x86: doc: move x86-generic documentation from Doc/x86/i386

The boot protocol, USB legacy support, and zero-page documentation is
common to the x86 platform, not i386-specific.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 0 insertions, 900 deletions

diff --git a/Documentation/x86/i386/boot.txt b/Documentation/x86/i386/boot.txt
deleted file mode 100644
index 147bfe511cd..00000000000
--- a/Documentation/x86/i386/boot.txt
+++ /dev/null
@@ -1,900 +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.
-
-**** 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	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
-0226/2	N/A	pad1		Unused
-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
-0235/3	N/A	pad2		Unused
-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
-
-(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.
-
-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:	readmode_swtch
-Type:		modify (optional)
-Offset/size:	0x208/4
-Protocol:	2.00+
-
-  Boot loader hook (see ADVANCED BOOT LOADER HOOKS below.)
-
-Field name:	start_sys
-Type:		read
-Offset/size:	0x20c/4
-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.
-
-  Assigned boot loader ids:
-	0  LILO			(0x00 reserved for pre-2.00 bootloader)
-	1  Loadlin
-	2  bootsect-loader	(0x20, all other values reserved)
-	3  SYSLINUX
-	4  EtherBoot
-	5  ELILO
-	7  GRuB
-	8  U-BOOT
-	9  Xen
-	A  Gujin
-	B  Qemu
-
-  Please contact <hpa@zytor.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 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:	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 (reloc)
-Offset/size:	0x230/4
-Protocol:	2.05+
-
-  Alignment unit required by the kernel (if relocatable_kernel is true.)
-
-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:	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
-
-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 end of the
-  real-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. Currently only gzip compressed ELF is used.
-  
-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.
-
-
-**** 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/kernel-parameters.txt 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 setupping 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; __BOOS_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.