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.
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 ... ]
-a[dhlns]
-D
-f
-I path
.include directives
-K
-L
-o objfile
-R
-v
as version
-W
-- | files ...
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.
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).
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.
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
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.
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.
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.
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 TextThe 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.
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.
-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'.
-D
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
.
-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),
.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.
-KOn 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.
-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'.
-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.
-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.
-vYou 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.
-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.
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.
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.
\008 has the value 010, and \009 the value 011.
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.
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.
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:
(address) - (start-address of section)?
In fact, every address ever uses is expressed as
(section) + (offset into section)Further, every expression
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.
These sections hold your program. and treat them as
separate but equal sections. Anything you can say of one section is
true another.
An idealized example of three relocatable sections follows. Memory addresses are on the horizontal axis.
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.
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.
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:
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.
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 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 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
digit
^A
ordinal number
For instance, the first 1: is named L1^A1, the 44th
3: is named L3^A44.
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'.
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.
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.
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.
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.
has the following prefix operators. They each take
one argument, which must be absolute.
-
~
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.
*
/
%
<
<<
>
>>
|
Bitwise Inclusive Or.
&
^
!
+
+ 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.
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.
.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 to
quit also. One day .abort will not be supported.
.align abs-expr , abs-exprPad 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.
.ejectForce a page break at this point, when generating assembly listings.
.else
.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
.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
.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 expressionsThis expects zero or more expressions, and emits a 16 bit number for each.
.ident
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
.ifndef symbol
ifnotdef symbol
.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 expressionsExpect 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 .
.lflags
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'.
.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.
.long expressions
.long is the same as `.int', see section .int expressions.
.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.
.octa bignumsThis 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 , columnsUse 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, expressionThis 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 , fillThis 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:
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
"".
.stabs string , type , other , desc , value
.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 expressionsThis 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.
One day these directives won't work. They are included for compatibility with older assemblers.
@lowersections
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.
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".
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`$6.9') are rendered correctly. Again, rounding is towards zero in the boundary case.
The .float directive produces f format numbers.
The .double directive produces d format numbers.
The Vax version of the assembler supports four directives for generating Vax floating point constants. They are described in the table below.
.dfloat
d format 64-bit floating point constants.
.ffloat
f format 32-bit floating point constants.
.gfloat
g format 64-bit floating point constants.
.hfloat
h format 128-bit floating point constants.
All DEC mnemonics are supported. Beware that case...
instructions have exactly 3 operands. The dispatch table that
follows the case... instruction should be made with
.word statements. This is compatible with all unix
assemblers we know of.
Certain pseudo opcodes are permitted. They are for branch instructions. They expand to the shortest branch instruction that will reach the target. Generally these mnemonics are made by substituting `j' for `b' at the start of a DEC mnemonic. This feature is included both for compatibility and to help compilers. If you don't need this feature, don't use these opcodes. Here are the mnemonics, and the code they can expand into.
jbsb
neq, nequ, eql, eqlu, gtr,
geq, lss, gtru, lequ, vc, vs,
gequ, cc, lssu, cs.
COND may also be one of the bit tests
bs, bc, bss, bcs, bsc, bcc,
bssi, bcci, lbs, lbc.
NOTCOND is the opposite condition to COND.
b d f g h l w.
OPCODE ..., foo ; brb bar ; foo: jmp ... ; bar:
lss leq.
geq gtr.
OPCODE ..., foo ; brb bar ; foo: brw destination ; bar:
OPCODE ..., foo ; brb bar ; foo: jmp destination ; bar:
OPCODE ..., foo ; brb bar ; foo: brw destination ; bar:
OPCODE ..., foo ; brb bar ; foo: jmp destination ; bar:
The immediate character is `$' 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.
Vax bit fields can not be assembled with . Someone
can add the required code if they really need it.
`;' 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).
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):
%%expression---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
The AMD 29K family uses IEEE floating-point numbers.
.block size , fill
In other versions of the GNU assembler, this directive is called `.space'.
.cputype
.file
Warning: in other versions of the GNU assembler,.fileis used for the directive called.app-filein the AMD 29K support.
.line
.sect
.use section name
.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.
has no additional command-line options for the Hitachi
H8/300 family.
`;' 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.
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.
understands the following addressing modes for the H8/300:
rn
@rn
@(d, rn)
@(d:16, rn)
@(d:24, rn)
@rn+
@-rn
@aa@aa:8@aa:16@aa:24aa. (The address size `:24' only makes
sense on the H8/300H.)
#xx
#xx:8
#xx:16
#xx:32
@@aa@@aa:8
The H8/300 family has no hardware floating point, but the .float
directive generates IEEE floating-point numbers for compatibility
with other development tools.
has only one machine-dependent directive for the
H8/300:
.h300h
.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.
Legend:
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.
-ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC
`-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.
-b
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'.
-norelax
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'.
generates IEEE floating-point numbers for the directives
`.float', `.double', `.extended', and `.single'.
.bss symbol, length, align
.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
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
Both arguments are required; index must be between 0 and 31 (inclusive).
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.
callj
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:
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:
a6
is also known as `fp', the Frame Pointer.
or `apc@(register:size:scale)'
or `apc@(digits)@(register:size:scale)'
or `apc@(register:size:scale)@(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'.
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:
a6
is also known as `fp', the Frame Pointer.
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.
.float
Single precision floating point constants.
.double
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.
In order to be compatible with the Sun assembler the 680x0 assembler understands the following directives.
.data1
.data 1 directive.
.data2
.data 2 directive.
.even
.align 1 directive.
.skip
.space directive.
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:
Displacement
+-------------------------------------------------
| 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
jbsr
jra
jXX