Using {No value for ‘AS’}

The GNU Assembler

for the {No value for ‘TARGET’} family

January 1994

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 © 1991, 1992, 1993, 1994 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 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.

H8/300

H8/500

1 Overview

Here is a brief summary of how to invoke {No value for `AS'}. For details, see section Comand-Line Options.

{No value for `AS'} [ -a[dhlns] ] [ -D ] [ -f ] [ --help ]
 [ -I dir ] [ -J ] [ -K ] [ -L ] [ -o objfile ]
 [ -R ] [ --statistics ] [ -v ] [ -version ] [ --version ]
 [ -W ] [ -w ] [ -x ] [ -Z ]
 [ -- | files … ]

-a[dhlns]

Turn on listings, in any of a variety of ways:

-ad

omit debugging directives

-ah

include high-level source

-al

include assembly

-an

omit forms processing

-as

include symbols

You may combine these options; for example, use ‘-aln’ for assembly listing without forms processing. By itself, ‘-a’ defaults to ‘-ahls’—that is, all listings turned on.

-D

Ignored. This option is accepted for script compatibility with calls to other assemblers.

-f

“fast”—skip whitespace and comment preprocessing (assume source is compiler output).

--help

Print a summary of the command line options and exit.

-I dir

Add directory dir to the search list for .include directives.

-J

Don’t warn about signed overflow.

-K

This option is accepted but has no effect on the {No value for ‘TARGET’} family.

-L

Keep (in the symbol table) local symbols, starting with ‘L’.

-o objfile

Name the object-file output from {No value for `AS'} objfile.

-R

Fold the data section into the text section.

--statistics

Print the maximum space (in bytes) and total time (in seconds) used by assembly.

-v

-version

Print the as version.

--version

Print the as version and exit.

-W

Suppress warning messages.

-w

Ignored.

-x

Ignored.

-Z

Generate an object file even after errors.

-- | files …

Standard input, or source files to assemble.

1.1 Structure of this Manual

This manual is intended to describe what you need to know to use GNU {No value for `AS'}. We cover the syntax expected in source files, including notation for symbols, constants, and expressions; the directives that {No value for `AS'} understands; and of course how to invoke {No value for `AS'}.

We also cover special features in the {No value for ‘TARGET’} configuration of {No value for `AS'}, 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. H8/300 For information on the H8/300 machine instruction set, see H8/300 Series Programming Manual (Hitachi ADE–602–025). For the H8/300H, see H8/300H Series Programming Manual (Hitachi).

H8/500 For information on the H8/500 machine instruction set, see H8/500 Series Programming Manual (Hitachi M21T001).

1.2 {No value for ‘AS’}, the GNU Assembler

GNU as is really a family of assemblers. This manual describes {No value for `AS'}, a member of that family which is configured for the {No value for ‘TARGET’} 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.

{No value for `AS'} is primarily intended to assemble the output of the GNU C compiler {No value for `GCC'} for use by the linker {No value for `LD'}. Nevertheless, we’ve tried to make {No value for `AS'} assemble correctly everything that other assemblers for the same machine would assemble.

Unlike older assemblers, {No value for `AS'} 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).

1.3 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 {No value for ‘TARGET’}, {No value for `AS'} is configured to produce {No value for ‘OBJ-NAME’} format object files.

1.4 Command Line

After the program name {No value for `AS'}, 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 {No value for `AS'} to assemble.

Except for ‘--’ any command line argument that begins with a hyphen (‘-’) is an option. Each option changes the behavior of {No value for `AS'}. 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:

{No value for `AS'} -o my-object-file.o mumble.s
{No value for `AS'} -omy-object-file.o mumble.s

1.5 Input Files

We use the phrase source program, abbreviated source, to describe the program input to one run of {No value for `AS'}. 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 {No value for `AS'} 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 {No value for `AS'} 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 value for `AS'} no file names it attempts to read one input file from the {No value for `AS'} standard input, which is normally your terminal. You may have to type <ctl-D> to tell {No value for `AS'} 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, {No value for `AS'} produces 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 {No value for `AS'}.

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 {No value for `AS'} source is itself synthesized from other files. See section .app-file.

1.6 Output (Object) File

Every time you run {No value for `AS'} it produces an output file, which is your assembly language program translated into numbers. This file is the object file. Its default name is a.out. You can give it another name by using the -o option. Conventionally, object file names end with ‘.o’. The default name 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 the a.out format.)

The object file is meant for input to the linker {No value for `LD'}. It contains assembled program code, information to help {No value for `LD'} integrate the assembled program into a runnable file, and (optionally) symbolic information for the debugger.

1.7 Error and Warning Messages

{No value for `AS'} may write warnings and error messages to the standard error file (usually your terminal). This should not happen when a compiler runs {No value for `AS'} automatically. Warnings report an assumption made so that {No value for `AS'} 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) 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) 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.

2 Command-Line Options

This chapter describes command-line options available in all versions of the GNU assembler; @pxref{Machine Dependencies}, for options specific to the {No value for ‘TARGET’}.

If you are invoking {No value for `AS'} 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

emits a listing to standard output with high-level and assembly source.

Usually you do not need to use this ‘-Wa’ mechanism, since many compiler command-line options are automatically passed to the assembler by the compiler. (You can call the GNU compiler driver with the ‘-v’ option to see precisely what options it passes to each compilation pass, including the assembler.)

2.1 Enable Listings: -a[dhlns]

These options enable listing output from the assembler. By itself, ‘-a’ requests high-level, assembly, and symbols listing. You can use other letters 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.

Use the ‘-ad’ option to omit debugging directives 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’.

2.2 -D

This option has no effect whatsoever, but it is accepted to make it more likely that scripts written for other assemblers also work with {No value for `AS'}.

2.3 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 preprocessing on the input file(s) before assembling them. See section Preprocessing.

Warning: if you use ‘-f’ when the files actually need to be preprocessed (if they contain comments, for example), {No value for `AS'} does not work correctly.

2.4 .include search path: -I path

Use this option to add a path to the list of directories {No value for `AS'} searches for files specified in .include directives (see section .include). 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, {No value for `AS'} searches any ‘-I’ directories in the same order as they were specified (left to right) on the command line.

2.5 Difference Tables: -K

On the {No value for ‘TARGET’} 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 {No value for ‘TARGET’} family does not have the addressing limitations that sometimes lead to this alteration on other platforms.

2.6 Include Local Labels: -L

Labels beginning with ‘L’ (upper case only) are called local labels. See section Symbol Names. Normally you do not 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 {No value for `AS'} and {No value for `LD'} discard such labels, so you do not normally debug with them.

This option tells {No value for `AS'} to retain those ‘L…’ symbols in the object file. Usually if you do this you also tell the linker {No value for `LD'} to preserve symbols whose names begin with ‘L’.

By default, a local label is any label beginning with ‘L’, but each target is allowed to redefine the local label prefix.

2.7 Name the Object File: -o

There is always one object file output when you run {No value for `AS'}. By default it has the name ‘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, {No value for `AS'} overwrites any existing file of the same name.

2.8 Join Data and Text Sections: -R

-R tells {No value for `AS'} 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 do not have to cross between text and data section). We refrain from doing this simply for compatibility with older versions of {No value for `AS'}. In future, -R may work this way.

2.9 Display Assembly Statistics: --statistics

Use ‘--statistics’ to display two statistics about the resources used by {No value for `AS'}: the maximum amount of space allocated during the assembly (in bytes), and the total execution time taken for the assembly (in CPU seconds).

2.10 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.

2.11 Suppress Warnings: -W

{No value for `AS'} should never give a warning or error message when assembling compiler output. But programs written by people often cause {No value for `AS'} 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 {No value for `AS'} assembles your file. Errors, which stop the assembly, are still reported.

2.12 Generate Object File in Spite of Errors: -Z

After an error message, {No value for `AS'} normally produces no output. If for some reason you are interested in object file output even after {No value for `AS'} gives an error message on your program, use the ‘-Z’ option. If there are any errors, {No value for `AS'} continues anyways, and writes an object file after a final warning message of the form ‘n errors, m warnings, generating bad object file.’

3 Syntax

This chapter describes the machine-independent syntax allowed in a source file. {No value for `AS'} syntax is similar to what many other assemblers use; it is inspired by the BSD 4.2 assembler.

3.1 Preprocessing

The {No value for `AS'} internal preprocessor:

• adjusts and removes extra whitespace. It leaves one space or tab before the keywords on a line, and turns any other whitespace on the line into a single space.
• removes all comments, replacing them with a single space, or an appropriate number of newlines.
• converts character constants into the appropriate numeric values.

It does not do macro processing, include file handling, or anything else you may get from your C compiler’s preprocessor. You can do include file processing with the .include directive (see section .include). You can use the GNU C compiler driver to get other “CPP” style preprocessing, by giving the input file a ‘.S’ suffix. See Options Controlling the Kind of Output in Using GNU CC.

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

If the first line of an input file is #NO_APP or if you use the ‘-f’ option, whitespace and comments are not removed from the input file. Within an input file, you can ask for whitespace and comment removal in specific portions of the by putting a line that says #APP before the text that may contain whitespace or comments, and putting a line that says #NO_APP after this text. This feature is mainly intend to support asm statements in compilers whose output is otherwise free of comments and whitespace.

3.2 Whitespace

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.

3.3 Comments

There are two ways of rendering comments to {No value for `AS'}. 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 H8/300 ‘;’ for the H8/300 family;

H8/500 ‘!’ for the H8/500 family;

see @ref{Machine Dependencies}.

To be compatible with past assemblers, lines that begin with ‘#’ have a special interpretation. Following the ‘#’ should be an absolute expression (see section Expressions): 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 {No value for `AS'}.

3.4 Symbols

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.

3.5 Statements

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 do not 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 {No value for `AS'} 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 assembles 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, …

3.6 Constants

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.

3.6.1 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.

3.6.1.1 Strings

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 {No value for `AS'} to interpret the second character literally as a backslash (which prevents {No value for `AS'} from recognizing the second \ as an escape character). The complete list of escapes follows.

\b

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

\f

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

\n

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

\r

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

\t

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 \ gives a warning, but assembles 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 {No value for `AS'} has no other interpretation, so {No value for `AS'} 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, do not use an escape sequence.

3.6.1.2 Characters

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. {No value for `AS'} assumes your character code is ASCII: 'A means 65, 'B means 66, and so on.

3.6.2 Number Constants

{No value for `AS'} 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.

3.6.2.1 Integers

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 Operators).

3.6.2.2 Bignums

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.

3.6.2.3 Flonums

A flonum represents a floating point number. The translation is indirect: a decimal floating point number from the text is converted by {No value for `AS'} 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 {No value for `AS'} specialized to that computer.

A flonum is written by writing (in order)

• The digit ‘0’.
• A letter, to tell {No value for `AS'} the rest of the number is a flonum. One of the letters ‘DFPRSX’ (in upper or lower case).
• An optional sign: either ‘+’ or ‘-’.
• An optional integer part: zero or more decimal digits.
• An optional fractional part: ‘.’ followed by zero or more decimal digits.
• An optional exponent, consisting of:
  • An ‘E’ or ‘e’.
  • Optional sign: either ‘+’ or ‘-’.
  • One or more decimal digits.

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

{No value for `AS'} does all processing using integers. Flonums are computed independently of any floating point hardware in the computer running {No value for `AS'}.

4 Sections and Relocation

4.1 Background

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 {No value for `LD'} reads many object files (partial programs) and combines their contents to form a runnable program. When {No value for `AS'} emits an object file, the partial program is assumed to start at address 0. {No value for `LD'} assigns the final addresses for the partial program, so that different partial programs do not overlap. This is actually an oversimplification, but it suffices to explain how {No value for `AS'} uses sections.

{No value for `LD'} 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. For the H8/300 and H8/500, and for the Hitachi SH, {No value for `AS'} pads sections if needed to ensure they end on a word (sixteen bit) boundary.

An object file written by {No value for `AS'} has at least three sections, any of which may be empty. These are named text, data and bss sections.

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 {No value for `LD'} know which data changes when the sections are relocated, and how to change that data, {No value for `AS'} also writes to the object file details of the relocation needed. To perform relocation {No value for `LD'} must know, each time an address in the object file is mentioned:

• Where in the object file is the beginning of this reference to an address?
• How long (in bytes) is this reference?
• Which section does the address refer to? What is the numeric value of

  (address) - (start-address of section)?
  

• Is the reference to an address “Program-Counter relative”?

In fact, every address {No value for `AS'} ever uses is expressed as

(section) + (offset into section)

Further, most expressions {No value for `AS'} computes have this section-relative nature.

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 {No value for `LD'} mixes partial programs, addresses in the absolute section remain unchanged. For example, address {absolute 0} is “relocated” to run-time address 0 by {No value for `LD'}. Although the linker never arranges two partial programs’ data sections with overlapping addresses after linking, by definition their absolute sections must overlap. Address {absolute 239} in one part of a program is always the same address when the program is running as address {absolute 239} in any other part of the 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 is 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. {No value for `LD'} 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 programs’ text sections. Likewise for data and bss sections.

Some sections are manipulated by {No value for `LD'}; others are invented for use of {No value for `AS'} and have no meaning except during assembly.

4.2 {No value for ‘LD’} Sections

{No value for `LD'} deals with just four kinds of sections, summarized below.

These sections hold your program. {No value for `AS'} and {No value for `LD'} 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 {No value for `LD'} must not change when relocating. In this sense we speak of absolute addresses being “unrelocatable”: they do not 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.

4.3 {No value for ‘AS’} Internal Sections

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

ASSEMBLER-INTERNAL-LOGIC-ERROR!

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.

4.4 Sub-Sections

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. {No value for `AS'} 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 go into the object file together with other objects in the same subsection. 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 do not use subsections, everything goes in subsection number zero.

On the H8/300 and H8/500 platforms, each subsection is zero-padded to a word boundary (two bytes). The same is true on the Hitachi SH.

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; {No value for `LD'} and other programs that manipulate object files 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. 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 {No value for `AS'} there is no concept of a subsection location counter. There is no way to directly manipulate a location counter—but the .align directive changes it, and any label definition captures its current value. The location counter of the section where statements are being assembled is said to be the active location counter.

4.5 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, see section .lcomm.

5 Symbols

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: {No value for `AS'} does not place symbols in the object file in the same order they were declared. This may break some debuggers.

5.1 Labels

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.

5.2 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.

5.3 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 @ref{Machine Dependencies}. That character may be followed by any string of digits, letters, dollar signs (unless otherwise noted in @ref{Machine Dependencies}), 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:

L

All local labels begin with ‘L’. Normally both {No value for `AS'} and {No value for `LD'} forget symbols that start with ‘L’. These labels are used for symbols you are never intended to see. If you use the ‘-L’ option then {No value for `AS'} retains these symbols in the object file. If you also instruct {No value for `LD'} to retain these symbols, you may use them in debugging.

digit

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:’.

A

This unusual character is included so you do not 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 L1A1, the 44th 3: is named L3A44.

5.4 The Special Dot Symbol

The special symbol ‘.’ refers to the current address that {No value for `AS'} is assembling into. Thus, the expression ‘melvin: .long .’ defines 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’.

5.5 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, {No value for `AS'} 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.

5.5.1 Value

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 {No value for `LD'} 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 file, and {No value for `LD'} tries to determine its value from other files linked into the same program. 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.

5.5.2 Type

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.

6 Expressions

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

The result of an expression must be an absolute number, or else an offset into a particular section. If an expression is not absolute, and there is not enough information when {No value for `AS'} sees the expression to know its section, a second pass over the source program might be necessary to interpret the expression—but the second pass is currently not implemented. {No value for `AS'} aborts with an error message in this situation.

6.1 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 {No value for `AS'} assumes a value of (absolute) 0. This is compatible with other assemblers.

6.2 Integer Expressions

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

6.2.1 Arguments

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 {No value for `AS'} 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.

6.2.2 Operators

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.

6.2.3 Prefix Operator

{No value for `AS'} has the following prefix operators. They each take one argument, which must be absolute.

-

Negation. Two’s complement negation.

~

Complementation. Bitwise not.

6.2.4 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.

2. Highest Precedence

   *

   Multiplication.

   /

   Division. Truncation is the same as the C operator ‘/’

   %

   Remainder.

   <

   <<

   Shift Left. Same as the C operator ‘<<’.

   >

   >>

   Shift Right. Same as the C operator ‘>>’.

3. Intermediate precedence

   |

   Bitwise Inclusive Or.

   &

   Bitwise And.

   ^

   Bitwise Exclusive Or.

   !

   Bitwise Or Not.

4. Lowest Precedence

   +

   Addition. If either argument is absolute, the result has the section of the other argument. You may not add together arguments from different sections.

   -

   Subtraction. If the right argument is absolute, the result has the section of the left argument. If both arguments are in the same section, the result is absolute. You may not subtract arguments from different sections.

In short, it’s only meaningful to add or subtract the offsets in an address; you can only have a defined section in one of the two arguments.

7 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.

7.1 .abort

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 {No value for `AS'} to quit also. One day .abort will not be supported.

7.2 .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 must have after advancement. For example ‘.align 3’ advances 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.

7.3 .app-file string

.app-file (which may also be spelled ‘.file’) tells {No value for `AS'} 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 {No value for `AS'} programs.

7.4 .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.

7.5 .asciz "string"…

.asciz is just like .ascii, but each string is followed by a zero byte. The “z” in ‘.asciz’ stands for “zero”.

7.6 .byte expressions

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

7.7 .comm symbol , length

.comm declares a named common area in the bss section. Normally {No value for `LD'} reserves memory addresses for it during linking, so no partial program defines the location of the symbol. Use .comm to tell {No value for `LD'} that it must be at least length bytes long. {No value for `LD'} allocates 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.

7.8 .data subsection

.data tells {No value for `AS'} 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.

7.9 .double flonums

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

7.10 .eject

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

7.11 .else

.else is part of the {No value for `AS'} support for conditional assembly; see section .if. It marks the beginning of a section of code to be assembled if the condition for the preceding .if was false.

7.12 .endif

.endif is part of the {No value for `AS'} support for conditional assembly; it marks the end of a block of code that is only assembled conditionally. See section .if.

7.13 .equ symbol, expression

This directive sets the value of symbol to expression. It is synonymous with ‘.set’; see section .set.

7.14 .extern

.extern is accepted in the source program—for compatibility with other assemblers—but it is ignored. {No value for `AS'} treats all undefined symbols as external.

7.15 .file string

.file (which may also be spelled ‘.app-file’) tells {No value for `AS'} 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 {No value for `AS'} programs.

7.16 .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 {No value for `AS'} 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.

7.17 .float flonums

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

7.18 .global symbol, .globl symbol

.global makes the symbol visible to {No value for `LD'}. If you define symbol in your partial program, its value is made available to other partial programs that are linked with it. Otherwise, symbol takes its attributes from a symbol of the same name from another file linked into the same program.

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

7.19 .hword expressions

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

7.20 .ident

This directive is used by some assemblers to place tags in object files. {No value for `AS'} simply accepts the directive for source-file compatibility with such assemblers, but does not actually emit anything for it.

7.21 .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.

7.22 .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.

7.23 .int expressions

Expect zero or more expressions, of any section, separated by commas. For each expression, emit a number that, at run time, is the value of that expression. The byte order and bit size of the number depends on what kind of target the assembly is for.

On the H8/500 and most forms of the H8/300, .int emits 16-bit integers. On the H8/300H and the Hitachi SH, however, .int emits 32-bit integers.

7.24 .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 that at run-time the bytes start off zeroed. Symbol is not declared global (see section .global), so is normally not visible to {No value for `LD'}.

7.25 .lflags

{No value for `AS'} accepts this directive, for compatibility with other assemblers, but ignores it.

7.26 .line line-number

Even though this is a directive associated with the a.out or b.out object-code formats, {No value for `AS'} still recognizes it when producing COFF output, and treats ‘.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.

7.27 .ln line-number

‘.ln’ is a synonym for ‘.line’.

7.28 .list

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.

7.29 .long expressions

.long is the same as ‘.int’, see section .int.

7.30 .nolist

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.

7.31 .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.

7.32 .org new-lc , fill

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, {No value for `AS'} issues a warning, then pretends 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 {No value for `AS'} 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.

7.33 .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 do not use .psize, listings use a default line-count of 60. You may omit the comma and columns specification; the default width is 200 columns.

{No value for `AS'} generates 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.

7.34 .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.

7.35 .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.

7.36 .set symbol, expression

Set the value of symbol to expression. This changes 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 you .set a global symbol, the value stored in the object file is the last value stored into it.

7.37 .short expressions

7.38 .single flonums

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

7.39 .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.

7.40 .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 {No value for `AS'} hash table: they cannot be referenced elsewhere in the source file. Up to five fields are required:

string

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.

type

An absolute expression. The symbol’s type is set to the low 8 bits of this expression. Any bit pattern is permitted, but {No value for `LD'} and debuggers choke on silly bit patterns.

other

An absolute expression. The symbol’s “other” attribute is set to the low 8 bits of this expression.

desc

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

value

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; you 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 is the address of the location counter 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.

7.41 .string "str"

Copy the characters in str to the object file. You may specify more than one string to copy, separated by commas. Unless otherwise specified for a particular machine, the assembler marks the end of each string with a 0 byte. You can use any of the escape sequences described in Strings.

7.42 .text subsection

Tells {No value for `AS'} 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.

7.43 .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.

7.44 .word expressions

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

7.45 Deprecated Directives

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

.abort

.app-file

.line

H8/300

8 H8/300 Dependent Features

8.1 Options

{No value for `AS'} has no additional command-line options for the Hitachi H8/300 family.

8.2 Syntax

8.2.1 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.

8.2.2 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.

8.2.3 Addressing Modes

{No value for ‘AS’} understands the following addressing modes for the H8/300:

rn

Register direct

@rn

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.)

@rn+

Register indirect with post-increment

@-rn

Register indirect with pre-decrement

@aa

@aa:8

@aa:16

@aa:24

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

#xx

#xx:8

#xx:16

#xx:32

Immediate data xx. You may specify the ‘:8’, ‘:16’, or ‘:32’ for clarity, if you wish; but {No value for `AS'} neither requires this nor uses it—the data size required is taken from context.

@@aa

@@aa:8

Memory indirect. You may specify the ‘:8’ for clarity, if you wish; but {No value for `AS'} neither requires this nor uses it.

8.3 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.

8.4 H8/300 Machine Directives

{No value for `AS'} has only one machine-dependent directive for the H8/300:

.h8300h

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.

8.5 Opcodes

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).

{No value for `AS'} implements all the standard H8/300 opcodes. No additional pseudo-instructions are needed on this family.

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. {No value for `AS'} supports these suffixes, but does not require them; since one of the operands is always a register, {No value for `AS'} 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, {No value for `AS'} issues a warning when the suffix and the register size do not match.

H8/500

9 H8/500 Dependent Features

9.1 Options

{No value for `AS'} has no additional command-line options for the Hitachi H8/500 family.

9.2 Syntax

9.2.1 Special Characters

‘!’ is the line comment character.

‘;’ can be used instead of a newline to separate statements.

Since ‘$’ has no special meaning, you may use it in symbol names.

9.2.2 Register Names

You can use the predefined symbols ‘r0’, ‘r1’, ‘r2’, ‘r3’, ‘r4’, ‘r5’, ‘r6’, and ‘r7’ to refer to the H8/500 registers.

The H8/500 also has these control registers:

cp

code pointer

dp

data pointer

bp

base pointer

tp

stack top pointer

ep

extra pointer

sr

status register

ccr

condition code register

All registers are 16 bits long. To represent 32 bit numbers, use two adjacent registers; for distant memory addresses, use one of the segment pointers (cp for the program counter; dp for r0–r3; ep for r4 and r5; and tp for r6 and r7.

9.2.3 Addressing Modes

{No value for ‘AS’} understands the following addressing modes for the H8/500:

Rn

Register direct

@Rn

Register indirect

@(d:8, Rn)

Register indirect with 8 bit signed displacement

@(d:16, Rn)

Register indirect with 16 bit signed displacement

@-Rn

Register indirect with pre-decrement

@Rn+

Register indirect with post-increment

@aa:8

8 bit absolute address

@aa:16

16 bit absolute address

#xx:8

8 bit immediate

#xx:16

16 bit immediate

9.3 Floating Point

The H8/500 family uses IEEE floating-point numbers.

9.4 H8/500 Machine Directives

{No value for `AS'} has no machine-dependent directives for the H8/500. However, on this platform the ‘.int’ and ‘.word’ directives generate 16-bit numbers.

9.5 Opcodes

For detailed information on the H8/500 machine instruction set, see H8/500 Series Programming Manual (Hitachi M21T001).

{No value for `AS'} implements all the standard H8/500 opcodes. No additional pseudo-instructions are needed on this family.

10 Acknowledgements

If you have contributed to {No value for `AS'} 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 (January 1994), the maintainer is Ken Raeburn (email address raeburn@cygnus.com).

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 back ends (including heavy rewrite, testing, an integration of the coff and b.out back ends), 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 and cpu32, did 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 directives. 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 proverbial one-bit fix.

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

Steve Chamberlain made {No value for `AS'} able to generate listings.

Hewlett-Packard contributed support for the HP9000/300.

Jeff Law wrote GAS and BFD support for the native HPPA object format (SOM) along with a fairly extensive HPPA testsuite (for both SOM and ELF object formats). This work was supported by both the Center for Software Science at the University of Utah and Cygnus Support.

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 have 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 are not intentionally leaving anyone out.

Index