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> On the x86 platform, the Linux kernel uses a rather complicated boot
Last update 2007-05-23
On the i386 platform, the Linux kernel uses a rather complicated boot
convention. This has evolved partially due to historical aspects, as 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 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 bootable image, the complicated PC memory model and due to changed
expectations in the PC industry caused by the effective demise of expectations in the PC industry caused by the effective demise of
real-mode DOS as a mainstream operating system. 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 Old kernels: zImage/Image support only. Some very early kernels
may not even support a command line. may not even support a command line.
...@@ -372,10 +369,17 @@ Protocol: 2.00+ ...@@ -372,10 +369,17 @@ Protocol: 2.00+
- If 0, the protected-mode code is loaded at 0x10000. - If 0, the protected-mode code is loaded at 0x10000.
- If 1, the protected-mode code is loaded at 0x100000. - 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 Bit 6 (write): KEEP_SEGMENTS
Protocol: 2.07+ Protocol: 2.07+
- if 0, 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. - 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 Assume that %cs %ds %ss %es are all set to flat segments with
a base of 0 (or the equivalent for their environment). a base of 0 (or the equivalent for their environment).
...@@ -504,7 +508,7 @@ Protocol: 2.06+ ...@@ -504,7 +508,7 @@ Protocol: 2.06+
maximum size was 255. maximum size was 255.
Field name: hardware_subarch Field name: hardware_subarch
Type: write Type: write (optional, defaults to x86/PC)
Offset/size: 0x23c/4 Offset/size: 0x23c/4
Protocol: 2.07+ Protocol: 2.07+
...@@ -520,11 +524,13 @@ Protocol: 2.07+ ...@@ -520,11 +524,13 @@ Protocol: 2.07+
0x00000002 Xen 0x00000002 Xen
Field name: hardware_subarch_data Field name: hardware_subarch_data
Type: write Type: write (subarch-dependent)
Offset/size: 0x240/8 Offset/size: 0x240/8
Protocol: 2.07+ Protocol: 2.07+
A pointer to data that is specific to hardware subarch 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 Field name: payload_offset
Type: read Type: read
...@@ -545,6 +551,34 @@ Protocol: 2.08+ ...@@ -545,6 +551,34 @@ Protocol: 2.08+
The length of the payload. 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 **** THE IMAGE CHECKSUM
From boot protocol version 2.08 onwards the CRC-32 is calculated over 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 ...@@ -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 file; therefore the CRC of the file up to the limit specified in the
syssize field of the header is always 0. syssize field of the header is always 0.
**** THE KERNEL COMMAND LINE **** THE KERNEL COMMAND LINE
The kernel command line has become an important way for the boot The kernel command line has become an important way for the boot
...@@ -584,28 +619,6 @@ command line is entered using the following protocol: ...@@ -584,28 +619,6 @@ command line is entered using the following protocol:
covered by setup_move_size, so you may need to adjust this covered by setup_move_size, so you may need to adjust this
field. 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 **** MEMORY LAYOUT OF THE REAL-MODE CODE
......
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