[PATCH -v6 3/3] x86 boot: document for 32 bit boot protocol
From: Huang, Ying
Date: Mon Oct 22 2007 - 03:15:29 EST
This patch defines a 32-bit boot protocol and adds corresponding
document. It is based on the proposal of Peter Anvin.
Signed-off-by: Huang Ying <ying.huang@xxxxxxxxx>
---
boot.txt | 68 ++++++++++++++++++++++++++++++
zero-page.txt | 129 +++++++++++++---------------------------------------------
2 files changed, 97 insertions(+), 100 deletions(-)
Index: linux-2.6.23/Documentation/i386/boot.txt
===================================================================
--- linux-2.6.23.orig/Documentation/i386/boot.txt 2007-10-22 13:32:20.000000000 +0800
+++ linux-2.6.23/Documentation/i386/boot.txt 2007-10-22 13:32:46.000000000 +0800
@@ -2,7 +2,7 @@
----------------------------
H. Peter Anvin <hpa@xxxxxxxxx>
- Last update 2007-05-23
+ Last update 2007-10-22
On the i386 platform, the Linux kernel uses a rather complicated boot
convention. This has evolved partially due to historical aspects, as
@@ -42,6 +42,9 @@
Protocol 2.06: (Kernel 2.6.22) Added a field that contains the size of
the boot command line
+Protocol 2.07: (kernel 2.6.23) Added a field of 64-bit physical
+ pointer to single linked list of struct setup_data.
+ Added 32-bit boot protocol.
**** MEMORY LAYOUT
@@ -168,6 +171,9 @@
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 N/A pad3 Unused
+0240/8 2.07+ 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.
@@ -480,6 +486,37 @@
cmdline_size characters. With protocol version 2.05 and earlier, the
maximum size was 255.
+Field name: setup_data
+Type: write (obligatory)
+Offset/size: 0x240/8
+Protocol: 2.07+
+
+ 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];
+ } __attribute__((packed));
+
+ 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.
+
+ With this field, to add a new boot parameter written by bootloaders,
+ it is not needed to add a new field to real mode header, just add a
+ new setup_data type is sufficient. But to add a new boot parameter
+ read by bootloader, it is still needed to add a new field.
+
+ During kernel bootstrap, the linked list of setup_data will be
+ copied to the memory area righ after the _end of kernel. So
+ bootloaders should avoid put linked list of setup_data there.
+
**** THE KERNEL COMMAND LINE
@@ -753,3 +790,32 @@
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 need
+to be defined.
+
+In 32-bit boot protocol, the first step in loading a Linux kernel
+should still be to load the real-mode code and then examine the kernel
+header at offset 0x01f1. But, it is not necessary to load all
+real-mode code, just first 4K bytes traditionally known as "zero page"
+is needed.
+
+In addition to read/modify/write kernel header of the zero page as
+that of 16-bit boot protocol, the boot loader should also fill the
+additional fields of the zero page as that described in zero-page.txt.
+
+After loading and setuping the zero page, 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; the CS and DS must be 4G flat segments; %esi holds the base
+address of the "zero page"; %esp, %ebp, %edi should be zero.
Index: linux-2.6.23/Documentation/i386/zero-page.txt
===================================================================
--- linux-2.6.23.orig/Documentation/i386/zero-page.txt 2007-10-22 13:32:20.000000000 +0800
+++ linux-2.6.23/Documentation/i386/zero-page.txt 2007-10-22 13:32:28.000000000 +0800
@@ -1,99 +1,30 @@
----------------------------------------------------------------------------
-!!!!!!!!!!!!!!!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 zero page as a part of 32-bit boot protocol
+of kernel. These should be filled by bootloader or 16-bit real-mode
+code of the kernel. References/settings to it mainly are in:
+
+ include/asm-i386/bootparam.h
+
+
+Offset Proto Name Meaning
+/Size
+
+000/040 2.07+ screen_info Text mode or frame buffer information
+ (struct screen_info)
+040/014 2.07+ apm_bios_info APM BIOS information (struct apm_bios_info)
+060/010 2.07+ ist_info Intel SpeedStep (IST) BIOS support information
+ (struct ist_info)
+080/010 2.07+ hd0_info hd0 disk parameter, OBSOLETE!!
+090/010 2.07+ hd1_info hd1 disk parameter, OBSOLETE!!
+0A0/010 2.07+ sys_desc_table System description table (struct sys_desc_table)
+140/080 2.07+ edid_info Video mode setup (struct edid_info)
+1C0/020 2.07+ efi_info EFI 32 information (struct efi_info)
+1E0/004 2.07+ alk_mem_k Alternative mem check, in KB
+1E4/004 2.07+ scratch Scratch field for the kernel setup code
+1E8/001 2.07+ e820_entries Number of entries in e820_map (below)
+1E9/001 2.07+ eddbuf_entries Number of entries in eddbuf (below)
+1EA/001 2.07+ edd_mbr_sig_buf_entries Number of entries in edd_mbr_sig_buffer
+ (below)
+290/040 2.07+ edd_mbr_sig_buffer EDD MBR signatures
+2D0/A00 2.07+ e820_map E820 memory map table
+ (array of struct e820entry)
+D00/1EC 2.07+ eddbuf EDD data (array of struct edd_info)
-
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