banan-os/bootloader/boot.S

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.code16
#########################################
#
# STAGE 1 BOOTLOADER
#
# its sole purpose is to load stage2 from
# bios boot partition
#
#########################################
.section .stage1
.global stage1_main
stage1_main:
# setup segments
movw $0, %ax
movw %ax, %ds
movw %ax, %es
# setup stack
movw %ax, %ss
movl $0x7C00, %esp
# save boot disk number
call read_stage2_into_memory
jmp stage2_main
.global print_and_halt
print_and_halt:
call puts
halt:
hlt
jmp halt
#########################################
#
# STAGE 2 BOOTLOADER
#
#########################################
.section .stage2
stage2_main:
# clear screen and enter 80x25 text mode
movb $0x03, %al
movb $0x00, %ah
int $0x10
# print hello message
movw $hello_msg, %si
call puts; call print_newline
call enter_unreal_mode
movw $unreal_enter_msg, %si
call puts; call print_newline
call get_memory_map
call read_user_command_line
call print_newline
movw $start_kernel_load_msg, %si
call puts; call print_newline
call print_memory_map
call find_root_disk
call find_root_partition
call print_root_partition_info
call print_newline
call has_ext2_filesystem
testb %al, %al
jz print_and_halt
call ext2_find_kernel
jmp halt
enter_unreal_mode:
cli
pushw %ds
lgdt gdtr
movl %cr0, %eax
orb $1, %al
movl %eax, %cr0
ljmpl $0x8, $.enter_unreal_mode_pmode
.enter_unreal_mode_pmode:
movw $0x10, %bx
movw %bx, %ds
andb 0xFE, %al
movl %eax, %cr0
ljmpl $0x0, $.enter_unreal_mode_unreal
.enter_unreal_mode_unreal:
popw %ds
sti
ret
hello_msg:
.asciz "This is banan-os bootloader"
unreal_enter_msg:
.asciz "Entered unreal mode"
start_kernel_load_msg:
.asciz "Starting to load kernel"
gdt:
.quad 0x0000000000000000
.quad 0x00009A000000FFFF
.quad 0x00CF92000000FFFF
gdtr:
.short . - gdt - 1
.quad gdt