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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>
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@ -1,17 +1,14 @@
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THE LINUX/I386 BOOT PROTOCOL
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----------------------------
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THE LINUX/x86 BOOT PROTOCOL
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---------------------------
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H. Peter Anvin <hpa@zytor.com>
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Last update 2007-05-23
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On the i386 platform, the Linux kernel uses a rather complicated boot
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On the x86 platform, the Linux kernel uses a rather complicated boot
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convention. This has evolved partially due to historical aspects, as
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well as the desire in the early days to have the kernel itself be a
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bootable image, the complicated PC memory model and due to changed
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expectations in the PC industry caused by the effective demise of
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real-mode DOS as a mainstream operating system.
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Currently, the following versions of the Linux/i386 boot protocol exist.
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Currently, the following versions of the Linux/x86 boot protocol exist.
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Old kernels: zImage/Image support only. Some very early kernels
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may not even support a command line.
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@ -372,10 +369,17 @@ Protocol: 2.00+
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- If 0, the protected-mode code is loaded at 0x10000.
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- If 1, the protected-mode code is loaded at 0x100000.
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Bit 5 (write): QUIET_FLAG
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- If 0, print early messages.
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- If 1, suppress early messages.
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This requests to the kernel (decompressor and early
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kernel) to not write early messages that require
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accessing the display hardware directly.
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Bit 6 (write): KEEP_SEGMENTS
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Protocol: 2.07+
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- if 0, reload the segment registers in the 32bit entry point.
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- if 1, do not reload the segment registers in the 32bit entry point.
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- If 0, reload the segment registers in the 32bit entry point.
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- If 1, do not reload the segment registers in the 32bit entry point.
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Assume that %cs %ds %ss %es are all set to flat segments with
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a base of 0 (or the equivalent for their environment).
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@ -504,7 +508,7 @@ Protocol: 2.06+
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maximum size was 255.
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Field name: hardware_subarch
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Type: write
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Type: write (optional, defaults to x86/PC)
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Offset/size: 0x23c/4
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Protocol: 2.07+
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@ -520,11 +524,13 @@ Protocol: 2.07+
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0x00000002 Xen
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Field name: hardware_subarch_data
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Type: write
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Type: write (subarch-dependent)
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Offset/size: 0x240/8
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Protocol: 2.07+
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A pointer to data that is specific to hardware subarch
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This field is currently unused for the default x86/PC environment,
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do not modify.
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Field name: payload_offset
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Type: read
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@ -545,6 +551,34 @@ Protocol: 2.08+
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The length of the payload.
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Field name: setup_data
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Type: write (special)
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Offset/size: 0x250/8
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Protocol: 2.09+
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The 64-bit physical pointer to NULL terminated single linked list of
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struct setup_data. This is used to define a more extensible boot
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parameters passing mechanism. The definition of struct setup_data is
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as follow:
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struct setup_data {
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u64 next;
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u32 type;
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u32 len;
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u8 data[0];
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};
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Where, the next is a 64-bit physical pointer to the next node of
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linked list, the next field of the last node is 0; the type is used
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to identify the contents of data; the len is the length of data
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field; the data holds the real payload.
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This list may be modified at a number of points during the bootup
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process. Therefore, when modifying this list one should always make
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sure to consider the case where the linked list already contains
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entries.
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**** THE IMAGE CHECKSUM
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From boot protocol version 2.08 onwards the CRC-32 is calculated over
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@ -553,6 +587,7 @@ initial remainder of 0xffffffff. The checksum is appended to the
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file; therefore the CRC of the file up to the limit specified in the
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syssize field of the header is always 0.
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**** THE KERNEL COMMAND LINE
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The kernel command line has become an important way for the boot
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@ -584,28 +619,6 @@ command line is entered using the following protocol:
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covered by setup_move_size, so you may need to adjust this
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field.
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Field name: setup_data
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Type: write (obligatory)
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Offset/size: 0x250/8
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Protocol: 2.09+
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The 64-bit physical pointer to NULL terminated single linked list of
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struct setup_data. This is used to define a more extensible boot
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parameters passing mechanism. The definition of struct setup_data is
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as follow:
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struct setup_data {
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u64 next;
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u32 type;
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u32 len;
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u8 data[0];
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};
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Where, the next is a 64-bit physical pointer to the next node of
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linked list, the next field of the last node is 0; the type is used
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to identify the contents of data; the len is the length of data
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field; the data holds the real payload.
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**** MEMORY LAYOUT OF THE REAL-MODE CODE
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