253 lines
7.7 KiB
ArmAsm
253 lines
7.7 KiB
ArmAsm
#-
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# Copyright (c) 2007 Yahoo!, Inc.
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# All rights reserved.
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# Written by: John Baldwin <jhb@FreeBSD.org>
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions
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# are met:
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# 1. Redistributions of source code must retain the above copyright
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# notice, this list of conditions and the following disclaimer.
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# 2. Redistributions in binary form must reproduce the above copyright
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# notice, this list of conditions and the following disclaimer in the
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# documentation and/or other materials provided with the distribution.
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# 3. Neither the name of the author nor the names of any co-contributors
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# may be used to endorse or promote products derived from this software
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# without specific prior written permission.
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#
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# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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# ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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# SUCH DAMAGE.
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#
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# $FreeBSD$
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#
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# Partly from: src/sys/boot/i386/mbr/mbr.s 1.7
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# A 512 byte PMBR boot manager that looks for a FreeBSD boot GPT partition
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# and boots it.
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.set LOAD,0x7c00 # Load address
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.set EXEC,0x600 # Execution address
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.set MAGIC,0xaa55 # Magic: bootable
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.set SECSIZE,0x200 # Size of a single disk sector
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.set DISKSIG,440 # Disk signature offset
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.set STACK,EXEC+SECSIZE*4 # Stack address
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.set GPT_ADDR,STACK # GPT header address
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.set GPT_SIG,0
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.set GPT_SIG_0,0x20494645 # "EFI "
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.set GPT_SIG_1,0x54524150 # "PART"
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.set GPT_MYLBA,24
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.set GPT_PART_LBA,72
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.set GPT_NPART,80
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.set GPT_PART_SIZE,84
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.set PART_ADDR,GPT_ADDR+SECSIZE # GPT partition array address
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.set PART_TYPE,0
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.set PART_START_LBA,32
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.set PART_END_LBA,40
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.set DPBUF,PART_ADDR+SECSIZE
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.set DPBUF_SEC,0x10 # Number of sectors
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.set NHRDRV,0x475 # Number of hard drives
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.globl start # Entry point
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.code16
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#
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# Setup the segment registers for flat addressing and setup the stack.
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#
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start: cld # String ops inc
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xorw %ax,%ax # Zero
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movw %ax,%es # Address
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movw %ax,%ds # data
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movw %ax,%ss # Set up
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movw $STACK,%sp # stack
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#
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# Relocate ourself to a lower address so that we have more room to load
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# other sectors.
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#
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movw $main-EXEC+LOAD,%si # Source
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movw $main,%di # Destination
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movw $SECSIZE-(main-start),%cx # Byte count
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rep # Relocate
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movsb # code
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#
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# Jump to the relocated code.
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#
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jmp main-LOAD+EXEC # To relocated code
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#
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# Validate drive number in %dl.
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#
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main: cmpb $0x80,%dl # Drive valid?
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jb main.1 # No
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movb NHRDRV,%dh # Calculate the highest
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addb $0x80,%dh # drive number available
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cmpb %dh,%dl # Within range?
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jb main.2 # Yes
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main.1: movb $0x80,%dl # Assume drive 0x80
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#
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# Load the GPT header and verify signature. Try LBA 1 for the primary one and
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# the last LBA for the backup if it is broken.
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#
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main.2: call getdrvparams # Read drive parameters
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movb $1,%dh # %dh := 1 (reading primary)
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main.2a: movw $GPT_ADDR,%bx
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movw $lba,%si
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call read # Read header and check GPT sig
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cmpl $GPT_SIG_0,GPT_ADDR+GPT_SIG
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jnz main.2b
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cmpl $GPT_SIG_1,GPT_ADDR+GPT_SIG+4
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jnz main.2b
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jmp load_part
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main.2b: cmpb $1,%dh # Reading primary?
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jne err_pt # If no - invalid table found
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#
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# Try alternative LBAs from the last sector for the GPT header.
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#
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main.3: movb $0,%dh # %dh := 0 (reading backup)
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movw $DPBUF+DPBUF_SEC,%si # %si = last sector + 1
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movw $lba,%di # %di = $lba
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main.3a: decl (%si) # 0x0(%si) = last sec (0-31)
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movw $2,%cx
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rep
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movsw # $lastsec--, copy it to $lba
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jmp main.2a # Read the next sector
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#
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# Load a partition table sector from disk and look for a FreeBSD boot
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# partition.
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#
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load_part: movw $GPT_ADDR+GPT_PART_LBA,%si
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movw $PART_ADDR,%bx
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call read
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scan: movw %bx,%si # Compare partition UUID
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movw $boot_uuid,%di # with FreeBSD boot UUID
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movb $0x10,%cl
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repe cmpsb
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jnz next_part # Didn't match, next partition
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#
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# We found a boot partition. Load it into RAM starting at 0x7c00.
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#
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movw %bx,%di # Save partition pointer in %di
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leaw PART_START_LBA(%di),%si
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movw $LOAD/16,%bx
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movw %bx,%es
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xorw %bx,%bx
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load_boot: push %si # Save %si
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call read
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pop %si # Restore
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movl PART_END_LBA(%di),%eax # See if this was the last LBA
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cmpl (%si),%eax
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jnz next_boot
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movl PART_END_LBA+4(%di),%eax
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cmpl 4(%si),%eax
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jnz next_boot
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mov %bx,%es # Reset %es to zero
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jmp LOAD # Jump to boot code
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next_boot: incl (%si) # Next LBA
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adcl $0,4(%si)
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mov %es,%ax # Adjust segment for next
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addw $SECSIZE/16,%ax # sector
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cmp $0x9000,%ax # Don't load past 0x90000,
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jae err_big # 545k should be enough for
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mov %ax,%es # any boot code. :)
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jmp load_boot
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#
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# Move to the next partition. If we walk off the end of the sector, load
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# the next sector. We assume that partition entries are smaller than 64k
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# and that they won't span a sector boundary.
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#
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# XXX: Should we int 0x18 instead of err_noboot if we hit the end of the table?
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#
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next_part: decl GPT_ADDR+GPT_NPART # Was this the last partition?
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jz err_noboot
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movw GPT_ADDR+GPT_PART_SIZE,%ax
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addw %ax,%bx # Next partition
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cmpw $PART_ADDR+0x200,%bx # Still in sector?
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jb scan
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incl GPT_ADDR+GPT_PART_LBA # Next sector
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adcl $0,GPT_ADDR+GPT_PART_LBA+4
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jmp load_part
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#
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# Load a sector (64-bit LBA at %si) from disk %dl into %es:%bx by creating
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# a EDD packet on the stack and passing it to the BIOS. Trashes %ax and %si.
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#
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read: pushl 0x4(%si) # Set the LBA
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pushl 0x0(%si) # address
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pushw %es # Set the address of
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pushw %bx # the transfer buffer
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pushw $0x1 # Read 1 sector
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pushw $0x10 # Packet length
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movw %sp,%si # Packer pointer
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movw $0x4200,%ax # BIOS: LBA Read from disk
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int $0x13 # Call the BIOS
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add $0x10,%sp # Restore stack
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jc err_rd # If error
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ret
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#
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# Check the number of LBAs on the drive index %dx. Trashes %ax and %si.
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#
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getdrvparams:
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movw $DPBUF,%si # Set the address of result buf
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movw $0x001e,(%si) # len
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movw $0x4800,%ax # BIOS: Read Drive Parameters
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int $0x13 # Call the BIOS
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jc err_rd # "I/O error" if error
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ret
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#
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# Various error message entry points.
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#
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err_big: movw $msg_big,%si # "Boot loader too
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jmp putstr # large"
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err_pt: movw $msg_pt,%si # "Invalid partition
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jmp putstr # table"
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err_rd: movw $msg_rd,%si # "I/O error loading
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jmp putstr # boot loader"
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err_noboot: movw $msg_noboot,%si # "Missing boot
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jmp putstr # loader"
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#
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# Output an ASCIZ string to the console via the BIOS.
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#
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putstr.0: movw $0x7,%bx # Page:attribute
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movb $0xe,%ah # BIOS: Display
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int $0x10 # character
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putstr: lodsb # Get character
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testb %al,%al # End of string?
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jnz putstr.0 # No
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putstr.1: jmp putstr.1 # Await reset
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msg_big: .asciz "Boot loader too large"
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msg_pt: .asciz "Invalid partition table"
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msg_rd: .asciz "I/O error loading boot loader"
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msg_noboot: .asciz "Missing boot loader"
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lba: .quad 1 # LBA of GPT header
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boot_uuid: .long 0x83bd6b9d
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.word 0x7f41
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.word 0x11dc
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.byte 0xbe
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.byte 0x0b
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.byte 0x00
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.byte 0x15
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.byte 0x60
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.byte 0xb8
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.byte 0x4f
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.byte 0x0f
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.org DISKSIG,0x90
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sig: .long 0 # OS Disk Signature
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.word 0 # "Unknown" in PMBR
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partbl: .fill 0x10,0x4,0x0 # Partition table
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.word MAGIC # Magic number
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