linux 2.6.11 bootsect.s解读

/*

 *	bootsect.S		Copyright (C) 1991, 1992 Linus Torvalds

 *

 *	modified by Drew Eckhardt

 *	modified by Bruce Evans (bde)

 *	modified by Chris Noe (May 1999) (as86 -> gas)

 *	gutted by H. Peter Anvin (Jan 2003)

 *

 * BIG FAT NOTE: We're in real mode using 64k segments.  Therefore segment

 * addresses must be multiplied by 16 to obtain their respective linear

 * addresses. To avoid confusion, linear addresses are written using leading

 * hex while segment addresses are written as segment:offset.

 *

 */



#include 



SETUPSECTS	= 4			/* default nr of setup-sectors */

BOOTSEG		= 0x07C0		/* original address of boot-sector */

INITSEG		= DEF_INITSEG		/* we move boot here - out of the way */

SETUPSEG	= DEF_SETUPSEG		/* setup starts here */

SYSSEG		= DEF_SYSSEG		/* system loaded at 0x10000 (65536) */

SYSSIZE		= DEF_SYSSIZE		/* system size: # of 16-byte clicks */

					/* to be loaded */

ROOT_DEV	= 0 			/* ROOT_DEV is now written by "build" */

SWAP_DEV	= 0			/* SWAP_DEV is now written by "build" */



#ifndef SVGA_MODE

#define SVGA_MODE ASK_VGA

#endif



#ifndef RAMDISK

#define RAMDISK 0

#endif



#ifndef ROOT_RDONLY

#define ROOT_RDONLY 1

#endif



.code16

.text



.global _start

_start:



	# Normalize the start address

	jmpl	$BOOTSEG, $start2



start2:

	movw	%cs, %ax

	movw	%ax, %ds

	movw	%ax, %es

	movw	%ax, %ss

	movw	$0x7c00, %sp

	sti

	cld



	movw	$bugger_off_msg, %si



msg_loop:

	lodsb

	andb	%al, %al

	jz	die

	movb	$0xe, %ah

	movw	$7, %bx

	int	$0x10

	jmp	msg_loop



die:

	# Allow the user to press a key, then reboot

	xorw	%ax, %ax

	int	$0x16

	int	$0x19



	# int 0x19 should never return.  In case it does anyway,

	# invoke the BIOS reset code...

	ljmp	$0xf000,$0xfff0





bugger_off_msg:

	.ascii	"Direct booting from floppy is no longer supported./r/n"

	.ascii	"Please use a boot loader program instead./r/n"

	.ascii	"/n"

	.ascii	"Remove disk and press any key to reboot . . ./r/n"

	.byte	0

	



	# Kernel attributes; used by setup



	.org 497

setup_sects:	.byte SETUPSECTS

root_flags:	.word ROOT_RDONLY

syssize:	.word SYSSIZE

swap_dev:	.word SWAP_DEV

ram_size:	.word RAMDISK

vid_mode:	.word SVGA_MODE

root_dev:	.word ROOT_DEV

boot_flag:	.word 0xAA55

Linux2.6不再使用bootsect.s来引导，而需要使用LILO。GRUB等Boot Loader程序。所以bootsect.s对于2.6来说

已经不再具有引导的功能，而只会打印错误信息。