.\" SPDX-License-Identifier: MIT
.\"
.Dd September 30, 2025
.Dt RGBASM 1
.Os
.Sh NAME
.Nm rgbasm
.Nd Game Boy assembler
.Sh SYNOPSIS
.Nm
.Op Fl EhVvw
.Op Fl B Ar param
.Op Fl b Ar chars
.Op Fl \-color Ar when
.Op Fl D Ar name Ns Op = Ns Ar value
.Op Fl g Ar chars
.Op Fl I Ar path
.Op Fl M Ar depend_file
.Op Fl MG
.Op Fl MC
.Op Fl MP
.Op Fl MT Ar target_file
.Op Fl MQ Ar target_file
.Op Fl o Ar out_file
.Op Fl P Ar include_file
.Op Fl p Ar pad_value
.Op Fl Q Ar fix_precision
.Op Fl r Ar recursion_depth
.Op Fl s Ar features Ns : Ns Ar state_file
.Op Fl W Ar warning
.Op Fl X Ar max_errors
.Ar asmfile
.Sh DESCRIPTION
The
.Nm
program creates an RGB object file from an assembly source file.
The object file format is documented in
.Xr rgbds 5 .
.Sh ARGUMENTS
.Nm
accepts the usual short and long options, such as
.Fl V
and 
.Fl -version .
Options later in the command line override those set earlier, except for when duplicate options are considered an error.
Options can be abbreviated as long as the abbreviation is unambiguous:
.Fl \-verb
is
.Fl \-verbose ,
but
.Fl \-ver
is invalid because it could also be
.Fl \-version .
.Pp
Unless otherwise noted, passing
.Ql -
(a single dash) as a file name makes
.Nm
use standard input (for input files) or standard output (for output files).
To suppress this behavior, and open a file in the current directory actually called
.Ql - ,
pass
.Ql ./-
instead.
Using standard input or output for more than one file in a single command may produce unexpected results.
.Pp
.Nm
accepts decimal, hexadecimal, octal, and binary for numeric option arguments.
Decimal numbers are written as usual; hexadecimal numbers must be prefixed with either
.Ql $
or
.Ql 0x ;
octal numbers must be prefixed with either
.Ql &
or
.Ql 0o ;
and binary numbers must be prefixed with either
.Ql %
or
.Ql 0b .
(The prefixes
.Ql $
and
.Ql &
will likely need escaping or quoting to avoid being interpreted by the shell.)
Leading zeros (after the base prefix, if any) are accepted, and letters are not case-sensitive.
For example, all of these are equivalent:
.Ql 42 ,
.Ql 042 ,
.Ql 0x2A ,
.Ql 0X2A ,
.Ql 0x2a ,
.Ql &52 ,
.Ql 0o52 ,
.Ql 0O052 ,
.Ql 0b00101010 ,
.Ql 0B101010 .
.Pp
The following options are accepted:
.Bl -tag -width Ds
.It Fl B Ar param , Fl \-backtrace Ar param
Configures how location backtraces are printed if warnings or errors occur.
This flag may be specified multiple times with different parameters that combine meaningfully.
If
.Ar param
is a positive number, it specifies the maximum backtrace depth, abbreviating deeper ones.
Other valid parameter values are the following:
.Bl -tag -width Ds
.It Cm 0
Do not limit the maximum backtrace depth; this is the default.
.It Cm all
Force all locations to be printed, even "quiet" ones (see
.Dq Excluding locations from backtraces
in
.Xr rgbasm 5
for details).
.It Cm no-all
Do not print "quieted" locations in backtraces; this is the default.
.It Cm collapse
Print all locations on one line.
.It Cm no-collapse
Print one location per line; this is the default.
.El
.It Fl b Ar chars , Fl \-binary-digits Ar chars
Allow two characters to be used for binary constants in addition to the default
.Sq 0
and
.Sq 1 .
Valid characters are numbers other than
.Sq 0
and
.Sq 1 ,
letters,
.Sq \&. ,
.Sq # ,
or
.Sq @ .
.It Fl \-color Ar when
Specify when to highlight warning and error messages with color:
.Ql always ,
.Ql never ,
or
.Ql auto .
.Ql auto
determines whether to use colors based on the
.Ql Lk https://no-color.org/ NO_COLOR
or
.Ql Lk https://force-color.org/ FORCE_COLOR
environment variables, or whether the output is to a TTY.
.It Fl D Ar name Ns Oo = Ns Ar value Oc , Fl \-define Ar name Ns Oo = Ns Ar value Oc
Add a string symbol to the compiled source code.
This is equivalent to
.Ql Ar name Ic EQUS No \(dq Ns Ar value Ns \(dq
in code, or
.Ql Ar name Ic EQUS No \(dq1\(dq
if
.Ar value
is not specified.
.It Fl E , Fl \-export-all
Export all labels, including unreferenced and local labels.
.It Fl g Ar chars , Fl \-gfx-chars Ar chars
Allow four characters to be used for graphics constants in addition to the default
.Sq 0 ,
.Sq 1 ,
.Sq 2 ,
and
.Sq 3 .
Valid characters are numbers other than
.Sq 0
to
.Sq 3 ,
letters,
.Sq \&. ,
.Sq # ,
or
.Sq @ .
The defaults are 0123.
.It Fl h , Fl \-help
Print help text for the program and exit.
.It Fl I Ar path , Fl \-include Ar path
Add a new
.Dq include path ;
.Ar path
must point to a directory.
When any
.Ic INCLUDE
.Pq including the implicit one from Fl P ,
.Ic INCBIN ,
or
.Ic READFILE
is attempted,
.Nm
first looks up the provided path from its working directory; if this fails, it tries again from each of the
.Dq include path
directories, in the order they were provided.
.It Fl M Ar depend_file , Fl \-dependfile Ar depend_file
Write
.Xr make 1
dependencies to
.Ar depend_file .
.It Fl MG
To be used in conjunction with
.Fl M .
This makes
.Nm
assume that missing files are auto-generated: when any
.Ic INCLUDE
.Pq including the implicit one from Fl P ,
.Ic INCBIN ,
or
.Ic READFILE
is attempted on a non-existent file, it is added as a dependency, then
.Nm
exits normally or continues processing (depending on whether
.Fl MC
was enabled) instead of erroring out.
This feature is used in automatic updating of Makefiles.
.It Fl MC
Implies
.Fl MG .
This makes
.Nm
continue processing after a non-existent dependency file, instead of exiting.
Note that this is
.Em not
recommended if any non-existent dependencies would have influenced subsequent processing, e.g. by causing an
.Ic IF
condition to take a different branch.
.It Fl MP
When enabled, this adds a phony target to the rules emitted by
.Fl M
for each dependency other than the main file.
This prevents
.Xr make 1
from erroring out when dependency files are deleted.
.It Fl MT Ar target_file
Add a target to the rules emitted by
.Fl M .
The exact string provided will be written, including spaces and special characters.
.Dl Fl MT No fileA Fl MT No fileB
is equivalent to
.Dl Fl MT No 'fileA fileB' .
If neither this nor
.Fl MQ
is specified, the output file name is used.
.It Fl MQ Ar target_file
Same as
.Fl MT ,
but additionally escapes any special
.Xr make 1
characters, essentially
.Sq $ .
.It Fl o Ar out_file , Fl \-output Ar out_file
Write an object file to the given filename.
.It Fl P Ar include_file , Fl \-preinclude Ar include_file
Pre-include a file.
This acts as if a
.Ql Ic INCLUDE Qq Ar include_file
was read before the input
.Ar asmfile .
Multiple files can be pre-included in the order they were provided.
.It Fl p Ar pad_value , Fl \-pad-value Ar pad_value
Use this as the value for
.Ic DS
directives in ROM sections, unless overridden.
The default is 0x00.
.It Fl Q Ar fix_precision , Fl \-q-precision Ar fix_precision
Use this as the precision of fixed-point numbers after the decimal point, unless they specify their own precision.
The default is 16, so fixed-point numbers are Q16.16 (since they are 32-bit integers).
The argument may start with a
.Ql \&.
to match the Q notation, for example,
.Ql Fl Q Ar .16 .
.It Fl r Ar recursion_depth , Fl \-recursion-depth Ar recursion_depth
Specifies the recursion depth past which
.Nm
will assume being in an infinite loop.
The default is 64.
.It Fl s Ar features Ns : Ns Ar state_file , Fl \-state Ar features Ns : Ns Ar state_file
Write the specified
.Ar features
to
.Ar state_file ,
based on the final state of
.Nm
at the end of its input.
The expected
.Ar features
are a comma-separated subset of the following:
.Bl -tag -width Ds
.It Cm equ
Write all numeric constants as
.Ql Ic def Ar name Ic equ Ar value .
.It Cm var
Write all variables as
.Ql Ic def Ar name Ic = Ar value .
.It Cm equs
Write all string constants as
.Ql Ic def Ar name Ic equs Qq Ar value .
.It Cm char
Write all characters as
.Ql Ic charmap Ar name , Ar value .
.It Cm macro
Write all macros as
.Ql Ic macro Ar name No ... Ic endm .
.It Cm all
Acts like
.Cm equ,var,equs,char,macro .
.El
.Pp
This flag may be specified multiple times with different feature subsets to write them to different files (see
.Sx EXAMPLES
below).
.It Fl V , Fl \-version
Print the version of the program and exit.
.It Fl v , Fl \-verbose
Be verbose.
The verbosity level is increased by one each time the flag is specified, with each level including the previous:
.Bl -enum -compact
.It
Print the
.Nm
configuration before taking actions.
.It
Print a notice before significant actions.
.It
Print some of the actions' intermediate results.
.It
Print some internal debug information.
.It
Print detailed internal information.
.El
The verbosity level does not go past 6.
.Pp
Note that verbose output is only intended to be consumed by humans, and may change without notice between RGBDS releases; relying on those for scripts is not advised.
.It Fl W Ar warning , Fl \-warning Ar warning
Set warning flag
.Ar warning .
A warning message will be printed if
.Ar warning
is an unknown warning flag.
See the
.Sx DIAGNOSTICS
section for a list of warnings.
.It Fl w
Disable all warning output, even when turned into errors.
.It Fl X Ar max_errors , Fl \-max-errors Ar max_errors
If more than this number of errors (not warnings) occur, then abort the assembly process;
.Fl X Ar 0
disables this behavior.
The default is 100 if
.Nm
is printing errors to a terminal, and 0 otherwise.
.El
.Sh DIAGNOSTICS
Warnings are diagnostic messages that indicate possibly erroneous behavior that does not necessarily compromise the assembling process.
The following options alter the way warnings are processed.
.Bl -tag -width Ds
.It Fl Werror
Make all warnings into errors.
This can be negated as
.Fl Wno-error
to prevent turning all warnings into errors.
.It Fl Werror=
Make the specified warning or meta warning into an error.
A warning's name is appended
.Pq example: Fl Werror=obsolete ,
and this warning is implicitly enabled and turned into an error.
This can be negated as
.Fl Wno-error=
to prevent turning a specified warning into an error, even if
.Fl Werror
is in effect.
.El
.Pp
The following warnings are
.Dq meta
warnings, that enable a collection of other warnings.
If a specific warning is toggled via a meta flag and a specific one, the more specific one takes priority.
The position on the command-line acts as a tie breaker, the last one taking effect.
.Bl -tag -width Ds
.It Fl Wall
This enables warnings that are likely to indicate an error or undesired behavior, and that can easily be fixed.
.It Fl Wextra
This enables extra warnings that are less likely to pose a problem, but that may still be wanted.
.It Fl Weverything
Enables literally every warning.
.El
.Pp
The following warnings are actual warning flags; with each description, the corresponding warning flag is included.
Note that each of these flags also has a negation (for example,
.Fl Wobsolete
enables the warning that
.Fl Wno-obsolete
disables; and
.Fl Wall
enables every warning that
.Fl Wno-all
disables).
Only the non-default flag is listed here.
Ignoring the
.Dq no-
prefix, entries are listed alphabetically.
.Bl -tag -width Ds
.It Fl Wno-assert
Warn when
.Ic WARN Ns No -type
assertions fail. (See
.Dq Aborting the assembly process
in
.Xr rgbasm 5
for
.Ic ASSERT ) .
.It Fl Wbackwards-for
Warn when
.Ic FOR
loops have their start and stop values switched according to the step value.
This warning is enabled by
.Fl Wall .
.It Fl Wbuiltin-args
Warn about incorrect arguments to built-in functions, such as
.Fn STRSLICE
with indexes outside of the string's bounds.
This warning is enabled by
.Fl Wall .
.It Fl Wcharmap-redef
Warn when re-defining a charmap mapping.
This warning is enabled by
.Fl Wall .
.It Fl Wdiv
Warn when dividing the smallest negative integer (-2**31) by -1, which yields itself due to integer overflow.
.It Fl Wempty-data-directive
Warn when
.Ic DB ,
.Ic DW ,
or
.Ic DL
is used without an argument in a ROM section.
This warning is enabled by
.Fl Wall .
.It Fl Wempty-macro-arg
Warn when a macro argument is empty.
This warning is enabled by
.Fl Wextra .
.It Fl Wempty-strrpl
Warn when
.Fn STRRPL
is called with an empty string as its second argument (the substring to replace).
This warning is enabled by
.Fl Wall .
.It Fl Wexport-undefined
Warn when exporting an undefined symbol.
This warning is enabled by
.Fl Wall .
.It Fl Wno-large-constant
Warn when a constant too large to fit in a signed 32-bit integer is encountered.
.It Fl Wmacro-shift
Warn when shifting macro arguments past their limits.
This warning is enabled by
.Fl Wextra .
.It Fl Wno-nested-comment
Warn when the block comment start sequence
.Ql /*
is found inside of a block comment.
Block comments cannot be nested, so the first
.Ql */
will end the whole comment.
.It Fl Wno-obsolete
Warn when obsolete features are encountered, which have been deprecated and may later be removed.
.It Fl Wnumeric-string=
Warn when a multi-character string is treated as a number.
.Fl Wnumeric-string=0
or
.Fl Wno-numeric-string
disables this warning.
.Fl Wnumeric-string=1
or just
.Fl Wnumeric-string
warns about strings longer than four characters, since four or fewer characters fit within a 32-bit integer.
.Fl Wnumeric-string=2
warns about any multi-character string.
.It Fl Wpurge=
Warn when purging symbols which are likely to have been necessary.
.Fl Wpurge=0
or
.Fl Wno-purge
disables this warning.
.Fl Wpurge=1
warns when purging any exported symbol (regardless of type).
.Fl Wpurge=2
or just
.Fl Wpurge
also warns when purging any label (even if not exported).
.It Fl Wshift
Warn when shifting right a negative value.
Use a division by 2**N instead.
.It Fl Wshift-amount
Warn when a shift's operand is negative or greater than 32.
.It Fl Wtruncation=
Warn when an implicit truncation (for example,
.Ic db
to an 8-bit value) loses some bits.
.Fl Wtruncation=0
or
.Fl Wno-truncation
disables this warning.
.Fl Wtruncation=1
or just
.Fl Wtruncation
warns when an N-bit value is 2**N or greater, or less than -2**N.
.Fl Wtruncation=2
also warns when an N-bit value is less than -2**(N-1), which will not fit in two's complement encoding.
.It Fl Wunmapped-char=
Warn when a character goes through charmap conversion but has no defined mapping.
.Fl Wunmapped-char=0
or
.Fl Wno-unmapped-char
disables this warning.
.Fl Wunmapped-char=1
or just
.Fl Wunmapped-char
only warns if the active charmap is not empty.
.Fl Wunmapped-char=2
warns if the active charmap is empty, and/or is not the default charmap
.Sq main .
.It Fl Wunmatched-directive
Warn when a
.Ic PUSHC , PUSHO ,
or
.Ic PUSHS
directive does not have a corresponding
.Ic POPC , POPO ,
or
.Ic POPS .
This warning is enabled by
.Fl Wextra .
.It Fl Wunterminated-load
Warn when a
.Ic LOAD
block is not terminated by an
.Ic ENDL .
This warning is enabled by
.Fl Wextra .
.It Fl Wno-user
Warn when the
.Ic WARN
built-in is executed. (See
.Dq Aborting the assembly process
in
.Xr rgbasm 5
for
.Ic WARN ) .
.El
.Sh EXAMPLES
You can assemble a source file in two ways.
.Pp
Straightforward way:
.Dl $ rgbasm -o bar.o foo.asm
.Pp
Pipes way:
.Dl $ cat foo.asm | rgbasm -o bar.o -
.Dl $ rgbasm -o bar.o - < foo.asm
.Pp
The resulting object file is not yet a usable ROM image\(emit must first be run through
.Xr rgblink 1
and then
.Xr rgbfix 1 .
.Pp
Writing the final assembler state to a file:
.Dl $ rgbasm -s all:state.dump.asm foo.asm
.Pp
Or to multiple files:
.Dl $ rgbasm -s equ,var:numbers.dump.asm -s equs:strings.dump.asm foo.asm
.Sh BUGS
Please report bugs or mistakes in this documentation on
.Lk https://github.com/gbdev/rgbds/issues GitHub .
.Sh SEE ALSO
.Xr rgbasm 5 ,
.Xr rgblink 1 ,
.Xr rgbfix 1 ,
.Xr rgbgfx 1 ,
.Xr gbz80 7 ,
.Xr rgbasm-old 5 ,
.Xr rgbds 5 ,
.Xr rgbds 7
.Sh HISTORY
.Nm
was originally written by
.An Carsten S\(/orensen
as part of the ASMotor package, and was later repackaged in RGBDS by
.An Justin Lloyd .
It is now maintained by a number of contributors at
.Lk https://github.com/gbdev/rgbds .