StupidOS/boot/loader/loader.asm

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;; File: loader.asm
format binary
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include '../common/const.inc'
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include '../common/macro.inc'
include 'multiboot.inc'
org LOADER_BASE
use32
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jmp _start
align 4
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multiboot_header:
mb_header MultibootHeader multiboot_header
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;; Function: _start
;; Loader entry point.
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_start:
cmp eax, MULTIBOOT_MAGIC
je multiboot
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use16
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align 2
; =========================================================================
; real mode code
; =========================================================================
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push cs
pop ds
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mov [uDrive], dl
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mov si, szMsgStage2
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call bios_log
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; enable A20 line
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call a20_enable
jc .error_a20
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; check drive type
; dl <= 0x7F == floppy
; dl >= 0x80 == hard drive
; dl == 0xE0 ~= CD/DVD
; dl <= 0xFF == hard drive
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mov dl, [uDrive]
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cmp dl, 0x7F
; skip disk extension check
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jle @f
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; check disk extensions
mov ah, 0x41
mov bx, 0x55AA
int 0x13
jc @f
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mov [bDriveLBA], TRUE
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@@:
; detect filesystem (FAT12/16 or StpdFS)
; load kernel from filesystem
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; StupidFS layout
; +---------+---------+---------....--+----....---+
; | bootsec | stpd sb | i-nodes ... | data |
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; +---------+---------+---------....--+----....---+
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; 0 512 1024 XXXX XXXX
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;
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; for now fat12 is asumed
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call fat_load_root
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mov si, szKernelFile
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call fat_search_root
jc .error_not_found
mov [pKernelStartFat], ax
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mov [uKernelSize], ebx
push ebx
mov si, szMsgKernelFound
call bios_log
; load fat
xor ax, ax
mov al, [FAT_count]
mul word [sectors_per_FAT]
mov cx, ax
mov ax, [reserved_sectors]
xor bx, bx
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call disk_read_sectors
; load stage 2
mov ax, KERNEL_PRELOAD/0x10
mov es, ax
mov ax, [pKernelStartFat]
xor bx, bx
call fat_load_binary
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; fetch memory map from bios
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call memory_get_map
jc .error_memory
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call boot_info_print_mmap
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; video information
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;call video_setup
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; load GDT and enter Protected-Mode
lgdt [gdt_ptr]
; enable protected mode
mov eax, cr0
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or al, CR0_PE
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mov cr0, eax
; reload ds, es, fs, gs, ss
mov ax, 0x10
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
jmp 0x8:common32
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.error_not_found:
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mov si, szMsgErrorNotFound
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jmp .error
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.error_memory:
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mov si, szMsgErrorMemory
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jmp .error
.error_a20:
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mov si, szMsgErrorA20
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.error:
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call bios_log
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@@:
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hlt
jmp @b
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include 'a20.inc'
include '../common/bios.inc'
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include '../common/fat12.inc'
include 'disk.inc'
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include 'logger.inc'
include 'memory.inc'
include 'video.inc'
include 'gdt.inc'
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include '../common/bootinfo.inc'
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include '../../kernel/sys/register.inc'
include '../../kernel/sys/mmu.inc'
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uDrive rb 1
bDriveLBA db FALSE
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pKernelStartFat dw 0
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uKernelSize dd 0
szMsgStage2 db "StupidOS Loader", 0
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szKernelFile db "VMSTUPIDSYS", 0
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szMsgKernelFound db "Kernel found, size: %x", 0
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szMsgErrorA20 db "ERROR: can't enable a20 line", 0
szMsgErrorMemory db "ERROR: can't detect available memory", 0
szMsgErrorSector db "ERROR: reading sector", CR, LF, 0
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szMsgErrorNotFound db "ERROR: kernel not found", 0
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use32
; =========================================================================
; protected mode code
; =========================================================================
multiboot:
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; https://www.gnu.org/software/grub/manual/multiboot/multiboot.html#Machine-state
; get screen information
; get memory map
; get kernel from module
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common32:
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mov [0xB8000], dword 0x07690748
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; move kernel to 0x100000
mov ecx, [uKernelSize]
mov esi, KERNEL_PRELOAD
mov edi, KERNEL_BASE
rep movsb
; identity map first 1MB
xor esi, esi
xor ecx, ecx
mov edi, boot_0_page_table
@@:
mov edx, esi
or edx, (PTE_P or PTE_W)
mov [edi], edx
add edi, 4
add esi, 4096
inc ecx
cmp ecx, 1024
jb @b
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mov dword [boot_page_directory], boot_0_page_table + (PDE_P or PDE_W) ; preset and writable
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mov dword [boot_page_directory + (768 * 4)], boot_0_page_table + (PDE_P or PDE_W)
mov eax, boot_page_directory
mov cr3, eax
mov eax, cr0
or eax, (CR0_PG or CR0_WP)
mov cr0, eax
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mov eax, STPDBOOT_MAGIC
mov ebx, boot_structure
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mov ecx, 0xC0000000 + KERNEL_BASE
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jmp ecx
hang:
hlt
jmp $
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_edata:
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boot_structure BootInfo
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align 4096
boot_page_directory:
rb 4096
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boot_0_page_table:
rb 4096
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_end: