grldrstart.s

grub4dos-0.4.4-2008- 08-src.zip

	#;// booted from no-emulation-mode bootable CDROM
	#;movb	$0xff, %dh	// partition 0xff means whole drive(for CDROM)
	#;			#; if needed, 0xfe can be used as an indicator
	#;			#; here for the bootable CDROM and changed to
	#;			#; 0xff later.
	#;1:
	#;
	#;//if not booted from CDROM, don't touch the boot partition number(dh)

	cli
	xorw	%ax, %ax
	movw	%ax, %ss
	movw	$0x0400, %sp	/* tmp use real-mode IDT as stack */
	movw	%cs, %bp	/* save CS to BP */
	call	1f
1:
	popw	%bx		/* BX=Instruction Pointer of 1b */
	subw	$(1b - _start1), %bx
	movw	%bx, %cx
	shrw	$4, %bx
	addw	%bp, %bx
	pushw	%bx		/* new CS */
	andw	$0x000f, %cx
	addw	$(1f - _start1), %cx
	pushw	%cx		/* new IP */
	lret
1:
	pushw	%cs
	popw	%ds

	/* CS=DS=BX, CS:0000 = _start1 */

	addw	$((pre_stage2_start - _start1) >> 4), %bx

	/* BX:0000 = pre_stage2_start */

	cmpw	$0x820, %bx
	jb	2f

	movw	$((0x8200 - (pre_stage2_start - _start1) - 0x400) >> 4), %cx

	/* Now CS(=DS) >= CX+0x40 */

	movw	%cx, %es
	xorw	%di, %di
	xorw	%si, %si

	/////////////////////////////////////////////////////////////
	//
	//                    CS
	//                    DS          0x820     BX
	//                    _start1---------------pre_stage2_start
	//          CX+0x40---------------0x820
	//   CX
	//   ES
	//
	/////////////////////////////////////////////////////////////

	movw	$0x200, %cx	/* move 2 sectors */
	cld
	repz movsw

	pushw	%es		/* ES:0000 = _start */
	pushw	$(1f - _start)
	lret			/* CS=ES, CS:0000 = _start1 */
1:

	/* move BX:0000 to 0820:0000 upward since BX >= 0x820 */

	cld

	movw	%bx, %ds
	movw	$0x820, %bx
	movw	%bx, %es

	xorw	%si, %si
	xorw	%di, %di

	movw	$6, %bx		/* 64K pages: 0x20000 - 0x7ffff */
1:
	movw	$0x8000, %cx
	repz movsw
	movw	%ds, %ax
	addw	$0x1000, %ax
	movw	%ax, %ds
	movw	%es, %ax
	addw	$0x1000, %ax
	movw	%ax, %es
	decw	%bx
	jnz	1b

	jmp	3f
2:

	/* move BX:0000 to 0820:0000 downward since BX < 0x820 */

	std

	addw	$0x7000, %bx
	movw	%bx, %ds
	movw	$0x7820, %bx
	movw	%bx, %es

	movw	$0xfffe, %si
	movw	%si, %di

	movw	$8, %bx		/* 64K pages: 0x08200 - 0x881ff */
1:
	movw	$0x8000, %cx
	repz movsw
	movw	%ds, %ax
	subw	$0x1000, %ax
	movw	%ax, %ds
	movw	%es, %ax
	subw	$0x1000, %ax
	movw	%ax, %es
	decw	%bx
	jnz	1b

	cld

3:

	/* put the config file name */
	xorw	%ax, %ax
	movw	%ax, %es
	movw	%ax, %ds

	xorl	%ebp, %ebp
	
	movb	%dh, 0x820A	/* this is the boot partition number */

	#; clear saved_entryno so that force_cdrom_as_boot_device be cleared
	#; later in common.c

	movl	%ebp, 0x820C	/* EBP=0, clear saved_entryno */

	movw    $0x0010, %cx	/* set max length of grub version string */
	movw    $0x8212, %di	/* version string */
	cld
	/* AL is already 0. Locate the end of version string */
	repnz scasb	/* find the location of the default config file name */

	jcxz	1f	/* failed, will not use the default config file name */

	movw    $0x4e, %cx	/* max length of config file name */

	movw	%cs, %si	/* CS:0000 = _start1 */
	shlw	$4, %si		/* 0000:SI = _start1 */

	addw	$(default_config_file - _start1), %si

	//movw	$(default_config_file + 0x8200 - pre_stage2_start), %si
	cld
	repz movsb	/* move file name to the config-file field of stage2 */
1:

	movw	$0x0003, %ax	/* set display mode: 80*25 color text */
	int	$0x10

	xorw	%bx, %bx
	movw	$(launch_pre_stage2 - _start1), %si
	call	print_message	/* CS:SI points to message string */

	xorw	%ax, %ax
	movw	%ax, %ss
	movw	$0x2000, %sp

	sti

	ljmp	$0, $0x8200

launch_pre_stage2:
	.ascii	"\r\n\r\nBooting GRLDR...\r\n"

	.byte	0		/* mark the end of ascii zero string */

default_config_file:
//#ifndef PRESET_MENU_STRING
	.ascii	"/menu.lst"
//#else
//	.ascii	"[default menu is disabled]"
//#endif

	.byte	0		/* mark the end of ascii zero string */
#endif	/* ! defined(GRLDR_MBR) && (! defined(GRLDR_INSTALL)) */

	. = _start1 + 0x400

#define ALTERNATIVE_KERNEL


/*
 * The following is based on FreeDOS, modified heavily by Tinybit in Feb, 2004
 *
 * Merges LBA and CHS boot sectors to ONE FAT32 boot sector!
 *
 * Memory layout for GRLDR FAT32 single stage boot process:
 *
 *	...
 *	|-------| 1FE0:7E00
 *	|BOOTSEC| (GRUB does not use this relocation area)
 *	|RELOC.	| (overwritten by kernel loaded)
 *	|-------| 1FE0:7C00
 *	...
 *	|-------|
 *	|KERNEL	| (overwrites bootsec reloc.)
 *	|LOADED	| (holds 1 sector directory buffer before kernel load)
 *	|-------| 2000:0000
 *	...
 *	|-------| 0000:7E00
 *	|BOOTSEC| GRUB always run inside this sector,
 *	|ORIGIN | no relocation.
 *	|-------| 0000:7C00
 *	...
 *	|-------| 0060:0200
 *	|  FAT  | (only 1 sector buffered)
 *	|-------| 0060:0000
 *	...
 *
 */

/*
; This is an LBA-enabled FreeDOS FAT32 boot sector (single sector!).
; You can use and copy source code and binaries under the terms of the
; GNU Public License (GPL), version 2 or newer. See www.gnu.org for more.

; Based on earlier work by FreeDOS kernel hackers, modified heavily by
; Eric Auer and Jon Gentle in 7 / 2003.
;
; Features: Uses LBA and calculates all variables from BPB/EBPB data,
; thus making partition move / resize / image-restore easier. FreeDOS
; can boot from FAT32 partitions which start > 8 GB boundary with this
; boot sector. Disk geometry knowledge is not needed for booting.
;
; Windows uses 2-3 sectors for booting (sector stage, statistics sector,
; filesystem stage). Only using 1 sector for FreeDOS makes multi-booting
; of FreeDOS and Windows on the same filesystem easier.
;
; Requirements: LBA BIOS and 386 or better CPU. Use the older CHS-only
; boot sector if you want FAT32 on really old PCs (problems: you cannot
; boot from > 8 GB boundary, cannot move / resize / ... without applying
; SYS again if you use the CHS-only FAT32 boot sector).
;
; FAT12 / FAT16 hints: Use the older CHS-only boot sector unless you
; have to boot from > 8 GB. The LBA-and-CHS FAT12 / FAT16 boot sector
; needs applying SYS again after move / resize / ... a variant of that
; boot sector without CHS support but with better move / resize / ...
; support would be good for use on LBA harddisks.


; Memory layout for the FreeDOS FAT32 single stage boot process:

;	...
;	|-------| 1FE0:7E00
;	|BOOTSEC|
;	|RELOC.	|
;	|-------| 1FE0:7C00
;	...
;	|-------| 2000:0200
;	|  FAT  | (only 1 sector buffered)
;	|-------| 2000:0000
;	...
;	|-------| 0000:7E00
;	|BOOTSEC| overwritten by the kernel, so the
;	|ORIGIN | bootsector relocates itself up...
;	|-------| 0000:7C00
;	...
;	|-------|
;	|KERNEL	| maximum size 134k (overwrites bootsec origin)
;	|LOADED	| (holds 1 sector directory buffer before kernel load)
;	|-------| 0060:0000
;	...
*/

#define BOOTGRUB	/* undef this if compiled for loading FreeDOS */
//#undef BOOTGRUB

#ifdef	BOOTGRUB
#define LOADSEG		0x2000
#define FATSEG		0x0060
#else
#define LOADSEG		0x0060
#define FATSEG		0x2000
#endif

Entry_32:
	jmp	1f

	. = Entry_32 + 0x02

	/* The default mode is CHS. This is for maximum compatiblity with
	 * small-sized disks, e.g., floppies.
	 *
	 * Valid values are 0x90 for CHS mode, or 0x0e for LBA mode.
	 *
	 * If the BIOS int13 supports LBA, this byte can be safely set to 0x0e.
	 *
	 * Some USB BIOSes might have bugs when using CHS mode, so the format
	 * program should set this byte to 0x0e. It seems that (generally) all
	 * USB BIOSes have LBA support.
	 *
	 * If the format program does not know whether the BIOS has LBA
	 * support, it may operate this way:
	 *
	 * if (partition_start + total_sectors_in_partition) exceeds the CHS
	 * addressing ability(especially when it is greater than 1024*256*63),
	 * the caller should set this byte to 0x0e, otherwise, set to 0x90.
	 */

	.byte	0x90	/* for CHS. Another possible value is 0x0e for LBA */


	. = Entry_32 + 0x03

#ifdef	BOOTGRUB
	.ascii	"GRLDR   "	/* OEM name string (of OS which formatted the disk). */
#endif

	. = Entry_32 + 0x0b

	.word	0x200		/* bytes per sector. Must be 512 */

	. = Entry_32 + 0x0d

	/* Sectors per cluster. Valid values are 1, 2, 4, 8, 16, 32, 64 and 128.
	 * But a cluster size larger than 32K should not occur.
	 */

	.byte	1		/* sectors per cluster */

	. = Entry_32 + 0x0e

	/* Reserved sectors(number of sectors before the first FAT,
	 * including the boot sector), usually 1.
	 */

	.word	1		/* reserved sectors */

	. = Entry_32 + 0x10

	/* Number of FATs(nearly always 2). */

	.byte	2		/* number of FATs */

	. = Entry_32 + 0x11

	/* (Maximum number of root directory entries)Must be 0. */

	.word	0		/* Max dir entries for FAT12/FAT16 */

	. = Entry_32 + 0x13

	/* (Total number of sectors for small disks only)Must be 0. */

	.word	0		/* total sectors for FAT12/FAT16 */

	. = Entry_32 + 0x15

	/* Media descriptor byte, pretty meaningless now. */

	.byte	0xf8		/* media descriptor */

	. = Entry_32 + 0x16

	/* (Sectors per FAT)Must be 0. */

	.word	0		/* sectors per FAT for FAT12/FAT16 */

	. = Entry_32 + 0x18

	.word	18		/* sectors per track */

	. = Entry_32 + 0x1a

	.word	2		/* number of heads */

	. = Entry_32 + 0x1c

	/* Number of hidden sectors (those preceding the boot sector).
	 * Also referred to as the starting sector of the partition.
	 * For floppies, it should be 0.
	 */

	.long	0		/* hidden sectors */

	. = Entry_32 + 0x20

	/* Total number of sectors in the filesystem. */

	.long	0		/* total sectors for FAT32 */

	. = Entry_32 + 0x24

	/* FAT32 sectors per FAT. */

	.long	0

	. = Entry_32 + 0x28

	/* If bit 7 is clear then all FATs are updated, otherwise bits 0-3
	 * give the current active FAT, all other bits are reserved.
	 * This word is not used by grldr boot code.
	 */

	.word	0

	. = Entry_32 + 0x2a

	/* High byte is major revision number, low byte is minor revision
	 * number, currently both are 0.
	 * This word is not used by grldr boot code.
	 */

	.word	0

	. = Entry_32 + 0x2c

	/* Root directory starting cluster. */

	.long	0

	. = Entry_32 + 0x30

	/* File system information sector number.
	 * This word is not used by grldr boot code.
	 */

	.word	0

	. = Entry_32 + 0x32

	/* If non-zero this gives the sector which holds a copy of the
	 * boot record, usually 6.
	 * This word is not used by grldr boot code.
	 */

	.word	6

	. = Entry_32 + 0x34

	/* Reserved, 12 bytes, set to 0. */

	.long	0
	.long	0
	.long	0

	. = Entry_32 + 0x40

	/* drive number of the boot device.
	 * This byte is ignored for read. The program will write DL onto
	 * this byte. The caller should set drive number in DL. 
	 * We assume all BIOSes pass correct drive number in DL.
	 * That is to say, buggy BIOSes are not supported!!
	 */

	.byte	0

	. = Entry_32 + 0x41

	/* partition number of this filesystem in the boot drive.
	 * This byte is ignored for read. The boot code will write partition
	 * number onto this byte. See Entry + 0x5d below. 
	 */

	.byte	0

	. = Entry_32 + 0x42

	/* Signature (must be 28h or 29h to be recognised by NT). */

	.byte	0x29		/* extended boot signature for FAT12/FAT16 */

	. = Entry_32 + 0x43

	.long	0x0AC4AF63	/* volume serial number */

	. = Entry_32 + 0x47

	.ascii	"NO NAME    "	/* volume label, 11 bytes. */

	. = Entry_32 + 0x52

	.ascii	"FAT32   "	/* filesystem ID, 8 bytes. */

/*
;	bp is initialized to 7c00h
; %define bsOemName	bp+0x03	; OEM label (8)
%define bsBytesPerSec	bp+0x0b ; bytes/sector (dw)
%define bsSecPerClust	bp+0x0d	; sectors/allocation unit (db)
%define bsResSectors	bp+0x0e	; # reserved sectors (dw)
%define bsFATs		bp+0x10	; # of fats (db)
; %define bsRootDirEnts	bp+0x11	; # of root dir entries (dw, 0 for FAT32)
			; (FAT32 has root dir in a cluster chain)
; %define bsSectors	bp+0x13	; # sectors total in image (dw, 0 for FAT32)
			; (if 0 use nSectorHuge even if FAT16)
; %define bsMedia	bp+0x15	; media descriptor: fd=2side9sec, etc... (db)
; %define sectPerFat	bp+0x16	; # sectors in a fat (dw, 0 for FAT32)
			; (FAT32 always uses xsectPerFat)
%define sectPerTrack	bp+0x18	; # sectors/track
; %define nHeads	bp+0x1a	; # heads (dw)
%define nHidden		bp+0x1c	; # hidden sectors (dd)
; %define nSectorHuge	bp+0x20	; # sectors if > 65536 (dd)
%define xsectPerFat	bp+0x24	; Sectors/Fat (dd)
			; +0x28 dw flags (for fat mirroring)
			; +0x2a dw filesystem version (usually 0)
%define xrootClst	bp+0x2c	; Starting cluster of root directory (dd)
			; +0x30 dw -1 or sector number of fs.-info sector
			; +0x32 dw -1 or sector number of boot sector backup
			; (+0x34 .. +0x3f reserved)
%define drive		bp+0x40	; Drive number
			bp+0x41	; partition number for GRLDR

%define fat_sector	bp+0x44		; last accessed FAT sector (dd)
					; (overwriting unused bytes)
%define fat_start	bp+0x48		; first FAT sector (dd)
					; (overwriting unused bytes)
%define data_start	bp+0x4c		; first data sector (dd)
					; (overwriting unused bytes)

*/
		/* not used: [0x42] = byte 0x29 (ext boot param flag)
		 * [0x43] = dword serial
		 * [0x47] = label (padded with 00, 11 bytes)
		 * [0x52] = "FAT32",32,32,32 (not used by Windows)
		 * ([0x5a] is where FreeDOS parts start)
		 */

	. = Entry_32 + 0x5a
1:
	cli
	cld

#ifdef	BOOTGRUB

	. = Entry_32 + 0x5c

	/* the byte at offset 0x5d stores the real partition number for read.
	 * the format program or the caller should set it to a correct value.
	 * For floppies, it should be 0xff, which stands for whole drive.
	 */

	movb	$0xff, %dh	/* boot partition number */

	cmpb	$0xff, %dh	/* is floppy? */
	jne	1f
	movb	$0, %dl		/* yes, let drive number = 0 */
1:
#endif