arch/x86/boot/header.S - linux - Git at Google

 /* SPDX-License-Identifier: GPL-2.0 */
 /*
  *	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 <linux/pe.h>
 #include <asm/segment.h>
 #include <asm/boot.h>
 #include <asm/page_types.h>
 #include <asm/setup.h>
 #include <asm/bootparam.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 ROOT_RDONLY
 #define ROOT_RDONLY 1
 #endif

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

 	.global bootsect_start
 bootsect_start:
 #ifdef CONFIG_EFI_STUB
 	# "MZ", MS-DOS header
 	.word	MZ_MAGIC
 #endif

 	# 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

 #ifdef CONFIG_EFI_STUB
 	.org	0x3c
 	#
 	# Offset to the PE header.
 	#
 	.long	pe_header
 #endif /* CONFIG_EFI_STUB */

 	.section ".bsdata", "a"
 bugger_off_msg:
 	.ascii	"Use a boot loader.\r\n"
 	.ascii	"\n"
 	.ascii	"Remove disk and press any key to reboot...\r\n"
 	.byte	0

 #ifdef CONFIG_EFI_STUB
 pe_header:
 	.long	PE_MAGIC

 coff_header:
 #ifdef CONFIG_X86_32
 	.set	image_file_add_flags, IMAGE_FILE_32BIT_MACHINE
 	.set	pe_opt_magic, PE_OPT_MAGIC_PE32
 	.word	IMAGE_FILE_MACHINE_I386
 #else
 	.set	image_file_add_flags, 0
 	.set	pe_opt_magic, PE_OPT_MAGIC_PE32PLUS
 	.word	IMAGE_FILE_MACHINE_AMD64
 #endif
 	.word	section_count			# nr_sections
 	.long	0 				# TimeDateStamp
 	.long	0				# PointerToSymbolTable
 	.long	1				# NumberOfSymbols
 	.word	section_table - optional_header	# SizeOfOptionalHeader
 	.word	IMAGE_FILE_EXECUTABLE_IMAGE	| \
 		image_file_add_flags		| \
 		IMAGE_FILE_DEBUG_STRIPPED	| \
 		IMAGE_FILE_LINE_NUMS_STRIPPED	# Characteristics

 optional_header:
 	.word	pe_opt_magic
 	.byte	0x02				# MajorLinkerVersion
 	.byte	0x14				# MinorLinkerVersion

 	# Filled in by build.c
 	.long	0				# SizeOfCode

 	.long	0				# SizeOfInitializedData
 	.long	0				# SizeOfUninitializedData

 	# Filled in by build.c
 	.long	0x0000				# AddressOfEntryPoint

 	.long	0x0200				# BaseOfCode
 #ifdef CONFIG_X86_32
 	.long	0				# data
 #endif

 extra_header_fields:
 	# PE specification requires ImageBase to be 64k aligned
 	.set	image_base, (LOAD_PHYSICAL_ADDR + 0xffff) & ~0xffff
 #ifdef CONFIG_X86_32
 	.long	image_base			# ImageBase
 #else
 	.quad	image_base			# ImageBase
 #endif
 	.long	0x20				# SectionAlignment
 	.long	0x20				# FileAlignment
 	.word	0				# MajorOperatingSystemVersion
 	.word	0				# MinorOperatingSystemVersion
 	.word	LINUX_EFISTUB_MAJOR_VERSION	# MajorImageVersion
 	.word	LINUX_EFISTUB_MINOR_VERSION	# MinorImageVersion
 	.word	0				# MajorSubsystemVersion
 	.word	0				# MinorSubsystemVersion
 	.long	0				# Win32VersionValue

 	#
 	# The size of the bzImage is written in tools/build.c
 	#
 	.long	0				# SizeOfImage

 	.long	0x200				# SizeOfHeaders
 	.long	0				# CheckSum
 	.word	IMAGE_SUBSYSTEM_EFI_APPLICATION	# Subsystem (EFI application)
 #ifdef CONFIG_EFI_DXE_MEM_ATTRIBUTES
 	.word	IMAGE_DLL_CHARACTERISTICS_NX_COMPAT	# DllCharacteristics
 #else
 	.word	0				# DllCharacteristics
 #endif
 #ifdef CONFIG_X86_32
 	.long	0				# SizeOfStackReserve
 	.long	0				# SizeOfStackCommit
 	.long	0				# SizeOfHeapReserve
 	.long	0				# SizeOfHeapCommit
 #else
 	.quad	0				# SizeOfStackReserve
 	.quad	0				# SizeOfStackCommit
 	.quad	0				# SizeOfHeapReserve
 	.quad	0				# SizeOfHeapCommit
 #endif
 	.long	0				# LoaderFlags
 	.long	(section_table - .) / 8		# NumberOfRvaAndSizes

 	.quad	0				# ExportTable
 	.quad	0				# ImportTable
 	.quad	0				# ResourceTable
 	.quad	0				# ExceptionTable
 	.quad	0				# CertificationTable
 	.quad	0				# BaseRelocationTable

 	# Section table
 section_table:
 	#
 	# The offset & size fields are filled in by build.c.
 	#
 	.ascii	".setup"
 	.byte	0
 	.byte	0
 	.long	0
 	.long	0x0				# startup_{32,64}
 	.long	0				# Size of initialized data
 						# on disk
 	.long	0x0				# startup_{32,64}
 	.long	0				# PointerToRelocations
 	.long	0				# PointerToLineNumbers
 	.word	0				# NumberOfRelocations
 	.word	0				# NumberOfLineNumbers
 	.long	IMAGE_SCN_CNT_CODE		| \
 		IMAGE_SCN_MEM_READ		| \
 		IMAGE_SCN_MEM_EXECUTE		| \
 		IMAGE_SCN_ALIGN_16BYTES		# Characteristics

 	#
 	# The EFI application loader requires a relocation section
 	# because EFI applications must be relocatable. The .reloc
 	# offset & size fields are filled in by build.c.
 	#
 	.ascii	".reloc"
 	.byte	0
 	.byte	0
 	.long	0
 	.long	0
 	.long	0				# SizeOfRawData
 	.long	0				# PointerToRawData
 	.long	0				# PointerToRelocations
 	.long	0				# PointerToLineNumbers
 	.word	0				# NumberOfRelocations
 	.word	0				# NumberOfLineNumbers
 	.long	IMAGE_SCN_CNT_INITIALIZED_DATA	| \
 		IMAGE_SCN_MEM_READ		| \
 		IMAGE_SCN_MEM_DISCARDABLE	| \
 		IMAGE_SCN_ALIGN_1BYTES		# Characteristics

 #ifdef CONFIG_EFI_MIXED
 	#
 	# The offset & size fields are filled in by build.c.
 	#
 	.asciz	".compat"
 	.long	0
 	.long	0x0
 	.long	0				# Size of initialized data
 						# on disk
 	.long	0x0
 	.long	0				# PointerToRelocations
 	.long	0				# PointerToLineNumbers
 	.word	0				# NumberOfRelocations
 	.word	0				# NumberOfLineNumbers
 	.long	IMAGE_SCN_CNT_INITIALIZED_DATA	| \
 		IMAGE_SCN_MEM_READ		| \
 		IMAGE_SCN_MEM_DISCARDABLE	| \
 		IMAGE_SCN_ALIGN_1BYTES		# Characteristics
 #endif

 	#
 	# The offset & size fields are filled in by build.c.
 	#
 	.ascii	".text"
 	.byte	0
 	.byte	0
 	.byte	0
 	.long	0
 	.long	0x0				# startup_{32,64}
 	.long	0				# Size of initialized data
 						# on disk
 	.long	0x0				# startup_{32,64}
 	.long	0				# PointerToRelocations
 	.long	0				# PointerToLineNumbers
 	.word	0				# NumberOfRelocations
 	.word	0				# NumberOfLineNumbers
 	.long	IMAGE_SCN_CNT_CODE		| \
 		IMAGE_SCN_MEM_READ		| \
 		IMAGE_SCN_MEM_EXECUTE		| \
 		IMAGE_SCN_ALIGN_16BYTES		# Characteristics

 	.set	section_count, (. - section_table) / 40
 #endif /* CONFIG_EFI_STUB */

 	# Kernel attributes; used by setup.  This is part 1 of the
 	# header, from the old boot sector.

 	.section ".header", "a"
 	.globl	sentinel
 sentinel:	.byte 0xff, 0xff        /* Used to detect broken loaders */

 	.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	0x020f		# 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.rst for
 					# assigned ids

 # flags, unused bits must be zero (RFU) bit within loadflags
 loadflags:
 		.byte	LOADED_HIGH	# The kernel is to be 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.

 initrd_addr_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

 xloadflags:
 #ifdef CONFIG_X86_64
 # define XLF0 XLF_KERNEL_64			/* 64-bit kernel */
 #else
 # define XLF0 0
 #endif

 #if defined(CONFIG_RELOCATABLE) && defined(CONFIG_X86_64)
    /* kernel/boot_param/ramdisk could be loaded above 4g */
 # define XLF1 XLF_CAN_BE_LOADED_ABOVE_4G
 #else
 # define XLF1 0
 #endif

 #ifdef CONFIG_EFI_STUB
 # ifdef CONFIG_EFI_MIXED
 #  define XLF23 (XLF_EFI_HANDOVER_32|XLF_EFI_HANDOVER_64)
 # else
 #  ifdef CONFIG_X86_64
 #   define XLF23 XLF_EFI_HANDOVER_64		/* 64-bit EFI handover ok */
 #  else
 #   define XLF23 XLF_EFI_HANDOVER_32		/* 32-bit EFI handover ok */
 #  endif
 # endif
 #else
 # define XLF23 0
 #endif

 #if defined(CONFIG_X86_64) && defined(CONFIG_EFI) && defined(CONFIG_KEXEC_CORE)
 # define XLF4 XLF_EFI_KEXEC
 #else
 # define XLF4 0
 #endif

 #ifdef CONFIG_X86_64
 #ifdef CONFIG_X86_5LEVEL
 #define XLF56 (XLF_5LEVEL|XLF_5LEVEL_ENABLED)
 #else
 #define XLF56 XLF_5LEVEL
 #endif
 #else
 #define XLF56 0
 #endif

 			.word XLF0 | XLF1 | XLF23 | XLF4 | XLF56

 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

 #
 # Getting to provably safe in-place decompression is hard. Worst case
 # behaviours need to be analyzed. Here let's take the decompression of
 # a gzip-compressed kernel as example, to illustrate it:
 #
 # The file layout of gzip compressed kernel is:
 #
 #    magic[2]
 #    method[1]
 #    flags[1]
 #    timestamp[4]
 #    extraflags[1]
 #    os[1]
 #    compressed data blocks[N]
 #    crc[4] orig_len[4]
 #
 # ... resulting in +18 bytes overhead of uncompressed data.
 #
 # (For more information, please refer to RFC 1951 and RFC 1952.)
 #
 # Files divided into blocks
 # 1 bit (last block flag)
 # 2 bits (block type)
 #
 # 1 block occurs every 32K -1 bytes or when there 50% compression
 # has been achieved. The smallest block type encoding is always used.
 #
 # stored:
 #    32 bits length in bytes.
 #
 # fixed:
 #    magic fixed tree.
 #    symbols.
 #
 # dynamic:
 #    dynamic tree encoding.
 #    symbols.
 #
 #
 # The buffer for decompression in place is the length of the uncompressed
 # data, plus a small amount extra to keep the algorithm safe. The
 # compressed data is placed at the end of the buffer.  The output pointer
 # is placed at the start of the buffer and the input pointer is placed
 # where the compressed data starts. Problems will occur when the output
 # pointer overruns the input pointer.
 #
 # The output pointer can only overrun the input pointer if the input
 # pointer is moving faster than the output pointer.  A condition only
 # triggered by data whose compressed form is larger than the uncompressed
 # form.
 #
 # The worst case at the block level is a growth of the compressed data
 # of 5 bytes per 32767 bytes.
 #
 # The worst case internal to a compressed block is very hard to figure.
 # The worst case can at least be bounded by having one bit that represents
 # 32764 bytes and then all of the rest of the bytes representing the very
 # very last byte.
 #
 # All of which is enough to compute an amount of extra data that is required
 # to be safe.  To avoid problems at the block level allocating 5 extra bytes
 # per 32767 bytes of data is sufficient.  To avoid problems internal to a
 # block adding an extra 32767 bytes (the worst case uncompressed block size)
 # is sufficient, to ensure that in the worst case the decompressed data for
 # block will stop the byte before the compressed data for a block begins.
 # To avoid problems with the compressed data's meta information an extra 18
 # bytes are needed.  Leading to the formula:
 #
 # extra_bytes = (uncompressed_size >> 12) + 32768 + 18
 #
 # Adding 8 bytes per 32K is a bit excessive but much easier to calculate.
 # Adding 32768 instead of 32767 just makes for round numbers.
 #
 # Above analysis is for decompressing gzip compressed kernel only. Up to
 # now 6 different decompressor are supported all together. And among them
 # xz stores data in chunks and has maximum chunk of 64K. Hence safety
 # margin should be updated to cover all decompressors so that we don't
 # need to deal with each of them separately. Please check
 # the description in lib/decompressor_xxx.c for specific information.
 #
 # extra_bytes = (uncompressed_size >> 12) + 65536 + 128
 #
 # LZ4 is even worse: data that cannot be further compressed grows by 0.4%,
 # or one byte per 256 bytes. OTOH, we can safely get rid of the +128 as
 # the size-dependent part now grows so fast.
 #
 # extra_bytes = (uncompressed_size >> 8) + 65536
 #
 # ZSTD compressed data grows by at most 3 bytes per 128K, and only has a 22
 # byte fixed overhead but has a maximum block size of 128K, so it needs a
 # larger margin.
 #
 # extra_bytes = (uncompressed_size >> 8) + 131072

 #define ZO_z_extra_bytes	((ZO_z_output_len >> 8) + 131072)
 #if ZO_z_output_len > ZO_z_input_len
 # define ZO_z_extract_offset	(ZO_z_output_len + ZO_z_extra_bytes - \
 				 ZO_z_input_len)
 #else
 # define ZO_z_extract_offset	ZO_z_extra_bytes
 #endif

 /*
  * The extract_offset has to be bigger than ZO head section. Otherwise when
  * the head code is running to move ZO to the end of the buffer, it will
  * overwrite the head code itself.
  */
 #if (ZO__ehead - ZO_startup_32) > ZO_z_extract_offset
 # define ZO_z_min_extract_offset ((ZO__ehead - ZO_startup_32 + 4095) & ~4095)
 #else
 # define ZO_z_min_extract_offset ((ZO_z_extract_offset + 4095) & ~4095)
 #endif

 #define ZO_INIT_SIZE	(ZO__end - ZO_startup_32 + ZO_z_min_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
 handover_offset:	.long 0			# Filled in by build.c
 kernel_info_offset:	.long 0			# Filled in by build.c

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

 	.section ".entrytext", "ax"
 start_of_setup:
 # 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"
	/* SPDX-License-Identifier: GPL-2.0 */
	/*
	* 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 <linux/pe.h>
	#include <asm/segment.h>
	#include <asm/boot.h>
	#include <asm/page_types.h>
	#include <asm/setup.h>
	#include <asm/bootparam.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 ROOT_RDONLY
	#define ROOT_RDONLY 1
	#endif

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

	.global bootsect_start
	bootsect_start:
	#ifdef CONFIG_EFI_STUB
	# "MZ", MS-DOS header
	.word MZ_MAGIC
	#endif

	# 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

	#ifdef CONFIG_EFI_STUB
	.org 0x3c
	#
	# Offset to the PE header.
	#
	.long pe_header
	#endif /* CONFIG_EFI_STUB */

	.section ".bsdata", "a"
	bugger_off_msg:
	.ascii "Use a boot loader.\r\n"
	.ascii "\n"
	.ascii "Remove disk and press any key to reboot...\r\n"
	.byte 0

	#ifdef CONFIG_EFI_STUB
	pe_header:
	.long PE_MAGIC

	coff_header:
	#ifdef CONFIG_X86_32
	.set image_file_add_flags, IMAGE_FILE_32BIT_MACHINE
	.set pe_opt_magic, PE_OPT_MAGIC_PE32
	.word IMAGE_FILE_MACHINE_I386
	#else
	.set image_file_add_flags, 0
	.set pe_opt_magic, PE_OPT_MAGIC_PE32PLUS
	.word IMAGE_FILE_MACHINE_AMD64
	#endif
	.word section_count # nr_sections
	.long 0 # TimeDateStamp
	.long 0 # PointerToSymbolTable
	.long 1 # NumberOfSymbols
	.word section_table - optional_header # SizeOfOptionalHeader
	.word IMAGE_FILE_EXECUTABLE_IMAGE \| \
	image_file_add_flags \| \
	IMAGE_FILE_DEBUG_STRIPPED \| \
	IMAGE_FILE_LINE_NUMS_STRIPPED # Characteristics

	optional_header:
	.word pe_opt_magic
	.byte 0x02 # MajorLinkerVersion
	.byte 0x14 # MinorLinkerVersion

	# Filled in by build.c
	.long 0 # SizeOfCode

	.long 0 # SizeOfInitializedData
	.long 0 # SizeOfUninitializedData

	# Filled in by build.c
	.long 0x0000 # AddressOfEntryPoint

	.long 0x0200 # BaseOfCode
	#ifdef CONFIG_X86_32
	.long 0 # data
	#endif

	extra_header_fields:
	# PE specification requires ImageBase to be 64k aligned
	.set image_base, (LOAD_PHYSICAL_ADDR + 0xffff) & ~0xffff
	#ifdef CONFIG_X86_32
	.long image_base # ImageBase
	#else
	.quad image_base # ImageBase
	#endif
	.long 0x20 # SectionAlignment
	.long 0x20 # FileAlignment
	.word 0 # MajorOperatingSystemVersion
	.word 0 # MinorOperatingSystemVersion
	.word LINUX_EFISTUB_MAJOR_VERSION # MajorImageVersion
	.word LINUX_EFISTUB_MINOR_VERSION # MinorImageVersion
	.word 0 # MajorSubsystemVersion
	.word 0 # MinorSubsystemVersion
	.long 0 # Win32VersionValue

	#
	# The size of the bzImage is written in tools/build.c
	#
	.long 0 # SizeOfImage

	.long 0x200 # SizeOfHeaders
	.long 0 # CheckSum
	.word IMAGE_SUBSYSTEM_EFI_APPLICATION # Subsystem (EFI application)
	#ifdef CONFIG_EFI_DXE_MEM_ATTRIBUTES
	.word IMAGE_DLL_CHARACTERISTICS_NX_COMPAT # DllCharacteristics
	#else
	.word 0 # DllCharacteristics
	#endif
	#ifdef CONFIG_X86_32
	.long 0 # SizeOfStackReserve
	.long 0 # SizeOfStackCommit
	.long 0 # SizeOfHeapReserve
	.long 0 # SizeOfHeapCommit
	#else
	.quad 0 # SizeOfStackReserve
	.quad 0 # SizeOfStackCommit
	.quad 0 # SizeOfHeapReserve
	.quad 0 # SizeOfHeapCommit
	#endif
	.long 0 # LoaderFlags
	.long (section_table - .) / 8 # NumberOfRvaAndSizes

	.quad 0 # ExportTable
	.quad 0 # ImportTable
	.quad 0 # ResourceTable
	.quad 0 # ExceptionTable
	.quad 0 # CertificationTable
	.quad 0 # BaseRelocationTable

	# Section table
	section_table:
	#
	# The offset & size fields are filled in by build.c.
	#
	.ascii ".setup"
	.byte 0
	.byte 0
	.long 0
	.long 0x0 # startup_{32,64}
	.long 0 # Size of initialized data
	# on disk
	.long 0x0 # startup_{32,64}
	.long 0 # PointerToRelocations
	.long 0 # PointerToLineNumbers
	.word 0 # NumberOfRelocations
	.word 0 # NumberOfLineNumbers
	.long IMAGE_SCN_CNT_CODE \| \
	IMAGE_SCN_MEM_READ \| \
	IMAGE_SCN_MEM_EXECUTE \| \
	IMAGE_SCN_ALIGN_16BYTES # Characteristics

	#
	# The EFI application loader requires a relocation section
	# because EFI applications must be relocatable. The .reloc
	# offset & size fields are filled in by build.c.
	#
	.ascii ".reloc"
	.byte 0
	.byte 0
	.long 0
	.long 0
	.long 0 # SizeOfRawData
	.long 0 # PointerToRawData
	.long 0 # PointerToRelocations
	.long 0 # PointerToLineNumbers
	.word 0 # NumberOfRelocations
	.word 0 # NumberOfLineNumbers
	.long IMAGE_SCN_CNT_INITIALIZED_DATA \| \
	IMAGE_SCN_MEM_READ \| \
	IMAGE_SCN_MEM_DISCARDABLE \| \
	IMAGE_SCN_ALIGN_1BYTES # Characteristics

	#ifdef CONFIG_EFI_MIXED
	#
	# The offset & size fields are filled in by build.c.
	#
	.asciz ".compat"
	.long 0
	.long 0x0
	.long 0 # Size of initialized data
	# on disk
	.long 0x0
	.long 0 # PointerToRelocations
	.long 0 # PointerToLineNumbers
	.word 0 # NumberOfRelocations
	.word 0 # NumberOfLineNumbers
	.long IMAGE_SCN_CNT_INITIALIZED_DATA \| \
	IMAGE_SCN_MEM_READ \| \
	IMAGE_SCN_MEM_DISCARDABLE \| \
	IMAGE_SCN_ALIGN_1BYTES # Characteristics
	#endif

	#
	# The offset & size fields are filled in by build.c.
	#
	.ascii ".text"
	.byte 0
	.byte 0
	.byte 0
	.long 0
	.long 0x0 # startup_{32,64}
	.long 0 # Size of initialized data
	# on disk
	.long 0x0 # startup_{32,64}
	.long 0 # PointerToRelocations
	.long 0 # PointerToLineNumbers
	.word 0 # NumberOfRelocations
	.word 0 # NumberOfLineNumbers
	.long IMAGE_SCN_CNT_CODE \| \
	IMAGE_SCN_MEM_READ \| \
	IMAGE_SCN_MEM_EXECUTE \| \
	IMAGE_SCN_ALIGN_16BYTES # Characteristics

	.set section_count, (. - section_table) / 40
	#endif /* CONFIG_EFI_STUB */

	# Kernel attributes; used by setup. This is part 1 of the
	# header, from the old boot sector.

	.section ".header", "a"
	.globl sentinel
	sentinel: .byte 0xff, 0xff /* Used to detect broken loaders */

	.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 0x020f # 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.rst for
	# assigned ids

	# flags, unused bits must be zero (RFU) bit within loadflags
	loadflags:
	.byte LOADED_HIGH # The kernel is to be 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.

	initrd_addr_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

	xloadflags:
	#ifdef CONFIG_X86_64
	# define XLF0 XLF_KERNEL_64 /* 64-bit kernel */
	#else
	# define XLF0 0
	#endif

	#if defined(CONFIG_RELOCATABLE) && defined(CONFIG_X86_64)
	/* kernel/boot_param/ramdisk could be loaded above 4g */
	# define XLF1 XLF_CAN_BE_LOADED_ABOVE_4G
	#else
	# define XLF1 0
	#endif

	#ifdef CONFIG_EFI_STUB
	# ifdef CONFIG_EFI_MIXED
	# define XLF23 (XLF_EFI_HANDOVER_32\|XLF_EFI_HANDOVER_64)
	# else
	# ifdef CONFIG_X86_64
	# define XLF23 XLF_EFI_HANDOVER_64 /* 64-bit EFI handover ok */
	# else
	# define XLF23 XLF_EFI_HANDOVER_32 /* 32-bit EFI handover ok */
	# endif
	# endif
	#else
	# define XLF23 0
	#endif

	#if defined(CONFIG_X86_64) && defined(CONFIG_EFI) && defined(CONFIG_KEXEC_CORE)
	# define XLF4 XLF_EFI_KEXEC
	#else
	# define XLF4 0
	#endif

	#ifdef CONFIG_X86_64
	#ifdef CONFIG_X86_5LEVEL
	#define XLF56 (XLF_5LEVEL\|XLF_5LEVEL_ENABLED)
	#else
	#define XLF56 XLF_5LEVEL
	#endif
	#else
	#define XLF56 0
	#endif

	.word XLF0 \| XLF1 \| XLF23 \| XLF4 \| XLF56

	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

	#
	# Getting to provably safe in-place decompression is hard. Worst case
	# behaviours need to be analyzed. Here let's take the decompression of
	# a gzip-compressed kernel as example, to illustrate it:
	#
	# The file layout of gzip compressed kernel is:
	#
	# magic[2]
	# method[1]
	# flags[1]
	# timestamp[4]
	# extraflags[1]
	# os[1]
	# compressed data blocks[N]
	# crc[4] orig_len[4]
	#
	# ... resulting in +18 bytes overhead of uncompressed data.
	#
	# (For more information, please refer to RFC 1951 and RFC 1952.)
	#
	# Files divided into blocks
	# 1 bit (last block flag)
	# 2 bits (block type)
	#
	# 1 block occurs every 32K -1 bytes or when there 50% compression
	# has been achieved. The smallest block type encoding is always used.
	#
	# stored:
	# 32 bits length in bytes.
	#
	# fixed:
	# magic fixed tree.
	# symbols.
	#
	# dynamic:
	# dynamic tree encoding.
	# symbols.
	#
	#
	# The buffer for decompression in place is the length of the uncompressed
	# data, plus a small amount extra to keep the algorithm safe. The
	# compressed data is placed at the end of the buffer. The output pointer
	# is placed at the start of the buffer and the input pointer is placed
	# where the compressed data starts. Problems will occur when the output
	# pointer overruns the input pointer.
	#
	# The output pointer can only overrun the input pointer if the input
	# pointer is moving faster than the output pointer. A condition only
	# triggered by data whose compressed form is larger than the uncompressed
	# form.
	#
	# The worst case at the block level is a growth of the compressed data
	# of 5 bytes per 32767 bytes.
	#
	# The worst case internal to a compressed block is very hard to figure.
	# The worst case can at least be bounded by having one bit that represents
	# 32764 bytes and then all of the rest of the bytes representing the very
	# very last byte.
	#
	# All of which is enough to compute an amount of extra data that is required
	# to be safe. To avoid problems at the block level allocating 5 extra bytes
	# per 32767 bytes of data is sufficient. To avoid problems internal to a
	# block adding an extra 32767 bytes (the worst case uncompressed block size)
	# is sufficient, to ensure that in the worst case the decompressed data for
	# block will stop the byte before the compressed data for a block begins.
	# To avoid problems with the compressed data's meta information an extra 18
	# bytes are needed. Leading to the formula:
	#
	# extra_bytes = (uncompressed_size >> 12) + 32768 + 18
	#
	# Adding 8 bytes per 32K is a bit excessive but much easier to calculate.
	# Adding 32768 instead of 32767 just makes for round numbers.
	#
	# Above analysis is for decompressing gzip compressed kernel only. Up to
	# now 6 different decompressor are supported all together. And among them
	# xz stores data in chunks and has maximum chunk of 64K. Hence safety
	# margin should be updated to cover all decompressors so that we don't
	# need to deal with each of them separately. Please check
	# the description in lib/decompressor_xxx.c for specific information.
	#
	# extra_bytes = (uncompressed_size >> 12) + 65536 + 128
	#
	# LZ4 is even worse: data that cannot be further compressed grows by 0.4%,
	# or one byte per 256 bytes. OTOH, we can safely get rid of the +128 as
	# the size-dependent part now grows so fast.
	#
	# extra_bytes = (uncompressed_size >> 8) + 65536
	#
	# ZSTD compressed data grows by at most 3 bytes per 128K, and only has a 22
	# byte fixed overhead but has a maximum block size of 128K, so it needs a
	# larger margin.
	#
	# extra_bytes = (uncompressed_size >> 8) + 131072

	#define ZO_z_extra_bytes ((ZO_z_output_len >> 8) + 131072)
	#if ZO_z_output_len > ZO_z_input_len
	# define ZO_z_extract_offset (ZO_z_output_len + ZO_z_extra_bytes - \
	ZO_z_input_len)
	#else
	# define ZO_z_extract_offset ZO_z_extra_bytes
	#endif

	/*
	* The extract_offset has to be bigger than ZO head section. Otherwise when
	* the head code is running to move ZO to the end of the buffer, it will
	* overwrite the head code itself.
	*/
	#if (ZO__ehead - ZO_startup_32) > ZO_z_extract_offset
	# define ZO_z_min_extract_offset ((ZO__ehead - ZO_startup_32 + 4095) & ~4095)
	#else
	# define ZO_z_min_extract_offset ((ZO_z_extract_offset + 4095) & ~4095)
	#endif

	#define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_min_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
	handover_offset: .long 0 # Filled in by build.c
	kernel_info_offset: .long 0 # Filled in by build.c

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

	.section ".entrytext", "ax"
	start_of_setup:
	# 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"