.\" Copyright (c) 1999 Daniel C. Sobral
.\" Copyright 2019 OmniOS Community Edition (OmniOSce) Association.
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.\"
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.Dd March 30, 2023
.Dt LOADER 7
.Os
.Sh NAME
.Nm loader
.Nd kernel bootstrapping final stage
.Sh DESCRIPTION
The
.Nm
is the final stage of
.Nm illumos Ns 's
kernel bootstrapping process.
The actual name for the stage depends on the platform.
On IA32 (i386) architectures with BIOS firmware, it is a
.Pa BTX
client and named
.Nm loader .
It is linked statically to libstand and usually located in the directory
.Pa /boot .
.Pp
.Nm
supports booting from
.Cm ZFS ,
.Cm UFS ,
.Cm PCFS ,
.Cm HSFS
and
.Cm NFS
file systems.
Additionally,
.Nm
can load files from the
.Cm TFTP
file service.
The NFS and TFTP based boot is enabled via
.Xr pxeboot 7 .
The
.Nm
also does support uncompressing gzip files while reading.
The uncompression will happen automatically if the compressed file is stored
without .gz suffix or if the file is accessed by leaving out the .gz suffix from
the name.
If the file is referred by full name, including .gz suffix, then the file
content is read as is and the uncompression is not performed.
.Pp
.Nm
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-friendliness.
The bigger component is an
.Tn ANS
Forth compatible Forth interpreter based on FICL, by
.An John Sadler .
.Pp
During initialization,
.Nm
will probe for a console and set the
.Va console
variable, or set it to serial console
.Pq Do Li ttya Dc - Dq Li ttyd
if the previous boot stage used that.
If multiple consoles are selected, they will be listed separated by commas.
Then, devices are probed,
.Va currdev
and
.Va loaddev
are set, and
.Va screen-#cols ,
.Va screen-#rows ,
and
.Va ISADIR
are set.
Next,
.Tn FICL
is initialized, the builtin words are added to its vocabulary.
The inner interpreter
.Nm
will use with
.Tn FICL
is then set to
.Ic interpret ,
which is
.Tn FICL Ns 's
default.
After that,
.Pa /boot/loader.rc
is processed if available.
These files are processed through the
.Ic include
command, which reads all of them into memory before processing them,
making disk changes possible.
.Pp
At this point, if an
.Ic autoboot
has not been tried, and if
.Va autoboot_delay
is not set to
.Dq Li NO
(not case sensitive), then an
.Ic autoboot
will be tried.
If the system gets past this point,
.Va prompt
will be set and
.Nm
will engage interactive mode.
Please note that historically even when
.Va autoboot_delay
is set to
.Dq Li 0
user will be able to interrupt autoboot process by pressing some key
on the console while kernel and modules are being loaded.
In some
cases such behaviour may be undesirable, to prevent it set
.Va autoboot_delay
to
.Dq Li -1 ,
in this case
.Nm
will engage interactive mode only if
.Ic autoboot
has failed.
.Ss Builtin Commands
In
.Nm ,
builtin commands take parameters from the command line.
If an error condition occurs, an exception will be generated,
which can be intercepted using
.Tn 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.
.Pp
The builtin commands available are:
.Pp
.Bl -tag -width Ds -compact
.It Ic autoboot Op Ar seconds Op Ar prompt
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.
.Pp
.It Ic bcachestat
Displays statistics about disk cache usage.
For debugging only.
.Pp
.It Ic boot
.It Ic boot Ar kernelname Op Cm ...
.It Ic boot Fl flag Cm ...
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.
.Pp
.Em WARNING :
The behavior of this builtin is changed if
.Xr loader.4th 7
is loaded.
.Pp
.It Ic chain Ar device
Chain load another boot loader from the specified device.
Device can be either disk name, partition or file name.
In case of x86 BIOS boot, the file must be copy of MBR or PBR.
For UEFI boot, the file is efi application.
.Pp
.It Ic echo Xo
.Op Fl n
.Op Aq message
.Xc
Displays text on the screen.
A new line will be printed unless
.Fl n
is specified.
.Pp
.It Ic heap
Displays memory usage statistics.
For debugging purposes only.
.Pp
.It Ic help Op topic Op subtopic
Shows help messages read from
.Pa /boot/loader.help .
The special topic
.Em index
will list the topics available.
.Pp
.It Ic include Ar file Op Ar
Process script files.
Each file, in turn, is completely read into memory,
and then each of its lines is passed to the command line interpreter.
If any error is returned by the interpreter, the include
command aborts immediately, without reading any other files, and
returns an error itself (see
.Sx ERRORS ) .
.Pp
.It Ic load Xo
.Op Fl t Ar type
.Ar file Cm ...
.Xc
Loads a kernel or file of opaque contents tagged as being of the type
.Ar 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.
.Pp
.It Ic ls Xo
.Op Fl l
.Op Ar path
.Xc
Displays a listing of files in the directory
.Ar path ,
or the root directory if
.Ar path
is not specified.
If
.Fl l
is specified, file sizes will be shown too.
.Pp
.It Ic lsdev Op Fl v
Lists all of the devices from which it may be possible to load modules.
In addition to disks and partitions, ZFS pools are also listed.
If
.Fl v
is specified, more details are printed.
For ZFS pools the output resembles
.Nm zpool Cm status
output.
.Pp
.It Ic lsmod Op Fl v
Displays loaded modules.
If
.Fl v
is specified, more details are shown.
.Pp
.It Ic lszfs Ar filesystem
A ZFS extended command that can be used to explore the ZFS filesystem
hierarchy in a pool.
Lists the immediate children of the
.Ar filesystem .
The filesystem hierarchy is rooted at a filesystem with the same name
as the pool.
.Pp
.It Ic more Ar file Op Ar
Display the files specified, with a pause at each
.Va screen-#rows
displayed.
.Pp
.It Ic read Xo
.Op Fl t Ar seconds
.Op Fl p Ar prompt
.Op Va variable
.Xc
Reads a line of input from the terminal, storing it in
.Va variable
if specified.
A timeout can be specified with
.Fl t ,
though it will be canceled at the first key pressed.
A prompt may also be displayed through the
.Fl p
flag.
.Pp
.It Ic reboot Op Fl f
Immediately reboots the system.
On a
.Sy UEFI
system, if the
.Fl f
flag is set, or the
.Va BOOT_TO_FW_UI
environment variable exists, and the firmware supports this feature,
the system will automatically enter the firmware setup after reboot.
.Pp
.It Ic set Ar variable
.It Ic set Ar variable Ns = Ns Ar value
Set loader's environment variables.
.Pp
.It Ic show Op Va variable
Displays the specified variable's value, or all variables and their
values if
.Va variable
is not specified.
.Pp
.It Ic unload
Remove all modules from memory.
.Pp
.It Ic unset Va variable
Removes
.Va variable
from the environment.
.Pp
.It Ic \&?
Lists available commands.
.El
.Ss ZFS Features
.Nm
supports the following format for specifying ZFS filesystems which
can be used wherever
.Nm
refers to a device specification:
.Pp
.Ar zfs:pool/filesystem:
.Pp
where
.Pa pool/filesystem
is a ZFS filesystem name as described in
.Xr zfs 8 .
.Ss Builtin Environment Variables
The
.Nm
has actually two different kinds of
.Sq environment
variables.
There are ANS Forth's
.Em environmental queries ,
and a separate space of environment variables used by builtins, which
are not directly available to Forth words.
It is the latter type that this section covers.
.Pp
Environment variables can be set and unset through the
.Ic set
and
.Ic unset
builtins, and can have their values interactively examined through the
use of the
.Ic show
builtin.
Their values can also be accessed as described in
.Sx BUILTIN PARSER .
.Pp
Notice that these environment variables are not inherited by any shell
after the system has been booted.
.Pp
A few variables are set automatically by
.Nm .
Others can affect the behavior of either
.Nm
or the kernel at boot.
Some options may require a value,
while others define behavior just by being set.
Both types of builtin variables are described below.
.Bl -tag -width bootfile
.It Va autoboot_delay
Number of seconds
.Ic autoboot
will wait before booting.
If this variable is not defined,
.Ic autoboot
will default to 10 seconds.
.Pp
If set to
.Dq Li NO ,
no
.Ic autoboot
will be automatically attempted after processing
.Pa /boot/loader.rc ,
though explicit
.Ic autoboot Ns 's
will be processed normally, defaulting to 10 seconds delay.
.Pp
If set to
.Dq Li 0 ,
no delay will be inserted, but user still will be able to interrupt
.Ic autoboot
process and escape into the interactive mode by pressing some key
on the console while kernel and
modules are being loaded.
.Pp
If set to
.Dq Li -1 ,
no delay will be inserted and
.Nm
will engage interactive mode only if
.Ic autoboot
has failed for some reason.
.It Va boot_ask
Will set
.Xr kernel 8
.Fl a
option.
.It Va boot_debug
Will set
.Xr kernel 8
.Fl d
option.
.It Va boot_kmdb
Will set
.Xr kernel 8
.Fl k
option.
.It Va boot_reconfigure
Will set
.Xr kernel 8
.Fl r
option.
.It Va boot_single
Will set
.Xr kernel 8
.Fl s
option.
.It Va boot_verbose
Will set
.Xr kernel 8
.Fl v
option.
.It Va boot-args
Will set custom arguments for the kernel.
If set in
.Nm
configuration, the
.Nm
startup will parse the
.Va boot-args
value to set boot prefixed variables listed above, any unrecognized options
are added to kernel command line verbatim.
.It Va bootfile
The name of the kernel.
.It Va chain_disk
If set, contains the device or file name used with
.Cm chain
command and will cause chain command menu entry to appear on
.Nm
main menu.
The alternate method to use chain loader is to add menu entries
into
.Xr menu.lst 5
file.
.It Va console
Defines the current console or consoles.
Multiple consoles may be specified.
In that case, the first listed console will become the default console for
the
.Xr kernel 8 .
.It Va currdev
Selects the default device.
Syntax for devices is odd.
.It Va interpret
Has the value
.Dq Li ok
if the Forth's current state is interpreting.
.It Va screen-#rows
Define the number of lines on the screen, to be used by the pager.
.It Va module_path
Sets the list of directories which will be searched for modules
named in a load command or implicitly required by a dependency.
The default value for this variable is
.Dq Li /platform/i86pc/${ISADIR}
.It Va prompt
Value of
.Nm Ns 's
prompt.
Defaults to
.Dq Li "${interpret}" .
If variable
.Va prompt
is unset, the default prompt is
.Ql > .
.It Va os_console
If set, the value is used to set
.Xr kernel 8
.Va console
property.
.It Va twiddle_divisor
Throttles the output of the
.Sq twiddle
I/O progress indicator displayed while loading the kernel and modules.
This is useful on slow serial consoles where the time spent waiting for
these characters to be written can add up to many seconds.
The spinner is updated only once every
.Va twiddle_divisor
operations.
The default value for
.Va twiddle_divisor
is 16.
.El
.Pp
Other variables are used for loader or to set kernel properties or for
informational purposes.
.Ss 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.
.Pp
This special parser applies the following rules to the parsed text:
.Bl -enum
.It
All backslash characters are preprocessed.
.Bl -bullet
.It
\eb , \ef , \er , \en and \et are processed as in C.
.It
\es is converted to a space.
.It
\ev is converted to
.Tn ASCII
11.
.It
\ez is just skipped.
Useful for things like
.Dq \e0xf\ez\e0xf .
.It
\e0xN and \e0xNN are replaced by the hex N or NN.
.It
\eNNN is replaced by the octal NNN
.Tn ASCII
character.
.It
\e" , \e' and \e$ will escape these characters, preventing them from
receiving special treatment in Step 2, described below.
.It
\e\e will be replaced with a single \e .
.It
In any other occurrence, backslash will just be removed.
.El
.It
Every string between non-escaped quotes or double-quotes will be treated
as a single word for the purposes of the remaining steps.
.It
Replace any
.Li $VARIABLE
or
.Li ${VARIABLE}
with the value of the environment variable
.Va VARIABLE .
.It
Space-delimited arguments are passed to the called builtin command.
Spaces can also be escaped through the use of \e\e .
.El
.Pp
An exception to this parsing rule exists, and is described in
.Sx Builtins And FORTH .
.Ss 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.
.Pp
If compiled, the builtin words expect to find, at execution time, the
following parameters on the stack:
.D1 Ar addrN lenN ... addr2 len2 addr1 len1 N
where
.Ar 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.
.Pp
If no arguments are passed, a 0
.Em must
be passed, even if the builtin accepts no arguments.
.Pp
While this behavior has benefits, it has its trade-offs.
If the execution token of a builtin is acquired (through
.Ic '
or
.Ic ['] ) ,
and then passed to
.Ic catch
or
.Ic execute ,
the builtin behavior will depend on the system state
.Bf Em
at the time
.Ic catch
or
.Ic execute
is processed!
.Ef
This is particularly annoying for programs that want or need to
handle exceptions.
In this case, the use of a proxy is recommended.
For example:
.Dl : (boot) boot ;
.Ss FICL
.Tn 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.
.Pp
In
.Nm ,
each line read interactively is then fed to
.Tn FICL ,
which may call
.Nm
back to execute the builtin words.
The builtin
.Ic include
will also feed
.Tn FICL ,
one line at a time.
.Pp
The words available to
.Tn FICL
can be classified into four groups.
The
.Tn ANS
Forth standard words, extra
.Tn FICL
words, extra
.Fx
words, and the builtin commands;
the latter were already described.
The
.Tn ANS
Forth standard words are listed in the
.Sx STANDARDS
section.
The words falling in the two other groups are described in the
following subsections.
.Ss FICL Extra Words
.Bl -tag -width wid-set-super
.It Ic .env
.It Ic .ver
.It Ic -roll
.It Ic 2constant
.It Ic >name
.It Ic body>
.It Ic compare
This is the STRING word set's
.Ic compare .
.It Ic compile-only
.It Ic endif
.It Ic forget-wid
.It Ic parse-word
.It Ic sliteral
This is the STRING word set's
.Ic sliteral .
.It Ic wid-set-super
.It Ic w@
.It Ic w!
.It Ic x.
.It Ic empty
.It Ic cell-
.It Ic -rot
.El
.Ss Loader Extra Words
.Bl -tag -width XXXXXXXX
.It Ic \&$ Pq --
Evaluates the remainder of the input buffer, after having printed it first.
.It Ic \&% Pq --
Evaluates the remainder of the input buffer under a
.Ic catch
exception guard.
.It Ic .#
Works like
.Ic \&.
but without outputting a trailing space.
.It Ic fclose Pq Ar fd --
Closes a file.
.It Ic fkey Pq Ar fd -- char
Reads a single character from a file.
.It Ic fload Pq Ar fd --
Processes a file
.Em fd .
.It Ic fopen Pq Ar addr len mode Li -- Ar fd
Opens a file.
Returns a file descriptor, or \-1 in case of failure.
The
.Ar mode
parameter selects whether the file is to be opened for read access, write
access, or both.
The constants
.Dv O_RDONLY , O_WRONLY ,
and
.Dv O_RDWR
are defined in
.Pa /boot/forth/support.4th ,
indicating read only, write only, and read-write access, respectively.
.It Xo
.Ic fread
.Pq Ar fd addr len -- len'
.Xc
Tries to read
.Em len
bytes from file
.Em fd
into buffer
.Em addr .
Returns the actual number of bytes read, or -1 in case of error or end of
file.
.It Ic heap? Pq -- Ar cells
Return the space remaining in the dictionary heap, in cells.
This is not related to the heap used by dynamic memory allocation words.
.It Ic inb Pq Ar port -- char
Reads a byte from a port.
.It Ic isvirtualized? Pq -- Ar addr len flag | Ar flag
Returns
.Ic true
and string with virtualization engine name or
.Ic false .
.It Ic key Pq -- Ar char
Reads a single character from the console.
.It Ic key? Pq -- Ar flag
Returns
.Ic true
if there is a character available to be read from the console.
.It Ic ms Pq Ar u --
Waits
.Em u
microseconds.
.It Ic outb Pq Ar port char --
Writes a byte to a port.
.It Ic seconds Pq -- Ar u
Returns the number of seconds since midnight.
.It Ic tib> Pq -- Ar addr len
Returns the remainder of the input buffer as a string on the stack.
.El
.Ss Loader Extra Framebuffer Words
.Bl -tag -width XXXXXXXX
.It Ic fb-bezier Pq Ar x1 y1 x2 y2 x3 y3 width --
Draws a quadratic Bezier curve in the current foreground color using the
three provided points and specified line with.
.It Ic fb-drawrect Pq Ar x1 y1 x2 y2 fill --
Draws a rectangle to the screen with the top left at
.Em (x1,y1)
and the bottom right at
.Em (x2,y2)
, using the current foreground color.
If
.Em fill
is
.Ic true
then the rectangle will be filled in.
.It Ic fb-line Pq Ar x1 y1 x2 y2 width --
Draws a line from
.Em (x1,y1)
to
.Em (x2,y2)
in the current foreground color and with the specified width.
.It Ic fb-putimage Pq Ar flags x1 y1 x2 y2 addr len -- flag
Outputs an image to the screen.
Returns
.Ic true
if the image was able to be written and
.Ic false
otherwise.
Only truecolor PNG images are supported and the path to the file
must be provided through the
.Em addr
and
.Em len
arguments on the stack.
The image will be displayed in the rectangular screen region with the top left
at
.Em (x1,y1)
and the bottom right at
.Em (x2,y2)
.
.Pp
Either
.Em x2
or
.Em y2
can be set to "0" which causes it to be calculated to maintain the aspect
ratio of the image.
If both are "0" then the native resolution of the image will be used.
.Pp
If
.Em x1
is "0", then the image will be placed as far over to the right of the
screen as possible.
Similarly, if
.Em y1
is "0", then the image will be placed as far down the screen as possible.
.Pp
Flags is a bitfield; the following bits are defined:
.Bl -tag -width XXXXX -offset indent
.It 1
Draw a single pixel border around the image in the current foreground color.
.It 2
Do not scroll the image with the rest of the screen.
.It 128
Output diagnostic information (for debugging).
.El
.It Ic fb-setpixel Pq Ar x y --
Colors the pixel at
.Em (x,y)
with the current foreground color.
.It Ic term-drawrect Pq Ar x1 y1 x2 y2 --
Draws a rectangle with rounded corners using terminal coordinates and the
current foreground color.
.El
.Ss Loader Defined Environmental Queries
.Bl -tag -width Ds
.It arch-i386
.Ic TRUE
if the architecture is IA32.
.It loader_version
.Nm
version.
.El
.Ss Errors
The following values are thrown by
.Nm :
.Bl -tag -width XXXXX -offset indent
.It 100
Any type of error in the processing of a builtin.
.It -1
.Ic Abort
executed.
.It -2
.Ic Abort"
executed.
.It -56
.Ic Quit
executed.
.It -256
Out of interpreting text.
.It -257
Need more text to succeed -- will finish on next run.
.It -258
.Ic Bye
executed.
.It -259
Unspecified error.
.El
.Sh FILES
.Bl -tag -width /boot/defaults/loader.conf -compact
.It Pa /boot/defaults/loader.conf
.It Pa /boot/conf.d/*
.It Pa /boot/loader.conf
.It Pa /boot/loader.conf.local
.Nm
configuration files, as described in
.Xr loader.conf 5 .
.It Pa /boot/loader.help
Loaded by
.Ic help .
Contains the help messages.
.It Pa /boot/loader.rc
.Nm
bootstrapping script.
.It Pa /boot/forth/loader.4th
Extra builtin-like words.
.It Pa /boot/forth/support.4th
.Pa loader.conf
processing words.
.It Pa /boot/loader
.Nm
itself.
.El
.Sh EXAMPLES
Boot in single user mode:
.Pp
.Dl boot -s
.Pp
Load the kernel, a boot_archive, and then autoboot in five seconds.
Notice that a kernel must be loaded before any other
.Ic load
command is attempted.
.Bd -literal -offset indent
load /platform/i86pc/kernel/amd64/unix
load -t rootfs /platform/i86pc/amd64/boot_archive
autoboot 5
.Ed
.Pp
Set the default device used for loading a kernel from a ZFS filesystem:
.Bd -literal -offset indent
set currdev=zfs:rpool/ROOT/knowngood:
.Ed
.Sh NOTES
Although setting the
.Va currdev
as shown in the example above is supported, it is advisable to use loader
beadm command or boot environment menu instead.
The reason is, the beadm or menu selection will also instruct loader to clean up
the currently set configuration and load configuration from the new boot
environment.
.Sh SEE ALSO
.Xr btxld 1onbld ,
.Xr loader.conf 5 ,
.Xr menu.lst 5 ,
.Xr boot 8
.Sh STANDARDS
For the purposes of ANS Forth compliance, loader is an
.Bf Em
ANS Forth System with Environmental Restrictions, Providing
.Ef
.Bf Li
.No .( ,
.No :noname ,
.No ?do ,
parse, pick, roll, refill, to, value, \e, false, true,
.No <> ,
.No 0<> ,
compile\&, , erase, nip, tuck
.Ef
.Em and
.Li marker
.Bf Em
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
.Ef
.Bf Li
\&.s,
bye, forget, see, words,
\&[if],
\&[else]
.Ef
.Em and
.Li [then]
.Bf Em
from the Programming-Tools extension word set, Providing the
Search-Order extensions word set.
.Ef