grldrstart.s

grub4dos-0.4.4-2008- 08-src.zip

	popw	%ax		/* AX=0 */
	jc	5f		/* floppy failure, issue "Error" and hang */
	cwd			/* DX=0 */
	xchgw	%ax, %cx	/* this moves CL to AL, and CX=0 */
	andb	$63, %al	/* AL=sectors per track */
	jz	5f		/* invalid value. floppy failure. hangs */
	//movw	$1, %cx
	incw	%cx
	jmp	7b

5:
Error_or_prev_MBR:

	/* GRLDR not found, print "Error" or launch previous MBR */
	movw	$(message_string - _start1), %si

	call	print_message	/* CS:SI points to message string */
3:	jmp	3b

int13:
	pushw	%ds
	pushw	%es
//	pushw	%bx
	pushw	%dx
	pushw	%si
	pushw	%di
	pushw	%bp
	stc
	int	$0x13
	popw	%bp
	popw	%di
	popw	%si
	popw	%dx
//	popw	%bx
	popw	%es
	popw	%ds
	ret

#if (! defined(GRLDR_MBR)) && (! defined(GRLDR_INSTALL))
filesystem_boot:
	/* The partition boot record successfully modified, just boot it */

	/*
	 * The boot might fail, but we want to take back the control.
	 * So we save the registers now.
	 */
	pushw	%ds
	pushw	%es
	pushal

	/* DS=CS=GRLDR_CS, ES=FS_BOOT */

	/* save GRLDR_CS */

	movw	%es, %bx	# save old ES to BX

	cli
	lgdt	gdt - _start1
	movl	%cr0, %eax
	orb	$1, %al
	movl	%eax, %cr0

	movw	$8, %si
	movw	%si, %es

	xorl	%esi, %esi
	xorl	%edi, %edi
	movl	$(0x9000 / 4), %ecx

	cld
	repz movsl

	movw	$16, %si
	movw	%si, %es

	andb	$0xfe, %al
	movl	%eax, %cr0

	movw	%bx, %es	# restore ES from BX

	/* move FS_BOOT:0000 to 0:7c00 */
#if 0
	/* for single sector boot record */
	movw	$0x0200, %cx	/* move 2 sectors, the old FS_BOOT:0000 will keep untouched.  */
#else
	/* for 4-sector NTFS boot record */
	movw	$0x0400, %cx	/* move 4 sectors, the old FS_BOOT:0000 will keep untouched.  */
#endif
	xorw	%si, %si
	pushw	%si	/* SI=0, for the segment of 0000:7c00 */
	movw	$0x7c00, %di
	pushw	%di	/* DI=0x7c00, for the offset of 0000:7c00 */
	pushw	%es	/* ES=FS_BOOT */
	popw	%ds	/* DS=FS_BOOT */
	pushw	%si	/* SI=0 */
	popw	%es	/* ES=0 */
	cld
	repz movsw

	movw	$MONITOR, %di
	movw	$(restore_GRLDR_CS - _start1), %si
	movw	$((gdt_end - restore_GRLDR_CS) / 4), %cx
	cld
	repz cs movsl		/* CS segment override prefix(=0x2E) */

	pushw	%es	/* ES=0 */
	popw	%ds	/* DS=0 */
	sti
	lret	//ljmp	$0, $0x7c00
#endif

try_next_partition:

	cli
	movw	$GRLDR_CS, %ax
	movw	%ax, %ss
	movw	$(0x9000-36), %sp
	sti

	/* restore the registers and continue */
	popal
	popw	%es
	popw	%ds
	jmp	add_sub_si

#if (defined(GRLDR_MBR)) || (defined(GRLDR_INSTALL))
read_disk_with_reset_and_dec_di:
	pushaw
//	int	$0x13
	call	int13
	popaw

	jnc	3f

	pushaw
	xorw	%ax, %ax
//	int	$0x13
	call	int13
	popaw
	decw	%di
	stc
3:
	ret
#endif

	/* prints string CS:SI (modifies AX BX SI) */
3:
	//xorw	%bx, %bx	/* video page 0 */
	movb	$0x0e, %ah	/* print char in AL */
	int	$0x10		/* via TTY mode */

print_message:

	lodsb	%cs:(%si), %al	/* get token */
	cmpb	$0, %al		/* end of string? */
	jne	3b
	ret

message_string:

#if (! defined(GRLDR_MBR)) && (! defined(GRLDR_INSTALL))
	.ascii	"\r\nMissing helper.\0"
#else
	.ascii	"\r\nMissing MBR-helper.\0"
#endif

#;buggy_bios_string:
#;
#;	.ascii	"\r\nBuggy BIOS!\0"

	/* Make sure the above code does not occupy the partition table */

#if (! defined(GRLDR_MBR)) && (! defined(GRLDR_INSTALL))
	/* offset value here must be less than or equal to 0x1be */
	. = . - ((. - _start1) / 0x1bf)
#else
	/* offset value here must be less than or equal to 0x1b8 */
	. = . - ((. - _start1) / 0x1b9)
#endif

	/* The following code may occupy the same area as the partition table */

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

	/* we are not booted from MBR. So we can reuse the area of partition
	 * table for our code.
	 */

	. = _start1 + 0x1be

cdrom_check:

	/* DS=CS points to the sector start. */

	/* BX segment points to near the end of GRLDR image. */

	popw	%ax	/* old return IP */

	/* set BX as the new safe stack. */
	movw	%bx, %ss
	movw	$0xFFF0, %sp

	pushw	%ax	/* old return IP */

	/* check if DL is no-emulation-mode bootable CDROM. */
	pushw	%ds

	cmpb	$0x80, %dl
	jb	1f	/* not a valid no-emulation-mode cdrom drive number */

	cmpw	$0xAA55, 0x7FE		/* 2048 bytes loaded? */
	jne	1f

//	cmpw	$0xAA55, 0x5FE		/* 2048 bytes loaded? */
//	jne	1f

	movw	$0x0180, %si
	movw	$0x4B01, %ax
	pushw	$0x0040
	//.byte	0x6A, 0x40
	popw	%ds
	pushw	%ds
	popw	%es
	movb	$0x13, (%si)
	call	int13
//	pushw	%ds
//	pushw	%dx
//	int	$0x13
//	popw	%dx
//	popw	%ds

	/* ignore CF */
#;	jc	2f	/* not in emulation mode */
	xorl	%eax, %eax
	xorw	%bp, %bp
	testb	$0x0F, 1(%si)	/* boot media type is No Emulation? */
	jnz	2f	/* no, it simulates floppy or hard disk. */
	cmpb	%dl, 2(%si)	/* drive number */
	jnz	2f	/* invalid drive */

	/* OK! it is no-emulation-mode cdrom drive. */
	movl	4(%si), %eax	/* LBA of GRLDR */
	incw	%bp

2:
	jmp	cdrom_helper
1:
	popw	%ds
	ret

#else

	. = _start1 + 0x1fe	/* boot signature */

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

/* partition entries in the extended partitions will overwrite code here upto
 * 0x3fd.
 *
 * the extended partition entries will occupy a temp area at 0x9be00-0x9c3ff 
 */

#if (defined(GRLDR_MBR)) || (defined(GRLDR_INSTALL))
	.word	0xaa55
#endif

	. = _start1 + 0x200

/* if it is in the Master Boot Track, the second sector can be used to backup
 * the previously working MBR, typically, the MS MBR. if the backup copy of
 * the MBR cannot boot(because, e.g., it depends on another sector of code
 * that does not exist for now), then please do not set the ending signature
 * to 0xAA55, that is to say, if the signature is already 0xAA55, you should
 * change it to another value(for example, 0x0000).
 */

#if (! defined(GRLDR_INSTALL))
#if 0
print_cl:
	pushaw

	movw	%cx, %ax
	movb	$16, %cl
	divb	%cl		# quo=AL, rem=AH
	orw	$0x3030, %ax

	cmpb	$0x39, %ah
	jbe	1f
	addb	$7, %ah
1:
	cmpb	$0x39, %al
	jbe	1f
	addb	$7, %al
1:
	movb	%ah, %cl

	xorw	%bx, %bx

	movb	$0x0e, %ah
	int	$0x10

	movb	$0x0e, %ah
	movb	%cl, %al
	int	$0x10

	movw	$0x0e20, %ax
	int	$0x10

	popaw
	ret
#else
#if 0
	.word	5, 0x47, 0x52, 0x4c, 0x44, 0x52, 4, 0x24
	.word	0x49, 0x33, 0x30, 0xe000, 0, 0x3000, 0, 0
#else
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90

	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
#endif
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90

	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90

	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90

	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
#endif
	. = _start1 + 0x256	/* cmdcons comes here */

#if 0
	jmp	1f
#else
	.byte	0x90, 0x90
#endif

	. = _start1 + 0x258

	.byte	0x90, 0x90

	. = _start1 + 0x25a

	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90
	.byte	0x90, 0x90

	. = _start1 + 0x26a
1:
	//movw	%cs, %ax
	//movw	%ax, %ds
	//jmp	single_boot_sector

	/* a value < 0x80 here means we are not booted from no-emulation-mode
	 * bootable CD.
	 */
	movb	$0x7F, %dl
	jmp	_start1

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

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

	/* IP and old_DS is on the stack. */

	/* DS=ES=40h */

	/* Stack is high and safe. */

	/* EAX is LBA. if EAX==0, LBA is unknown. */

	/* check if the first sector is the same as the current one */

	/* load the first sector onto the sector immediately follows */
1:
	pushw	%cs
	popw	%bx		/* BX=CS=old_DS=load_segment */
	addw	$0x0080, %bx	/* buffer segment */
	movw	%bx, %es	/* ES changed! */
	call	load_cd_sector

	/* compare the two sectors */
	movw	$0x200, %cx
	xorw	%si, %si
	xorw	%di, %di
	cld
	cs repz cmpsl
	je	load_the_rest	/* 1st sector is ok, continue */
not_grldr:
	testw	%bp, %bp
	jz	2f
	xorw	%bp, %bp
	xorl	%eax, %eax
2:
	incl	%eax
	jnz	1b		/* try next */

cd_no_grldr:

	popw	%ds		/* DS=load_segment */

	# Here we use error message and routine in FAT32 boot sector
	# which is also inside the 2048-byte CD sector.

	movw	$(msg_BootError_32 - _start1), %si
	jmp	boot_error_32
	
load_cd_sector:
	/* input:	EAX	LBA
	 *		BX	buffer segment(buffer offset=0)
	 *		DS	0x40 (or another safe one)
	 * output:
	 *		SI			changed(=0x1A0)
	 *		16 bytes at DS:SI	destroyed
	 */

	movw	$0x1A0, %si

	/* disk address packet */
	movl	$0x00010010, (%si)	/* load 1 sector each time. */
	movw	$0, 4(%si)		/* buffer offset=0 */
	movw	%bx, 6(%si)		/* buffer segment */
	movl	%eax, 8(%si)		/* LBA lo 32 bits */
	movl	$0, 12(%si)		/* LBA hi 32 bits */

//	pushw	%ds
//	pushw	%es
	pushal
	movb	$0x42, %ah
	call	int13
//	int	$0x13
	popal
//	popw	%es
//	popw	%ds
	ret

load_the_rest:

	/* load all sectors (except the first one) */

	/* EAX = first sector(LBA) of GRLDR */

	pushl	%eax

	pushw	%cs
	popw	%bx		/* BX=CS=old_DS=load_segment */
//	movw	%bx, %es
	/* 6144 = 0x1800 = 3 sectors > 4KB, this is for the additional 4KB-preset-menu at the end of grldr */
	movw	$((grldr_signature - _start1 + 4 + STAGE2_SIZE - 1 + 6144) / 2048), %cx	/* sectors to load */
1:
	incl	%eax		/* next sector */
	addw	$0x0080, %bx	/* buffer segment */

	call	load_cd_sector

	loop	1b

	/* loading is completed. BX=segment of the last sector. */

	subw	$0x0181, %bx	/* decw	%bx */
	movw	%bx, %ds

	popl	%eax
//	subl	$((grldr_signature - _start1 + 4 + STAGE2_SIZE - 1 + 6144) / 2048), %eax

	/* check the ending signature */
	cmpl	$0xCE1A02B0, ((grldr_signature - _start1 + 4 + STAGE2_SIZE - 1) % 2048) + 13
	jne	not_grldr
#;	je	grldr_real_start	/* yes. boot it! */

#;	/* it is not our grldr image, return and use MBR-helper. */
#;
#;4:
#;	//jmp	grldr_real_start
#;	popw	%ds
#;	ret

grldr_real_start:

	#; FAT_12_16 no longer be used. So comment out.
	#;je	1f	/* jc	1f */
	#;//ZF=0	/* CF cleared, so we are coming from FAT_12_16 */
	#;popw	%dx		/* discard the cluster number */
	#;popw	%dx		/* this is our boot_drive/boot_partition */
	#;1:

	#; The partition number for no-emulation-mode bootable CDROM will be
	#; set to 0xFF later(in common.c). So comment out.
	#;cli
	#;movw	%cs, %ax
	#;cmpw	$0x1000, %ax
	#;jne	1f
	#;
	#;/* CS=0x1000, may be booted from ext2 or no-emulation-mode CDROM */
	#;
	#;cmpw	$0x1000, %di
	#;jne	2f
	#;cmpw	$0x7c00, %bp
	#;jne	2f
	#;movw	%es, %ax
	#;cmpw	$0x1000, %ax
	#;jbe	2f
	#;cmpw	$0x7c00, %si
	#;jbe	2f
	#;movl	%edx, %eax
	#;shrl	$16, %eax
	#;jnz	2f
	#;jecxz	1f		// booted from ext2 partition
	#;2: