grldrstart.s

grub4dos-0.4.4-2008- 08-src.zip

/*
 *  grldrstart.S -- Startup code for GRLDR
 *  Copyright (C) 2004-2007  Tinybit([e-mail])
 *  Copyright (C) 2007  Bean([e-mail])
 *
 *  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 2 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, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 * This program is used to generate the GRLDR file.
 *
 * Use the following shell command to generate the GRLDR file:
 *
 * 	cat grldrstart pre_stage2 > grldr
 *
 */

#define ASM_FILE
#include <shared.h>
#define ASM_FILE
	
#ifndef STAGE1_5
#include <stage2_size.h>
#else
#error cannot compile with STAGE1_5
#endif

#ifdef GRLDR_MBR
	.file	"mbrstart.S"
#elif defined(GRLDR_INSTALL)
	.file	"bootlacestart.S"
#else
	.file	"grldrstart.S"
#endif

#ifdef GRLDR_INSTALL
	//.data
#else
	.text

	.globl	start, _start

start:
_start:
#endif

_start1:

	/* Tell GAS to generate 16-bit real mode instructions */

	.code16

	. = _start1 + 0x00

	/* 1 byte at offset 0x00 will be overwritten for storing the EBIOS
	 * indicator later. This is safe because the jmp instruction only
	 * get executed once. The write happens after the jmp instruction
	 * have got executed.
	 *
	 * The value written would be 0x42 for EBIOS present(LBA) and 0x02
	 * for non-present(CHS).
	 *
	 */

	/* No cli, we use stack! BIOS or caller usually sets SS:SP=0000:0400 */

	jmp	1f	/* FAT32/NTFS routine comes to offset 0 */

	. = _start1 + 0x02

	.byte	0x80	/* bit0=1: disable GRLDR search on floppy */
			/* bit1=1: disable the boot of the previous MBR with
			 *	   invalid partition table */
			/* bit2=1: disable the feature of unconditional
			 *	   entrance to the command-line */
			/* bit7=1: disable the boot of the previous MBR prior
				   to the search for GRLDR */

	/* GRLDR.MBR uses offset 0x03 to indicate a timer counter. */

	/* 0xff indicates waiting forever,
	 * other value specifies the time in seconds to wait */

	. = _start1 + 0x03

	.byte	5

	/* a key press to wait. if AX returned from int16 equals this word,
	 * the desired action will occur. */

	. = _start1 + 0x04

	.word	0x3920		/* the space bar */

	. = _start1 + 0x06

	.byte	0xff	/* preferred boot drive number, 0xff for no-drive(i.e., drive not defined) */
	.byte	0xff	/* preferred partition number, 0xff for whole drive(a floppy that has no partition table) */

	. = _start1 + 8

	/* 2 bytes at offset 0x08 will be overwritten for storing the geometry
	 * reported by INT 13/AH=8.
	 *
	 * lo byte = Sectors Per Track
	 * hi byte = Max Head Number(=number of heads minus 1)
	 *
	 * If INT 13/AH=8 returns error, then the word here will be 0xFFFF. 
	 *
	 */

#if (! defined(GRLDR_MBR)) && (! defined(GRLDR_INSTALL))

	/* filled in by mkisofs using the -boot-info-table option */

#;bi_pvd:	.long 0xDEADBEEF	/* LBA of primary volume descript */
#;bi_file:	.long 0xDEADBEEF	/* LBA of boot file */
#;bi_length:	.long 0xDEADBEEF	/* Length of boot file */
#;bi_csum:	.long 0xDEADBEEF	/* Checksum of boot file */
#;bi_reserved:	.space (10*4)		/* Reserved */

	. = _start1 + 0x40

#else

	/* filled in with BPB in case the drive(typically USB) is treated as floppy by buggy BIOSes */

	. = _start1 + 0x60

#endif	/* ! defined(GRLDR_MBR) && (! defined(GRLDR_INSTALL)) */

1:
	call	1f

#if (! defined(GRLDR_MBR)) && (! defined(GRLDR_INSTALL))

	. = _start1 + 0x43

#else

	. = _start1 + 0x63

#endif	/* ! defined(GRLDR_MBR) && (! defined(GRLDR_INSTALL)) */

1:
	popw	%bx			/* Instruction Pointer of 1b */

#if (! defined(GRLDR_MBR)) && (! defined(GRLDR_INSTALL))

	subw	$(1b - _start1), %bx	/* CS:BX=_start1 */

#else

	subw	$(1b - _start1), %bx	/* CS:BX=_start1 */

#endif	/* ! defined(GRLDR_MBR) && (! defined(GRLDR_INSTALL)) */

	shrw	$4, %bx
	movw	%cs, %ax
	addw	%ax, %bx		/* BX:0000=_start1 */

#if (! defined(GRLDR_MBR)) && (! defined(GRLDR_INSTALL))

	/* we are booted from BOOT.INI, or whole GRLDR image already loaded */

	/* Let CS:0000=_start1 */
	pushw	%bx			/* BX:0000=_start1 */

	#;pushw	$(1f - _start1)
	.byte	0x6A, (1f - _start1)

	lret
	. = . - (. - _start1) / 0x80
1:
	addw	$((grldr_signature - _start1 + 4 + STAGE2_SIZE - 4) >> 4), %bx
	movw	%bx, %ds

	cmpl	$0xCE1A02B0, ((STAGE2_SIZE - 4) & 0x0F)
	pushw	%cs
	popw	%ds			/* DS:0000=_start1 */
	je	grldr_real_start	/* whole image loaded. boot it! */

	/* bad! we might be loaded by a buggy BIOS with a no-emulation-mode
	 * bootable CD. The buggy BIOS might load only 1 CD-ROM sector(2048
	 * bytes) of our grldr image. So we need this check.
	 */

	/* Our cdrom_check code begins at 0x1BE and overlaps the partition
	 * table. Just in case someone replace it with a partition table and
	 * use this sector as an MBR, we do this additional test for safety.
	 */

	/* We should avoid using opcode 0x00 and 0x80 at cdrom_check. */

	/* Note that if cdrom_check code is present, then we are booting from
	 * no-emulation mode cdrom.
	 */

	testb	$0x7F, cdrom_check - _start1	/* is it 0x00 or 0x80? */
	jz	1f			/* yes, cdrom_check not found */
	call	cdrom_check		/* no, cdrom_check is present */
1:
//	/* DS:0000=_start1 */
//
//	/* Let CS:0000=_start1 */
//	pushw	%ds
//
//	#;pushw	$(1f - _start1)
//	.byte	0x6A, (1f - _start1)
//
//	lret
//	. = . - (. - _start1) / 0x80
//1:
#else
	/* BX:0000=_start1 */

	movw	%bx, %ds

	/* Let CS:0000=_start1 */
	pushw	%bx

	#;pushw	$(1f - _start1)
	.byte	0x6A, (1f - _start1)

	lret
	. = . - (. - _start1) / 0x80
1:
	testb	$0x04, 0x02
	jz	1f

	/* set the DUCE indicator */
	xorw	%ax, %ax
	movw	%ax, %es
	movw	$0x5FC, %di
	movl	$0x45435544, %eax
	stosl
1:
#endif

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

	/* we are loaded by BIOS or another boot loader */

#define GRLDR_CS 0x2000		/* grldr code segment */
				/* hope this segment never be used by all */
				/*	subsequent partition boot records */
#if 0
	/* for single sector boot record */
#define	MONITOR	0x7e10
#else
	/* for 4-sector NTFS boot record */
#define	MONITOR	0x8410
#endif

//	cli
	pushw	$GRLDR_CS
	popw	%ss
	movw	$0x9000, %sp	/* SS:SP=0x9d000, keep away from EBDA data */
//	sti
	
	/* Extended BIOS Data Area should not take up space below 0x9d000 */
	
	/* 
	 * 0x07c00-0x07dff	This sector. Another boot loader load us here
	 * 0x0d000-0x14dff	partition/floppy boot track(bootsector,etc)
	 * 0x94000-0x9bdff	master boot track(MBR,etc,usually 63 sectors)
	 * 0x9be00-0x9c3ff	3 sectors for temp extended partition entries
	 * 0x9c400-0x9cfff	6 sectors for stack
	 */

#define FS_BOOT	0xd00		/* segment of partition boot track */

	xorw	%cx, %cx
	pushw	%cx		/* CX=0 */
	movw	$0x0080, %dx
//	pushw	%dx
	movb	$8, %ah		/* read drive parameters changes DX,ES,DI,BX */
	call	int13
//	stc
//	int	$0x13
//	popw	%dx
	popw	%ax		/* AX=0 */

	pushw	%ss		/* SS=0x9400 */
	popw	%es		/* ES=0x9400 */

	jc	1f

	andb	$63, %cl	/* AL=sectors per track, CF cleared */

	stc
	jz	1f

	xchgw	%ax, %cx	/* this moves CL to AL, and CX=0 */
	movb	$0x02, %ah
	movw	%ax, %bp	/* save AX to BP: read 1 track */
	xorw	%bx, %bx	/* ES already has a known value of 0x9400 */
	incw	%cx
//	pushw	%dx
	call	int13
//	stc
//	int	$0x13		/* read master boot track to ES:0000 */
//	popw	%dx
	jc	1f
	negb	%ah		/* set CF=1 if non-zero */
1:
	pushw	%cs		/* DS=0 */
	popw	%ds		/* DS=CS */
	pushfw			/* CF=1 on error */
	
	/* CS=DS=old segment. ES=SS=new segment. */

	/* Move the code and error messages from DS:0000 to 9400:0000, do not
	 * touch the partition table
	 */
	xorw	%si, %si
	xorw	%di, %di
	movw	$223, %cx	/* 223 words = 446 bytes = 0x1be bytes */
	cld
	repz movsw		/* SI=DI=0x1be, CX=0 */

	/********************************************************************/
	/*  At this moment we are still not sure whether the helper is ok.  */
	/********************************************************************/

disk_serial_number_structure:

#if (defined(GRLDR_MBR)) || (defined(GRLDR_INSTALL))

	/********************************************************************/
	/* This piece of code is structured! It contains address 0x1FFC and */
	/* a disk serial number that can be created by grub4dos installer.  */
	/********************************************************************/

	movw	$0x1FFC, %bx		/* .byte 0xBB, 0xFC, 0x1F */

	/* if the boot loader has loaded more than one sector, we use them */
	movl	$0x93cb4d05, %eax	/* date-time for disk serial number */

		/* "MOV EAX"(0x66, 0xB8) followed by the changeable S.N. */
#else
	movw	$(grldr_signature - _start1), %bx	/* BX=0x1FFC */

	/* if the boot loader has loaded more than one sector, we use them */
	movl	$0xAA555247, %eax	/* "GR" 0x55 0xAA */
#endif

disk_serial_number_structure_end:

//#if (! defined(GRLDR_MBR)) && (! defined(GRLDR_INSTALL))
	cmpl	%eax, (%bx)		/* DS=old segment of 07C0:0000 */
	jne	1f

	/* The MOVE_HELPER code is in the old segment of 07C0:0000 */

	call	move_helper	/* SI=0x1be, CX=0 */
1:
//#endif

	/* Jump to new segment! */
#if 1
	ljmp	$GRLDR_CS, $(1f - _start1)
#else
	pushw	%ss		/* 0x9400 */

	//pushw	$(1f - _start1)
	.byte	0x6A, (1f - _start1)

	lret
	. = . - (. - _start1) / 0x80
#endif
1:

	/* We are at the new segment. CS=ES=SS=new segment. */

	/* But DS is still old segment. */

	pushw	%ss
	popw	%ds

	/* CS=DS=ES=SS=new segment. */

	//movw	$0x01be, %si

	/* check the existence of helper */
	cmpl	%eax, (%bx)

#if (! defined(GRLDR_MBR)) && (! defined(GRLDR_INSTALL))

	jne	Error_or_prev_MBR	/* Missing helper */

#else

	je	1f

	/* try to load helper from floppy */

	pushal

	movw	0x18, %ax	/* BPB sectors per track at offset 0x18 */

	cmpw	$0x3F, %ax
	ja	3f

	cmpb	$((pre_stage2_start - _start1) >> 9), %al
	jb	3f

	decw	%ax		/* skip the first sector already loaded */
	
	movw	$3, %di		/* retry 3 times on read failure */
2:
	movb	$2, %ah		/* BIOS disk read */
	cwd			/* DX=0 for floppy head 0 */
	movw	$0x200, %bx	/* ES:BX immediately follow this sector */
	movw	$2, %cx		/* skip the first sector already loaded */

	call	read_disk_with_reset_and_dec_di
	jnc	3f

	jnz	2b
3:
	popal
	cmpl	%eax, (%bx)		/* helper loaded? */

	jne	Error_or_prev_MBR	/* Missing helper */

	/* Helper is loaded from floppy, so we set floppy as preferred. */
	//movw	$0xff00, 0x06
	//movw	%cx, 0x06	/* CX=0 */
	call	set_floppy_preferred
1:
#endif

	popfw			/* CF=1 on error */
	jc	try_floppy	/* harddisk (hd0) failed, try floppy (fd0) */

	/*********************************/
	/* Helper is successfully loaded */
	/*********************************/
1:
	pushw	%cs
	popw	%ds
	lodsw
	movb	%ah, %dh	/* head number */
	lodsw
	movw	%ax, %cx	/* sector and cylinder number */
	andb	$63, %al
	//stc
	jz	helper_call_c
	
	/* use BP to calculate the sectors to read within 1 track */
	subw	%bp, %ax
	decw	%ax		/* decb	%al */
	negb	%al		/* AL=sectors upto the end of the track */
7:
	movw	$3, %di		/* retry 3 times on read failure */
2:
	movb	$2, %ah
	pushw	$FS_BOOT
	popw	%es		/* ES=FS_BOOT */
	xorw	%bx, %bx	/* read partition boot track to FS_BOOT:0000 */

#if (! defined(GRLDR_MBR)) && (! defined(GRLDR_INSTALL))
	pushaw
//	int	$0x13		/* read partition boot track to FS_BOOT:0000 */
	call	int13
	popaw

	jnc	helper_call

	pushaw
	xorw	%ax, %ax
//	int	$0x13
	call	int13
	popaw
	decw	%di
#else
	call	read_disk_with_reset_and_dec_di
	jnc	helper_call
#endif

	jnz	2b

helper_call_c:

	stc

helper_call:
	/* find GRLDR in this partition
	 * before the call:
	 *	CF=1		: indicates an invalid or corrupt entry
	 *	CF=0		: indicates a valid entry
	 *
	 * on return:
	 * 	CF=1		: means "below", try next entry
	 *	CF=0,ZF=1	: means "equal", helper did nothing, so we need
	 *			  a further try to boot via NT bootsector
	 *	CF=0,ZF=0	: means "above", helper succeeded, boot it now
	 */
	call	helper_start	/* change to jmp 6f if helper not present */
	ja	filesystem_boot	/* helper succeeded, directly boot it */
6:

add_sub_si:

	/* extended partition check routine will adjust this to
	 *
	 *	0x83, 0xEE, 0x04 for "subw $4, %si"
	 *
	 *			 or
	 *
	 *	0x83, 0xC6, 0xFC for "addw $-4, %si" 
	 *
	 * so that SI keeps the value 0x1fe.
	 */
	addw	$12, %si	/* 0x83, 0xC6, 0x0C */

	. = add_sub_si + 3

	/* extended partition check routine will adjust the word 0x1fe at
	 * (add_sub_si + 5). The value 0x1ff or greater indicates there are
	 * entries need to be treated. The value 0x1fe indicates no entries
	 * left, and the floppy should be checked.
	 */

	cmpw	$0x01fe, %si	/* 0x81, 0xFE, 0xfe, 0x01 */
				/* All entries checked done? */
	jb	1b		/* No, check the next entry */
	ja	5f		/* floppy already checked. Fail and hang */

try_floppy:

	movw	$0x31b2, %si	/* a value big enough */
	movb	$8, %ah		/* read drive parameters changes DX,ES,DI,BX */
	cwd			/* DL=0 for floppy */
	pushw	%dx		/* DX=0 */
//	int	$0x13
	call	int13