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: Huang Ying <ying.huang@intel.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Huang, Ying
Thomas Gleixner
parent
076e21a014
commit
aa69432a68
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@ -785,3 +785,41 @@ IMPORTANT: All the hooks are required to preserve %esp, %ebp, %esi and
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After completing your hook, you should jump to the address
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that was in this field before your boot loader overwrote it
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(relocated, if appropriate.)
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**** 32-bit BOOT PROTOCOL
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For machine with some new BIOS other than legacy BIOS, such as EFI,
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LinuxBIOS, etc, and kexec, the 16-bit real mode setup code in kernel
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based on legacy BIOS can not be used, so a 32-bit boot protocol needs
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to be defined.
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In 32-bit boot protocol, the first step in loading a Linux kernel
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should be to setup the boot parameters (struct boot_params,
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traditionally known as "zero page"). The memory for struct boot_params
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should be allocated and initialized to all zero. Then the setup header
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from offset 0x01f1 of kernel image on should be loaded into struct
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boot_params and examined. The end of setup header can be calculated as
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follow:
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0x0202 + byte value at offset 0x0201
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In addition to read/modify/write the setup header of the struct
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boot_params as that of 16-bit boot protocol, the boot loader should
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also fill the additional fields of the struct boot_params as that
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described in zero-page.txt.
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After setupping the struct boot_params, the boot loader can load the
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32/64-bit kernel in the same way as that of 16-bit boot protocol.
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In 32-bit boot protocol, the kernel is started by jumping to the
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32-bit kernel entry point, which is the start address of loaded
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32/64-bit kernel.
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At entry, the CPU must be in 32-bit protected mode with paging
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disabled; a GDT must be loaded with the descriptors for selectors
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__BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G flat
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segment; __BOOS_CS must have execute/read permission, and __BOOT_DS
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must have read/write permission; CS must be __BOOT_CS and DS, ES, SS
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must be __BOOT_DS; interrupt must be disabled; %esi must hold the base
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address of the struct boot_params; %ebp, %edi and %ebx must be zero.
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@ -1,99 +1,31 @@
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---------------------------------------------------------------------------
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!!!!!!!!!!!!!!!WARNING!!!!!!!!
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The zero page is a kernel internal data structure, not a stable ABI. It might change
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without warning and the kernel has no way to detect old version of it.
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If you're writing some external code like a boot loader you should only use
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the stable versioned real mode boot protocol described in boot.txt. Otherwise the kernel
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might break you at any time.
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!!!!!!!!!!!!!WARNING!!!!!!!!!!!
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----------------------------------------------------------------------------
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The additional fields in struct boot_params as a part of 32-bit boot
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protocol of kernel. These should be filled by bootloader or 16-bit
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real-mode setup code of the kernel. References/settings to it mainly
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are in:
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Summary of boot_params layout (kernel point of view)
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( collected by Hans Lermen and Martin Mares )
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The contents of boot_params are used to pass parameters from the
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16-bit realmode code of the kernel to the 32-bit part. References/settings
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to it mainly are in:
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include/asm-x86/bootparam.h
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arch/i386/boot/setup.S
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arch/i386/boot/video.S
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arch/i386/kernel/head.S
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arch/i386/kernel/setup.c
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Offset Type Description
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------ ---- -----------
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0 32 bytes struct screen_info, SCREEN_INFO
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ATTENTION, overlaps the following !!!
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2 unsigned short EXT_MEM_K, extended memory size in Kb (from int 0x15)
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0x20 unsigned short CL_MAGIC, commandline magic number (=0xA33F)
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0x22 unsigned short CL_OFFSET, commandline offset
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Address of commandline is calculated:
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0x90000 + contents of CL_OFFSET
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(only taken, when CL_MAGIC = 0xA33F)
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0x40 20 bytes struct apm_bios_info, APM_BIOS_INFO
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0x60 16 bytes Intel SpeedStep (IST) BIOS support information
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0x80 16 bytes hd0-disk-parameter from intvector 0x41
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0x90 16 bytes hd1-disk-parameter from intvector 0x46
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Offset Proto Name Meaning
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/Size
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0xa0 16 bytes System description table truncated to 16 bytes.
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( struct sys_desc_table_struct )
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0xb0 - 0x13f Free. Add more parameters here if you really need them.
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0x140- 0x1be EDID_INFO Video mode setup
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0x1c4 unsigned long EFI system table pointer
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0x1c8 unsigned long EFI memory descriptor size
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0x1cc unsigned long EFI memory descriptor version
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0x1d0 unsigned long EFI memory descriptor map pointer
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0x1d4 unsigned long EFI memory descriptor map size
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0x1e0 unsigned long ALT_MEM_K, alternative mem check, in Kb
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0x1e4 unsigned long Scratch field for the kernel setup code
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0x1e8 char number of entries in E820MAP (below)
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0x1e9 unsigned char number of entries in EDDBUF (below)
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0x1ea unsigned char number of entries in EDD_MBR_SIG_BUFFER (below)
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0x1f1 char size of setup.S, number of sectors
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0x1f2 unsigned short MOUNT_ROOT_RDONLY (if !=0)
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0x1f4 unsigned short size of compressed kernel-part in the
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(b)zImage-file (in 16 byte units, rounded up)
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0x1f6 unsigned short swap_dev (unused AFAIK)
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0x1f8 unsigned short RAMDISK_FLAGS
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0x1fa unsigned short VGA-Mode (old one)
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0x1fc unsigned short ORIG_ROOT_DEV (high=Major, low=minor)
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0x1ff char AUX_DEVICE_INFO
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0x200 short jump to start of setup code aka "reserved" field.
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0x202 4 bytes Signature for SETUP-header, ="HdrS"
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0x206 unsigned short Version number of header format
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Current version is 0x0201...
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0x208 8 bytes (used by setup.S for communication with boot loaders,
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look there)
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0x210 char LOADER_TYPE, = 0, old one
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else it is set by the loader:
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0xTV: T=0 for LILO
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1 for Loadlin
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2 for bootsect-loader
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3 for SYSLINUX
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4 for ETHERBOOT
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5 for ELILO
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7 for GRuB
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8 for U-BOOT
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9 for Xen
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V = version
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0x211 char loadflags:
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bit0 = 1: kernel is loaded high (bzImage)
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bit7 = 1: Heap and pointer (see below) set by boot
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loader.
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0x212 unsigned short (setup.S)
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0x214 unsigned long KERNEL_START, where the loader started the kernel
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0x218 unsigned long INITRD_START, address of loaded ramdisk image
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0x21c unsigned long INITRD_SIZE, size in bytes of ramdisk image
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0x220 4 bytes (setup.S)
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0x224 unsigned short setup.S heap end pointer
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0x226 unsigned short zero_pad
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0x228 unsigned long cmd_line_ptr
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0x22c unsigned long ramdisk_max
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0x230 16 bytes trampoline
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0x290 - 0x2cf EDD_MBR_SIG_BUFFER (edd.S)
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0x2d0 - 0xd00 E820MAP
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0xd00 - 0xeff EDDBUF (edd.S) for disk signature read sector
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0xd00 - 0xeeb EDDBUF (edd.S) for edd data
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000/040 ALL screen_info Text mode or frame buffer information
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(struct screen_info)
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040/014 ALL apm_bios_info APM BIOS information (struct apm_bios_info)
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060/010 ALL ist_info Intel SpeedStep (IST) BIOS support information
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(struct ist_info)
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080/010 ALL hd0_info hd0 disk parameter, OBSOLETE!!
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090/010 ALL hd1_info hd1 disk parameter, OBSOLETE!!
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0A0/010 ALL sys_desc_table System description table (struct sys_desc_table)
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140/080 ALL edid_info Video mode setup (struct edid_info)
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1C0/020 ALL efi_info EFI 32 information (struct efi_info)
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1E0/004 ALL alk_mem_k Alternative mem check, in KB
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1E4/004 ALL scratch Scratch field for the kernel setup code
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1E8/001 ALL e820_entries Number of entries in e820_map (below)
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1E9/001 ALL eddbuf_entries Number of entries in eddbuf (below)
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1EA/001 ALL edd_mbr_sig_buf_entries Number of entries in edd_mbr_sig_buffer
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(below)
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290/040 ALL edd_mbr_sig_buffer EDD MBR signatures
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2D0/A00 ALL e820_map E820 memory map table
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(array of struct e820entry)
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D00/1EC ALL eddbuf EDD data (array of struct edd_info)
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