The Free Software Foundation Inc. thanks The Nice Computer Company of Australia for loaning Dean Elsner to write the first (Vax) version of as for Project GNU. The proprietors, management and staff of TNCCA thank FSF for distracting the boss while they got some work done.

Copyright (C) 1991, 1992, 1993 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English.


This manual is a user guide to the GNU assembler . This version of the manual describes configured to generate code for architectures.

Here is a brief summary of how to invoke . For details, see section Command-Line Options.

   [ -a[dhlns] ] [ -D ] [ -f ]
   [ -I path ] [ -K ] [ -L ]
   [ -o objfile ] [ -R ] [ -v ] [ -w ]
   [ -- | files ... ]

Turn on listings; `-ad', omit debugging pseudo-ops from listing, `-ah', include high-level source, `-al', assembly listing, `-an', no forms processing, `-as', symbols. These options may be combined; e.g., `-aln' for assembly listing without forms processing. By itself, `-a' defaults to `-ahls' -- that is, all listings turned on.

This option is accepted only for script compatibility with calls to other assemblers; it has no effect on .

"fast"---skip whitespace and comment preprocessing (assume source is compiler output)

-I path
Add path to the search list for .include directives

This option is accepted but has no effect on the family.

Keep (in symbol table) local symbols, starting with `L'

-o objfile
Name the object-file output from

Fold data section into text section

Announce as version

Suppress warning messages

-- | files ...
Standard input, or source files to assemble.

Structure of this Manual

This manual is intended to describe what you need to know to use GNU . We cover the syntax expected in source files, including notation for symbols, constants, and expressions; the directives that understands; and of course how to invoke .

We also cover special features in the configuration of , including assembler directives.

On the other hand, this manual is not intended as an introduction to programming in assembly language--let alone programming in general! In a similar vein, we make no attempt to introduce the machine architecture; we do not describe the instruction set, standard mnemonics, registers or addressing modes that are standard to a particular architecture.

, the GNU Assembler

GNU as is really a family of assemblers. This manual describes , a member of that family which is configured for the architectures. If you use (or have used) the GNU assembler on one architecture, you should find a fairly similar environment when you use it on another architecture. Each version has much in common with the others, including object file formats, most assembler directives (often called pseudo-ops) and assembler syntax.

is primarily intended to assemble the output of the GNU C compiler for use by the linker . Nevertheless, we've tried to make assemble correctly everything that other assemblers for the same machine would assemble.

Unlike older assemblers, is designed to assemble a source program in one pass of the source file. This has a subtle impact on the .org directive (see section .org new-lc , fill).

Object File Formats

The GNU assembler can be configured to produce several alternative object file formats. For the most part, this does not affect how you write assembly language programs; but directives for debugging symbols are typically different in different file formats. See section Symbol Attributes. On the , is configured to produce format object files.

Command Line

After the program name , the command line may contain options and file names. Options may appear in any order, and may be before, after, or between file names. The order of file names is significant.

`--' (two hyphens) by itself names the standard input file explicitly, as one of the files for to assemble.

Except for `--' any command line argument that begins with a hyphen (`-') is an option. Each option changes the behavior of . No option changes the way another option works. An option is a `-' followed by one or more letters; the case of the letter is important. All options are optional.

Some options expect exactly one file name to follow them. The file name may either immediately follow the option's letter (compatible with older assemblers) or it may be the next command argument (GNU standard). These two command lines are equivalent:

 -o my-object-file.o mumble.s
 -omy-object-file.o mumble.s

Input Files

We use the phrase source program, abbreviated source, to describe the program input to one run of . The program may be in one or more files; how the source is partitioned into files doesn't change the meaning of the source.

The source program is a concatenation of the text in all the files, in the order specified.

Each time you run it assembles exactly one source program. The source program is made up of one or more files. (The standard input is also a file.)

You give a command line that has zero or more input file names. The input files are read (from left file name to right). A command line argument (in any position) that has no special meaning is taken to be an input file name.

If you give no file names it attempts to read one input file from the standard input, which is normally your terminal. You may have to type ctl-D to tell there is no more program to assemble.

Use `--' if you need to explicitly name the standard input file in your command line.

If the source is empty, will produce a small, empty object file.

Filenames and Line-numbers

There are two ways of locating a line in the input file (or files) and either may be used in reporting error messages. One way refers to a line number in a physical file; the other refers to a line number in a "logical" file. See section Error and Warning Messages.

Physical files are those files named in the command line given to .

Logical files are simply names declared explicitly by assembler directives; they bear no relation to physical files. Logical file names help error messages reflect the original source file, when source is itself synthesized from other files. See section .app-file string.

Output (Object) File

Every time you run it produces an output file, which is your assembly language program translated into numbers. This file is the object file, named a.out, unless you tell to give it another name by using the -o option. Conventionally, object file names end with `.o'. The default name of `a.out' is used for historical reasons: older assemblers were capable of assembling self-contained programs directly into a runnable program. (For some formats, this isn't currently possible, but it can be done for a.out format.)

The object file is meant for input to the linker . It contains assembled program code, information to help integrate the assembled program into a runnable file, and (optionally) symbolic information for the debugger.

Error and Warning Messages

may write warnings and error messages to the standard error file (usually your terminal). This should not happen when a compiler runs automatically. Warnings report an assumption made so that could keep assembling a flawed program; errors report a grave problem that stops the assembly.

Warning messages have the format

file_name:NNN:Warning Message Text

(where NNN is a line number). If a logical file name has been given (see section .app-file string) it is used for the filename, otherwise the name of the current input file is used. If a logical line number was given (see section .line line-number) then it is used to calculate the number printed, otherwise the actual line in the current source file is printed. The message text is intended to be self explanatory (in the grand Unix tradition).

Error messages have the format

file_name:NNN:FATAL:Error Message Text
The file name and line number are derived as for warning messages. The actual message text may be rather less explanatory because many of them aren't supposed to happen.

Command-Line Options

This chapter describes command-line options available in all versions of the GNU assembler; see section VAX Dependent Features, for options specific to the .

If you are invoking via the GNU C compiler (version 2), you can use the `-Wa' option to pass arguments through to the assembler. The assembler arguments must be separated from each other (and the `-Wa') by commas. For example:

gcc -c -g -O -Wa,-alh,-L file.c

will cause a listing to be emitted to standard output with high-level and assembly source.

Many compiler command-line options, such as `-R' and many machine-specific options, will be automatically be passed to the assembler by the compiler, so usually you do not need to use this `-Wa' mechanism.

Enable Listings: -a[dhlns]

These options enable listing output from the assembler. By itself, `-a' requests high-level, assembly, and symbols listing. Other letters may be used to select specific options for the list: `-ah' requests a high-level language listing, `-al' requests an output-program assembly listing, and `-as' requests a symbol table listing. High-level listings require that a compiler debugging option like `-g' be used, and that assembly listings (`-al') be requested also.

The `-ad' option may be used to omit debugging pseudo-ops from the listing.

Once you have specified one of these options, you can further control listing output and its appearance using the directives .list, .nolist, .psize, .eject, .title, and .sbttl. The `-an' option turns off all forms processing. If you do not request listing output with one of the `-a' options, the listing-control directives have no effect.

The letters after `-a' may be combined into one option, e.g., `-aln'.


This option has no effect whatsoever, but it is accepted to make it more likely that scripts written for other assemblers will also work with .

Work Faster: -f

`-f' should only be used when assembling programs written by a (trusted) compiler. `-f' stops the assembler from doing whitespace and comment pre-processing on the input file(s) before assembling them. See section Pre-Processing.

Warning: if the files actually need to be pre-processed (if they contain comments, for example), will not work correctly if `-f' is used.

.include search path: -I path

Use this option to add a path to the list of directories will search for files specified in .include directives (see section .include "file"). You may use -I as many times as necessary to include a variety of paths. The current working directory is always searched first; after that, searches any `-I' directories in the same order as they were specified (left to right) on the command line.

Difference Tables: -K

On the family, this option is allowed, but has no effect. It is permitted for compatibility with the GNU assembler on other platforms, where it can be used to warn when the assembler alters the machine code generated for `.word' directives in difference tables. The family does not have the addressing limitations that sometimes lead to this alteration on other platforms.

Include Local Labels: -L

Labels beginning with `L' (upper case only) are called local labels. See section Symbol Names. Normally you don't see such labels when debugging, because they are intended for the use of programs (like compilers) that compose assembler programs, not for your notice. Normally both and discard such labels, so you don't normally debug with them.

This option tells to retain those `L...' symbols in the object file. Usually if you do this you also tell the linker to preserve symbols whose names begin with `L'.

Name the Object File: -o

There is always one object file output when you run . By default it has the name `a.out'. `a.out'. You use this option (which takes exactly one filename) to give the object file a different name.

Whatever the object file is called, will overwrite any existing file of the same name.

Join Data and Text Sections: -R

-R tells to write the object file as if all data-section data lives in the text section. This is only done at the very last moment: your binary data are the same, but data section parts are relocated differently. The data section part of your object file is zero bytes long because all its bytes are appended to the text section. (See section Sections and Relocation.)

When you specify -R it would be possible to generate shorter address displacements (because we don't have to cross between text and data section). We refrain from doing this simply for compatibility with older versions of . In future, -R may work this way.

Announce Version: -v

You can find out what version of as is running by including the option `-v' (which you can also spell as `-version') on the command line.

Suppress Warnings: -W

should never give a warning or error message when assembling compiler output. But programs written by people often cause to give a warning that a particular assumption was made. All such warnings are directed to the standard error file. If you use this option, no warnings are issued. This option only affects the warning messages: it does not change any particular of how assembles your file. Errors, which stop the assembly, are still reported.


This chapter describes the machine-independent syntax allowed in a source file. syntax is similar to what many other assemblers use; it is inspired by the BSD 4.2 assembler.


The internal pre-processor:

Note that it does not do macro processing, include file handling, or anything else you may get from your C compiler's pre-processor. You can do include file processing with the .include directive (see section .include "file"). Other "CPP" style pre-processing can be done with the GNU C compiler, by giving the input file a .S suffix; see the compiler documentation for details.

Excess whitespace, comments, and character constants cannot be used in the portions of the input text that are not pre-processed.

If the first line of an input file is #NO_APP or the `-f' option is given, the input file will not be pre-processed. Within such an input file, parts of the file can be pre-processed by putting a line that says #APP before the text that should be pre-processed, and putting a line that says #NO_APP after them. This feature is mainly intend to support asm statements in compilers whose output normally does not need to be pre-processed.


Whitespace is one or more blanks or tabs, in any order. Whitespace is used to separate symbols, and to make programs neater for people to read. Unless within character constants (see section Character Constants), any whitespace means the same as exactly one space.


There are two ways of rendering comments to . In both cases the comment is equivalent to one space.

Anything from `/*' through the next `*/' is a comment. This means you may not nest these comments.

  The only way to include a newline ('\n') in a comment
  is to use this sort of comment.

/* This sort of comment does not nest. */

Anything from the line comment character to the next newline is considered a comment and is ignored. The line comment character is see section VAX Dependent Features.

To be compatible with past assemblers, a special interpretation is given to lines that begin with `#'. Following the `#' an absolute expression (see section Expressions) is expected: this will be the logical line number of the next line. Then a string (See section Strings.) is allowed: if present it is a new logical file name. The rest of the line, if any, should be whitespace.

If the first non-whitespace characters on the line are not numeric, the line is ignored. (Just like a comment.)

                          # This is an ordinary comment.
# 42-6 "new_file_name"    # New logical file name
                          # This is logical line # 36.
This feature is deprecated, and may disappear from future versions of .


A symbol is one or more characters chosen from the set of all letters (both upper and lower case), digits and the three characters `_.$'. No symbol may begin with a digit. Case is significant. There is no length limit: all characters are significant. Symbols are delimited by characters not in that set, or by the beginning of a file (since the source program must end with a newline, the end of a file is not a possible symbol delimiter). See section Symbols.


A statement ends at a newline character (`\n') or at a semicolon (`;'). The newline or semicolon is considered part of the preceding statement. Newlines and semicolons within character constants are an exception: they don't end statements.

It is an error to end any statement with end-of-file: the last character of any input file should be a newline.

You may write a statement on more than one line if you put a backslash (\) immediately in front of any newlines within the statement. When reads a backslashed newline both characters are ignored. You can even put backslashed newlines in the middle of symbol names without changing the meaning of your source program.

An empty statement is allowed, and may include whitespace. It is ignored.

A statement begins with zero or more labels, optionally followed by a key symbol which determines what kind of statement it is. The key symbol determines the syntax of the rest of the statement. If the symbol begins with a dot `.' then the statement is an assembler directive: typically valid for any computer. If the symbol begins with a letter the statement is an assembly language instruction: it will assemble into a machine language instruction.

A label is a symbol immediately followed by a colon (:). Whitespace before a label or after a colon is permitted, but you may not have whitespace between a label's symbol and its colon. See section Labels.

label:     .directive    followed by something
another_label:           # This is an empty statement.
           instruction   operand_1, operand_2, ...


A constant is a number, written so that its value is known by inspection, without knowing any context. Like this:

.byte  74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value.
.ascii "Ring the bell\7"                  # A string constant.
.octa  0x123456789abcdef0123456789ABCDEF0 # A bignum.
.float 0f-314159265358979323846264338327\
95028841971.693993751E-40                 # - pi, a flonum.

Character Constants

There are two kinds of character constants. A character stands for one character in one byte and its value may be used in numeric expressions. String constants (properly called string literals) are potentially many bytes and their values may not be used in arithmetic expressions.


A string is written between double-quotes. It may contain double-quotes or null characters. The way to get special characters into a string is to escape these characters: precede them with a backslash `\' character. For example `\\' represents one backslash: the first \ is an escape which tells to interpret the second character literally as a backslash (which prevents from recognizing the second \ as an escape character). The complete list of escapes follows.

Mnemonic for backspace; for ASCII this is octal code 010.

Mnemonic for FormFeed; for ASCII this is octal code 014.

Mnemonic for newline; for ASCII this is octal code 012.

Mnemonic for carriage-Return; for ASCII this is octal code 015.

Mnemonic for horizontal Tab; for ASCII this is octal code 011.

\ digit digit digit
An octal character code. The numeric code is 3 octal digits. For compatibility with other Unix systems, 8 and 9 are accepted as digits: for example, \008 has the value 010, and \009 the value 011.

Represents one `\' character.

Represents one `"' character. Needed in strings to represent this character, because an unescaped `"' would end the string.

\ anything-else
Any other character when escaped by \ will give a warning, but assemble as if the `\' was not present. The idea is that if you used an escape sequence you clearly didn't want the literal interpretation of the following character. However has no other interpretation, so knows it is giving you the wrong code and warns you of the fact.

Which characters are escapable, and what those escapes represent, varies widely among assemblers. The current set is what we think the BSD 4.2 assembler recognizes, and is a subset of what most C compilers recognize. If you are in doubt, don't use an escape sequence.


A single character may be written as a single quote immediately followed by that character. The same escapes apply to characters as to strings. So if you want to write the character backslash, you must write '\\ where the first \ escapes the second \. As you can see, the quote is an acute accent, not a grave accent. A newline (or semicolon `;') immediately following an acute accent is taken as a literal character and does not count as the end of a statement. The value of a character constant in a numeric expression is the machine's byte-wide code for that character. assumes your character code is ASCII: 'A means 65, 'B means 66, and so on.

Number Constants

distinguishes three kinds of numbers according to how they are stored in the target machine. Integers are numbers that would fit into an int in the C language. Bignums are integers, but they are stored in more than 32 bits. Flonums are floating point numbers, described below.


A binary integer is `0b' or `0B' followed by zero or more of the binary digits `01'.

An octal integer is `0' followed by zero or more of the octal digits (`01234567').

A decimal integer starts with a non-zero digit followed by zero or more digits (`0123456789').

A hexadecimal integer is `0x' or `0X' followed by one or more hexadecimal digits chosen from `0123456789abcdefABCDEF'.

Integers have the usual values. To denote a negative integer, use the prefix operator `-' discussed under expressions (see section Prefix Operator).


A bignum has the same syntax and semantics as an integer except that the number (or its negative) takes more than 32 bits to represent in binary. The distinction is made because in some places integers are permitted while bignums are not.


A flonum represents a floating point number. The translation is indirect: a decimal floating point number from the text is converted by to a generic binary floating point number of more than sufficient precision. This generic floating point number is converted to a particular computer's floating point format (or formats) by a portion of specialized to that computer.

A flonum is written by writing (in order)

At least one of the integer part or the fractional part must be present. The floating point number has the usual base-10 value.

does all processing using integers. Flonums are computed independently of any floating point hardware in the computer running .

into a field whose width depends on which assembler directive has the bit-field as its argument. Overflow (a result from the bitwise and requiring more binary digits to represent) is not an error; instead, more constants are generated, of the specified width, beginning with the least significant digits.

The directives .byte, .hword, .int, .long, .short, and .word accept bit-field arguments.

Sections and Relocation


Roughly, a section is a range of addresses, with no gaps; all data "in" those addresses is treated the same for some particular purpose. For example there may be a "read only" section.

The linker reads many object files (partial programs) and combines their contents to form a runnable program. When emits an object file, the partial program is assumed to start at address 0. will assign the final addresses the partial program occupies, so that different partial programs don't overlap. This is actually an over-simplification, but it will suffice to explain how uses sections.

moves blocks of bytes of your program to their run-time addresses. These blocks slide to their run-time addresses as rigid units; their length does not change and neither does the order of bytes within them. Such a rigid unit is called a section. Assigning run-time addresses to sections is called relocation. It includes the task of adjusting mentions of object-file addresses so they refer to the proper run-time addresses.

An object file written by has at least three sections, any of which may be empty. These are named text, data and bss sections.

can also generate whatever other named sections you specify using the `.section' directive (@xref{Section,,.section}). If you don't use any directives that place output in the `.text' or `.data' sections, these sections will still exist, but will be empty.

Within the object file, the text section starts at address 0, the data section follows, and the bss section follows the data section.

To let know which data will change when the sections are relocated, and how to change that data, also writes to the object file details of the relocation needed. To perform relocation must know, each time an address in the object file is mentioned:

In fact, every address ever uses is expressed as

(section) + (offset into section)
Further, every expression computes is of this section-relative nature. Absolute expression means an expression with section "absolute" (see section Sections). A pass1 expression means an expression with section "pass1" (see section Internal Sections). In this manual we use the notation {secname N} to mean "offset N into section secname".

Apart from text, data and bss sections you need to know about the absolute section. When mixes partial programs, addresses in the absolute section remain unchanged. For example, address {absolute 0} is "relocated" to run-time address 0 by . Although two partial programs' data sections will not overlap addresses after linking, by definition their absolute sections will overlap. Address {absolute 239} in one partial program will always be the same address when the program is running as address {absolute 239} in any other partial program.

The idea of sections is extended to the undefined section. Any address whose section is unknown at assembly time is by definition rendered {undefined U}--where U will be filled in later. Since numbers are always defined, the only way to generate an undefined address is to mention an undefined symbol. A reference to a named common block would be such a symbol: its value is unknown at assembly time so it has section undefined.

By analogy the word section is used to describe groups of sections in the linked program. puts all partial programs' text sections in contiguous addresses in the linked program. It is customary to refer to the text section of a program, meaning all the addresses of all partial program's text sections. Likewise for data and bss sections.

Some sections are manipulated by ; others are invented for use of and have no meaning except during assembly.


deals with just four kinds of sections, summarized below.

These sections hold your program. and treat them as separate but equal sections. Anything you can say of one section is true another.

bss section
This section contains zeroed bytes when your program begins running. It is used to hold unitialized variables or common storage. The length of each partial program's bss section is important, but because it starts out containing zeroed bytes there is no need to store explicit zero bytes in the object file. The bss section was invented to eliminate those explicit zeros from object files.

absolute section
Address 0 of this section is always "relocated" to runtime address 0. This is useful if you want to refer to an address that must not change when relocating. In this sense we speak of absolute addresses being "unrelocatable": they don't change during relocation.

undefined section
This "section" is a catch-all for address references to objects not in the preceding sections.

An idealized example of three relocatable sections follows. Memory addresses are on the horizontal axis.

Internal Sections

These sections are meant only for the internal use of . They have no meaning at run-time. You don't really need to know about these sections for most purposes; but they can be mentioned in warning messages, so it might be helpful to have an idea of their meanings to . These sections are used to permit the value of every expression in your assembly language program to be a section-relative address.

An internal assembler logic error has been found. This means there is a bug in the assembler.

expr section
The assembler stores complex expression internally as combinations of symbols. When it needs to represent an expression as a symbol, it puts it in the expr section.


fall into two sections: text and data. You may have separate groups of data in named sections that you want to end up near to each other in the object file, even though they are not contiguous in the assembler source. allows you to use subsections for this purpose. Within each section, there can be numbered subsections with values from 0 to 8192. Objects assembled into the same subsection will be grouped with other objects in the same subsection when they are all put into the object file. For example, a compiler might want to store constants in the text section, but might not want to have them interspersed with the program being assembled. In this case, the compiler could issue a `.text 0' before each section of code being output, and a `.text 1' before each group of constants being output.

Subsections are optional. If you don't use subsections, everything will be stored in subsection number zero.

Subsections appear in your object file in numeric order, lowest numbered to highest. (All this to be compatible with other people's assemblers.) The object file contains no representation of subsections; and other programs that manipulate object files will see no trace of them. They just see all your text subsections as a text section, and all your data subsections as a data section.

To specify which subsection you want subsequent statements assembled into, use a numeric argument to specify it, in a `.text expression' or a `.data expression' statement. You can also use an extra subsection argument with arbitrary named sections: `.section name, expression'. Expression should be an absolute expression. (See section Expressions.) If you just say `.text' then `.text 0' is assumed. Likewise `.data' means `.data 0'. Assembly begins in text 0. For instance:

.text 0     # The default subsection is text 0 anyway.
.ascii "This lives in the first text subsection. *"
.text 1
.ascii "But this lives in the second text subsection."
.data 0
.ascii "This lives in the data section,"
.ascii "in the first data subsection."
.text 0
.ascii "This lives in the first text section,"
.ascii "immediately following the asterisk (*)."

Each section has a location counter incremented by one for every byte assembled into that section. Because subsections are merely a convenience restricted to there is no concept of a subsection location counter. There is no way to directly manipulate a location counter--but the .align directive will change it, and any label definition will capture its current value. The location counter of the section that statements are being assembled into is said to be the active location counter.

bss Section

The bss section is used for local common variable storage. You may allocate address space in the bss section, but you may not dictate data to load into it before your program executes. When your program starts running, all the contents of the bss section are zeroed bytes.

Addresses in the bss section are allocated with special directives; you may not assemble anything directly into the bss section. Hence there are no bss subsections. See section .comm symbol , length , see section .lcomm symbol , length.


Symbols are a central concept: the programmer uses symbols to name things, the linker uses symbols to link, and the debugger uses symbols to debug.

Warning: does not place symbols in the object file in the same order they were declared. This may break some debuggers.


A label is written as a symbol immediately followed by a colon `:'. The symbol then represents the current value of the active location counter, and is, for example, a suitable instruction operand. You are warned if you use the same symbol to represent two different locations: the first definition overrides any other definitions.

Giving Symbols Other Values

A symbol can be given an arbitrary value by writing a symbol, followed by an equals sign `=', followed by an expression (see section Expressions). This is equivalent to using the .set directive. See section .set symbol, expression.

Symbol Names

Symbol names begin with a letter or with one of `._'. On most machines, you can also use $ in symbol names; exceptions are noted in section VAX Dependent Features. That character may be followed by any string of digits, letters, dollar signs (unless otherwise noted in section VAX Dependent Features), and underscores.

Case of letters is significant: foo is a different symbol name than Foo.

Each symbol has exactly one name. Each name in an assembly language program refers to exactly one symbol. You may use that symbol name any number of times in a program.

Local Symbol Names

Local symbols help compilers and programmers use names temporarily. There are ten local symbol names, which are re-used throughout the program. You may refer to them using the names `0' `1' ... `9'. To define a local symbol, write a label of the form `N:' (where N represents any digit). To refer to the most recent previous definition of that symbol write `Nb', using the same digit as when you defined the label. To refer to the next definition of a local label, write `Nf'---where N gives you a choice of 10 forward references. The `b' stands for "backwards" and the `f' stands for "forwards".

Local symbols are not emitted by the current GNU C compiler.

There is no restriction on how you can use these labels, but remember that at any point in the assembly you can refer to at most 10 prior local labels and to at most 10 forward local labels.

Local symbol names are only a notation device. They are immediately transformed into more conventional symbol names before the assembler uses them. The symbol names stored in the symbol table, appearing in error messages and optionally emitted to the object file have these parts:

All local labels begin with `L'. Normally both and forget symbols that start with `L'. These labels are used for symbols you are never intended to see. If you give the `-L' option then will retain these symbols in the object file. If you also instruct to retain these symbols, you may use them in debugging.

If the label is written `0:' then the digit is `0'. If the label is written `1:' then the digit is `1'. And so on up through `9:'.

This unusual character is included so you don't accidentally invent a symbol of the same name. The character has ASCII value `\001'.

ordinal number
This is a serial number to keep the labels distinct. The first `0:' gets the number `1'; The 15th `0:' gets the number `15'; etc.. Likewise for the other labels `1:' through `9:'.

For instance, the first 1: is named L1^A1, the 44th 3: is named L3^A44.

The Special Dot Symbol

The special symbol `.' refers to the current address that is assembling into. Thus, the expression `melvin: .long .' will cause melvin to contain its own address. Assigning a value to . is treated the same as a .org directive. Thus, the expression `.=.+4' is the same as saying `.space 4'.

Symbol Attributes

Every symbol has, as well as its name, the attributes "Value" and "Type". Depending on output format, symbols can also have auxiliary attributes.

If you use a symbol without defining it, assumes zero for all these attributes, and probably won't warn you. This makes the symbol an externally defined symbol, which is generally what you would want.


The value of a symbol is (usually) 32 bits. For a symbol which labels a location in the text, data, bss or absolute sections the value is the number of addresses from the start of that section to the label. Naturally for text, data and bss sections the value of a symbol changes as changes section base addresses during linking. Absolute symbols' values do not change during linking: that is why they are called absolute.

The value of an undefined symbol is treated in a special way. If it is 0 then the symbol is not defined in this assembler source program, and will try to determine its value from other programs it is linked with. You make this kind of symbol simply by mentioning a symbol name without defining it. A non-zero value represents a .comm common declaration. The value is how much common storage to reserve, in bytes (addresses). The symbol refers to the first address of the allocated storage.


The type attribute of a symbol contains relocation (section) information, any flag settings indicating that a symbol is external, and (optionally), other information for linkers and debuggers. The exact format depends on the object-code output format in use.

Symbol Attributes: a.out


This is an arbitrary 16-bit value. You may establish a symbol's descriptor value by using a .desc statement (@xref{Desc,,.desc}). A descriptor value means nothing to .


This is an arbitrary 8-bit value. It means nothing to .


An expression specifies an address or numeric value. Whitespace may precede and/or follow an expression.

Empty Expressions

An empty expression has no value: it is just whitespace or null. Wherever an absolute expression is required, you may omit the expression and will assume a value of (absolute) 0. This is compatible with other assemblers.

Integer Expressions

An integer expression is one or more arguments delimited by operators.


Arguments are symbols, numbers or subexpressions. In other contexts arguments are sometimes called "arithmetic operands". In this manual, to avoid confusing them with the "instruction operands" of the machine language, we use the term "argument" to refer to parts of expressions only, reserving the word "operand" to refer only to machine instruction operands.

Symbols are evaluated to yield {section NNN} where section is one of text, data, bss, absolute, or undefined. NNN is a signed, 2's complement 32 bit integer.

Numbers are usually integers.

A number can be a flonum or bignum. In this case, you are warned that only the low order 32 bits are used, and pretends these 32 bits are an integer. You may write integer-manipulating instructions that act on exotic constants, compatible with other assemblers.

Subexpressions are a left parenthesis `(' followed by an integer expression, followed by a right parenthesis `)'; or a prefix operator followed by an argument.


Operators are arithmetic functions, like + or %. Prefix operators are followed by an argument. Infix operators appear between their arguments. Operators may be preceded and/or followed by whitespace.

Prefix Operator

has the following prefix operators. They each take one argument, which must be absolute.

Negation. Two's complement negation.
Complementation. Bitwise not.

Infix Operators

Infix operators take two arguments, one on either side. Operators have precedence, but operations with equal precedence are performed left to right. Apart from + or -, both arguments must be absolute, and the result is absolute.

  1. Highest Precedence


    Division. Truncation is the same as the C operator `/'


    Shift Left. Same as the C operator `<<'.

    Shift Right. Same as the C operator `>>'.

  2. Intermediate precedence


    Bitwise Inclusive Or.

    Bitwise And.

    Bitwise Exclusive Or.

    Bitwise Or Not.

  3. Lowest Precedence

    Addition. If either argument is absolute, the result has the section of the other argument. If either argument is pass1 or undefined, the result is pass1. Otherwise + is illegal.

    Subtraction. If the right argument is absolute, the result has the section of the left argument. If either argument is pass1 the result is pass1. If either argument is undefined the result is difference section. If both arguments are in the same section, the result is absolute--provided that section is one of text, data or bss. Otherwise subtraction is illegal.

The sense of the rule for addition is that it's only meaningful to add the offsets in an address; you can only have a defined section in one of the two arguments.

Similarly, you can't subtract quantities from two different sections.

Assembler Directives

All assembler directives have names that begin with a period (`.'). The rest of the name is letters, usually in lower case.

This chapter discusses directives that are available regardless of the target machine configuration for the GNU assembler.


This directive stops the assembly immediately. It is for compatibility with other assemblers. The original idea was that the assembly language source would be piped into the assembler. If the sender of the source quit, it could use this directive tells to quit also. One day .abort will not be supported.

.align abs-expr , abs-expr

Pad the location counter (in the current subsection) to a particular storage boundary. The first expression (which must be absolute) is the number of low-order zero bits the location counter will have after advancement. For example `.align 3' will advance the location counter until it a multiple of 8. If the location counter is already a multiple of 8, no change is needed.

The second expression (also absolute) gives the value to be stored in the padding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are zero.

.app-file string

.app-file (which may also be spelled `.file') tells that we are about to start a new logical file. string is the new file name. In general, the filename is recognized whether or not it is surrounded by quotes `"'; but if you wish to specify an empty file name is permitted, you must give the quotes--"". This statement may go away in future: it is only recognized to be compatible with old programs.

.ascii "string"...

.ascii expects zero or more string literals (see section Strings) separated by commas. It assembles each string (with no automatic trailing zero byte) into consecutive addresses.

.asciz "string"...

.asciz is just like .ascii, but each string is followed by a zero byte. The "z" in `.asciz' stands for "zero".

.byte expressions

.byte expects zero or more expressions, separated by commas. Each expression is assembled into the next byte.

.comm symbol , length

.comm declares a named common area in the bss section. Normally reserves memory addresses for it during linking, so no partial program defines the location of the symbol. Use .comm to tell that it must be at least length bytes long. will allocate space for each .comm symbol that is at least as long as the longest .comm request in any of the partial programs linked. length is an absolute expression.

.data subsection

.data tells to assemble the following statements onto the end of the data subsection numbered subsection (which is an absolute expression). If subsection is omitted, it defaults to zero.

.double flonums

.double expects zero or more flonums, separated by commas. It assembles floating point numbers.


Force a page break at this point, when generating assembly listings.


.else is part of the support for conditional assembly; see section .if absolute expression. It marks the beginning of a section of code to be assembled if the condition for the preceding .if was false.


.endif is part of the support for conditional assembly; it marks the end of a block of code that is only assembled conditionally. See section .if absolute expression.

.equ symbol, expression

This directive sets the value of symbol to expression. It is synonymous with `.set'; see section .set symbol, expression.


.extern is accepted in the source program--for compatibility with other assemblers--but it is ignored. treats all undefined symbols as external.

.file string

.file (which may also be spelled `.app-file') tells that we are about to start a new logical file. string is the new file name. In general, the filename is recognized whether or not it is surrounded by quotes `"'; but if you wish to specify an empty file name, you must give the quotes--"". This statement may go away in future: it is only recognized to be compatible with old programs.

.fill repeat , size , value

result, size and value are absolute expressions. This emits repeat copies of size bytes. Repeat may be zero or more. Size may be zero or more, but if it is more than 8, then it is deemed to have the value 8, compatible with other people's assemblers. The contents of each repeat bytes is taken from an 8-byte number. The highest order 4 bytes are zero. The lowest order 4 bytes are value rendered in the byte-order of an integer on the computer is assembling for. Each size bytes in a repetition is taken from the lowest order size bytes of this number. Again, this bizarre behavior is compatible with other people's assemblers.

size and value are optional. If the second comma and value are absent, value is assumed zero. If the first comma and following tokens are absent, size is assumed to be 1.

.float flonums

This directive assembles zero or more flonums, separated by commas. It has the same effect as .single.

.global symbol, .globl symbol

.global makes the symbol visible to . If you define symbol in your partial program, its value is made available to other partial programs that are linked with it. Otherwise, symbol will take its attributes from a symbol of the same name from another partial program it is linked with.

Both spellings (`.globl' and `.global') are accepted, for compatibility with other assemblers.

.hword expressions

This expects zero or more expressions, and emits a 16 bit number for each.


This directive is used by some assemblers to place tags in object files. simply accepts the directive for source-file compatibility with such assemblers, but does not actually emit anything for it.

.if absolute expression

.if marks the beginning of a section of code which is only considered part of the source program being assembled if the argument (which must be an absolute expression) is non-zero. The end of the conditional section of code must be marked by .endif (see section .endif); optionally, you may include code for the alternative condition, flagged by .else (see section .else.

The following variants of .if are also supported:

.ifdef symbol
Assembles the following section of code if the specified symbol has been defined.

.ifndef symbol
ifnotdef symbol
Assembles the following section of code if the specified symbol has not been defined. Both spelling variants are equivalent.

.include "file"

This directive provides a way to include supporting files at specified points in your source program. The code from file is assembled as if it followed the point of the .include; when the end of the included file is reached, assembly of the original file continues. You can control the search paths used with the `-I' command-line option (see section Command-Line Options). Quotation marks are required around file.

.int expressions

Expect zero or more expressions, of any section, separated by commas. For each expression, emit a 32-bit number that will, at run time, be the value of that expression. The byte order of the expression depends on what kind of computer will run the program.

.lcomm symbol , length

Reserve length (an absolute expression) bytes for a local common denoted by symbol. The section and value of symbol are those of the new local common. The addresses are allocated in the bss section, so at run-time the bytes will start off zeroed. Symbol is not declared global (see section .global symbol, .globl symbol), so is normally not visible to .


accepts this directive, for compatibility with other assemblers, but ignores it.

.line line-number

Even though this is a directive associated with the a.out or b.out object-code formats, will still recognize it when producing COFF output, and will treat `.line' as though it were the COFF `.ln' if it is found outside a .def/.endef pair.

Inside a .def, `.line' is, instead, one of the directives used by compilers to generate auxiliary symbol information for debugging.

.ln line-number

`.ln' is a synonym for `.line'.


Control (in conjunction with the .nolist directive) whether or not assembly listings are generated. These two directives maintain an internal counter (which is zero initially). .list increments the counter, and .nolist decrements it. Assembly listings are generated whenever the counter is greater than zero.

By default, listings are disabled. When you enable them (with the `-a' command line option; see section Command-Line Options), the initial value of the listing counter is one.

.long expressions

.long is the same as `.int', see section .int expressions.


Control (in conjunction with the .list directive) whether or not assembly listings are generated. These two directives maintain an internal counter (which is zero initially). .list increments the counter, and .nolist decrements it. Assembly listings are generated whenever the counter is greater than zero.

.octa bignums

This directive expects zero or more bignums, separated by commas. For each bignum, it emits a 16-byte integer.

The term "octa" comes from contexts in which a "word" is two bytes; hence octa-word for 16 bytes.

.org new-lc , fill

.org will advance the location counter of the current section to new-lc. new-lc is either an absolute expression or an expression with the same section as the current subsection. That is, you can't use .org to cross sections: if new-lc has the wrong section, the .org directive is ignored. To be compatible with former assemblers, if the section of new-lc is absolute, will issue a warning, then pretend the section of new-lc is the same as the current subsection.

.org may only increase the location counter, or leave it unchanged; you cannot use .org to move the location counter backwards.

Because tries to assemble programs in one pass new-lc may not be undefined. If you really detest this restriction we eagerly await a chance to share your improved assembler.

Beware that the origin is relative to the start of the section, not to the start of the subsection. This is compatible with other people's assemblers.

When the location counter (of the current subsection) is advanced, the intervening bytes are filled with fill which should be an absolute expression. If the comma and fill are omitted, fill defaults to zero.

.psize lines , columns

Use this directive to declare the number of lines--and, optionally, the number of columns--to use for each page, when generating listings.

If you don't use .psize, listings will use a default line-count of 60. You may omit the comma and columns specification; the default width is 200 columns.

will generate formfeeds whenever the specified number of lines is exceeded (or whenever you explicitly request one, using .eject).

If you specify lines as 0, no formfeeds are generated save those explicitly specified with .eject.

.quad bignums

.quad expects zero or more bignums, separated by commas. For each bignum, it emits an 8-byte integer. If the bignum won't fit in 8 bytes, it prints a warning message; and just takes the lowest order 8 bytes of the bignum.

The term "quad" comes from contexts in which a "word" is two bytes; hence quad-word for 8 bytes.

.sbttl "subheading"

Use subheading as the title (third line, immediately after the title line) when generating assembly listings.

This directive affects subsequent pages, as well as the current page if it appears within ten lines of the top of a page.

.set symbol, expression

This directive sets the value of symbol to expression. This will change symbol's value and type to conform to expression. If symbol was flagged as external, it remains flagged. (See section Symbol Attributes.)

You may .set a symbol many times in the same assembly. If the expression's section is unknowable during pass 1, a second pass over the source program will be forced. The second pass is currently not implemented. will abort with an error message if one is required.

If you .set a global symbol, the value stored in the object file is the last value stored into it.

.short expressions

.single flonums

This directive assembles zero or more flonums, separated by commas. It has the same effect as .float.

.space size , fill

This directive emits size bytes, each of value fill. Both size and fill are absolute expressions. If the comma and fill are omitted, fill is assumed to be zero.

.stabd, .stabn, .stabs

There are three directives that begin `.stab'. All emit symbols (see section Symbols), for use by symbolic debuggers. The symbols are not entered in the hash table: they cannot be referenced elsewhere in the source file. Up to five fields are required:

This is the symbol's name. It may contain any character except `\000', so is more general than ordinary symbol names. Some debuggers used to code arbitrarily complex structures into symbol names using this field.

An absolute expression. The symbol's type is set to the low 8 bits of this expression. Any bit pattern is permitted, but and debuggers will choke on silly bit patterns.

An absolute expression. The symbol's "other" attribute is set to the low 8 bits of this expression.

An absolute expression. The symbol's descriptor is set to the low 16 bits of this expression.

An absolute expression which becomes the symbol's value.

If a warning is detected while reading a .stabd, .stabn, or .stabs statement, the symbol has probably already been created and you will get a half-formed symbol in your object file. This is compatible with earlier assemblers!

.stabd type , other , desc

The "name" of the symbol generated is not even an empty string. It is a null pointer, for compatibility. Older assemblers used a null pointer so they didn't waste space in object files with empty strings.

The symbol's value is set to the location counter, relocatably. When your program is linked, the value of this symbol will be where the location counter was when the .stabd was assembled.

.stabn type , other , desc , value
The name of the symbol is set to the empty string "".

.stabs string , type , other , desc , value
All five fields are specified.

.text subsection

Tells to assemble the following statements onto the end of the text subsection numbered subsection, which is an absolute expression. If subsection is omitted, subsection number zero is used.

.title "heading"

Use heading as the title (second line, immediately after the source file name and pagenumber) when generating assembly listings.

This directive affects subsequent pages, as well as the current page if it appears within ten lines of the top of a page.

.word expressions

This directive expects zero or more expressions, of any section, separated by commas.

In order to assemble compiler output into something that will work, will occasionlly do strange things to `.word' directives. Directives of the form `.word sym1-sym2' are often emitted by compilers as part of jump tables. Therefore, when assembles a directive of the form `.word sym1-sym2', and the difference between sym1 and sym2 does not fit in 16 bits, will create a secondary jump table, immediately before the next label. This secondary jump table will be preceded by a short-jump to the first byte after the secondary table. This short-jump prevents the flow of control from accidentally falling into the new table. Inside the table will be a long-jump to sym2. The original `.word' will contain sym1 minus the address of the long-jump to sym2.

If there were several occurrences of `.word sym1-sym2' before the secondary jump table, all of them will be adjusted. If there was a `.word sym3-sym4', that also did not fit in sixteen bits, a long-jump to sym4 will be included in the secondary jump table, and the .word directives will be adjusted to contain sym3 minus the address of the long-jump to sym4; and so on, for as many entries in the original jump table as necessary.

Deprecated Directives

One day these directives won't work. They are included for compatibility with older assemblers.



VAX Dependent Features

VAX Command-Line Options

The Vax version of accepts any of the following options, gives a warning message that the option was ignored and proceeds. These options are for compatibility with scripts designed for other people's assemblers.

-D (Debug)
-S (Symbol Table)
-T (Token Trace)
These are obsolete options used to debug old assemblers.

-d (Displacement size for JUMPs)
This option expects a number following the -d. Like options that expect filenames, the number may immediately follow the -d (old standard) or constitute the whole of the command line argument that follows -d (GNU standard).

-V (Virtualize Interpass Temporary File)
Some other assemblers use a temporary file. This option commanded them to keep the information in active memory rather than in a disk file. always does this, so this option is redundant.

-J (JUMPify Longer Branches)
Many 32-bit computers permit a variety of branch instructions to do the same job. Some of these instructions are short (and fast) but have a limited range; others are long (and slow) but can branch anywhere in virtual memory. Often there are 3 flavors of branch: short, medium and long. Some other assemblers would emit short and medium branches, unless told by this option to emit short and long branches.

-t (Temporary File Directory)
Some other assemblers may use a temporary file, and this option takes a filename being the directory to site the temporary file. Since does not use a temporary disk file, this option makes no difference. -t needs exactly one filename.

The Vax version of the assembler accepts two options when compiled for VMS. They are -h, and -+. The -h option prevents from modifying the symbol-table entries for symbols that contain lowercase characters (I think). The -+ option causes to print warning messages if the FILENAME part of the object file, or any symbol name is larger than 31 characters. The -+ option also insertes some code following the `_main' symbol so that the object file will be compatible with Vax-11 "C".

VAX Floating Point

Conversion of flonums to floating point is correct, and compatible with previous assemblers. Rounding is towards zero if the remainder is exactly half the least significant bit.

D, F, G and H floating point formats are understood.

Immediate floating literals (e.g. `S`$6.9') are rendered correctly. Again, rounding is towards zero in the boundary case.

The .float directive produces f format numbers. The .double directive produces d format numbers.

Vax Machine Directives

The Vax version of the assembler supports four directives for generating Vax floating point constants. They are described in the table below.

This expects zero or more flonums, separated by commas, and assembles Vax d format 64-bit floating point constants.

This expects zero or more flonums, separated by commas, and assembles Vax f format 32-bit floating point constants.

This expects zero or more flonums, separated by commas, and assembles Vax g format 64-bit floating point constants.

This expects zero or more flonums, separated by commas, and assembles Vax h format 128-bit floating point constants.

VAX Opcodes

All DEC mnemonics are supported. Beware that case... instructions have exactly 3 operands. The dispatch table that follows the case... instruction should be made with .word statements. This is compatible with all unix assemblers we know of.

VAX Branch Improvement

Certain pseudo opcodes are permitted. They are for branch instructions. They expand to the shortest branch instruction that will reach the target. Generally these mnemonics are made by substituting `j' for `b' at the start of a DEC mnemonic. This feature is included both for compatibility and to help compilers. If you don't need this feature, don't use these opcodes. Here are the mnemonics, and the code they can expand into.

`Jsb' is already an instruction mnemonic, so we chose `jbsb'.
(byte displacement)
bsbb ...
(word displacement)
bsbw ...
(long displacement)
jsb ...
  • jbr
  • jr Unconditional branch.
    (byte displacement)
    brb ...
    (word displacement)
    brw ...
    (long displacement)
    jmp ...
  • jCOND COND may be any one of the conditional branches neq, nequ, eql, eqlu, gtr, geq, lss, gtru, lequ, vc, vs, gequ, cc, lssu, cs. COND may also be one of the bit tests bs, bc, bss, bcs, bsc, bcc, bssi, bcci, lbs, lbc. NOTCOND is the opposite condition to COND.
    (byte displacement)
    bCOND ...
    (word displacement)
    bNOTCOND foo ; brw ... ; foo:
    (long displacement)
    bNOTCOND foo ; jmp ... ; foo:
  • jacbX X may be one of b d f g h l w.
    (word displacement)
    OPCODE ...
    (long displacement)
    OPCODE ..., foo ;
    brb bar ;
    foo: jmp ... ;
  • jaobYYY YYY may be one of lss leq.
  • jsobZZZ ZZZ may be one of geq gtr.
    (byte displacement)
    OPCODE ...
    (word displacement)
    OPCODE ..., foo ;
    brb bar ;
    foo: brw destination ;
    (long displacement)
    OPCODE ..., foo ;
    brb bar ;
    foo: jmp destination ;
  • aobleq
  • aoblss
  • sobgeq
  • sobgtr
    (byte displacement)
    OPCODE ...
    (word displacement)
    OPCODE ..., foo ;
    brb bar ;
    foo: brw destination ;
    (long displacement)
    OPCODE ..., foo ;
    brb bar ;
    foo: jmp destination ;
  • VAX Operands

    The immediate character is `$' for Unix compatibility, not `#' as DEC writes it.

    The indirect character is `*' for Unix compatibility, not `@' as DEC writes it.

    The displacement sizing character is ``' (an accent grave) for Unix compatibility, not `^' as DEC writes it. The letter preceding ``' may have either case. `G' is not understood, but all other letters (b i l s w) are understood.

    Register names understood are r0 r1 r2 ... r15 ap fp sp pc. Any case of letters will do.

    For instance

    tstb *w`$4(r5)

    Any expression is permitted in an operand. Operands are comma separated.

    Not Supported on VAX

    Vax bit fields can not be assembled with . Someone can add the required code if they really need it.

    AMD 29K Dependent Features


    has no additional command-line options for the AMD 29K family.


    Special Characters

    `;' is the line comment character.

    `@' can be used instead of a newline to separate statements.

    The character `?' is permitted in identifiers (but may not begin an identifier).

    Register Names

    General-purpose registers are represented by predefined symbols of the form `GRnnn' (for global registers) or `LRnnn' (for local registers), where nnn represents a number between 0 and 127, written with no leading zeros. The leading letters may be in either upper or lower case; for example, `gr13' and `LR7' are both valid register names.

    You may also refer to general-purpose registers by specifying the register number as the result of an expression (prefixed with `%%' to flag the expression as a register number):

    ---where expression must be an absolute expression evaluating to a number between 0 and 255. The range [0, 127] refers to global registers, and the range [128, 255] to local registers.

    In addition, understands the following protected special-purpose register names for the AMD 29K family:

      vab    chd    pc0
      ops    chc    pc1
      cps    rbp    pc2
      cfg    tmc    mmu
      cha    tmr    lru

    These unprotected special-purpose register names are also recognized:

      ipc    alu    fpe
      ipa    bp     inte
      ipb    fc     fps
      q      cr     exop

    Floating Point

    The AMD 29K family uses IEEE floating-point numbers.

    AMD 29K Machine Directives

    .block size , fill
    This directive emits size bytes, each of value fill. Both size and fill are absolute expressions. If the comma and fill are omitted, fill is assumed to be zero.

    In other versions of the GNU assembler, this directive is called `.space'.

    This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers.

    This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers.

    Warning: in other versions of the GNU assembler, .file is used for the directive called .app-file in the AMD 29K support.

    This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers.

    This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers.

    .use section name
    Establishes the section and subsection for the following code; section name may be one of .text, .data, .data1, or .lit. With one of the first three section name options, `.use' is equivalent to the machine directive section name; the remaining case, `.use .lit', is the same as `.data 200'.


    implements all the standard AMD 29K opcodes. No additional pseudo-instructions are needed on this family.

    For information on the 29K machine instruction set, see Am29000 User's Manual, Advanced Micro Devices, Inc.

    H8/300 Dependent Features


    has no additional command-line options for the Hitachi H8/300 family.


    Special Characters

    `;' is the line comment character.

    `$' can be used instead of a newline to separate statements. Therefore you may not use `$' in symbol names on the H8/300.

    Register Names

    You can use predefined symbols of the form `rnh' and `rnl' to refer to the H8/300 registers as sixteen 8-bit general-purpose registers. n is a digit from `0' to `7'); for instance, both `r0h' and `r7l' are valid register names.

    You can also use the eight predefined symbols `rn' to refer to the H8/300 registers as 16-bit registers (you must use this form for addressing).

    On the H8/300H, you can also use the eight predefined symbols `ern' (`er0' ... `er7') to refer to the 32-bit general purpose registers.

    The two control registers are called pc (program counter; a 16-bit register, except on the H8/300H where it is 24 bits) and ccr (condition code register; an 8-bit register). r7 is used as the stack pointer, and can also be called sp.

    Addressing Modes

    understands the following addressing modes for the H8/300:

    Register direct

    Register indirect

    @(d, rn)
    @(d:16, rn)
    @(d:24, rn)
    Register indirect: 16-bit or 24-bit displacement d from register n. (24-bit displacements are only meaningful on the H8/300H.)

    Register indirect with post-increment

    Register indirect with pre-decrement

    Absolute address aa. (The address size `:24' only makes sense on the H8/300H.)

    Immediate data xx. You may specify the `:8', `:16', or `:32' for clarity, if you wish; but neither requires this nor uses it--the data size required is taken from context.

    Memory indirect. You may specify the `:8' for clarity, if you wish; but neither requires this nor uses it.

    Floating Point

    The H8/300 family has no hardware floating point, but the .float directive generates IEEE floating-point numbers for compatibility with other development tools.

    H8/300 Machine Directives

    has only one machine-dependent directive for the H8/300:

    Recognize and emit additional instructions for the H8/300H variant, and also make .int emit 32-bit numbers rather than the usual (16-bit) for the H8/300 family.

    On the H8/300 family (including the H8/300H) `.word' directives generate 16-bit numbers.


    For detailed information on the H8/300 machine instruction set, see H8/300 Series Programming Manual (Hitachi ADE--602--025). For information specific to the H8/300H, see H8/300H Series Programming Manual (Hitachi).

    implements all the standard H8/300 opcodes. No additional pseudo-instructions are needed on this family.

    The following table summarizes the H8/300 opcodes, and their arguments. Entries marked `*' are opcodes used only on the H8/300H.

                Rs   source register
                Rd   destination register
                abs  absolute address
                imm  immediate data
             disp:N  N-bit displacement from a register
            pcrel:N  N-bit displacement relative to program counter
       add.b #imm,rd              *  andc #imm,ccr
       add.b rs,rd                   band #imm,rd
       add.w rs,rd                   band #imm,@rd
    *  add.w #imm,rd                 band #imm,@abs:8
    *  add.l rs,rd                   bra  pcrel:8
    *  add.l #imm,rd              *  bra  pcrel:16
       adds #imm,rd                  bt   pcrel:8
       addx #imm,rd               *  bt   pcrel:16
       addx rs,rd                    brn  pcrel:8
       and.b #imm,rd              *  brn  pcrel:16
       and.b rs,rd                   bf   pcrel:8
    *  and.w rs,rd                *  bf   pcrel:16
    *  and.w #imm,rd                 bhi  pcrel:8
    *  and.l #imm,rd              *  bhi  pcrel:16
    *  and.l rs,rd                   bls  pcrel:8
    *  bls  pcrel:16                 bld  #imm,rd
       bcc  pcrel:8                  bld  #imm,@rd
    *  bcc  pcrel:16                 bld  #imm,@abs:8
       bhs  pcrel:8                  bnot #imm,rd
    *  bhs  pcrel:16                 bnot #imm,@rd
       bcs  pcrel:8                  bnot #imm,@abs:8
    *  bcs  pcrel:16                 bnot rs,rd
       blo  pcrel:8                  bnot rs,@rd
    *  blo  pcrel:16                 bnot rs,@abs:8
       bne  pcrel:8                  bor  #imm,rd
    *  bne  pcrel:16                 bor  #imm,@rd
       beq  pcrel:8                  bor  #imm,@abs:8
    *  beq  pcrel:16                 bset #imm,rd
       bvc  pcrel:8                  bset #imm,@rd
    *  bvc  pcrel:16                 bset #imm,@abs:8
       bvs  pcrel:8                  bset rs,rd
    *  bvs  pcrel:16                 bset rs,@rd
       bpl  pcrel:8                  bset rs,@abs:8
    *  bpl  pcrel:16                 bsr  pcrel:8
       bmi  pcrel:8                  bsr  pcrel:16
    *  bmi  pcrel:16                 bst  #imm,rd
       bge  pcrel:8                  bst  #imm,@rd
    *  bge  pcrel:16                 bst  #imm,@abs:8
       blt  pcrel:8                  btst #imm,rd
    *  blt  pcrel:16                 btst #imm,@rd
       bgt  pcrel:8                  btst #imm,@abs:8
    *  bgt  pcrel:16                 btst rs,rd
       ble  pcrel:8                  btst rs,@rd
    *  ble  pcrel:16                 btst rs,@abs:8
       bclr #imm,rd                  bxor #imm,rd
       bclr #imm,@rd                 bxor #imm,@rd
       bclr #imm,@abs:8              bxor #imm,@abs:8
       bclr rs,rd                    cmp.b #imm,rd
       bclr rs,@rd                   cmp.b rs,rd
       bclr rs,@abs:8                cmp.w rs,rd
       biand #imm,rd                 cmp.w rs,rd
       biand #imm,@rd             *  cmp.w #imm,rd
       biand #imm,@abs:8          *  cmp.l #imm,rd
       bild #imm,rd               *  cmp.l rs,rd
       bild #imm,@rd                 daa  rs
       bild #imm,@abs:8              das  rs
       bior #imm,rd                  dec.b rs
       bior #imm,@rd              *  dec.w #imm,rd
       bior #imm,@abs:8           *  dec.l #imm,rd
       bist #imm,rd                  divxu.b rs,rd
       bist #imm,@rd              *  divxu.w rs,rd
       bist #imm,@abs:8           *  divxs.b rs,rd
       bixor #imm,rd              *  divxs.w rs,rd
       bixor #imm,@rd                eepmov
       bixor #imm,@abs:8          *  eepmovw
    *  exts.w rd                     mov.w rs,@abs:16
    *  exts.l rd                  *  mov.l #imm,rd
    *  extu.w rd                  *  mov.l rs,rd
    *  extu.l rd                  *  mov.l @rs,rd
       inc  rs                    *  mov.l @(disp:16,rs),rd
    *  inc.w #imm,rd              *  mov.l @(disp:24,rs),rd
    *  inc.l #imm,rd              *  mov.l @rs+,rd
       jmp  @rs                   *  mov.l @abs:16,rd
       jmp  abs                   *  mov.l @abs:24,rd
       jmp  @@abs:8               *  mov.l rs,@rd
       jsr  @rs                   *  mov.l rs,@(disp:16,rd)
       jsr  abs                   *  mov.l rs,@(disp:24,rd)
       jsr  @@abs:8               *  mov.l rs,@-rd
       ldc  #imm,ccr              *  mov.l rs,@abs:16
       ldc  rs,ccr                *  mov.l rs,@abs:24
    *  ldc  @abs:16,ccr              movfpe @abs:16,rd
    *  ldc  @abs:24,ccr              movtpe rs,@abs:16
    *  ldc  @(disp:16,rs),ccr        mulxu.b rs,rd
    *  ldc  @(disp:24,rs),ccr     *  mulxu.w rs,rd
    *  ldc  @rs+,ccr              *  mulxs.b rs,rd
    *  ldc  @rs,ccr               *  mulxs.w rs,rd
    *  mov.b @(disp:24,rs),rd        neg.b rs
    *  mov.b rs,@(disp:24,rd)     *  neg.w rs
       mov.b @abs:16,rd           *  neg.l rs
       mov.b rs,rd                   nop
       mov.b @abs:8,rd               not.b rs
       mov.b rs,@abs:8            *  not.w rs
       mov.b rs,rd                *  not.l rs
       mov.b #imm,rd                 or.b #imm,rd
       mov.b @rs,rd                  or.b rs,rd
       mov.b @(disp:16,rs),rd     *  or.w #imm,rd
       mov.b @rs+,rd              *  or.w rs,rd
       mov.b @abs:8,rd            *  or.l #imm,rd
       mov.b rs,@rd               *  or.l rs,rd
       mov.b rs,@(disp:16,rd)        orc  #imm,ccr
       mov.b rs,@-rd                 pop.w rs
       mov.b rs,@abs:8            *  pop.l rs
       mov.w rs,@rd                  push.w rs
    *  mov.w @(disp:24,rs),rd     *  push.l rs
    *  mov.w rs,@(disp:24,rd)        rotl.b rs
    *  mov.w @abs:24,rd           *  rotl.w rs
    *  mov.w rs,@abs:24           *  rotl.l rs
       mov.w rs,rd                   rotr.b rs
       mov.w #imm,rd              *  rotr.w rs
       mov.w @rs,rd               *  rotr.l rs
       mov.w @(disp:16,rs),rd        rotxl.b rs
       mov.w @rs+,rd              *  rotxl.w rs
       mov.w @abs:16,rd           *  rotxl.l rs
       mov.w rs,@(disp:16,rd)        rotxr.b rs
       mov.w rs,@-rd              *  rotxr.w rs
    *  rotxr.l rs                 *  stc  ccr,@(disp:24,rd)
       bpt                        *  stc  ccr,@-rd
       rte                        *  stc  ccr,@abs:16
       rts                        *  stc  ccr,@abs:24
       shal.b rs                     sub.b rs,rd
    *  shal.w rs                     sub.w rs,rd
    *  shal.l rs                  *  sub.w #imm,rd
       shar.b rs                  *  sub.l rs,rd
    *  shar.w rs                  *  sub.l #imm,rd
    *  shar.l rs                     subs #imm,rd
       shll.b rs                     subx #imm,rd
    *  shll.w rs                     subx rs,rd
    *  shll.l rs                  *  trapa #imm
       shlr.b rs                     xor  #imm,rd
    *  shlr.w rs                     xor  rs,rd
    *  shlr.l rs                  *  xor.w #imm,rd
       sleep                      *  xor.w rs,rd
       stc  ccr,rd                *  xor.l #imm,rd
    *  stc  ccr,@rs               *  xor.l rs,rd
    *  stc  ccr,@(disp:16,rd)        xorc #imm,ccr

    Four H8/300 instructions (add, cmp, mov, sub) are defined with variants using the suffixes `.b', `.w', and `.l' to specify the size of a memory operand. supports these suffixes, but does not require them; since one of the operands is always a register, can deduce the correct size.

    For example, since r0 refers to a 16-bit register,

    mov    r0,@foo
    is equivalent to
    mov.w  r0,@foo

    If you use the size suffixes, issues a warning when the suffix and the register size do not match.

    Intel 80960 Dependent Features

    i960 Command-line Options

    -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
    Select the 80960 architecture. Instructions or features not supported by the selected architecture cause fatal errors.

    `-ACA' is equivalent to `-ACA_A'; `-AKC' is equivalent to `-AMC'. Synonyms are provided for compatibility with other tools.

    If none of these options is specified, will generate code for any instruction or feature that is supported by some version of the 960 (even if this means mixing architectures!). In principle, will attempt to deduce the minimal sufficient processor type if none is specified; depending on the object code format, the processor type may be recorded in the object file. If it is critical that the output match a specific architecture, specify that architecture explicitly.

    Add code to collect information about conditional branches taken, for later optimization using branch prediction bits. (The conditional branch instructions have branch prediction bits in the CA, CB, and CC architectures.) If BR represents a conditional branch instruction, the following represents the code generated by the assembler when `-b' is specified:

            call    increment routine
            .word   0       # pre-counter
    Label:  BR
            call    increment routine
            .word   0       # post-counter

    The counter following a branch records the number of times that branch was not taken; the differenc between the two counters is the number of times the branch was taken.

    A table of every such Label is also generated, so that the external postprocessor gbr960 (supplied by Intel) can locate all the counters. This table is always labelled `__BRANCH_TABLE__'; this is a local symbol to permit collecting statistics for many separate object files. The table is word aligned, and begins with a two-word header. The first word, initialized to 0, is used in maintaining linked lists of branch tables. The second word is a count of the number of entries in the table, which follow immediately: each is a word, pointing to one of the labels illustrated above.

    The first word of the header is used to locate multiple branch tables, since each object file may contain one. Normally the links are maintained with a call to an initialization routine, placed at the beginning of each function in the file. The GNU C compiler will generate these calls automatically when you give it a `-b' option. For further details, see the documentation of `gbr960'.

    Normally, Compare-and-Branch instructions with targets that require displacements greater than 13 bits (or that have external targets) are replaced with the corresponding compare (or `chkbit') and branch instructions. You can use the `-norelax' option to specify that should generate errors instead, if the target displacement is larger than 13 bits.

    This option does not affect the Compare-and-Jump instructions; the code emitted for them is always adjusted when necessary (depending on displacement size), regardless of whether you use `-norelax'.

    Floating Point

    generates IEEE floating-point numbers for the directives `.float', `.double', `.extended', and `.single'.

    i960 Machine Directives

    .bss symbol, length, align
    Reserve length bytes in the bss section for a local symbol, aligned to the power of two specified by align. length and align must be positive absolute expressions. This directive differs from `.lcomm' only in that it permits you to specify an alignment. See section .lcomm symbol , length.

    .extended flonums
    .extended expects zero or more flonums, separated by commas; for each flonum, `.extended' emits an IEEE extended-format (80-bit) floating-point number.

    .leafproc call-lab, bal-lab
    You can use the `.leafproc' directive in conjunction with the optimized callj instruction to enable faster calls of leaf procedures. If a procedure is known to call no other procedures, you may define an entry point that skips procedure prolog code (and that does not depend on system-supplied saved context), and declare it as the bal-lab using `.leafproc'. If the procedure also has an entry point that goes through the normal prolog, you can specify that entry point as call-lab.

    A `.leafproc' declaration is meant for use in conjunction with the optimized call instruction `callj'; the directive records the data needed later to choose between converting the `callj' into a bal or a call.

    call-lab is optional; if only one argument is present, or if the two arguments are identical, the single argument is assumed to be the bal entry point.

    .sysproc name, index
    The `.sysproc' directive defines a name for a system procedure. After you define it using `.sysproc', you can use name to refer to the system procedure identified by index when calling procedures with the optimized call instruction `callj'.

    Both arguments are required; index must be between 0 and 31 (inclusive).

    i960 Opcodes

    All Intel 960 machine instructions are supported; see section i960 Command-line Options for a discussion of selecting the instruction subset for a particular 960 architecture.

    Some opcodes are processed beyond simply emitting a single corresponding instruction: `callj', and Compare-and-Branch or Compare-and-Jump instructions with target displacements larger than 13 bits.


    You can write callj to have the assembler or the linker determine the most appropriate form of subroutine call: `call', `bal', or `calls'. If the assembly source contains enough information--a `.leafproc' or `.sysproc' directive defining the operand--then will translate the callj; if not, it will simply emit the callj, leaving it for the linker to resolve.


    The 960 architectures provide combined Compare-and-Branch instructions that permit you to store the branch target in the lower 13 bits of the instruction word itself. However, if you specify a branch target far enough away that its address won't fit in 13 bits, the assembler can either issue an error, or convert your Compare-and-Branch instruction into separate instructions to do the compare and the branch.

    Whether gives an error or expands the instruction depends on two choices you can make: whether you use the `-norelax' option, and whether you use a "Compare and Branch" instruction or a "Compare and Jump" instruction. The "Jump" instructions are always expanded if necessary; the "Branch" instructions are expanded when necessary unless you specify -norelax---in which case gives an error instead.

    These are the Compare-and-Branch instructions, their "Jump" variants, and the instruction pairs they may expand into:

    M680x0 Dependent Features

    M680x0 Options

    The Motorola 680x0 version of has two machine dependent options. One shortens undefined references from 32 to 16 bits, while the other is used to tell what kind of machine it is assembling for.

    You can use the -l option to shorten the size of references to undefined symbols. If the -l option is not given, references to undefined symbols will be a full long (32 bits) wide. (Since cannot know where these symbols will end up, can only allocate space for the linker to fill in later. Since doesn't know how far away these symbols will be, it allocates as much space as it can.) If this option is given, the references will only be one word wide (16 bits). This may be useful if you want the object file to be as small as possible, and you know that the relevant symbols will be less than 17 bits away.

    The 680x0 version of is most frequently used to assemble programs for the Motorola MC68020 microprocessor. Occasionally it is used to assemble programs for the mostly similar, but slightly different MC68000 or MC68010 microprocessors. You can give the options `-m68000', `-mc68000', `-m68010', `-mc68010', `-m68020', and `-mc68020' to tell it what processor is the target.


    This syntax for the Motorola 680x0 was developed at MIT.

    The 680x0 version of uses syntax similar to the Sun assembler. Intervening periods are now ignored; for example, `movl' is equivalent to `move.l'.

    In the following table apc stands for any of the address registers (`a0' through `a7'), nothing, (`'), the Program Counter (`pc'), or the zero-address relative to the program counter (`zpc').

    The following addressing modes are understood:


    Data Register
    `d0' through `d7'

    Address Register
    `a0' through `a7'

    Address Register Indirect
    `a0@' through `a7@'
    `a7' is also known as `sp', i.e. the Stack Pointer. a6 is also known as `fp', the Frame Pointer.

    Address Register Postincrement
    `a0@+' through `a7@+'

    Address Register Predecrement
    `a0@-' through `a7@-'

    Indirect Plus Offset


    or `apc@(register:size:scale)'


    or `apc@(digits)@(register:size:scale)'


    or `apc@(register:size:scale)@(digits)'

    Memory Indirect

    `symbol', or `digits'

    For some configurations, especially those where the compiler normally does not prepend an underscore to the names of user variables, the assembler requires a `%' before any use of a register name. This is intended to let the assembler distinguish between user variables and registers named `a0' through `a7', et cetera. The `%' is always accepted, but is only required for some configurations, notably `m68k-coff'.

    Motorola Syntax

    The standard Motorola syntax for this chip differs from the syntax already discussed (see section Syntax). can accept both kinds of syntax, even within a single instruction. The syntaxes are fully compatible, because the Motorola syntax never uses the `@' character and the MIT syntax always does, except in cases where the syntaxes are identical.

    In particular, you may write or generate M68K assembler with the following conventions:

    (In the following table apc stands for any of the address registers (`a0' through `a7'), nothing, (`'), the Program Counter (`pc'), or the zero-address relative to the program counter (`zpc').)

    The following additional addressing modes are understood:

    Address Register Indirect
    `a0' through `a7'
    `a7' is also known as `sp', i.e. the Stack Pointer. a6 is also known as `fp', the Frame Pointer.

    Address Register Postincrement
    `(a0)+' through `(a7)+'

    Address Register Predecrement
    `-(a0)' through `-(a7)'

    Indirect Plus Offset

    or `(apc,register.size*scale)'
    In either case, size and scale are optional (scale defaults to `1', size defaults to `l'). scale can be `1', `2', `4', or `8'. size can be `w' or `l'. scale is only supported on the 68020 and greater.

    Floating Point

    The floating point code is not too well tested, and may have subtle bugs in it.

    Packed decimal (P) format floating literals are not supported. Feel free to add the code!

    The floating point formats generated by directives are these.

    Single precision floating point constants.

    Double precision floating point constants.

    There is no directive to produce regions of memory holding extended precision numbers, however they can be used as immediate operands to floating-point instructions. Adding a directive to create extended precision numbers would not be hard, but it has not yet seemed necessary.

    680x0 Machine Directives

    In order to be compatible with the Sun assembler the 680x0 assembler understands the following directives.

    This directive is identical to a .data 1 directive.

    This directive is identical to a .data 2 directive.

    This directive is identical to a .align 1 directive.

    This directive is identical to a .space directive.


    Branch Improvement

    Certain pseudo opcodes are permitted for branch instructions. They expand to the shortest branch instruction that will reach the target. Generally these mnemonics are made by substituting `j' for `b' at the start of a Motorola mnemonic.

    The following table summarizes the pseudo-operations. A * flags cases that are more fully described after the table:

              |                68020   68000/10
    Pseudo-Op |BYTE    WORD    LONG    LONG      non-PC relative
         jbsr |bsrs    bsr     bsrl    jsr       jsr
          jra |bras    bra     bral    jmp       jmp
    *     jXX |bXXs    bXX     bXXl    bNXs;jmpl bNXs;jmp
    *    dbXX |dbXX    dbXX        dbXX; bra; jmpl
    *    fjXX |fbXXw   fbXXw   fbXXl             fbNXw;jmp
    XX: condition
    NX: negative of condition XX
    *---see full description below

    These are the simplest jump pseudo-operations; they always map to one particular machine instruction, depending on the displacement to the branch target.

    Here, `jXX' stands for an entire family of pseudo-operations, where XX is a conditional branch or condition-code test. The full list of pseudo-ops in this family is:
     jhi   jls   jcc   jcs   jne   jeq   jvc
     jvs   jpl   jmi   jge   jlt   jgt   jle

    For the cases of non-PC relative displacements and long displacements on the 68000 or 68010, will issue a longer code fragment in terms of NX, the opposite condition to XX. For example, for the non-PC relative case:

        jXX foo
         bNXs oof
         jmp foo

    The full family of pseudo-operations covered here is
     dbhi   dbls   dbcc   dbcs   dbne   dbeq   dbvc
     dbvs   dbpl   dbmi   dbge   dblt   dbgt   dble
     dbf    dbra   dbt

    Other than for word and byte displacements, when the source reads `dbXX foo', will emit

         dbXX oo1
         bra oo2
     oo1:jmpl foo

    This family includes
     fjne   fjeq   fjge   fjlt   fjgt   fjle   fjf
     fjt    fjgl   fjgle  fjnge  fjngl  fjngle fjngt
     fjnle  fjnlt  fjoge  fjogl  fjogt  fjole  fjolt
     fjor   fjseq  fjsf   fjsne  fjst   fjueq  fjuge
     fjugt  fjule  fjult  fjun

    For branch targets that are not PC relative, emits

         fbNX oof
         jmp foo
    when it encounters `fjXX foo'.

    Special Characters

    The immediate character is `#' for Sun compatibility. The line-comment character is `|'. If a `#' appears at the beginning of a line, it is treated as a comment unless it looks like `# line file', in which case it is treated normally.

    SPARC Dependent Features


    The SPARC chip family includes several successive levels (or other variants) of chip, using the same core instruction set, but including a few additional instructions at each level.

    By default, assumes the core instruction set (SPARC v6), but "bumps" the architecture level as needed: it switches to successively higher architectures as it encounters instructions that only exist in the higher levels.

    -Av6 | -Av7 | -Av8 | -Asparclite
    Use one of the `-A' options to select one of the SPARC architectures explicitly. If you select an architecture explicitly, reports a fatal error if it encounters an instruction or feature requiring a higher level.

    Permit the assembler to "bump" the architecture level as required, but warn whenever it is necessary to switch to another level.

    Floating Point

    The Sparc uses IEEE floating-point numbers.

    Sparc Machine Directives

    The Sparc version of supports the following additional machine directives:

    This must be followed by a symbol name, a positive number, and "bss". This behaves somewhat like .comm, but the syntax is different.

    This is functionally identical to .short.

    This directive is ignored. Any text following it on the same line is also ignored.

    This must be followed by a symbol name, a positive number, and "bss". This behaves somewhat like .lcomm, but the syntax is different.

    This must be followed by "text", "data", or "data1". It behaves like .text, .data, or .data 1.

    This is functionally identical to the .space directive.

    On the Sparc, the .word directive produces 32 bit values, instead of the 16 bit values it produces on many other machines.

    80386 Dependent Features


    The 80386 has no machine dependent options.

    AT&T Syntax versus Intel Syntax

    In order to maintain compatibility with the output of , supports AT&T System V/386 assembler syntax. This is quite different from Intel syntax. We mention these differences because almost all 80386 documents used only Intel syntax. Notable differences between the two syntaxes are:

    Opcode Naming

    Opcode names are suffixed with one character modifiers which specify the size of operands. The letters `b', `w', and `l' specify byte, word, and long operands. If no suffix is specified by an instruction and it contains no memory operands then tries to fill in the missing suffix based on the destination register operand (the last one by convention). Thus, `mov %ax, %bx' is equivalent to `movw %ax, %bx'; also, `mov $1, %bx' is equivalent to `movw $1, %bx'. Note that this is incompatible with the AT&T Unix assembler which assumes that a missing opcode suffix implies long operand size. (This incompatibility does not affect compiler output since compilers always explicitly specify the opcode suffix.)

    Almost all opcodes have the same names in AT&T and Intel format. There are a few exceptions. The sign extend and zero extend instructions need two sizes to specify them. They need a size to sign/zero extend from and a size to zero extend to. This is accomplished by using two opcode suffixes in AT&T syntax. Base names for sign extend and zero extend are `movs...' and `movz...' in AT&T syntax (`movsx' and `movzx' in Intel syntax). The opcode suffixes are tacked on to this base name, the from suffix before the to suffix. Thus, `movsbl %al, %edx' is AT&T syntax for "move sign extend from %al to %edx." Possible suffixes, thus, are `bl' (from byte to long), `bw' (from byte to word), and `wl' (from word to long).

    The Intel-syntax conversion instructions

    are called `cbtw', `cwtl', `cwtd', and `cltd' in AT&T naming. accepts either naming for these instructions.

    Far call/jump instructions are `lcall' and `ljmp' in AT&T syntax, but are `call far' and `jump far' in Intel convention.

    Register Naming

    Register operands are always prefixes with `%'. The 80386 registers consist of

    Opcode Prefixes

    Opcode prefixes are used to modify the following opcode. They are used to repeat string instructions, to provide section overrides, to perform bus lock operations, and to give operand and address size (16-bit operands are specified in an instruction by prefixing what would normally be 32-bit operands with a "operand size" opcode prefix). Opcode prefixes are usually given as single-line instructions with no operands, and must directly precede the instruction they act upon. For example, the `scas' (scan string) instruction is repeated with:


    Here is a list of opcode prefixes:

    Memory References

    An Intel syntax indirect memory reference of the form

    section:[base + index*scale + disp]

    is translated into the AT&T syntax

    section:disp(base, index, scale)

    where base and index are the optional 32-bit base and index registers, disp is the optional displacement, and scale, taking the values 1, 2, 4, and 8, multiplies index to calculate the address of the operand. If no scale is specified, scale is taken to be 1. section specifies the optional section register for the memory operand, and may override the default section register (see a 80386 manual for section register defaults). Note that section overrides in AT&T syntax must have be preceded by a `%'. If you specify a section override which coincides with the default section register, will not output any section register override prefixes to assemble the given instruction. Thus, section overrides can be specified to emphasize which section register is used for a given memory operand.

    Here are some examples of Intel and AT&T style memory references:

    AT&T: `-4(%ebp)', Intel: `[ebp - 4]'
    base is `%ebp'; disp is `-4'. section is missing, and the default section is used (`%ss' for addressing with `%ebp' as the base register). index, scale are both missing.

    AT&T: `foo(,%eax,4)', Intel: `[foo + eax*4]'
    index is `%eax' (scaled by a scale 4); disp is `foo'. All other fields are missing. The section register here defaults to `%ds'.

    AT&T: `foo(,1)'; Intel `[foo]'
    This uses the value pointed to by `foo' as a memory operand. Note that base and index are both missing, but there is only one `,'. This is a syntactic exception.

    AT&T: `%gs:foo'; Intel `gs:foo'
    This selects the contents of the variable `foo' with section register section being `%gs'.

    Absolute (as opposed to PC relative) call and jump operands must be prefixed with `*'. If no `*' is specified, will always choose PC relative addressing for jump/call labels.

    Any instruction that has a memory operand must specify its size (byte, word, or long) with an opcode suffix (`b', `w', or `l', respectively).

    Handling of Jump Instructions

    Jump instructions are always optimized to use the smallest possible displacements. This is accomplished by using byte (8-bit) displacement jumps whenever the target is sufficiently close. If a byte displacement is insufficient a long (32-bit) displacement is used. We do not support word (16-bit) displacement jumps (i.e. prefixing the jump instruction with the `addr16' opcode prefix), since the 80386 insists upon masking `%eip' to 16 bits after the word displacement is added.

    Note that the `jcxz', `jecxz', `loop', `loopz', `loope', `loopnz' and `loopne' instructions only come in byte displacements, so that it is possible that use of these instructions ( does not use them) will cause the assembler to print an error message (and generate incorrect code). The AT&T 80386 assembler tries to get around this problem by expanding `jcxz foo' to

             jcxz cx_zero
             jmp cx_nonzero
    cx_zero: jmp foo

    Floating Point

    All 80387 floating point types except packed BCD are supported. (BCD support may be added without much difficulty). These data types are 16-, 32-, and 64- bit integers, and single (32-bit), double (64-bit), and extended (80-bit) precision floating point. Each supported type has an opcode suffix and a constructor associated with it. Opcode suffixes specify operand's data types. Constructors build these data types into memory.

    Register to register operations do not require opcode suffixes, so that `fst %st, %st(1)' is equivalent to `fstl %st, %st(1)'.

    Since the 80387 automatically synchronizes with the 80386 `fwait' instructions are almost never needed (this is not the case for the 80286/80287 and 8086/8087 combinations). Therefore, suppresses the `fwait' instruction whenever it is implicitly selected by one of the `fn...' instructions. For example, `fsave' and `fnsave' are treated identically. In general, all the `fn...' instructions are made equivalent to `f...' instructions. If `fwait' is desired it must be explicitly coded.


    There is some trickery concerning the `mul' and `imul' instructions that deserves mention. The 16-, 32-, and 64-bit expanding multiplies (base opcode `0xf6'; extension 4 for `mul' and 5 for `imul') can be output only in the one operand form. Thus, `imul %ebx, %eax' does not select the expanding multiply; the expanding multiply would clobber the `%edx' register, and this would confuse output. Use `imul %ebx' to get the 64-bit product in `%edx:%eax'.

    We have added a two operand form of `imul' when the first operand is an immediate mode expression and the second operand is a register. This is just a shorthand, so that, multiplying `%eax' by 69, for example, can be done with `imul $69, %eax' rather than `imul $69, %eax, %eax'.

    Z8000 Dependent Features

    The Z8000 supports both members of the Z8000 family: the unsegmented Z8002, with 16 bit addresses, and the segmented Z8001 with 24 bit addresses.

    When the assembler is in unsegmented mode (specified with the unsegm directive), an address will take up one word (16 bit) sized register. When the assembler is in segmented mode (specified with the segm directive), a 24-bit address takes up a long (32 bit) register. See section Assembler Directives for the Z8000, for a list of other Z8000 specific assembler directives.


    has no additional command-line options for the Zilog Z8000 family.


    Special Characters

    `!' is the line comment character.

    You can use `;' instead of a newline to separate statements.

    Register Names

    The Z8000 has sixteen 16 bit registers, numbered 0 to 15. You can refer to different sized groups of registers by register number, with the prefix `r' for 16 bit registers, `rr' for 32 bit registers and `rq' for 64 bit registers. You can also refer to the contents of the first eight (of the sixteen 16 bit registers) by bytes. They are named `rnh' and `rnl'.

    byte registers
    r0l r0h r1h r1l r2h r2l r3h r3l
    r4h r4l r5h r5l r6h r6l r7h r7l
    word registers
    r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r13 r14 r15
    long word registers
    rr0 rr2 rr4 rr6 rr8 rr10 rr12 rr14
    quad word registers
    rq0 rq4 rq8 rq12

    Addressing Modes

    understands the following addressing modes for the Z8000:

    Register direct

    Indirect register

    Direct: the 16 bit or 24 bit address (depending on whether the assembler is in segmented or unsegmented mode) of the operand is in the instruction.

    Indexed: the 16 or 24 bit address is added to the 16 bit register to produce the final address in memory of the operand.

    Base Address: the 16 or 24 bit register is added to the 16 bit sign extended immediate displacement to produce the final address in memory of the operand.

    Base Index: the 16 or 24 bit register rn is added to the sign extended 16 bit index register rm to produce the final address in memory of the operand.

    Immediate data xx.

    Assembler Directives for the Z8000

    The Z8000 port of includes these additional assembler directives, for compatibility with other Z8000 assemblers. As shown, these do not begin with `.' (unlike the ordinary directives).

    Generates code for the segmented Z8001.

    Generates code for the unsegmented Z8002.

    Synonym for .file

    Synonum for .global

    Synonym for .word

    Synonym for .long

    Synonym for .byte

    Assemble a string. sval expects one string literal, delimited by single quotes. It assembles each byte of the string into consecutive addresses. You can use the escape sequence `%xx' (where xx represents a two-digit hexadecimal number) to represent the character whose ASCII value is xx. Use this feature to describe single quote and other characters that may not appear in string literals as themselves. For example, the C statement `char *a = "he said \"it's 50% off\"";' is represented in Z8000 assembly language (shown with the assembler output in hex at the left) as

    @begingroup @let@nonarrowing=@comment

    68652073    sval    'he said %22it%27s 50%25 off%22%00'

    synonym for .section

    synonym for .space

    synonym for .align 1


    For detailed information on the Z8000 machine instruction set, see Z8000 Technical Manual.

    The following table summarizes the opcodes and their arguments: @begingroup @let@nonarrowing=@comment

                rs   16 bit source register
                rd   16 bit destination register
                rbs   8 bit source register
                rbd   8 bit destination register
                rrs   32 bit source register
                rrd   32 bit destination register
                rqs   64 bit source register
                rqd   64 bit destination register
                addr 16/24 bit address
                imm  immediate data
    adc rd,rs               clrb addr               cpsir @rd,@rs,rr,cc
    adcb rbd,rbs            clrb addr(rd)           cpsirb @rd,@rs,rr,cc
    add rd,@rs              clrb rbd                dab rbd
    add rd,addr             com @rd                 dbjnz rbd,disp7
    add rd,addr(rs)         com addr                dec @rd,imm4m1
    add rd,imm16            com addr(rd)            dec addr(rd),imm4m1
    add rd,rs               com rd                  dec addr,imm4m1
    addb rbd,@rs            comb @rd                dec rd,imm4m1
    addb rbd,addr           comb addr               decb @rd,imm4m1
    addb rbd,addr(rs)       comb addr(rd)           decb addr(rd),imm4m1
    addb rbd,imm8           comb rbd                decb addr,imm4m1
    addb rbd,rbs            comflg flags            decb rbd,imm4m1
    addl rrd,@rs            cp @rd,imm16            di i2
    addl rrd,addr           cp addr(rd),imm16       div rrd,@rs
    addl rrd,addr(rs)       cp addr,imm16           div rrd,addr
    addl rrd,imm32          cp rd,@rs               div rrd,addr(rs)
    addl rrd,rrs            cp rd,addr              div rrd,imm16
    and rd,@rs              cp rd,addr(rs)          div rrd,rs
    and rd,addr             cp rd,imm16             divl rqd,@rs
    and rd,addr(rs)         cp rd,rs                divl rqd,addr
    and rd,imm16            cpb @rd,imm8            divl rqd,addr(rs)
    and rd,rs               cpb addr(rd),imm8       divl rqd,imm32
    andb rbd,@rs            cpb addr,imm8           divl rqd,rrs
    andb rbd,addr           cpb rbd,@rs             djnz rd,disp7
    andb rbd,addr(rs)       cpb rbd,addr            ei i2
    andb rbd,imm8           cpb rbd,addr(rs)        ex rd,@rs
    andb rbd,rbs            cpb rbd,imm8            ex rd,addr
    bit @rd,imm4            cpb rbd,rbs             ex rd,addr(rs)
    bit addr(rd),imm4       cpd rd,@rs,rr,cc        ex rd,rs
    bit addr,imm4           cpdb rbd,@rs,rr,cc      exb rbd,@rs
    bit rd,imm4             cpdr rd,@rs,rr,cc       exb rbd,addr
    bit rd,rs               cpdrb rbd,@rs,rr,cc     exb rbd,addr(rs)
    bitb @rd,imm4           cpi rd,@rs,rr,cc        exb rbd,rbs
    bitb addr(rd),imm4      cpib rbd,@rs,rr,cc      ext0e imm8
    bitb addr,imm4          cpir rd,@rs,rr,cc       ext0f imm8
    bitb rbd,imm4           cpirb rbd,@rs,rr,cc     ext8e imm8
    bitb rbd,rs             cpl rrd,@rs             ext8f imm8
    bpt                     cpl rrd,addr            exts rrd
    call @rd                cpl rrd,addr(rs)        extsb rd
    call addr               cpl rrd,imm32           extsl rqd
    call addr(rd)           cpl rrd,rrs             halt
    calr disp12             cpsd @rd,@rs,rr,cc      in rd,@rs
    clr @rd                 cpsdb @rd,@rs,rr,cc     in rd,imm16
    clr addr                cpsdr @rd,@rs,rr,cc     inb rbd,@rs
    clr addr(rd)            cpsdrb @rd,@rs,rr,cc    inb rbd,imm16
    clr rd                  cpsi @rd,@rs,rr,cc      inc @rd,imm4m1
    clrb @rd                cpsib @rd,@rs,rr,cc     inc addr(rd),imm4m1
    inc addr,imm4m1         ldb rbd,rs(rx)          mult rrd,addr(rs)
    inc rd,imm4m1           ldb rd(imm16),rbs       mult rrd,imm16
    incb @rd,imm4m1         ldb rd(rx),rbs          mult rrd,rs
    incb addr(rd),imm4m1    ldctl ctrl,rs           multl rqd,@rs
    incb addr,imm4m1        ldctl rd,ctrl           multl rqd,addr
    incb rbd,imm4m1         ldd @rs,@rd,rr          multl rqd,addr(rs)
    ind @rd,@rs,ra          lddb @rs,@rd,rr         multl rqd,imm32
    indb @rd,@rs,rba        lddr @rs,@rd,rr         multl rqd,rrs
    inib @rd,@rs,ra         lddrb @rs,@rd,rr        neg @rd
    inibr @rd,@rs,ra        ldi @rd,@rs,rr          neg addr
    iret                    ldib @rd,@rs,rr         neg addr(rd)
    jp cc,@rd               ldir @rd,@rs,rr         neg rd
    jp cc,addr              ldirb @rd,@rs,rr        negb @rd
    jp cc,addr(rd)          ldk rd,imm4             negb addr
    jr cc,disp8             ldl @rd,rrs             negb addr(rd)
    ld @rd,imm16            ldl addr(rd),rrs        negb rbd
    ld @rd,rs               ldl addr,rrs            nop
    ld addr(rd),imm16       ldl rd(imm16),rrs       or rd,@rs
    ld addr(rd),rs          ldl rd(rx),rrs          or rd,addr
    ld addr,imm16           ldl rrd,@rs             or rd,addr(rs)
    ld addr,rs              ldl rrd,addr            or rd,imm16
    ld rd(imm16),rs         ldl rrd,addr(rs)        or rd,rs
    ld rd(rx),rs            ldl rrd,imm32           orb rbd,@rs
    ld rd,@rs               ldl rrd,rrs             orb rbd,addr
    ld rd,addr              ldl rrd,rs(imm16)       orb rbd,addr(rs)
    ld rd,addr(rs)          ldl rrd,rs(rx)          orb rbd,imm8
    ld rd,imm16             ldm @rd,rs,n            orb rbd,rbs
    ld rd,rs                ldm addr(rd),rs,n       out @rd,rs
    ld rd,rs(imm16)         ldm addr,rs,n           out imm16,rs
    ld rd,rs(rx)            ldm rd,@rs,n            outb @rd,rbs
    lda rd,addr             ldm rd,addr(rs),n       outb imm16,rbs
    lda rd,addr(rs)         ldm rd,addr,n           outd @rd,@rs,ra
    lda rd,rs(imm16)        ldps @rs                outdb @rd,@rs,rba
    lda rd,rs(rx)           ldps addr               outib @rd,@rs,ra
    ldar rd,disp16          ldps addr(rs)           outibr @rd,@rs,ra
    ldb @rd,imm8            ldr disp16,rs           pop @rd,@rs
    ldb @rd,rbs             ldr rd,disp16           pop addr(rd),@rs
    ldb addr(rd),imm8       ldrb disp16,rbs         pop addr,@rs
    ldb addr(rd),rbs        ldrb rbd,disp16         pop rd,@rs
    ldb addr,imm8           ldrl disp16,rrs         popl @rd,@rs
    ldb addr,rbs            ldrl rrd,disp16         popl addr(rd),@rs
    ldb rbd,@rs             mbit                    popl addr,@rs
    ldb rbd,addr            mreq rd                 popl rrd,@rs
    ldb rbd,addr(rs)        mres                    push @rd,@rs
    ldb rbd,imm8            mset                    push @rd,addr
    ldb rbd,rbs             mult rrd,@rs            push @rd,addr(rs)
    ldb rbd,rs(imm16)       mult rrd,addr           push @rd,imm16
    push @rd,rs             set addr,imm4           subl rrd,imm32
    pushl @rd,@rs           set rd,imm4             subl rrd,rrs
    pushl @rd,addr          set rd,rs               tcc cc,rd
    pushl @rd,addr(rs)      setb @rd,imm4           tccb cc,rbd
    pushl @rd,rrs           setb addr(rd),imm4      test @rd
    res @rd,imm4            setb addr,imm4          test addr
    res addr(rd),imm4       setb rbd,imm4           test addr(rd)
    res addr,imm4           setb rbd,rs             test rd
    res rd,imm4             setflg imm4             testb @rd
    res rd,rs               sinb rbd,imm16          testb addr
    resb @rd,imm4           sinb rd,imm16           testb addr(rd)
    resb addr(rd),imm4      sind @rd,@rs,ra         testb rbd
    resb addr,imm4          sindb @rd,@rs,rba       testl @rd
    resb rbd,imm4           sinib @rd,@rs,ra        testl addr
    resb rbd,rs             sinibr @rd,@rs,ra       testl addr(rd)
    resflg imm4             sla rd,imm8             testl rrd
    ret cc                  slab rbd,imm8           trdb @rd,@rs,rba
    rl rd,imm1or2           slal rrd,imm8           trdrb @rd,@rs,rba
    rlb rbd,imm1or2         sll rd,imm8             trib @rd,@rs,rbr
    rlc rd,imm1or2          sllb rbd,imm8           trirb @rd,@rs,rbr
    rlcb rbd,imm1or2        slll rrd,imm8           trtdrb @ra,@rb,rbr
    rldb rbb,rba            sout imm16,rs           trtib @ra,@rb,rr
    rr rd,imm1or2           soutb imm16,rbs         trtirb @ra,@rb,rbr
    rrb rbd,imm1or2         soutd @rd,@rs,ra        trtrb @ra,@rb,rbr
    rrc rd,imm1or2          soutdb @rd,@rs,rba      tset @rd
    rrcb rbd,imm1or2        soutib @rd,@rs,ra       tset addr
    rrdb rbb,rba            soutibr @rd,@rs,ra      tset addr(rd)
    rsvd36                  sra rd,imm8             tset rd
    rsvd38                  srab rbd,imm8           tsetb @rd
    rsvd78                  sral rrd,imm8           tsetb addr
    rsvd7e                  srl rd,imm8             tsetb addr(rd)
    rsvd9d                  srlb rbd,imm8           tsetb rbd
    rsvd9f                  srll rrd,imm8           xor rd,@rs
    rsvdb9                  sub rd,@rs              xor rd,addr
    rsvdbf                  sub rd,addr             xor rd,addr(rs)
    sbc rd,rs               sub rd,addr(rs)         xor rd,imm16
    sbcb rbd,rbs            sub rd,imm16            xor rd,rs
    sc imm8                 sub rd,rs               xorb rbd,@rs
    sda rd,rs               subb rbd,@rs            xorb rbd,addr
    sdab rbd,rs             subb rbd,addr           xorb rbd,addr(rs)
    sdal rrd,rs             subb rbd,addr(rs)       xorb rbd,imm8
    sdl rd,rs               subb rbd,imm8           xorb rbd,rbs
    sdlb rbd,rs             subb rbd,rbs            xorb rbd,rbs
    sdll rrd,rs             subl rrd,@rs
    set @rd,imm4            subl rrd,addr
    set addr(rd),imm4       subl rrd,addr(rs)

    MIPS Dependent Features

    The MIPS supports the MIPS R2000 and R3000 processors.

    It ignores the -nocpp, -EL, and -EB options.

    Not all traditional MIPS macro instructions are currently supported. Specifically, li.d and li.s are not currently supported.

    When using with MIPS , must be configured using the -with-gnu-as switch (this is the case for Cygnus distributions) or must be invoked with the -mgas option.

    Assembling for a MIPS ECOFF target supports some additional sections besides the usual .text, .data and .bss. The additional sections are .rdata, used for readonly data, .sdata, used for small data, and .sbss, used for small common objects.

    When assembling for ECOFF, the assembler will automatically use the $gp ($28) register when forming the address of a small object. Any object in the .sdata or .sbss sections is considered to be small. For external objects or objects in the .bss section, the -G switch may be used to control the size of objects for which the $gp register will be used; the default value is 8, meaning that a reference to any object eight bytes or smaller will use $gp. Passing -G 0 to will prevent it from using the $gp register. The size of an object in the .bss section is set by the .comm or .lcomm pseudo-op that defines it. The size of an external object may be set using the .extern pseudo-op. For example, `.extern sym,4' declares that the object at sym is 4 bytes in length, whie leaving sym otherwise undefined.

    Using small ECOFF objects requires linker support, and assumes that the $gp register has been correctly initialized (normally done automatically by the startup code). MIPS ECOFF assembly code must avoid modifying the $gp register.

    MIPS ECOFF supports several pseudo-ops used for generating debugging information which are not support by traditional MIPS assemblers. These are .def, .endef, .dim, .file, .scl, .size, .tag, .type, .val, .stabd, .stabn, and .stabs. The debugging information generated by the three .stab pseudo-ops can only be read by GDB, not by traditional MIPS debuggers (this enhancement is required to fully support C++ debugging). These psuedo-ops are primarily used by compilers, not assembly language programmers, and are described elsewhere in the manual.


    If you've contributed to and your name isn't listed here, it is not meant as a slight. We just don't know about it. Send mail to the maintainer, and we'll correct the situation. Currently (June 1993), the maintainer is Ken Raeburn (email address

    Dean Elsner wrote the original GNU assembler for the VAX.(1)

    Jay Fenlason maintained GAS for a while, adding support for gdb-specific debug information and the 68k series machines, most of the preprocessing pass, and extensive changes in messages.c, input-file.c, write.c.

    K. Richard Pixley maintained GAS for a while, adding various enhancements and many bug fixes, including merging support for several processors, breaking GAS up to handle multiple object file format backends (including heavy rewrite, testing, an integration of the coff and b.out backends), adding configuration including heavy testing and verification of cross assemblers and file splits and renaming, converted GAS to strictly ansi C including full prototypes, added support for m680[34]0 & cpu32, considerable work on i960 including a COFF port (including considerable amounts of reverse engineering), a SPARC opcode file rewrite, DECstation, rs6000, and hp300hpux host ports, updated "know" assertions and made them work, much other reorganization, cleanup, and lint.

    Ken Raeburn wrote the high-level BFD interface code to replace most of the code in format-specific I/O modules.

    The original VMS support was contributed by David L. Kashtan. Eric Youngdale has done much work with it since.

    The Intel 80386 machine description was written by Eliot Dresselhaus.

    Minh Tran-Le at IntelliCorp contributed some AIX 386 support.

    The Motorola 88k machine description was contributed by Devon Bowen of Buffalo University and Torbjorn Granlund of the Swedish Institute of Computer Science.

    Keith Knowles at the Open Software Foundation wrote the original MIPS back end (tc-mips.c, tc-mips.h), and contributed Rose format support (which hasn't been merged in yet). Ralph Campbell worked with the MIPS code to support a.out format.

    Support for the Zilog Z8k and Hitachi H8/300 and H8/500 processors (tc-z8k, tc-h8300, tc-h8500), and IEEE 695 object file format (obj-ieee), was written by Steve Chamberlain of Cygnus Support. Steve also modified the COFF back end to use BFD for some low-level operations, for use with the H8/300 and AMD 29k targets.

    John Gilmore built the AMD 29000 support, added .include support, and simplified the configuration of which versions accept which pseudo-ops. He updated the 68k machine description so that Motorola's opcodes always produced fixed-size instructions (e.g. jsr), while synthetic instructions remained shrinkable (jbsr). John fixed many bugs, including true tested cross-compilation support, and one bug in relaxation that took a week and required the apocryphal one-bit fix.

    Ian Lance Taylor of Cygnus Support merged the Motorola and MIT syntaxes for the 68k, completed support for some COFF targets (68k, i386 SVR3, and SCO Unix), and made a few other minor patches.

    Steve Chamberlain made able to generate listings.

    Support for the HP9000/300 was contributed by Hewlett-Packard.

    Support for ELF format files has been worked on by Mark Eichin of Cygnus Support (original, incomplete implementation for SPARC), Pete Hoogenboom and Jeff Law at the University of Utah (HPPA mainly), Michael Meissner of the Open Software Foundation (i386 mainly), and Ken Raeburn of Cygnus Support (sparc, and some initial 64-bit support).

    Several engineers at Cygnus Support have also provided many small bug fixes and configuration enhancements.

    Many others have contributed large or small bugfixes and enhancements. If you've contributed significant work and are not mentioned on this list, and want to be, let us know. Some of the history has been lost; we aren't intentionally leaving anyone out.



  • #
  • #APP
  • #NO_APP


  • -+ option, VAX/VMS
  • --
  • -a
  • -A options, i960
  • -ad
  • -ah
  • -al
  • -an
  • -as
  • -Asparclite
  • -Av6
  • -Av8
  • -b option, i960
  • -D
  • -D, ignored on VAX
  • -d, VAX option
  • -f
  • -h option, VAX/VMS
  • -I path
  • -J, ignored on VAX
  • -K
  • -L
  • -l option, M680x0
  • -m68000 and related options
  • -norelax option, i960
  • -o
  • -R
  • -S, ignored on VAX
  • -t, ignored on VAX
  • -T, ignored on VAX
  • -v
  • -V, redundant on VAX
  • -version
  • -W


  • . (symbol)
  • .o


  • 29K support


  • : (label)


  • version


  • \" (doublequote character)
  • \\ (`\' character)
  • \b (backspace character)
  • \ddd (octal character code)
  • \f (formfeed character)
  • \n (newline character)
  • \r (carriage return character)
  • \t (tab)


  • a.out
  • a.out symbol attributes
  • abort directive
  • absolute section
  • addition, permitted arguments
  • addresses
  • addresses, format of
  • addressing modes, H8/300
  • addressing modes, M680x0
  • addressing modes, Z8000
  • advancing location counter
  • align directive
  • alternate syntax for the 680x0
  • AMD 29K floating point (IEEE)
  • AMD 29K identifiers
  • AMD 29K line comment character
  • AMD 29K line separator
  • AMD 29K machine directives
  • AMD 29K opcodes
  • AMD 29K options (none)
  • AMD 29K protected registers
  • AMD 29K register names
  • AMD 29K special purpose registers
  • AMD 29K statement separator
  • AMD 29K support
  • app-file directive
  • architecture options, i960
  • architecture options, M680x0
  • architectures, SPARC
  • arguments for addition
  • arguments for subtraction
  • arguments in expressions
  • arithmetic functions
  • arithmetic operands
  • ascii directive
  • asciz directive
  • assembler internal logic error
  • assembler, and linker
  • assembly listings, enabling
  • assigning values to symbols
  • attributes, symbol
  • Av7


  • backslash (\\)
  • backspace (\b)
  • bignums
  • binary integers
  • bitfields, not supported on VAX
  • block
  • block directive, AMD 29K
  • branch improvement, M680x0
  • branch improvement, VAX
  • branch recording, i960
  • branch statistics table, i960
  • bss directive, i960
  • bss section
  • bus lock prefixes, i386
  • bval
  • byte directive


  • call instructions, i386
  • callj, i960 pseudo-opcode
  • carriage return (\r)
  • character constants
  • character escape codes
  • character, single
  • characters used in symbols
  • comm directive
  • command line conventions
  • command-line options ignored, VAX
  • comments
  • comments, M680x0
  • comments, removed by preprocessor
  • common directive, SPARC
  • common variable storage
  • compare and jump expansions, i960
  • compare/branch instructions, i960
  • conditional assembly
  • constant, single character
  • constants
  • constants, bignum
  • constants, character
  • constants, converted by preprocessor
  • constants, floating point
  • constants, integer
  • constants, number
  • constants, string
  • continuing statements
  • conversion instructions, i386
  • coprocessor wait, i386
  • cputype directive, AMD 29K
  • current address
  • current address, advancing


  • data and text sections, joining
  • data directive
  • data1 directive, M680x0
  • data2 directive, M680x0
  • debuggers, and symbol order
  • decimal integers
  • deprecated directives
  • descriptor, of a.out symbol
  • dfloat directive, VAX
  • directives and instructions
  • directives, M680x0
  • directives, machine independent
  • directives, Z8000
  • displacement sizing character, VAX
  • dot (symbol)
  • double directive
  • double directive, i386
  • double directive, M680x0
  • double directive, VAX
  • doublequote (\")


  • eight-byte integer
  • eject directive
  • else directive
  • empty expressions
  • endif directive
  • EOF, newline must precede
  • equ directive
  • error messsages
  • escape codes, character
  • even
  • even directive, M680x0
  • expr (internal section)
  • expression arguments
  • expressions
  • expressions, empty
  • expressions, integer
  • extended directive, i960
  • extern directive


  • faster processing (-f)
  • ffloat directive, VAX
  • file directive
  • file directive, AMD 29K
  • file name, logical
  • files, including
  • files, input
  • fill directive
  • filling memory
  • float directive
  • float directive, i386
  • float directive, M680x0
  • float directive, VAX
  • floating point numbers
  • floating point numbers (double)
  • floating point numbers (single)
  • floating point, AMD 29K (IEEE)
  • floating point, H8/300 (IEEE)
  • floating point, i386
  • floating point, i960 (IEEE)
  • floating point, M680x0
  • floating point, SPARC (IEEE)
  • floating point, VAX
  • flonums
  • format of error messages
  • format of warning messages
  • formfeed (\f)
  • functions, in expressions
  • fwait instruction, i386


  • gbr960, i960 postprocessor
  • gfloat directive, VAX
  • global
  • global directive
  • grouping data


  • H8/300 addressing modes
  • H8/300 floating point (IEEE)
  • H8/300 line comment character
  • H8/300 line separator
  • H8/300 machine directives (none)
  • H8/300 opcode summary
  • H8/300 options (none)
  • H8/300 registers
  • H8/300 size suffixes
  • H8/300 support
  • H8/300H, assembling for
  • half directive, SPARC
  • hexadecimal integers
  • hfloat directive, VAX
  • hword directive


  • i386 conversion instructions
  • i386 floating point
  • i386 fwait instruction
  • i386 immediate operands
  • i386 jump optimization
  • i386 jump, call, return
  • i386 jump/call operands
  • i386 memory references
  • i386 mul, imul instructions
  • i386 opcode naming
  • i386 opcode prefixes
  • i386 options (none)
  • i386 register operands
  • i386 registers
  • i386 sections
  • i386 size suffixes
  • i386 source, destination operands
  • i386 support
  • i386 syntax compatibility
  • i80306 support
  • i960 architecture options
  • i960 branch recording
  • i960 callj pseudo-opcode
  • i960 compare and jump expansions
  • i960 compare/branch instructions
  • i960 floating point (IEEE)
  • i960 machine directives
  • i960 opcodes
  • i960 options
  • i960 support
  • ident directive
  • identifiers, AMD 29K
  • if directive
  • ifdef directive
  • ifndef directive
  • ifnotdef directive
  • immediate character, M680x0
  • immediate character, VAX
  • immediate operands, i386
  • imul instruction, i386
  • include directive
  • include directive search path
  • indirect character, VAX
  • infix operators
  • inhibiting interrupts, i386
  • input
  • input file linenumbers
  • instruction set, M680x0
  • instruction summary, H8/300
  • instruction summary, Z8000
  • instructions and directives
  • int directive
  • int directive, H8/300
  • int directive, i386
  • integer expressions
  • integer, 16-byte
  • integer, 8-byte
  • integers
  • integers, 16-bit
  • integers, 32-bit
  • integers, binary
  • integers, decimal
  • integers, hexadecimal
  • integers, octal
  • integers, one byte
  • internal sections
  • invocation summary


  • joining text and data sections
  • jump instructions, i386
  • jump optimization, i386
  • jump/call operands, i386


  • label (:)
  • labels
  • lcomm directive
  • ld
  • leafproc directive, i960
  • length of symbols
  • lflags directive (ignored)
  • line comment character
  • line comment character, AMD 29K
  • line comment character, H8/300
  • line comment character, M680x0
  • line comment character, Z8000
  • line directive
  • line directive, AMD 29K
  • line numbers, in input files
  • line numbers, in warnings/errors
  • line separator character
  • line separator, AMD 29K
  • line separator, H8/300
  • line separator, Z8000
  • lines starting with #
  • linker
  • linker, and assembler
  • list directive
  • listing control, turning off
  • listing control, turning on
  • listing control: new page
  • listing control: paper size
  • listing control: subtitle
  • listing control: title line
  • listings, enabling
  • ln directive
  • local common symbols
  • local labels, retaining in output
  • local symbol names
  • location counter
  • location counter, advancing
  • logical file name
  • logical line number
  • logical line numbers
  • long directive
  • long directive, i386
  • lval


  • M680x0 addressing modes
  • M680x0 architecture options
  • M680x0 branch improvement
  • M680x0 directives
  • M680x0 floating point
  • M680x0 immediate character
  • M680x0 line comment character
  • M680x0 opcodes
  • M680x0 options
  • M680x0 pseudo-opcodes
  • M680x0 size modifiers
  • M680x0 support
  • M680x0 syntax
  • machine directives, AMD 29K
  • machine directives, H8/300 (none)
  • machine directives, i960
  • machine directives, SPARC
  • machine directives, VAX
  • machine independent directives
  • machine instructions (not covered)
  • machine-independent syntax
  • manual, structure and purpose
  • memory references, i386
  • merging text and data sections
  • messages from
  • minus, permitted arguments
  • MIT
  • mnemonics for opcodes, VAX
  • mnemonics, H8/300
  • mnemonics, Z8000
  • Motorola syntax for the 680x0
  • mul instruction, i386
  • multi-line statements


  • name
  • names, symbol
  • naming object file
  • new page, in listings
  • newline (\n)
  • newline, required at file end
  • nolist directive
  • null-terminated strings
  • number constants
  • numbered subsections
  • numbers, 16-bit
  • numeric values


  • object file
  • object file format
  • object file name
  • obsolescent directives
  • octa directive
  • octal character code (\ddd)
  • octal integers
  • opcode mnemonics, VAX
  • opcode naming, i386
  • opcode prefixes, i386
  • opcode suffixes, i386
  • opcode summary, H8/300
  • opcode summary, Z8000
  • opcodes for AMD 29K
  • opcodes, i960
  • opcodes, M680x0
  • operand delimiters, i386
  • operand notation, VAX
  • operands in expressions
  • operator precedence
  • operators, in expressions
  • operators, permitted arguments
  • option summary
  • options for AMD29K (none)
  • options for i386 (none)
  • options for SPARC
  • options for VAX/VMS
  • options, all versions of
  • options, command line
  • options, H8/300 (none)
  • options, i960
  • options, M680x0
  • options, Z8000
  • org directive
  • other attribute, of a.out symbol
  • output file


  • padding the location counter
  • page, in listings
  • paper size, for listings
  • paths for .include
  • patterns, writing in memory
  • plus, permitted arguments
  • precedence of operators
  • precision, floating point
  • prefix operators
  • prefixes, i386
  • preprocessing
  • preprocessing, turning on and off
  • proc directive, SPARC
  • protected registers, AMD 29K
  • pseudo-opcodes, M680x0
  • pseudo-ops for branch, VAX
  • pseudo-ops, machine independent
  • psize directive
  • purpose of GNU


  • quad directive
  • quad directive, i386


  • register names, AMD 29K
  • register names, H8/300
  • register names, VAX
  • register operands, i386
  • registers, i386
  • registers, Z8000
  • relocation
  • relocation example
  • repeat prefixes, i386
  • reserve directive, SPARC
  • return instructions, i386
  • rsect


  • sbttl directive
  • search path for .include
  • sect directive, AMD 29K
  • section override prefixes, i386
  • section-relative addressing
  • sections
  • sections in messages, internal
  • sections, i386
  • seg directive, SPARC
  • segm
  • set directive
  • short directive
  • single character constant
  • single directive
  • single directive, i386
  • sixteen bit integers
  • sixteen byte integer
  • size modifiers, M680x0
  • size prefixes, i386
  • size suffixes, H8/300
  • sizes operands, i386
  • skip directive, M680x0
  • skip directive, SPARC
  • source program
  • source, destination operands; i386
  • space directive
  • SPARC architectures
  • SPARC floating point (IEEE)
  • SPARC machine directives
  • SPARC options
  • SPARC support
  • special characters, M680x0
  • special purpose registers, AMD 29K
  • stabd directive
  • stabn directive
  • stabs directive
  • stabx directives
  • standard sections
  • standard input, as input file
  • statement on multiple lines
  • statement separator character
  • statement separator, AMD 29K
  • statement separator, H8/300
  • statement separator, Z8000
  • statements, structure of
  • stopping the assembly
  • string constants
  • string literals
  • subexpressions
  • subtitles for listings
  • subtraction, permitted arguments
  • summary of options
  • supporting files, including
  • suppressing warnings
  • sval
  • symbol attributes
  • symbol attributes, a.out
  • symbol names
  • symbol names, local
  • symbol names, temporary
  • symbol type
  • symbol value
  • symbol value, setting
  • symbol values, assigning
  • symbol, common
  • symbol, making visible to linker
  • symbolic debuggers, information for
  • symbols
  • symbols with lowercase, VAX/VMS
  • symbols, assigning values to
  • symbols, local common
  • syntax compatibility, i386
  • syntax, M680x0
  • syntax, machine-independent
  • sysproc directive, i960


  • tab (\t)
  • temporary symbol names
  • text and data sections, joining
  • text directive
  • tfloat directive, i386
  • title directive
  • trusted compiler
  • turning preprocessing on and off
  • type of a symbol


  • undefined section
  • unsegm
  • use directive, AMD 29K


  • value of a symbol
  • VAX bitfields not supported
  • VAX branch improvement
  • VAX command-line options ignored
  • VAX displacement sizing character
  • VAX floating point
  • VAX immediate character
  • VAX indirect character
  • VAX machine directives
  • VAX opcode mnemonics
  • VAX operand notation
  • VAX register names
  • VAX support
  • Vax-11 C compatibility
  • VAX/VMS options
  • version of
  • VMS (VAX) options


  • warning messages
  • warnings, suppressing
  • whitespace
  • whitespace, removed by preprocessor
  • wide floating point directives, VAX
  • word directive
  • word directive, H8/300
  • word directive, i386
  • word directive, SPARC
  • writing patterns in memory
  • wval


  • Z800 addressing modes
  • Z8000 directives
  • Z8000 line comment character
  • Z8000 line separator
  • Z8000 opcode summary
  • Z8000 options
  • Z8000 registers
  • Z8000 support
  • zero-terminated strings