Re: [PATCH v3 02/27] Documentation: x86: convert boot.txt to reST

From: Mauro Carvalho Chehab
Date: Mon May 06 2019 - 13:54:02 EST

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Em Tue, 7 May 2019 01:08:58 +0800
Changbin Du <changbin.du@xxxxxxxxx> escreveu:

> 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@xxxxxxxxx>
> Cc: Mauro Carvalho Chehab <mchehab+samsung@xxxxxxxxxx>
> ---
> Documentation/x86/{boot.txt => boot.rst} | 530 ++++++++++++++---------
> Documentation/x86/index.rst | 2 +
> 2 files changed, 329 insertions(+), 203 deletions(-)
> rename Documentation/x86/{boot.txt => boot.rst} (73%)
>
> diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.rst
> similarity index 73%
> rename from Documentation/x86/boot.txt
> rename to Documentation/x86/boot.rst
> index 223e484a1304..5f20de0ced23 100644
> --- a/Documentation/x86/boot.txt
> +++ b/Documentation/x86/boot.rst
> @@ -1,5 +1,8 @@
> - THE LINUX/x86 BOOT PROTOCOL
> - ---------------------------
> +.. 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
> @@ -10,88 +13,91 @@ 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
> +============= ============================================================
> +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
> +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 2.01 (Kernel 1.3.76) Added a heap overrun warning.
>
> -Protocol 2.02: (Kernel 2.4.0-test3-pre3) New command line protocol.
> +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
> +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 2.04 (Kernel 2.6.14) Extend the syssize field to four bytes.
>
> -Protocol 2.05: (Kernel 2.6.20) Make protected mode kernel relocatable.
> +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
> +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.
> +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
> +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
> +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
> +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 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
> +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.
>
> -Protocol 2.13: (Kernel 3.14) Support 32- and 64-bit flags being set in
> +Protocol 2.13 (Kernel 3.14) Support 32- and 64-bit flags being set in
> xloadflags to support booting a 64-bit kernel from 32-bit
> EFI
> +============= ============================================================
>
> -**** 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 +------------------------+
> +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,
> @@ -116,36 +122,36 @@ zImage or old bzImage kernels, which need data written into the
> 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
> +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
> @@ -159,61 +165,63 @@ 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.
> +=========== ======== ===================== ============================================
> +Offset/Size Proto Name Meaning
> +=========== ======== ===================== ============================================
> +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
> +=========== ======== ===================== ============================================
> +
> +.. note::
> + (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:
> +following parameters should be assumed::
>
> Image type = zImage
> initrd not supported
> @@ -225,7 +233,8 @@ setting fields in the header, you must make sure only to set fields
> supported by the protocol version in use.
>
>
> -**** DETAILS OF HEADER FIELDS
> +Details of Harder Fileds
> +========================
>
> For each field, some are information from the kernel to the bootloader
> ("read"), some are expected to be filled out by the bootloader
> @@ -239,106 +248,132 @@ 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
> +============ =================
> +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
> @@ -348,17 +383,21 @@ Protocol: 2.00+
> 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:
> + 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.
> + 0x1c00 >> 9 = 14
> +
> + So the minimum value for setup_secs is 15.

IMO, this belongs to the literal block.

>
> +============ ==================
> 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
> @@ -369,17 +408,20 @@ Protocol: 2.00+
> 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:
> + For example, for T = 0x15, V = 0x234, write::
>
> - type_of_loader <- 0xE4
> - ext_loader_type <- 0x05
> - ext_loader_ver <- 0x23
> + 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)
> + == ==============================

The table markup line here is too short.

> + 0 LILO
> + (0x00 reserved for pre-2.00 bootloader)
> 1 Loadlin
> - 2 bootsect-loader (0x20, all other values reserved)
> + 2 bootsect-loader
> + (0x20, all other values reserved)
> 3 Syslinux
> 4 Etherboot/gPXE/iPXE
> 5 ELILO
> @@ -390,55 +432,70 @@ Protocol: 2.00+
> 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
> + 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
> + == ==============================

Same here: extending the line above will require extending it here too.

With the above changes:

Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@xxxxxxxxxx>

>
> - Please contact <hpa@xxxxxxxxx> if you need a bootloader ID
> - value assigned.
> + Please contact <hpa@xxxxxxxxx> 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.
> +
> + - 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
> @@ -447,14 +504,16 @@ Protocol: 2.00-2.01
> 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
> @@ -462,47 +521,57 @@ Protocol: 2.00+
>
> This field can be modified for two purposes:
>
> - 1. as a boot loader hook (see ADVANCED BOOT LOADER HOOKS below.)
> + 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.
> + 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
> @@ -514,10 +583,12 @@ Protocol: 2.02+
> 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
> @@ -528,10 +599,12 @@ Protocol: 2.02+
> 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
> @@ -544,10 +617,12 @@ Protocol: 2.02+
> 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
> @@ -556,10 +631,12 @@ Protocol: 2.03+
> 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
> @@ -571,25 +648,29 @@ Protocol: 2.05+ (read), 2.10+ (modify)
> 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 field with the alignment unit desired; typically::
>
> kernel_alignment = 1 << min_alignment
>
> @@ -597,44 +678,56 @@ Protocol: 2.10+
> 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+
> +============ ==========
> +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
> @@ -643,25 +736,31 @@ Protocol: 2.07+
> 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.
> @@ -674,29 +773,33 @@ Protocol: 2.08+
> 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:
> + as follow::
>
> - struct setup_data {
> - u64 next;
> - u32 type;
> - u32 len;
> - u8 data[0];
> - };
> + 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
> @@ -708,10 +811,12 @@ Protocol: 2.09+
> 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
> @@ -720,9 +825,11 @@ Protocol: 2.10+
> 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
> @@ -731,16 +838,18 @@ Offset/size: 0x260/4
> 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:
> + The kernel runtime start address is determined by the following algorithm::
>
> - if (relocatable_kernel)
> + if (relocatable_kernel)
> runtime_start = align_up(load_address, kernel_alignment)
> - else
> + 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
> @@ -749,7 +858,8 @@ Offset/size: 0x264/4
> See EFI HANDOVER PROTOCOL below for more details.
>
>
> -**** THE IMAGE CHECKSUM
> +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
> @@ -758,7 +868,8 @@ 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
> +=======================
>
> The kernel command line has become an important way for the boot
> loader to communicate with the kernel. Some of its options are also
> @@ -778,19 +889,20 @@ 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 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).
>
> - 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.
> + - 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
> +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
> @@ -806,10 +918,11 @@ 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.
> +.. note::
> + 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.
>
> @@ -822,24 +935,29 @@ The kernel command line should not be located below the real-mode
> code, nor should it be located in high memory.
>
>
> -**** SAMPLE BOOT CONFIGURATION
> +Sample Boot Configuartion
> +=========================
>
> As a sample configuration, assume the following layout of the real
> -mode segment:
> +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:
> +Such a boot loader should enter the following fields in the header::
>
> unsigned long base_ptr; /* base address for real-mode segment */
>
> @@ -898,7 +1016,8 @@ Such a boot loader should enter the following fields in the header:
> }
>
>
> -**** LOADING THE REST OF THE KERNEL
> +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.)
> @@ -906,7 +1025,7 @@ 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:
> +bit (LOAD_HIGH) in the loadflags field is set::
>
> is_bzImage = (protocol >= 0x0200) && (loadflags & 0x01);
> load_address = is_bzImage ? 0x100000 : 0x10000;
> @@ -916,8 +1035,8 @@ 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
> +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.
> @@ -966,7 +1085,8 @@ or configuration-specified command line. Otherwise, "init=/bin/sh"
> gets confused by the "auto" option.
>
>
> -**** RUNNING THE KERNEL
> +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
> @@ -980,7 +1100,7 @@ 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:
> +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 */
> @@ -1003,7 +1123,8 @@ switched off, especially if the loaded kernel has the floppy driver as
> a demand-loaded module!
>
>
> -**** ADVANCED BOOT LOADER HOOKS
> +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
> @@ -1032,7 +1153,8 @@ IMPORTANT: All the hooks are required to preserve %esp, %ebp, %esi and
> (relocated, if appropriate.)
>
>
> -**** 32-bit BOOT PROTOCOL
> +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
> @@ -1045,7 +1167,7 @@ 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:
> +follow::
>
> 0x0202 + byte value at offset 0x0201
>
> @@ -1069,7 +1191,8 @@ 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
> +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.
> @@ -1080,7 +1203,7 @@ 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:
> +can be calculated as follows::
>
> 0x0202 + byte value at offset 0x0201
>
> @@ -1107,7 +1230,8 @@ 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
> +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)
> @@ -1115,7 +1239,7 @@ 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,
> +The function prototype for the handover entry point looks like this::
>
> efi_main(void *handle, efi_system_table_t *table, struct boot_params *bp)
>
> @@ -1124,11 +1248,11 @@ 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,
> +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)
> + - 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/index.rst b/Documentation/x86/index.rst
> index 9f34545a9c52..d7fc8efac192 100644
> --- a/Documentation/x86/index.rst
> +++ b/Documentation/x86/index.rst
> @@ -7,3 +7,5 @@ x86-specific Documentation
> .. toctree::
> :maxdepth: 2
> :numbered:
> +
> + boot

Thanks,
Mauro

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