The GNU Assembler

The GNU assembler as is primarily intended to assemble the output of the GNU C compiler for use by the linker, so it may be regarded as an internal part of TIGCC package. However, it may be called as a standalone program, and the GNU team tried to make as assemble everything correctly that other assemblers for the same machine would assemble. Any exceptions are documented explicitly. This doesn't mean as always uses the same syntax as other assemblers for the same architecture; for example, there exist several incompatible versions of the MC 68000 assembly language syntax, so the syntax used in the GNU assembler is not exactly the same as in some other assemblers (like the A68k Assembler, which is the most frequently used assembler for the TI-89 and TI-92+, and which is also included in the TIGCC package as a standalone program).

This documentation will cover as features which are applicable to TIGCC. The most frequent use of as is probably as an inline assembler, which allows mixing assembly statements with C code using the asm keyword.

This documentation is not intended as an introduction to programming in assembly language. In a similar vein, you will not find here details about machine architecture: here you can not expect detailed description of the instruction set, standard mnemonics, registers or addressing modes. You may want to consult the Motorola manufacturer's machine architecture manual for such information.

Note: It is possible to use source files for the GNU Assembler together with C source files in TIGCC projects.

Original author: Free Software Foundation, Inc.
Authors of the modifications: Zeljko Juric, Sebastian Reichelt, and Kevin Kofler
See the History section for details and copyright information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

GNU Assembler Command Line

After the program name 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 as to assemble.

Except for -- any command line argument that begins with a hyphen (-) is an option. Each option changes the behavior of 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:

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


Invoking the GNU Assembler from TIGCC

If you are invoking as via tigcc, 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:

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


This passes two options to the assembler: '-alh' (emit a listing to standard output with high-level and assembly source) and '-L' (retain local symbols in the symbol table).

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.)

GNU Assembler Command-Line Options

Here is a brief summary of how to invoke as.

-a[cdhlmns]

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

-ac

omit false conditionals

omit debugging directives

-ah

include high-level source

-al

include assembly

-am

include macro expansions

-an

omit forms processing

-as

include symbols

=file

set the name of the listing file

You may combine these options; for example, use '-aln' for assembly listing without forms processing. The '=file' option, if used, must be the last one. By itself, '-a' defaults to '-ahls'.

--all-relocs

Output all references to non-absolute symbols in the assembled file as relocation items in the object file, even if the form of a reference would permit the assembler to resolve it. This especially affects pc-relative references to symbols defined in the same section, and certain calculations with symbols. For some calculations, this requires special TIGCC-specific support for negative relocation items, which makes object files unusable with older versions of TIGCC. If a calculation cannot be output without being resolved, an error message is generated. This option implies '--keep-locals'. The assembler also outputs a special symbol __ld_all_relocs to tell the linker that there are no implicit dependencies between different locations inside the sections.

-D

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

--defsym sym=value

Define the symbol sym to be value before assembling the input file. value must be an integer constant. As in C, a leading 0x indicates a hexadecimal value, and a leading 0 indicates an octal value.

-f

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

This option should only be used when assembling programs written by a (trusted) compiler. It stops the assembler from doing whitespace and comment preprocessing on the input file(s) before assembling them. See Preprocessing.

Warning: if you use '-f' when the files actually need to be preprocessed (if they contain comments, for example), as does not work correctly.

--gdwarf2

Generate DWARF 2 debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it.

--gstabs

Generate stabs debugging information for each assembler line. This may help debugging assembler code, if the debugger can handle it.

--help

Print a summary of the command line options and exit.

--target-help

Print a summary of all target specific options and exit.

-I dir

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

-J

-K

This option is accepted but has no effect on the 680x0 family.

-L
--keep-locals

Keep (in the symbol table) local symbols. On traditional a.out systems these start with L, but different systems have different local label prefixes. See Including Local Labels.

--listing-lhs-width=number

Set the maximum width, in words, of the output data column for an assembler listing to number.

--listing-lhs-width2=number

Set the maximum width, in words, of the output data column for continuation lines in an assembler listing to number.

--listing-rhs-width=number

Set the maximum width of an input source line, as displayed in a listing, to number bytes.

--listing-cont-lines=number

Set the maximum number of lines printed in a listing for a single line of input to number+1.

-M
--mri

Use MRI compatibility mode. See Assembling in MRI Compatibility Mode.

--MD depfile

Generate a dependency file. This file consists of a single rule suitable for make describing the dependencies of the main source file. The rule is written to the file named in its argument. This feature is used in the automatic updating of makefiles. It is not particulary useful for TIGCC.

-o objfile

Name the object-file output from as objfile. See Naming the Output File.

-R

Fold the data section into the text section. See Joining the Data and Text Sections.

--statistics

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

--strip-local-absolute

Remove local absolute symbols from the outgoing symbol table.

-v
-version

Print the as version.

--version

Print the as version and exit.

-W
--no-warn

Suppress warning messages.

--fatal-warnings

Treat warnings as errors.

--warn

Don't suppress warning messages or treat them as errors.

-w

Ignored.

-x

Ignored.

-Z

Generate an object file even after errors.

-- | files

Standard input, or source files to assemble.

M680x0 Options

The Motorola 680x0 version of as has a few machine dependent options:

-l

You can use the '-l' option to shorten the size of references to undefined symbols. If you do not use the '-l' option, references to undefined symbols are wide enough for a full long (32 bits). (Since as cannot know where these symbols end up, as can only allocate space for the linker to fill in later. Since as does not know how far away these symbols are, it allocates as much space as it can.) If you use this option, the references are only 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 are always less 32 KB away. This option implies '--short-jumps'.

--short-jumps

The '--short-jumps' option shortens the size of branches to undefined symbols. Unlike '-l', other references to undefined symbols are kept wide enough for a full long (32 bits), unless an explicit size is specified. This enables you to optimize a modular program that is smaller than 32 KB as well as possible, while still being able to reference an external BSS or data section (since no jumps can point into these sections). Previously (and in non-TIGCC assemblers), the '-l' option acted like this, but the documentation did not say this.

--register-prefix-optional

Since the compiler as configured for TIGCC 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 C variables and functions named a0 through a7, and so on. The '--register-prefix-optional' option may be used to permit omitting the % even in TIGCC. If this is done, it will generally be impossible to refer to C variables and functions with the same names as register names.

--bitwise-or

Normally the character | is treated as a comment character, which means that it can not be used in expressions. The '--bitwise-or' option turns | into a normal character. In this mode, you must either use C style comments, or start comments with a # character at the beginning of a line.

--base-size-default-16
--base-size-default-32

If you use an addressing mode with a base register without specifying the size, as will normally use the full 32 bit value. For example, the addressing mode %a0@(%d0) is equivalent to %a0@(%d0:l). You may use the '--base-size-default-16' option to tell as to default to using the 16 bit value. In this case, %a0@(%d0) is equivalent to %a0@(%d0:w). You may use the '--base-size-default-32' option to restore the default behaviour.

--disp-size-default-16
--disp-size-default-32

If you use an addressing mode with a displacement, and the value of the displacement is not known, as will normally assume that the value is 32 bits. For example, if the symbol disp has not been defined, as will assemble the addressing mode %a0@(disp,%d0) as though disp is a 32 bit value. You may use the '--disp-size-default-16' option to tell as to instead assume that the displacement is 16 bits. In this case, as will assemble %a0@(disp,%d0) as though disp is a 16 bit value. You may use the '--disp-size-default-32' option to restore the default behaviour.

--pcrel

Always keep branches PC-relative. In the M680x0 architecture all branches are defined as PC-relative. However, on some processors (including the M68000 used in calculators) they are limited to word displacements maximum. When as needs a long branch that is not available, it normally emits an absolute jump instead. This option disables this substitution. When this option is given and no long branches are available, only word branches will be emitted. An error message will be generated if a word branch cannot reach its target. See Branch Improvement.

-m680x0

as can assemble code for several different members of the Motorola 680x0 family. The default in TIGCC is to assemble code for the 68000 microprocessor. The following options may be used to change the default. These options control which instructions and addressing modes are permitted. The members of the 680x0 family are very similar. For detailed information about the differences, see the Motorola manuals. (These options are not very useful for TIGCC.)

-m68000
-m68ec000
-m68hc000
-m68hc001
-m68008
-m68302
-m68306
-m68307
-m68322
-m68356

Assemble for the 68000. '-m68008', '-m68302', and so on are synonyms for '-m68000', since the chips are the same from the point of view of the assembler.

-m68010

Assemble for the 68010.

-m68020
-m68ec020

Assemble for the 68020.

-m68030
-m68ec030

Assemble for the 68030.

-m68040
-m68ec040

Assemble for the 68040.

-m68060
-m68ec060

Assemble for the 68060.

-mcpu32
-m68330
-m68331
-m68332
-m68333
-m68334
-m68336
-m68340
-m68341
-m68349
-m68360

Assemble for the CPU32 family of chips.

-m5200

Assemble for the ColdFire family of chips.

-m68881
-m68882

Assemble 68881 floating point instructions. This is the default for the 68020, 68030, and the CPU32. The 68040 and 68060 always support floating point instructions.

-mno-68881

Do not assemble 68881 floating point instructions. This is the default for 68000 and the 68010. The 68040 and 68060 always support floating point instructions, even if this option is used.

-m68851

Assemble 68851 MMU instructions. This is the default for the 68020, 68030, and 68060. The 68040 accepts a somewhat different set of MMU instructions; '-m68851' and '-m68040' should not be used together.

-mno-68851

Do not assemble 68851 MMU instructions. This is the default for the 68000, 68010, and the CPU32. The 68040 accepts a somewhat different set of MMU instructions.

Enabling Listings

The options starting with '-a' 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 '-ac' option to omit false conditionals from a listing. Any lines which are not assembled because of a false .if (or .ifdef, or any other conditional), or a true .if followed by an .else, will be omitted from the listing.

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'.

Note if the assembler source is coming from the standard input (e.g. because it is being created by gcc and the '-pipe' command line switch is being used) then the listing will not contain any comments or preprocessor directives. This is because the listing code buffers input source lines from stdin only after they have been preprocessed by the assembler. This reduces memory usage and makes the code more efficient.

Configuring Listing Output

The listing feature of the assembler can be enabled via the command line switch '-a' (see Enabling Listings). This feature combines the input source file(s) with a hex dump of the corresponding locations in the output object file, and displays them as a listing file. The format of this listing can be controlled by pseudo ops inside the assembler source (see Enabling Listings for details) and also by the following switches:

--listing-lhs-width=number

Sets the maximum width, in words, of the first line of the hex byte dump. This dump appears on the left hand side of the listing output.

--listing-lhs-width2=number

Sets the maximum width, in words, of any further lines of the hex byte dump for a given input source line. If this value is not specified, it defaults to being the same as the value specified for '--listing-lhs-width'. If neither switch is used the default is to one.

--listing-rhs-width=number

Sets the maximum width, in characters, of the source line that is displayed alongside the hex dump. The default value for this parameter is 100. The source line is displayed on the right hand side of the listing output.

--listing-cont-lines=number

Sets the maximum number of continuation lines of hex dump that will be displayed for a given single line of source input. The default value is 4.

Naming the Object File

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

Whatever the object file is called, as overwrites any existing file of the same name.

Controlling Warnings

as should never give a warning or error message when assembling compiler output. But programs written by people often cause as to give a warning that a particular assumption was made. All such warnings are directed to the standard error file.

If you use the '-W' and '--no-warn' options, no warnings are issued. This only affects the warning messages: it does not change any particular of how as assembles your file. Errors, which stop the assembly, are still reported.

If you use the '--fatal-warnings' option, as considers files that generate warnings to be in error.

You can switch these options off again by specifying '--warn', which causes warnings to be output as usual.

Joining the Data and Text Sections

The '-R' option tells 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 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 as. In the future, '-R' may work this way.

When as is configured for COFF output (which is the case in TIGCC), this option is only useful if you use sections named .text and .data.

Including Local Labels

Labels beginning with L (upper case only) are called local labels. See 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 as and ld discard such labels, so you do not normally debug with them.

The '-L' option tells as to retain those L... symbols in the object file. Usually, if you do this, you also tell the linker 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.

For some targets, the output of as is different in some ways from the output of some existing assembler. The '--traditional-format' switch requests as to use the traditional format instead.

For example, it disables the exception frame optimizations which as normally does by default on gcc output.

Assembling in MRI Compatibility Mode

The '-M' or '--mri' option selects MRI compatibility mode. This changes the syntax and pseudo-op handling of as to make it compatible with the ASM68K assembler from Microtec Research. The exact nature of the MRI syntax will not be documented here; see the MRI manuals for more information. Note in particular that the handling of macros and macro arguments is somewhat different. The purpose of this option is to permit assembling existing MRI assembler code using as.

The MRI compatibility is not complete. Certain operations of the MRI assembler depend upon its object file format, and can not be supported using other object file formats. Supporting these would require enhancing each object file format individually. These are:

• global symbols in common section The m68k MRI assembler supports common sections which are merged by the linker. Other object file formats do not support this. as handles common sections by treating them as a single common symbol. It permits local symbols to be defined within a common section, but it can not support global symbols, since it has no way to describe them.

• complex relocations The MRI assemblers support relocations against a negated section address, and relocations which combine the start addresses of two or more sections. These are not support by other object file formats.

• END pseudo-op specifying start address The MRI END pseudo-op permits the specification of a start address. This is not supported by other object file formats. The start address may instead be specified using the '-e' option to the linker, or in a linker script.

• IDNT, .ident and NAME pseudo-ops The MRI IDNT, .ident and NAME pseudo-ops assign a module name to the output file. This is not supported by other object file formats.

• ORG pseudo-op The m68k MRI ORG pseudo-op begins an absolute section at a given address. This differs from the usual as .org pseudo-op, which changes the location within the current section. Absolute sections are not supported by other object file formats. The address of a section may be assigned within a linker script.

There are some other features of the MRI assembler which are not supported by as, typically either because they are difficult or because they seem of little consequence. Some of these may be supported in future releases.

• EBCDIC strings EBCDIC strings are not supported.

• packed binary coded decimal Packed binary coded decimal is not supported. This means that the DC.P and DCB.P pseudo-ops are not supported.

• FEQU pseudo-op The m68k FEQU pseudo-op is not supported.

• NOOBJ pseudo-op The m68k NOOBJ pseudo-op is not supported.

• OPT branch control options The m68k OPT branch control options - B, BRS, BRB, BRL, and BRW - are ignored. as automatically relaxes all branches, whether forward or backward, to an appropriate size, so these options serve no purpose.

• OPT list control options The following m68k OPT list control options are ignored: C, CEX, CL, CRE, E, G, I, M, MEX, MC, MD, X.

• other OPT options The following m68k OPT options are ignored: NEST, O, OLD, OP, P, PCO, PCR, PCS, R.

• OPT D option is default The m68k OPT D option is the default, unlike the MRI assembler. OPT NOD may be used to turn it off.

• XREF pseudo-op. The m68k XREF pseudo-op is ignored.

• .debug pseudo-op The i960 .debug pseudo-op is not supported.

• .extended pseudo-op The i960 .extended pseudo-op is not supported.

• .list pseudo-op. The various options of the i960 .list pseudo-op are not supported.

• .optimize pseudo-op The i960 .optimize pseudo-op is not supported.

• .output pseudo-op The i960 .output pseudo-op is not supported.

• .setreal pseudo-op The i960 .setreal pseudo-op is not supported.

GNU Assembler Input and Output

Input Files

We use the phrase source program, abbreviated source, to describe the program input to one run of 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 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 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 as no file names it attempts to read one input file from the as standard input, which is normally your terminal. You may have to type Ctrl-D to tell 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, as produces a small, empty object file.

Assembler File Names 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 Error and Warning Messages.

Physical files are those files named in the command line given to 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 as source is itself synthesized from other files. as understands the # directives emitted by the gcc preprocessor. See also .file.

Output (Object) File

Every time you run 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 ld. It contains assembled program code, information to help ld integrate the assembled program into a runnable file, and (optionally) symbolic information for the debugger.

Assembler Error and Warning Messages

as may write warnings and error messages to the standard error file (usually your terminal). This should not happen when a compiler runs as automatically. Warnings report an assumption made so that 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 .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 .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.

GNU Assembler Syntax

The machine-independent syntax used by the GNU assembler is similar to what many other assemblers use; it is inspired by the BSD 4.2 assembler. Motorola-specific features are explained at the end of this chapter.

Preprocessing

The 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 .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, gcc.info, 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.

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 Character Constants), any whitespace means the same as exactly one space.

There are two ways of rendering comments to 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 | on the 680x0 family of processors.

To be compatible with past assemblers, lines that begin with # have a special interpretation. Following the # should be an absolute expression (see Expressions): the logical line number of the next line. Then a string (see 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 as.

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 Symbols. 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. 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 Labels. label: .directive followed by something another_label: # This is an empty statement. instruction operand_1, operand_2, ...  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.  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. 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 as to interpret the second character literally as a backslash (which prevents 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. \x hex-digits... A hex character code. All trailing hex digits are combined. Either upper or lower case x works. \\ 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 as has no other interpretation, so 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. 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. as assumes your character code is ASCII: 'A means 65, 'B means 66, and so on. Number Constants 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. 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 Prefix Operators). 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. Flonums A flonum represents a floating point number. The translation is indirect: a decimal floating point number from the text is converted by 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 as specialized to that computer. The version of as used by TIGCC does not use TI's SMAP II BCD format; it emits standard IEEE floating point numbers. It would be pointless to implement the correct behavior, since the appropriate numbers are easy to write, and converting between base 2 and 10 can decrease precision. A flonum is written by writing (in order) • The digit 0. • A letter, to tell as the rest of the number is a flonum. • 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. as does all processing using integers. Flonums are computed independently of any floating point hardware in the computer running as. Motorola 680x0 Dependent Features In this configuration of as (which 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 C variables and functions named 'a0' through 'a7', and so on. Two different syntaxes for the Motorola 680x0 are widely used. The first one was developed at MIT. The second one is the standard Motorola syntax for this chip, and it differs from the MIT syntax. as can accept Motorola syntax for operands, even if MIT syntax is used for other operands in the same instruction. The two kinds of syntax are fully compatible. MIT Syntax The MIT syntax uses instructions names and syntax compatible with the Sun assembler. Intervening periods are ignored; for example, movl is equivalent to mov.l. In the following table, apc stands for any of the address registers (%a0 through %a7), the program counter (%pc), the zero-address relative to the program counter (%zpc), a suppressed address register (%za0 through %za7), or it may be omitted entirely. The use of size means one of w or l, and it may be omitted, along with the leading colon, unless a scale is also specified. The use of scale means one of 1, 2, 4, or 8, and it may always be omitted along with the leading colon. The following addressing modes are understood (note that some of them are valid only on 68020 or later processors, not on the ordinary 68000 used in TI calculators): Immediate #number Data Register %d0 through %d7 Address Register %a0 through %a7 %a7 is also known as %sp, i.e. the Stack Pointer. %a6 is also known as %fp, the Frame Pointer. Address Register Indirect %a0@ through %a7@ Address Register Postincrement %a0@+ through %a7@+ Address Register Predecrement %a0@- through %a7@- Indirect Plus Offset apc@(number) Index apc@(number,register:size:scale) The number may be omitted. Postindex apc@(number)@(onumber,register:size:scale) The onumber or the register, but not both, may be omitted. Preindex apc@(number,register:size:scale)@(onumber) The number may be omitted. Omitting the register produces the Postindex addressing mode. Absolute symbol, or digits, optionally followed by :b, :w, or :l. Motorola Syntax In the following table, apc stands for any of the address registers (%a0 through %a7), the program counter (%pc), the zero-address relative to the program counter (%zpc), or a suppressed address register (%za0 through %za7). The use of size means one of w or l, and it may always be omitted along with the leading dot. The use of scale means one of 1, 2, 4, or 8, and it may always be omitted along with the leading asterisk. The following additional addressing modes are understood (note that some of them are valid only on 68020 or later processors, not on the ordinary 68000 used in TI calculators): Address Register Indirect (%a0) through (%a7) %a7 is also known as %sp, i.e. the Stack Pointer. %a6 is also known as %fp, the Frame Pointer. Address Register Postincrement (%a0)+ through (%a7)+ Address Register Predecrement -(%a0) through -(%a7) Indirect Plus Offset number(%a0) through number(%a7), or number(%pc). The number may also appear within the parentheses, as in (number,%a0). When used with the pc, the number may be omitted (with an address register, omitting the number produces Address Register Indirect mode). Index number(apc,register.size*scale) The number may be omitted, or it may appear within the parentheses. The apc may be omitted. The register and the apc may appear in either order. If both apc and register are address registers, and the size and scale are omitted, then the first register is taken as the base register, and the second as the index register. Postindex ([number,apc],register.size*scale,onumber) The onumber, or the register, or both, may be omitted. Either the number or the apc may be omitted, but not both. Preindex ([number,apc,register.size*scale],onumber) The number, or the apc, or the register, or any two of them, may be omitted. The onumber may be omitted. The register and the apc may appear in either order. If both apc and register are address registers, and the size and scale are omitted, then the first register is taken as the base register, and the second as the index register. Branch Improvement Certain pseudo opcodes are permitted for branch instructions. They expand to the shortest branch instruction that 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 for the 68000 processor; the 68020 has some more possibilites. Note that the 68000 LONG operations are always absolute and require runtime relocation. They will not be used if the '--pcrel' option is given. A (*) flags cases that are more fully described after the table:  Displacement Pseudo-Op BYTE WORD LONG jbsr bsr.s bsr jsr jra bra.s bra jmp jXX (*) bXX.s bXX bNX; jmp dbXX (*) dbXX dbXX dbXX; bra; jmp XX: condition NX: negative of condition XX jbsr jra These are the simplest jump pseudo-operations; they always map to one particular machine instruction, depending on the displacement to the branch target. This instruction will be a byte or word branch if that is sufficient. Otherwise, if the '--pcrel' option is not given, an absolute long jump will be emitted. If the '--pcrel' option is given and a word branch cannot reach the target, an error message is generated. In addition to standard branch operands, as allows these pseudo-operations to have all operands that are allowed for jsr and jmp, substituting these instructions if the operand given is not valid for a branch instruction. jXX Here, jXX stands for an entire family of pseudo-operations, where XX is a conditional branch or condition-code test. The full list of pseudo-ops in this family is:  jhi jls jcc jcs jne jeq jvc jvs jpl jmi jge jlt jgt jle Usually, each of these pseudo-operations expands to a single branch instruction. However, if a word branch is not sufficient and the '--pcrel' option is not given, as issues a longer code fragment in terms of NX, the opposite condition to XX. For example, under these conditions:  jXX foo  gives  bNXs oof jmp foo oof:  dbXX The full family of pseudo-operations covered here is:  dbhi dbls dbcc dbcs dbne dbeq dbvc dbvs dbpl dbmi dbge dblt dbgt dble dbf dbra dbt Motorola dbXX instructions allow word displacements only. When a word displacement is sufficient, each of these pseudo-operations expands to the corresponding Motorola instruction. When a word displacement is not sufficient and long branches are available, when the source reads dbXX foo, as emits  dbXX oo1 bra.s oo2 oo1: jmp foo oo2:  Special Characters The immediate character is # for Sun compatibility. The line-comment character is | (unless the '--bitwise-or' option is used). If a # appears at the beginning of a line, it is treated as a comment unless it looks like # line file, in which case it is treated normally. Sections and Relocation Roughly, a section is a range of addresses, with no gaps; all data "in" those addresses is treated the same for some particular purpose. For example there may be a "read only" section. The linker ld reads many object files (partial programs) and combines their contents to form a runnable program. When as emits an object file, the partial program is assumed to start at address 0. 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 as uses sections. 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. An object file written by as has at least three sections, any of which may be empty. These are named text, data and bss sections. as can also generate whatever other named sections you specify using the .section directive. If you do not use any directives that place output in the .text or .data sections, these sections still exist, but are 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 ld know which data changes when the sections are relocated, and how to change that data, as also writes to the object file details of the relocation needed. To perform relocation 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 as ever uses is expressed as (section) + (offset into section) Further, most expressions 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 ld mixes partial programs, addresses in the absolute section remain unchanged. For example, address {absolute 0} is "relocated" to run-time address 0 by 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. 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 ld; others are invented for use of as and have no meaning except during assembly. Linker Sections ld deals with just four kinds of sections, summarized below. These sections hold your program. as and ld treat them as separate but equal sections. Anything you can say of one section is true of another. When the program is running, however, it is customary for the text section to be unalterable. The text section is often shared among processes: it contains instructions, constants and the like. The data section of a running program is usually alterable: for example, C variables would be stored in the data section. bss section This section contains zeroed bytes when your program begins running. It is used to hold uninitialized 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 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.  + - --+ - -+--+ partial program # 1: |ttttt|dddd|00| + - --+ - -+--+ text data bss seg. seg. seg. + - + - + - + partial program # 2: |TTT|DDD|000| + - + - + - + +--+ - + - --+--+ - -+ - + - --+~~ linked program: | |TTT|ttttt| |dddd|DDD|00000| +--+ - + - --+--+ - -+ - + - --+~~ addresses: 0 ...  Assembler Internal Sections These sections are meant only for the internal use of 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 as warning messages, so it might be helpful to have an idea of their meanings to 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. 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. 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. 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; 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. You can also use an extra subsection argument with arbitrarily named sections: .section name, expression. Expression should be an absolute expression. (see 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 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. 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. The .lcomm pseudo-op defines a symbol in the bss section. The .comm pseudo-op may be used to declare a common symbol, which is another form of uninitialized symbol. You may switch into the .bss section and define symbols as usual (see .section). You may only assemble zero values into the section. Typically the section will only contain symbol definitions and .skip directives. Assembler 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. Note that as does not place symbols in the object file in the same order they were declared. This may break some debuggers. 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. 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 Expressions). This is equivalent to using the .set directive. Symbol Names Symbol names begin with a letter or with ., _, or . That character may be followed by any string of digits, letters, dollar signs, 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. They create symbols which are guaranteed to be unique over the entire scope of the input source code and which can be referred to by a simple notation. To define a local symbol, write a label of the form N: (where N represents any positive integer). To refer to the most recent previous definition of that symbol write Nb, using the same number as when you defined the label. To refer to the next definition of a local label, write Nf - The b stands for "backwards" and the f stands for "forwards".

There is no restriction on how you can use these labels, and you can reuse them as well. So it is possible to repeatedly define the same local label (using the same number N), although you can only refer to the most recently defined local label of that number (for a backwards reference) or the next definition of a specific local label for a forward reference. It is also worth noting that the first 10 local labels (0:...9:) are implemented in a slightly more efficient manner than the others.

Here is an example:

1:        jra 1f
2:        jra 1b
1:        jra 2f
2:        jra 1b


Which is the equivalent of:

label_1:  jra label_3
label_2:  jra label_1
label_3:  jra label_4
label_4:  jra label_3


Local symbol names are only a notational 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. The names are constructed using these parts:

L

All local labels begin with L. Normally both as and 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, as retains these symbols in the object file. If you also instruct ld to retain these symbols, you may use them in debugging.

N

This is the number that was used in the local label definition. So if the label is written 55:, the number is 55.

\002

This unusual character is included so you do not accidentally invent a symbol of the same name.

ordinal number

This is a serial number to keep the labels distinct. The first definition of 0: gets the number 1. The 15th definition of 0: gets the number 15, and so on. Likewise the first definition of 1: gets the number 1 and its 15th defintion gets 15 as well.

Dollar Local Labels

as also supports an even more local form of local labels called dollar labels. These labels go out of scope (i.e. they become undefined) as soon as a non-local label is defined. Thus they remain valid for only a small region of the input source code. Normal local labels, by contrast, remain in scope for the entire file, or until they are redefined by another occurrence of the same local label.

Dollar labels are defined in exactly the same way as ordinary local labels, except that instead of being terminated by a colon, they are terminated by a dollar sign (for example, 55\$).

They can also be distinguished from ordinary local labels by their transformed name which uses ASCII character \001 (control-A) as the magic character to distinguish them from ordinary labels.

The Special Dot Symbol

The special symbol . refers to the current address that 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.

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, 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.

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 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 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.

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.

Symbol Attributes for COFF

The COFF format supports a multitude of auxiliary symbol attributes; like the primary symbol attributes, they are set between .def and .endef directives.

Primary Attributes

The symbol name is set with .def; the value and type, respectively, with .val and .type.

Auxiliary Attributes

The as directives .dim, .line, .scl, .size, and .tag can generate auxiliary symbol table information for COFF.

Assembler 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 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. as aborts with an error message in this situation.

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 as assumes a value of (absolute) 0. This is compatible with other assemblers.

Integer Expressions

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

Arguments

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. In principle, a number can be a flonum or bignum. In this case, you are warned that only the low order 32 bits are used, and 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.

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.

Prefix Operators

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

-

Negation. Two's complement negation.

~

Complementation. Bitwise NOT.

Infix Operators

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

1. Highest Precedence

*

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 >>.

2. Intermediate precedence

|

Bitwise Inclusive OR.

&

Bitwise AND.

^

Bitwise Exclusive OR.

!

Bitwise OR NOT.

3. Low 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.

==

Is Equal To.

<>

Is Not Equal To.

<

Is Less Than.

>

Is Greater Than.

>=

Is Greater Than Or Equal To.

<=

Is Less Than Or Equal To.

The comparison operators can be used as infix operators. A true results has a value of -1 whereas a false result has a value of 0. Note, these operators perform signed comparisons.

4. &&

Logical AND.

||

Logical OR.

These two logical operations can be used to combine the results of sub expressions. Note, unlike the comparison operators a true result returns a value of 1. Also note that the logical OR operator has a slightly lower precedence than logical AND.

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.

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 mostly 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 to tell as to quit also. One day .abort will not be supported.

.ABORT is accepted as an alternate spelling of .abort.

.align

Syntax: .align alignment[, [fill][, max]]

Pad the location counter (in the current subsection) to a particular storage boundary. alignment (which must be absolute) is the alignment required, as described below.

fill (also absolute) gives the fill value to be stored in the padding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally zero. However, on some systems, if the section is marked as containing code and the fill value is omitted, the space is filled with no-op instructions (I didn't checked whether this is the case in TIGCC).

max is also absolute, and is also optional. If it is present, it is the maximum number of bytes that should be skipped by this alignment directive. If doing the alignment would require skipping more bytes than the specified maximum, then the alignment is not done at all. You can omit the fill value (the second argument) entirely by simply using two commas after the required alignment; this can be useful if you want the alignment to be filled with no-op instructions when appropriate.

The way the required alignment is specified varies from system to system. For the a29k, hppa, m68k, m88k, w65, sparc, Xtensa, and Renesas / SuperH SH, and i386 using ELF format, the first expression is the alignment request in bytes. For example .align 8 advances the location counter until it is a multiple of 8. If the location counter is already a multiple of 8, no change is needed.

For other systems, including the i386 using a.out format, and the arm and strongarm, it 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.

This inconsistency is due to the different behaviors of the various native assemblers for these systems which as must emulate. as also provides .balign and .p2align directives, which have a consistent behavior across all architectures (but are specific to as).

.ascii

Syntax: .ascii strings

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

.asciz

Syntax: .asciz strings

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

.balign[wl]

Syntax: .balign[wl] alignment[, [fill][, max]]

Pad the location counter (in the current subsection) to a particular storage boundary. alignment (which must be absolute) is the alignment request in bytes. For example .balign 8 advances the location counter until it is a multiple of 8. If the location counter is already a multiple of 8, no change is needed.

fill (also absolute) gives the fill value to be stored in the padding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally zero. However, on some systems, if the section is marked as containing code and the fill value is omitted, the space is filled with no-op instructions (I didn't checked whether this is the case in TIGCC).

max is also absolute, and is also optional. If it is present, it is the maximum number of bytes that should be skipped by this alignment directive. If doing the alignment would require skipping more bytes than the specified maximum, then the alignment is not done at all. You can omit the fill value (the second argument) entirely by simply using two commas after the required alignment; this can be useful if you want the alignment to be filled with no-op instructions when appropriate.

The .balignw and .balignl directives are variants of the .balign directive. The .balignw directive treats the fill pattern as a two byte word value. The .balignl directives treats the fill pattern as a four byte longword value. For example, .balignw 4,0x368d will align to a multiple of 4. If it skips two bytes, they will be filled in with the value 0x368d (the exact placement of the bytes depends upon the endianness of the processor). If it skips 1 or 3 bytes, the fill value is undefined.

.byte

Syntax: .byte expressions

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

.comm

Syntax: .comm symbol, length

.comm declares a common symbol named symbol. When linking, a common symbol in one object file may be merged with a defined or common symbol of the same name in another object file. If ld does not see a definition for the symbol - just one or more common symbols - then it will allocate length bytes of uninitialized memory. length must be an absolute expression. If ld sees multiple common symbols with the same name, and they do not all have the same size, it will allocate space using the largest size.

.data

Syntax: .data [subsection]

.data tells 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.

In order to be compatible with the Sun assembler, the 680x0 assembler understands the directives .data1 and .data2 as alternatives to .data 1 and .data 2.

.def

Syntax: .def name

Begin defining debugging information for a symbol name; the definition extends until the .endef directive is encountered.

.dim

This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside .def/.endef pairs.

.double

Syntax: .double flonums

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

.eject

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

.else

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

.end

.end marks the end of the assembly file. as does not process anything in the file past the .end directive.

.elseif

.elseif is part of the as support for conditional assembly; see .if. It is shorthand for beginning a new .if block that would otherwise fill the entire .else section.

.endef

This directive flags the end of a symbol definition begun with .def.

.endfunc

.endfunc marks the end of a function specified with .func.

.endif

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

.endm

.endm terminates a .macro directive.

.endr

.endr can terminate either an .irp or an .irpc directive.

.equ

Syntax: .equ symbol, expression

This directive sets the value of symbol to expression. It is synonymous with .set.

.equiv

Syntax: .equiv symbol, expression

The .equiv directive is like .equ and .set, except that the assembler will signal an error if symbol is already defined. Note a symbol which has been referenced but not actually defined is considered to be undefined.

Except for the contents of the error message, this is roughly equivalent to

.ifdef SYM
.err
.endif
.equ SYM,VAL


.err

If as assembles a .err directive, it will print an error message and, unless the '-Z' option was used, it will not generate an object file. This can be used to signal error an conditionally compiled code.

.even

This directive is a special case of the .align directive; it aligns the output to an even byte boundary. It is 680x0-specific; introduced in order to be compatible with the Sun assembler.

.exitm

Exit early from the current macro definition. See .macro.

.extern

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

.fail

Generates an error or a warning. If the value of the expression is 500 or more, as will print a warning message. If the value is less than 500, as will print an error message. The message will include the value of expression. This can occasionally be useful inside complex nested macros or conditional assembly.

.file

Syntax: .file string

.file tells 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 "".

.fill

Syntax: .fill repeat[, size[, value]]

repeat, 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 as is assembling for (big-endian for 680x0). 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

Syntax: .float flonums

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

.func

Syntax: .func name[, label]

.func emits debugging information to denote function name, and is ignored unless the file is assembled with debugging enabled. Only '--gstabs' is currently supported. label is the entry point of the function, and if omitted, name prepended with the leading character is used (no leading character in TIGCC). All functions are currently defined to have void return type. The function must be terminated with .endfunc.

.global

Syntax: .global symbol

.global makes the symbol visible to 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. .xdef is also accepted as a synonym for .global.

.hword

Syntax: .hword expressions

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

On this target, this directive is a synonym for both .short and .word.

.ident

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

.if

Syntax: .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; optionally, you may include code for the alternative condition, flagged by .else. If you have several conditions to check, .elseif may be used to avoid nesting blocks if/else within each subsequent .else block.

The following variants of .if are also supported:

.ifdef symbol

Assembles the following section of code if the specified symbol has been defined. Note a symbol which has been referenced but not yet defined is considered to be undefined.

.ifc string1, string2

Assembles the following section of code if the two strings are the same. The strings may be optionally quoted with single quotes. If they are not quoted, the first string stops at the first comma, and the second string stops at the end of the line. Strings which contain whitespace should be quoted. The string comparison is case sensitive.

.ifeq absolute expression

Assembles the following section of code if the argument is zero.

.ifeqs string1, string2

Another form of .ifc. The strings must be quoted using double quotes.

.ifge absolute expression

Assembles the following section of code if the argument is greater than or equal to zero.

.ifgt absolute expression

Assembles the following section of code if the argument is greater than zero.

.ifle absolute expression

Assembles the following section of code if the argument is less than or equal to zero.

.iflt absolute expression

Assembles the following section of code if the argument is less than zero.

.ifnc string1, string2.

Like .ifc, but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same.

.ifndef symbol
.ifnotdef symbol

Assembles the following section of code if the specified symbol has not been defined. Both spelling variants are equivalent. Note a symbol which has been referenced but not yet defined is considered to be undefined.

.ifne absolute expression

Assembles the following section of code if the argument is not equal to zero (in other words, this is equivalent to .if).

.ifnes string1, string2

Like .ifeqs, but the sense of the test is reversed: this assembles the following section of code if the two strings are not the same.

.include

Syntax: .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 Command-Line Options). Quotation marks are required around file.

.incbin

Syntax: .incbin "file"[, skip[, count]]

The incbin directive includes file verbatim at the current location. You can control the search paths used with the '-I' command-line option (see Command-Line Options). Quotation marks are required around file.

The skip argument skips a number of bytes from the start of the file. The count argument indicates the maximum number of bytes to read. Note that the data is not aligned in any way, so it is the user's responsibility to make sure that proper alignment is provided both before and after the incbin directive.

.int

Syntax: .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 (big endian 32-bit for MC 68000; be aware that in TIGCC, C language int variables occupy 16 bits by default).

.irp

Syntax: .irp symbol[, value[, value][, ...]]

Evaluate a sequence of statements assigning different values to symbol. The sequence of statements starts at the .irp directive, and is terminated by an .endr directive. For each value, symbol is set to value, and the sequence of statements is assembled. If no value is listed, the sequence of statements is assembled once, with symbol set to the null string. To refer to symbol within the sequence of statements, use \symbol.

For example, assembling

        .irp   param,1,2,3
move.l %d\param,-(%sp)
.endr


is equivalent to assembling

        move    %d1,-(%sp)
move.l %d2,-(%sp)
move.l %d3,-(%sp)


.irpc

Syntax: .irpc symbol[, value]

Evaluate a sequence of statements assigning different values to symbol. The sequence of statements starts at the .irpc directive, and is terminated by an .endr directive. For each character in value, symbol is set to the character, and the sequence of statements is assembled. If no value is listed, the sequence of statements is assembled once, with symbol set to the null string. To refer to symbol within the sequence of statements, use \symbol.

For example, assembling

        .irpc    param,123
move.l  %d\param,-(%sp)
.endr


is equivalent to assembling

        move.l %d1,-(%sp)
move.l %d2,-(%sp)
move.l %d3,-(%sp)


.lcomm

Syntax: .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 .global), so is normally not visible to ld.

.lflags

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

.line

Syntax: .line line-number

Even though this is a directive associated with the a.out or b.out object-code formats, 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.

.ln

Syntax: .ln line-number

Change the logical line number. line-number must be an absolute expression. The next line has that logical line number. Therefore any other statements on the current line (after a statement separator character) are reported as on logical line number line-number-1.

.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 Command-Line Options), the initial value of the listing counter is one.

.long

Syntax: .long expressions

On this target, .long is the same as .int.

.macro

Syntax: .macro macname [macargs...]

The commands .macro and .endm allow you to define macros that generate assembly output. For example, this definition specifies a macro sum that puts a sequence of numbers into memory:

        .macro  sum from=0, to=5
.long   \from
.if     \to-\from
sum     "(\from+1)",\to
.endif
.endm


With that (recursive) definition, SUM 0,5 is equivalent to this assembly input:

        .long   0
.long   1
.long   2
.long   3
.long   4
.long   5


.macro macname
.macro macname macargs

Begin the definition of a macro called macname. If your macro definition requires arguments, specify their names after the macro name, separated by commas or spaces. You can supply a default value for any macro argument by following the name with =deflt. For example, these are all valid .macro statements:

.macro comm

Begin the definition of a macro called comm, which takes no arguments.

.macro plus1 p, p1
.macro plus1 p p1

Either statement begins the definition of a macro called plus1, which takes two arguments; within the macro definition, write \p or \p1 to evaluate the arguments.

.macro reserve_str p1=0 p2

Begin the definition of a macro called reserve_str, with two arguments. The first argument has a default value, but not the second. After the definition is complete, you can call the macro either as reserve_str a,b (with \p1 evaluating to a and \p2 evaluating to b), or as reserve_str ,b (with \p1 evaluating as the default, in this case 0, and \p2 evaluating to b).

When you call a macro, you can specify the argument values either by position, or by keyword. For example, sum 9,17 is equivalent to sum to=17, from=9.

.endm

Mark the end of a macro definition.

.exitm

Exit early from the current macro definition.

\

as maintains a counter of how many macros it has executed in this pseudo-variable; you can copy that number to your output with \@, but only within a macro definition.

.mri

Syntax: .mri val

If val is non-zero, this tells as to enter MRI mode. If val is zero, this tells as to exit MRI mode. This change affects code assembled until the next .mri directive, or until the end of the file.

.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

Syntax: .octa bignums

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

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

.org

Syntax: .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, 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 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.

.p2align[wl]

Syntax: .p2align[wl] alignment[, [fill][, max]]

Pad the location counter (in the current subsection) to a particular storage boundary. alignment (which must be absolute) is the number of low-order zero bits the location counter must have after advancement. For example .p2align 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.

fill (also absolute) gives the fill value to be stored in the padding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are normally zero. However, on some systems, if the section is marked as containing code and the fill value is omitted, the space is filled with no-op instructions (I didn't checked whether this is the case in TIGCC).

max is also absolute, and is also optional. If it is present, it is the maximum number of bytes that should be skipped by this alignment directive. If doing the alignment would require skipping more bytes than the specified maximum, then the alignment is not done at all. You can omit the fill value (the second argument) entirely by simply using two commas after the required alignment; this can be useful if you want the alignment to be filled with no-op instructions when appropriate.

The .p2alignw and .p2alignl directives are variants of the .p2align directive. The .p2alignw directive treats the fill pattern as a two byte word value. The .p2alignl directives treats the fill pattern as a four byte longword value. For example, .p2alignw 2,0x368d will align to a multiple of 4. If it skips two bytes, they will be filled in with the value 0x368d (the exact placement of the bytes depends upon the endianness of the processor). If it skips 1 or 3 bytes, the fill value is undefined.

.print

Syntax: .print string

as will print string on the standard output during assembly. You must put string in double quotes.

.psize

Syntax: .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.

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.

.purgem

Syntax: .purgem macname

Undefine the macro macname, so that later uses of the string will not be expanded.

.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.

.rept

Syntax: .rept count

Repeat the sequence of lines between the .rept directive and the next .endr directive count times.

For example, assembling

        .rept   3
.long   0
.endr


is equivalent to assembling

        .long   0
.long   0
.long   0


.sbttl

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.

.scl

Syntax: .scl class

Set the storage-class value for a symbol. This directive may only be used inside a .def/.endef pair. Storage class may flag whether a symbol is static or external, or it may record further symbolic debugging information.

.section

Syntax: .section name[, "flags"] or .section name[, subsegment]

Use the .section directive to assemble the following code into a section named name.

If the optional argument is quoted, it is taken as flags to use for the section. Each flag is a single character. The following flags are recognized:

b

bss section (uninitialized data)

n

w

writable section

d

data section

r

x

executable section

m

mergeable section (TIGCC extension, symbols in the section are considered mergeable constants)

u

unaligned section (TIGCC extension, the contents of the section need not be aligned)

s

shared section (meaningful for PE targets, useless for TIGCC)

a

ignored (for compatibility with the ELF version)

If no flags are specified, the default flags depend upon the section name. If the section name is not recognized, the default will be for the section to be loaded and writable. Note the n and w flags remove attributes from the section, rather than adding them, so if they are used on their own it will be as if no flags had been specified at all.

If the optional argument to the .section directive is not quoted, it is taken as a subsegment number (see Sub-Sections).

.set

Syntax: .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 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.

.short

Syntax: .short expressions

On this target, .short is the same as .word.

.single

Syntax: .single flonums

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

.size

Syntax: .size expression

This directive, permitted only within .def/.endef pairs, is used to set the size associated with a symbol.

.sleb128

Syntax: .sleb128 expressions

sleb128 stands for "signed little endian base 128." This is a compact, variable length representation of numbers used by the DWARF symbolic debugging format.

.skip

.skip is recognized on the 680x0 platform as a synonym for .space.

.space

Syntax: .space size[, fill]

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

.stabd

Syntax: .stabd type, other, desc

There are three directives that begin .stab. All emit symbols (see Symbols), for use by symbolic debuggers. The symbols are not entered in the 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 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!

If .stabd is used, 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. If .stabn is used, the name of the symbol is set to the empty string "". If .stabs is used, all five fields are required.

.stabn

Syntax: .stabn type, other, desc, value

See .stabd.

.stabs

Syntax: .stabs string, type, other, desc, value

See .stabd.

.string

Syntax: .string "str"

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

.struct

Syntax: .struct expression

Switch to the absolute section, and set the section offset to expression, which must be an absolute expression. You might use this as follows:

        .struct 0
field1:
.struct field1 + 4
field2:
.struct field2 + 4
field3:


This would define the symbol field1 to have the value 0, the symbol field2 to have the value 4, and the symbol field3 to have the value 8. Assembly would be left in the absolute section, and you would need to use a .section directive of some sort to change to some other section before further assembly.

.tag

Syntax: .tag structname

This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside .def/.endef pairs. Tags are used to link structure definitions in the symbol table with instances of those structures.

.text

Syntax: .text [subsection]

Tells 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.

.title

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.

.type

Syntax: .type int

This directive, permitted only within .def/.endef pairs, records the integer int as the type attribute of a symbol table entry.

.uleb128

Syntax: .uleb128 expressions

uleb128 stands for "unsigned little endian base 128." This is a compact, variable length representation of numbers used by the DWARF symbolic debugging format.

.val

This directive, permitted only within .def/.endef pairs, records the address addr as the value attribute of a symbol table entry.

.vtable_entry

Syntax: .vtable_entry table, offset

This directive finds or creates a symbol table and creates a VTABLE_ENTRY relocation for it with an addend of offset.

.word

Syntax: .word expressions

This directive expects zero or more expressions, of any section, separated by commas. For each expression, as emits a 16-bit number for this target.

Acknowledgements

If you have contributed to 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 the maintainer is Ken Raeburn (email address raeburn@cygnus.com). (Note: Since this is a modified version of the manual, please check the original version as well before sending a mail.)

Dean Elsner wrote the original GNU assembler for the VAX. Any more details?

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 Renesas 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, wrote the initial RS/6000 and PowerPC assembler, and made a few other minor patches.

Steve Chamberlain made 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).

Linas Vepstas added GAS support for the ESA/390 "IBM 370" architecture.

Richard Henderson rewrote the Alpha assembler. Klaus Kaempf wrote GAS and BFD support for openVMS/Alpha.

Timothy Wall, Michael Hayes, and Greg Smart contributed to the various tic* flavors.

David Heine, Sterling Augustine, Bob Wilson and John Ruttenberg from Tensilica, Inc. added support for Xtensa processors.

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.

History

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