rgbasm - Man Page

Game Boy assembler


rgbasm[-EHhLlVvw] [-b chars] [-D name[=value]] [-g chars] [-I path] [-M depend_file] [-MG] [-MP] [-MT target_file] [-MQ target_file] [-o out_file] [-P include_file] [-p pad_value] [-Q fix_precision] [-r recursion_depth] [-W warning] asmfile


The rgbasm program creates an RGB object file from an assembly source file. The input asmfile can be a path to a file, or - to read from standard input.

Note that options can be abbreviated as long as the abbreviation is unambiguous: --verb is --verbose, but --ver is invalid because it could also be --version. The arguments are as follows:

-b chars, --binary-digits chars

Change the two characters used for binary constants. The defaults are 01.

-D name[=value], --define name[=value]

Add a string symbol to the compiled source code. This is equivalent to ‘name EQUS "value"’ in code, or ‘name EQUS "1"’ if value is not specified.

-E, --export-all

Export all labels, including unreferenced and local labels.

-g chars, --gfx-chars chars

Change the four characters used for gfx constants. The defaults are 0123.

-H, --nop-after-halt

By default, rgbasm inserts a nop instruction immediately after any halt instruction, but this has been deprecated and prints a warning message the first time it occurs. The -H option opts into this insertion, so no warning will be printed.

-h, --halt-without-nop

Disables inserting a nop instruction immediately after any halt instruction.

-I path, --include path

Add a new “include path; path” must point to a directory. When a INCLUDE (including the implicit one from -P) or INCBIN is attempted, rgbasm first looks up the provided path from its working directory; if this fails, it tries again from each of the “include path” directories, in the order they were provided.

-L, --preserve-ld

By default, rgbasm optimizes loads of the form LD [$FF00+n8],A into the opcode LDH [$FF00+n8],A, but this has been deprecated and prints a warning message the first time it occurs. The -L option disables this optimization.

-l, --auto-ldh

Optimize loads of the form LD [$FF00+n8],A into the opcode LDH [$FF00+n8],A.

-M depend_file, --dependfile depend_file

Print make(1) dependencies to depend_file.


To be used in conjunction with -M. This makes rgbasm assume that missing files are auto-generated: when INCLUDE (including the implicit one from -P) or INCBIN is attempted on a non-existent file, it is added as a dependency, then rgbasm exits normally instead of erroring out. This feature is used in automatic updating of makefiles.


When enabled, this causes a phony target to be added for each dependency other than the main file. This prevents make(1) from erroring out when dependency files are deleted.

-MT target_file

Add a target to the rules emitted by -M. The exact string provided will be written, including spaces and special characters.

-MT fileA -MT fileB

is equivalent to

-MT 'fileA fileB'.

If neither this nor -MQ is specified, the output file name is used.

-MQ target_file

Same as -MT, but additionally escapes any special make(1) characters, essentially ‘$’.

-o out_file, --output out_file

Write an object file to the given filename.

-P include_file, --preinclude include_file

Pre-include a file. This acts as if a ‘INCLUDE "include_file"’ was read before the input asmfile.

-p pad_value, --pad-value pad_value

When padding an image, pad with this value. The default is 0x00.

-Q fix_precision, --q-precision 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 ‘.’ to match the Q notation, for example, ‘-Q .16’.

-r recursion_depth, --recursion-depth recursion_depth

Specifies the recursion depth past which RGBASM will assume being in an infinite loop. The default is 64.

-V, --version

Print the version of the program and exit.

-v, --verbose

Be verbose.

-W warning, --warning warning

Set warning flag warning. A warning message will be printed if warning is an unknown warning flag. See the Diagnostics section for a list of warnings.


Disable all warning output, even when turned into errors.


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.


Make all warnings into errors.


Make the specified warning into an error. A warning's name is appended (example: -Werror=obsolete), and this warning is implicitly enabled and turned into an error. This is an error if used with a meta warning, such as -Werror=all.

The following warnings are “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.


This enables warnings that are likely to indicate an error or undesired behavior, and that can easily be fixed.


This enables extra warnings that are less likely to pose a problem, but that may still be wanted.


Enables literally every warning.

The following warnings are actual warning flags; with each description, the corresponding warning flag is included. Note that each of these flag also has a negation (for example, -Wcharmap-redef enables the warning that -Wno-charmap-redef disables). Only the non-default flag is listed here. Ignoring the “no-” prefix, entries are listed alphabetically.


Warn when WARN-type assertions fail. (See “Aborting the assembly process” in rgbasm(5) for ASSERT).


Warn when FOR loops have their start and stop values switched according to the step value. This warning is enabled by -Wall.


Warn about incorrect arguments to built-in functions, such as STRSUB() with indexes outside of the string's bounds. This warning is enabled by -Wall.


Warn when re-defining a charmap mapping. This warning is enabled by -Wall.


Warn when dividing the smallest negative integer (-2**31) by -1, which yields itself due to integer overflow.


Warn when a macro argument is empty. This warning is enabled by -Wextra.


Warn when STRRPL() is called with an empty string as its second argument (the substring to replace). This warning is enabled by -Wall.


Warn when a constant too large to fit in a signed 32-bit integer is encountered. This warning is enabled by -Wall.


Warn when a string too long to fit in internal buffers is encountered. This warning is enabled by -Wall.


Warn when shifting macro arguments past their limits. This warning is enabled by -Wextra.


Warn when obsolete constructs such as the _PI constant or PRINTT directive are encountered.


Warn when a multi-character string is treated as a number. -Wnumeric-string=0 or -Wno-numeric-string disables this warning. -Wnumeric-string=1 or just -Wnumeric-string warns about strings longer than four characters, since four or fewer characters fit within a 32-bit integer. -Wnumeric-string=2 warns about any multi-character string.


Warn when shifting right a negative value. Use a division by 2**N instead.


Warn when a shift's operand is negative or greater than 32.


Warn when an implicit truncation (for example, db to an 8-bit value) loses some bits. -Wtruncation=0 or -Wno-truncation disables this warning. -Wtruncation=1 warns when an N-bit value's absolute value is 2**N or greater. -Wtruncation=2 or just -Wtruncation also warns when an N-bit value is less than -2**(N-1), which will not fit in two's complement encoding.


Warn when a character goes through charmap conversion but has no defined mapping. -Wunmapped-char=0 or -Wunmapped-char disables this warning. -Wunmapped-char=1 or just -Wunmapped-char only warns if the active charmap is not empty. -Wunmapped-char=2 warns if the active charmap is empty, and/or is not the default charmap ‘main’.


Warn when the WARN built-in is executed. (See “Aborting the assembly process” in rgbasm(5) for WARN).


You can assemble a source file in two ways.

Straightforward way:

$ rgbasm -o bar.o foo.asm

Pipes way:

$ cat foo.asm | rgbasm -o bar.o -

$ rgbasm -o bar.o - < foo.asm

The resulting object file is not yet a usable ROM image—it must first be run through rgblink(1) and then rgbfix(1).


Please report bugs on GitHub.

See Also

rgbasm(5), rgbfix(1), rgblink(1), rgbds(5), rgbds(7), gbz80(7)


rgbasm was originally written by Carsten Sørensen as part of the ASMotor package, and was later packaged in RGBDS by Justin Lloyd. It is now maintained by a number of contributors at https://github.com/gbdev/rgbds.

Referenced By

gbz80(7), rgbasm(5), rgbds(5), rgbds(7), rgbfix(1), rgbgfx(1), rgblink(1), rgblink(5).

March 28, 2021