9LOAD(10.8) 9LOAD(10.8)
NAME
9load, ld, 9pxeload - PC bootstrap program
SYNOPSIS
(Under MS-DOS)
[ drive :][ path ]ld [ 9load ]
DESCRIPTION
On the PC, bootstrap programs from Plan 9 are used to boot Inferno as
well (hence the naming convention). 9load and ld are programs that
reside in a FAT file system and bootstrap Inferno. 9load loads the
kernel, but it cannot be run from DOS; use ld to bootstrap (by starting
9load) if DOS is running. 9load is run automatically by the boot pro‐
cedures described below; it cannot be run directly by hand. 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 program, 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 parti‐
tion. A copy of the Plan 9 PBS is kept in /Inferno/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 /Inferno/386/pbslba, and then
only if the machine's BIOS supports linear block addressing (LBA) mode
for disk transfers.
When booting from floppy or hard disk, the BIOS loads the first sector
of the medium at location 0x7C00. In the case of a floppy, this is the
PBS. In the case of a hard disk it it the master boot record (MBR).
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
/Inferno/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 /Inferno/386/mbr detects
whether the BIOS supports LBA and acts appropriately, defaulting to CHS
mode when LBA is not present. The PBSs cannot do this due to code size
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 is: BIOS, MBR, PBS, 9load, kernel.
Because it contains many device drivers for different disks and net‐
works, 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 parti‐
tion. 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 compiled from the same source.
9load begins execution at address 0x80010000 (64K) and loads the boot‐
file at the entry address specified by the header, usually 0x80100020.
After loading, control is passed to the entry location.
Finally, 9pxeload is a version of 9load that can be booted using the
PXE download found on some ethernet card BIOSs.
In summary, Inferno and Plan 9 can be booted on a PC three different
ways: either by booting MS-DOS and using ld to start 9load in the
appropriate directory, by booting directly from an Inferno/Plan 9 boot
floppy or disk partition prepared using format to install the appropri‐
ate files and bootstrap sectors (see prep(8)), or by using a PXE capa‐
ble BIOS to boot 9pxeload directly over the ethernet.
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 ether‐
net, by a BOOTP server. If the plan9.ini file contains multiple boot‐
file= 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!parti‐
tion!file. If !file is omitted, the default for the particular device
is used. Supported devices are
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 hard disks, a parti‐
tion may be given, but only dos is recognized: fd0!dos!file.
ethern Ethernet. N specifies the Ethernet device number. If a parti‐
tion is specified, it is taken to be the name of a host machine
from which to load the kernel. file is determined by the
/lib/ndb (see ndb(6)) entry for this PC.
sdCn Non-floppy 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 Inferno/Plan 9 partitions
to contain a small FAT file system for configuration. By con‐
vention, this partition is called 9fat. There is no default
partition or pathname.
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. 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(10.6)) 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
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 available 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 prioritized 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 omitted 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 prompt.
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 ini‐
tialize partitions so that a file system in a partition can be found
and mounted as the root file system. A more extensive partitioning is
typically done by system initialisation in osinit.dis (see root(3)).
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 key‐
board).
When loaded from a PBS (rather than from ld.com), 9load must be con‐
tiguously allocated on the disk. See dossrv(4) for information on
ensuring this.
FILES
[drive:] [ path ]9load
[drive:] [ path ]ld
FAT filesystem:\plan9\plan9.ini
FAT filesystem:\plan9.ini
SOURCE
/os/boot/pc
SEE ALSO
plan9.ini(10.6), 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.
9LOAD(10.8)
