banan-os/bootloader/bios/boot.S

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.include "common.S"
.code16
#########################################
#
# STAGE 1 BOOTLOADER
#
# its sole purpose is to load stage2 from
# bios boot partition
#
#########################################
.section .stage1
.global stage1_main
stage1_main:
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# setup segments and stack
xorw %ax, %ax
movw %ax, %ds
movw %ax, %es
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
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lgdt gdtr
call enter_unreal_mode
movw $unreal_enter_msg, %si
call puts; call print_newline
call enable_a20
call get_memory_map
call print_newline
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
movl $ext2_inode_read_bytes, %esi
call elf_read_kernel_to_memory
call vesa_set_video_mode
cli
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# kernel entry point
movl %eax, %ecx
# setup kernel parameters
movl $0xD3C60CFF, %eax
movl $banan_boot_info, %ebx
# setup protected mode
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movl %cr0, %edx
orb $1, %dl
movl %edx, %cr0
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# jump to protected mode
ljmpl $GDT_CODE32, $protected_mode
.code32
protected_mode:
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# setup protected mode segments
movw $GDT_DATA32, %dx
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movw %dx, %ds
movw %dx, %es
movw %dx, %fs
movw %dx, %gs
movw %dx, %ss
# jump to kernel entry
jmp *%ecx
.code16
enter_unreal_mode:
cli
pushw %ds
movl %cr0, %eax
orb $1, %al
movl %eax, %cr0
ljmpl $GDT_CODE16, $.enter_unreal_mode_pmode
.enter_unreal_mode_pmode:
movw $GDT_DATA32, %bx
movw %bx, %ds
andb $0xFE, %al
movl %eax, %cr0
ljmpl $0x00, $.enter_unreal_mode_unreal
.enter_unreal_mode_unreal:
popw %ds
sti
ret
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.section .data
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
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.quad 0x008F9A000000FFFF # 16-bit code
.quad 0x00CF92000000FFFF # 32-bit data
.quad 0x00CF9A000000FFFF # 32-bit code
gdtr:
.short . - gdt - 1
.long gdt
banan_boot_info:
boot_command_line:
.long command_line
boot_framebuffer:
.long framebuffer
boot_memory_map:
.long memory_map