lodsb                           # Get character
  195                 testb %al,%al                   # End of string?
  196                 jnz putstr.0                    # No
  197 putstr.1:       jmp putstr.1                    # Await reset
  198 
  199 msg_big:        .asciz "Boot loader too large"
  200 msg_pt:         .asciz "Invalid partition table"
  201 msg_rd:         .asciz "I/O error loading boot loader"
  202 msg_noboot:     .asciz "Missing boot loader"
  203 
  204 lba:            .quad 1                         # LBA of GPT header 
  205 
  206 boot_uuid:      .long 0x83bd6b9d
  207                 .word 0x7f41
  208                 .word 0x11dc
  209                 .byte 0xbe
  210                 .byte 0x0b
  211                 .byte 0x00
  212                 .byte 0x15
  213                 .byte 0x60
  214                 .byte 0xb8
  215                 .byte 0x4f
  216                 .byte 0x0f
  217 
  218                 .org DISKSIG,0x90
  219 sig:            .long 0                         # OS Disk Signature
  220                 .word 0                         # "Unknown" in PMBR
  221 
  222 partbl:         .fill 0x10,0x4,0x0              # Partition table
  223                 .word MAGIC                     # Magic number

Cache object: bc6c1a8e20f37cf9d8d4ce0e7abb57ca


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