/* -*-Asm-*- *//* *  GRUB  --  GRand Unified Bootloader *  Copyright (C) 1999,2000,2001,2002,2005,2006,2007  Free Software Foundation, Inc. * *  GRUB 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. * *  GRUB 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 GRUB.  If not, see <http://www.gnu.org/licenses/>. */#include <grub/boot.h>#include <grub/machine/boot.h>	/* *  defines for the code go here */	/* Absolute addresses	   This makes the assembler generate the address without support	   from the linker. (ELF can't relocate 16-bit addresses!) */#define ABS(x) (x-_start+0x7c00)	/* Print message string */#define MSG(x)	movw $ABS(x), %si; call message	/* XXX:	binutils-2.9.1.0.x doesn't produce a short opcode for this. */#define	MOV_MEM_TO_AL(x)	.byte 0xa0;  .word x		.file	"boot.S"	.text	/* Tell GAS to generate 16-bit instructions so that this code works	   in real mode. */	.code16.globl _start; _start:	/*	 * _start is loaded at 0x7c00 and is jumped to with CS:IP 0:0x7c00	 */	/*	 * Beginning of the sector is compatible with the FAT/HPFS BIOS	 * parameter block.	 */	jmp	after_BPB	nop	/* do I care about this ??? */	/*	 * This space is for the BIOS parameter block!!!!  Don't change	 * the first jump, nor start the code anywhere but right after	 * this area.	 */	. = _start + 4	/* scratch space */mode:	.byte	0disk_address_packet:	sectors:	.long	0heads:	.long	0cylinders:	.word	0sector_start:	.byte	0head_start:	.byte	0cylinder_start:	.word	0	/* more space... */	. = _start + GRUB_BOOT_MACHINE_BPB_END	/*	 * End of BIOS parameter block.	 */boot_version:		.byte	GRUB_BOOT_VERSION_MAJOR, GRUB_BOOT_VERSION_MINORkernel_address:	.word	GRUB_BOOT_MACHINE_KERNEL_ADDRkernel_segment:	.word	GRUB_BOOT_MACHINE_KERNEL_SEGkernel_sector:	.long	1, 0boot_drive:		.byte 0xff	/* the disk to load kernel from */			/* 0xff means use the boot drive */after_BPB:/* general setup */	cli		/* we're not safe here! */        /*         * This is a workaround for buggy BIOSes which don't pass boot         * drive correctly. If GRUB is installed into a HDD, check if         * DL is masked correctly. If not, assume that the BIOS passed         * a bogus value and set DL to 0x80, since this is the only         * possible boot drive. If GRUB is installed into a floppy,         * this does nothing (only jump).         */boot_drive_check:        jmp     1f	/* grub-setup may overwrite this jump */        testb   $0x80, %dl        jnz     1f        movb    $0x80, %dl1:		/*	 * ljmp to the next instruction because some bogus BIOSes	 * jump to 07C0:0000 instead of 0000:7C00.	 */	ljmp	$0, $ABS(real_start)real_start:		/* set up %ds and %ss as offset from 0 */	xorw	%ax, %ax	movw	%ax, %ds	movw	%ax, %ss	/* set up the REAL stack */	movw	$GRUB_BOOT_MACHINE_STACK_SEG, %sp	sti		/* we're safe again */	/*	 *  Check if we have a forced disk reference here	 */	MOV_MEM_TO_AL(ABS(boot_drive))	/* movb	ABS(boot_drive), %al */	cmpb	$0xff, %al	je	1f	movb	%al, %dl1:	/* save drive reference first thing! */	pushw	%dx	/* print a notification message on the screen */	MSG(notification_string)	/* set %si to the disk address packet */	movw	$ABS(disk_address_packet), %si		/* do not probe LBA if the drive is a floppy */	testb	$GRUB_BOOT_MACHINE_BIOS_HD_FLAG, %dl	jz	chs_mode				/* check if LBA is supported */	movb	$0x41, %ah	movw	$0x55aa, %bx	int	$0x13	/* 	 *  %dl may have been clobbered by INT 13, AH=41H.	 *  This happens, for example, with AST BIOS 1.04.	 */	popw	%dx	pushw	%dx	/* use CHS if fails */	jc	chs_mode	cmpw	$0xaa55, %bx	jne	chs_mode	andw	$1, %cx	jz	chs_mode	lba_mode:	xorw	%ax, %ax	movw	%ax, 4(%si)	incw	%ax		/* set the mode to non-zero */	movb	%al, -1(%si)		/* the blocks */	movw	%ax, 2(%si)	/* the size and the reserved byte */	movw	$0x0010, (%si)	/* the absolute address */	movl	ABS(kernel_sector), %ebx	movl	%ebx, 8(%si)	movl	ABS(kernel_sector + 4), %ebx	movl	%ebx, 12(%si)	/* the segment of buffer address */	movw	$GRUB_BOOT_MACHINE_BUFFER_SEG, 6(%si)/* * BIOS call "INT 0x13 Function 0x42" to read sectors from disk into memory *	Call with	%ah = 0x42 *			%dl = drive number *			%ds:%si = segment:offset of disk address packet *	Return: *			%al = 0x0 on success; err code on failure */	movb	$0x42, %ah	int	$0x13	/* LBA read is not supported, so fallback to CHS.  */	jc	chs_mode	movw	$GRUB_BOOT_MACHINE_BUFFER_SEG, %bx	jmp	copy_buffer		chs_mode:		/*	 *  Determine the hard disk geometry from the BIOS!	 *  We do this first, so that LS-120 IDE floppies work correctly.	 */	movb	$8, %ah	int	$0x13	jnc	final_init	/*	 *  The call failed, so maybe use the floppy probe instead.	 */	testb	$GRUB_BOOT_MACHINE_BIOS_HD_FLAG, %dl	jz	floppy_probe	/* Nope, we definitely have a hard disk, and we're screwed. */	jmp	hd_probe_errorfinal_init:	/* set the mode to zero */	movzbl	%dh, %eax	movb	%ah, -1(%si)		/* save number of heads */	incw	%ax	movl	%eax, 4(%si)	movzbw	%cl, %dx	shlw	$2, %dx	movb	%ch, %al	movb	%dh, %ah	/* save number of cylinders */	incw	%ax	movw	%ax, 8(%si)	movzbw	%dl, %ax	shrb	$2, %al	/* save number of sectors */	movl	%eax, (%si)setup_sectors:	/* load logical sector start (top half) */	movl	ABS(kernel_sector + 4), %eax	orl	%eax, %eax	jnz	geometry_error		/* load logical sector start (bottom half) */	movl	ABS(kernel_sector), %eax	/* zero %edx */	xorl	%edx, %edx	/* divide by number of sectors */	divl	(%si)	/* save sector start */	movb	%dl, %cl	xorw	%dx, %dx	/* zero %edx */	divl	4(%si)		/* divide by number of heads */	/* do we need too many cylinders? */	cmpw	8(%si), %ax	jge	geometry_error	/* normalize sector start (1-based) */	incb	%cl	/* low bits of cylinder start */	movb	%al, %ch	/* high bits of cylinder start */	xorb	%al, %al	shrw	$2, %ax	orb	%al, %cl	/* save head start */	movb	%dl, %al	/* restore %dl */	popw	%dx	/* head start */	movb	%al, %dh/* * BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory *	Call with	%ah = 0x2 *			%al = number of sectors *			%ch = cylinder *			%cl = sector (bits 6-7 are high bits of "cylinder") *			%dh = head *			%dl = drive (0x80 for hard disk, 0x0 for floppy disk) *			%es:%bx = segment:offset of buffer *	Return: *			%al = 0x0 on success; err code on failure */	movw	$GRUB_BOOT_MACHINE_BUFFER_SEG, %bx	movw	%bx, %es	/* load %es segment with disk buffer */	xorw	%bx, %bx	/* %bx = 0, put it at 0 in the segment */	movw	$0x0201, %ax	/* function 2 */	int	$0x13	jc	read_error	movw	%es, %bx	copy_buffer:	movw	ABS(kernel_segment), %es	/*	 * We need to save %cx and %si because the startup code in	 * kernel uses them without initializing them.	 */	pusha	pushw	%ds		movw	$0x100, %cx	movw	%bx, %ds	xorw	%si, %si	xorw	%di, %di		cld		rep	movsw	popw	%ds	popa	/* boot kernel */	jmp	*(kernel_address)/* END OF MAIN LOOP *//* * BIOS Geometry translation error (past the end of the disk geometry!). */geometry_error:	MSG(geometry_error_string)	jmp	general_error/* * Disk probe failure. */hd_probe_error:	MSG(hd_probe_error_string)	jmp	general_error/* * Read error on the disk. */read_error:	MSG(read_error_string)general_error:	MSG(general_error_string)/* go here when you need to stop the machine hard after an error condition */        /* tell the BIOS a boot failure, which may result in no effect */        int	$0x18stop:	jmp	stopnotification_string:	.string "GRUB "geometry_error_string:	.string "Geom"hd_probe_error_string:	.string "Hard Disk"read_error_string:	.string "Read"general_error_string:	.string " Error"/* * message: write the string pointed to by %si * *   WARNING: trashes %si, %ax, and %bx */	/*	 * Use BIOS "int 10H Function 0Eh" to write character in teletype mode	 *	%ah = 0xe	%al = character	 *	%bh = page	%bl = foreground color (graphics modes)	 */1:	movw	$0x0001, %bx	movb	$0xe, %ah	int	$0x10		/* display a byte */message:	lodsb	cmpb	$0, %al	jne	1b	/* if not end of string, jmp to display */	ret	/*	 *  Windows NT breaks compatibility by embedding a magic	 *  number here.	 */	. = _start + GRUB_BOOT_MACHINE_WINDOWS_NT_MAGICnt_magic:		.long 0	.word 0	/*	 *  This is where an MBR would go if on a hard disk.  The code	 *  here isn't even referenced unless we're on a floppy.  Kinda	 *  sneaky, huh?	 */part_start:		. = _start + GRUB_BOOT_MACHINE_PART_STARTprobe_values:	.byte	36, 18, 15, 9, 0floppy_probe:/* *  Perform floppy probe. */	movw	$ABS(probe_values-1), %siprobe_loop:	/* reset floppy controller INT 13h AH=0 */	xorw	%ax, %ax	int	$0x13	incw	%si	movb	(%si), %cl	/* if number of sectors is 0, display error and die */	cmpb	$0, %cl	jne	1f/* * Floppy disk probe failure. */	MSG(fd_probe_error_string)	jmp	general_errorfd_probe_error_string:	.string "Floppy"1:	/* perform read */	movw	$GRUB_BOOT_MACHINE_BUFFER_SEG, %bx	movw	$0x201, %ax	movb	$0, %ch	movb	$0, %dh	int	$0x13	/* if error, jump to "probe_loop" */	jc	probe_loop	/* %cl is already the correct value! */	movb	$1, %dh	movb	$79, %ch	jmp	final_init	. = _start + GRUB_BOOT_MACHINE_PART_END/* the last 2 bytes in the sector 0 contain the signature */	.word	GRUB_BOOT_MACHINE_SIGNATURE