freebsd-skq/sys/boot/i386/boot2/boot1.S

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/*
* Copyright (c) 1998 Robert Nordier
* All rights reserved.
*
* Redistribution and use in source and binary forms are freely
* permitted provided that the above copyright notice and this
* paragraph and the following disclaimer are duplicated in all
* such forms.
*
* This software is provided "AS IS" and without any express or
* implied warranties, including, without limitation, the implied
* warranties of merchantability and fitness for a particular
* purpose.
*
* $FreeBSD$
*/
/* Memory Locations */
.set MEM_REL,0x700 # Relocation address
.set MEM_ARG,0x900 # Arguments
.set MEM_ORG,0x7c00 # Origin
.set MEM_BUF,0x8c00 # Load area
.set MEM_BTX,0x9000 # BTX start
.set MEM_JMP,0x9010 # BTX entry point
.set MEM_USR,0xa000 # Client start
.set BDA_BOOT,0x472 # Boot howto flag
/* Partition Constants */
.set PRT_OFF,0x1be # Partition offset
.set PRT_NUM,0x4 # Partitions
.set PRT_BSD,0xa5 # Partition type
/* Flag Bits */
.set FL_PACKET,0x80 # Packet mode
/* Misc. Constants */
.set SIZ_PAG,0x1000 # Page size
.set SIZ_SEC,0x200 # Sector size
.set NSECT,0x10
.globl start
.globl xread
.code16
start: jmp main # Start recognizably
/*
* This is the start of a standard BIOS Parameter Block (BPB). Most bootable
* FAT disks have this at the start of their MBR. While normal BIOS's will
* work fine without this section, IBM's El Torito emulation "fixes" up the
* BPB by writing into the memory copy of the MBR. Rather than have data
* written into our xread routine, we'll define a BPB to work around it.
* The data marked with (T) indicates a field required for a ThinkPad to
* recognize the disk and (W) indicates fields written from IBM BIOS code.
* The use of the BPB is based on what OpenBSD and NetBSD implemented in
* their boot code but the required fields were determined by trial and error.
*
* Note: If additional space is needed in boot1, one solution would be to
* move the "prompt" message data (below) to replace the OEM ID.
*/
.org 0x03, 0x00
oemid: .space 0x08, 0x00 # OEM ID
.org 0x0b, 0x00
bpb: .word 512 # sector size (T)
.byte 0 # sectors/clustor
.word 0 # reserved sectors
.byte 0 # number of FATs
.word 0 # root entries
.word 0 # small sectors
.byte 0 # media type (W)
.word 0 # sectors/fat
.word 18 # sectors per track (T)
.word 2 # number of heads (T)
.long 0 # hidden sectors (W)
.long 0 # large sectors
.org 0x24, 0x00
ebpb: .byte 0 # BIOS physical drive number (W)
.org 0x25,0x90
/*
* Trampoline used by boot2 to call read to read data from the disk via
* the BIOS. Call with:
*
* %cx:%ax - long - LBA to read in
* %es:(%bx) - caddr_t - buffer to read data into
* %dl - byte - drive to read from
* %dh - byte - num sectors to read
*/
xread: push %ss # Address
pop %ds # data
/*
* Setup an EDD disk packet and pass it to read
*/
xread.1: # Starting
pushl $0x0 # absolute
push %cx # block
push %ax # number
push %es # Address of
push %bx # transfer buffer
xor %ax,%ax # Number of
movb %dh,%al # blocks to
push %ax # transfer
push $0x10 # Size of packet
mov %sp,%bp # Packet pointer
callw read # Read from disk
lea 0x10(%bp),%sp # Clear stack
lret # To far caller
/*
* Load the rest of boot2 and BTX up, copy the parts to the right locations,
* and start it all up.
*/
/*
* Setup the segment registers to flat addressing (segment 0) and setup the
* stack to end just below the start of our code.
*/
main: cld # String ops inc
xor %cx,%cx # Zero
mov %cx,%es # Address
mov %cx,%ds # data
mov %cx,%ss # Set up
mov $start,%sp # stack
/*
* Relocate ourself to MEM_REL. Since %cx == 0, the inc %ch sets
* %cx == 0x100.
*/
mov %sp,%si # Source
mov $MEM_REL,%di # Destination
incb %ch # Word count
rep # Copy
movsw # code
/*
* If we are on a hard drive, then load the MBR and look for the first
* FreeBSD slice. We use the fake partition entry below that points to
* the MBR when we call nread. The first pass looks for the first active
* FreeBSD slice. The second pass looks for the first non-active FreeBSD
* slice if the first one fails.
*/
mov $part4,%si # Partition
cmpb $0x80,%dl # Hard drive?
jb main.4 # No
movb $0x1,%dh # Block count
callw nread # Read MBR
mov $0x1,%cx # Two passes
main.1: mov $MEM_BUF+PRT_OFF,%si # Partition table
movb $0x1,%dh # Partition
main.2: cmpb $PRT_BSD,0x4(%si) # Our partition type?
jne main.3 # No
jcxz main.5 # If second pass
testb $0x80,(%si) # Active?
jnz main.5 # Yes
main.3: add $0x10,%si # Next entry
incb %dh # Partition
cmpb $0x1+PRT_NUM,%dh # In table?
jb main.2 # Yes
dec %cx # Do two
jcxz main.1 # passes
/*
* If we get here, we didn't find any FreeBSD slices at all, so print an
* error message and die.
*/
mov $msg_part,%si # Message
jmp error # Error
/*
* Floppies use partition 0 of drive 0.
*/
main.4: xor %dx,%dx # Partition:drive
/*
* Ok, we have a slice and drive in %dx now, so use that to locate and load
* boot2. %si references the start of the slice we are looking for, so go
* ahead and load up the first 16 sectors (boot1 + boot2) from that. When
* we read it in, we conveniently use 0x8c00 as our transfer buffer. Thus,
* boot1 ends up at 0x8c00, and boot2 starts at 0x8c00 + 0x200 = 0x8e00.
* The first part of boot2 is the disklabel, which is 0x200 bytes long.
* The second part is BTX, which is thus loaded into 0x9000, which is where
* it also runs from. The boot2.bin binary starts right after the end of
* BTX, so we have to figure out where the start of it is and then move the
* binary to 0xc000. Normally, BTX clients start at MEM_USR, or 0xa000, but
* when we use btxld to create boot2, we use an entry point of 0x2000. That
* entry point is relative to MEM_USR; thus boot2.bin starts at 0xc000.
*/
main.5: mov %dx,MEM_ARG # Save args
movb $NSECT,%dh # Sector count
callw nread # Read disk
mov $MEM_BTX,%bx # BTX
mov 0xa(%bx),%si # Get BTX length and set
add %bx,%si # %si to start of boot2.bin
mov $MEM_USR+SIZ_PAG*2,%di # Client page 2
mov $MEM_BTX+(NSECT-1)*SIZ_SEC,%cx # Byte
sub %si,%cx # count
rep # Relocate
movsb # client
/*
* Enable A20 so we can access memory above 1 meg.
* Use the zero-valued %cx as a timeout for embedded hardware which do not
* have a keyboard controller.
*/
seta20: cli # Disable interrupts
seta20.1: dec %cx # Timeout?
jz seta20.3 # Yes
inb $0x64,%al # Get status
testb $0x2,%al # Busy?
jnz seta20.1 # Yes
movb $0xd1,%al # Command: Write
outb %al,$0x64 # output port
seta20.2: inb $0x64,%al # Get status
testb $0x2,%al # Busy?
jnz seta20.2 # Yes
movb $0xdf,%al # Enable
outb %al,$0x60 # A20
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seta20.3: sti # Enable interrupts
jmp start+MEM_JMP-MEM_ORG # Start BTX
/*
* Trampoline used to call read from within boot1.
*/
nread: mov $MEM_BUF,%bx # Transfer buffer
mov 0x8(%si),%ax # Get
mov 0xa(%si),%cx # LBA
push %cs # Read from
callw xread.1 # disk
jnc return # If success, return
mov $msg_read,%si # Otherwise, set the error
# message and fall through to
# the error routine
/*
* Print out the error message pointed to by %ds:(%si) followed
* by a prompt, wait for a keypress, and then reboot the machine.
*/
error: callw putstr # Display message
mov $prompt,%si # Display
callw putstr # prompt
xorb %ah,%ah # BIOS: Get
int $0x16 # keypress
movw $0x1234, BDA_BOOT # Do a warm boot
ljmp $0xf000,$0x0 # reboot the machine
/*
* Display a null-terminated string using the BIOS output.
*/
putstr.0: mov $0x7,%bx # Page:attribute
movb $0xe,%ah # BIOS: Display
int $0x10 # character
putstr: lodsb # Get char
testb %al,%al # End of string?
jne putstr.0 # No
/*
* Overused return code. ereturn is used to return an error from the
* read function. Since we assume putstr succeeds, we (ab)use the
* same code when we return from putstr.
*/
ereturn: movb $0x1,%ah # Invalid
stc # argument
return: retw # To caller
/*
* Reads sectors from the disk. If EDD is enabled, then check if it is
* installed and use it if it is. If it is not installed or not enabled, then
* fall back to using CHS. Since we use a LBA, if we are using CHS, we have to
* fetch the drive parameters from the BIOS and divide it out ourselves.
* Call with:
*
* %dl - byte - drive number
* stack - 10 bytes - EDD Packet
*/
read: testb $FL_PACKET,%cs:MEM_REL+flags-start # LBA support enabled?
jz read.1 # No, use CHS
cmpb $0x80,%dl # Hard drive?
jb read.1 # No, use CHS
mov $0x55aa,%bx # Magic
push %dx # Save
movb $0x41,%ah # BIOS: Check
int $0x13 # extensions present
pop %dx # Restore
jc read.1 # If error, use CHS
cmp $0xaa55,%bx # Magic?
jne read.1 # No, so use CHS
testb $0x1,%cl # Packet interface?
jz read.1 # No, so use CHS
mov %bp,%si # Disk packet
movb $0x42,%ah # BIOS: Extended
int $0x13 # read
retw # To caller
read.1: push %dx # Save
movb $0x8,%ah # BIOS: Get drive
int $0x13 # parameters
movb %dh,%ch # Max head number
pop %dx # Restore
jc return # If error
andb $0x3f,%cl # Sectors per track
jz ereturn # If zero
cli # Disable interrupts
mov 0x8(%bp),%eax # Get LBA
push %dx # Save
movzbl %cl,%ebx # Divide by
xor %edx,%edx # sectors
div %ebx # per track
movb %ch,%bl # Max head number
movb %dl,%ch # Sector number
inc %bx # Divide by
xorb %dl,%dl # number
div %ebx # of heads
movb %dl,%bh # Head number
pop %dx # Restore
cmpl $0x3ff,%eax # Cylinder number supportable?
sti # Enable interrupts
ja ereturn # No, return an error
xchgb %al,%ah # Set up cylinder
rorb $0x2,%al # number
orb %ch,%al # Merge
inc %ax # sector
xchg %ax,%cx # number
movb %bh,%dh # Head number
subb %ah,%al # Sectors this track
mov 0x2(%bp),%ah # Blocks to read
cmpb %ah,%al # To read
jb read.2 # this
#ifdef TRACK_AT_A_TIME
movb %ah,%al # track
#else
movb $1,%al # one sector
#endif
read.2: mov $0x5,%di # Try count
read.3: les 0x4(%bp),%bx # Transfer buffer
push %ax # Save
movb $0x2,%ah # BIOS: Read
int $0x13 # from disk
pop %bx # Restore
jnc read.4 # If success
dec %di # Retry?
jz read.6 # No
xorb %ah,%ah # BIOS: Reset
int $0x13 # disk system
xchg %bx,%ax # Block count
jmp read.3 # Continue
read.4: movzbw %bl,%ax # Sectors read
add %ax,0x8(%bp) # Adjust
jnc read.5 # LBA,
incw 0xa(%bp) # transfer
read.5: shlb %bl # buffer
add %bl,0x5(%bp) # pointer,
sub %al,0x2(%bp) # block count
ja read.1 # If not done
read.6: retw # To caller
/* Messages */
msg_read: .asciz "Read"
msg_part: .asciz "Boot"
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prompt: .asciz " error\r\n"
flags: .byte FLAGS # Flags
.org PRT_OFF,0x90
/* Partition table */
.fill 0x30,0x1,0x0
part4: .byte 0x80, 0x00, 0x01, 0x00
.byte 0xa5, 0xfe, 0xff, 0xff
.byte 0x00, 0x00, 0x00, 0x00
.byte 0x50, 0xc3, 0x00, 0x00 # 50000 sectors long, bleh
.word 0xaa55 # Magic number