arch/x86/boot/header.S - kernel/mindspeed - Git at Google

 /*
  *	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/x86/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"
	/*
	* 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/x86/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"