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: H. Peter Anvin <hpa@zytor.com>
diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt
index 95ad15c..147bfe5 100644
--- a/Documentation/i386/boot.txt
+++ b/Documentation/i386/boot.txt
@@ -1,17 +1,14 @@
- 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 @@
- 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 @@
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 @@
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 @@
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 @@
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 @@
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