dxa - 6502/R65C02 disassembler
dxa [OPTION]... FILE
dxa is the semi-official disassembler option for the xa(1)
package, a weakly patched version of Marko Mäkelä's d65
disassembler that generates output similar to the de facto
coding conventions used for xa(1). The package is designed
to intelligently(?) scan arbitrary code and (with hints) can
identify the difference between data and valid machine code,
generating a sane looking, "perfect" disassembly with data
and code portions.
Perfect, in this case, means that you can take what dxa
spits out and feed it right back into xa(1), and get the
exact same object file you started with, even if sometimes
dxa can't identify everything correctly. With a few extra
options, you can tease and twist the output to generate
something not quite so parseable, or even more like true
For historical and compatibility reasons, the long options
(--) only exist if dxa were compiled with LONG_OPTIONS
enabled in options.h.
Defines the memory range xxxx to yyyy (hexadecimal,
inclusive) to be a data block. The memory range can be
* If the range is preceded by ! (an exclamation
point), such as !c000-cfff, then it is further
defined to be a data block with no vectors in it
* If the range is preceded by ? (a question mark),
then it is further defined to be a data block that
is completely unused and therefore no valid
routine may contain instructions whose parameter
lie in this range. Useful for providing enhanced
protection against misinterpreting data to be
program code, but be careful, or some code may be
listed as data. For instance, the Commodore 64
firmware uses the base address $CFFF when
initializing the video chip, and the BASIC
interpreter uses the addresses $9FEA and $9FEB
while loading the instruction pointers. In
addition to this, there are a number of BIT
instructions used for skipping the next
instruction. Thus, you must allow addresses like
$1A9, $2A9 and so on.
Reads data blocks from file filename as if they had
been specified on the command line, one per line (such
as xxxx-yyyy, ?xxxx-yyyy, etc.).
Causes label names to be read from file filename. This
file format is the same as the labelfile/symbol table
file generated by xa(1) with the -l option. The -l was
chosen on purpose for consistency with xa(1).
Specifies an address (in hexadecimal) that is declared
to be a valid routine. It is strongly recommended that
you specify the initial execution address as a routine.
For example, for a Commodore 64 binary with a BASIC
header that performs SYS 2064, specify -r0810 so that
disassembly starts at that location (or use the -U
option, which can automatically do this for you). Note
that specifying this manually may have interactions
with datablock detection (-d).
Causes a list of routines to be read from file
filename, one per line as if they had been specified on
the command line.
Determines if and what kind of address information
should be dumped with the disassembly, if any. Note
that this may make your output no longer intelligible
to xa(1). The valid options are:
Dump source only with no address information. This
is the default.
Write the current address at the beginning of each
dump Write the current address at the beginning of each
line, along with a hexdump of the bytes for which
the statement was generated.
-n A purely cosmetic option to determine how labels are
emitted. Many people, including myself, prefer a
listing where the label is given, then a tab, then the
code (-n). Since this is my preference, it's the
default. On the other hand, there are also many who
prefer to have the label demarcated by a colon and a
newline, and the code beginning indented on the next
line. This is the way d65 used to do it, and is still
supported with -N.
Specify the instruction set. Note that specifying an
instruction set that permits and disassembles illegal
and/or undocumented NMOS opcodes may make your output
unintelligible to xa(1). Only one may be specified.
The valid options are:
Only official opcodes will be recognized. This is
Opcodes specific to the Rockwell 65C02 (R65C02)
will also be allowed.
Allows all 256 NMOS opcodes to be disassembled,
whether documented or undocumented. Note that
instructions generated by this mode are not
guaranteed to work on all NMOS 6502s.
Only allows "rational" undocumented instructions.
This excludes ANE, SHA, SHS, SHY, SHX, LXA and
LAXS. This is a judgment call.
Only allows "useful" undocumented instructions.
This excludes ANE, SHA, SHS, SHY, SHX, LXA, LAXS,
NOOP and STP. This is a judgment call.
Only allows the most widely accepted undocumented
instructions based on combinations of ALU and RMW
operations. This excludes ANE, SHA, SHS, SHY, SHX,
LXA, LAXS, NOOP, STP, ARR, ASR, ANC, SBX and USBC.
This is a judgment call.
Enables or disables automatic starting address
detection. If enabled (the default), dxa looks at the
first two bytes as a 16-bit word in 6502 little-endian
format and considers that to be the starting address
for the object, discarding them without further
interpretation. This is very useful for Commodore
computers in particular. If your binary does not have a
starting address, you must specify one using -g or --
no-get-sa followed by a hexadecimal address. The
starting address will then be encoded into the output
using * =.
-Q Only relevant if automatic starting address detection
is enabled. If so, the default is to also emit the
starting address as a .word pseudo-op before the
starting address indicated with * = so that it will be
regenerated on re-assembly (-Q). Otherwise, if this
option is disabled, the starting address word will not
be re-emitted and will need to be tacked back on if the
target requires it. If you specify an address with -g,
then that address will be used here too.
-U If the starting address is recognized as a typical
BASIC entry point (currently supported for Commodore
computers), then dxa will attempt to see if a BASIC
header is present, and if so, determine its length and
mark the section as a completely dead datablock not
eligible for further disassembly or referencing. If the
first line is a construct such as 10 SYS 2061, then dxa
will additionally parse the provided address and mark
it as a valid routine if the address is within the
boundaries of the disassembled file. Note that
although its heuristics are designed to be permissive,
it may nevertheless misinterpret certain files with
intentionally pathologic line link addresses, and
unusual applications where the linked machine code is
designed to actually modify the BASIC text may not
disassemble correctly with this option. These are
highly atypical situations, so this option will likely
become the default in a future release.
-v Enables verbose output, which may or may not be useful
in the same way that Schroedinger's Cat may or may not
-V A quick summary of options.
The following options control how program code is scanned
and determined to be a valid (or invalid) portion of a
This controls how the program automatically detects
data blocks for addresses where no previous hints are
specified. Only one method may be specified. The valid
poor As much as the object as possible will be listed
as program code, even if there are illegal
instructions present. This is the default.
Assumes that all declared routines call and
execute only valid instructions. If any portion of
code declared as a routine leads to an address
block containing illegal opcodes, a consistency
error will occur and disassembly will stop.
Program addresses that are not referenced by any
routine will not be scanned for valid routines
(thus data a priori).
-E Controls whether labels should be generated for
addresses outside of the program itself. The default is
not to (i.e., leave the addresses absolute).
Controls detection of address tables/dispatch tables.
The following options are available:
Don't attempt to detect address tables.
Address tables referencing any label will be
Address tables with labels whose addresses lie
within the program's address range will be
detected. This is the default.
-J These options indicate whether JSRs are always expected
to return to the following instruction or not. This
will affect how routines are parsed. For example, the
Commodore 128 KERNAL has a routine called PRIMM that
prints a null-terminated string directly following the
JSR instruction, returning after the null byte. In this
case, -J should be specified to alert the disassembler
that this is possible. The default is to expect
"normal" JSRs (i.e., -j).
-O These options permit or inhibit a single RTS, RTI or
BRK instruction (or STP if enabled by the instruction
set), or a conditional branch, from being automatically
identified as a routine. The default is to inhibit
this; specific cases may be selectively overridden with
the -r option.
-M These options consider jumps or branches to the current
address (such as JMP *, BCC *) to be invalid or valid
code depending on which is specified. Note that BVC *
is always accepted as the V flag can sometimes be
toggled by an external hardware signal. The default is
to consider them invalid otherwise.
-W These options control if BRK (or STP if enabled by the
instruction set) should be treated as a valid exit from
a routine, just like RTS or RTI. The default is not to
-C These options are rarely needed, but account for the
case where a program may intentionally obfuscate its
code using branches with unusual destination addresses
like LDA #96:BEQ *-1. In the default case, this would
be considered to be invalid and not treated as a
routine (-c); if -C is specified, it would be accepted
Files that are longer than 64K, or (factoring in the given
starting address) extend beyond address $FFFF, are truncated
and a warning is displayed. The reason is that code at such
an address is by definition unpossible, at least until 65816
mode is supported. If you are trying to disassemble a file
that is streamed into memory in parts and is larger than
64K, you will have to block it into segments first and give
the segments to dxa individually.
There are probably quite a few bugs yet to be found.
65816 opcodes are not (yet) supported.
There are a few options Marko created that aren't hooked up
to anything (and are not documented here on purpose). I
might finish these later.
xa(1), file65(1), ldo65(1), printcbm(1), reloc65(1),
This manual page was written by Cameron Kaiser
<firstname.lastname@example.org>. dxa is based on d65 0.2.1 by Marko
Mäkelä. Original package (C)1993, 1994, 2000 Marko Mäkelä.
Additional changes (C)2006-2022 Cameron Kaiser. dxa is
Man(1) output converted with