Bootloader: Split bootloader into multiple files

This cleans up the code since bootloader is starting to near 1k lines
This commit is contained in:
Bananymous 2023-11-14 03:26:03 +02:00
parent 055b1a2a1a
commit b0b39c56ba
7 changed files with 922 additions and 821 deletions

View File

@ -1,10 +1,3 @@
# FIXME: don't assume 512 byte sectors
.set SECTOR_SIZE_SHIFT, 9
.set SECTOR_SIZE, 1 << SECTOR_SIZE_SHIFT
.set SCREEN_WIDTH, 80
.set SCREEN_HEIGHT, 25
.code16
#########################################
@ -18,166 +11,7 @@
.section .stage1
stage1_start:
jmp stage1_main
# prints character to screen
# al: ascii character to print
putc:
pusha
movb $0x0E, %ah
movb $0x00, %bh
int $0x10
popa
ret
# prints null terminated string to screen
# ds:si: string address
puts:
pushw %si
pushw %bx
pushw %ax
movb $0x0E, %ah
movb $0x00, %bh
.puts_loop:
lodsb
test %al, %al
jz .puts_done
int $0x10
jmp .puts_loop
.puts_done:
popw %ax
popw %bx
popw %si
ret
# compares memory between addresses
# si: ptr1
# di: ptr2
# cx: bytes count
# return:
# al: 1 if equal, 0 otherwise
memcmp:
pushw %si
pushw %di
cld
repe cmpsb
setzb %al
popw %di
popw %si
ret
# read sectors from disk
# bx:eax: lba start
# cx: lba count (has to less than 0x80)
# dl: drive number
# ds:di: physical address
# returns only on success
read_from_disk:
push %ax
push %si
# prepare disk read packet
mov $disk_address_packet, %si
movb $0x10, 0x00(%si) # packet size
movb $0x00, 0x01(%si) # always 0
movw %cx, 0x02(%si) # lba count
movw %di, 0x04(%si) # offset
movw %ds, 0x06(%si) # segment
movl %eax, 0x08(%si) # 32 bit lower lba
movw %bx, 0x0C(%si) # 16 bit upper lba
movw $0, 0x0E(%si) # zero
# issue read command
clc
mov $0x42, %ah
int $0x13
jc .read_failed
pop %si
pop %ax
ret
# Validates that GPT header is valid and usable
# doesn't return on invalid header
validate_gpt_header:
# confirm header (starts with 'EFI PART')
cmpl $0x20494645, (gpt_header + 0)
jne .not_gpt_partition
cmpl $0x54524150, (gpt_header + 4)
jne .not_gpt_partition
ret
# Find partition entry with type guid
# si: address of type guid
# dl: drive number
# returns:
# al: non-zero if found
# di: address of partition entry
find_gpt_partition_entry:
# eax := entry_count
movl (gpt_header + 80), %eax
test %eax, %eax
jz .no_gpt_partition_found
# edx:eax := eax * entry_size
pushw %dx
mull (gpt_header + 84)
test %edx, %edx
jnz .too_gpt_big_entries
popw %dx
# FIXME: read one entry array section at a time
# sector count := (arr_size + SECTOR_SIZE - 1) / SECTOR_SIZE
movl %eax, %ecx
shrl $SECTOR_SIZE_SHIFT, %ecx
# start lba
movl (gpt_header + 72), %eax
movw (gpt_header + 76), %bx
movw $gpt_entry_data, %di
call read_from_disk
# NOTE: 'only' 0xFFFF partitions supported,
# although read will fail with more than 0x80
movw (gpt_header + 80), %cx
.loop_gpt_entries:
pushw %cx
movw $16, %cx
call memcmp
popw %cx
testb %al, %al
jnz .gpt_partition_found
# add entry size to entry pointer
addw (gpt_header + 84), %di
loop .loop_gpt_entries
.no_gpt_partition_found:
movb $0, %al
ret
.gpt_partition_found:
movb $1, %al
ret
.global stage1_main
stage1_main:
# setup segments
movw $0, %ax
@ -189,107 +23,17 @@ stage1_main:
movl $0x7C00, %esp
# save boot disk number
movb %dl, (boot_disk_number)
call read_stage2_into_memory
# FIXME: validate boot disk (needs size optizations)
# confirm that int 13h extensions are available
clc
movb $0x41, %ah
movw $0x55AA, %bx
movb (boot_disk_number), %dl
int $0x13
jc .no_int13h_ext
# read gpt header
movl $1, %eax
movw $0, %bx
movw $1, %cx
movb (boot_disk_number), %dl
movw $gpt_header, %di
call read_from_disk
call validate_gpt_header
movw $bios_boot_guid, %si
movb boot_disk_number, %dl
call find_gpt_partition_entry
testb %al, %al
jz .no_bios_boot_partition
# BIOS boot partiton found!
# first lba
movl 32(%di), %eax
movw $0, %bx
# count := last lba - first lba + 1
movl 40(%di), %ecx
subl %eax, %ecx
addl $1, %ecx
# calculate stage2 sector count
movw $((stage2_end - stage2_start + SECTOR_SIZE - 1) / SECTOR_SIZE), %cx
movb (boot_disk_number), %dl
movw $stage2_start, %di
call read_from_disk
jmp stage2_main
.global print_and_halt
print_and_halt:
call puts
halt:
hlt
jmp halt
.no_int13h_ext:
mov $no_int13_ext_msg, %si
jmp print_and_halt
.read_failed:
mov $read_failed_msg, %si
jmp print_and_halt
.not_gpt_partition:
mov $not_gpt_partition_msg, %si
jmp print_and_halt
.no_bios_boot_partition:
mov $no_bios_boot_partition_msg, %si
jmp print_and_halt
.too_gpt_big_entries:
mov $too_gpt_big_entries_msg, %si
jmp print_and_halt
# 21686148-6449-6E6F-744E-656564454649
bios_boot_guid:
.long 0x21686148 # little endian
.word 0x6449 # little endian
.word 0x6E6F # little endian
.word 0x4E74 # big endian
.quad 0x494645646565 # big endian
no_int13_ext_msg:
.asciz "no INT 13h ext"
read_failed_msg:
.asciz "read error"
not_gpt_partition_msg:
.asciz "not GPT"
no_bios_boot_partition_msg:
.asciz "no bios boot partition"
too_gpt_big_entries_msg:
.asciz "too big GPT array"
boot_disk_number:
.skip 1
#########################################
#
@ -299,477 +43,6 @@ boot_disk_number:
.section .stage2
stage2_start:
# read a character from keyboard
# return:
# al: ascii
# ah: bios scan code
getc:
movb $0x00, %ah
int $0x16
ret
# prints newline to screen
print_newline:
pushw %ax
movb $'\r', %al
call putc
movb $'\n', %al
call putc
pop %ax
ret
# prints backspace to screen, can go back a line
print_backspace:
pusha
# get cursor position
movb $0x03, %ah
movb $0x00, %bh
int $0x10
# don't do anyting if on first row
testb %dh, %dh
jz .print_backspace_done
# go one line up if on first column
test %dl, %dl
jz .print_backspace_go_line_up
# otherwise decrease column
decb %dl
jmp .print_backspace_do_print
.print_backspace_go_line_up:
# decrease row and set column to the last one
decb %dh
movb $(SCREEN_WIDTH - 1), %dl
.print_backspace_do_print:
# set cursor position
movb $0x02, %ah
int $0x10
# print 'empty' character (space)
mov $' ', %al
call putc
# set cursor position
movb $0x02, %ah
int $0x10
.print_backspace_done:
popa
ret
# print number to screen
# ax: number to print
# bx: number base
# cx: min width (zero pads if shorter)
printnum:
pusha
pushw %cx
movw $printnum_buffer, %si
xorw %cx, %cx
.printnum_fill_loop:
# fill buffer with all remainders ax % bx
xorw %dx, %dx
divw %bx
movb %dl, (%si)
incw %si
incw %cx
testw %ax, %ax
jnz .printnum_fill_loop
# check if zero pad is required
popw %dx
cmpw %cx, %dx
jbe .printnum_print_loop
xchgw %dx, %cx
subw %dx, %cx
movb $'0', %al
.printnum_pad_zeroes:
call putc
loop .printnum_pad_zeroes
movw %dx, %cx
.printnum_print_loop:
decw %si
movb (%si), %al
cmpb $10, %al
jae 1f
addb $'0', %al
jmp 2f
1: addb $('a' - 10), %al
2: call putc
loop .printnum_print_loop
popa
ret
# test if character is printable ascii
# al: character to test
# sets ZF if is printable
isprint:
cmpb $0x20, %al
jb .isprint_done
cmpb $0x7E, %al
ja .isprint_done
cmpb %al, %al
.isprint_done:
ret
# check if drive exists
# dl: drive number
# return:
# al: 1 if disk is usable, 0 otherwise
drive_exists:
pusha
movb $0x48, %ah
movw $disk_drive_parameters, %si
movw $0x1A, (disk_drive_parameters) # set buffer size
clc
int $0x13
jc .drive_exists_nope
popa
movb $1, %al
ret
.drive_exists_nope:
popa
movb $0, %al
ret
# fills memory map data structure
# doesn't return on error
# NO REGISTERS SAVED
get_memory_map:
movl $0, (memory_map_entry_count)
movl $0x0000E820, %eax
movl $0x534D4150, %edx
xorl %ebx, %ebx
movl $20, %ecx
movw $memory_map_entries, %di
clc
int $0x15
# If first call returs with CF set, the call failed
jc .get_memory_map_error
.get_memory_map_rest:
cmpl $0x534D4150, %eax
jne .get_memory_map_error
# FIXME: don't assume BIOS to always return 20 bytes
cmpl $20, %ecx
jne .get_memory_map_error
# increment entry count
incl (memory_map_entry_count)
# increment entry pointer
addw %cx, %di
# BIOS can indicate end of list by 0 in ebx
testl %ebx, %ebx
jz .get_memory_map_done
movl $0x0000E820, %eax
movl $0x534D4150, %edx
clc
int $0x15
# BIOS can indicate end of list by setting CF
jnc .get_memory_map_rest
.get_memory_map_done:
ret
.get_memory_map_error:
movw $memory_map_error_msg, %si
jmp print_and_halt
# fills command line buffer
# NO REGISTERS SAVED
get_command_line:
movw $command_line_enter_msg, %si
call puts
movw $command_line_buffer, %di
.get_command_line_loop:
call getc
cmpb $'\b', %al
je .get_command_line_backspace
# Not sure if some BIOSes return '\n' as enter, but check it just in case
cmpb $'\r', %al
je .get_command_line_done
cmpb $'\n', %al
je .get_command_line_done
call isprint
jnz .get_command_line_loop
# put byte to buffer
movb %al, (%di)
incw %di
# print byte
call putc
jmp .get_command_line_loop
.get_command_line_backspace:
# don't do anything if at the beginning
cmpw $command_line_buffer, %di
je .get_command_line_loop
# decrement buffer pointer
decw %di
# erase byte in display
call print_backspace
jmp .get_command_line_loop
.get_command_line_done:
# null terminate command line
movb $0, (%di)
call print_newline
ret
# print memory map from memory_map_entries
# NO REGISTERS SAVED
print_memory_map:
movw $memory_map_msg, %si
call puts
call print_newline
movl (memory_map_entry_count), %edx
movw $memory_map_entries, %si
movw $16, %bx
movw $4, %cx
.loop_memory_map:
movb $' ', %al
call putc
call putc
call putc
call putc
movw 0x06(%si), %ax
call printnum
movw 0x04(%si), %ax
call printnum
movw 0x02(%si), %ax
call printnum
movw 0x00(%si), %ax
call printnum
movb $',', %al
call putc
movb $' ', %al
call putc
movw 0x0E(%si), %ax
call printnum
movw 0x0C(%si), %ax
call printnum
movw 0x0A(%si), %ax
call printnum
movw 0x08(%si), %ax
call printnum
movb $',', %al
call putc
movb $' ', %al
call putc
movw 0x12(%si), %ax
call printnum
movw 0x10(%si), %ax
call printnum
call print_newline
addw $20, %si
decl %edx
jnz .loop_memory_map
ret
# find root disk and populate root_disk_drive_number field
# NO REGISTERS SAVED
find_root_disk:
movb $0x80, %dl
.find_root_disk_loop:
call drive_exists
testb %al, %al
jz .find_root_disk_not_found
# read GPT header
xorw %bx, %bx
movl $1, %eax
movw $1, %cx
movw $gpt_header, %di
call read_from_disk
# confirm header (starts with 'EFI PART')
cmpl $0x20494645, (gpt_header + 0)
jne .find_root_disk_next_disk
cmpl $0x54524150, (gpt_header + 4)
jne .find_root_disk_next_disk
# compare disk GUID
movw $root_disk_guid, %si
movw $(gpt_header + 56), %di
movw $16, %cx
call memcmp
testb %al, %al
jz .find_root_disk_next_disk
movb %dl, (root_disk_drive_number)
ret
.find_root_disk_next_disk:
incb %dl
jmp .find_root_disk_loop
.find_root_disk_not_found:
movw $no_root_disk_msg, %si
jmp print_and_halt
# finds root partition from root disk
# fills root_partition_entry data structure
# NOTE: assumes GPT header is in `gpt_header`
# NO REGISTERS SAVED
find_root_partition:
pushl %ebp
movl %esp, %ebp
subl $16, %esp
# esp + 0: 8 byte entry array lba
movl (gpt_header + 72), %eax
movl %eax, 0(%esp)
movl (gpt_header + 76), %eax
movl %eax, 4(%esp)
# FIXME: check that bits 48-63 are zero
# esp + 8: 4 byte entries per sector
xorl %edx, %edx
movl $SECTOR_SIZE, %eax
divl (gpt_header + 84)
movl %eax, 8(%esp)
# esp + 12: 4 byte entries remaining
movl (gpt_header + 80), %eax
testl %eax, %eax
jz .find_root_partition_not_found
movl %eax, 12(%esp)
.find_root_partition_read_entry_section:
movl 0(%esp), %eax
movl 4(%esp), %ebx
movw $1, %cx
movb (root_disk_drive_number), %dl
movw $sector_buffer, %di
call read_from_disk
# ecx: min(entries per section, entries remaining)
movl 8(%esp), %ecx
cmpl 12(%esp), %ecx
jae .find_root_partition_got_entry_count
movl 12(%esp), %ecx
.find_root_partition_got_entry_count:
# update entries remaining
subl %ecx, 12(%esp)
# si: entry pointer
movw $sector_buffer, %si
.find_root_partition_loop_entries:
# temporarily save cx in dx
movw %cx, %dx
# check that entry is used
movw $16, %cx
movw $zero_guid, %di
call memcmp
test %al, %al
jnz .find_root_partition_next_entry
# compare entry guid to root guid
movw $16, %cx
addw $16, %si
movw $root_partition_guid, %di
call memcmp
subw $16, %si
testb %al, %al
jnz .find_root_partition_found
.find_root_partition_next_entry:
# restore cx
movw %dx, %cx
# entry pointer += entry size
addw (gpt_header + 84), %si
loop .find_root_partition_loop_entries
# entry not found in this sector
# increment 8 byte entry array lba
incl 0(%esp)
jno .find_root_partition_no_overflow
incl 4(%esp)
.find_root_partition_no_overflow:
# loop to read next section if entries remaining
cmpl $0, 12(%esp)
jnz .find_root_partition_read_entry_section
.find_root_partition_not_found:
movw $no_root_partition_msg, %si
jmp print_and_halt
.find_root_partition_found:
# copy entry to buffer
movw $root_partition_entry, %di
movw $128, %cx
rep movsb
leavel
ret
stage2_main:
# clear screen and enter 80x25 text mode
movb $0x03, %al
@ -781,7 +54,7 @@ stage2_main:
call puts; call print_newline
call get_memory_map
call get_command_line
call read_user_command_line
call print_newline
@ -791,101 +64,14 @@ stage2_main:
call print_memory_map
call find_root_disk
movw $root_disk_found_msg, %si
call puts; call print_newline
call find_root_partition
movw $root_partition_found_msg, %si
call puts; call print_newline
movw $16, %bx
movw $2, %cx
movw (root_partition_entry + 38), %ax; call printnum
movw (root_partition_entry + 36), %ax; call printnum
movw (root_partition_entry + 34), %ax; call printnum
movw (root_partition_entry + 32), %ax; call printnum
movb $'-', %al; call putc
movb $'>', %al; call putc
movw (root_partition_entry + 46), %ax; call printnum
movw (root_partition_entry + 44), %ax; call printnum
movw (root_partition_entry + 42), %ax; call printnum
movw (root_partition_entry + 40), %ax; call printnum
call print_root_partition_info
jmp halt
# These will be patched during bootloader installation
root_disk_guid:
.ascii "root disk guid "
root_partition_guid:
.ascii "root part guid "
zero_guid:
.quad 0
.quad 0
hello_msg:
.asciz "This is banan-os bootloader"
command_line_msg:
command_line_enter_msg:
.asciz "cmdline: "
memory_map_msg:
.asciz "memmap:"
memory_map_error_msg:
.asciz "Failed to get memory map"
start_kernel_load_msg:
.asciz "Starting to load kernel"
root_disk_found_msg:
.asciz "Root disk found!"
no_root_disk_msg:
.asciz "Root disk not found"
root_partition_found_msg:
.asciz "Root partition found!"
no_root_partition_msg:
.asciz "Root partition not found"
stage2_end:
.section .bss
.align SECTOR_SIZE
gpt_header:
.skip SECTOR_SIZE
gpt_entry_data:
.skip SECTOR_SIZE
sector_buffer:
.skip SECTOR_SIZE
disk_drive_parameters:
.skip 0x1A
disk_address_packet:
.skip 16
printnum_buffer:
.skip 10
root_disk_drive_number:
.skip 1
root_partition_entry:
.skip 128
memory_map_entry_count:
.skip 4
# 100 entries should be enough...
memory_map_entries:
.skip 20 * 100
# 100 character command line
command_line_buffer:
.skip 100

69
bootloader/command_line.S Normal file
View File

@ -0,0 +1,69 @@
.code16
.section .stage2
# fills command line buffer
# NO REGISTERS SAVED
.global read_user_command_line
read_user_command_line:
movw $command_line_enter_msg, %si
call puts
movw $command_line_buffer, %di
.read_user_command_line_loop:
call getc
cmpb $'\b', %al
je .read_user_command_line_backspace
# Not sure if some BIOSes return '\n' as enter, but check it just in case
cmpb $'\r', %al
je .read_user_command_line_done
cmpb $'\n', %al
je .read_user_command_line_done
call isprint
testb %al, %al
jnz .read_user_command_line_loop
# put byte to buffer
movb %al, (%di)
incw %di
# print byte
call putc
jmp .read_user_command_line_loop
.read_user_command_line_backspace:
# don't do anything if at the beginning
cmpw $command_line_buffer, %di
je .read_user_command_line_loop
# decrement buffer pointer
decw %di
# erase byte in display
call print_backspace
jmp .read_user_command_line_loop
.read_user_command_line_done:
# null terminate command line
movb $0, (%di)
call print_newline
ret
command_line_enter_msg:
.asciz "cmdline: "
.section .bss
# 100 character command line
command_line_buffer:
.skip 100

491
bootloader/disk.S Normal file
View File

@ -0,0 +1,491 @@
# FIXME: don't assume 512 byte sectors
.set SECTOR_SIZE_SHIFT, 9
.set SECTOR_SIZE, 1 << SECTOR_SIZE_SHIFT
.code16
.section .stage1
.global stage2_start
.global stage2_end
# check that drive has int13 ext
# dl: drive number
# returns only if drive does have the extension
drive_has_int13_ext:
pusha
movb $0x41, %ah
movw $0x55AA, %bx
int $0x13
jc .drive_has_int13_ext_no_int13_ext
popa
ret
.drive_has_int13_ext_no_int13_ext:
mov $no_int13_ext_msg, %si
jmp print_and_halt
# read sectors from disk
# bx:eax: lba start
# cx: lba count (has to less than 0x80)
# dl: drive number
# ds:di: physical address
# returns only on success
.global read_from_disk
read_from_disk:
pusha
call drive_has_int13_ext
# prepare disk read packet
mov $disk_address_packet, %si
movb $0x10, 0x00(%si) # packet size
movb $0x00, 0x01(%si) # always 0
movw %cx, 0x02(%si) # lba count
movw %di, 0x04(%si) # offset
movw %ds, 0x06(%si) # segment
movl %eax, 0x08(%si) # 32 bit lower lba
movw %bx, 0x0C(%si) # 16 bit upper lba
movw $0, 0x0E(%si) # zero
# issue read command
mov $0x42, %ah
int $0x13
jc .read_from_disk_failed
popa
ret
.read_from_disk_failed:
mov $read_from_disk_msg, %si
jmp print_and_halt
# Reads GPT header into gpt_header buffer
# dl: drive number
# return:
# ax: 1 if has GPT header, 0 otherwise
.global read_gpt_header
read_gpt_header:
pushw %bx
pushw %cx
pushw %di
xorw %bx, %bx
movl $1, %eax
movw $1, %cx
movw $gpt_header, %di
call read_from_disk
xorw %bx, %bx
movw $1, %ax
# check if header starts with 'EFI PART'
cmpl $0x20494645, (gpt_header + 0)
cmovnew %bx, %ax
cmpl $0x54524150, (gpt_header + 4)
cmovnew %bx, %ax
popw %di
popw %cx
popw %bx
ret
# Find bios boot partition from boot drive
# returns:
# bx:eax: first lba
# cx: sector count
find_stage2_partition:
# read boot disk GPT header
movb (boot_disk_number), %dl
call read_gpt_header
testb %al, %al
jz .find_stage2_partition_not_gpt
# eax := entry_count
movl (gpt_header + 80), %eax
test %eax, %eax
jz .find_stage2_partition_not_found
# edx:eax := eax * entry_size
mull (gpt_header + 84)
test %edx, %edx
jnz .find_stage2_partition_too_big_entries
# FIXME: read one entry array section at a time
# sector count := (arr_size + SECTOR_SIZE - 1) / SECTOR_SIZE
movl %eax, %ecx
shrl $SECTOR_SIZE_SHIFT, %ecx
# start lba
movl (gpt_header + 72), %eax
movw (gpt_header + 76), %bx
movw $gpt_entry_data, %di
movw $bios_boot_guid, %si
movb (boot_disk_number), %dl
call read_from_disk
# NOTE: 'only' 0xFFFF partitions supported,
# although read will fail with more than 0x80
movw (gpt_header + 80), %cx
.find_stage2_partition_loop_gpt_entries:
pushw %cx
movw $16, %cx
call memcmp
popw %cx
testb %al, %al
jnz .find_stage2_partition_found
# add entry size to entry pointer
addw (gpt_header + 84), %di
loop .find_stage2_partition_loop_gpt_entries
# fall through to not found case
.find_stage2_partition_not_found:
movw $no_bios_boot_partition_msg, %si
jmp print_and_halt
.find_stage2_partition_not_gpt:
movw $not_gpt_partition_msg, %si
jmp print_and_halt
.find_stage2_partition_too_big_entries:
movw $too_gpt_big_entries_msg, %si
jmp print_and_halt
.find_stage2_partition_found:
# first lba
movl 32(%di), %eax
movw 36(%di), %bx
# count := last lba - first lba + 1
movl 40(%di), %ecx
subl %eax, %ecx
incl %ecx
ret
# reads stage2 into memory
# dl: boot drive number
# returns only on success
.global read_stage2_into_memory
read_stage2_into_memory:
movb %dl, (boot_disk_number)
# push stage2 sector count
movl $stage2_end, %eax
subl $stage2_start, %eax
addl $(SECTOR_SIZE - 1), %eax
movl $SECTOR_SIZE, %ecx
xorl %edx, %edx
divl %ecx
pushl %eax
call find_stage2_partition
movb (boot_disk_number), %dl
popl %ecx # FIXME: validate that partition has enough sectors
movw $stage2_start, %di
call read_from_disk
ret
# 21686148-6449-6E6F-744E-656564454649
.align 4
bios_boot_guid:
.long 0x21686148 # little endian
.word 0x6449 # little endian
.word 0x6E6F # little endian
.word 0x4E74 # big endian
.quad 0x494645646565 # big endian
boot_disk_number:
.skip 1
read_from_disk_msg:
.asciz "read error"
no_int13_ext_msg:
.asciz "no INT13 ext"
no_bios_boot_partition_msg:
.asciz "no bios boot"
too_gpt_big_entries_msg:
.asciz "too big GPT array"
not_gpt_partition_msg:
.asciz "not GPT"
.section .stage2
# check if drive exists
# dl: drive number
# return:
# al: 1 if disk is usable, 0 otherwise
drive_exists:
pusha
movb $0x48, %ah
movw $disk_drive_parameters, %si
movw $0x1A, (disk_drive_parameters) # set buffer size
int $0x13
jc .drive_exists_nope
popa
movb $1, %al
ret
.drive_exists_nope:
popa
movb $0, %al
ret
# find root disk and populate root_disk_drive_number field
# NO REGISTERS SAVED
.global find_root_disk
find_root_disk:
movb $0x80, %dl
.find_root_disk_loop:
call drive_exists
testb %al, %al
jz .find_root_disk_not_found
# read GPT header
xorw %bx, %bx
movl $1, %eax
movw $1, %cx
movw $gpt_header, %di
call read_from_disk
# confirm header (starts with 'EFI PART')
cmpl $0x20494645, (gpt_header + 0)
jne .find_root_disk_next_disk
cmpl $0x54524150, (gpt_header + 4)
jne .find_root_disk_next_disk
# compare disk GUID
movw $root_disk_guid, %si
movw $(gpt_header + 56), %di
movw $16, %cx
call memcmp
testb %al, %al
jz .find_root_disk_next_disk
movw $root_disk_found_msg, %si
call puts; call print_newline
movb %dl, (root_disk_drive_number)
ret
.find_root_disk_next_disk:
incb %dl
jmp .find_root_disk_loop
.find_root_disk_not_found:
movw $root_disk_not_found_msg, %si
jmp print_and_halt
# finds root partition from root disk
# fills root_partition_entry data structure
# NOTE: assumes GPT header is in `gpt_header`
# NO REGISTERS SAVED
.global find_root_partition
find_root_partition:
pushl %ebp
movl %esp, %ebp
subl $16, %esp
# esp + 0: 8 byte entry array lba
movl (gpt_header + 72), %eax
movl %eax, 0(%esp)
movl (gpt_header + 76), %eax
movl %eax, 4(%esp)
# FIXME: check that bits 48-63 are zero
# esp + 8: 4 byte entries per sector
xorl %edx, %edx
movl $SECTOR_SIZE, %eax
divl (gpt_header + 84)
movl %eax, 8(%esp)
# esp + 12: 4 byte entries remaining
movl (gpt_header + 80), %eax
testl %eax, %eax
jz .find_root_partition_not_found
movl %eax, 12(%esp)
.find_root_partition_read_entry_section:
movl 0(%esp), %eax
movl 4(%esp), %ebx
movw $1, %cx
movb (root_disk_drive_number), %dl
movw $sector_buffer, %di
call read_from_disk
# ecx: min(entries per section, entries remaining)
movl 8(%esp), %ecx
cmpl 12(%esp), %ecx
jae .find_root_partition_got_entry_count
movl 12(%esp), %ecx
.find_root_partition_got_entry_count:
# update entries remaining
subl %ecx, 12(%esp)
# si: entry pointer
movw $sector_buffer, %si
.find_root_partition_loop_entries:
# temporarily save cx in dx
movw %cx, %dx
# check that entry is used
movw $16, %cx
movw $zero_guid, %di
call memcmp
test %al, %al
jnz .find_root_partition_next_entry
# compare entry guid to root guid
movw $16, %cx
addw $16, %si
movw $root_partition_guid, %di
call memcmp
subw $16, %si
testb %al, %al
jnz .find_root_partition_found
.find_root_partition_next_entry:
# restore cx
movw %dx, %cx
# entry pointer += entry size
addw (gpt_header + 84), %si
loop .find_root_partition_loop_entries
# entry not found in this sector
# increment 8 byte entry array lba
incl 0(%esp)
jno .find_root_partition_no_overflow
incl 4(%esp)
.find_root_partition_no_overflow:
# loop to read next section if entries remaining
cmpl $0, 12(%esp)
jnz .find_root_partition_read_entry_section
.find_root_partition_not_found:
movw $root_partition_not_found_msg, %si
jmp print_and_halt
.find_root_partition_found:
# copy entry to buffer
movw $root_partition_entry, %di
movw $128, %cx
rep movsb
movw $root_partition_found_msg, %si
call puts; call print_newline
leavel
ret
# print information about root partition
.global print_root_partition_info
print_root_partition_info:
pushw %ax
pushw %bx
pushw %cx
pushw %si
movw $root_partition_info_start_msg, %si
call puts;
movw $16, %bx
movw $2, %cx
movw (root_partition_entry + 38), %ax; call print_number
movw (root_partition_entry + 36), %ax; call print_number
movw (root_partition_entry + 34), %ax; call print_number
movw (root_partition_entry + 32), %ax; call print_number
movb $'-', %al; call putc
movb $'>', %al; call putc
movw (root_partition_entry + 46), %ax; call print_number
movw (root_partition_entry + 44), %ax; call print_number
movw (root_partition_entry + 42), %ax; call print_number
movw (root_partition_entry + 40), %ax; call print_number
call print_newline
popw %si
popw %cx
popw %bx
popw %ax
ret
# These will be patched during bootloader installation
root_disk_guid:
.ascii "root disk guid "
root_partition_guid:
.ascii "root part guid "
zero_guid:
.skip 16, 0
root_disk_found_msg:
.asciz "Root disk found!"
root_disk_not_found_msg:
.asciz "Root disk not found"
root_partition_found_msg:
.asciz "Root partition found!"
root_partition_not_found_msg:
.asciz "Root partition not found"
root_partition_info_start_msg:
.asciz "Root partition: "
.section .bss
.align SECTOR_SIZE
gpt_header:
.skip SECTOR_SIZE
gpt_entry_data:
.skip SECTOR_SIZE
sector_buffer:
.skip SECTOR_SIZE
disk_address_packet:
.skip 16
disk_drive_parameters:
.skip 0x1A
.skip 2 # padding
root_disk_drive_number:
.skip 1
.skip 3 # padding
root_partition_entry:
.skip 128

View File

@ -30,10 +30,14 @@ make
mkdir -p $BUILD_DIR
echo compiling bootloader
x86_64-banan_os-as $CURRENT_DIR/boot.S -o $BUILD_DIR/bootloader.o
x86_64-banan_os-as $CURRENT_DIR/boot.S -o $BUILD_DIR/boot.o
x86_64-banan_os-as $CURRENT_DIR/command_line.S -o $BUILD_DIR/command_line.o
x86_64-banan_os-as $CURRENT_DIR/disk.S -o $BUILD_DIR/disk.o
x86_64-banan_os-as $CURRENT_DIR/memory_map.S -o $BUILD_DIR/memory_map.o
x86_64-banan_os-as $CURRENT_DIR/utils.S -o $BUILD_DIR/utils.o
echo linking bootloader
x86_64-banan_os-ld -nostdlib -T $CURRENT_DIR/linker.ld $BUILD_DIR/bootloader.o -o $BUILD_DIR/bootloader
x86_64-banan_os-ld -nostdlib -T $CURRENT_DIR/linker.ld $BUILD_DIR/boot.o $BUILD_DIR/command_line.o $BUILD_DIR/disk.o $BUILD_DIR/memory_map.o $BUILD_DIR/utils.o -o $BUILD_DIR/bootloader
echo installing bootloader to
$INSTALLER_BUILD_DIR/x86_64-banan_os-bootloader-installer $BUILD_DIR/bootloader $BANAN_DISK_IMAGE_PATH $ROOT_PARTITION_GUID

View File

@ -1,10 +1,14 @@
ENTRY(stage1_main)
SECTIONS
{
. = 0x7C00;
.stage1 : { *(.stage1) }
. = ALIGN(512);
stage2_start = .;
.stage2 : { *(.stage2) }
stage2_end = .;
. = ALIGN(512);
.bss : { *(.bss) }

129
bootloader/memory_map.S Normal file
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@ -0,0 +1,129 @@
.code16
.section .stage2
# fills memory map data structure
# doesn't return on error
# NO REGISTERS SAVED
.global get_memory_map
get_memory_map:
movl $0, (memory_map_entry_count)
movl $0x0000E820, %eax
movl $0x534D4150, %edx
xorl %ebx, %ebx
movl $20, %ecx
movw $memory_map_entries, %di
clc
int $0x15
# If first call returs with CF set, the call failed
jc .get_memory_map_error
.get_memory_map_rest:
cmpl $0x534D4150, %eax
jne .get_memory_map_error
# FIXME: don't assume BIOS to always return 20 bytes
cmpl $20, %ecx
jne .get_memory_map_error
# increment entry count
incl (memory_map_entry_count)
# increment entry pointer
addw %cx, %di
# BIOS can indicate end of list by 0 in ebx
testl %ebx, %ebx
jz .get_memory_map_done
movl $0x0000E820, %eax
movl $0x534D4150, %edx
clc
int $0x15
# BIOS can indicate end of list by setting CF
jnc .get_memory_map_rest
.get_memory_map_done:
ret
.get_memory_map_error:
movw $memory_map_error_msg, %si
jmp print_and_halt
# print memory map from memory_map_entries
# NO REGISTERS SAVED
.global print_memory_map
print_memory_map:
movw $memory_map_msg, %si
call puts
call print_newline
movl (memory_map_entry_count), %edx
movw $memory_map_entries, %si
movw $16, %bx
movw $4, %cx
.loop_memory_map:
movb $' ', %al
call putc; call putc; call putc; call putc
movw 0x06(%si), %ax
call print_number
movw 0x04(%si), %ax
call print_number
movw 0x02(%si), %ax
call print_number
movw 0x00(%si), %ax
call print_number
movb $',', %al
call putc
movb $' ', %al
call putc
movw 0x0E(%si), %ax
call print_number
movw 0x0C(%si), %ax
call print_number
movw 0x0A(%si), %ax
call print_number
movw 0x08(%si), %ax
call print_number
movb $',', %al
call putc
movb $' ', %al
call putc
movw 0x12(%si), %ax
call print_number
movw 0x10(%si), %ax
call print_number
call print_newline
addw $20, %si
decl %edx
jnz .loop_memory_map
ret
memory_map_msg:
.asciz "memmap:"
memory_map_error_msg:
.asciz "Failed to get memory map"
.section .bss
memory_map_entry_count:
.skip 4
# 100 entries should be enough...
memory_map_entries:
.skip 20 * 100

218
bootloader/utils.S Normal file
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@ -0,0 +1,218 @@
.set SCREEN_WIDTH, 80
.set SCREEN_HEIGHT, 25
.code16
.section .stage1
# prints character to screen
# al: ascii character to print
.global putc
putc:
pushw %ax
pushw %bx
movb $0x0E, %ah
xorb %bh, %bh
int $0x10
popw %bx
popw %ax
ret
# prints null terminated string to screen
# ds:si: string address
.global puts
puts:
pushw %si
pushw %bx
pushw %ax
movb $0x0E, %ah
xorb %bh, %bh
.puts_loop:
lodsb
test %al, %al
jz .puts_done
int $0x10
jmp .puts_loop
.puts_done:
popw %ax
popw %bx
popw %si
ret
# compares memory between addresses
# si: ptr1
# di: ptr2
# cx: bytes count
# return:
# al: 1 if equal, 0 otherwise
.global memcmp
memcmp:
# NOTE: using pusha + popa to save space
pusha
cld
repe cmpsb
popa
setzb %al
ret
.section .stage2
# read a character from keyboard
# return:
# al: ascii
# ah: bios scan code
.global getc
getc:
movb $0x00, %ah
int $0x16
ret
# prints newline to screen
.global print_newline
print_newline:
pushw %ax
movb $'\r', %al
call putc
movb $'\n', %al
call putc
pop %ax
ret
# prints backspace to screen, can go back a line
.global print_backspace
print_backspace:
pushw %ax
pushw %bx
pushw %cx
pushw %dx
# get cursor position
movb $0x03, %ah
movb $0x00, %bh
int $0x10
# don't do anyting if on first row
testb %dh, %dh
jz .print_backspace_done
# go one line up if on first column
test %dl, %dl
jz .print_backspace_go_line_up
# otherwise decrease column
decb %dl
jmp .print_backspace_do_print
.print_backspace_go_line_up:
# decrease row and set column to the last one
decb %dh
movb $(SCREEN_WIDTH - 1), %dl
.print_backspace_do_print:
# set cursor position
movb $0x02, %ah
int $0x10
# print 'empty' character (space)
mov $' ', %al
call putc
# set cursor position
movb $0x02, %ah
int $0x10
.print_backspace_done:
popw %dx
popw %cx
popw %bx
popw %ax
ret
# print number to screen
# ax: number to print
# bx: number base
# cx: min width (zero pads if shorter)
.global print_number
print_number:
pusha
pushl %ebp
movl %esp, %ebp
# save min width
subl $4, %esp
movw %cx, (%esp)
movw $print_number_buffer, %si
xorw %cx, %cx
.print_number_fill_loop:
# fill buffer with all remainders ax % bx
xorw %dx, %dx
divw %bx
movb %dl, (%si)
incw %si
incw %cx
testw %ax, %ax
jnz .print_number_fill_loop
# check if zero pad is required
cmpw (%esp), %cx
jae .print_number_print_loop
# dx: saved number count
# cx: zero pad count
movw %cx, %dx
movw (%esp), %cx
subw %dx, %cx
movb $'0', %al
.print_number_pad_zeroes:
call putc
loop .print_number_pad_zeroes
# restore number count
movw %dx, %cx
.print_number_print_loop:
decw %si
movb (%si), %al
cmpb $10, %al
jae .print_number_hex
addb $'0', %al
jmp .print_number_do_print
.print_number_hex:
addb $('a' - 10), %al
.print_number_do_print:
call putc
loop .print_number_print_loop
leavel
popa
ret
# test if character is printable ascii
# al: character to test
# return:
# al: 1 if is printable, 0 otherwise
.global isprint
isprint:
subb $0x20, %al
cmpb $(0x7E - 0x20), %al
ja .isprint_not_printable
movb $1, %al
ret
.isprint_not_printable:
movb $0, %al
ret
.section .bss
# enough for base 2 printing
print_number_buffer:
.skip 16