LOADER(8)

NAME
loader - system bootstrap stage three

DESCRIPTION
The program called loader is the third stage of FreeBSD's three stage bootstrap. It is a BTX client linked statically to libstand(3) and usually located in the directory /boot.

It provides a scripting language that can be used to automate tasks, do pre-configuration or assist in recovery procedures. This scripting language is roughly divided in two main components. The smaller one is a set of commands designed for direct use by the casual user, called "builtin commands" for historical reasons. The main drive behind these commands is user-friendlyness. The bigger component is an ANS Forth compatible Forth interpreter based on ficl, by John Sadler.

During initialization, loader will probe for a console and set the console variable, or set it to serial console (“comconsole”) if the previous boot stage used that. Then, devices are probed, currdev and loaddev are set, and LINES is set to 24 . Next, FICL is initialized, the builtin words are added to its vocabulary, and /boot/boot.4th will be processed if it exists. No disk switching is possible while that file is being read. The inner interpreter loader will use with FICL is then set to interpret, which is FICL's default. After that, /boot/loader.rc is processed if available, and, failing that, /boot/boot.conf will be read for historical reasons. These files are processed through the include command, which read all of them into memory before processing them, making disk changes possible.

At this point, if an autoboot has not been tried, and if autoboot_delay is not set to “NO” (not case sensitive), then an autoboot will be tried. If the system gets past this point, prompt will be set and loader will engage interactive mode.

BUILTIN COMMANDS
Loader's builtin commands take its parameters from the command line. Presently, the only way to call them from a script is by using evaluate on a string. If an error condition occurs, an exception will be generated, which can be intercepted using ANS Forth exception handling words. If not intercepted, an error message will be displayed and the interpreter's state will be reset, emptying the stack and restoring interpreting mode.

The builtin commands available are:

autoboot [seconds]
    Proceeds to bootstrap the system after a number of seconds, if not interrupted by the user. Displays a countdown prompt warning the user the system is about to be booted, unless interrupted by a key press. The kernel will be loaded first if necessary. Defaults to 10 seconds.

bcachestat
    Displays statistics about disk cache usage. For depuration only.

boot
boot kernelname [...]
boot -flag ...
    Immediately proceeds to bootstrap the system, loading the kernel if necessary. Any flags or arguments are passed to the kernel, but they must precede the kernel name, if a kernel name is provided.

echo
    [-n] [<message>] Displays a text on the screen. A new line will be printed unless -n is specified.

heap
    Displays memory usage statistics. For debugging purposes only.

help [topic [subtopic]]
    Shows help messages read from /boot/loader.help. The special topic index will list the topics available.

include file [file ...]
    Process script files. Each file is, at a turn, completely read into memory, and then have each of its lines passed to the command line interpreter. If any error is returned by the interpreter, the include commands aborts immediately, without reading any other files, and returns an error itself (see ERRORS).

load
    [-t type] file ... Loads a kernel, kernel loadable module (kld), or a file of opaque contents tagged as being of the type type. Kernel and modules can be either in a.out or elf format. Any arguments passed after the name of the file to be loaded will be passed as arguments to that file. Notice, though, that, at the present, this does not work for the kernel.

ls  [-l] [path] Displays a listing of files in the directory path, or the root directory if path is not specified. If -l is specified, file sizes will be shown too.

lsdev [-v]
    Lists all of the devices from which it may be possible to load modules. If -v is specified, more details are printed.

lsmod [-v]
    Displays loaded modules. If -v is specified, more details are shown.

more file [file ...]
    Display the files specified, with a pause at each LINES displayed.

pnpscan [-v]
    Scans for Plug-and-Play devices. This is not functional at the present.

read
    [-t seconds] [-p prompt] [variable] Reads a line of input from the terminal, storing it in variable if specified. A timeout can be specified with -t, though it will be canceled at the first key pressed. A prompt may also be displayed through the -p flag.

reboot
    Immediately reboots the system.

set variable
set variable=value
    Set loader's environment variables.

show [variable]
    Displays the specified variable's value, or all variables and their values if variable is not specified.

unload
    Remove all modules from memory.

unset variable
    Removes variable from the environment.

?   Same as “help index”.

  BUILTIN ENVIRONMENT VARIABLES
The loader has actually two different kinds of ‘environment’ variables. There are ANS Forth's environmental queries, and a separate space of environment variables used by builtins, which are not directly available to Forth words. It is the later ones that this session covers.

Environment variables can be set and unset through the use of the set and unset builtins, and have their value interactively examined through the use of the show builtin. Their values can also be accessed as described in BUILTIN PARSER.

Notice that this environment variables are not inherited by any shell after the system has been booted.

A few variables are set automatically by loader. Others can affect either loader or kernel's behavior at boot. While some of these may require a value, others define behavior just by being set. These are described below.

autoboot_delay
    Number of seconds autoboot will wait before booting. If this variable is not defined, autoboot will default to 10 seconds.

    If set to “NO”, no autoboot will be automatically attempted after processing /boot/loader.rc, though explict autoboot's will be processed normally, defaulting to 10 seconds delay.

boot_askname
    Instructs the kernel to prompt the user for the name of the root device when the kernel is booted.

boot_ddb
    Instructs the kernel to start in the DDB debugger, rather than proceeding to initialise when booted.

boot_gdb
    Selects gdb-remote mode for the kernel debugger by default.

boot_single
    Prevents the kernel from initiating a multi-user startup, single-user mode will be entered when the kernel has finished device probes.

boot_userconfig
    Requests that the kernel's interactive device configuration program be run when the kernel is booted.

boot_verbose
    Setting this variable causes extra debugging information to be printed by the kernel during the boot phase.

bootfile
    List of semicolon-separated search path for bootable kernels. The default is “kernel;kernel.old”.

console
    Defines the current console.

currdev
    Selects the default device. Syntax for devices is odd.

init_path
    Sets the list of binaries which the kernel will try to run as initial process. The default is “/sbin/init:/sbin/oinit:/sbin/init.bak:/stand/sysinstall”.

interpret
    Has the value “ok” if the Forth's current state is interpreting.

LINES
    Define the number of lines on the screen, to be used by the pager.

module_path
    Sets the list of directories which will be searched in for modules named in a load command or implicitly required by a dependancy. The default value for this variable is “/;/boot;/modules”.

num_ide_disks
    Sets the number of IDE disks as a work around for some problems in finding the root disk at boot. This has been deprecated in favour of root_disk_unit.

prompt
    Value of loader's prompt. Defaults to “${currdev}>”.

root_disk_unit
    If the code which detects the disk unit number for the root disk is confused, eg. by a mix of SCSI and IDE disks, or IDE disks with gaps in the sequence (eg. no primary slave), the unit number can be forced by setting this variable.

rootdev
    By default the value of currdev is used to set the root filesystem when the kernel is booted. This can be overridden by setting rootdev explicitly.

Other variables are used to override kernel tunnable parameters. The following tunables are available:

kern.ipc.nmbclusters
    Set the number of mbuf clusters to be allocated. The value cannot be set below the default determined when the kernel was compiled. Modifies NMBCLUSTERS.

kern.vm.kmem.size
    Sets the size of kernel memory (bytes). This overrides completely the value determined when the kernel was compiled. Modifies VM_KMEM_SIZE.

machdep.pccard.pcic_irq
    Overrides the IRQ normally assigned to a PCCARD controller. Typically the first available interrupt will be allocated, which may conflict with other hardware. If this value is set to 0, an interrupt will not be assigned and the controller will operate in polled mode only.

net.inet.tcp.tcbhashsize
    Overrides the compile-time set value of TCBHASHSIZE or the preset default of 512. Must be a power of 2.

  BUILTIN PARSER
When a builtin command is executed, the rest of the line is taken by it as arguments, and it is processed by a special parser which is not used for regular Forth commands.

This special parser applies the following rules to the parsed text:

1.  All backslash characters are preprocessed.

    •   \b , \f , \r , \n and \t are processed as by C's printf().

    •   \s is converted to a space.

    •   \v is converted to ASCII 11.

    •   \z is just skipped. Useful for things like “\0xf\z\0xf”.

    •   \0xN and \0xNN are replaced by the hex N or NN.

    •   \NNN is replaced by the octal NNN ASCII character.

    •   \" , \' and \$ will escape these characters, preventing them from receiving special semantics on the step 2 described below.

    •   \\ will be replaced with a single \ .

    •   In any other occurance, backslash will just be removed.

2.  Every string between non-escaped quotes or double-quotes will be treated as a single word for the purposes of the remaining steps.

3.  Replace any $VARIABLE or ${VARIABLE} with the value of the environemnt variable VARIABLE.

4.  Passes multiple space-delimited arguments to the builtin command called. Spaces can also be escaped through the use of \\ .

An exception to this parsing rule exists, and is described in BUILTINS AND FORTH.

  BUILTINS AND FORTH
All builtin words are state-smart, immediate words. If interpreted, they behave exactly as described previously. If they are compiled, though, they extract their arguments from the stack instead of the command line.

If compiled, the builtin words expect to find, at execution time, the following parameters on the stack:
    addrN lenN ... addr2 len2 addr1 len1 N
where addrX lenX are strings which will compose the command line that will be parsed into the builtin's arguments. Internally, these strings are concatenated in from 1 to N, with a space put between each one.

If no arguments are passed, a 0 must be passed, even if the builtin accepts no arguments.

While this behavior has benefits, it has its trade-offs. If the execution token of a builtin is acquired (through ' or [']), and then passed to catch or execute, the builtin behavior will depend on the system state at the time catch or execute is processed ! This is particular annoying for programs that want or need to treat exceptions. In this case, it is recommended the use of a proxy. For example:
    : (boot) boot;

FICL
FICL is a Forth interpreter written in C, in the form of a forth virtual machine library that can be called by C functions and vice versa.

In loader, each line read interactively is then fed to FICL, which may call loader back to execute the builtin words. The builtin include will also feed FICL, one line at a time.

The words available to FICL can be classified in four groups. The ANS Forth standard words, extra FICL words, extra words, and the builtin commands. The later were already described. The ANS Forth standard words are listed in the STANDARDS section. The words falling in the two other groups are described in the following subsections.

  FICL EXTRA WORDS

.env

.ver

-roll

2constant

>name

body>

compare
    This the STRING word set's compare.

compile-only

endif

forget-wid

parse-word

sliteral
    This is the STRING word set's sliteral.

wid-set-super

w@

w!

x.

empty

cell-

-rot

  FREEBSD EXTRA WORDS

tib> (-- addr len)
    Returns the remainder of the input buffer as a string on the stack.

% (--)
    Evaluates the remainder of the input buffer under a catch exception guard.

$ (--)
    Evaluates the remainder of the input buffer, after having printed it first.

fopen (addr len -- fd)
    Open a file. Returns a file descriptor, or -1 in case of failure.

fclose (fd --)
    Closes a file.

    fread (fd addr len -- len') Tries to read len bytes from file fd into buffer addr. Returns the actual number of bytes read, or -1 in case of error or end of file.

fload (fd --)
    Process file fd.

fkey (fd -- char)
    Reads a single character from a file.

key (-- char)
    Reads a single character from the console.

key? (-- flag)
    Returns true if there is a character available to be read from the console.

ms (u --)
    Waits u microseconds.

seconds (-- u)
    Returns the number of seconds since midnight.

trace! (flag --)
    Activates or deactivates tracing. Does not work with catch.

outb (port char --)
    Writes a byte to a port.

inb (port -- char)
    Reads a byte from a port.

  FREEBSD DEFINED ENVIRONMENTAL QUERIES

arch-i386
    TRUE if the architecture is IA32.

arch-alpha
    TRUE if the architecture is AXP.

FreeBSD_version
    FreeBSD version at compile time.

loader_version
    loader version.

  SYSTEM DOCUMENTATION

FILES
/boot/loader
    loader itself.
/boot/boot.4th
    Additional FICL initialization.
/boot/boot.conf
    loader bootstrapping script. Deprecated.
/boot/loader.rc
    loader bootstrapping script.
/boot/loader.help
    Loaded by help. Contains the help messages.

EXAMPLES
Boot in single user mode:

    boot -s

Loads kernel's user configuration file. Notice that a kernel must be loaded before any other load command is attempted.

    load kernel
    load -t userconfig_script /boot/kernel.conf

Loads the kernel, a splash screen, and then autoboots in five seconds.

    load kernel
    load splash_bmp
    load -t splash_image_data /boot/chuckrulez.bmp
    autoboot 5

Sets the disk unit of the root device to 2, and then boots. This would be needed in the case of a two IDE disks system, with the second IDE hardwired to wd2 instead of wd1.

    set root_disk_unit=2
    boot /kernel

See also:

/boot/loader.4th
    Extra builtin-like words.

/boot/support.4th
    loader.conf processing words.

/usr/share/examples/bootforth/
    Assorted examples.

ERRORS
The following values are thrown by loader:

100 Any type of error in the processing of a builtin.

-1  Abort executed.

-2  Abort" executed.

-56 Quit executed.

-256
    Out of interpreting text.

-257
    Need more text to succeed -- will finish on next run.

-258
    Bye executed.

-259
    Unspecified error.

SEE ALSO
libstand(3), loader.conf(5), boot(8), btxld(8)

STANDARDS
For the purposes of ANS Forth compliance, loader is an ANS Forth System with Environmental Restrictions, Providing .(, :noname, ?do, parse, pick, roll, refill, to, value, \, false, true, <>, 0<>, compile, , erase, nip, tuck and marker from the Core Extensions word set, Providing the Exception Extensions word set, Providing the Locals Extensions word set, Providing the Memory-Allocation Extensions word set, Providing .s , bye, forget, see, words, [if] , [else] and [then] from the Programming-Tools extension word set, Providing the Search-Order extensions word set.

HISTORY
loader first appeared in FreeBSD 3.1.

AUTHORS

loader was written by Michael Smith <msmith@freebsd.org>.

FICL was written by John Sadler <john_sadler@alum.mit.edu>.

BUGS
FICL is case sensitive. Though this is not a standard violation, all Forth words are lower cased, which would result in a standard violation. Do not rely on this bug.

The expect and accept words will read from the input buffer instead of the console. The latter will be fixed, but the former will not.