1 files changed, 85 insertions, 0 deletions
diff --git a/libparted/mbr.s b/libparted/mbr.s
new file mode 100644
index 0000000..8ac2240
--- /dev/null
+++ b/libparted/mbr.s
@@ -0,0 +1,85 @@
+;   libparted - a library for manipulating disk partitions
+;   Copyright (C) 1999-2000, 2007, 2009-2014, 2019-2023 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