9LOAD(8) 9LOAD(8)
NAME
9load, ld, 9pxeload - PC bootstrap program
SYNOPSIS
(Under MS-DOS)
[drive:][path]ld [ 9load ]
DESCRIPTION
9load and ld are programs that reside in a FAT file system
and bootstrap Plan 9. 9load loads a 386 or amd64 kernel,
but it cannot be run from DOS; use ld to bootstrap (by
starting 9load) if DOS is running. 9load is run automati-
cally by the boot procedures described below; it cannot be
run directly by hand. 9pxeload is a version of 9load that
can be booted using the PXE download (BOOTP/DHCP followed by
TFTP) found in any reasonable ethernet card's BIOS. 9load
will not use BIOS device drivers. There are three bootstrap
sequences:
- BIOS, MBR, disk partition PBS, 9load, kernel
- BIOS, floppy PBS, 9load, kernel
- BIOS, MBR, DOS, ld, 9load, kernel.
Details follow.
9load is a bootstrap program that loads and starts a pro-
gram, typically the kernel, on a PC. It is run by the PC
partition boot sector program (PBS), which usually resides
in the first sector of the active partition. A copy of the
Plan 9 PBS is kept in /386/pbs, but due to the ``cylinder-
head-sector'' (CHS) addressing mode of old BIOSes, it can
only operate up to 8.5GB into the disk. Plan 9 partitions
further into the disk can only be booted using /386/pbslba,
and then only if the machine's BIOS supports linear block
addressing (LBA) mode for disk transfers.
When booting from disk or floppy, the BIOS loads the first
sector of the medium at location 0x7C00. In the case of a
disk, it is the master boot record (MBR). In the case of a
floppy, this is the PBS. The MBR copies itself to address
0x600, finds the active partition and loads its PBS at
address 0x7C00. A copy of the Plan 9 MBR is kept in
/386/mbr; some commercial MBRs cannot read sectors past 2GB.
The Plan 9 MBR can read sectors up to 8.5GB into the disk,
and further if the BIOS supports LBA. The single file
/386/mbr detects whether the BIOS supports LBA and acts
appropriately, defaulting to CHS mode when LBA is not pre-
sent. The PBSs cannot do this due to code size
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9LOAD(8) 9LOAD(8)
considerations. The Plan 9 MBR is suitable for booting
non-Plan 9 operating systems, and (modulo the large disk
constraints just described) non-Plan 9 MBRs are suitable for
booting Plan 9.
Thus the default sequence when booting from disk is: BIOS,
MBR, PBS, 9load, kernel.
Because it contains many device drivers for different disks
and networks, 9load is larger than 64K and cannot be run as
a DOS ``.com'' executable. A stripped-down version that
knows about disks but not networks, called ld (really
ld.com), fits in 64K and can be used under DOS to load and
start a program (default 9load) from the FAT16 partition.
Its command line argument is of the same format as the
bootfile specifiers described below. This profusion of
loaders is unfortunate, but at least ld and 9load are com-
piled from the same source.
9load begins execution at virtual address 0x80010000 (64K)
and loads the bootfile at the entry address specified by the
header, usually virtual 0xF0100020 for 386 kernels. After
loading, control is passed to the entry location.
In summary, Plan 9 can be booted on a PC three different
ways: either by using a PXE-capable BIOS to boot 9pxeload
directly over the ethernet, by booting directly from a Plan
9 disk partition or boot floppy prepared using format to
install the appropriate files and bootstrap sectors (see
prep(8)), or rarely by booting MS-DOS and using ld to start
9load in the appropriate directory.
Bootfile
The bootfile, which may be compressed with gzip(1), can be
specified to 9load as a bootfile= entry in plan9.ini, or if
booting from the ethernet, by a BOOTP server (see Kernel
loading below). If the plan9.ini file contains multiple
bootfile= entries, 9load will present a numerical menu of
the choices; type the corresponding number to select an
entry.
The format of the bootfile name is device!file or
device!partition!file. If !file is omitted, the default for
the particular device is used. Supported devices are
ethern Ethernet. N specifies the Ethernet device number.
If a partition is specified, it is taken to be the
name of a host machine from which to load the ker-
nel. file is determined by the /lib/ndb (see
ndb(6)) entry for this PC.
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9LOAD(8) 9LOAD(8)
sdCn Normal disk. The device name format is described in
sd(3). A partition must be given and must name a
partition containing a FAT file system. The name
dos refers to the first DOS partition on a given
device. It is common for Plan 9 partitions to con-
tain a small FAT file system for configuration. By
convention, this partition is called 9fat. There is
no default partition or pathname.
fdn An MS-DOS floppy disk. N specifies the floppy
drive, either 0 or 1. The bootfile is the contents
of the MS-DOS file. There is no default file. For
compatibility with normal disks, a partition may be
given, but only dos is recognized: fd0!dos!file.
bios0 (Not in 9pxeload.) 9load loads from a FAT file sys-
tem on the first LBA device in the BIOS's list of
devices to try to boot from, using the BIOS INT 13
calls also used by pbslba. It does not understand
any form of partition table; see the EXAMPLES in
prep(8) for how to format such a device. This has
been mostly useful for booting from USB devices so
far.
sdB0 (Not in 9pxeload.) A special case of sdCn that uses
bios0 to read from a FAT file system. Partitions
are understood.
Kernel loading
When 9load starts running at physical address 0x10000, it
switches to 32-bit mode. It then double maps the first 16Mb
of physical memory to virtual addresses 0 and 0x80000000.
Physical memory from 0x300000 upwards is used as data space.
9pxeload differs slightly in operation from 9load. It is
initially loaded by the PXE BIOS at physical address 0x7C00.
Only devices which can be automatically configured, e.g.
most PCI ethernet adapters, will be recognised. If the file
/cfg/pxe/ether can be located via a DHCP server, where ether
is the lower-case MAC address of a recognised ethernet
adapter, the contents are obtained and used as a plan9.ini.
Next, in order to find configuration information, 9load
searches all units on devices fd and sdCn, in that order,
for a file called plan9\plan9.ini or plan9.ini (see
plan9.ini(8)) on a partition named dos or 9fat. If one is
found, searching stops and the file is read into memory at
physical address 0x1200 where it can be found later by any
loaded bootfile. Some options in plan9.ini are used by
9load:
console
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9LOAD(8) 9LOAD(8)
baud Specifies the console device and baud rate
if not a display.
ethern Ethernet interfaces. These can be used to
load the bootfile over a network. Probing
for Ethernet interfaces is too prone to
error.
bootfile=bootfile
Specifies the bootfile. This option is
overridden by a command-line argument.
bootfile=auto Default.
bootfile=local Like auto, but do not attempt to load over
the network.
bootfile=manual After determining which devices are avail-
able for loading from, enter prompt mode.
When the search for plan9.ini is done, 9load proceeds to
determine which bootfile to load. If there was no bootfile
option, 9load chooses a default from the following priori-
tized device list:
fd sd ether
9load then attempts to load the bootfile unless the
bootfile=manual option was given, in which case prompt mode
is entered immediately. If the default device is fd, 9load
will prompt the user for input before proceeding with the
default bootfile load after 5 seconds; this prompt is omit-
ted if a command-line argument or bootfile option was given.
9load prints the list of available devices and enters prompt
mode on encountering any error or if directed to do so by a
bootfile=manual option. In prompt mode, the user is
required to type a bootfile in response to the `Boot from:'
prompt.
Other facilities and caveats
9load parses the master boot record and Plan 9 partition
tables (see prep(8)), leaving partitioning information
appended to the in-memory contents of plan9.ini for the
bootfile. This is used by sd(3) to initialize partitions so
that fossil(4) or kfs(4) file systems can be mounted as the
root file system. A more extensive partitioning is typi-
cally done by fdisk and prep as part of termrc or cpurc (see
cpurc(8)).
A control-P character typed at any time on the console
causes 9load to perform a hardware reset (Ctrl-Alt-Del can
also be used on a PC keyboard).
When loaded from a PBS (rather than from ld.com), 9load must
be contiguously allocated on the disk. See dossrv(4) for
information on ensuring this.
9pxeload differs slightly in operation from 9load. It is
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9LOAD(8) 9LOAD(8)
initially loaded by the PXE BIOS at physical address 0x7C00.
Only devices which can be automatically configured, e.g.
most PCI ethernet adapters, will be recognised. If the file
/cfg/pxe/XXXXXXXXXXXX can be located via a DHCP server,
where XXXXXXXXXXXX is the MAC address of a recognised ether-
net adapter, the contents are obtained and used as a
plan9.ini.
FILES
[drive:][path]9load
[drive:][path]ld
FAT-filesystem:\plan9\plan9.ini
FAT-filesystem:\plan9.ini
/386 most of these binaries reside here
/cfg/pxe directory of plan9.ini files on your TFTP server
SOURCE
/sys/src/boot/pc
SEE ALSO
booting(8), dhcpd(8), plan9.ini(8), prep(8)
BUGS
Much of the work done by 9load is duplicated by the loaded
kernel.
If ld detects an installed MS-DOS Extended Memory Manager,
it attempts to de-install it, but the technique used may not
always work. It is safer not to install the Extended Memory
Manager before running ld.
The way 9pxeload obtains the information normally found in a
disc plan9.ini file, and thereby the kernel to load and
boot, is not ideal and may change in the future.
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