Commit 4039feb5 authored by H. Peter Anvin's avatar H. Peter Anvin

x86: update Documentation/i386/boot.txt

Document QUIET_FLAG, correct the definition of several fields, make it
clear this applies to the entire x86 architecture, not just i386.
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 3b6b9293
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.
......@@ -372,10 +369,17 @@ Protocol: 2.00+
- 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).
......@@ -504,7 +508,7 @@ Protocol: 2.06+
maximum size was 255.
Field name: hardware_subarch
Type: write
Type: write (optional, defaults to x86/PC)
Offset/size: 0x23c/4
Protocol: 2.07+
......@@ -520,11 +524,13 @@ 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
......@@ -545,6 +551,34 @@ Protocol: 2.08+
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
......@@ -553,6 +587,7 @@ initial remainder of 0xffffffff. The checksum is appended to the
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
......@@ -584,28 +619,6 @@ command line is entered using the following protocol:
covered by setup_move_size, so you may need to adjust this
field.
Field name: setup_data
Type: write (obligatory)
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.
**** MEMORY LAYOUT OF THE REAL-MODE CODE
......
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