Commit aa69432a authored by Huang, Ying's avatar Huang, Ying Committed by Thomas Gleixner

x86 boot: document for 32 bit boot protocol

This patch documents the 32-bit boot protocol of x86. It has been used
by Kexec and LinuxBIOS. This patch is based on the proposal of Peter
Anvin.
Signed-off-by: default avatarHuang Ying <ying.huang@intel.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 076e21a0
......@@ -785,3 +785,41 @@ IMPORTANT: All the hooks are required to preserve %esp, %ebp, %esi and
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.
---------------------------------------------------------------------------
!!!!!!!!!!!!!!!WARNING!!!!!!!!
The zero page is a kernel internal data structure, not a stable ABI. It might change
without warning and the kernel has no way to detect old version of it.
If you're writing some external code like a boot loader you should only use
the stable versioned real mode boot protocol described in boot.txt. Otherwise the kernel
might break you at any time.
!!!!!!!!!!!!!WARNING!!!!!!!!!!!
----------------------------------------------------------------------------
The additional fields in struct boot_params as a part of 32-bit boot
protocol of kernel. These should be filled by bootloader or 16-bit
real-mode setup code of the kernel. References/settings to it mainly
are in:
Summary of boot_params layout (kernel point of view)
( collected by Hans Lermen and Martin Mares )
The contents of boot_params are used to pass parameters from the
16-bit realmode code of the kernel to the 32-bit part. References/settings
to it mainly are in:
include/asm-x86/bootparam.h
arch/i386/boot/setup.S
arch/i386/boot/video.S
arch/i386/kernel/head.S
arch/i386/kernel/setup.c
Offset Type Description
------ ---- -----------
0 32 bytes struct screen_info, SCREEN_INFO
ATTENTION, overlaps the following !!!
2 unsigned short EXT_MEM_K, extended memory size in Kb (from int 0x15)
0x20 unsigned short CL_MAGIC, commandline magic number (=0xA33F)
0x22 unsigned short CL_OFFSET, commandline offset
Address of commandline is calculated:
0x90000 + contents of CL_OFFSET
(only taken, when CL_MAGIC = 0xA33F)
0x40 20 bytes struct apm_bios_info, APM_BIOS_INFO
0x60 16 bytes Intel SpeedStep (IST) BIOS support information
0x80 16 bytes hd0-disk-parameter from intvector 0x41
0x90 16 bytes hd1-disk-parameter from intvector 0x46
Offset Proto Name Meaning
/Size
0xa0 16 bytes System description table truncated to 16 bytes.
( struct sys_desc_table_struct )
0xb0 - 0x13f Free. Add more parameters here if you really need them.
0x140- 0x1be EDID_INFO Video mode setup
0x1c4 unsigned long EFI system table pointer
0x1c8 unsigned long EFI memory descriptor size
0x1cc unsigned long EFI memory descriptor version
0x1d0 unsigned long EFI memory descriptor map pointer
0x1d4 unsigned long EFI memory descriptor map size
0x1e0 unsigned long ALT_MEM_K, alternative mem check, in Kb
0x1e4 unsigned long Scratch field for the kernel setup code
0x1e8 char number of entries in E820MAP (below)
0x1e9 unsigned char number of entries in EDDBUF (below)
0x1ea unsigned char number of entries in EDD_MBR_SIG_BUFFER (below)
0x1f1 char size of setup.S, number of sectors
0x1f2 unsigned short MOUNT_ROOT_RDONLY (if !=0)
0x1f4 unsigned short size of compressed kernel-part in the
(b)zImage-file (in 16 byte units, rounded up)
0x1f6 unsigned short swap_dev (unused AFAIK)
0x1f8 unsigned short RAMDISK_FLAGS
0x1fa unsigned short VGA-Mode (old one)
0x1fc unsigned short ORIG_ROOT_DEV (high=Major, low=minor)
0x1ff char AUX_DEVICE_INFO
0x200 short jump to start of setup code aka "reserved" field.
0x202 4 bytes Signature for SETUP-header, ="HdrS"
0x206 unsigned short Version number of header format
Current version is 0x0201...
0x208 8 bytes (used by setup.S for communication with boot loaders,
look there)
0x210 char LOADER_TYPE, = 0, old one
else it is set by the loader:
0xTV: T=0 for LILO
1 for Loadlin
2 for bootsect-loader
3 for SYSLINUX
4 for ETHERBOOT
5 for ELILO
7 for GRuB
8 for U-BOOT
9 for Xen
V = version
0x211 char loadflags:
bit0 = 1: kernel is loaded high (bzImage)
bit7 = 1: Heap and pointer (see below) set by boot
loader.
0x212 unsigned short (setup.S)
0x214 unsigned long KERNEL_START, where the loader started the kernel
0x218 unsigned long INITRD_START, address of loaded ramdisk image
0x21c unsigned long INITRD_SIZE, size in bytes of ramdisk image
0x220 4 bytes (setup.S)
0x224 unsigned short setup.S heap end pointer
0x226 unsigned short zero_pad
0x228 unsigned long cmd_line_ptr
0x22c unsigned long ramdisk_max
0x230 16 bytes trampoline
0x290 - 0x2cf EDD_MBR_SIG_BUFFER (edd.S)
0x2d0 - 0xd00 E820MAP
0xd00 - 0xeff EDDBUF (edd.S) for disk signature read sector
0xd00 - 0xeeb EDDBUF (edd.S) for edd data
000/040 ALL screen_info Text mode or frame buffer information
(struct screen_info)
040/014 ALL apm_bios_info APM BIOS information (struct apm_bios_info)
060/010 ALL ist_info Intel SpeedStep (IST) BIOS support information
(struct ist_info)
080/010 ALL hd0_info hd0 disk parameter, OBSOLETE!!
090/010 ALL hd1_info hd1 disk parameter, OBSOLETE!!
0A0/010 ALL sys_desc_table System description table (struct sys_desc_table)
140/080 ALL edid_info Video mode setup (struct edid_info)
1C0/020 ALL efi_info EFI 32 information (struct efi_info)
1E0/004 ALL alk_mem_k Alternative mem check, in KB
1E4/004 ALL scratch Scratch field for the kernel setup code
1E8/001 ALL e820_entries Number of entries in e820_map (below)
1E9/001 ALL eddbuf_entries Number of entries in eddbuf (below)
1EA/001 ALL edd_mbr_sig_buf_entries Number of entries in edd_mbr_sig_buffer
(below)
290/040 ALL edd_mbr_sig_buffer EDD MBR signatures
2D0/A00 ALL e820_map E820 memory map table
(array of struct e820entry)
D00/1EC ALL eddbuf EDD data (array of struct edd_info)
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