Linux-2.6.34 / arch / x86 / boot / header.S

Linux-2.6.34/arch/x86/boot/header.S
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/*

*	header.S
*
*	Copyright (C) 1991, 1992 Linus Torvalds
*
*	Based on bootsect.S and setup.S
*	modified by more people than can be counted
*
*	Rewritten as a common file by H. Peter Anvin (Apr 2007)
*
* 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 <asm/segment.h>

#include <generated/utsrelease.h>

#include <asm/boot.h>

#include <asm/e820.h>

#include <asm/page_types.h>

#include <asm/setup.h>

#include "boot.h"

#include "voffset.h"

#include "zoffset.h"

BOOTSEG = 0x07C0 /* original address of boot-sector */ SYSSEG = 0x1000 /* historical load address >> 4 */

#ifndef SVGA_MODE

#define SVGA_MODE ASK_VGA

#endif

#ifndef RAMDISK

#define RAMDISK 0

#endif

#ifndef ROOT_RDONLY

#define ROOT_RDONLY 1

#endif

	.code16
	.section ".bstext", "ax"

	.global bootsect_start

bootsect_start:

	# Normalize the start address
	ljmp	$BOOTSEG, $start2

start2:

	movw	%cs, %ax
	movw	%ax, %ds
	movw	%ax, %es
	movw	%ax, %ss
	xorw	%sp, %sp
	sti
	cld

	movw	$bugger_off_msg, %si

msg_loop:

	lodsb
	andb	%al, %al
	jz	bs_die
	movb	$0xe, %ah
	movw	$7, %bx
	int	$0x10
	jmp	msg_loop

bs_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

	.section ".bsdata", "a"

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.  This is part 1 of the
	# header, from the old boot sector.

	.section ".header", "a"
	.globl	hdr

hdr: setup_sects: .byte 0 /* Filled in by build.c */ root_flags: .word ROOT_RDONLY syssize: .long 0 /* Filled in by build.c */ ram_size: .word 0 /* Obsolete */ vid_mode: .word SVGA_MODE root_dev: .word 0 /* Filled in by build.c */ boot_flag: .word 0xAA55

	# offset 512, entry point

	.globl	_start

_start:

		# Explicitly enter this as bytes, or the assembler
		# tries to generate a 3-byte jump here, which causes
		# everything else to push off to the wrong offset.
		.byte	0xeb		# short (2-byte) jump
		.byte	start_of_setup-1f

1:

	# Part 2 of the header, from the old setup.S

		.ascii	"HdrS"		# header signature
		.word	0x020a		# header version number (>= 0x0105)
					# or else old loadlin-1.5 will fail)
		.globl realmode_swtch

realmode_swtch: .word 0, 0 # default_switch, SETUPSEG start_sys_seg: .word SYSSEG # obsolete and meaningless, but just

					# in case something decided to "use" it
		.word	kernel_version-512 # pointing to kernel version string
					# above section of header is compatible
					# with loadlin-1.5 (header v1.5). Don't
					# change it.

type_of_loader: .byte 0 # 0 means ancient bootloader, newer

					# bootloaders know to change this.
					# See Documentation/i386/boot.txt for
					# assigned ids

# flags, unused bits must be zero (RFU) bit within loadflags loadflags: LOADED_HIGH = 1 # If set, the kernel is loaded high CAN_USE_HEAP = 0x80 # If set, the loader also has set

					# heap_end_ptr to tell how much
					# space behind setup.S can be used for
					# heap purposes.
					# Only the loader knows what is free
		.byte	LOADED_HIGH

setup_move_size: .word 0x8000 # size to move, when setup is not

					# loaded at 0x90000. We will move setup
					# to 0x90000 then just before jumping
					# into the kernel. However, only the
					# loader knows how much data behind
					# us also needs to be loaded.

code32_start: # here loaders can put a different

					# start address for 32-bit code.
		.long	0x100000	# 0x100000 = default for big kernel

ramdisk_image: .long 0 # address of loaded ramdisk image

					# Here the loader puts the 32-bit
					# address where it loaded the image.
					# This only will be read by the kernel.

ramdisk_size: .long 0 # its size in bytes

bootsect_kludge:

		.long	0		# obsolete

heap_end_ptr: .word _end+STACK_SIZE-512

					# (Header version 0x0201 or later)
					# space from here (exclusive) down to
					# end of setup code can be used by setup
					# for local heap purposes.

ext_loader_ver:

		.byte	0		# Extended boot loader version

ext_loader_type:

		.byte	0		# Extended boot loader type

cmd_line_ptr: .long 0 # (Header version 0x0202 or later)

					# If nonzero, a 32-bit pointer
					# to the kernel command line.
					# The command line should be
					# located between the start of
					# setup and the end of low
					# memory (0xa0000), or it may
					# get overwritten before it
					# gets read.  If this field is
					# used, there is no longer
					# anything magical about the
					# 0x90000 segment; the setup
					# can be located anywhere in
					# low memory 0x10000 or higher.

ramdisk_max: .long 0x7fffffff

					# (Header version 0x0203 or later)
					# The highest safe address for
					# the contents of an initrd
					# The current kernel allows up to 4 GB,
					# but leave it at 2 GB to avoid
					# possible bootloader bugs.

kernel_alignment: .long CONFIG_PHYSICAL_ALIGN #physical addr alignment

						#required for protected mode
						#kernel

#ifdef CONFIG_RELOCATABLE relocatable_kernel: .byte 1

#else relocatable_kernel: .byte 0

#endif min_alignment: .byte MIN_KERNEL_ALIGN_LG2 # minimum alignment pad3: .word 0

cmdline_size: .long COMMAND_LINE_SIZE-1 #length of the command line,

                                               #added with boot protocol
                                               #version 2.06

hardware_subarch: .long 0 # subarchitecture, added with 2.07

						# default to 0 for normal x86 PC

hardware_subarch_data: .quad 0

payload_offset: .long ZO_input_data payload_length: .long ZO_z_input_len

setup_data: .quad 0 # 64-bit physical pointer to

						# single linked list of
						# struct setup_data

pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr

#define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_extract_offset)

#define VO_INIT_SIZE (VO__end - VO__text)

#if ZO_INIT_SIZE > VO_INIT_SIZE

#define INIT_SIZE ZO_INIT_SIZE

#else

#define INIT_SIZE VO_INIT_SIZE

#endif init_size: .long INIT_SIZE # kernel initialization size

# End of setup header #####################################################

	.section ".entrytext", "ax"

start_of_setup:

#ifdef SAFE_RESET_DISK_CONTROLLER

# Reset the disk controller.

	movw	$0x0000, %ax		# Reset disk controller
	movb	$0x80, %dl		# All disks
	int	$0x13

#endif

# Force %es = %ds

	movw	%ds, %ax
	movw	%ax, %es
	cld

# Apparently some ancient versions of LILO invoked the kernel with %ss != %ds,

# which happened to work by accident for the old code. Recalculate the stack

# pointer if %ss is invalid. Otherwise leave it alone, LOADLIN sets up the

# stack behind its own code, so we can't blindly put it directly past the heap.

	movw	%ss, %dx
	cmpw	%ax, %dx	# %ds == %ss?
	movw	%sp, %dx
	je	2f		# -> assume %sp is reasonably set

	# Invalid %ss, make up a new stack
	movw	$_end, %dx
	testb	$CAN_USE_HEAP, loadflags
	jz	1f
	movw	heap_end_ptr, %dx

1: addw $STACK_SIZE, %dx

	jnc	2f
	xorw	%dx, %dx	# Prevent wraparound

2: # Now %dx should point to the end of our stack space

	andw	$~3, %dx	# dword align (might as well...)
	jnz	3f
	movw	$0xfffc, %dx	# Make sure we're not zero

3: movw %ax, %ss

	movzwl	%dx, %esp	# Clear upper half of %esp
	sti			# Now we should have a working stack

# We will have entered with %cs = %ds+0x20, normalize %cs so

# it is on par with the other segments.

	pushw	%ds
	pushw	$6f
	lretw

6:

# Check signature at end of setup

	cmpl	$0x5a5aaa55, setup_sig
	jne	setup_bad

# Zero the bss

	movw	$__bss_start, %di
	movw	$_end+3, %cx
	xorl	%eax, %eax
	subw	%di, %cx
	shrw	$2, %cx
	rep; stosl

# Jump to C code (should not return)

	calll	main

# Setup corrupt somehow... setup_bad:

	movl	$setup_corrupt, %eax
	calll	puts
	# Fall through...

	.globl	die
	.type	die, @function

die:

	hlt
	jmp	die

	.size	die, .-die

	.section ".initdata", "a"

setup_corrupt:

	.byte	7
	.string	"No setup signature found...\n"