Message-Id: <20190423162932.21428-39-changbin.du@gmail.com>
Date:   Wed, 24 Apr 2019 00:29:07 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Jonathan Corbet <corbet@....net>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, rjw@...ysocki.net,
        linux-pci@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        x86@...nel.org, fenghua.yu@...el.com,
        linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
        linux-gpio@...r.kernel.org, mchehab+samsung@...nel.org,
        Changbin Du <changbin.du@...il.com>
Subject: [PATCH v4 38/63] Documentation: x86: convert boot.txt to reST

This converts the plain text documentation to reStructuredText format and
add it to Sphinx TOC tree. No essential content change.

Signed-off-by: Changbin Du <changbin.du@...il.com>
---
 Documentation/x86/boot.rst  | 1205 +++++++++++++++++++++++++++++++++++
 Documentation/x86/boot.txt  | 1130 --------------------------------
 Documentation/x86/index.rst |    2 +
 3 files changed, 1207 insertions(+), 1130 deletions(-)
 create mode 100644 Documentation/x86/boot.rst
 delete mode 100644 Documentation/x86/boot.txt

diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst
new file mode 100644
index 000000000000..9f55e832bc47
--- /dev/null
+++ b/Documentation/x86/boot.rst
@@ -0,0 +1,1205 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===========================
+The Linux/x86 Boot Protocol
+===========================
+
+On the x86 platform, the Linux kernel uses a rather complicated boot
+convention.  This has evolved partially due to historical aspects, as
+well as the desire in the early days to have the kernel itself be a
+bootable image, the complicated PC memory model and due to changed
+expectations in the PC industry caused by the effective demise of
+real-mode DOS as a mainstream operating system.
+
+Currently, the following versions of the Linux/x86 boot protocol exist.
+
+Old kernels:
+  zImage/Image support only.  Some very early kernels
+  may not even support a command line.
+
+Protocol 2.00:
+  (Kernel 1.3.73) Added bzImage and initrd support, as
+  well as a formalized way to communicate between the
+  boot loader and the kernel.  setup.S made relocatable,
+  although the traditional setup area still assumed writable.
+
+Protocol 2.01:
+  (Kernel 1.3.76) Added a heap overrun warning.
+
+Protocol 2.02:
+  (Kernel 2.4.0-test3-pre3) New command line protocol.
+  Lower the conventional memory ceiling.	No overwrite
+  of the traditional setup area, thus making booting
+  safe for systems which use the EBDA from SMM or 32-bit
+  BIOS entry points.  zImage deprecated but still supported.
+
+Protocol 2.03:
+  (Kernel 2.4.18-pre1) Explicitly makes the highest possible
+  initrd address available to the bootloader.
+
+Protocol 2.04:
+  (Kernel 2.6.14) Extend the syssize field to four bytes.
+
+Protocol 2.05:
+  (Kernel 2.6.20) Make protected mode kernel relocatable.
+  Introduce relocatable_kernel and kernel_alignment fields.
+
+Protocol 2.06:
+  (Kernel 2.6.22) Added a field that contains the size of
+  the boot command line.
+
+Protocol 2.07:
+  (Kernel 2.6.24) Added paravirtualised boot protocol.
+  Introduced hardware_subarch and hardware_subarch_data
+  and KEEP_SEGMENTS flag in load_flags.
+
+Protocol 2.08:
+  (Kernel 2.6.26) Added crc32 checksum and ELF format
+  payload. Introduced payload_offset and payload_length
+  fields to aid in locating the payload.
+
+Protocol 2.09:
+  (Kernel 2.6.26) Added a field of 64-bit physical
+  pointer to single linked list of struct	setup_data.
+
+Protocol 2.10:
+  (Kernel 2.6.31) Added a protocol for relaxed alignment
+  beyond the kernel_alignment added, new init_size and
+  pref_address fields.  Added extended boot loader IDs.
+
+Protocol 2.11:
+  (Kernel 3.6) Added a field for offset of EFI handover
+  protocol entry point.
+
+Protocol 2.12:
+  (Kernel 3.8) Added the xloadflags field and extension fields
+  to struct boot_params for loading bzImage and ramdisk
+  above 4G in 64bit.
+
+MEMORY LAYOUT
+=============
+
+The traditional memory map for the kernel loader, used for Image or
+zImage kernels, typically looks like::
+
+    |			 |
+  0A0000	+------------------------+
+    |  Reserved for BIOS	 |	Do not use.  Reserved for BIOS EBDA.
+  09A000	+------------------------+
+    |  Command line		 |
+    |  Stack/heap		 |	For use by the kernel real-mode code.
+  098000	+------------------------+	
+    |  Kernel setup		 |	The kernel real-mode code.
+  090200	+------------------------+
+    |  Kernel boot sector	 |	The kernel legacy boot sector.
+  090000	+------------------------+
+    |  Protected-mode kernel |	The bulk of the kernel image.
+  010000	+------------------------+
+    |  Boot loader		 |	<- Boot sector entry point 0000:7C00
+  001000	+------------------------+
+    |  Reserved for MBR/BIOS |
+  000800	+------------------------+
+    |  Typically used by MBR |
+  000600	+------------------------+ 
+    |  BIOS use only	 |
+  000000	+------------------------+
+
+
+When using bzImage, the protected-mode kernel was relocated to
+0x100000 ("high memory"), and the kernel real-mode block (boot sector,
+setup, and stack/heap) was made relocatable to any address between
+0x10000 and end of low memory. Unfortunately, in protocols 2.00 and
+2.01 the 0x90000+ memory range is still used internally by the kernel;
+the 2.02 protocol resolves that problem.
+
+It is desirable to keep the "memory ceiling" -- the highest point in
+low memory touched by the boot loader -- as low as possible, since
+some newer BIOSes have begun to allocate some rather large amounts of
+memory, called the Extended BIOS Data Area, near the top of low
+memory.	 The boot loader should use the "INT 12h" BIOS call to verify
+how much low memory is available.
+
+Unfortunately, if INT 12h reports that the amount of memory is too
+low, there is usually nothing the boot loader can do but to report an
+error to the user.  The boot loader should therefore be designed to
+take up as little space in low memory as it reasonably can.  For
+zImage or old bzImage kernels, which need data written into the
+0x90000 segment, the boot loader should make sure not to use memory
+above the 0x9A000 point; too many BIOSes will break above that point.
+
+For a modern bzImage kernel with boot protocol version >= 2.02, a
+memory layout like the following is suggested::
+
+    ~                        ~
+          |  Protected-mode kernel |
+  100000  +------------------------+
+    |  I/O memory hole	 |
+  0A0000	+------------------------+
+    |  Reserved for BIOS	 |	Leave as much as possible unused
+    ~                        ~
+    |  Command line		 |	(Can also be below the X+10000 mark)
+  X+10000	+------------------------+
+    |  Stack/heap		 |	For use by the kernel real-mode code.
+  X+08000	+------------------------+	
+    |  Kernel setup		 |	The kernel real-mode code.
+    |  Kernel boot sector	 |	The kernel legacy boot sector.
+  X       +------------------------+
+    |  Boot loader		 |	<- Boot sector entry point 0000:7C00
+  001000	+------------------------+
+    |  Reserved for MBR/BIOS |
+  000800	+------------------------+
+    |  Typically used by MBR |
+  000600	+------------------------+ 
+    |  BIOS use only	 |
+  000000	+------------------------+
+
+... where the address X is as low as the design of the boot loader
+permits.
+
+
+THE REAL-MODE KERNEL HEADER
+===========================
+
+In the following text, and anywhere in the kernel boot sequence, "a
+sector" refers to 512 bytes.  It is independent of the actual sector
+size of the underlying medium.
+
+The first step in loading a Linux kernel should be to load the
+real-mode code (boot sector and setup code) and then examine the
+following header at offset 0x01f1.  The real-mode code can total up to
+32K, although the boot loader may choose to load only the first two
+sectors (1K) and then examine the bootup sector size.
+
+The header looks like::
+
+  Offset	Proto	Name		Meaning
+  /Size
+
+  01F1/1	ALL(1	setup_sects	The size of the setup in sectors
+  01F2/2	ALL	root_flags	If set, the root is mounted readonly
+  01F4/4	2.04+(2	syssize		The size of the 32-bit code in 16-byte paras
+  01F8/2	ALL	ram_size	DO NOT USE - for bootsect.S use only
+  01FA/2	ALL	vid_mode	Video mode control
+  01FC/2	ALL	root_dev	Default root device number
+  01FE/2	ALL	boot_flag	0xAA55 magic number
+  0200/2	2.00+	jump		Jump instruction
+  0202/4	2.00+	header		Magic signature "HdrS"
+  0206/2	2.00+	version		Boot protocol version supported
+  0208/4	2.00+	realmode_swtch	Boot loader hook (see below)
+  020C/2	2.00+	start_sys_seg	The load-low segment (0x1000) (obsolete)
+  020E/2	2.00+	kernel_version	Pointer to kernel version string
+  0210/1	2.00+	type_of_loader	Boot loader identifier
+  0211/1	2.00+	loadflags	Boot protocol option flags
+  0212/2	2.00+	setup_move_size	Move to high memory size (used with hooks)
+  0214/4	2.00+	code32_start	Boot loader hook (see below)
+  0218/4	2.00+	ramdisk_image	initrd load address (set by boot loader)
+  021C/4	2.00+	ramdisk_size	initrd size (set by boot loader)
+  0220/4	2.00+	bootsect_kludge	DO NOT USE - for bootsect.S use only
+  0224/2	2.01+	heap_end_ptr	Free memory after setup end
+  0226/1	2.02+(3 ext_loader_ver	Extended boot loader version
+  0227/1	2.02+(3	ext_loader_type	Extended boot loader ID
+  0228/4	2.02+	cmd_line_ptr	32-bit pointer to the kernel command line
+  022C/4	2.03+	initrd_addr_max	Highest legal initrd address
+  0230/4	2.05+	kernel_alignment Physical addr alignment required for kernel
+  0234/1	2.05+	relocatable_kernel Whether kernel is relocatable or not
+  0235/1	2.10+	min_alignment	Minimum alignment, as a power of two
+  0236/2	2.12+	xloadflags	Boot protocol option flags
+  0238/4	2.06+	cmdline_size	Maximum size of the kernel command line
+  023C/4	2.07+	hardware_subarch Hardware subarchitecture
+  0240/8	2.07+	hardware_subarch_data Subarchitecture-specific data
+  0248/4	2.08+	payload_offset	Offset of kernel payload
+  024C/4	2.08+	payload_length	Length of kernel payload
+  0250/8	2.09+	setup_data	64-bit physical pointer to linked list
+          of struct setup_data
+  0258/8	2.10+	pref_address	Preferred loading address
+  0260/4	2.10+	init_size	Linear memory required during initialization
+  0264/4	2.11+	handover_offset	Offset of handover entry point
+
+(1) For backwards compatibility, if the setup_sects field contains 0, the
+    real value is 4.
+
+(2) For boot protocol prior to 2.04, the upper two bytes of the syssize
+    field are unusable, which means the size of a bzImage kernel
+    cannot be determined.
+
+(3) Ignored, but safe to set, for boot protocols 2.02-2.09.
+
+If the "HdrS" (0x53726448) magic number is not found at offset 0x202,
+the boot protocol version is "old".  Loading an old kernel, the
+following parameters should be assumed::
+
+	Image type = zImage
+	initrd not supported
+	Real-mode kernel must be located at 0x90000.
+
+Otherwise, the "version" field contains the protocol version,
+e.g. protocol version 2.01 will contain 0x0201 in this field.  When
+setting fields in the header, you must make sure only to set fields
+supported by the protocol version in use.
+
+
+DETAILS OF HEADER FIELDS
+========================
+
+For each field, some are information from the kernel to the bootloader
+("read"), some are expected to be filled out by the bootloader
+("write"), and some are expected to be read and modified by the
+bootloader ("modify").
+
+All general purpose boot loaders should write the fields marked
+(obligatory).  Boot loaders who want to load the kernel at a
+nonstandard address should fill in the fields marked (reloc); other
+boot loaders can ignore those fields.
+
+The byte order of all fields is littleendian (this is x86, after all.)
+::
+
+  Field name:	setup_sects
+  Type:		read
+  Offset/size:	0x1f1/1
+  Protocol:	ALL
+
+The size of the setup code in 512-byte sectors.  If this field is
+0, the real value is 4.  The real-mode code consists of the boot
+sector (always one 512-byte sector) plus the setup code.
+::
+
+  Field name:	 root_flags
+  Type:		 modify (optional)
+  Offset/size:	 0x1f2/2
+  Protocol:	 ALL
+
+If this field is nonzero, the root defaults to readonly.  The use of
+this field is deprecated; use the "ro" or "rw" options on the
+command line instead.
+::
+
+  Field name:	syssize
+  Type:		read
+  Offset/size:	0x1f4/4 (protocol 2.04+) 0x1f4/2 (protocol ALL)
+  Protocol:	2.04+
+
+The size of the protected-mode code in units of 16-byte paragraphs.
+For protocol versions older than 2.04 this field is only two bytes
+wide, and therefore cannot be trusted for the size of a kernel if
+the LOAD_HIGH flag is set.
+::
+
+  Field name:	ram_size
+  Type:		kernel internal
+  Offset/size:	0x1f8/2
+  Protocol:	ALL
+
+This field is obsolete.
+::
+
+  Field name:	vid_mode
+  Type:		modify (obligatory)
+  Offset/size:	0x1fa/2
+
+Please see the section on SPECIAL COMMAND LINE OPTIONS.
+::
+
+  Field name:	root_dev
+  Type:		modify (optional)
+  Offset/size:	0x1fc/2
+  Protocol:	ALL
+
+The default root device device number.  The use of this field is
+deprecated, use the "root=" option on the command line instead.
+::
+
+  Field name:	boot_flag
+  Type:		read
+  Offset/size:	0x1fe/2
+  Protocol:	ALL
+
+Contains 0xAA55.  This is the closest thing old Linux kernels have
+to a magic number.
+::
+
+  Field name:	jump
+  Type:		read
+  Offset/size:	0x200/2
+  Protocol:	2.00+
+
+Contains an x86 jump instruction, 0xEB followed by a signed offset
+relative to byte 0x202.  This can be used to determine the size of
+the header.
+::
+
+  Field name:	header
+  Type:		read
+  Offset/size:	0x202/4
+  Protocol:	2.00+
+
+Contains the magic number "HdrS" (0x53726448).
+::
+
+  Field name:	version
+  Type:		read
+  Offset/size:	0x206/2
+  Protocol:	2.00+
+
+Contains the boot protocol version, in (major << 8)+minor format,
+e.g. 0x0204 for version 2.04, and 0x0a11 for a hypothetical version
+10.17.
+::
+
+  Field name:	realmode_swtch
+  Type:		modify (optional)
+  Offset/size:	0x208/4
+  Protocol:	2.00+
+
+Boot loader hook (see ADVANCED BOOT LOADER HOOKS below.)
+::
+
+  Field name:	start_sys_seg
+  Type:		read
+  Offset/size:	0x20c/2
+  Protocol:	2.00+
+
+The load low segment (0x1000).  Obsolete.
+::
+
+  Field name:	kernel_version
+  Type:		read
+  Offset/size:	0x20e/2
+  Protocol:	2.00+
+
+If set to a nonzero value, contains a pointer to a NUL-terminated
+human-readable kernel version number string, less 0x200.  This can
+be used to display the kernel version to the user.  This value
+should be less than (0x200*setup_sects).
+
+For example, if this value is set to 0x1c00, the kernel version
+number string can be found at offset 0x1e00 in the kernel file.
+This is a valid value if and only if the "setup_sects" field
+contains the value 15 or higher, as::
+
+	0x1c00  < 15*0x200 (= 0x1e00) but
+	0x1c00 >= 14*0x200 (= 0x1c00)
+
+	0x1c00 >> 9 = 14, so the minimum value for setup_secs is 15.
+
+::
+
+  Field name:	type_of_loader
+  Type:		write (obligatory)
+  Offset/size:	0x210/1
+  Protocol:	2.00+
+
+If your boot loader has an assigned id (see table below), enter
+0xTV here, where T is an identifier for the boot loader and V is
+a version number.  Otherwise, enter 0xFF here.
+
+For boot loader IDs above T = 0xD, write T = 0xE to this field and
+write the extended ID minus 0x10 to the ext_loader_type field.
+Similarly, the ext_loader_ver field can be used to provide more than
+four bits for the bootloader version.
+
+For example, for T = 0x15, V = 0x234, write::
+
+  type_of_loader  <- 0xE4
+  ext_loader_type <- 0x05
+  ext_loader_ver  <- 0x23
+
+Assigned boot loader ids (hexadecimal)::
+
+	0  LILO			(0x00 reserved for pre-2.00 bootloader)
+	1  Loadlin
+	2  bootsect-loader	(0x20, all other values reserved)
+	3  Syslinux
+	4  Etherboot/gPXE/iPXE
+	5  ELILO
+	7  GRUB
+	8  U-Boot
+	9  Xen
+	A  Gujin
+	B  Qemu
+	C  Arcturus Networks uCbootloader
+	D  kexec-tools
+	E  Extended		(see ext_loader_type)
+	F  Special		(0xFF = undefined)
+       10  Reserved
+       11  Minimal Linux Bootloader <http://sebastian-plotz.blogspot.de>
+       12  OVMF UEFI virtualization stack
+
+Please contact <hpa@...or.com> if you need a bootloader ID value assigned.
+::
+
+  Field name:	loadflags
+  Type:		modify (obligatory)
+  Offset/size:	0x211/1
+  Protocol:	2.00+
+
+This field is a bitmask.
+::
+
+  Bit 0 (read):	LOADED_HIGH
+	- If 0, the protected-mode code is loaded at 0x10000.
+	- If 1, the protected-mode code is loaded at 0x100000.
+
+  Bit 1 (kernel internal): KASLR_FLAG
+	- Used internally by the compressed kernel to communicate
+	  KASLR status to kernel proper.
+	  If 1, KASLR enabled.
+	  If 0, KASLR disabled.
+
+  Bit 5 (write): QUIET_FLAG
+	- If 0, print early messages.
+	- If 1, suppress early messages.
+		This requests to the kernel (decompressor and early
+		kernel) to not write early messages that require
+		accessing the display hardware directly.
+
+  Bit 6 (write): KEEP_SEGMENTS
+	Protocol: 2.07+
+	- If 0, reload the segment registers in the 32bit entry point.
+	- If 1, do not reload the segment registers in the 32bit entry point.
+		Assume that %cs %ds %ss %es are all set to flat segments with
+		a base of 0 (or the equivalent for their environment).
+
+  Bit 7 (write): CAN_USE_HEAP
+	Set this bit to 1 to indicate that the value entered in the
+	heap_end_ptr is valid.  If this field is clear, some setup code
+	functionality will be disabled.
+
+::
+
+  Field name:	setup_move_size
+  Type:		modify (obligatory)
+  Offset/size:	0x212/2
+  Protocol:	2.00-2.01
+
+When using protocol 2.00 or 2.01, if the real mode kernel is not
+loaded at 0x90000, it gets moved there later in the loading
+sequence.  Fill in this field if you want additional data (such as
+the kernel command line) moved in addition to the real-mode kernel
+itself.
+
+The unit is bytes starting with the beginning of the boot sector.
+  
+This field is can be ignored when the protocol is 2.02 or higher, or
+if the real-mode code is loaded at 0x90000.
+::
+
+  Field name:	code32_start
+  Type:		modify (optional, reloc)
+  Offset/size:	0x214/4
+  Protocol:	2.00+
+
+The address to jump to in protected mode.  This defaults to the load
+address of the kernel, and can be used by the boot loader to
+determine the proper load address.
+
+This field can be modified for two purposes:
+
+  1. as a boot loader hook (see ADVANCED BOOT LOADER HOOKS below.)
+
+  2. if a bootloader which does not install a hook loads a
+     relocatable kernel at a nonstandard address it will have to modify
+     this field to point to the load address.
+
+::
+
+  Field name:	ramdisk_image
+  Type:		write (obligatory)
+  Offset/size:	0x218/4
+  Protocol:	2.00+
+
+The 32-bit linear address of the initial ramdisk or ramfs.  Leave at
+zero if there is no initial ramdisk/ramfs.
+::
+
+  Field name:	ramdisk_size
+  Type:		write (obligatory)
+  Offset/size:	0x21c/4
+  Protocol:	2.00+
+
+Size of the initial ramdisk or ramfs.  Leave at zero if there is no
+initial ramdisk/ramfs.
+::
+
+  Field name:	bootsect_kludge
+  Type:		kernel internal
+  Offset/size:	0x220/4
+  Protocol:	2.00+
+
+This field is obsolete.
+::
+
+  Field name:	heap_end_ptr
+  Type:		write (obligatory)
+  Offset/size:	0x224/2
+  Protocol:	2.01+
+
+Set this field to the offset (from the beginning of the real-mode
+code) of the end of the setup stack/heap, minus 0x0200.
+::
+
+  Field name:	ext_loader_ver
+  Type:		write (optional)
+  Offset/size:	0x226/1
+  Protocol:	2.02+
+
+This field is used as an extension of the version number in the
+type_of_loader field.  The total version number is considered to be
+(type_of_loader & 0x0f) + (ext_loader_ver << 4).
+
+The use of this field is boot loader specific.  If not written, it
+is zero.
+
+Kernels prior to 2.6.31 did not recognize this field, but it is safe
+to write for protocol version 2.02 or higher.
+::
+
+  Field name:	ext_loader_type
+  Type:		write (obligatory if (type_of_loader & 0xf0) == 0xe0)
+  Offset/size:	0x227/1
+  Protocol:	2.02+
+
+This field is used as an extension of the type number in
+type_of_loader field.  If the type in type_of_loader is 0xE, then
+the actual type is (ext_loader_type + 0x10).
+
+This field is ignored if the type in type_of_loader is not 0xE.
+
+Kernels prior to 2.6.31 did not recognize this field, but it is safe
+to write for protocol version 2.02 or higher.
+::
+
+  Field name:	cmd_line_ptr
+  Type:		write (obligatory)
+  Offset/size:	0x228/4
+  Protocol:	2.02+
+
+Set this field to the linear address of the kernel command line.
+The kernel command line can be located anywhere between the end of
+the setup heap and 0xA0000; it does not have to be located in the
+same 64K segment as the real-mode code itself.
+
+Fill in this field even if your boot loader does not support a
+command line, in which case you can point this to an empty string
+(or better yet, to the string "auto".)  If this field is left at
+zero, the kernel will assume that your boot loader does not support
+the 2.02+ protocol.
+::
+
+  Field name:	initrd_addr_max
+  Type:		read
+  Offset/size:	0x22c/4
+  Protocol:	2.03+
+
+The maximum address that may be occupied by the initial
+ramdisk/ramfs contents.  For boot protocols 2.02 or earlier, this
+field is not present, and the maximum address is 0x37FFFFFF.  (This
+address is defined as the address of the highest safe byte, so if
+your ramdisk is exactly 131072 bytes long and this field is
+0x37FFFFFF, you can start your ramdisk at 0x37FE0000.)
+::
+
+  Field name:	kernel_alignment
+  Type:		read/modify (reloc)
+  Offset/size:	0x230/4
+  Protocol:	2.05+ (read), 2.10+ (modify)
+
+Alignment unit required by the kernel (if relocatable_kernel is
+true.)  A relocatable kernel that is loaded at an alignment
+incompatible with the value in this field will be realigned during
+kernel initialization.
+
+Starting with protocol version 2.10, this reflects the kernel
+alignment preferred for optimal performance; it is possible for the
+loader to modify this field to permit a lesser alignment.  See the
+min_alignment and pref_address field below.
+::
+
+  Field name:	relocatable_kernel
+  Type:		read (reloc)
+  Offset/size:	0x234/1
+  Protocol:	2.05+
+
+If this field is nonzero, the protected-mode part of the kernel can
+be loaded at any address that satisfies the kernel_alignment field.
+After loading, the boot loader must set the code32_start field to
+point to the loaded code, or to a boot loader hook.
+::
+
+  Field name:	min_alignment
+  Type:		read (reloc)
+  Offset/size:	0x235/1
+  Protocol:	2.10+
+
+This field, if nonzero, indicates as a power of two the minimum
+alignment required, as opposed to preferred, by the kernel to boot.
+If a boot loader makes use of this field, it should update the
+kernel_alignment field with the alignment unit desired; typically::
+
+	kernel_alignment = 1 << min_alignment
+
+There may be a considerable performance cost with an excessively
+misaligned kernel.  Therefore, a loader should typically try each
+power-of-two alignment from kernel_alignment down to this alignment.
+::
+
+  Field name:     xloadflags
+  Type:           read
+  Offset/size:    0x236/2
+  Protocol:       2.12+
+
+This field is a bitmask.
+::
+
+  Bit 0 (read):	XLF_KERNEL_64
+	- If 1, this kernel has the legacy 64-bit entry point at 0x200.
+
+  Bit 1 (read): XLF_CAN_BE_LOADED_ABOVE_4G
+        - If 1, kernel/boot_params/cmdline/ramdisk can be above 4G.
+
+  Bit 2 (read):	XLF_EFI_HANDOVER_32
+	- If 1, the kernel supports the 32-bit EFI handoff entry point
+          given at handover_offset.
+
+  Bit 3 (read): XLF_EFI_HANDOVER_64
+	- If 1, the kernel supports the 64-bit EFI handoff entry point
+          given at handover_offset + 0x200.
+
+  Bit 4 (read): XLF_EFI_KEXEC
+	- If 1, the kernel supports kexec EFI boot with EFI runtime support.
+
+::
+
+  Field name:	cmdline_size
+  Type:		read
+  Offset/size:	0x238/4
+  Protocol:	2.06+
+
+The maximum size of the command line without the terminating
+zero. This means that the command line can contain at most
+cmdline_size characters. With protocol version 2.05 and earlier, the
+maximum size was 255.
+::
+
+  Field name:	hardware_subarch
+  Type:		write (optional, defaults to x86/PC)
+  Offset/size:	0x23c/4
+  Protocol:	2.07+
+
+In a paravirtualized environment the hardware low level architectural
+pieces such as interrupt handling, page table handling, and
+accessing process control registers needs to be done differently.
+
+This field allows the bootloader to inform the kernel we are in one
+one of those environments.
+::
+
+  0x00000000	The default x86/PC environment
+  0x00000001	lguest
+  0x00000002	Xen
+  0x00000003	Moorestown MID
+  0x00000004	CE4100 TV Platform
+
+::
+
+  Field name:	hardware_subarch_data
+  Type:		write (subarch-dependent)
+  Offset/size:	0x240/8
+  Protocol:	2.07+
+
+A pointer to data that is specific to hardware subarch
+This field is currently unused for the default x86/PC environment,
+do not modify.
+::
+
+  Field name:	payload_offset
+  Type:		read
+  Offset/size:	0x248/4
+  Protocol:	2.08+
+
+If non-zero then this field contains the offset from the beginning
+of the protected-mode code to the payload.
+
+The payload may be compressed. The format of both the compressed and
+uncompressed data should be determined using the standard magic
+numbers.  The currently supported compression formats are gzip
+(magic numbers 1F 8B or 1F 9E), bzip2 (magic number 42 5A), LZMA
+(magic number 5D 00), XZ (magic number FD 37), and LZ4 (magic number
+02 21).  The uncompressed payload is currently always ELF (magic
+number 7F 45 4C 46).
+::
+
+  Field name:	payload_length
+  Type:		read
+  Offset/size:	0x24c/4
+  Protocol:	2.08+
+
+The length of the payload.
+::
+
+  Field name:	setup_data
+  Type:		write (special)
+  Offset/size:	0x250/8
+  Protocol:	2.09+
+
+The 64-bit physical pointer to NULL terminated single linked list of
+struct setup_data. This is used to define a more extensible boot
+parameters passing mechanism. The definition of struct setup_data is
+as follow::
+
+  struct setup_data {
+	  u64 next;
+	  u32 type;
+	  u32 len;
+	  u8  data[0];
+  };
+
+Where, the next is a 64-bit physical pointer to the next node of
+linked list, the next field of the last node is 0; the type is used
+to identify the contents of data; the len is the length of data
+field; the data holds the real payload.
+
+This list may be modified at a number of points during the bootup
+process.  Therefore, when modifying this list one should always make
+sure to consider the case where the linked list already contains
+entries.
+::
+
+  Field name:	pref_address
+  Type:		read (reloc)
+  Offset/size:	0x258/8
+  Protocol:	2.10+
+
+This field, if nonzero, represents a preferred load address for the
+kernel.  A relocating bootloader should attempt to load at this
+address if possible.
+
+A non-relocatable kernel will unconditionally move itself and to run
+at this address.
+::
+
+  Field name:	init_size
+  Type:		read
+  Offset/size:	0x260/4
+
+This field indicates the amount of linear contiguous memory starting
+at the kernel runtime start address that the kernel needs before it
+is capable of examining its memory map.  This is not the same thing
+as the total amount of memory the kernel needs to boot, but it can
+be used by a relocating boot loader to help select a safe load
+address for the kernel.
+
+The kernel runtime start address is determined by the following algorithm::
+
+  if (relocatable_kernel)
+    runtime_start = align_up(load_address, kernel_alignment)
+  else
+    runtime_start = pref_address
+
+::
+
+  Field name:	handover_offset
+  Type:		read
+  Offset/size:	0x264/4
+
+This field is the offset from the beginning of the kernel image to
+the EFI handover protocol entry point. Boot loaders using the EFI
+handover protocol to boot the kernel should jump to this offset.
+
+See EFI HANDOVER PROTOCOL below for more details.
+
+
+THE IMAGE CHECKSUM
+==================
+
+From boot protocol version 2.08 onwards the CRC-32 is calculated over
+the entire file using the characteristic polynomial 0x04C11DB7 and an
+initial remainder of 0xffffffff.  The checksum is appended to the
+file; therefore the CRC of the file up to the limit specified in the
+syssize field of the header is always 0.
+
+
+THE KERNEL COMMAND LINE
+=======================
+
+The kernel command line has become an important way for the boot
+loader to communicate with the kernel.  Some of its options are also
+relevant to the boot loader itself, see "special command line options"
+below.
+
+The kernel command line is a null-terminated string. The maximum
+length can be retrieved from the field cmdline_size.  Before protocol
+version 2.06, the maximum was 255 characters.  A string that is too
+long will be automatically truncated by the kernel.
+
+If the boot protocol version is 2.02 or later, the address of the
+kernel command line is given by the header field cmd_line_ptr (see
+above.)  This address can be anywhere between the end of the setup
+heap and 0xA0000.
+
+If the protocol version is *not* 2.02 or higher, the kernel
+command line is entered using the following protocol:
+
+  - At offset 0x0020 (word), "cmd_line_magic", enter the magic
+    number 0xA33F.
+
+  - At offset 0x0022 (word), "cmd_line_offset", enter the offset
+    of the kernel command line (relative to the start of the
+    real-mode kernel).
+
+  - The kernel command line *must* be within the memory region
+    covered by setup_move_size, so you may need to adjust this
+    field.
+
+
+MEMORY LAYOUT OF THE REAL-MODE CODE
+===================================
+
+The real-mode code requires a stack/heap to be set up, as well as
+memory allocated for the kernel command line.  This needs to be done
+in the real-mode accessible memory in bottom megabyte.
+
+It should be noted that modern machines often have a sizable Extended
+BIOS Data Area (EBDA).  As a result, it is advisable to use as little
+of the low megabyte as possible.
+
+Unfortunately, under the following circumstances the 0x90000 memory
+segment has to be used:
+
+	- When loading a zImage kernel ((loadflags & 0x01) == 0).
+	- When loading a 2.01 or earlier boot protocol kernel.
+
+	     For the 2.00 and 2.01 boot protocols, the real-mode code
+	     can be loaded at another address, but it is internally
+	     relocated to 0x90000.  For the "old" protocol, the
+	     real-mode code must be loaded at 0x90000.
+
+When loading at 0x90000, avoid using memory above 0x9a000.
+
+For boot protocol 2.02 or higher, the command line does not have to be
+located in the same 64K segment as the real-mode setup code; it is
+thus permitted to give the stack/heap the full 64K segment and locate
+the command line above it.
+
+The kernel command line should not be located below the real-mode
+code, nor should it be located in high memory.
+
+
+SAMPLE BOOT CONFIGURATION
+=========================
+
+As a sample configuration, assume the following layout of the real
+mode segment.
+
+When loading below 0x90000, use the entire segment::
+
+	0x0000-0x7fff	Real mode kernel
+	0x8000-0xdfff	Stack and heap
+	0xe000-0xffff	Kernel command line
+
+When loading at 0x90000 OR the protocol version is 2.01 or earlier::
+
+	0x0000-0x7fff	Real mode kernel
+	0x8000-0x97ff	Stack and heap
+	0x9800-0x9fff	Kernel command line
+
+Such a boot loader should enter the following fields in the header::
+
+	unsigned long base_ptr;	/* base address for real-mode segment */
+
+	if ( setup_sects == 0 ) {
+		setup_sects = 4;
+	}
+
+	if ( protocol >= 0x0200 ) {
+		type_of_loader = <type code>;
+		if ( loading_initrd ) {
+			ramdisk_image = <initrd_address>;
+			ramdisk_size = <initrd_size>;
+		}
+
+		if ( protocol >= 0x0202 && loadflags & 0x01 )
+			heap_end = 0xe000;
+		else
+			heap_end = 0x9800;
+
+		if ( protocol >= 0x0201 ) {
+			heap_end_ptr = heap_end - 0x200;
+			loadflags |= 0x80; /* CAN_USE_HEAP */
+		}
+
+		if ( protocol >= 0x0202 ) {
+			cmd_line_ptr = base_ptr + heap_end;
+			strcpy(cmd_line_ptr, cmdline);
+		} else {
+			cmd_line_magic	= 0xA33F;
+			cmd_line_offset = heap_end;
+			setup_move_size = heap_end + strlen(cmdline)+1;
+			strcpy(base_ptr+cmd_line_offset, cmdline);
+		}
+	} else {
+		/* Very old kernel */
+
+		heap_end = 0x9800;
+
+		cmd_line_magic	= 0xA33F;
+		cmd_line_offset = heap_end;
+
+		/* A very old kernel MUST have its real-mode code
+		   loaded at 0x90000 */
+
+		if ( base_ptr != 0x90000 ) {
+			/* Copy the real-mode kernel */
+			memcpy(0x90000, base_ptr, (setup_sects+1)*512);
+			base_ptr = 0x90000;		 /* Relocated */
+		}
+
+		strcpy(0x90000+cmd_line_offset, cmdline);
+
+		/* It is recommended to clear memory up to the 32K mark */
+		memset(0x90000 + (setup_sects+1)*512, 0,
+		       (64-(setup_sects+1))*512);
+	}
+
+
+LOADING THE REST OF THE KERNEL
+==============================
+
+The 32-bit (non-real-mode) kernel starts at offset (setup_sects+1)*512
+in the kernel file (again, if setup_sects == 0 the real value is 4.)
+It should be loaded at address 0x10000 for Image/zImage kernels and
+0x100000 for bzImage kernels.
+
+The kernel is a bzImage kernel if the protocol >= 2.00 and the 0x01
+bit (LOAD_HIGH) in the loadflags field is set::
+
+	is_bzImage = (protocol >= 0x0200) && (loadflags & 0x01);
+	load_address = is_bzImage ? 0x100000 : 0x10000;
+
+Note that Image/zImage kernels can be up to 512K in size, and thus use
+the entire 0x10000-0x90000 range of memory.  This means it is pretty
+much a requirement for these kernels to load the real-mode part at
+0x90000.  bzImage kernels allow much more flexibility.
+
+
+SPECIAL COMMAND LINE OPTIONS
+============================
+
+If the command line provided by the boot loader is entered by the
+user, the user may expect the following command line options to work.
+They should normally not be deleted from the kernel command line even
+though not all of them are actually meaningful to the kernel.  Boot
+loader authors who need additional command line options for the boot
+loader itself should get them registered in
+Documentation/admin-guide/kernel-parameters.rst to make sure they will not
+conflict with actual kernel options now or in the future.
+
+  vga=<mode>
+	<mode> here is either an integer (in C notation, either
+	decimal, octal, or hexadecimal) or one of the strings
+	"normal" (meaning 0xFFFF), "ext" (meaning 0xFFFE) or "ask"
+	(meaning 0xFFFD).  This value should be entered into the
+	vid_mode field, as it is used by the kernel before the command
+	line is parsed.
+
+  mem=<size>
+	<size> is an integer in C notation optionally followed by
+	(case insensitive) K, M, G, T, P or E (meaning << 10, << 20,
+	<< 30, << 40, << 50 or << 60).  This specifies the end of
+	memory to the kernel. This affects the possible placement of
+	an initrd, since an initrd should be placed near end of
+	memory.  Note that this is an option to *both* the kernel and
+	the bootloader!
+
+  initrd=<file>
+	An initrd should be loaded.  The meaning of <file> is
+	obviously bootloader-dependent, and some boot loaders
+	(e.g. LILO) do not have such a command.
+
+In addition, some boot loaders add the following options to the
+user-specified command line:
+
+  BOOT_IMAGE=<file>
+	The boot image which was loaded.  Again, the meaning of <file>
+	is obviously bootloader-dependent.
+
+  auto
+	The kernel was booted without explicit user intervention.
+
+If these options are added by the boot loader, it is highly
+recommended that they are located *first*, before the user-specified
+or configuration-specified command line.  Otherwise, "init=/bin/sh"
+gets confused by the "auto" option.
+
+
+RUNNING THE KERNEL
+==================
+
+The kernel is started by jumping to the kernel entry point, which is
+located at *segment* offset 0x20 from the start of the real mode
+kernel.  This means that if you loaded your real-mode kernel code at
+0x90000, the kernel entry point is 9020:0000.
+
+At entry, ds = es = ss should point to the start of the real-mode
+kernel code (0x9000 if the code is loaded at 0x90000), sp should be
+set up properly, normally pointing to the top of the heap, and
+interrupts should be disabled.  Furthermore, to guard against bugs in
+the kernel, it is recommended that the boot loader sets fs = gs = ds =
+es = ss.
+
+In our example from above, we would do::
+
+	/* Note: in the case of the "old" kernel protocol, base_ptr must
+	   be == 0x90000 at this point; see the previous sample code */
+
+	seg = base_ptr >> 4;
+
+	cli();	/* Enter with interrupts disabled! */
+
+	/* Set up the real-mode kernel stack */
+	_SS = seg;
+	_SP = heap_end;
+
+	_DS = _ES = _FS = _GS = seg;
+	jmp_far(seg+0x20, 0);	/* Run the kernel */
+
+If your boot sector accesses a floppy drive, it is recommended to
+switch off the floppy motor before running the kernel, since the
+kernel boot leaves interrupts off and thus the motor will not be
+switched off, especially if the loaded kernel has the floppy driver as
+a demand-loaded module!
+
+
+ADVANCED BOOT LOADER HOOKS
+==========================
+
+If the boot loader runs in a particularly hostile environment (such as
+LOADLIN, which runs under DOS) it may be impossible to follow the
+standard memory location requirements.  Such a boot loader may use the
+following hooks that, if set, are invoked by the kernel at the
+appropriate time.  The use of these hooks should probably be
+considered an absolutely last resort!
+
+IMPORTANT: All the hooks are required to preserve %esp, %ebp, %esi and
+%edi across invocation.
+
+  realmode_swtch:
+	A 16-bit real mode far subroutine invoked immediately before
+	entering protected mode.  The default routine disables NMI, so
+	your routine should probably do so, too.
+
+  code32_start:
+	A 32-bit flat-mode routine *jumped* to immediately after the
+	transition to protected mode, but before the kernel is
+	uncompressed.  No segments, except CS, are guaranteed to be
+	set up (current kernels do, but older ones do not); you should
+	set them up to BOOT_DS (0x18) yourself.
+
+	After completing your hook, you should jump to the address
+	that was in this field before your boot loader overwrote it
+	(relocated, if appropriate.)
+
+
+32-bit BOOT PROTOCOL
+====================
+
+For machine with some new BIOS other than legacy BIOS, such as EFI,
+LinuxBIOS, etc, and kexec, the 16-bit real mode setup code in kernel
+based on legacy BIOS can not be used, so a 32-bit boot protocol needs
+to be defined.
+
+In 32-bit boot protocol, the first step in loading a Linux kernel
+should be to setup the boot parameters (struct boot_params,
+traditionally known as "zero page"). The memory for struct boot_params
+should be allocated and initialized to all zero. Then the setup header
+from offset 0x01f1 of kernel image on should be loaded into struct
+boot_params and examined. The end of setup header can be calculated as
+follow::
+
+	0x0202 + byte value at offset 0x0201
+
+In addition to read/modify/write the setup header of the struct
+boot_params as that of 16-bit boot protocol, the boot loader should
+also fill the additional fields of the struct boot_params as that
+described in zero-page.txt.
+
+After setting up the struct boot_params, the boot loader can load the
+32/64-bit kernel in the same way as that of 16-bit boot protocol.
+
+In 32-bit boot protocol, the kernel is started by jumping to the
+32-bit kernel entry point, which is the start address of loaded
+32/64-bit kernel.
+
+At entry, the CPU must be in 32-bit protected mode with paging
+disabled; a GDT must be loaded with the descriptors for selectors
+__BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G flat
+segment; __BOOT_CS must have execute/read permission, and __BOOT_DS
+must have read/write permission; CS must be __BOOT_CS and DS, ES, SS
+must be __BOOT_DS; interrupt must be disabled; %esi must hold the base
+address of the struct boot_params; %ebp, %edi and %ebx must be zero.
+
+64-bit BOOT PROTOCOL
+====================
+
+For machine with 64bit cpus and 64bit kernel, we could use 64bit bootloader
+and we need a 64-bit boot protocol.
+
+In 64-bit boot protocol, the first step in loading a Linux kernel
+should be to setup the boot parameters (struct boot_params,
+traditionally known as "zero page"). The memory for struct boot_params
+could be allocated anywhere (even above 4G) and initialized to all zero.
+Then, the setup header at offset 0x01f1 of kernel image on should be
+loaded into struct boot_params and examined. The end of setup header
+can be calculated as follows::
+
+	0x0202 + byte value at offset 0x0201
+
+In addition to read/modify/write the setup header of the struct
+boot_params as that of 16-bit boot protocol, the boot loader should
+also fill the additional fields of the struct boot_params as described
+in zero-page.txt.
+
+After setting up the struct boot_params, the boot loader can load
+64-bit kernel in the same way as that of 16-bit boot protocol, but
+kernel could be loaded above 4G.
+
+In 64-bit boot protocol, the kernel is started by jumping to the
+64-bit kernel entry point, which is the start address of loaded
+64-bit kernel plus 0x200.
+
+At entry, the CPU must be in 64-bit mode with paging enabled.
+The range with setup_header.init_size from start address of loaded
+kernel and zero page and command line buffer get ident mapping;
+a GDT must be loaded with the descriptors for selectors
+__BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G flat
+segment; __BOOT_CS must have execute/read permission, and __BOOT_DS
+must have read/write permission; CS must be __BOOT_CS and DS, ES, SS
+must be __BOOT_DS; interrupt must be disabled; %rsi must hold the base
+address of the struct boot_params.
+
+EFI HANDOVER PROTOCOL
+=====================
+
+This protocol allows boot loaders to defer initialisation to the EFI
+boot stub. The boot loader is required to load the kernel/initrd(s)
+from the boot media and jump to the EFI handover protocol entry point
+which is hdr->handover_offset bytes from the beginning of
+startup_{32,64}.
+
+The function prototype for the handover entry point looks like this::
+
+    efi_main(void *handle, efi_system_table_t *table, struct boot_params *bp)
+
+'handle' is the EFI image handle passed to the boot loader by the EFI
+firmware, 'table' is the EFI system table - these are the first two
+arguments of the "handoff state" as described in section 2.3 of the
+UEFI specification. 'bp' is the boot loader-allocated boot params.
+
+The boot loader *must* fill out the following fields in bp::
+
+  - hdr.code32_start
+  - hdr.cmd_line_ptr
+  - hdr.ramdisk_image (if applicable)
+  - hdr.ramdisk_size  (if applicable)
+
+All other fields should be zero.
diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
deleted file mode 100644
index f4c2a97bfdbd..000000000000
--- a/Documentation/x86/boot.txt
+++ /dev/null
@@ -1,1130 +0,0 @@
-		     THE LINUX/x86 BOOT PROTOCOL
-		     ---------------------------
-
-On the x86 platform, the Linux kernel uses a rather complicated boot
-convention.  This has evolved partially due to historical aspects, as
-well as the desire in the early days to have the kernel itself be a
-bootable image, the complicated PC memory model and due to changed
-expectations in the PC industry caused by the effective demise of
-real-mode DOS as a mainstream operating system.
-
-Currently, the following versions of the Linux/x86 boot protocol exist.
-
-Old kernels:	zImage/Image support only.  Some very early kernels
-		may not even support a command line.
-
-Protocol 2.00:	(Kernel 1.3.73) Added bzImage and initrd support, as
-		well as a formalized way to communicate between the
-		boot loader and the kernel.  setup.S made relocatable,
-		although the traditional setup area still assumed
-		writable.
-
-Protocol 2.01:	(Kernel 1.3.76) Added a heap overrun warning.
-
-Protocol 2.02:	(Kernel 2.4.0-test3-pre3) New command line protocol.
-		Lower the conventional memory ceiling.	No overwrite
-		of the traditional setup area, thus making booting
-		safe for systems which use the EBDA from SMM or 32-bit
-		BIOS entry points.  zImage deprecated but still
-		supported.
-
-Protocol 2.03:	(Kernel 2.4.18-pre1) Explicitly makes the highest possible
-		initrd address available to the bootloader.
-
-Protocol 2.04:	(Kernel 2.6.14) Extend the syssize field to four bytes.
-
-Protocol 2.05:	(Kernel 2.6.20) Make protected mode kernel relocatable.
-		Introduce relocatable_kernel and kernel_alignment fields.
-
-Protocol 2.06:	(Kernel 2.6.22) Added a field that contains the size of
-		the boot command line.
-
-Protocol 2.07:	(Kernel 2.6.24) Added paravirtualised boot protocol.
-		Introduced hardware_subarch and hardware_subarch_data
-		and KEEP_SEGMENTS flag in load_flags.
-
-Protocol 2.08:	(Kernel 2.6.26) Added crc32 checksum and ELF format
-		payload. Introduced payload_offset and payload_length
-		fields to aid in locating the payload.
-
-Protocol 2.09:	(Kernel 2.6.26) Added a field of 64-bit physical
-		pointer to single linked list of struct	setup_data.
-
-Protocol 2.10:	(Kernel 2.6.31) Added a protocol for relaxed alignment
-		beyond the kernel_alignment added, new init_size and
-		pref_address fields.  Added extended boot loader IDs.
-
-Protocol 2.11:	(Kernel 3.6) Added a field for offset of EFI handover
-		protocol entry point.
-
-Protocol 2.12:	(Kernel 3.8) Added the xloadflags field and extension fields
-		to struct boot_params for loading bzImage and ramdisk
-		above 4G in 64bit.
-
-**** MEMORY LAYOUT
-
-The traditional memory map for the kernel loader, used for Image or
-zImage kernels, typically looks like:
-
-	|			 |
-0A0000	+------------------------+
-	|  Reserved for BIOS	 |	Do not use.  Reserved for BIOS EBDA.
-09A000	+------------------------+
-	|  Command line		 |
-	|  Stack/heap		 |	For use by the kernel real-mode code.
-098000	+------------------------+	
-	|  Kernel setup		 |	The kernel real-mode code.
-090200	+------------------------+
-	|  Kernel boot sector	 |	The kernel legacy boot sector.
-090000	+------------------------+
-	|  Protected-mode kernel |	The bulk of the kernel image.
-010000	+------------------------+
-	|  Boot loader		 |	<- Boot sector entry point 0000:7C00
-001000	+------------------------+
-	|  Reserved for MBR/BIOS |
-000800	+------------------------+
-	|  Typically used by MBR |
-000600	+------------------------+ 
-	|  BIOS use only	 |
-000000	+------------------------+
-
-
-When using bzImage, the protected-mode kernel was relocated to
-0x100000 ("high memory"), and the kernel real-mode block (boot sector,
-setup, and stack/heap) was made relocatable to any address between
-0x10000 and end of low memory. Unfortunately, in protocols 2.00 and
-2.01 the 0x90000+ memory range is still used internally by the kernel;
-the 2.02 protocol resolves that problem.
-
-It is desirable to keep the "memory ceiling" -- the highest point in
-low memory touched by the boot loader -- as low as possible, since
-some newer BIOSes have begun to allocate some rather large amounts of
-memory, called the Extended BIOS Data Area, near the top of low
-memory.	 The boot loader should use the "INT 12h" BIOS call to verify
-how much low memory is available.
-
-Unfortunately, if INT 12h reports that the amount of memory is too
-low, there is usually nothing the boot loader can do but to report an
-error to the user.  The boot loader should therefore be designed to
-take up as little space in low memory as it reasonably can.  For
-zImage or old bzImage kernels, which need data written into the
-0x90000 segment, the boot loader should make sure not to use memory
-above the 0x9A000 point; too many BIOSes will break above that point.
-
-For a modern bzImage kernel with boot protocol version >= 2.02, a
-memory layout like the following is suggested:
-
-	~                        ~
-        |  Protected-mode kernel |
-100000  +------------------------+
-	|  I/O memory hole	 |
-0A0000	+------------------------+
-	|  Reserved for BIOS	 |	Leave as much as possible unused
-	~                        ~
-	|  Command line		 |	(Can also be below the X+10000 mark)
-X+10000	+------------------------+
-	|  Stack/heap		 |	For use by the kernel real-mode code.
-X+08000	+------------------------+	
-	|  Kernel setup		 |	The kernel real-mode code.
-	|  Kernel boot sector	 |	The kernel legacy boot sector.
-X       +------------------------+
-	|  Boot loader		 |	<- Boot sector entry point 0000:7C00
-001000	+------------------------+
-	|  Reserved for MBR/BIOS |
-000800	+------------------------+
-	|  Typically used by MBR |
-000600	+------------------------+ 
-	|  BIOS use only	 |
-000000	+------------------------+
-
-... where the address X is as low as the design of the boot loader
-permits.
-
-
-**** THE REAL-MODE KERNEL HEADER
-
-In the following text, and anywhere in the kernel boot sequence, "a
-sector" refers to 512 bytes.  It is independent of the actual sector
-size of the underlying medium.
-
-The first step in loading a Linux kernel should be to load the
-real-mode code (boot sector and setup code) and then examine the
-following header at offset 0x01f1.  The real-mode code can total up to
-32K, although the boot loader may choose to load only the first two
-sectors (1K) and then examine the bootup sector size.
-
-The header looks like:
-
-Offset	Proto	Name		Meaning
-/Size
-
-01F1/1	ALL(1	setup_sects	The size of the setup in sectors
-01F2/2	ALL	root_flags	If set, the root is mounted readonly
-01F4/4	2.04+(2	syssize		The size of the 32-bit code in 16-byte paras
-01F8/2	ALL	ram_size	DO NOT USE - for bootsect.S use only
-01FA/2	ALL	vid_mode	Video mode control
-01FC/2	ALL	root_dev	Default root device number
-01FE/2	ALL	boot_flag	0xAA55 magic number
-0200/2	2.00+	jump		Jump instruction
-0202/4	2.00+	header		Magic signature "HdrS"
-0206/2	2.00+	version		Boot protocol version supported
-0208/4	2.00+	realmode_swtch	Boot loader hook (see below)
-020C/2	2.00+	start_sys_seg	The load-low segment (0x1000) (obsolete)
-020E/2	2.00+	kernel_version	Pointer to kernel version string
-0210/1	2.00+	type_of_loader	Boot loader identifier
-0211/1	2.00+	loadflags	Boot protocol option flags
-0212/2	2.00+	setup_move_size	Move to high memory size (used with hooks)
-0214/4	2.00+	code32_start	Boot loader hook (see below)
-0218/4	2.00+	ramdisk_image	initrd load address (set by boot loader)
-021C/4	2.00+	ramdisk_size	initrd size (set by boot loader)
-0220/4	2.00+	bootsect_kludge	DO NOT USE - for bootsect.S use only
-0224/2	2.01+	heap_end_ptr	Free memory after setup end
-0226/1	2.02+(3 ext_loader_ver	Extended boot loader version
-0227/1	2.02+(3	ext_loader_type	Extended boot loader ID
-0228/4	2.02+	cmd_line_ptr	32-bit pointer to the kernel command line
-022C/4	2.03+	initrd_addr_max	Highest legal initrd address
-0230/4	2.05+	kernel_alignment Physical addr alignment required for kernel
-0234/1	2.05+	relocatable_kernel Whether kernel is relocatable or not
-0235/1	2.10+	min_alignment	Minimum alignment, as a power of two
-0236/2	2.12+	xloadflags	Boot protocol option flags
-0238/4	2.06+	cmdline_size	Maximum size of the kernel command line
-023C/4	2.07+	hardware_subarch Hardware subarchitecture
-0240/8	2.07+	hardware_subarch_data Subarchitecture-specific data
-0248/4	2.08+	payload_offset	Offset of kernel payload
-024C/4	2.08+	payload_length	Length of kernel payload
-0250/8	2.09+	setup_data	64-bit physical pointer to linked list
-				of struct setup_data
-0258/8	2.10+	pref_address	Preferred loading address
-0260/4	2.10+	init_size	Linear memory required during initialization
-0264/4	2.11+	handover_offset	Offset of handover entry point
-
-(1) For backwards compatibility, if the setup_sects field contains 0, the
-    real value is 4.
-
-(2) For boot protocol prior to 2.04, the upper two bytes of the syssize
-    field are unusable, which means the size of a bzImage kernel
-    cannot be determined.
-
-(3) Ignored, but safe to set, for boot protocols 2.02-2.09.
-
-If the "HdrS" (0x53726448) magic number is not found at offset 0x202,
-the boot protocol version is "old".  Loading an old kernel, the
-following parameters should be assumed:
-
-	Image type = zImage
-	initrd not supported
-	Real-mode kernel must be located at 0x90000.
-
-Otherwise, the "version" field contains the protocol version,
-e.g. protocol version 2.01 will contain 0x0201 in this field.  When
-setting fields in the header, you must make sure only to set fields
-supported by the protocol version in use.
-
-
-**** DETAILS OF HEADER FIELDS
-
-For each field, some are information from the kernel to the bootloader
-("read"), some are expected to be filled out by the bootloader
-("write"), and some are expected to be read and modified by the
-bootloader ("modify").
-
-All general purpose boot loaders should write the fields marked
-(obligatory).  Boot loaders who want to load the kernel at a
-nonstandard address should fill in the fields marked (reloc); other
-boot loaders can ignore those fields.
-
-The byte order of all fields is littleendian (this is x86, after all.)
-
-Field name:	setup_sects
-Type:		read
-Offset/size:	0x1f1/1
-Protocol:	ALL
-
-  The size of the setup code in 512-byte sectors.  If this field is
-  0, the real value is 4.  The real-mode code consists of the boot
-  sector (always one 512-byte sector) plus the setup code.
-
-Field name:	 root_flags
-Type:		 modify (optional)
-Offset/size:	 0x1f2/2
-Protocol:	 ALL
-
-  If this field is nonzero, the root defaults to readonly.  The use of
-  this field is deprecated; use the "ro" or "rw" options on the
-  command line instead.
-
-Field name:	syssize
-Type:		read
-Offset/size:	0x1f4/4 (protocol 2.04+) 0x1f4/2 (protocol ALL)
-Protocol:	2.04+
-
-  The size of the protected-mode code in units of 16-byte paragraphs.
-  For protocol versions older than 2.04 this field is only two bytes
-  wide, and therefore cannot be trusted for the size of a kernel if
-  the LOAD_HIGH flag is set.
-
-Field name:	ram_size
-Type:		kernel internal
-Offset/size:	0x1f8/2
-Protocol:	ALL
-
-  This field is obsolete.
-
-Field name:	vid_mode
-Type:		modify (obligatory)
-Offset/size:	0x1fa/2
-
-  Please see the section on SPECIAL COMMAND LINE OPTIONS.
-
-Field name:	root_dev
-Type:		modify (optional)
-Offset/size:	0x1fc/2
-Protocol:	ALL
-
-  The default root device device number.  The use of this field is
-  deprecated, use the "root=" option on the command line instead.
-
-Field name:	boot_flag
-Type:		read
-Offset/size:	0x1fe/2
-Protocol:	ALL
-
-  Contains 0xAA55.  This is the closest thing old Linux kernels have
-  to a magic number.
-
-Field name:	jump
-Type:		read
-Offset/size:	0x200/2
-Protocol:	2.00+
-
-  Contains an x86 jump instruction, 0xEB followed by a signed offset
-  relative to byte 0x202.  This can be used to determine the size of
-  the header.
-
-Field name:	header
-Type:		read
-Offset/size:	0x202/4
-Protocol:	2.00+
-
-  Contains the magic number "HdrS" (0x53726448).
-
-Field name:	version
-Type:		read
-Offset/size:	0x206/2
-Protocol:	2.00+
-
-  Contains the boot protocol version, in (major << 8)+minor format,
-  e.g. 0x0204 for version 2.04, and 0x0a11 for a hypothetical version
-  10.17.
-
-Field name:	realmode_swtch
-Type:		modify (optional)
-Offset/size:	0x208/4
-Protocol:	2.00+
-
-  Boot loader hook (see ADVANCED BOOT LOADER HOOKS below.)
-
-Field name:	start_sys_seg
-Type:		read
-Offset/size:	0x20c/2
-Protocol:	2.00+
-
-  The load low segment (0x1000).  Obsolete.
-
-Field name:	kernel_version
-Type:		read
-Offset/size:	0x20e/2
-Protocol:	2.00+
-
-  If set to a nonzero value, contains a pointer to a NUL-terminated
-  human-readable kernel version number string, less 0x200.  This can
-  be used to display the kernel version to the user.  This value
-  should be less than (0x200*setup_sects).
-
-  For example, if this value is set to 0x1c00, the kernel version
-  number string can be found at offset 0x1e00 in the kernel file.
-  This is a valid value if and only if the "setup_sects" field
-  contains the value 15 or higher, as:
-
-	0x1c00  < 15*0x200 (= 0x1e00) but
-	0x1c00 >= 14*0x200 (= 0x1c00)
-
-	0x1c00 >> 9 = 14, so the minimum value for setup_secs is 15.
-
-Field name:	type_of_loader
-Type:		write (obligatory)
-Offset/size:	0x210/1
-Protocol:	2.00+
-
-  If your boot loader has an assigned id (see table below), enter
-  0xTV here, where T is an identifier for the boot loader and V is
-  a version number.  Otherwise, enter 0xFF here.
-
-  For boot loader IDs above T = 0xD, write T = 0xE to this field and
-  write the extended ID minus 0x10 to the ext_loader_type field.
-  Similarly, the ext_loader_ver field can be used to provide more than
-  four bits for the bootloader version.
-
-  For example, for T = 0x15, V = 0x234, write:
-
-  type_of_loader  <- 0xE4
-  ext_loader_type <- 0x05
-  ext_loader_ver  <- 0x23
-
-  Assigned boot loader ids (hexadecimal):
-
-	0  LILO			(0x00 reserved for pre-2.00 bootloader)
-	1  Loadlin
-	2  bootsect-loader	(0x20, all other values reserved)
-	3  Syslinux
-	4  Etherboot/gPXE/iPXE
-	5  ELILO
-	7  GRUB
-	8  U-Boot
-	9  Xen
-	A  Gujin
-	B  Qemu
-	C  Arcturus Networks uCbootloader
-	D  kexec-tools
-	E  Extended		(see ext_loader_type)
-	F  Special		(0xFF = undefined)
-       10  Reserved
-       11  Minimal Linux Bootloader <http://sebastian-plotz.blogspot.de>
-       12  OVMF UEFI virtualization stack
-
-  Please contact <hpa@...or.com> if you need a bootloader ID
-  value assigned.
-
-Field name:	loadflags
-Type:		modify (obligatory)
-Offset/size:	0x211/1
-Protocol:	2.00+
-
-  This field is a bitmask.
-
-  Bit 0 (read):	LOADED_HIGH
-	- If 0, the protected-mode code is loaded at 0x10000.
-	- If 1, the protected-mode code is loaded at 0x100000.
-
-  Bit 1 (kernel internal): KASLR_FLAG
-	- Used internally by the compressed kernel to communicate
-	  KASLR status to kernel proper.
-	  If 1, KASLR enabled.
-	  If 0, KASLR disabled.
-
-  Bit 5 (write): QUIET_FLAG
-	- If 0, print early messages.
-	- If 1, suppress early messages.
-		This requests to the kernel (decompressor and early
-		kernel) to not write early messages that require
-		accessing the display hardware directly.
-
-  Bit 6 (write): KEEP_SEGMENTS
-	Protocol: 2.07+
-	- If 0, reload the segment registers in the 32bit entry point.
-	- If 1, do not reload the segment registers in the 32bit entry point.
-		Assume that %cs %ds %ss %es are all set to flat segments with
-		a base of 0 (or the equivalent for their environment).
-
-  Bit 7 (write): CAN_USE_HEAP
-	Set this bit to 1 to indicate that the value entered in the
-	heap_end_ptr is valid.  If this field is clear, some setup code
-	functionality will be disabled.
-
-Field name:	setup_move_size
-Type:		modify (obligatory)
-Offset/size:	0x212/2
-Protocol:	2.00-2.01
-
-  When using protocol 2.00 or 2.01, if the real mode kernel is not
-  loaded at 0x90000, it gets moved there later in the loading
-  sequence.  Fill in this field if you want additional data (such as
-  the kernel command line) moved in addition to the real-mode kernel
-  itself.
-
-  The unit is bytes starting with the beginning of the boot sector.
-  
-  This field is can be ignored when the protocol is 2.02 or higher, or
-  if the real-mode code is loaded at 0x90000.
-
-Field name:	code32_start
-Type:		modify (optional, reloc)
-Offset/size:	0x214/4
-Protocol:	2.00+
-
-  The address to jump to in protected mode.  This defaults to the load
-  address of the kernel, and can be used by the boot loader to
-  determine the proper load address.
-
-  This field can be modified for two purposes:
-
-  1. as a boot loader hook (see ADVANCED BOOT LOADER HOOKS below.)
-
-  2. if a bootloader which does not install a hook loads a
-     relocatable kernel at a nonstandard address it will have to modify
-     this field to point to the load address.
-
-Field name:	ramdisk_image
-Type:		write (obligatory)
-Offset/size:	0x218/4
-Protocol:	2.00+
-
-  The 32-bit linear address of the initial ramdisk or ramfs.  Leave at
-  zero if there is no initial ramdisk/ramfs.
-
-Field name:	ramdisk_size
-Type:		write (obligatory)
-Offset/size:	0x21c/4
-Protocol:	2.00+
-
-  Size of the initial ramdisk or ramfs.  Leave at zero if there is no
-  initial ramdisk/ramfs.
-
-Field name:	bootsect_kludge
-Type:		kernel internal
-Offset/size:	0x220/4
-Protocol:	2.00+
-
-  This field is obsolete.
-
-Field name:	heap_end_ptr
-Type:		write (obligatory)
-Offset/size:	0x224/2
-Protocol:	2.01+
-
-  Set this field to the offset (from the beginning of the real-mode
-  code) of the end of the setup stack/heap, minus 0x0200.
-
-Field name:	ext_loader_ver
-Type:		write (optional)
-Offset/size:	0x226/1
-Protocol:	2.02+
-
-  This field is used as an extension of the version number in the
-  type_of_loader field.  The total version number is considered to be
-  (type_of_loader & 0x0f) + (ext_loader_ver << 4).
-
-  The use of this field is boot loader specific.  If not written, it
-  is zero.
-
-  Kernels prior to 2.6.31 did not recognize this field, but it is safe
-  to write for protocol version 2.02 or higher.
-
-Field name:	ext_loader_type
-Type:		write (obligatory if (type_of_loader & 0xf0) == 0xe0)
-Offset/size:	0x227/1
-Protocol:	2.02+
-
-  This field is used as an extension of the type number in
-  type_of_loader field.  If the type in type_of_loader is 0xE, then
-  the actual type is (ext_loader_type + 0x10).
-
-  This field is ignored if the type in type_of_loader is not 0xE.
-
-  Kernels prior to 2.6.31 did not recognize this field, but it is safe
-  to write for protocol version 2.02 or higher.
-
-Field name:	cmd_line_ptr
-Type:		write (obligatory)
-Offset/size:	0x228/4
-Protocol:	2.02+
-
-  Set this field to the linear address of the kernel command line.
-  The kernel command line can be located anywhere between the end of
-  the setup heap and 0xA0000; it does not have to be located in the
-  same 64K segment as the real-mode code itself.
-
-  Fill in this field even if your boot loader does not support a
-  command line, in which case you can point this to an empty string
-  (or better yet, to the string "auto".)  If this field is left at
-  zero, the kernel will assume that your boot loader does not support
-  the 2.02+ protocol.
-
-Field name:	initrd_addr_max
-Type:		read
-Offset/size:	0x22c/4
-Protocol:	2.03+
-
-  The maximum address that may be occupied by the initial
-  ramdisk/ramfs contents.  For boot protocols 2.02 or earlier, this
-  field is not present, and the maximum address is 0x37FFFFFF.  (This
-  address is defined as the address of the highest safe byte, so if
-  your ramdisk is exactly 131072 bytes long and this field is
-  0x37FFFFFF, you can start your ramdisk at 0x37FE0000.)
-
-Field name:	kernel_alignment
-Type:		read/modify (reloc)
-Offset/size:	0x230/4
-Protocol:	2.05+ (read), 2.10+ (modify)
-
-  Alignment unit required by the kernel (if relocatable_kernel is
-  true.)  A relocatable kernel that is loaded at an alignment
-  incompatible with the value in this field will be realigned during
-  kernel initialization.
-
-  Starting with protocol version 2.10, this reflects the kernel
-  alignment preferred for optimal performance; it is possible for the
-  loader to modify this field to permit a lesser alignment.  See the
-  min_alignment and pref_address field below.
-
-Field name:	relocatable_kernel
-Type:		read (reloc)
-Offset/size:	0x234/1
-Protocol:	2.05+
-
-  If this field is nonzero, the protected-mode part of the kernel can
-  be loaded at any address that satisfies the kernel_alignment field.
-  After loading, the boot loader must set the code32_start field to
-  point to the loaded code, or to a boot loader hook.
-
-Field name:	min_alignment
-Type:		read (reloc)
-Offset/size:	0x235/1
-Protocol:	2.10+
-
-  This field, if nonzero, indicates as a power of two the minimum
-  alignment required, as opposed to preferred, by the kernel to boot.
-  If a boot loader makes use of this field, it should update the
-  kernel_alignment field with the alignment unit desired; typically:
-
-	kernel_alignment = 1 << min_alignment
-
-  There may be a considerable performance cost with an excessively
-  misaligned kernel.  Therefore, a loader should typically try each
-  power-of-two alignment from kernel_alignment down to this alignment.
-
-Field name:     xloadflags
-Type:           read
-Offset/size:    0x236/2
-Protocol:       2.12+
-
-  This field is a bitmask.
-
-  Bit 0 (read):	XLF_KERNEL_64
-	- If 1, this kernel has the legacy 64-bit entry point at 0x200.
-
-  Bit 1 (read): XLF_CAN_BE_LOADED_ABOVE_4G
-        - If 1, kernel/boot_params/cmdline/ramdisk can be above 4G.
-
-  Bit 2 (read):	XLF_EFI_HANDOVER_32
-	- If 1, the kernel supports the 32-bit EFI handoff entry point
-          given at handover_offset.
-
-  Bit 3 (read): XLF_EFI_HANDOVER_64
-	- If 1, the kernel supports the 64-bit EFI handoff entry point
-          given at handover_offset + 0x200.
-
-  Bit 4 (read): XLF_EFI_KEXEC
-	- If 1, the kernel supports kexec EFI boot with EFI runtime support.
-
-Field name:	cmdline_size
-Type:		read
-Offset/size:	0x238/4
-Protocol:	2.06+
-
-  The maximum size of the command line without the terminating
-  zero. This means that the command line can contain at most
-  cmdline_size characters. With protocol version 2.05 and earlier, the
-  maximum size was 255.
-
-Field name:	hardware_subarch
-Type:		write (optional, defaults to x86/PC)
-Offset/size:	0x23c/4
-Protocol:	2.07+
-
-  In a paravirtualized environment the hardware low level architectural
-  pieces such as interrupt handling, page table handling, and
-  accessing process control registers needs to be done differently.
-
-  This field allows the bootloader to inform the kernel we are in one
-  one of those environments.
-
-  0x00000000	The default x86/PC environment
-  0x00000001	lguest
-  0x00000002	Xen
-  0x00000003	Moorestown MID
-  0x00000004	CE4100 TV Platform
-
-Field name:	hardware_subarch_data
-Type:		write (subarch-dependent)
-Offset/size:	0x240/8
-Protocol:	2.07+
-
-  A pointer to data that is specific to hardware subarch
-  This field is currently unused for the default x86/PC environment,
-  do not modify.
-
-Field name:	payload_offset
-Type:		read
-Offset/size:	0x248/4
-Protocol:	2.08+
-
-  If non-zero then this field contains the offset from the beginning
-  of the protected-mode code to the payload.
-
-  The payload may be compressed. The format of both the compressed and
-  uncompressed data should be determined using the standard magic
-  numbers.  The currently supported compression formats are gzip
-  (magic numbers 1F 8B or 1F 9E), bzip2 (magic number 42 5A), LZMA
-  (magic number 5D 00), XZ (magic number FD 37), and LZ4 (magic number
-  02 21).  The uncompressed payload is currently always ELF (magic
-  number 7F 45 4C 46).
-
-Field name:	payload_length
-Type:		read
-Offset/size:	0x24c/4
-Protocol:	2.08+
-
-  The length of the payload.
-
-Field name:	setup_data
-Type:		write (special)
-Offset/size:	0x250/8
-Protocol:	2.09+
-
-  The 64-bit physical pointer to NULL terminated single linked list of
-  struct setup_data. This is used to define a more extensible boot
-  parameters passing mechanism. The definition of struct setup_data is
-  as follow:
-
-  struct setup_data {
-	  u64 next;
-	  u32 type;
-	  u32 len;
-	  u8  data[0];
-  };
-
-  Where, the next is a 64-bit physical pointer to the next node of
-  linked list, the next field of the last node is 0; the type is used
-  to identify the contents of data; the len is the length of data
-  field; the data holds the real payload.
-
-  This list may be modified at a number of points during the bootup
-  process.  Therefore, when modifying this list one should always make
-  sure to consider the case where the linked list already contains
-  entries.
-
-Field name:	pref_address
-Type:		read (reloc)
-Offset/size:	0x258/8
-Protocol:	2.10+
-
-  This field, if nonzero, represents a preferred load address for the
-  kernel.  A relocating bootloader should attempt to load at this
-  address if possible.
-
-  A non-relocatable kernel will unconditionally move itself and to run
-  at this address.
-
-Field name:	init_size
-Type:		read
-Offset/size:	0x260/4
-
-  This field indicates the amount of linear contiguous memory starting
-  at the kernel runtime start address that the kernel needs before it
-  is capable of examining its memory map.  This is not the same thing
-  as the total amount of memory the kernel needs to boot, but it can
-  be used by a relocating boot loader to help select a safe load
-  address for the kernel.
-
-  The kernel runtime start address is determined by the following algorithm:
-
-  if (relocatable_kernel)
-	runtime_start = align_up(load_address, kernel_alignment)
-  else
-	runtime_start = pref_address
-
-Field name:	handover_offset
-Type:		read
-Offset/size:	0x264/4
-
-  This field is the offset from the beginning of the kernel image to
-  the EFI handover protocol entry point. Boot loaders using the EFI
-  handover protocol to boot the kernel should jump to this offset.
-
-  See EFI HANDOVER PROTOCOL below for more details.
-
-
-**** THE IMAGE CHECKSUM
-
-From boot protocol version 2.08 onwards the CRC-32 is calculated over
-the entire file using the characteristic polynomial 0x04C11DB7 and an
-initial remainder of 0xffffffff.  The checksum is appended to the
-file; therefore the CRC of the file up to the limit specified in the
-syssize field of the header is always 0.
-
-
-**** THE KERNEL COMMAND LINE
-
-The kernel command line has become an important way for the boot
-loader to communicate with the kernel.  Some of its options are also
-relevant to the boot loader itself, see "special command line options"
-below.
-
-The kernel command line is a null-terminated string. The maximum
-length can be retrieved from the field cmdline_size.  Before protocol
-version 2.06, the maximum was 255 characters.  A string that is too
-long will be automatically truncated by the kernel.
-
-If the boot protocol version is 2.02 or later, the address of the
-kernel command line is given by the header field cmd_line_ptr (see
-above.)  This address can be anywhere between the end of the setup
-heap and 0xA0000.
-
-If the protocol version is *not* 2.02 or higher, the kernel
-command line is entered using the following protocol:
-
-	At offset 0x0020 (word), "cmd_line_magic", enter the magic
-	number 0xA33F.
-
-	At offset 0x0022 (word), "cmd_line_offset", enter the offset
-	of the kernel command line (relative to the start of the
-	real-mode kernel).
-	
-	The kernel command line *must* be within the memory region
-	covered by setup_move_size, so you may need to adjust this
-	field.
-
-
-**** MEMORY LAYOUT OF THE REAL-MODE CODE
-
-The real-mode code requires a stack/heap to be set up, as well as
-memory allocated for the kernel command line.  This needs to be done
-in the real-mode accessible memory in bottom megabyte.
-
-It should be noted that modern machines often have a sizable Extended
-BIOS Data Area (EBDA).  As a result, it is advisable to use as little
-of the low megabyte as possible.
-
-Unfortunately, under the following circumstances the 0x90000 memory
-segment has to be used:
-
-	- When loading a zImage kernel ((loadflags & 0x01) == 0).
-	- When loading a 2.01 or earlier boot protocol kernel.
-
-	  -> For the 2.00 and 2.01 boot protocols, the real-mode code
-	     can be loaded at another address, but it is internally
-	     relocated to 0x90000.  For the "old" protocol, the
-	     real-mode code must be loaded at 0x90000.
-
-When loading at 0x90000, avoid using memory above 0x9a000.
-
-For boot protocol 2.02 or higher, the command line does not have to be
-located in the same 64K segment as the real-mode setup code; it is
-thus permitted to give the stack/heap the full 64K segment and locate
-the command line above it.
-
-The kernel command line should not be located below the real-mode
-code, nor should it be located in high memory.
-
-
-**** SAMPLE BOOT CONFIGURATION
-
-As a sample configuration, assume the following layout of the real
-mode segment:
-
-    When loading below 0x90000, use the entire segment:
-
-	0x0000-0x7fff	Real mode kernel
-	0x8000-0xdfff	Stack and heap
-	0xe000-0xffff	Kernel command line
-
-    When loading at 0x90000 OR the protocol version is 2.01 or earlier:
-
-	0x0000-0x7fff	Real mode kernel
-	0x8000-0x97ff	Stack and heap
-	0x9800-0x9fff	Kernel command line
-
-Such a boot loader should enter the following fields in the header:
-
-	unsigned long base_ptr;	/* base address for real-mode segment */
-
-	if ( setup_sects == 0 ) {
-		setup_sects = 4;
-	}
-
-	if ( protocol >= 0x0200 ) {
-		type_of_loader = <type code>;
-		if ( loading_initrd ) {
-			ramdisk_image = <initrd_address>;
-			ramdisk_size = <initrd_size>;
-		}
-
-		if ( protocol >= 0x0202 && loadflags & 0x01 )
-			heap_end = 0xe000;
-		else
-			heap_end = 0x9800;
-
-		if ( protocol >= 0x0201 ) {
-			heap_end_ptr = heap_end - 0x200;
-			loadflags |= 0x80; /* CAN_USE_HEAP */
-		}
-
-		if ( protocol >= 0x0202 ) {
-			cmd_line_ptr = base_ptr + heap_end;
-			strcpy(cmd_line_ptr, cmdline);
-		} else {
-			cmd_line_magic	= 0xA33F;
-			cmd_line_offset = heap_end;
-			setup_move_size = heap_end + strlen(cmdline)+1;
-			strcpy(base_ptr+cmd_line_offset, cmdline);
-		}
-	} else {
-		/* Very old kernel */
-
-		heap_end = 0x9800;
-
-		cmd_line_magic	= 0xA33F;
-		cmd_line_offset = heap_end;
-
-		/* A very old kernel MUST have its real-mode code
-		   loaded at 0x90000 */
-
-		if ( base_ptr != 0x90000 ) {
-			/* Copy the real-mode kernel */
-			memcpy(0x90000, base_ptr, (setup_sects+1)*512);
-			base_ptr = 0x90000;		 /* Relocated */
-		}
-
-		strcpy(0x90000+cmd_line_offset, cmdline);
-
-		/* It is recommended to clear memory up to the 32K mark */
-		memset(0x90000 + (setup_sects+1)*512, 0,
-		       (64-(setup_sects+1))*512);
-	}
-
-
-**** LOADING THE REST OF THE KERNEL
-
-The 32-bit (non-real-mode) kernel starts at offset (setup_sects+1)*512
-in the kernel file (again, if setup_sects == 0 the real value is 4.)
-It should be loaded at address 0x10000 for Image/zImage kernels and
-0x100000 for bzImage kernels.
-
-The kernel is a bzImage kernel if the protocol >= 2.00 and the 0x01
-bit (LOAD_HIGH) in the loadflags field is set:
-
-	is_bzImage = (protocol >= 0x0200) && (loadflags & 0x01);
-	load_address = is_bzImage ? 0x100000 : 0x10000;
-
-Note that Image/zImage kernels can be up to 512K in size, and thus use
-the entire 0x10000-0x90000 range of memory.  This means it is pretty
-much a requirement for these kernels to load the real-mode part at
-0x90000.  bzImage kernels allow much more flexibility.
-
-
-**** SPECIAL COMMAND LINE OPTIONS
-
-If the command line provided by the boot loader is entered by the
-user, the user may expect the following command line options to work.
-They should normally not be deleted from the kernel command line even
-though not all of them are actually meaningful to the kernel.  Boot
-loader authors who need additional command line options for the boot
-loader itself should get them registered in
-Documentation/admin-guide/kernel-parameters.rst to make sure they will not
-conflict with actual kernel options now or in the future.
-
-  vga=<mode>
-	<mode> here is either an integer (in C notation, either
-	decimal, octal, or hexadecimal) or one of the strings
-	"normal" (meaning 0xFFFF), "ext" (meaning 0xFFFE) or "ask"
-	(meaning 0xFFFD).  This value should be entered into the
-	vid_mode field, as it is used by the kernel before the command
-	line is parsed.
-
-  mem=<size>
-	<size> is an integer in C notation optionally followed by
-	(case insensitive) K, M, G, T, P or E (meaning << 10, << 20,
-	<< 30, << 40, << 50 or << 60).  This specifies the end of
-	memory to the kernel. This affects the possible placement of
-	an initrd, since an initrd should be placed near end of
-	memory.  Note that this is an option to *both* the kernel and
-	the bootloader!
-
-  initrd=<file>
-	An initrd should be loaded.  The meaning of <file> is
-	obviously bootloader-dependent, and some boot loaders
-	(e.g. LILO) do not have such a command.
-
-In addition, some boot loaders add the following options to the
-user-specified command line:
-
-  BOOT_IMAGE=<file>
-	The boot image which was loaded.  Again, the meaning of <file>
-	is obviously bootloader-dependent.
-
-  auto
-	The kernel was booted without explicit user intervention.
-
-If these options are added by the boot loader, it is highly
-recommended that they are located *first*, before the user-specified
-or configuration-specified command line.  Otherwise, "init=/bin/sh"
-gets confused by the "auto" option.
-
-
-**** RUNNING THE KERNEL
-
-The kernel is started by jumping to the kernel entry point, which is
-located at *segment* offset 0x20 from the start of the real mode
-kernel.  This means that if you loaded your real-mode kernel code at
-0x90000, the kernel entry point is 9020:0000.
-
-At entry, ds = es = ss should point to the start of the real-mode
-kernel code (0x9000 if the code is loaded at 0x90000), sp should be
-set up properly, normally pointing to the top of the heap, and
-interrupts should be disabled.  Furthermore, to guard against bugs in
-the kernel, it is recommended that the boot loader sets fs = gs = ds =
-es = ss.
-
-In our example from above, we would do:
-
-	/* Note: in the case of the "old" kernel protocol, base_ptr must
-	   be == 0x90000 at this point; see the previous sample code */
-
-	seg = base_ptr >> 4;
-
-	cli();	/* Enter with interrupts disabled! */
-
-	/* Set up the real-mode kernel stack */
-	_SS = seg;
-	_SP = heap_end;
-
-	_DS = _ES = _FS = _GS = seg;
-	jmp_far(seg+0x20, 0);	/* Run the kernel */
-
-If your boot sector accesses a floppy drive, it is recommended to
-switch off the floppy motor before running the kernel, since the
-kernel boot leaves interrupts off and thus the motor will not be
-switched off, especially if the loaded kernel has the floppy driver as
-a demand-loaded module!
-
-
-**** ADVANCED BOOT LOADER HOOKS
-
-If the boot loader runs in a particularly hostile environment (such as
-LOADLIN, which runs under DOS) it may be impossible to follow the
-standard memory location requirements.  Such a boot loader may use the
-following hooks that, if set, are invoked by the kernel at the
-appropriate time.  The use of these hooks should probably be
-considered an absolutely last resort!
-
-IMPORTANT: All the hooks are required to preserve %esp, %ebp, %esi and
-%edi across invocation.
-
-  realmode_swtch:
-	A 16-bit real mode far subroutine invoked immediately before
-	entering protected mode.  The default routine disables NMI, so
-	your routine should probably do so, too.
-
-  code32_start:
-	A 32-bit flat-mode routine *jumped* to immediately after the
-	transition to protected mode, but before the kernel is
-	uncompressed.  No segments, except CS, are guaranteed to be
-	set up (current kernels do, but older ones do not); you should
-	set them up to BOOT_DS (0x18) yourself.
-
-	After completing your hook, you should jump to the address
-	that was in this field before your boot loader overwrote it
-	(relocated, if appropriate.)
-
-
-**** 32-bit BOOT PROTOCOL
-
-For machine with some new BIOS other than legacy BIOS, such as EFI,
-LinuxBIOS, etc, and kexec, the 16-bit real mode setup code in kernel
-based on legacy BIOS can not be used, so a 32-bit boot protocol needs
-to be defined.
-
-In 32-bit boot protocol, the first step in loading a Linux kernel
-should be to setup the boot parameters (struct boot_params,
-traditionally known as "zero page"). The memory for struct boot_params
-should be allocated and initialized to all zero. Then the setup header
-from offset 0x01f1 of kernel image on should be loaded into struct
-boot_params and examined. The end of setup header can be calculated as
-follow:
-
-	0x0202 + byte value at offset 0x0201
-
-In addition to read/modify/write the setup header of the struct
-boot_params as that of 16-bit boot protocol, the boot loader should
-also fill the additional fields of the struct boot_params as that
-described in zero-page.txt.
-
-After setting up the struct boot_params, the boot loader can load the
-32/64-bit kernel in the same way as that of 16-bit boot protocol.
-
-In 32-bit boot protocol, the kernel is started by jumping to the
-32-bit kernel entry point, which is the start address of loaded
-32/64-bit kernel.
-
-At entry, the CPU must be in 32-bit protected mode with paging
-disabled; a GDT must be loaded with the descriptors for selectors
-__BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G flat
-segment; __BOOT_CS must have execute/read permission, and __BOOT_DS
-must have read/write permission; CS must be __BOOT_CS and DS, ES, SS
-must be __BOOT_DS; interrupt must be disabled; %esi must hold the base
-address of the struct boot_params; %ebp, %edi and %ebx must be zero.
-
-**** 64-bit BOOT PROTOCOL
-
-For machine with 64bit cpus and 64bit kernel, we could use 64bit bootloader
-and we need a 64-bit boot protocol.
-
-In 64-bit boot protocol, the first step in loading a Linux kernel
-should be to setup the boot parameters (struct boot_params,
-traditionally known as "zero page"). The memory for struct boot_params
-could be allocated anywhere (even above 4G) and initialized to all zero.
-Then, the setup header at offset 0x01f1 of kernel image on should be
-loaded into struct boot_params and examined. The end of setup header
-can be calculated as follows:
-
-	0x0202 + byte value at offset 0x0201
-
-In addition to read/modify/write the setup header of the struct
-boot_params as that of 16-bit boot protocol, the boot loader should
-also fill the additional fields of the struct boot_params as described
-in zero-page.txt.
-
-After setting up the struct boot_params, the boot loader can load
-64-bit kernel in the same way as that of 16-bit boot protocol, but
-kernel could be loaded above 4G.
-
-In 64-bit boot protocol, the kernel is started by jumping to the
-64-bit kernel entry point, which is the start address of loaded
-64-bit kernel plus 0x200.
-
-At entry, the CPU must be in 64-bit mode with paging enabled.
-The range with setup_header.init_size from start address of loaded
-kernel and zero page and command line buffer get ident mapping;
-a GDT must be loaded with the descriptors for selectors
-__BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G flat
-segment; __BOOT_CS must have execute/read permission, and __BOOT_DS
-must have read/write permission; CS must be __BOOT_CS and DS, ES, SS
-must be __BOOT_DS; interrupt must be disabled; %rsi must hold the base
-address of the struct boot_params.
-
-**** EFI HANDOVER PROTOCOL
-
-This protocol allows boot loaders to defer initialisation to the EFI
-boot stub. The boot loader is required to load the kernel/initrd(s)
-from the boot media and jump to the EFI handover protocol entry point
-which is hdr->handover_offset bytes from the beginning of
-startup_{32,64}.
-
-The function prototype for the handover entry point looks like this,
-
-    efi_main(void *handle, efi_system_table_t *table, struct boot_params *bp)
-
-'handle' is the EFI image handle passed to the boot loader by the EFI
-firmware, 'table' is the EFI system table - these are the first two
-arguments of the "handoff state" as described in section 2.3 of the
-UEFI specification. 'bp' is the boot loader-allocated boot params.
-
-The boot loader *must* fill out the following fields in bp,
-
-    o hdr.code32_start
-    o hdr.cmd_line_ptr
-    o hdr.ramdisk_image (if applicable)
-    o hdr.ramdisk_size  (if applicable)
-
-All other fields should be zero.
diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst
index 7612d3142b2a..8f08caf4fbbb 100644
--- a/Documentation/x86/index.rst
+++ b/Documentation/x86/index.rst
@@ -7,3 +7,5 @@ Linux x86 Support
 .. toctree::
    :maxdepth: 2
    :numbered:
+
+   boot
-- 
2.20.1

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