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; libparted - a library for manipulating disk partitions
; Copyright (C) 1999-2000, 2007, 2009-2014, 2019-2022 Free Software
; Foundation, Inc.
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 3 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program. If not, see <http://www.gnu.org/licenses/>.
; NOTE: I build this with:
; $ as86 -b /dev/stdout mbr.s | hexdump -e '8/1 "0x%02x, " "\n"'
;
; The build isn't done automagically by make, because as86 may not be on many
; machines (particularly non-x86). Also, it seems rather difficult to get
; as86 to build object files that can be linked, especially as it's 16 bit
; code...
USE16
; This code, plus the partition table is loaded into 0000:7C00 by the BIOS
.text
; set top of stack to 1000:B000
cli
mov ax, #0x1000
mov ss, ax
mov sp, #0xB000
mov ax, #0x0000
mov ds, ax
mov es, ax
sti
; Copy what the BIOS loaded (i.e. the MBR + head of partition table) from
; 0000:7c00 to 0000:0600
mov si, #0x7c00
mov di, #0x0600
mov cx, #0x200
rep
movsb
; Jump to the copy of the MBR
jmp 0x0000:find_boot_partition + 0x0600
find_boot_partition:
mov si, #0x07BE
check_next_bootable:
cmp [si], al
jnz found_bootable
add si, #0x0010
cmp si, #0x07FE
jnz check_next_bootable
jmp error
found_bootable:
; Load in the boot sector at 0000:7c00
mov ah, #2 ; BIOS command (read)
mov al, #1 ; count
mov bx, #0x7c00 ; destination pointer
mov dl, #0x80 ; drive
mov dh, byte ptr [si + 1] ; head
mov cx, word ptr [si + 2] ; sector / cylinder
int #0x13 ; BIOS read interrupt
jmp 0x0000:0x7c00 ; hand control to boot sector
error:
jmp error
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