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Comment this bad boy. Hopefully the next person that comes along won't

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have to spend a few hours reading the code to figure all this out.
This commit is contained in:
John Baldwin 2000-06-19 22:50:46 +00:00
parent 44a4178b09
commit 35bdac5bbd
2 changed files with 196 additions and 58 deletions
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127
sys/boot/i386/boot2/boot1.S
View File

@ -15,6 +15,7 @@
# $FreeBSD$
# Memory Locations
.set MEM_REL,0x700 # Relocation address
.set MEM_ARG,0x900 # Arguments
.set MEM_ORG,0x7c00 # Origin
@ -22,11 +23,16 @@
.set MEM_BTX,0x9000 # BTX start
.set MEM_JMP,0x9010 # BTX entry point
.set MEM_USR,0xa000 # Client start
# 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
@ -37,11 +43,21 @@
start: jmp main # Start recognizably
.org 0x4,0x90
# External read from disk
#
# 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
@ -56,20 +72,37 @@ xread.1: # Starting
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.
#
# Bootstrap
#
# 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
@ -89,29 +122,50 @@ main.3: add $0x10,%si # Next entry
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 boot2.ldr, which is 0x200 bytes of zeros.
# 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 0xb000. Normally, BTX clients start at MEM_USR, or 0xa000, but
# when we use btxld create boot2, we use an entry point of 0x1000. That
# entry point is relative, to MEM_USR, thus boot2.bin starts at 0xb000.
#
main.5: mov %dx,MEM_ARG # Save args
movb $0x10,%dh # Sector count
callw nread # Read disk
mov $MEM_BTX,%bx # BTX
mov 0xa(%bx),%si # Point past
add %bx,%si # it
mov 0xa(%bx),%si # Get BTX length and set
add %bx,%si # %si to start of boot2.bin
mov $MEM_USR+SIZ_PAG,%di # Client page 1
mov $MEM_BTX+0xe*SIZ_SEC,%cx # Byte
sub %si,%cx # count
rep # Relocate
movsb # client
sub %di,%cx # Byte count
xorb %al,%al # Zero
rep # assumed
stosb # bss
xorb %al,%al # Zero assumed bss from
rep # the end of boot2.bin
stosb # up to 0x10000
callw seta20 # Enable A20
jmp start+MEM_JMP-MEM_ORG # Start BTX
# Enable A20
#
# Enable A20 so we can access memory above 1 meg.
#
seta20: cli # Disable interrupts
seta20.1: inb $0x64,%al # Get status
testb $0x2,%al # Busy?
@ -125,28 +179,31 @@ seta20.2: inb $0x64,%al # Get status
outb %al,$0x60 # A20
sti # Enable interrupts
retw # To caller
# Local read from disk
#
# 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
mov $msg_read,%si # Message
# Error exit
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
int $0x19 # BIOS: Reboot
# Display string
#
# Display a null-terminated string using the BIOS output.
#
putstr.0: mov $0x7,%bx # Page:attribute
movb $0xe,%ah # BIOS: Display
int $0x10 # character
@ -154,13 +211,25 @@ 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
# Read from disk
read: testb $0x80,%cs:MEM_REL+flags-start # LBA support enabled?
#
# 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
mov $0x55aa,%bx # Magic
push %dx # Save
@ -252,6 +321,6 @@ flags: .byte FLAGS # Flags
part4: .byte 0x80, 0x00, 0x01, 0x00
.byte 0xa5, 0xff, 0xff, 0xff
.byte 0x00, 0x00, 0x00, 0x00
.byte 0x50, 0xc3, 0x00, 0x00
.byte 0x50, 0xc3, 0x00, 0x00 # 50000 sectors long, bleh
.word 0xaa55 # Magic number

127
sys/boot/i386/boot2/boot1.s
View File

@ -15,6 +15,7 @@
# $FreeBSD$
# Memory Locations
.set MEM_REL,0x700 # Relocation address
.set MEM_ARG,0x900 # Arguments
.set MEM_ORG,0x7c00 # Origin
@ -22,11 +23,16 @@
.set MEM_BTX,0x9000 # BTX start
.set MEM_JMP,0x9010 # BTX entry point
.set MEM_USR,0xa000 # Client start
# 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
@ -37,11 +43,21 @@
start: jmp main # Start recognizably
.org 0x4,0x90
# External read from disk
#
# 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
@ -56,20 +72,37 @@ xread.1: # Starting
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.
#
# Bootstrap
#
# 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
@ -89,29 +122,50 @@ main.3: add $0x10,%si # Next entry
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 boot2.ldr, which is 0x200 bytes of zeros.
# 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 0xb000. Normally, BTX clients start at MEM_USR, or 0xa000, but
# when we use btxld create boot2, we use an entry point of 0x1000. That
# entry point is relative, to MEM_USR, thus boot2.bin starts at 0xb000.
#
main.5: mov %dx,MEM_ARG # Save args
movb $0x10,%dh # Sector count
callw nread # Read disk
mov $MEM_BTX,%bx # BTX
mov 0xa(%bx),%si # Point past
add %bx,%si # it
mov 0xa(%bx),%si # Get BTX length and set
add %bx,%si # %si to start of boot2.bin
mov $MEM_USR+SIZ_PAG,%di # Client page 1
mov $MEM_BTX+0xe*SIZ_SEC,%cx # Byte
sub %si,%cx # count
rep # Relocate
movsb # client
sub %di,%cx # Byte count
xorb %al,%al # Zero
rep # assumed
stosb # bss
xorb %al,%al # Zero assumed bss from
rep # the end of boot2.bin
stosb # up to 0x10000
callw seta20 # Enable A20
jmp start+MEM_JMP-MEM_ORG # Start BTX
# Enable A20
#
# Enable A20 so we can access memory above 1 meg.
#
seta20: cli # Disable interrupts
seta20.1: inb $0x64,%al # Get status
testb $0x2,%al # Busy?
@ -125,28 +179,31 @@ seta20.2: inb $0x64,%al # Get status
outb %al,$0x60 # A20
sti # Enable interrupts
retw # To caller
# Local read from disk
#
# 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
mov $msg_read,%si # Message
# Error exit
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
int $0x19 # BIOS: Reboot
# Display string
#
# Display a null-terminated string using the BIOS output.
#
putstr.0: mov $0x7,%bx # Page:attribute
movb $0xe,%ah # BIOS: Display
int $0x10 # character
@ -154,13 +211,25 @@ 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
# Read from disk
read: testb $0x80,%cs:MEM_REL+flags-start # LBA support enabled?
#
# 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
mov $0x55aa,%bx # Magic
push %dx # Save
@ -252,6 +321,6 @@ flags: .byte FLAGS # Flags
part4: .byte 0x80, 0x00, 0x01, 0x00
.byte 0xa5, 0xff, 0xff, 0xff
.byte 0x00, 0x00, 0x00, 0x00
.byte 0x50, 0xc3, 0x00, 0x00
.byte 0x50, 0xc3, 0x00, 0x00 # 50000 sectors long, bleh
.word 0xaa55 # Magic number