; $Id: bootsec.asm,v 1.6 2002/04/25 21:00:41 reddawg Exp $
%include "gdtnasm.inc"
[ORG 0x7c00]
jmp start
nop
id db 'UbixFS' ;file system id
version dd 1h ; Filing System Version
fs_start dd 101 ; LBA address for start of root dir
krnl_size dd 59 ; Kernel size in sectors, starts at sector 1
BytesPerSector dw 512
SectorsPerTrack dw 18
TotalHeads dw 2
TotalSectors dd 2880 ; 1474560/512 for a 1.44meg disk
file_entry_nextdata equ 273 ; Offset in file_entry structure to the nextdata LBA pointer
data_entry_data equ 9 ; Offset in data_entry structure to the data
bootdrv db 0
start:
xor ax, ax
mov ds, ax
mov [bootdrv], dl
;mov al,0x13
;int 0x10
; First get into protected mode
cli
n5:
in al, 0x64 ;Enable A20 {4A} {5}
test al, 2
jnz n5
mov al, 0xD1
out 0x64, al
n6:
in al, 0x64
test al, 2
jnz n6
mov al, 0xDF
out 0x60, al
lgdt [gdtinfo] ;Load GDT
mov ecx, CR0 ;Switch to protected mode
inc cx
mov CR0, ecx
mov ax, flat_data-gdt_table ; Selector for 4Gb data seg
mov ds, ax ; {2} Extend limit for ds
mov es, ax ; Extend limit for es
mov fs, ax ; fs and...
mov gs, ax ; gs
dec cx ; switch back to real mode
mov CR0, ecx
sti
xor ax, ax
mov ds, ax
mov dl, [bootdrv]
mov bx, 0x60
mov es, bx
mov eax, 1
mov ecx, [krnl_size]
mov di, 1
load_loop:
call read_sectors
inc eax
mov bx, es
add bx, 32
mov es, bx
loop load_loop
; Turn off the floppy motor, its annoying leaving it on !
mov edx,0x3f2
mov al,0x0c
out dx,al
;lets convert the ELF file to a linear binary so we can execute it
cmp dword [0x600],464c457fh ; The ELF signature is \07fELF
jne ldr_ELF_err ; Ugh... not an ELF file !!!
cmp word [0x600+4],101h ; It should be statically linked etc.
jne ldr_ELF_err
cmp byte [0x600+6],1
jne ldr_ELF_err
jmp short skip_err_handler
ldr_ELF_err:
mov ax, 'E'+0x0E00
mov bx, 7
int 10h
mov al, 'L'
int 10h
mov al, 'F'
int 10h
cli
hlt
skip_err_handler:
mov eax, [0x600+18h]
mov [krnl_entry], eax
xor ecx,ecx ; Get the number of sections in cx
mov cx,[0x600+2ch]
sectionloop:
dec cx ; Next section
push cx ; Save cx on the stack while we load
; the section into memory
mov eax,[0x600+2ah] ; Get the program header entry size
mul cx ; Calculate the offset from the start
; of the program header table
mov ebx,[0x600+1ch] ; Get the PHT offset in ebx
add ebx,eax ; Add it to our PHT entry offset
add ebx,0x600 ; Calculate the address of the entry
cmp dword [bx],1 ; Does this section have to be
; loaded into memory ?
jne nextsect ; No, next section
mov dword ecx,[bx+4h] ; Get the offset of the segment in
; the ELF file
mov dword ebp,[bx+10h] ; Get the size of the segment in the
; ELF file
mov dword edi,[bx+8h] ; Get the memory address of the sect.
mov dword eax,[bx+14h] ; Get the size of the section in
mov ebx,eax ; the memory into ebx
; ds:dx = Address of ASCIIZ filename
; es:edi = Where in memory to put it
; ecx = Offset in file to start reading (bytes)
; ebp = Length of segment to read (bytes)
;
; Returns:
; eax = Length of file that was loaded
; eax = 0 if an error occured
push ebp
pusha
mov esi, 0x600
add esi, ecx
mov ecx, ebp
call memcopy
popa
pop eax
sub ebx,eax ; This amount needs to be zeroed
jz nextsect ; It's ok, next section
add edi,eax ; Zero the memory from this address
xor ax,ax ; edi is an absolute address
mov ecx,ebx
call zero_memblock ; Zero the rest of the section
nextsect:
pop cx ; Restore our section count
or cx,cx ; Was this the last one ?
jnz sectionloop
; Re-enter protected mode ! A20 is already enabled
cli ; No interrupts please at all
lgdt [gdtinfo]
mov ecx, cr0
inc cx
mov cr0, ecx
mov ax, flat_data-gdt_table
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
jmp dword (flat_code-gdt_table):pmode1
pmode1:
[BITS 32]
push dword 2
popfd
mov eax, [krnl_entry]
call eax
cli
hlt
;Hang the system..
hang: jmp hang
[BITS 16]
read_sectors:
; Input:
; EAX = LBN
; DI = sector count
; ES = segment
; Output:
; BL = low byte of ES
; EBX high half cleared
; DL = 0x80
; EDX high half cleared
; ESI = 0
pusha
cdq ;edx = 0
movzx ebx, byte [SectorsPerTrack]
div ebx ;EAX=track ;EDX=sector-1
mov cx, dx ;CL=sector-1 ;CH=0
inc cx ;CL=Sector number
xor dx, dx
mov bl, [TotalHeads]
div ebx
mov dh, dl ;Head
mov dl, [bootdrv] ;Drive 0
xchg ch, al ;CH=Low 8 bits of cylinder number; AL=0
shr ax, 2 ;AL[6:7]=High two bits of cylinder; AH=0
or cl, al ;CX = Cylinder and sector
mov ax, di ;AX = Maximum sectors to xfer
retry: mov ah, 2 ;Read
xor bx, bx
int 13h
jc retry
popa
ret
; zero_memblock: Fills the specified memory block with zeros (0x0)
;
; Takes parameters:
; ax = segment/selector of memory to be cleared
; edi = offset of memory to be cleared
; ecx = number of bytes to clear
;
; Returns:
; nothing
zero_memblock:
push eax ; Save the registers
push edi
push ecx
push es
mov es,ax
xor eax,eax ; Fill the memory with zeros (0x0)
cld ; Clear the direction flag; rep increments di
a32 rep stosb ; Fill the memory (one byte at a time)
pop es ; Restore the registers
pop ecx
pop edi
pop eax
ret ; Return to the main program
; Parameters
; DS:ESI = Source
; DS:EDI = Destination
; CX = length
memcopy:
pusha
memcopy_loop:
mov al, [esi]
mov [edi], al
inc edi
inc esi
loop memcopy_loop
popa
ret
print:
lodsb ; load next character
or al, al ; test for NUL character
jz .DONE
mov ah, 0x0E ; BIOS teletype
mov bh, 0x00 ; display page 0
mov bl, 0x07 ; text attribute
int 0x10 ; invoke BIOS
jmp print
.DONE:
ret
gdtinfo:
dw gdtlength
dd gdt_table
;********* GDT TABLE
gdt_table:
null_desc desc 0,0,0
flat_code desc 0, 0xFFFFF, D_CODE + D_READ + D_BIG + D_BIG_LIM
flat_data desc 0, 0xFFFFF, D_DATA + D_WRITE + D_BIG + D_BIG_LIM
gdtlength equ $ - gdt_table - 1
;********* END GDT TABLE
krnl_entry dd 0
bootMsg db 'Loading UbixOS' , 0x0D, 0x0A, 0x00
times 510-($-$$) db 0
dw 0xAA55
