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Date: Wed, 24 Oct 2007 10:18:49 +0800 From: "Huang, Ying" <ying.huang@...el.com> To: "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...e.de>, "Eric W. Biederman" <ebiederm@...ssion.com>, akpm@...ux-foundation.org, Linus Torvalds <torvalds@...ux-foundation.org> Cc: linux-kernel@...r.kernel.org Subject: [PATCH -v2] 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@...el.com> v2: - Fixes a bug about which registers should be set to zero. --- boot.txt | 38 ++++++++++++++++ zero-page.txt | 130 +++++++++++++--------------------------------------------- 2 files changed, 69 insertions(+), 99 deletions(-) Index: linux-2.6/Documentation/i386/boot.txt =================================================================== --- linux-2.6.orig/Documentation/i386/boot.txt 2007-10-24 09:21:57.000000000 +0800 +++ linux-2.6/Documentation/i386/boot.txt 2007-10-24 10:01:42.000000000 +0800 @@ -785,3 +785,41 @@ 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. Index: linux-2.6/Documentation/i386/zero-page.txt =================================================================== --- linux-2.6.orig/Documentation/i386/zero-page.txt 2007-10-24 09:21:57.000000000 +0800 +++ linux-2.6/Documentation/i386/zero-page.txt 2007-10-24 09:31:52.000000000 +0800 @@ -1,99 +1,31 @@ ---------------------------------------------------------------------------- -!!!!!!!!!!!!!!!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!!!!!!!!!!! ----------------------------------------------------------------------------- - -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: - - 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 - - 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 +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: + + include/asm-x86/bootparam.h + + +Offset Proto Name Meaning +/Size + +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) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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