9LOAD(8) 9LOAD(8) NAME 9load, 9pxeload, ld - 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 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. 9pxeload is a version of 9load that can be booted using the PXE download found in some ethernet card BIOSes. 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 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 is 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 /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 considera- tions. The Plan 9 MBR is suitable for booting non-Plan 9 operating systems, and (modulo the large disk constraints 9LOAD(8) 9LOAD(8) 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 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. After loading, control is passed to the entry location. In summary, 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 a Plan 9 boot floppy or disk partition prepared using format to install the appropriate files and bootstrap sectors (see prep(8)), or by using a PXE capable BIOS to boot 9pxeload directly over the ethernet. 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. If the plan9.ini file contains multiple bootfile= entries, 9load will present a numerical menu of the choices; type the cor- responding 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 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 partition may be given, but only dos is recognized: fd0!dos!file. 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 9LOAD(8) 9LOAD(8) 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 Plan 9 partitions to contain a small FAT file system for configuration. By convention, this partition is called 9fat. There is no default partition or pathname. 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 is 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/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. 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 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 9LOAD(8) 9LOAD(8) 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. FILES [drive:][path]9load [drive:][path]ld FAT-filesystem:\plan9\plan9.ini FAT-filesystem:\plan9.ini 9LOAD(8) 9LOAD(8) SOURCE /sys/src/boot/pc SEE ALSO 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. BIOS bugs force some limitions on reading via the BIOS. bios0 and sdB0 only work on the first LBA device in the BIOS's list of devices to try to boot from, which must also not be the sole device on that list.