- THE LINUX/I386 BOOT PROTOCOL
- ----------------------------
+ THE LINUX/x86 BOOT PROTOCOL
+ ---------------------------
- H. Peter Anvin <hpa@zytor.com>
- Last update 2007-05-23
-
-On the i386 platform, the Linux kernel uses a rather complicated boot
+On the x86 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, the following versions of the Linux/i386 boot protocol exist.
+Currently, the following versions of the Linux/x86 boot protocol exist.
Old kernels: zImage/Image support only. Some very early kernels
may not even support a command line.
Introduce relocatable_kernel and kernel_alignment fields.
Protocol 2.06: (Kernel 2.6.22) Added a field that contains the size of
- the boot command line
+ the boot command line.
+
+Protocol 2.07: (Kernel 2.6.24) Added paravirtualised boot protocol.
+ Introduced hardware_subarch and hardware_subarch_data
+ and KEEP_SEGMENTS flag in load_flags.
+
+Protocol 2.08: (Kernel 2.6.26) Added crc32 checksum and ELF format
+ payload. Introduced payload_offset and payload length
+ fields to aid in locating the payload.
+Protocol 2.09: (Kernel 2.6.26) Added a field of 64-bit physical
+ pointer to single linked list of struct setup_data.
**** MEMORY LAYOUT
0240/8 2.07+ hardware_subarch_data Subarchitecture-specific data
0248/4 2.08+ payload_offset Offset of kernel payload
024C/4 2.08+ payload_length Length of kernel payload
+0250/8 2.09+ 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.
- If 0, the protected-mode code is loaded at 0x10000.
- If 1, the protected-mode code is loaded at 0x100000.
+ Bit 5 (write): QUIET_FLAG
+ - If 0, print early messages.
+ - If 1, suppress early messages.
+ This requests to the kernel (decompressor and early
+ kernel) to not write early messages that require
+ accessing the display hardware directly.
+
Bit 6 (write): KEEP_SEGMENTS
Protocol: 2.07+
- - if 0, reload the segment registers in the 32bit entry point.
- - if 1, do not reload the segment registers in the 32bit entry point.
+ - If 0, reload the segment registers in the 32bit entry point.
+ - If 1, do not reload the segment registers in the 32bit entry point.
Assume that %cs %ds %ss %es are all set to flat segments with
a base of 0 (or the equivalent for their environment).
maximum size was 255.
Field name: hardware_subarch
-Type: write
+Type: write (optional, defaults to x86/PC)
Offset/size: 0x23c/4
Protocol: 2.07+
0x00000002 Xen
Field name: hardware_subarch_data
-Type: write
+Type: write (subarch-dependent)
Offset/size: 0x240/8
Protocol: 2.07+
A pointer to data that is specific to hardware subarch
+ This field is currently unused for the default x86/PC environment,
+ do not modify.
Field name: payload_offset
Type: read
The length of the payload.
+Field name: setup_data
+Type: write (special)
+Offset/size: 0x250/8
+Protocol: 2.09+
+
+ 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];
+ };
+
+ 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.
+
+ This list may be modified at a number of points during the bootup
+ process. Therefore, when modifying this list one should always make
+ sure to consider the case where the linked list already contains
+ entries.
+
+
**** THE IMAGE CHECKSUM
From boot protocol version 2.08 onwards the CRC-32 is calculated over
file; therefore the CRC of the file up to the limit specified in the
syssize field of the header is always 0.
+
**** THE KERNEL COMMAND LINE
The kernel command line has become an important way for the boot
projects / linux-2.6-omap-h63xx.git / blobdiff