path: root/Documentation/i386
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authorLinus Torvalds <>2005-04-16 15:20:36 -0700
committerLinus Torvalds <>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/i386
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'Documentation/i386')
4 files changed, 686 insertions, 0 deletions
diff --git a/Documentation/i386/IO-APIC.txt b/Documentation/i386/IO-APIC.txt
new file mode 100644
index 000000000000..435e69e6e9aa
--- /dev/null
+++ b/Documentation/i386/IO-APIC.txt
@@ -0,0 +1,117 @@
+Most (all) Intel-MP compliant SMP boards have the so-called 'IO-APIC',
+which is an enhanced interrupt controller, it enables us to route
+hardware interrupts to multiple CPUs, or to CPU groups.
+Linux supports all variants of compliant SMP boards, including ones with
+multiple IO-APICs. (multiple IO-APICs are used in high-end servers to
+distribute IRQ load further).
+There are (a few) known breakages in certain older boards, which bugs are
+usually worked around by the kernel. If your MP-compliant SMP board does
+not boot Linux, then consult the linux-smp mailing list archives first.
+If your box boots fine with enabled IO-APIC IRQs, then your
+/proc/interrupts will look like this one:
+ ---------------------------->
+ hell:~> cat /proc/interrupts
+ CPU0
+ 0: 1360293 IO-APIC-edge timer
+ 1: 4 IO-APIC-edge keyboard
+ 2: 0 XT-PIC cascade
+ 13: 1 XT-PIC fpu
+ 14: 1448 IO-APIC-edge ide0
+ 16: 28232 IO-APIC-level Intel EtherExpress Pro 10/100 Ethernet
+ 17: 51304 IO-APIC-level eth0
+ NMI: 0
+ ERR: 0
+ hell:~>
+ <----------------------------
+some interrupts are still listed as 'XT PIC', but this is not a problem,
+none of those IRQ sources is performance-critical.
+in the unlikely case that your board does not create a working mp-table,
+you can use the pirq= boot parameter to 'hand-construct' IRQ entries. This
+is nontrivial though and cannot be automated. One sample /etc/lilo.conf
+ append="pirq=15,11,10"
+the actual numbers depend on your system, on your PCI cards and on their
+PCI slot position. Usually PCI slots are 'daisy chained' before they are
+connected to the PCI chipset IRQ routing facility (the incoming PIRQ1-4
+ ,-. ,-. ,-. ,-. ,-.
+ PIRQ4 ----| |-. ,-| |-. ,-| |-. ,-| |--------| |
+ |S| \ / |S| \ / |S| \ / |S| |S|
+ PIRQ3 ----|l|-. `/---|l|-. `/---|l|-. `/---|l|--------|l|
+ |o| \/ |o| \/ |o| \/ |o| |o|
+ PIRQ2 ----|t|-./`----|t|-./`----|t|-./`----|t|--------|t|
+ |1| /\ |2| /\ |3| /\ |4| |5|
+ PIRQ1 ----| |- `----| |- `----| |- `----| |--------| |
+ `-' `-' `-' `-' `-'
+every PCI card emits a PCI IRQ, which can be INTA,INTB,INTC,INTD:
+ ,-.
+ INTD--| |
+ |S|
+ INTC--|l|
+ |o|
+ INTB--|t|
+ |x|
+ INTA--| |
+ `-'
+These INTA-D PCI IRQs are always 'local to the card', their real meaning
+depends on which slot they are in. If you look at the daisy chaining diagram,
+a card in slot4, issuing INTA IRQ, it will end up as a signal on PIRQ2 of
+the PCI chipset. Most cards issue INTA, this creates optimal distribution
+between the PIRQ lines. (distributing IRQ sources properly is not a
+necessity, PCI IRQs can be shared at will, but it's a good for performance
+to have non shared interrupts). Slot5 should be used for videocards, they
+do not use interrupts normally, thus they are not daisy chained either.
+so if you have your SCSI card (IRQ11) in Slot1, Tulip card (IRQ9) in
+Slot2, then you'll have to specify this pirq= line:
+ append="pirq=11,9"
+the following script tries to figure out such a default pirq= line from
+your PCI configuration:
+ echo -n pirq=; echo `scanpci | grep T_L | cut -c56-` | sed 's/ /,/g'
+note that this script wont work if you have skipped a few slots or if your
+board does not do default daisy-chaining. (or the IO-APIC has the PIRQ pins
+connected in some strange way). E.g. if in the above case you have your SCSI
+card (IRQ11) in Slot3, and have Slot1 empty:
+ append="pirq=0,9,11"
+[value '0' is a generic 'placeholder', reserved for empty (or non-IRQ emitting)
+generally, it's always possible to find out the correct pirq= settings, just
+permute all IRQ numbers properly ... it will take some time though. An
+'incorrect' pirq line will cause the booting process to hang, or a device
+won't function properly (if it's inserted as eg. a module).
+If you have 2 PCI buses, then you can use up to 8 pirq values. Although such
+boards tend to have a good configuration.
+Be prepared that it might happen that you need some strange pirq line:
+ append="pirq=0,0,0,0,0,0,9,11"
+use smart try-and-err techniques to find out the correct pirq line ...
+good luck and mail to or if you have any problems that are not covered
+by this document.
+-- mingo
diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt
new file mode 100644
index 000000000000..1c48f0eba6fb
--- /dev/null
+++ b/Documentation/i386/boot.txt
@@ -0,0 +1,441 @@
+ ----------------------------
+ H. Peter Anvin <>
+ Last update 2002-01-01
+On the i386 platform, the Linux kernel uses a rather complicated boot
+convention. This has evolved partially due to historical aspects, as
+well as the desire in the early days to have the kernel itself be a
+bootable image, the complicated PC memory model and due to changed
+expectations in the PC industry caused by the effective demise of
+real-mode DOS as a mainstream operating system.
+Currently, four versions of the Linux/i386 boot protocol exist.
+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
+ 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 2.02: (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
+ initrd address available to the bootloader.
+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 +------------------------+
+ | Stack/heap/cmdline | 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,
+setup, and stack/heap) was made relocatable to any address between
+0x10000 and end of low memory. Unfortunately, in protocols 2.00 and
+2.01 the command line is still required to live in the 0x9XXXX memory
+range, and that memory range is still overwritten by the early kernel.
+The 2.02 protocol resolves that problem.
+It is desirable to keep the "memory ceiling" -- the highest point in
+low memory touched by the boot loader -- as low as possible, since
+some newer BIOSes have begun to allocate some rather large amounts of
+memory, called the Extended BIOS Data Area, near the top of low
+memory. The boot loader should use the "INT 12h" BIOS call to verify
+how much low memory is available.
+Unfortunately, if INT 12h reports that the amount of memory is too
+low, there is usually nothing the boot loader can do but to report an
+error to the user. The boot loader should therefore be designed to
+take up as little space in low memory as it reasonably can. For
+zImage or old bzImage kernels, which need data written into the
+0x90000 segment, the boot loader should make sure not to use memory
+above the 0x9A000 point; too many BIOSes will break above that point.
+In the following text, and anywhere in the kernel boot sequence, "a
+sector" refers to 512 bytes. It is independent of the actual sector
+size of the underlying medium.
+The first step in loading a Linux kernel should be to load the
+real-mode code (boot sector and setup code) and then examine the
+following header at offset 0x01f1. The real-mode code can total up to
+32K, although the boot loader may choose to load only the first two
+sectors (1K) and then examine the bootup sector size.
+The header looks like:
+Offset Proto Name Meaning
+01F1/1 ALL setup_sects The size of the setup in sectors
+01F2/2 ALL root_flags If set, the root is mounted readonly
+01F4/2 ALL syssize DO NOT USE - for bootsect.S use only
+01F6/2 ALL swap_dev DO NOT USE - obsolete
+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 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
+0226/2 N/A pad1 Unused
+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
+For backwards compatibility, if the setup_sects field contains 0, the
+real value is 4.
+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:
+ Image type = zImage
+ initrd not supported
+ Real-mode kernel must be located at 0x90000.
+Otherwise, the "version" field contains the protocol version,
+e.g. protocol version 2.01 will contain 0x0201 in this field. When
+setting fields in the header, you must make sure only to set fields
+supported by the protocol version in use.
+The "kernel_version" field, if set to a nonzero value, contains a
+pointer to a null-terminated human-readable kernel version number
+string, less 0x200. This can be used to display the kernel version to
+the user. This value should be less than (0x200*setup_sects). 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
+14 or higher.
+Most boot loaders will simply load the kernel at its target address
+directly. Such boot loaders do not need to worry about filling in
+most of the fields in the header. The following fields should be
+filled out, however:
+ vid_mode:
+ Please see the section on SPECIAL COMMAND LINE OPTIONS.
+ type_of_loader:
+ 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
+ a version number. Otherwise, enter 0xFF here.
+ Assigned boot loader ids:
+ 0 LILO
+ 1 Loadlin
+ 2 bootsect-loader
+ 4 EtherBoot
+ 7 GRuB
+ 8 U-BOOT
+ Please contact <> if you need a bootloader ID
+ value assigned.
+ loadflags, heap_end_ptr:
+ If the protocol version is 2.01 or higher, enter the
+ offset limit of the setup heap into heap_end_ptr and set the
+ 0x80 bit (CAN_USE_HEAP) of loadflags. heap_end_ptr appears to
+ be relative to the start of setup (offset 0x0200).
+ setup_move_size:
+ 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 sequence. Fill in this field if you want
+ additional data (such as the kernel command line) moved in
+ addition to the real-mode kernel itself.
+ ramdisk_image, ramdisk_size:
+ If your boot loader has loaded an initial ramdisk (initrd),
+ set ramdisk_image to the 32-bit pointer to the ramdisk data
+ and the ramdisk_size to the size of the ramdisk data.
+ The initrd should typically be located as high in memory as
+ possible, as it may otherwise get overwritten by the early
+ kernel initialization sequence. However, it must never be
+ located above the address specified in the initrd_addr_max
+ field. The initrd should be at least 4K page aligned.
+ cmd_line_ptr:
+ If the protocol version is 2.02 or higher, this is a 32-bit
+ pointer to the kernel command line. The kernel command line
+ can be located anywhere between the end of setup and 0xA0000.
+ Fill in this field even if your boot loader does not support a
+ command line, in which case you can point this to an empty
+ string (or better yet, to the string "auto".) If this field
+ is left at zero, the kernel will assume that your boot loader
+ does not support the 2.02+ protocol.
+ ramdisk_max:
+ The maximum address that may be occupied by the initrd
+ contents. For boot protocols 2.02 or earlier, this field is
+ not present, and the maximum address is 0x37FFFFFF. (This
+ address is defined as the address of the highest safe byte, so
+ if your ramdisk is exactly 131072 bytes long and this field is
+ 0x37FFFFFF, you can start your ramdisk at 0x37FE0000.)
+The kernel command line has become an important way for the boot
+loader to communicate with the kernel. Some of its options are also
+relevant to the boot loader itself, see "special command line options"
+The kernel command line is a null-terminated string up to 255
+characters long, plus the final null.
+If the boot protocol version is 2.02 or later, the address of the
+kernel command line is given by the header field cmd_line_ptr (see
+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 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.
+As a sample configuration, assume the following layout of the real
+mode segment:
+ 0x0000-0x7FFF Real mode kernel
+ 0x8000-0x8FFF Stack and heap
+ 0x9000-0x90FF Kernel command line
+Such a boot loader should enter the following fields in the header:
+ unsigned long base_ptr; /* base address for real-mode segment */
+ if ( setup_sects == 0 ) {
+ setup_sects = 4;
+ }
+ if ( protocol >= 0x0200 ) {
+ type_of_loader = <type code>;
+ if ( loading_initrd ) {
+ ramdisk_image = <initrd_address>;
+ ramdisk_size = <initrd_size>;
+ }
+ if ( protocol >= 0x0201 ) {
+ heap_end_ptr = 0x9000 - 0x200;
+ loadflags |= 0x80; /* CAN_USE_HEAP */
+ }
+ if ( protocol >= 0x0202 ) {
+ cmd_line_ptr = base_ptr + 0x9000;
+ } else {
+ cmd_line_magic = 0xA33F;
+ cmd_line_offset = 0x9000;
+ setup_move_size = 0x9100;
+ }
+ } else {
+ /* Very old kernel */
+ cmd_line_magic = 0xA33F;
+ cmd_line_offset = 0x9000;
+ /* A very old kernel MUST have its real-mode code
+ loaded at 0x90000 */
+ if ( base_ptr != 0x90000 ) {
+ /* Copy the real-mode kernel */
+ memcpy(0x90000, base_ptr, (setup_sects+1)*512);
+ /* Copy the command line */
+ memcpy(0x99000, base_ptr+0x9000, 256);
+ base_ptr = 0x90000; /* Relocated */
+ }
+ /* It is recommended to clear memory up to the 32K mark */
+ memset(0x90000 + (setup_sects+1)*512, 0,
+ (64-(setup_sects+1))*512);
+ }
+The 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.) 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:
+ is_bzImage = (protocol >= 0x0200) && (loadflags & 0x01);
+ load_address = is_bzImage ? 0x100000 : 0x10000;
+Note that Image/zImage kernels can be up to 512K in size, and thus use
+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.
+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.
+They should normally not be deleted from the kernel command line even
+though not all of them are actually meaningful to the kernel. Boot
+loader authors who need additional command line options for the boot
+loader itself should get them registered in
+Documentation/kernel-parameters.txt to make sure they will not
+conflict with actual kernel options now or in the future.
+ vga=<mode>
+ <mode> here is either an integer (in C notation, either
+ decimal, octal, or hexadecimal) or one of the strings
+ "normal" (meaning 0xFFFF), "ext" (meaning 0xFFFE) or "ask"
+ (meaning 0xFFFD). This value should be entered into the
+ vid_mode field, as it is used by the kernel before the command
+ line is parsed.
+ mem=<size>
+ <size> is an integer in C notation optionally followed by K, M
+ or G (meaning << 10, << 20 or << 30). This specifies the end
+ of memory to the kernel. This affects the possible placement
+ of an initrd, since an initrd should be placed near end of
+ memory. Note that this is an option to *both* the kernel and
+ the bootloader!
+ initrd=<file>
+ An initrd should be loaded. The meaning of <file> is
+ obviously bootloader-dependent, and some boot loaders
+ (e.g. LILO) do not have such a command.
+In addition, some boot loaders add the following options to the
+user-specified command line:
+ BOOT_IMAGE=<file>
+ The boot image which was loaded. Again, the meaning of <file>
+ is obviously bootloader-dependent.
+ auto
+ The kernel was booted without explicit user intervention.
+If these options are added by the boot loader, it is highly
+recommended that they are located *first*, before the user-specified
+or configuration-specified command line. Otherwise, "init=/bin/sh"
+gets confused by the "auto" option.
+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
+kernel. This means that if you loaded your real-mode kernel code at
+0x90000, the kernel entry point is 9020:0000.
+At entry, ds = es = ss should point to the start of the real-mode
+kernel code (0x9000 if the code is loaded at 0x90000), sp should be
+set up properly, normally pointing to the top of the heap, and
+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:
+ /* Note: in the case of the "old" kernel protocol, base_ptr must
+ be == 0x90000 at this point; see the previous sample code */
+ seg = base_ptr >> 4;
+ cli(); /* Enter with interrupts disabled! */
+ /* Set up the real-mode kernel stack */
+ _SS = seg;
+ _SP = 0x9000; /* Load SP immediately after loading SS! */
+ _DS = _ES = _FS = _GS = seg;
+ jmp_far(seg+0x20, 0); /* Run the kernel */
+If your boot sector accesses a floppy drive, it is recommended to
+switch off the floppy motor before running the kernel, since the
+kernel boot leaves interrupts off and thus the motor will not be
+switched off, especially if the loaded kernel has the floppy driver as
+a demand-loaded module!
+If the boot loader runs in a particularly hostile environment (such as
+LOADLIN, which runs under DOS) it may be impossible to follow the
+standard memory location requirements. Such a boot loader may use the
+following hooks that, if set, are invoked by the kernel at the
+appropriate time. The use of these hooks should probably be
+considered an absolutely last resort!
+IMPORTANT: All the hooks are required to preserve %esp, %ebp, %esi and
+%edi across invocation.
+ realmode_swtch:
+ A 16-bit real mode far subroutine invoked immediately before
+ entering protected mode. The default routine disables NMI, so
+ your routine should probably do so, too.
+ code32_start:
+ A 32-bit flat-mode routine *jumped* to immediately after the
+ transition to protected mode, but before the kernel is
+ uncompressed. No segments, except CS, are set up; you should
+ set them up to KERNEL_DS (0x18) yourself.
+ After completing your hook, you should jump to the address
+ that was in this field before your boot loader overwrote it.
diff --git a/Documentation/i386/usb-legacy-support.txt b/Documentation/i386/usb-legacy-support.txt
new file mode 100644
index 000000000000..1894cdfc69d9
--- /dev/null
+++ b/Documentation/i386/usb-legacy-support.txt
@@ -0,0 +1,44 @@
+USB Legacy support
+Vojtech Pavlik <>, January 2004
+Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a
+feature that allows one to use the USB mouse and keyboard as if they were
+their classic PS/2 counterparts. This means one can use an USB keyboard to
+type in LILO for example.
+It has several drawbacks, though:
+1) On some machines, the emulated PS/2 mouse takes over even when no USB
+ mouse is present and a real PS/2 mouse is present. In that case the extra
+ features (wheel, extra buttons, touchpad mode) of the real PS/2 mouse may
+ not be available.
+2) If CONFIG_HIGHMEM64G is enabled, the PS/2 mouse emulation can cause
+ system crashes, because the SMM BIOS is not expecting to be in PAE mode.
+ The Intel E7505 is a typical machine where this happens.
+3) If AMD64 64-bit mode is enabled, again system crashes often happen,
+ because the SMM BIOS isn't expecting the CPU to be in 64-bit mode. The
+ BIOS manufacturers only test with Windows, and Windows doesn't do 64-bit
+ yet.
+Problem 1) can be solved by loading the USB drivers prior to loading the
+PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into
+the kernel unconditionally, this means the USB drivers need to be
+compiled-in, too.
+Problem 2) can currently only be solved by either disabling HIGHMEM64G
+in the kernel config or USB Legacy support in the BIOS. A BIOS update
+could help, but so far no such update exists.
+Problem 3) is usually fixed by a BIOS update. Check the board
+manufacturers web site. If an update is not available, disable USB
+Legacy support in the BIOS. If this alone doesn't help, try also adding
+idle=poll on the kernel command line. The BIOS may be entering the SMM
+on the HLT instruction as well.
diff --git a/Documentation/i386/zero-page.txt b/Documentation/i386/zero-page.txt
new file mode 100644
index 000000000000..67c053a099ed
--- /dev/null
+++ b/Documentation/i386/zero-page.txt
@@ -0,0 +1,84 @@
+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
+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
+ 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 - 0x600 E820MAP
+0x600 - 0x7ff EDDBUF (edd.S) for disk signature read sector
+0x600 - 0x7eb EDDBUF (edd.S) for edd data