\input texinfo @c -*-Texinfo-*- @c Copyright (c) 1991 1992 Free Software Foundation, Inc. @c %**start of header @setfilename as.info @settitle Using as @setchapternewpage odd @c @smallbook @c @cropmarks @c %**end of header @ifinfo @format START-INFO-DIR-ENTRY * As: (as). The GNU assembler. END-INFO-DIR-ENTRY @end format @end ifinfo @finalout @syncodeindex ky cp @c @ifinfo This file documents the GNU Assembler "as". Copyright (C) 1991 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. @ignore Permission is granted to process this file through Tex and print the results, provided the printed document carries copying permission notice identical to this one except for the removal of this paragraph (this paragraph not being relevant to the printed manual). @end ignore Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled ``GNU General Public License'' is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled ``GNU General Public License'' may be included in a translation approved by the Free Software Foundation instead of in the original English. @end ifinfo @titlepage @title Using as @subtitle The GNU Assembler @sp 1 @subtitle January 1992 @sp 1 @sp 13 The Free Software Foundation Inc. thanks The Nice Computer Company of Australia for loaning Dean Elsner to write the first (Vax) version of @code{as} for Project GNU. The proprietors, management and staff of TNCCA thank FSF for distracting the boss while they got some work done. @sp 3 @author Dean Elsner, Jay Fenlason & friends @c edited by: pesch@cygnus.com @page @tex \def\$#1${{#1}} % Kluge: collect RCS revision info without $...$ \xdef\manvers{\$Revision$} % For use in headers, footers too {\parskip=0pt \hfill {\it Using {\tt as}} \manvers\par \hfill \TeX{}info \texinfoversion\par \hfill Edited by Roland Pesch for Cygnus Support\par } %"boxit" macro for figures: %Modified from Knuth's ``boxit'' macro from TeXbook (answer to exercise 21.3) \gdef\boxit#1#2{\vbox{\hrule\hbox{\vrule\kern3pt \vbox{\parindent=0pt\parskip=0pt\hsize=#1\kern3pt\strut\hfil #2\hfil\strut\kern3pt}\kern3pt\vrule}\hrule}}%box with visible outline \gdef\ibox#1#2{\hbox to #1{#2\hfil}\kern8pt}% invisible box @end tex @vskip 0pt plus 1filll Copyright @copyright{} 1991 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled ``GNU General Public License'' is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled ``GNU General Public License'' may be included in a translation approved by the Free Software Foundation instead of in the original English. @end titlepage @page @node Top, Overview, (dir), (dir) @ifinfo This file is a user guide to the GNU assembler @code{as}. @end ifinfo @menu * Overview:: Overview * Invoking:: Command-Line Options * Syntax:: Syntax * Sections:: Sections and Relocation * Symbols:: Symbols * Expressions:: Expressions * Pseudo Ops:: Assembler Directives * Machine Dependent:: Machine Dependent Features * Copying:: GNU GENERAL PUBLIC LICENSE * Index:: Index @end menu @node Overview, Invoking, Top, Top @chapter Overview @iftex This manual is a user guide to the GNU assembler @code{as}. @end iftex @cindex invocation summary @cindex option summary @cindex summary of options Here is a brief summary of how to invoke @code{as}. For details, @pxref{Invoking,,Comand-Line Options}. @c We don't use deffn and friends for the following because they seem @c to be limited to one line for the header. @smallexample as [ -a | -al | -as ] [ -D ] [ -f ] [ -I @var{path} ] [ -K ] [ -L ] [ -o @var{objfile} ] [ -R ] [ -v ] [ -w ] @c am29k has no machine-dependent assembler options @c h8/300 has no machine-dependent assembler options @c see md_parse_option in i960.c [ -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC ] [ -b ] [ -norelax ] [ -l ] [ -mc68000 | -mc68010 | -mc68020 ] [ -- | @var{files} @dots{} ] @end smallexample @table @code @item -a | -al | -as Turn on assembly listings; @samp{-al}, listing only, @samp{-as}, symbols only, @samp{-a}, everything. @item -D This option is accepted only for script compatibility with calls to other assemblers; it has no effect on @code{as}. @item -f ``fast''---skip preprocessing (assume source is compiler output) @item -I @var{path} Add @var{path} to the search list for @code{.include} directives @item -K Issue warnings when difference tables altered for long displacements. @item -L Keep (in symbol table) local symbols, starting with @samp{L} @item -o @var{objfile} Name the object-file output from @code{as} @item -R Fold data section into text section @item -v Announce @code{as} version @item -W Suppress warning messages @item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC (When configured for Intel 960). Specify which variant of the 960 architecture is the target. @item -b (When configured for Intel 960). Add code to collect statistics about branches taken. @item -norelax (When configured for Intel 960). Do not alter compare-and-branch instructions for long displacements; error if necessary. @item -l (When configured for Motorola 68000). Shorten references to undefined symbols, to one word instead of two @item -mc68000 | -mc68010 | -mc68020 (When configured for Motorola 68000). Specify what processor in the 68000 family is the target (default 68020) @item -- | @var{files} @dots{} Standard input, or source files to assemble @end table @menu * Manual:: Structure of this Manual * GNU Assembler:: as, the GNU Assembler * Object Formats:: Object File Formats * Command Line:: Command Line * Input Files:: Input Files * Object:: Output (Object) File * Errors:: Error and Warning Messages @end menu @node Manual, GNU Assembler, Overview, Overview @section Structure of this Manual @cindex manual, structure and purpose This manual is intended to describe what you need to know to use @sc{gnu} @code{as}. We cover the syntax expected in source files, including notation for symbols, constants, and expressions; the directives that @code{as} understands; and of course how to invoke @code{as}. This manual also describes some of the machine-dependent features of various flavors of the assembler. @refill @cindex machine instructions (not covered) On the other hand, this manual is @emph{not} intended as an introduction to programming in assembly language---let alone programming in general! In a similar vein, we make no attempt to introduce the machine architecture; we do @emph{not} describe the instruction set, standard mnemonics, registers or addressing modes that are standard to a particular architecture. You may want to consult the manufacturer's machine architecture manual for this information. @c I think this is premature---pesch@cygnus.com, 17jan1991 @ignore Throughout this manual, we assume that you are running @dfn{GNU}, the portable operating system from the @dfn{Free Software Foundation, Inc.}. This restricts our attention to certain kinds of computer (in particular, the kinds of computers that GNU can run on); once this assumption is granted examples and definitions need less qualification. @code{as} is part of a team of programs that turn a high-level human-readable series of instructions into a low-level computer-readable series of instructions. Different versions of @code{as} are used for different kinds of computer. @end ignore @c There used to be a section "Terminology" here, which defined @c "contents", "byte", "word", and "long". Defining "word" to any @c particular size is confusing when the .word directive may generate 16 @c bits on one machine and 32 bits on another; in general, for the user @c version of this manual, none of these terms seem essential to define. @c They were used very little even in the former draft of the manual; @c this draft makes an effort to avoid them (except in names of @c directives). @node GNU Assembler, Object Formats, Manual, Overview @section as, the GNU Assembler GNU @code{as} is really a family of assemblers. If you use (or have used) the GNU assembler on one architecture, you should find a fairly similar environment when you use it on another architecture. Each version has much in common with the others, including object file formats, most assembler directives (often called @dfn{pseudo-ops)} and assembler syntax.@refill @cindex purpose of @sc{gnu} @code{as} @code{as} is primarily intended to assemble the output of the GNU C compiler @code{gcc} for use by the linker @code{ld}. Nevertheless, we've tried to make @code{as} assemble correctly everything that the native assembler would. Any exceptions are documented explicitly (@pxref{Machine Dependent}). This doesn't mean @code{as} always uses the same syntax as another assembler for the same architecture; for example, we know of several incompatible versions of 680x0 assembly language syntax. Unlike older assemblers, @code{as} is designed to assemble a source program in one pass of the source file. This has a subtle impact on the @kbd{.org} directive (@pxref{Org,,@code{.org}}). @node Object Formats, Command Line, GNU Assembler, Overview @section Object File Formats @cindex object file format The GNU assembler can be configured to produce several alternative object file formats. For the most part, this does not affect how you write assembly language programs; but directives for debugging symbols are typically different in different file formats. @xref{Symbol Attributes,,Symbol Attributes}. @node Command Line, Input Files, Object Formats, Overview @section Command Line @cindex command line conventions After the program name @code{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. @cindex standard input, as input file @kindex -- @file{--} (two hyphens) by itself names the standard input file explicitly, as one of the files for @code{as} to assemble. @cindex options, command line Except for @samp{--} any command line argument that begins with a hyphen (@samp{-}) is an option. Each option changes the behavior of @code{as}. No option changes the way another option works. An option is a @samp{-} 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: @smallexample as -o my-object-file.o mumble.s as -omy-object-file.o mumble.s @end smallexample @node Input Files, Object, Command Line, Overview @section Input Files @cindex input @cindex source program @cindex files, input We use the phrase @dfn{source program}, abbreviated @dfn{source}, to describe the program input to one run of @code{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. @c I added "con" prefix to "catenation" just to prove I can overcome my @c APL training... pesch@cygnus.com The source program is a concatenation of the text in all the files, in the order specified. Each time you run @code{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 @code{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 @code{as} no file names it attempts to read one input file from the @code{as} standard input, which is normally your terminal. You may have to type @key{ctl-D} to tell @code{as} there is no more program to assemble. Use @samp{--} if you need to explicitly name the standard input file in your command line. If the source is empty, @code{as} will produce a small, empty object file. @subheading Filenames and Line-numbers @cindex input file linenumbers @cindex line numbers, in input files 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. @xref{Errors, ,Error and Warning Messages}. @dfn{Physical files} are those files named in the command line given to @code{as}. @dfn{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 @code{as} source is itself synthesized from other files. @xref{App-File,,@code{.app-file}}. @node Object, Errors, Input Files, Overview @section Output (Object) File @cindex object file @cindex output file @kindex a.out @kindex .o Every time you run @code{as} it produces an output file, which is your assembly language program translated into numbers. This file is the object file, named @code{a.out} unless you tell @code{as} to give it another name by using the @code{-o} option. Conventionally, object file names end with @file{.o}. The default name of @file{a.out} is used for historical reasons: older assemblers were capable of assembling self-contained programs directly into a runnable program. @c This may still work, but hasn't been tested. @cindex linker @kindex ld The object file is meant for input to the linker @code{ld}. It contains assembled program code, information to help @code{ld} integrate the assembled program into a runnable file, and (optionally) symbolic information for the debugger. @c link above to some info file(s) like the description of a.out. @c don't forget to describe GNU info as well as Unix lossage. @node Errors, , Object, Overview @section Error and Warning Messages @cindex error messsages @cindex warning messages @cindex messages from @code{as} @code{as} may write warnings and error messages to the standard error file (usually your terminal). This should not happen when a compiler runs @code{as} automatically. Warnings report an assumption made so that @code{as} could keep assembling a flawed program; errors report a grave problem that stops the assembly. @cindex format of warning messages Warning messages have the format @smallexample file_name:@b{NNN}:Warning Message Text @end smallexample @noindent @cindex line numbers, in warnings/errors (where @b{NNN} is a line number). If a logical file name has been given (@pxref{App-File,,@code{.app-file}}) it is used for the filename, otherwise the name of the current input file is used. If a logical line number was given (@pxref{Ln,,@code{.ln}}) 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). @refill @cindex format of error messages Error messages have the format @smallexample file_name:@b{NNN}:FATAL:Error Message Text @end smallexample 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. @node Invoking, Syntax, Overview, Top @chapter Command-Line Options @cindex options, all versions of @code{as} This chapter describes command-line options available in @emph{all} versions of the GNU assembler; @pxref{Machine Dependent}, for options specific to particular machine architectures. @section Enable Listings: @code{-a}, @code{-al}, @code{-as} @kindex -a @kindex -al @kindex -as @cindex listings, enabling @cindex assembly listings, enabling These options enable listing output from the assembler. @samp{-a} by itself requests all listing output; @samp{-al} requests only the output-program listing, and @samp{-as} requests only a symbol table listing. Once you have specified one of these options, you can further control listing output and its appearance using the directives @code{.list}, @code{.nolist}, @code{.psize}, @code{.eject}, @code{.title}, and @code{.sbttl}. If you do not request listing output with one of the @samp{-a} options, the listing-control directives have no effect. @section @code{-D} @kindex -D This option has no effect whatsoever, but it is accepted to make it more likely that scripts written for other assemblers will also work with @code{as}. @section Work Faster: @code{-f} @kindex -f @cindex trusted compiler @cindex faster processing (@code{-f}) @samp{-f} should only be used when assembling programs written by a (trusted) compiler. @samp{-f} stops the assembler from pre-processing the input file(s) before assembling them. @xref{Pre-processing, ,Pre-processing}. @quotation @emph{Warning:} if the files actually need to be pre-processed (if they contain comments, for example), @code{as} will not work correctly if @samp{-f} is used. @end quotation @section @code{.include} search path: @code{-I} @var{path} @kindex -I @var{path} @cindex paths for @code{.include} @cindex search path for @code{.include} @cindex @code{include} directive search path Use this option to add a @var{path} to the list of directories @code{as} will search for files specified in @code{.include} directives (@pxref{Include,,@code{.include}}). You may use @code{-I} as many times as necessary to include a variety of paths. The current working directory is always searched first; after that, @code{as} searches any @samp{-I} directories in the same order as they were specified (left to right) on the command line. @section Difference Tables: @code{-K} @kindex -K @cindex difference tables, warning @cindex warning for altered difference tables @code{as} sometimes alters the code emitted for directives of the form @samp{.word @var{sym1}-@var{sym2}}; @pxref{Word,,@code{.word}}. You can use the @samp{-K} option if you want a warning issued when this is done. @section Include Local Labels: @code{-L} @kindex -L @cindex local labels, retaining in output Labels beginning with @samp{L} (upper case only) are called @dfn{local labels}. @xref{Symbol Names}. Normally you don't see such labels when debugging, because they are intended for the use of programs (like compilers) that compose assembler programs, not for your notice. Normally both @code{as} and @code{ld} discard such labels, so you don't normally debug with them. This option tells @code{as} to retain those @samp{L@dots{}} symbols in the object file. Usually if you do this you also tell the linker @code{ld} to preserve symbols whose names begin with @samp{L}. @section Name the Object File: @code{-o} @kindex -o @cindex naming object file @cindex object file name There is always one object file output when you run @code{as}. By default it has the name @file{a.out}. You use this option (which takes exactly one filename) to give the object file a different name. Whatever the object file is called, @code{as} will overwrite any existing file of the same name. @section Join Data and Text Sections: @code{-R} @kindex -R @cindex data and text sections, joining @cindex text and data sections, joining @cindex joining text and data sections @cindex merging text and data sections @code{-R} tells @code{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 it bytes are appended to the text section. (@xref{Sections,,Sections and Relocation}.) When you specify @code{-R} it would be possible to generate shorter address displacements (because we don't have to cross between text and data section). We refrain from doing this simply for compatibility with older versions of @code{as}. In future, @code{-R} may work this way. When @code{as} is configured for COFF output, this option is only useful if you use sections named @samp{.text} and @samp{.data}. @section Announce Version: @code{-v} @kindex -v @kindex -version @cindex @code{as} version @cindex version of @code{as} You can find out what version of as is running by including the option @samp{-v} (which you can also spell as @samp{-version}) on the command line. @section Suppress Warnings: @code{-W} @kindex -W @cindex suppressing warnings @cindex warnings, suppressing @code{as} should never give a warning or error message when assembling compiler output. But programs written by people often cause @code{as} to give a warning that a particular assumption was made. All such warnings are directed to the standard error file. If you use this option, no warnings are issued. This option only affects the warning messages: it does not change any particular of how @code{as} assembles your file. Errors, which stop the assembly, are still reported. @node Syntax, Sections, Invoking, Top @chapter Syntax @cindex machine-independent syntax @cindex syntax, machine-independent This chapter describes the machine-independent syntax allowed in a source file. @code{as} syntax is similar to what many other assemblers use; it is inspired in BSD 4.2 assembler, except that @code{as} does not assemble Vax bit-fields. @menu * Pre-processing:: Pre-processing * Whitespace:: Whitespace * Comments:: Comments * Symbol Intro:: Symbols * Statements:: Statements * Constants:: Constants @end menu @node Pre-processing, Whitespace, Syntax, Syntax @section Pre-Processing @cindex preprocessing The pre-processor: @itemize @bullet @cindex whitespace, removed by preprocessor @item 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. @cindex comments, removed by preprocessor @item removes all comments, replacing them with a single space, or an appropriate number of newlines. @cindex constants, converted by preprocessor @item converts character constants into the appropriate numeric values. @end itemize Excess whitespace, comments, and character constants cannot be used in the portions of the input text that are not pre-processed. @cindex turning preprocessing on and off @cindex preprocessing, turning on and off @kindex #NO_APP @kindex #APP If the first line of an input file is @code{#NO_APP} or the @samp{-f} option is given, the input file will not be pre-processed. Within such an input file, parts of the file can be pre-processed by putting a line that says @code{#APP} before the text that should be pre-processed, and putting a line that says @code{#NO_APP} after them. This feature is mainly intend to support @code{asm} statements in compilers whose output normally does not need to be pre-processed. @node Whitespace, Comments, Pre-processing, Syntax @section Whitespace @cindex whitespace @dfn{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 (@pxref{Characters,,Character Constants}), any whitespace means the same as exactly one space. @node Comments, Symbol Intro, Whitespace, Syntax @section Comments @cindex comments There are two ways of rendering comments to @code{as}. In both cases the comment is equivalent to one space. Anything from @samp{/*} through the next @samp{*/} is a comment. This means you may not nest these comments. @smallexample /* 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. */ @end smallexample @cindex line comment character Anything from the @dfn{line comment} character to the next newline is considered a comment and is ignored. The line comment character is @samp{#} on the Vax; @samp{#} on the i960; @samp{|} on the 680x0; @samp{;} for the AMD 29K family; @samp{;} for the machine specific family; @pxref{Machine Dependent}. @refill @c FIXME: fill in SPARC line comment char On some machines there are two different line comment characters. One will only begin a comment if it is the first non-whitespace character on a line, while the other will always begin a comment. @kindex # @cindex lines starting with @code{#} @cindex logical line numbers To be compatible with past assemblers, a special interpretation is given to lines that begin with @samp{#}. Following the @samp{#} an absolute expression (@pxref{Expressions}) is expected: this will be the logical line number of the @b{next} line. Then a string (@xref{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.) @smallexample # This is an ordinary comment. # 42-6 "new_file_name" # New logical file name # This is logical line # 36. @end smallexample This feature is deprecated, and may disappear from future versions of @code{as}. @node Symbol Intro, Statements, Comments, Syntax @section Symbols @cindex characters used in symbols A @dfn{symbol} is one or more characters chosen from the set of all letters (both upper and lower case), digits and the two characters @samp{_.} On most machines, you can also use @code{$} in symbol names; exceptions are noted in @ref{Machine Dependent}. 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). @xref{Symbols}. @cindex length of symbols @node Statements, Constants, Symbol Intro, Syntax @section Statements @cindex statements, structure of @cindex line separator character @cindex statement separator character A @dfn{statement} ends at a newline character (@samp{\n}) or line separator character. (The line separator is usually @samp{;}, unless this conflicts with the comment character; @pxref{Machine Dependent}.) The newline or separator character is considered part of the preceding statement. Newlines and separators within character constants are an exception: they don't end statements. @cindex newline, required at file end @cindex EOF, newline must precede It is an error to end any statement with end-of-file: the last character of any input file should be a newline.@refill @cindex continuing statements @cindex multi-line statements @cindex statement on multiple lines You may write a statement on more than one line if you put a backslash (@kbd{\}) immediately in front of any newlines within the statement. When @code{as} reads a backslashed newline both characters are ignored. You can even put backslashed newlines in the middle of symbol names without changing the meaning of your source program. An empty statement is allowed, and may include whitespace. It is ignored. @cindex instructions and directives @cindex directives and instructions @c "key symbol" is not used elsewhere in the document; seems pedantic to @c @defn{} it in that case, as was done previously... pesch@cygnus.com, @c 13feb91. 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 @samp{.} 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 @dfn{instruction}: it will assemble into a machine language instruction. Different versions of @code{as} for different computers will recognize different instructions. In fact, the same symbol may represent a different instruction in a different computer's assembly language.@refill @cindex @code{:} (label) @cindex label (@code{:}) A label is a symbol immediately followed by a colon (@code{:}). Whitespace before a label or after a colon is permitted, but you may not have whitespace between a label's symbol and its colon. @xref{Labels}. @smallexample label: .directive followed by something another_label: # This is an empty statement. instruction operand_1, operand_2, @dots{} @end smallexample @node Constants, , Statements, Syntax @section Constants @cindex constants A constant is a number, written so that its value is known by inspection, without knowing any context. Like this: @smallexample .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. @end smallexample @menu * Characters:: Character Constants * Numbers:: Number Constants @end menu @node Characters, Numbers, Constants, Constants @subsection Character Constants @cindex character constants @cindex constants, character There are two kinds of character constants. A @dfn{character} stands for one character in one byte and its value may be used in numeric expressions. String constants (properly called string @emph{literals}) are potentially many bytes and their values may not be used in arithmetic expressions. @menu * Strings:: Strings * Chars:: Characters @end menu @node Strings, Chars, Characters, Characters @subsubsection Strings @cindex string constants @cindex constants, string A @dfn{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 @dfn{escape} these characters: precede them with a backslash @samp{\} character. For example @samp{\\} represents one backslash: the first @code{\} is an escape which tells @code{as} to interpret the second character literally as a backslash (which prevents @code{as} from recognizing the second @code{\} as an escape character). The complete list of escapes follows. @cindex escape codes, character @cindex character escape codes @table @kbd @c @item \a @c Mnemonic for ACKnowledge; for ASCII this is octal code 007. @c @item \b @cindex @code{\b} (backspace character) @cindex backspace (@code{\b}) Mnemonic for backspace; for ASCII this is octal code 010. @c @item \e @c Mnemonic for EOText; for ASCII this is octal code 004. @c @item \f @cindex @code{\f} (formfeed character) @cindex formfeed (@code{\f}) Mnemonic for FormFeed; for ASCII this is octal code 014. @item \n @cindex @code{\n} (newline character) @cindex newline (@code{\n}) Mnemonic for newline; for ASCII this is octal code 012. @c @item \p @c Mnemonic for prefix; for ASCII this is octal code 033, usually known as @code{escape}. @c @item \r @cindex @code{\r} (carriage return character) @cindex carriage return (@code{\r}) Mnemonic for carriage-Return; for ASCII this is octal code 015. @c @item \s @c Mnemonic for space; for ASCII this is octal code 040. Included for compliance with @c other assemblers. @c @item \t @cindex @code{\t} (tab) @cindex tab (@code{\t}) Mnemonic for horizontal Tab; for ASCII this is octal code 011. @c @item \v @c Mnemonic for Vertical tab; for ASCII this is octal code 013. @c @item \x @var{digit} @var{digit} @var{digit} @c A hexadecimal character code. The numeric code is 3 hexadecimal digits. @c @item \ @var{digit} @var{digit} @var{digit} @cindex @code{\@var{ddd}} (octal character code) @cindex octal character code (@code{\@var{ddd}}) 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, @code{\008} has the value 010, and @code{\009} the value 011. @item \\ @cindex @code{\\} (@samp{\} character) @cindex backslash (@code{\\}) Represents one @samp{\} character. @c @item \' @c Represents one @samp{'} (accent acute) character. @c This is needed in single character literals @c (@xref{Characters,,Character Constants}.) to represent @c a @samp{'}. @c @item \" @cindex @code{\"} (doublequote character) @cindex doublequote (@code{\"}) Represents one @samp{"} character. Needed in strings to represent this character, because an unescaped @samp{"} would end the string. @item \ @var{anything-else} Any other character when escaped by @kbd{\} will give a warning, but assemble as if the @samp{\} 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 @code{as} has no other interpretation, so @code{as} knows it is giving you the wrong code and warns you of the fact. @end table Which characters are escapable, and what those escapes represent, varies widely among assemblers. The current set is what we think the BSD 4.2 assembler recognizes, and is a subset of what most C compilers recognize. If you are in doubt, don't use an escape sequence. @node Chars, , Strings, Characters @subsubsection Characters @cindex single character constant @cindex character, single @cindex constant, single character 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 @kbd{'\\} where the first @code{\} escapes the second @code{\}. As you can see, the quote is an acute accent, not a grave accent. A newline 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. @code{as} assumes your character code is ASCII: @kbd{'A} means 65, @kbd{'B} means 66, and so on. @refill @node Numbers, , Characters, Constants @subsection Number Constants @cindex constants, number @cindex number constants @code{as} distinguishes three kinds of numbers according to how they are stored in the target machine. @emph{Integers} are numbers that would fit into an @code{int} in the C language. @emph{Bignums} are integers, but they are stored in more than 32 bits. @emph{Flonums} are floating point numbers, described below. @menu * Integers:: Integers * Bignums:: Bignums * Flonums:: Flonums @end menu @node Integers, Bignums, Numbers, Numbers @subsubsection Integers @cindex integers @cindex constants, integer @cindex binary integers @cindex integers, binary A binary integer is @samp{0b} or @samp{0B} followed by zero or more of the binary digits @samp{01}. @cindex octal integers @cindex integers, octal An octal integer is @samp{0} followed by zero or more of the octal digits (@samp{01234567}). @cindex decimal integers @cindex integers, decimal A decimal integer starts with a non-zero digit followed by zero or more digits (@samp{0123456789}). @cindex hexadecimal integers @cindex integers, hexadecimal A hexadecimal integer is @samp{0x} or @samp{0X} followed by one or more hexadecimal digits chosen from @samp{0123456789abcdefABCDEF}. Integers have the usual values. To denote a negative integer, use the prefix operator @samp{-} discussed under expressions (@pxref{Prefix Ops,,Prefix Operators}). @node Bignums, Flonums, Integers, Numbers @subsubsection Bignums @cindex bignums @cindex constants, bignum A @dfn{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. @node Flonums, , Bignums, Numbers @subsubsection Flonums @cindex flonums @cindex floating point numbers @cindex constants, floating point @cindex precision, floating point A @dfn{flonum} represents a floating point number. The translation is indirect: a decimal floating point number from the text is converted by @code{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 @code{as} specialized to that computer. A flonum is written by writing (in order) @itemize @bullet @item The digit @samp{0}. @item A letter, to tell @code{as} the rest of the number is a flonum. @kbd{e} is recommended. Case is not important. @ignore @c FIXME: verify if flonum syntax really this vague for most cases (Any otherwise illegal letter will work here, but that might be changed. Vax BSD 4.2 assembler seems to allow any of @samp{defghDEFGH}.) @end ignore On the AMD 29K and H8/300 architectures, the letter must be: One of the letters @samp{DFPRSX} (in upper or lower case). On the Intel 960 architecture, the letter must be: One of the letters @samp{DFT} (in upper or lower case). @item An optional sign: either @samp{+} or @samp{-}. @item An optional @dfn{integer part}: zero or more decimal digits. @item An optional @dfn{fractional part}: @samp{.} followed by zero or more decimal digits. @item An optional exponent, consisting of: @itemize @bullet @item An @samp{E} or @samp{e}. @c I can't find a config where "EXP_CHARS" is other than 'eE', but in @c principle this can perfectly well be different on different targets. @item Optional sign: either @samp{+} or @samp{-}. @item One or more decimal digits. @end itemize @end itemize At least one of the integer part or the fractional part must be present. The floating point number has the usual base-10 value. @code{as} does all processing using integers. Flonums are computed independently of any floating point hardware in the computer running @code{as}. @node Sections, Symbols, Syntax, Top @chapter Sections and Relocation @cindex sections @cindex relocation @menu * Secs Background:: Background * ld Sections:: ld Sections * as Sections:: as Internal Sections * Sub-Sections:: Sub-Sections * bss:: bss Section @end menu @node Secs Background, ld Sections, Sections, Sections @section Background Roughly, a section is a range of addresses, with no gaps; all data ``in'' those addresses is treated the same for some particular purpose. For example there may be a ``read only'' section. @cindex linker, and assembler @cindex assembler, and linker The linker @code{ld} reads many object files (partial programs) and combines their contents to form a runnable program. When @code{as} emits an object file, the partial program is assumed to start at address 0. @code{ld} will assign the final addresses the partial program occupies, so that different partial programs don't overlap. This is actually an over-simplification, but it will suffice to explain how @code{as} uses sections. @code{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 @emph{section}. Assigning run-time addresses to sections is called @dfn{relocation}. It includes the task of adjusting mentions of object-file addresses so they refer to the proper run-time addresses. For the H8/300, @code{as} pads sections if needed to ensure they end on a word (sixteen bit) boundary. @cindex standard @code{as} sections An object file written by @code{as} has at least three sections, any of which may be empty. These are named @dfn{text}, @dfn{data} and @dfn{bss} sections. When it generates COFF output, @code{as} can also generate whatever other named sections you specify using the @samp{.section} directive (@pxref{Section,,@code{.section}}). If you don't use any directives that place output in the @samp{.text} or @samp{.data} sections, these sections will still exist, but will be empty. Within the object file, the text section starts at address @code{0}, the data section follows, and the bss section follows the data section. To let @code{ld} know which data will change when the sections are relocated, and how to change that data, @code{as} also writes to the object file details of the relocation needed. To perform relocation @code{ld} must know, each time an address in the object file is mentioned: @itemize @bullet @item Where in the object file is the beginning of this reference to an address? @item How long (in bytes) is this reference? @item Which section does the address refer to? What is the numeric value of @display (@var{address}) @minus{} (@var{start-address of section})? @end display @item Is the reference to an address ``Program-Counter relative''? @end itemize @cindex addresses, format of @cindex section-relative addressing In fact, every address @code{as} ever uses is expressed as @display (@var{section}) + (@var{offset into section}) @end display @noindent Further, every expression @code{as} computes is of this section-relative nature. @dfn{Absolute expression} means an expression with section ``absolute'' (@pxref{ld Sections}). A @dfn{pass1 expression} means an expression with section ``pass1'' (@pxref{as Sections,,as Internal Sections}). In this manual we use the notation @{@var{secname} @var{N}@} to mean ``offset @var{N} into section @var{secname}''. Apart from text, data and bss sections you need to know about the @dfn{absolute} section. When @code{ld} mixes partial programs, addresses in the absolute section remain unchanged. For example, address @code{@{absolute 0@}} is ``relocated'' to run-time address 0 by @code{ld}. Although two partial programs' data sections will not overlap addresses after linking, @emph{by definition} their absolute sections will overlap. Address @code{@{absolute@ 239@}} in one partial program will always be the same address when the program is running as address @code{@{absolute@ 239@}} in any other partial program. The idea of sections is extended to the @dfn{undefined} section. Any address whose section is unknown at assembly time is by definition rendered @{undefined @var{U}@}---where @var{U} will be filled in later. Since numbers are always defined, the only way to generate an undefined address is to mention an undefined symbol. A reference to a named common block would be such a symbol: its value is unknown at assembly time so it has section @emph{undefined}. By analogy the word @emph{section} is used to describe groups of sections in the linked program. @code{ld} puts all partial programs' text sections in contiguous addresses in the linked program. It is customary to refer to the @emph{text section} of a program, meaning all the addresses of all partial program's text sections. Likewise for data and bss sections. Some sections are manipulated by @code{ld}; others are invented for use of @code{as} and have no meaning except during assembly. @node ld Sections, as Sections, Secs Background, Sections @section ld Sections @code{ld} deals with just four kinds of sections, summarized below. @table @strong @cindex named sections @cindex sections, named @item named sections @cindex text section @cindex data section @item text section @itemx data section These sections hold your program. @code{as} and @code{ld} treat them as separate but equal sections. Anything you can say of one section is true 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 will contain 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. @cindex bss section @item bss section This section contains zeroed bytes when your program begins running. It is used to hold unitialized variables or common storage. The length of each partial program's bss section is important, but because it starts out containing zeroed bytes there is no need to store explicit zero bytes in the object file. The bss section was invented to eliminate those explicit zeros from object files. @cindex absolute section @item 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 @code{ld} must not change when relocating. In this sense we speak of absolute addresses being ``unrelocatable'': they don't change during relocation. @cindex undefined section @item undefined section This ``section'' is a catch-all for address references to objects not in the preceding sections. @c FIXME: ref to some other doc on obj-file formats could go here. @end table @cindex relocation example An idealized example of three relocatable sections follows. The example uses the traditional section names @samp{.text} and @samp{.data}. Memory addresses are on the horizontal axis. @c TEXI2ROFF-KILL @ifinfo @c END TEXI2ROFF-KILL @smallexample +-----+----+--+ 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 @dots{} @end smallexample @c TEXI2ROFF-KILL @end ifinfo @c FIXME make sure no page breaks inside figure!! @tex \line{\it Partial program \#1: \hfil} \line{\ibox{2.5cm}{\tt text}\ibox{2cm}{\tt data}\ibox{1cm}{\tt bss}\hfil} \line{\boxit{2.5cm}{\tt ttttt}\boxit{2cm}{\tt dddd}\boxit{1cm}{\tt 00}\hfil} \line{\it Partial program \#2: \hfil} \line{\ibox{1cm}{\tt text}\ibox{1.5cm}{\tt data}\ibox{1cm}{\tt bss}\hfil} \line{\boxit{1cm}{\tt TTT}\boxit{1.5cm}{\tt DDDD}\boxit{1cm}{\tt 000}\hfil} \line{\it linked program: \hfil} \line{\ibox{.5cm}{}\ibox{1cm}{\tt text}\ibox{2.5cm}{}\ibox{.75cm}{}\ibox{2cm}{\tt data}\ibox{1.5cm}{}\ibox{2cm}{\tt bss}\hfil} \line{\boxit{.5cm}{}\boxit{1cm}{\tt TTT}\boxit{2.5cm}{\tt ttttt}\boxit{.75cm}{}\boxit{2cm}{\tt dddd}\boxit{1.5cm}{\tt DDDD}\boxit{2cm}{\tt 00000}\ \dots\hfil} \line{\it addresses: \hfil} \line{0\dots\hfil} @end tex @c END TEXI2ROFF-KILL @node as Sections, Sub-Sections, ld Sections, Sections @section as Internal Sections @cindex internal @code{as} sections @cindex sections in messages, internal These sections are meant only for the internal use of @code{as}. They have no meaning at run-time. You don't really need to know about these sections for most purposes; but they can be mentioned in @code{as} warning messages, so it might be helpful to have an idea of their meanings to @code{as}. These sections are used to permit the value of every expression in your assembly language program to be a section-relative address. @table @b @item absent @cindex absent (internal section) An expression was expected and none was found. @item ASSEMBLER-INTERNAL-LOGIC-ERROR! @cindex assembler internal logic error An internal assembler logic error has been found. This means there is a bug in the assembler. @item bignum/flonum @cindex bignum/flonum (internal section) If a number can't be written as a C @code{int} constant (a bignum or a flonum, but not an integer), it is recorded as belonging to this ``section''. @code{as} has to remember that a flonum or a bignum does not fit into 32 bits, and cannot be an argument (@pxref{Arguments}) in an expression: this is done by making a flonum or bignum be in a separate internal section. This is purely for internal @code{as} convenience; bignum/flonum section behaves similarly to absolute section. @item pass1 section @cindex pass1 (internal section) The expression was impossible to evaluate in the first pass. The assembler will attempt a second pass (second reading of the source) to evaluate the expression. Your expression mentioned an undefined symbol in a way that defies the one-pass (section + offset in section) assembly process. No compiler need emit such an expression. @quotation @emph{Warning:} the second pass is currently not implemented. @code{as} will abort with an error message if one is required. @end quotation @item difference section @cindex difference (internal section) As an assist to the C compiler, expressions of the forms @display (@var{undefined symbol}) @minus{} (@var{expression}) @var{something} @minus{} (@var{undefined symbol}) (@var{undefined symbol}) @minus{} (@var{undefined symbol}) @end display are permitted, and belong to the difference section. @code{as} re-evaluates such expressions after the source file has been read and the symbol table built. If by that time there are no undefined symbols in the expression then the expression assumes a new section. The intention is to permit statements like @samp{.word label - base_of_table} to be assembled in one pass where both @code{label} and @code{base_of_table} are undefined. This is useful for compiling C and Algol switch statements, Pascal case statements, FORTRAN computed goto statements and the like. @c FIXME item debug @c FIXME item transfer[t] vector preload @c FIXME item transfer[t] vector postload @c FIXME item register @end table @node Sub-Sections, bss, as Sections, Sections @section Sub-Sections @cindex numbered subsections @cindex grouping data Assembled bytes conventionally fall into two sections: text and data. You may have separate groups of data in named sections that you want to end up near to each other in the object file, even though they are not contiguous in the assembler source. @code{as} allows you to use @dfn{subsections} for this purpose. Within each section, there can be numbered subsections with values from 0 to 8192. Objects assembled into the same subsection will be grouped with other objects in the same subsection when they are all put into the object file. For example, a compiler might want to store constants in the text section, but might not want to have them interspersed with the program being assembled. In this case, the compiler could issue a @samp{.text 0} before each section of code being output, and a @samp{.text 1} before each group of constants being output. Subsections are optional. If you don't use subsections, everything will be stored in subsection number zero. Each subsection is zero-padded up to a multiple of four bytes. (Subsections may be padded a different amount on different flavors of @code{as}.) 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; @code{ld} and other programs that manipulate object files will see no trace of them. They just see all your text subsections as a text section, and all your data subsections as a data section. To specify which subsection you want subsequent statements assembled into, use a numeric argument to specify it, in a @samp{.text @var{expression}} or a @samp{.data @var{expression}} statement. When generating COFF output, you can also use an extra subsection argument with arbitrary named sections: @samp{.section @var{name}, @var{expression}}. @var{Expression} should be an absolute expression. (@xref{Expressions}.) If you just say @samp{.text} then @samp{.text 0} is assumed. Likewise @samp{.data} means @samp{.data 0}. Assembly begins in @code{text 0}. For instance: @smallexample .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 (*)." @end smallexample Each section has a @dfn{location counter} incremented by one for every byte assembled into that section. Because subsections are merely a convenience restricted to @code{as} there is no concept of a subsection location counter. There is no way to directly manipulate a location counter---but the @code{.align} directive will change it, and any label definition will capture its current value. The location counter of the section that statements are being assembled into is said to be the @dfn{active} location counter. @node bss, , Sub-Sections, Sections @section bss Section @cindex bss section @cindex common variable storage The bss section is used for local common variable storage. You may allocate address space in the bss section, but you may not dictate data to load into it before your program executes. When your program starts running, all the contents of the bss section are zeroed bytes. Addresses in the bss section are allocated with special directives; you may not assemble anything directly into the bss section. Hence there are no bss subsections. @xref{Comm,,@code{.comm}}, @pxref{Lcomm,,@code{.lcomm}}. @node Symbols, Expressions, Sections, Top @chapter Symbols @cindex 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. @quotation @cindex debuggers, and symbol order @emph{Warning:} @code{as} does not place symbols in the object file in the same order they were declared. This may break some debuggers. @end quotation @menu * Labels:: Labels * Setting Symbols:: Giving Symbols Other Values * Symbol Names:: Symbol Names * Dot:: The Special Dot Symbol * Symbol Attributes:: Symbol Attributes @end menu @node Labels, Setting Symbols, Symbols, Symbols @section Labels @cindex labels A @dfn{label} is written as a symbol immediately followed by a colon @samp{:}. 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. @node Setting Symbols, Symbol Names, Labels, Symbols @section Giving Symbols Other Values @cindex assigning values to symbols @cindex symbol values, assigning A symbol can be given an arbitrary value by writing a symbol, followed by an equals sign @samp{=}, followed by an expression (@pxref{Expressions}). This is equivalent to using the @code{.set} directive. @xref{Set,,@code{.set}}. @node Symbol Names, Dot, Setting Symbols, Symbols @section Symbol Names @cindex symbol names @cindex names, symbol Symbol names begin with a letter or with one of @samp{_.} (On most machines, you can also use @code{$} in symbol names; exceptions are noted in @ref{Machine Dependent}.) That character may be followed by any string of digits, letters, dollar signs (unless otherwise noted in @ref{Machine Dependent}), and underscores. Case of letters is significant: @code{foo} is a different symbol name than @code{Foo}. For the AMD 29K family, @samp{?} is also allowed in the body of a symbol name, though not at its beginning. 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. @subheading Local Symbol Names @cindex local symbol names @cindex symbol names, local @cindex temporary symbol names @cindex symbol names, temporary Local symbols help compilers and programmers use names temporarily. There are ten local symbol names, which are re-used throughout the program. You may refer to them using the names @samp{0} @samp{1} @dots{} @samp{9}. To define a local symbol, write a label of the form @samp{@b{N}:} (where @b{N} represents any digit). To refer to the most recent previous definition of that symbol write @samp{@b{N}b}, using the same digit as when you defined the label. To refer to the next definition of a local label, write @samp{@b{N}f}---where @b{N} gives you a choice of 10 forward references. The @samp{b} stands for ``backwards'' and the @samp{f} stands for ``forwards''. Local symbols are not emitted by the current GNU C compiler. There is no restriction on how you can use these labels, but remember that at any point in the assembly you can refer to at most 10 prior local labels and to at most 10 forward local labels. Local symbol names are only a notation device. They are immediately transformed into more conventional symbol names before the assembler uses them. The symbol names stored in the symbol table, appearing in error messages and optionally emitted to the object file have these parts: @table @code @item L All local labels begin with @samp{L}. Normally both @code{as} and @code{ld} forget symbols that start with @samp{L}. These labels are used for symbols you are never intended to see. If you give the @samp{-L} option then @code{as} will retain these symbols in the object file. If you also instruct @code{ld} to retain these symbols, you may use them in debugging. @item @var{digit} If the label is written @samp{0:} then the digit is @samp{0}. If the label is written @samp{1:} then the digit is @samp{1}. And so on up through @samp{9:}. @item @ctrl{A} This unusual character is included so you don't accidentally invent a symbol of the same name. The character has ASCII value @samp{\001}. @item @emph{ordinal number} This is a serial number to keep the labels distinct. The first @samp{0:} gets the number @samp{1}; The 15th @samp{0:} gets the number @samp{15}; @emph{etc.}. Likewise for the other labels @samp{1:} through @samp{9:}. @end table For instance, the first @code{1:} is named @code{L1@ctrl{A}1}, the 44th @code{3:} is named @code{L3@ctrl{A}44}. @node Dot, Symbol Attributes, Symbol Names, Symbols @section The Special Dot Symbol @cindex dot (symbol) @cindex @code{.} (symbol) @cindex current address @cindex location counter The special symbol @samp{.} refers to the current address that @code{as} is assembling into. Thus, the expression @samp{melvin: .long .} will cause @code{melvin} to contain its own address. Assigning a value to @code{.} is treated the same as a @code{.org} directive. Thus, the expression @samp{.=.+4} is the same as saying @samp{.block 4}. @node Symbol Attributes, , Dot, Symbols @section Symbol Attributes @cindex symbol attributes @cindex attributes, symbol 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, @code{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. @menu * Symbol Value:: Value * Symbol Type:: Type * a.out Symbols:: Symbol Attributes: @code{a.out} * COFF Symbols:: Symbol Attributes for COFF @end menu @node Symbol Value, Symbol Type, Symbol Attributes, Symbol Attributes @subsection Value @cindex value of a symbol @cindex symbol 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 @code{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 program, and @code{ld} will try to determine its value from other programs it is linked with. You make this kind of symbol simply by mentioning a symbol name without defining it. A non-zero value represents a @code{.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. @node Symbol Type, a.out Symbols, Symbol Value, Symbol Attributes @subsection Type @cindex type of a symbol @cindex symbol 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. @node a.out Symbols, COFF Symbols, Symbol Type, Symbol Attributes @subsection Symbol Attributes: @code{a.out} @cindex @code{a.out} symbol attributes @cindex symbol attributes, @code{a.out} @menu * Symbol Desc:: Descriptor * Symbol Other:: Other @end menu @node Symbol Desc, Symbol Other, a.out Symbols, a.out Symbols @subsubsection Descriptor @cindex descriptor, of @code{a.out} symbol This is an arbitrary 16-bit value. You may establish a symbol's descriptor value by using a @code{.desc} statement (@pxref{Desc,,@code{.desc}}). A descriptor value means nothing to @code{as}. @node Symbol Other, , Symbol Desc, a.out Symbols @subsubsection Other @cindex other attribute, of @code{a.out} symbol This is an arbitrary 8-bit value. It means nothing to @code{as}. @node COFF Symbols, , a.out Symbols, Symbol Attributes @subsection Symbol Attributes for COFF @cindex COFF symbol attributes @cindex symbol attributes, COFF The COFF format supports a multitude of auxiliary symbol attributes; like the primary symbol attributes, they are set between @code{.def} and @code{.endef} directives. @subsubsection Primary Attributes @cindex primary attributes, COFF symbols The symbol name is set with @code{.def}; the value and type, respectively, with @code{.val} and @code{.type}. @subsubsection Auxiliary Attributes @cindex auxiliary attributes, COFF symbols The @code{as} directives @code{.dim}, @code{.line}, @code{.scl}, @code{.size}, and @code{.tag} can generate auxiliary symbol table information for COFF. @node Expressions, Pseudo Ops, Symbols, Top @chapter Expressions @cindex expressions @cindex addresses @cindex numeric values An @dfn{expression} specifies an address or numeric value. Whitespace may precede and/or follow an expression. @menu * Empty Exprs:: Empty Expressions * Integer Exprs:: Integer Expressions @end menu @node Empty Exprs, Integer Exprs, Expressions, Expressions @section Empty Expressions @cindex empty expressions @cindex expressions, empty An empty expression has no value: it is just whitespace or null. Wherever an absolute expression is required, you may omit the expression and @code{as} will assume a value of (absolute) 0. This is compatible with other assemblers. @node Integer Exprs, , Empty Exprs, Expressions @section Integer Expressions @cindex integer expressions @cindex expressions, integer An @dfn{integer expression} is one or more @emph{arguments} delimited by @emph{operators}. @menu * Arguments:: Arguments * Operators:: Operators * Prefix Ops:: Prefix Operators * Infix Ops:: Infix Operators @end menu @node Arguments, Operators, Integer Exprs, Integer Exprs @subsection Arguments @cindex expression arguments @cindex arguments in expressions @cindex operands in expressions @cindex arithmetic operands @dfn{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 @{@var{section} @var{NNN}@} where @var{section} is one of text, data, bss, absolute, or undefined. @var{NNN} is a signed, 2's complement 32 bit integer. Numbers are usually integers. A number can be a flonum or bignum. In this case, you are warned that only the low order 32 bits are used, and @code{as} pretends these 32 bits are an integer. You may write integer-manipulating instructions that act on exotic constants, compatible with other assemblers. @cindex subexpressions Subexpressions are a left parenthesis @samp{(} followed by an integer expression, followed by a right parenthesis @samp{)}; or a prefix operator followed by an argument. @node Operators, Prefix Ops, Arguments, Integer Exprs @subsection Operators @cindex operators, in expressions @cindex arithmetic functions @cindex functions, in expressions @dfn{Operators} are arithmetic functions, like @code{+} or @code{%}. Prefix operators are followed by an argument. Infix operators appear between their arguments. Operators may be preceded and/or followed by whitespace. @node Prefix Ops, Infix Ops, Operators, Integer Exprs @subsection Prefix Operator @cindex prefix operators @code{as} has the following @dfn{prefix operators}. They each take one argument, which must be absolute. @c the tex/end tex stuff surrounding this small table is meant to make @c it align, on the printed page, with the similar table in the next @c section (which is inside an enumerate). @tex \global\advance\leftskip by \itemindent @end tex @table @code @item - @dfn{Negation}. Two's complement negation. @item ~ @dfn{Complementation}. Bitwise not. @end table @tex \global\advance\leftskip by -\itemindent @end tex @node Infix Ops, , Prefix Ops, Integer Exprs @subsection Infix Operators @cindex infix operators @cindex operators, permitted arguments @dfn{Infix operators} take two arguments, one on either side. Operators have precedence, but operations with equal precedence are performed left to right. Apart from @code{+} or @code{-}, both arguments must be absolute, and the result is absolute. @enumerate @cindex operator precedence @cindex precedence of operators @item Highest Precedence @table @code @item * @dfn{Multiplication}. @item / @dfn{Division}. Truncation is the same as the C operator @samp{/} @item % @dfn{Remainder}. @item < @itemx << @dfn{Shift Left}. Same as the C operator @samp{<<} @item > @itemx >> @dfn{Shift Right}. Same as the C operator @samp{>>} @end table @item Intermediate precedence @table @code @item | @dfn{Bitwise Inclusive Or}. @item & @dfn{Bitwise And}. @item ^ @dfn{Bitwise Exclusive Or}. @item ! @dfn{Bitwise Or Not}. @end table @item Lowest Precedence @table @code @item + @cindex addition, permitted arguments @cindex plus, permitted arguments @cindex arguments for addition @dfn{Addition}. If either argument is absolute, the result has the section of the other argument. If either argument is pass1 or undefined, the result is pass1. Otherwise @code{+} is illegal. @item - @cindex subtraction, permitted arguments @cindex minus, permitted arguments @cindex arguments for subtraction @dfn{Subtraction}. If the right argument is absolute, the result has the section of the left argument. If either argument is pass1 the result is pass1. If either argument is undefined the result is difference section. If both arguments are in the same section, the result is absolute---provided that section is one of text, data or bss. Otherwise subtraction is illegal. @end table @end enumerate The sense of the rule for addition is that it's only meaningful to add the @emph{offsets} in an address; you can only have a defined section in one of the two arguments. Similarly, you can't subtract quantities from two different sections. @node Pseudo Ops, Machine Dependent, Expressions, Top @chapter Assembler Directives @cindex directives, machine independent @cindex pseudo-ops, machine independent @cindex machine independent directives All assembler directives have names that begin with a period (@samp{.}). The rest of the name is letters, usually in lower case. This chapter discusses directives present regardless of the target machine configuration for the GNU assembler. @menu * Abort:: @code{.abort} * coff-ABORT:: @code{.ABORT} * Align:: @code{.align @var{abs-expr} , @var{abs-expr}} * App-File:: @code{.app-file @var{string}} * Ascii:: @code{.ascii "@var{string}"}@dots{} * Asciz:: @code{.asciz "@var{string}"}@dots{} * Byte:: @code{.byte @var{expressions}} * Comm:: @code{.comm @var{symbol} , @var{length} } * Data:: @code{.data @var{subsection}} * Def:: @code{.def @var{name}} * Desc:: @code{.desc @var{symbol}, @var{abs-expression}} * Dim:: @code{.dim} * Double:: @code{.double @var{flonums}} * Eject:: @code{.eject} * Else:: @code{.else} * Endef:: @code{.endef} * Endif:: @code{.endif} * Equ:: @code{.equ @var{symbol}, @var{expression}} * Extern:: @code{.extern} * File:: @code{.file @var{string}} * Fill:: @code{.fill @var{repeat} , @var{size} , @var{value}} * Float:: @code{.float @var{flonums}} * Global:: @code{.global @var{symbol}}, @code{.globl @var{symbol}} * hword:: @code{.hword @var{expressions}} * Ident:: @code{.ident} * If:: @code{.if @var{absolute expression}} * Include:: @code{.include "@var{file}"} * Int:: @code{.int @var{expressions}} * Lcomm:: @code{.lcomm @var{symbol} , @var{length}} * Lflags:: @code{.lflags} * Line:: @code{.line @var{line-number}} * Ln:: @code{.ln @var{line-number}} * List:: @code{.list} * Long:: @code{.long @var{expressions}} * Lsym:: @code{.lsym @var{symbol}, @var{expression}} * Nolist:: @code{.nolist} * Octa:: @code{.octa @var{bignums}} * Org:: @code{.org @var{new-lc} , @var{fill}} * Psize:: @code{.psize @var{lines}, @var{columns}} * Quad:: @code{.quad @var{bignums}} * Sbttl:: @code{.sbttl "@var{subheading}"} * Scl:: @code{.scl @var{class}} * Section:: @code{.section @var{name}, @var{subsection}} * Set:: @code{.set @var{symbol}, @var{expression}} * Short:: @code{.short @var{expressions}} * Single:: @code{.single @var{flonums}} * Size:: @code{.size} * Space:: @code{.space @var{size} , @var{fill}} * Stab:: @code{.stabd, .stabn, .stabs} * Tag:: @code{.tag @var{structname}} * Text:: @code{.text @var{subsection}} * Title:: @code{.title "@var{heading}"} * Type:: @code{.type @var{int}} * Val:: @code{.val @var{addr}} * Word:: @code{.word @var{expressions}} * Deprecated:: Deprecated Directives @end menu @node Abort, coff-ABORT, Pseudo Ops, Pseudo Ops @section @code{.abort} @cindex @code{abort} directive @cindex stopping the assembly This directive stops the assembly immediately. It is for compatibility with other assemblers. The original idea was that the assembly language source would be piped into the assembler. If the sender of the source quit, it could use this directive tells @code{as} to quit also. One day @code{.abort} will not be supported. @node coff-ABORT, Align, Abort, Pseudo Ops @section @code{.ABORT} @cindex @code{ABORT} directive When producing COFF output, @code{as} accepts this directive as a synonym for @samp{.abort}. When producing @code{b.out} output, @code{as} accepts this directive, but ignores it. @node Align, App-File, coff-ABORT, Pseudo Ops @section @code{.align @var{abs-expr} , @var{abs-expr}} @cindex padding the location counter @cindex @code{align} directive Pad the location counter (in the current subsection) to a particular storage boundary. The first expression (which must be absolute) is the number of low-order zero bits the location counter will have after advancement. For example @samp{.align 3} will advance the location counter until it a multiple of 8. If the location counter is already a multiple of 8, no change is needed. The second expression (also absolute) gives the value to be stored in the padding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are zero. @node App-File, Ascii, Align, Pseudo Ops @section @code{.app-file @var{string}} @cindex logical file name @cindex file name, logical @cindex @code{app-file} directive @code{.app-file} tells @code{as} that we are about to start a new logical file. @var{string} is the new file name. In general, the filename is recognized whether or not it is surrounded by quotes @samp{"}; but if you wish to specify an empty file name is permitted, you must give the quotes--@code{""}. This statement may go away in future: it is only recognized to be compatible with old @code{as} programs.@refill @node Ascii, Asciz, App-File, Pseudo Ops @section @code{.ascii "@var{string}"}@dots{} @cindex @code{ascii} directive @cindex string literals @code{.ascii} expects zero or more string literals (@pxref{Strings}) separated by commas. It assembles each string (with no automatic trailing zero byte) into consecutive addresses. @node Asciz, Byte, Ascii, Pseudo Ops @section @code{.asciz "@var{string}"}@dots{} @cindex @code{asciz} directive @cindex zero-terminated strings @cindex null-terminated strings @code{.asciz} is just like @code{.ascii}, but each string is followed by a zero byte. The ``z'' in @samp{.asciz} stands for ``zero''. @node Byte, Comm, Asciz, Pseudo Ops @section @code{.byte @var{expressions}} @cindex @code{byte} directive @cindex integers, one byte @code{.byte} expects zero or more expressions, separated by commas. Each expression is assembled into the next byte. @node Comm, Data, Byte, Pseudo Ops @section @code{.comm @var{symbol} , @var{length} } @cindex @code{comm} directive @cindex symbol, common @code{.comm} declares a named common area in the bss section. Normally @code{ld} reserves memory addresses for it during linking, so no partial program defines the location of the symbol. Use @code{.comm} to tell @code{ld} that it must be at least @var{length} bytes long. @code{ld} will allocate space for each @code{.comm} symbol that is at least as long as the longest @code{.comm} request in any of the partial programs linked. @var{length} is an absolute expression. @node Data, Def, Comm, Pseudo Ops @section @code{.data @var{subsection}} @cindex @code{data} directive @code{.data} tells @code{as} to assemble the following statements onto the end of the data subsection numbered @var{subsection} (which is an absolute expression). If @var{subsection} is omitted, it defaults to zero. @node Def, Desc, Data, Pseudo Ops @section @code{.def @var{name}} @cindex @code{def} directive @cindex COFF symbols, debugging @cindex debugging COFF symbols Begin defining debugging information for a symbol @var{name}; the definition extends until the @code{.endef} directive is encountered. This directive is only observed when @code{as} is configured for COFF format output; when producing @code{b.out}, @samp{.def} is recognized, but ignored. @node Desc, Dim, Def, Pseudo Ops @section @code{.desc @var{symbol}, @var{abs-expression}} @cindex @code{desc} directive @cindex COFF symbol descriptor @cindex symbol descriptor, COFF This directive sets the descriptor of the symbol (@pxref{Symbol Attributes}) to the low 16 bits of an absolute expression. The @samp{.desc} directive is not available when @code{as} is configured for COFF output; it is only for @code{a.out} or @code{b.out} object format. For the sake of compatibility, @code{as} will accept it, but produce no output, when configured for COFF. @node Dim, Double, Desc, Pseudo Ops @section @code{.dim} @cindex @code{dim} directive @cindex COFF auxiliary symbol information @cindex auxiliary symbol information, COFF This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside @code{.def}/@code{.endef} pairs. @samp{.dim} is only meaningful when generating COFF format output; when @code{as} is generating @code{b.out}, it accepts this directive but ignores it. @node Double, Eject, Dim, Pseudo Ops @section @code{.double @var{flonums}} @cindex @code{double} directive @cindex floating point numbers (double) @code{.double} expects zero or more flonums, separated by commas. It assembles floating point numbers. The exact kind of floating point numbers emitted depends on how @code{as} is configured. @xref{Machine Dependent}. @node Eject, Else, Double, Pseudo Ops @section @code{.eject} @cindex @code{eject} directive @cindex new page, in listings @cindex page, in listings @cindex listing control: new page Force a page break at this point, when generating assembly listings. @node Else, Endef, Eject, Pseudo Ops @section @code{.else} @cindex @code{else} directive @code{.else} is part of the @code{as} support for conditional assembly; @pxref{If,,@code{.if}}. It marks the beginning of a section of code to be assembled if the condition for the preceding @code{.if} was false. @node Endef, Endif, Else, Pseudo Ops @section @code{.endef} @cindex @code{endef} directive This directive flags the end of a symbol definition begun with @code{.def}. @samp{.endef} is only meaningful when generating COFF format output; if @code{as} is configured to generate @code{b.out}, it accepts this directive but ignores it. @node Endif, Equ, Endef, Pseudo Ops @section @code{.endif} @cindex @code{endif} directive @code{.endif} is part of the @code{as} support for conditional assembly; it marks the end of a block of code that is only assembled conditionally. @xref{If,,@code{.if}}. @node Equ, Extern, Endif, Pseudo Ops @section @code{.equ @var{symbol}, @var{expression}} @cindex @code{equ} directive @cindex assigning values to symbols @cindex symbols, assigning values to This directive sets the value of @var{symbol} to @var{expression}. It is synonymous with @samp{.set}; @pxref{Set,,@code{.set}}. @node Extern, File, Equ, Pseudo Ops @section @code{.extern} @cindex @code{extern} directive @code{.extern} is accepted in the source program---for compatibility with other assemblers---but it is ignored. @code{as} treats all undefined symbols as external. @node File, Fill, Extern, Pseudo Ops @section @code{.file @var{string}} @cindex @code{file} directive @cindex logical file name @cindex file name, logical @code{.file} (which may also be spelled @samp{.app-file}) tells @code{as} that we are about to start a new logical file. @var{string} is the new file name. In general, the filename is recognized whether or not it is surrounded by quotes @samp{"}; but if you wish to specify an empty file name, you must give the quotes--@code{""}. This statement may go away in future: it is only recognized to be compatible with old @code{as} programs. In some configurations of @code{as}, @code{.file} has already been removed to avoid conflicts with other assemblers. @xref{Machine Dependent}. @node Fill, Float, File, Pseudo Ops @section @code{.fill @var{repeat} , @var{size} , @var{value}} @cindex @code{fill} directive @cindex writing patterns in memory @cindex patterns, writing in memory @var{result}, @var{size} and @var{value} are absolute expressions. This emits @var{repeat} copies of @var{size} bytes. @var{Repeat} may be zero or more. @var{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 @var{repeat} bytes is taken from an 8-byte number. The highest order 4 bytes are zero. The lowest order 4 bytes are @var{value} rendered in the byte-order of an integer on the computer @code{as} is assembling for. Each @var{size} bytes in a repetition is taken from the lowest order @var{size} bytes of this number. Again, this bizarre behavior is compatible with other people's assemblers. @var{size} and @var{value} are optional. If the second comma and @var{value} are absent, @var{value} is assumed zero. If the first comma and following tokens are absent, @var{size} is assumed to be 1. @node Float, Global, Fill, Pseudo Ops @section @code{.float @var{flonums}} @cindex floating point numbers (single) @cindex @code{float} directive This directive assembles zero or more flonums, separated by commas. It has the same effect as @code{.single}. The exact kind of floating point numbers emitted depends on how @code{as} is configured. @xref{Machine Dependent}. @node Global, hword, Float, Pseudo Ops @section @code{.global @var{symbol}}, @code{.globl @var{symbol}} @cindex @code{global} directive @cindex symbol, making visible to linker @code{.global} makes the symbol visible to @code{ld}. If you define @var{symbol} in your partial program, its value is made available to other partial programs that are linked with it. Otherwise, @var{symbol} will take its attributes from a symbol of the same name from another partial program it is linked with. Both spellings (@samp{.globl} and @samp{.global}) are accepted, for compatibility with other assemblers. @node hword, Ident, Global, Pseudo Ops @section @code{.hword @var{expressions}} @cindex @code{hword} directive @cindex integers, 16-bit @cindex numbers, 16-bit @cindex sixteen bit integers This expects zero or more @var{expressions}, and emits a 16 bit number for each. This directive is a synonym for @samp{.short}; depending on the target architecture, it may also be a synonym for @samp{.word}. @node Ident, If, hword, Pseudo Ops @section @code{.ident} @cindex @code{ident} directive This directive is used by some assemblers to place tags in object files. @code{as} simply accepts the directive for source-file compatibility with such assemblers, but does not actually emit anything for it. @node If, Include, Ident, Pseudo Ops @section @code{.if @var{absolute expression}} @cindex conditional assembly @cindex @code{if} directive @code{.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 @var{absolute expression}) is non-zero. The end of the conditional section of code must be marked by @code{.endif} (@pxref{Endif,,@code{.endif}}); optionally, you may include code for the alternative condition, flagged by @code{.else} (@pxref{Else,,@code{.else}}. The following variants of @code{.if} are also supported: @table @code @item .ifdef @var{symbol} @cindex @code{ifdef} directive Assembles the following section of code if the specified @var{symbol} has been defined. @item .ifndef @var{symbol} @itemx ifnotdef @var{symbol} @cindex @code{ifndef} directive @cindex @code{ifnotdef} directive Assembles the following section of code if the specified @var{symbol} has not been defined. Both spelling variants are equivalent. @end table @node Include, Int, If, Pseudo Ops @section @code{.include "@var{file}"} @cindex @code{include} directive @cindex supporting files, including @cindex files, including This directive provides a way to include supporting files at specified points in your source program. The code from @var{file} is assembled as if it followed the point of the @code{.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 @samp{-I} command-line option (@pxref{Invoking,,Command-Line Options}). Quotation marks are required around @var{file}. @node Int, Lcomm, Include, Pseudo Ops @section @code{.int @var{expressions}} @cindex @code{int} directive @cindex integers, 32-bit Expect zero or more @var{expressions}, of any section, separated by commas. For each expression, emit a 32-bit number that will, at run time, be the value of that expression. The byte order of the expression depends on what kind of computer will run the program. @node Lcomm, Lflags, Int, Pseudo Ops @section @code{.lcomm @var{symbol} , @var{length}} @cindex @code{lcomm} directive @cindex local common symbols @cindex symbols, local common Reserve @var{length} (an absolute expression) bytes for a local common denoted by @var{symbol}. The section and value of @var{symbol} are those of the new local common. The addresses are allocated in the bss section, so at run-time the bytes will start off zeroed. @var{Symbol} is not declared global (@pxref{Global,,@code{.global}}), so is normally not visible to @code{ld}. @node Lflags, Line, Lcomm, Pseudo Ops @section @code{.lflags} @cindex @code{lflags} directive (ignored) @code{as} accepts this directive, for compatibility with other assemblers, but ignores it. @node Line, Ln, Lflags, Pseudo Ops @section @code{.line @var{line-number}} @cindex @code{line} directive @cindex logical line number Tell @code{as} to change the logical line number. @var{line-number} must be an absolute expression. The next line will have that logical line number. So any other statements on the current line (after a statement separator character) will be reported as on logical line number @var{line-number} @minus{} 1. One day this directive will be unsupported: it is used only for compatibility with existing assembler programs. @refill @emph{Warning:} In the AMD29K configuration of as, this command is only available with the name @code{.ln}, rather than as either @code{.line} or @code{.ln}. Even though this is a directive associated with the @code{a.out} or @code{b.out} object-code formats, @code{as} will still recognize it when producing COFF output, and will treat @samp{.line} as though it were the COFF @samp{.ln} @emph{if} it is found outside a @code{.def}/@code{.endef} pair. Inside a @code{.def}, @samp{.line} is, instead, one of the directives used by compilers to generate auxiliary symbol information for debugging. @node Ln, List, Line, Pseudo Ops @section @code{.ln @var{line-number}} @cindex @code{ln} directive @samp{.ln} is a synonym for @samp{.line}. @node List, Long, Ln, Pseudo Ops @section @code{.list} @cindex @code{list} directive @cindex listing control, turning on Control (in conjunction with the @code{.nolist} directive) whether or not assembly listings are generated. These two directives maintain an internal counter (which is zero initially). @code{.list} increments the counter, and @code{.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 @samp{-a} command line option; @pxref{Invoking,,Command-Line Options}), the initial value of the listing counter is one. @node Long, Lsym, List, Pseudo Ops @section @code{.long @var{expressions}} @cindex @code{long} directive @code{.long} is the same as @samp{.int}, @pxref{Int,,@code{.int}}. @node Lsym, Nolist, Long, Pseudo Ops @section @code{.lsym @var{symbol}, @var{expression}} @cindex @code{lsym} directive @cindex symbol, not referenced in assembly @code{.lsym} creates a new symbol named @var{symbol}, but does not put it in the hash table, ensuring it cannot be referenced by name during the rest of the assembly. This sets the attributes of the symbol to be the same as the expression value: @smallexample @var{other} = @var{descriptor} = 0 @var{type} = @r{(section of @var{expression})} @var{value} = @var{expression} @end smallexample @noindent The new symbol is not flagged as external. @node Nolist, Octa, Lsym, Pseudo Ops @section @code{.nolist} @cindex @code{nolist} directive @cindex listing control, turning off Control (in conjunction with the @code{.list} directive) whether or not assembly listings are generated. These two directives maintain an internal counter (which is zero initially). @code{.list} increments the counter, and @code{.nolist} decrements it. Assembly listings are generated whenever the counter is greater than zero. @node Octa, Org, Nolist, Pseudo Ops @section @code{.octa @var{bignums}} @c FIXME: double size emitted for "octa" on i960, others? Or warn? @cindex @code{octa} directive @cindex integer, 16-byte @cindex sixteen byte integer 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 @emph{octa}-word for 16 bytes. @node Org, Psize, Octa, Pseudo Ops @section @code{.org @var{new-lc} , @var{fill}} @cindex @code{org} directive @cindex location counter, advancing @cindex advancing location counter @cindex current address, advancing @code{.org} will advance the location counter of the current section to @var{new-lc}. @var{new-lc} is either an absolute expression or an expression with the same section as the current subsection. That is, you can't use @code{.org} to cross sections: if @var{new-lc} has the wrong section, the @code{.org} directive is ignored. To be compatible with former assemblers, if the section of @var{new-lc} is absolute, @code{as} will issue a warning, then pretend the section of @var{new-lc} is the same as the current subsection. @code{.org} may only increase the location counter, or leave it unchanged; you cannot use @code{.org} to move the location counter backwards. @c double negative used below "not undefined" because this is a specific @c reference to "undefined" (as SEG_UNKNOWN is called in this manual) @c section. pesch@cygnus.com 18feb91 Because @code{as} tries to assemble programs in one pass @var{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 @var{fill} which should be an absolute expression. If the comma and @var{fill} are omitted, @var{fill} defaults to zero. @node Psize, Quad, Org, Pseudo Ops @section @code{.psize @var{lines} , @var{columns}} @cindex @code{psize} directive @cindex listing control: paper size @cindex paper size, for listings Use this directive to declare the number of lines---and, optionally, the number of columns---to use for each page, when generating listings. If you don't use @code{.psize}, listings will use a default line-count of 60. You may omit the comma and @var{columns} specification; the default width is 200 columns. @code{as} will generate formfeeds whenever the specified number of lines is exceeded (or whenever you explicitly request one, using @code{.eject}). If you specify @var{lines} as @code{0}, no formfeeds are generated save those explicitly specified with @code{.eject}. @node Quad, Sbttl, Psize, Pseudo Ops @section @code{.quad @var{bignums}} @cindex @code{quad} directive @code{.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.@refill @cindex eight-byte integer @cindex integer, 8-byte The term ``quad'' comes from contexts in which a ``word'' is two bytes; hence @emph{quad}-word for 8 bytes. @node Sbttl, Scl, Quad, Pseudo Ops @section @code{.sbttl "@var{subheading}"} @cindex @code{sbttl} directive @cindex subtitles for listings @cindex listing control: subtitle Use @var{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. @node Scl, Section, Sbttl, Pseudo Ops @section @code{.scl @var{class}} @cindex @code{scl} directive @cindex symbol storage class (COFF) @cindex COFF symbol storage class Set the storage-class value for a symbol. This directive may only be used inside a @code{.def}/@code{.endef} pair. Storage class may flag whether a symbol is static or external, or it may record further symbolic debugging information. The @samp{.scl} directive is primarily associated with COFF output; when configured to generate @code{b.out} output format, @code{as} will accept this directive but ignore it. @node Section, Set, Scl, Pseudo Ops @section @code{.section @var{name}, @var{subsection}} @cindex @code{section} directive @cindex named section (COFF) @cindex COFF named section Assemble the following code into end of subsection numbered @var{subsection} in the COFF named section @var{name}. If you omit @var{subsection}, @code{as} uses subsection number zero. @samp{.section .text} is equivalent to the @code{.text} directive; @samp{.section .data} is equivalent to the @code{.data} directive. @node Set, Short, Section, Pseudo Ops @section @code{.set @var{symbol}, @var{expression}} @cindex @code{set} directive @cindex symbol value, setting This directive sets the value of @var{symbol} to @var{expression}. This will change @var{symbol}'s value and type to conform to @var{expression}. If @var{symbol} was flagged as external, it remains flagged. (@xref{Symbol Attributes}.) You may @code{.set} a symbol many times in the same assembly. If the expression's section is unknowable during pass 1, a second pass over the source program will be forced. The second pass is currently not implemented. @code{as} will abort with an error message if one is required. If you @code{.set} a global symbol, the value stored in the object file is the last value stored into it. @node Short, Single, Set, Pseudo Ops @section @code{.short @var{expressions}} @cindex @code{short} directive @code{.short} is the same as @samp{.word}. @xref{Word,,@code{.word}}. @node Single, Size, Short, Pseudo Ops @section @code{.single @var{flonums}} @cindex @code{single} directive @cindex floating point numbers (single) This directive assembles zero or more flonums, separated by commas. It has the same effect as @code{.float}. The exact kind of floating point numbers emitted depends on how @code{as} is configured. @xref{Machine Dependent}. @node Size, Space, Single, Pseudo Ops @section @code{.size} @cindex @code{size} directive This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside @code{.def}/@code{.endef} pairs. @samp{.size} is only meaningful when generating COFF format output; when @code{as} is generating @code{b.out}, it accepts this directive but ignores it. @node Space, Stab, Size, Pseudo Ops @section @code{.space @var{size} , @var{fill}} @cindex @code{space} directive @cindex filling memory This directive emits @var{size} bytes, each of value @var{fill}. Both @var{size} and @var{fill} are absolute expressions. If the comma and @var{fill} are omitted, @var{fill} is assumed to be zero. On the AMD 29K, this directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. @quotation @emph{Warning:} In other versions of the GNU assembler, the directive @code{.space} has the effect of @code{.block} @xref{Machine Dependent}. @end quotation @node Stab, Tag, Space, Pseudo Ops @section @code{.stabd, .stabn, .stabs} @cindex symbolic debuggers, information for @cindex @code{stab@var{x}} directives There are three directives that begin @samp{.stab}. All emit symbols (@pxref{Symbols}), for use by symbolic debuggers. The symbols are not entered in the @code{as} hash table: they cannot be referenced elsewhere in the source file. Up to five fields are required: @table @var @item string This is the symbol's name. It may contain any character except @samp{\000}, so is more general than ordinary symbol names. Some debuggers used to code arbitrarily complex structures into symbol names using this field. @item type An absolute expression. The symbol's type is set to the low 8 bits of this expression. Any bit pattern is permitted, but @code{ld} and debuggers will choke on silly bit patterns. @item other An absolute expression. The symbol's ``other'' attribute is set to the low 8 bits of this expression. @item desc An absolute expression. The symbol's descriptor is set to the low 16 bits of this expression. @item value An absolute expression which becomes the symbol's value. @end table If a warning is detected while reading a @code{.stabd}, @code{.stabn}, or @code{.stabs} statement, the symbol has probably already been created and you will get a half-formed symbol in your object file. This is compatible with earlier assemblers! @table @code @cindex @code{stabd} directive @item .stabd @var{type} , @var{other} , @var{desc} The ``name'' of the symbol generated is not even an empty string. It is a null pointer, for compatibility. Older assemblers used a null pointer so they didn't waste space in object files with empty strings. The symbol's value is set to the location counter, relocatably. When your program is linked, the value of this symbol will be where the location counter was when the @code{.stabd} was assembled. @item .stabn @var{type} , @var{other} , @var{desc} , @var{value} @cindex @code{stabn} directive The name of the symbol is set to the empty string @code{""}. @item .stabs @var{string} , @var{type} , @var{other} , @var{desc} , @var{value} @cindex @code{stabs} directive All five fields are specified. @end table @node Tag, Text, Stab, Pseudo Ops @section @code{.tag @var{structname}} @cindex COFF structure debugging @cindex structure debugging, COFF @cindex @code{tag} directive This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside @code{.def}/@code{.endef} pairs. Tags are used to link structure definitions in the symbol table with instances of those structures. @samp{.tag} is only used when generating COFF format output; when @code{as} is generating @code{b.out}, it accepts this directive but ignores it. @node Text, Title, Tag, Pseudo Ops @section @code{.text @var{subsection}} @cindex @code{text} directive Tells @code{as} to assemble the following statements onto the end of the text subsection numbered @var{subsection}, which is an absolute expression. If @var{subsection} is omitted, subsection number zero is used. @node Title, Type, Text, Pseudo Ops @section @code{.title "@var{heading}"} @cindex @code{title} directive @cindex listing control: title line Use @var{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. @node Type, Val, Title, Pseudo Ops @section @code{.type @var{int}} @cindex COFF symbol type @cindex symbol type, COFF @cindex @code{type} directive This directive, permitted only within @code{.def}/@code{.endef} pairs, records the integer @var{int} as the type attribute of a symbol table entry. @samp{.type} is associated only with COFF format output; when @code{as} is configured for @code{b.out} output, it accepts this directive but ignores it. @node Val, Word, Type, Pseudo Ops @section @code{.val @var{addr}} @cindex @code{val} directive @cindex COFF value attribute @cindex value attribute, COFF This directive, permitted only within @code{.def}/@code{.endef} pairs, records the address @var{addr} as the value attribute of a symbol table entry. @samp{.val} is used only for COFF output; when @code{as} is configured for @code{b.out}, it accepts this directive but ignores it. @node Word, Deprecated, Val, Pseudo Ops @section @code{.word @var{expressions}} @cindex @code{word} directive This directive expects zero or more @var{expressions}, of any section, separated by commas. The size of the number emitted, and its byte order, depends on what kind of computer will run the program. @c on amd29k, i960, sparc the "special treatment to support compilers" doesn't @c happen---32-bit addressability, period; no long/short jumps. @cindex difference tables altered @cindex altered difference tables @quotation @emph{Warning: Special Treatment to support Compilers} @end quotation Machines with a 32-bit address space, but that do less than 32-bit addressing, require the following special treatment. If the machine of interest to you does 32-bit addressing (or doesn't require it; @pxref{Machine Dependent}), you can ignore this issue. In order to assemble compiler output into something that will work, @code{as} will occasionlly do strange things to @samp{.word} directives. Directives of the form @samp{.word sym1-sym2} are often emitted by compilers as part of jump tables. Therefore, when @code{as} assembles a directive of the form @samp{.word sym1-sym2}, and the difference between @code{sym1} and @code{sym2} does not fit in 16 bits, @code{as} will create a @dfn{secondary jump table}, immediately before the next label. This secondary jump table will be preceded by a short-jump to the first byte after the secondary table. This short-jump prevents the flow of control from accidentally falling into the new table. Inside the table will be a long-jump to @code{sym2}. The original @samp{.word} will contain @code{sym1} minus the address of the long-jump to @code{sym2}. If there were several occurrences of @samp{.word sym1-sym2} before the secondary jump table, all of them will be adjusted. If there was a @samp{.word sym3-sym4}, that also did not fit in sixteen bits, a long-jump to @code{sym4} will be included in the secondary jump table, and the @code{.word} directives will be adjusted to contain @code{sym3} minus the address of the long-jump to @code{sym4}; and so on, for as many entries in the original jump table as necessary. @node Deprecated, , Word, Pseudo Ops @section Deprecated Directives @cindex deprecated directives @cindex obsolescent directives One day these directives won't work. They are included for compatibility with older assemblers. @table @t @item .abort @item .app-file @item .line @end table @node Machine Dependent, Copying, Pseudo Ops, Top @chapter Machine Dependent Features @cindex machine dependencies The machine instruction sets are (almost by definition) different on each machine where @code{as} runs. Floating point representations vary as well, and @code{as} often supports a few additional directives or command-line options for compatibility with other assemblers on a particular platform. Finally, some versions of @code{as} support special pseudo-instructions for branch optimization. This chapter discusses most of these differences, though it does not include details on any machine's instruction set. For details on that subject, see the hardware manufacturer's manual. @menu * Vax-Dependent:: VAX Dependent Features * AMD29K-Dependent:: AMD 29K Dependent Features * H8/300-Dependent:: Hitachi H8/300 Dependent Features * i960-Dependent:: Intel 80960 Dependent Features * M68K-Dependent:: M680x0 Dependent Features * Sparc-Dependent:: SPARC Dependent Features * i386-Dependent:: 80386 Dependent Features @end menu @node Vax-Dependent, AMD29K-Dependent, Machine Dependent, Machine Dependent @section VAX Dependent Features @cindex VAX support @menu * Vax-Opts:: VAX Command-Line Options * VAX-float:: VAX Floating Point * VAX-directives:: Vax Machine Directives * VAX-opcodes:: VAX Opcodes * VAX-branch:: VAX Branch Improvement * VAX-operands:: VAX Operands * VAX-no:: Not Supported on VAX @end menu @node Vax-Opts, VAX-float, Vax-Dependent, Vax-Dependent @subsection VAX Command-Line Options @cindex command-line options ignored, VAX @cindex VAX command-line options ignored The Vax version of @code{as} accepts any of the following options, gives a warning message that the option was ignored and proceeds. These options are for compatibility with scripts designed for other people's assemblers. @table @asis @item @kbd{-D} (Debug) @itemx @kbd{-S} (Symbol Table) @itemx @kbd{-T} (Token Trace) @cindex @code{-D}, ignored on VAX @cindex @code{-S}, ignored on VAX @cindex @code{-T}, ignored on VAX These are obsolete options used to debug old assemblers. @item @kbd{-d} (Displacement size for JUMPs) @cindex @code{-d}, VAX option This option expects a number following the @kbd{-d}. Like options that expect filenames, the number may immediately follow the @kbd{-d} (old standard) or constitute the whole of the command line argument that follows @kbd{-d} (GNU standard). @item @kbd{-V} (Virtualize Interpass Temporary File) @cindex @code{-V}, redundant on VAX Some other assemblers use a temporary file. This option commanded them to keep the information in active memory rather than in a disk file. @code{as} always does this, so this option is redundant. @item @kbd{-J} (JUMPify Longer Branches) @cindex @code{-J}, ignored on VAX Many 32-bit computers permit a variety of branch instructions to do the same job. Some of these instructions are short (and fast) but have a limited range; others are long (and slow) but can branch anywhere in virtual memory. Often there are 3 flavors of branch: short, medium and long. Some other assemblers would emit short and medium branches, unless told by this option to emit short and long branches. @item @kbd{-t} (Temporary File Directory) @cindex @code{-t}, ignored on VAX Some other assemblers may use a temporary file, and this option takes a filename being the directory to site the temporary file. @code{as} does not use a temporary disk file, so this option makes no difference. @kbd{-t} needs exactly one filename. @end table @cindex VMS (VAX) options @cindex options for VAX/VMS @cindex VAX/VMS options @cindex @code{-h} option, VAX/VMS @cindex @code{-+} option, VAX/VMS @cindex Vax-11 C compatibility @cindex symbols with lowercase, VAX/VMS @c FIXME! look into "I think" below, correct if needed, delete. The Vax version of the assembler accepts two options when compiled for VMS. They are @kbd{-h}, and @kbd{-+}. The @kbd{-h} option prevents @code{as} from modifying the symbol-table entries for symbols that contain lowercase characters (I think). The @kbd{-+} option causes @code{as} to print warning messages if the FILENAME part of the object file, or any symbol name is larger than 31 characters. The @kbd{-+} option also insertes some code following the @samp{_main} symbol so that the object file will be compatible with Vax-11 "C". @node VAX-float, VAX-directives, Vax-Opts, Vax-Dependent @subsection VAX Floating Point @cindex VAX floating point @cindex floating point, VAX Conversion of flonums to floating point is correct, and compatible with previous assemblers. Rounding is towards zero if the remainder is exactly half the least significant bit. @code{D}, @code{F}, @code{G} and @code{H} floating point formats are understood. Immediate floating literals (@emph{e.g.} @samp{S`$6.9}) are rendered correctly. Again, rounding is towards zero in the boundary case. @cindex @code{float} directive, VAX @cindex @code{double} directive, VAX The @code{.float} directive produces @code{f} format numbers. The @code{.double} directive produces @code{d} format numbers. @node VAX-directives, VAX-opcodes, VAX-float, Vax-Dependent @subsection Vax Machine Directives @cindex machine directives, VAX @cindex VAX machine directives The Vax version of the assembler supports four directives for generating Vax floating point constants. They are described in the table below. @cindex wide floating point directives, VAX @table @code @item .dfloat @cindex @code{dfloat} directive, VAX This expects zero or more flonums, separated by commas, and assembles Vax @code{d} format 64-bit floating point constants. @item .ffloat @cindex @code{ffloat} directive, VAX This expects zero or more flonums, separated by commas, and assembles Vax @code{f} format 32-bit floating point constants. @item .gfloat @cindex @code{gfloat} directive, VAX This expects zero or more flonums, separated by commas, and assembles Vax @code{g} format 64-bit floating point constants. @item .hfloat @cindex @code{hfloat} directive, VAX This expects zero or more flonums, separated by commas, and assembles Vax @code{h} format 128-bit floating point constants. @end table @node VAX-opcodes, VAX-branch, VAX-directives, Vax-Dependent @subsection VAX Opcodes @cindex VAX opcode mnemonics @cindex opcode mnemonics, VAX @cindex mnemonics for opcodes, VAX All DEC mnemonics are supported. Beware that @code{case@dots{}} instructions have exactly 3 operands. The dispatch table that follows the @code{case@dots{}} instruction should be made with @code{.word} statements. This is compatible with all unix assemblers we know of. @node VAX-branch, VAX-operands, VAX-opcodes, Vax-Dependent @subsection VAX Branch Improvement @cindex VAX branch improvement @cindex branch improvement, VAX @cindex pseudo-ops for branch, VAX Certain pseudo opcodes are permitted. They are for branch instructions. They expand to the shortest branch instruction that will reach the target. Generally these mnemonics are made by substituting @samp{j} for @samp{b} at the start of a DEC mnemonic. This feature is included both for compatibility and to help compilers. If you don't need this feature, don't use these opcodes. Here are the mnemonics, and the code they can expand into. @table @code @item jbsb @samp{Jsb} is already an instruction mnemonic, so we chose @samp{jbsb}. @table @asis @item (byte displacement) @kbd{bsbb @dots{}} @item (word displacement) @kbd{bsbw @dots{}} @item (long displacement) @kbd{jsb @dots{}} @end table @item jbr @itemx jr Unconditional branch. @table @asis @item (byte displacement) @kbd{brb @dots{}} @item (word displacement) @kbd{brw @dots{}} @item (long displacement) @kbd{jmp @dots{}} @end table @item j@var{COND} @var{COND} may be any one of the conditional branches @code{neq}, @code{nequ}, @code{eql}, @code{eqlu}, @code{gtr}, @code{geq}, @code{lss}, @code{gtru}, @code{lequ}, @code{vc}, @code{vs}, @code{gequ}, @code{cc}, @code{lssu}, @code{cs}. @var{COND} may also be one of the bit tests @code{bs}, @code{bc}, @code{bss}, @code{bcs}, @code{bsc}, @code{bcc}, @code{bssi}, @code{bcci}, @code{lbs}, @code{lbc}. @var{NOTCOND} is the opposite condition to @var{COND}. @table @asis @item (byte displacement) @kbd{b@var{COND} @dots{}} @item (word displacement) @kbd{b@var{NOTCOND} foo ; brw @dots{} ; foo:} @item (long displacement) @kbd{b@var{NOTCOND} foo ; jmp @dots{} ; foo:} @end table @item jacb@var{X} @var{X} may be one of @code{b d f g h l w}. @table @asis @item (word displacement) @kbd{@var{OPCODE} @dots{}} @item (long displacement) @example @var{OPCODE} @dots{}, foo ; brb bar ; foo: jmp @dots{} ; bar: @end example @end table @item jaob@var{YYY} @var{YYY} may be one of @code{lss leq}. @item jsob@var{ZZZ} @var{ZZZ} may be one of @code{geq gtr}. @table @asis @item (byte displacement) @kbd{@var{OPCODE} @dots{}} @item (word displacement) @example @var{OPCODE} @dots{}, foo ; brb bar ; foo: brw @var{destination} ; bar: @end example @item (long displacement) @example @var{OPCODE} @dots{}, foo ; brb bar ; foo: jmp @var{destination} ; bar: @end example @end table @item aobleq @itemx aoblss @itemx sobgeq @itemx sobgtr @table @asis @item (byte displacement) @kbd{@var{OPCODE} @dots{}} @item (word displacement) @example @var{OPCODE} @dots{}, foo ; brb bar ; foo: brw @var{destination} ; bar: @end example @item (long displacement) @example @var{OPCODE} @dots{}, foo ; brb bar ; foo: jmp @var{destination} ; bar: @end example @end table @end table @node VAX-operands, VAX-no, VAX-branch, Vax-Dependent @subsection VAX Operands @cindex VAX operand notation @cindex operand notation, VAX @cindex immediate character, VAX @cindex VAX immediate character The immediate character is @samp{$} for Unix compatibility, not @samp{#} as DEC writes it. @cindex indirect character, VAX @cindex VAX indirect character The indirect character is @samp{*} for Unix compatibility, not @samp{@@} as DEC writes it. @cindex displacement sizing character, VAX @cindex VAX displacement sizing character The displacement sizing character is @samp{`} (an accent grave) for Unix compatibility, not @samp{^} as DEC writes it. The letter preceding @samp{`} may have either case. @samp{G} is not understood, but all other letters (@code{b i l s w}) are understood. @cindex register names, VAX @cindex VAX register names Register names understood are @code{r0 r1 r2 @dots{} r15 ap fp sp pc}. Any case of letters will do. For instance @smallexample tstb *w`$4(r5) @end smallexample Any expression is permitted in an operand. Operands are comma separated. @c There is some bug to do with recognizing expressions @c in operands, but I forget what it is. It is @c a syntax clash because () is used as an address mode @c and to encapsulate sub-expressions. @node VAX-no, , VAX-operands, Vax-Dependent @subsection Not Supported on VAX @cindex VAX bitfields not supported @cindex bitfields, not supported on VAX Vax bit fields can not be assembled with @code{as}. Someone can add the required code if they really need it. @node AMD29K-Dependent, H8/300-Dependent, Vax-Dependent, Machine Dependent @section AMD 29K Dependent Features @cindex AMD 29K support @cindex 29K support @menu * AMD29K Options:: Options * AMD29K Syntax:: Syntax * AMD29K Floating Point:: Floating Point * AMD29K Directives:: AMD 29K Machine Directives * AMD29K Opcodes:: Opcodes @end menu @node AMD29K Options, AMD29K Syntax, AMD29K-Dependent, AMD29K-Dependent @subsection Options @cindex AMD 29K options (none) @cindex options for AMD29K (none) @code{as} has no additional command-line options for the AMD 29K family. @node AMD29K Syntax, AMD29K Floating Point, AMD29K Options, AMD29K-Dependent @subsection Syntax @menu * AMD29K-Chars:: Special Characters * AMD29K-Regs:: Register Names @end menu @node AMD29K-Chars, AMD29K-Regs, AMD29K Syntax, AMD29K Syntax @subsubsection Special Characters @cindex line comment character, AMD 29K @cindex AMD 29K line comment character @samp{;} is the line comment character. @cindex line separator, AMD 29K @cindex AMD 29K line separator @cindex statement separator, AMD 29K @cindex AMD 29K statement separator @samp{@@} can be used instead of a newline to separate statements. @cindex identifiers, AMD 29K @cindex AMD 29K identifiers The character @samp{?} is permitted in identifiers (but may not begin an identifier). @node AMD29K-Regs, , AMD29K-Chars, AMD29K Syntax @subsubsection Register Names @cindex AMD 29K register names @cindex register names, AMD 29K General-purpose registers are represented by predefined symbols of the form @samp{GR@var{nnn}} (for global registers) or @samp{LR@var{nnn}} (for local registers), where @var{nnn} represents a number between @code{0} and @code{127}, written with no leading zeros. The leading letters may be in either upper or lower case; for example, @samp{gr13} and @samp{LR7} are both valid register names. You may also refer to general-purpose registers by specifying the register number as the result of an expression (prefixed with @samp{%%} to flag the expression as a register number): @smallexample %%@var{expression} @end smallexample @noindent ---where @var{expression} must be an absolute expression evaluating to a number between @code{0} and @code{255}. The range [0, 127] refers to global registers, and the range [128, 255] to local registers. @cindex special purpose registers, AMD 29K @cindex AMD 29K special purpose registers @cindex protected registers, AMD 29K @cindex AMD 29K protected registers In addition, @code{as} understands the following protected special-purpose register names for the AMD 29K family: @smallexample vab chd pc0 ops chc pc1 cps rbp pc2 cfg tmc mmu cha tmr lru @end smallexample These unprotected special-purpose register names are also recognized: @smallexample ipc alu fpe ipa bp inte ipb fc fps q cr exop @end smallexample @node AMD29K Floating Point, AMD29K Directives, AMD29K Syntax, AMD29K-Dependent @subsection Floating Point @cindex floating point, AMD 29K (@sc{ieee}) @cindex AMD 29K floating point (@sc{ieee}) The AMD 29K family uses @sc{ieee} floating-point numbers. @node AMD29K Directives, AMD29K Opcodes, AMD29K Floating Point, AMD29K-Dependent @subsection AMD 29K Machine Directives @cindex machine directives, AMD 29K @cindex AMD 29K machine directives @table @code @item .block @var{size} , @var{fill} @cindex @code{block} directive, AMD 29K This directive emits @var{size} bytes, each of value @var{fill}. Both @var{size} and @var{fill} are absolute expressions. If the comma and @var{fill} are omitted, @var{fill} is assumed to be zero. In other versions of the GNU assembler, this directive is called @samp{.space}. @end table @table @code @item .cputype @cindex @code{cputype} directive, AMD 29K This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. @item .file @cindex @code{file} directive, AMD 29K This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. @quotation @emph{Warning:} in other versions of the GNU assembler, @code{.file} is used for the directive called @code{.app-file} in the AMD 29K support. @end quotation @item .line @cindex @code{line} directive, AMD 29K This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. @item .reg @var{symbol}, @var{expression} @cindex @code{reg} directive, AMD 29K @code{.reg} has the same effect as @code{.lsym}; @pxref{Lsym,,@code{.lsym}}. @item .sect @cindex @code{sect} directive, AMD 29K This directive is ignored; it is accepted for compatibility with other AMD 29K assemblers. @item .use @var{section name} @cindex @code{use} directive, AMD 29K Establishes the section and subsection for the following code; @var{section name} may be one of @code{.text}, @code{.data}, @code{.data1}, or @code{.lit}. With one of the first three @var{section name} options, @samp{.use} is equivalent to the machine directive @var{section name}; the remaining case, @samp{.use .lit}, is the same as @samp{.data 200}. @end table @node AMD29K Opcodes, , AMD29K Directives, AMD29K-Dependent @subsection Opcodes @cindex AMD 29K opcodes @cindex opcodes for AMD 29K @code{as} implements all the standard AMD 29K opcodes. No additional pseudo-instructions are needed on this family. For information on the 29K machine instruction set, see @cite{Am29000 User's Manual}, Advanced Micro Devices, Inc. @node H8/300-Dependent, i960-Dependent, AMD29K-Dependent, Machine Dependent @section H8/300 Dependent Features @cindex H8/300 support @menu * H8/300 Options:: Options * H8/300 Syntax:: Syntax * H8/300 Floating Point:: Floating Point * H8/300 Directives:: H8/300 Machine Directives * H8/300 Opcodes:: Opcodes @end menu @node H8/300 Options, H8/300 Syntax, H8/300-Dependent, H8/300-Dependent @subsection Options @cindex H8/300 options (none) @cindex options, H8/300 (none) @code{as} has no additional command-line options for the Hitachi H8/300 family. @node H8/300 Syntax, H8/300 Floating Point, H8/300 Options, H8/300-Dependent @subsection Syntax @menu * H8/300-Chars:: Special Characters * H8/300-Regs:: Register Names * H8/300-Addressing:: Addressing Modes @end menu @node H8/300-Chars, H8/300-Regs, H8/300 Syntax, H8/300 Syntax @subsubsection Special Characters @cindex line comment character, H8/300 @cindex H8/300 line comment character @samp{;} is the line comment character. @cindex line separator, H8/300 @cindex statement separator, H8/300 @cindex H8/300 line separator @samp{$} can be used instead of a newline to separate statements. Therefore @emph{you may not use @samp{$} in symbol names} on the H8/300. @node H8/300-Regs, H8/300-Addressing, H8/300-Chars, H8/300 Syntax @subsubsection Register Names @cindex H8/300 registers @cindex registers, H8/300 You can use predefined symbols of the form @samp{r@var{n}h} and @samp{r@var{n}l} to refer to the H8/300 registers as sixteen 8-bit general-purpose registers. @var{n} is a digit from @samp{0} to @samp{7}); for instance, both @samp{r0h} and @samp{r7l} are valid register names. You can also use the eight predefined symbols @samp{r@var{n}} to refer to the H8/300 registers as 16-bit registers (you must use this form for addressing). The two control registers are called @code{pc} (program counter; a 16-bit register) and @code{ccr} (condition code register; an 8-bit register). @code{r7} is used as the stack pointer, and can also be called @code{sp}. @node H8/300-Addressing, , H8/300-Regs, H8/300 Syntax @subsubsection Addressing Modes @cindex addressing modes, H8/300 @cindex H8/300 addressing modes as understands the following addressing modes for the H8/300: @table @code @item r@var{n} Register direct @item @@r@var{n} Register indirect @item @@(@var{d}, r@var{n}) @itemx @@(@var{d}:16, r@var{n}) Register indirect: 16-bit displacement @var{d} from register @var{n}. (You may specify the @samp{:16} for clarity if you wish, but it is not required and has no effect.) @item @@r@var{n}+ Register indirect with post-increment @item @@-r@var{n} Register indirect with pre-decrement @item @code{@@}@var{aa} @itemx @code{@@}@var{aa}:8 @itemx @code{@@}@var{aa}:16 Absolute address @code{aa}. You may specify the @samp{:8} or @samp{:16} for clarity, if you wish; but @code{as} neither requires this nor uses it---the address size required is taken from context. @item #@var{xx} @itemx #@var{xx}:8 @itemx #@var{xx}:16 Immediate data @var{xx}. You may specify the @samp{:8} or @samp{:16} for clarity, if you wish; but @code{as} neither requires this nor uses it---the data size required is taken from context. @item @code{@@}@code{@@}@var{aa} @itemx @code{@@}@code{@@}@var{aa}:8 Memory indirect. You may specify the @samp{:8} for clarity, if you wish; but @code{as} neither requires this nor uses it. @end table @node H8/300 Floating Point, H8/300 Directives, H8/300 Syntax, H8/300-Dependent @subsection Floating Point @cindex floating point, H8/300 (@sc{ieee}) @cindex H8/300 floating point (@sc{ieee}) The H8/300 family uses @sc{ieee} floating-point numbers. @node H8/300 Directives, H8/300 Opcodes, H8/300 Floating Point, H8/300-Dependent @subsection H8/300 Machine Directives @cindex H8/300 machine directives (none) @cindex machine directives, H8/300 (none) @cindex @code{word} directive, H8/300 @cindex @code{int} directive, H8/300 @code{as} has no machine-dependent directives for the H8/300. However, on this platform the @samp{.int} and @samp{.word} directives generate 16-bit numbers. @node H8/300 Opcodes, , H8/300 Directives, H8/300-Dependent @subsection Opcodes @cindex H8/300 opcode summary @cindex opcode summary, H8/300 @cindex mnemonics, H8/300 @cindex instruction summary, H8/300 For detailed information on the H8/300 machine instruction set, see @cite{H8/300 Series Programming Manual} (Hitachi ADE--602--025). @code{as} implements all the standard H8/300 opcodes. No additional pseudo-instructions are needed on this family. The following table summarizes the opcodes and their arguments: @c kluge due to lack of group outside example @page @smallexample @group Rs @r{source register} Rd @r{destination register} imm @r{immediate data} x:3 @r{a bit (as a number between 0 and 7)} d:8 @r{eight bit displacement from @code{pc}} d:16 @r{sixteen bit displacement from @code{Rs}} add.b Rs,Rd biand #x:3,Rd add.b #imm:8,Rd biand #x:3,@@Rd add.w Rs,Rd biand #x:3,@@aa:8 adds #1,Rd bild #x:3,Rd adds #2,Rd bild #x:3,@@Rd addx #imm:8,Rd bild #x:3,@@aa:8 addx Rs,Rd bior #x:3,Rd and #imm:8,Rd bior #x:3,@@Rd and Rs,Rd bior #x:3,@@aa:8 andc #imm:8,ccr bist #x:3,Rd band #x:3,Rd bist #x:3,@@Rd band #x:3,@@Rd bist #x:3,@@aa:8 bra d:8 bixor #x:3,Rd bt d:8 bixor #x:3,@@Rd brn d:8 bixor #x:3,@@aa:8 bf d:8 bld #x:3,Rd bhi d:8 bld #x:3,@@Rd bls d:8 bld #x:3,@@aa:8 bcc d:8 bnot #x:3,Rd bhs d:8 bnot #x:3,@@Rd bcs d:8 bnot #x:3,@@aa:8 blo d:8 bnot Rs,Rd bne d:8 bnot Rs,@@Rd beq d:8 bnot Rs,@@aa:8 bvc d:8 bor #x:3,Rd bvs d:8 bor #x:3,@@Rd bpl d:8 bor #x:3,@@aa:8 bmi d:8 bset #x:3,@@Rd bge d:8 bset #x:3,@@aa:8 blt d:8 bset Rs,Rd bgt d:8 bset Rs,@@Rd ble d:8 bset Rs,@@aa:8 bclr #x:3,Rd bsr d:8 bclr #x:3,@@Rd bst #x:3,Rd bclr #x:3,@@aa:8 bst #x:3,@@Rd bclr Rs,Rd bst #x:3,@@aa:8 bclr Rs,@@Rd btst #x:3,Rd @end group @group btst #x:3,@@Rd mov.w @@(d:16, Rs),Rd btst #x:3,@@aa:8 mov.w @@Rs+,Rd btst Rs,Rd mov.w @@aa:16,Rd btst Rs,@@Rd mov.w Rs,@@Rd btst Rs,@@aa:8 mov.w Rs,@@(d:16, Rd) bxor #x:3,Rd mov.w Rs,@@-Rd bxor #x:3,@@Rd mov.w Rs,@@aa:16 bxor #x:3,@@aa:8 movfpe @@aa:16,Rd cmp.b #imm:8,Rd movtpe Rs,@@aa:16 cmp.b Rs,Rd mulxu Rs,Rd cmp.w Rs,Rd neg Rs daa Rs nop das Rs not Rs dec Rs or #imm:8,Rd divxu Rs,Rd or Rs,Rd eepmov orc #imm:8,ccr inc Rs pop Rs jmp @@Rs push Rs jmp @@aa:16 rotl Rs jmp @@@@aa rotr Rs jsr @@Rs rotxl Rs jsr @@aa:16 rotxr Rs jsr @@@@aa:8 rte ldc #imm:8,ccr rts ldc Rs,ccr shal Rs mov.b Rs,Rd shar Rs mov.b #imm:8,Rd shll Rs mov.b @@Rs,Rd shlr Rs mov.b @@(d:16, Rs),Rd sleep mov.b @@Rs+,Rd stc ccr,Rd mov.b @@aa:16,Rd sub.b Rs,Rd mov.b @@aa:8,Rd sub.w Rs,Rd mov.b Rs,@@Rd subs #1,Rd mov.b Rs,@@(d:16, Rd) subs #2,Rd mov.b Rs,@@-Rd subx #imm:8,Rd mov.b Rs,@@aa:16 subx Rs,Rd mov.b Rs,@@aa:8 xor #imm:8,Rd mov.w Rs,Rd xor Rs,Rd mov.w #imm:16,Rd xorc #imm:8,ccr mov.w @@Rs,Rd @end group @end smallexample @cindex size suffixes, H8/300 @cindex H8/300 size suffixes Four H8/300 instructions (@code{add}, @code{cmp}, @code{mov}, @code{sub}) are defined with variants using the suffixes @samp{.b} and @samp{.w} to specify the size of a memory operand. @code{as} supports these suffixes, but does not require them; since one of the operands is always a register, @code{as} can deduce the correct size. For example, since @code{r0} refers to a 16-bit register, @example mov r0,@@foo @exdent is equivalent to mov.w r0,@@foo @end example If you use the size suffixes, @code{as} will issue a warning if there's a mismatch between the suffix and the register size. @node i960-Dependent, M68K-Dependent, H8/300-Dependent, Machine Dependent @section Intel 80960 Dependent Features @cindex i960 support @menu * Options-i960:: i960 Command-line Options * Floating Point-i960:: Floating Point * Directives-i960:: i960 Machine Directives * Opcodes for i960:: i960 Opcodes @end menu @c FIXME! Add Syntax sec with discussion of bitfields here, at least so @c long as they're not turned on for other machines than 960. @node Options-i960, Floating Point-i960, i960-Dependent, i960-Dependent @subsection i960 Command-line Options @cindex i960 options @cindex options, i960 @table @code @item -ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC @cindex i960 architecture options @cindex architecture options, i960 @cindex @code{-A} options, i960 Select the 80960 architecture. Instructions or features not supported by the selected architecture cause fatal errors. @samp{-ACA} is equivalent to @samp{-ACA_A}; @samp{-AKC} is equivalent to @samp{-AMC}. Synonyms are provided for compatibility with other tools. If none of these options is specified, @code{as} will generate code for any instruction or feature that is supported by @emph{some} version of the 960 (even if this means mixing architectures!). In principle, @code{as} will attempt to deduce the minimal sufficient processor type if none is specified; depending on the object code format, the processor type may be recorded in the object file. If it is critical that the @code{as} output match a specific architecture, specify that architecture explicitly. @item -b @cindex @code{-b} option, i960 @cindex branch recording, i960 @cindex i960 branch recording Add code to collect information about conditional branches taken, for later optimization using branch prediction bits. (The conditional branch instructions have branch prediction bits in the CA, CB, and CC architectures.) If @var{BR} represents a conditional branch instruction, the following represents the code generated by the assembler when @samp{-b} is specified: @smallexample call @var{increment routine} .word 0 # pre-counter Label: @var{BR} call @var{increment routine} .word 0 # post-counter @end smallexample The counter following a branch records the number of times that branch was @emph{not} taken; the differenc between the two counters is the number of times the branch @emph{was} taken. @cindex @code{gbr960}, i960 postprocessor @cindex branch statistics table, i960 A table of every such @code{Label} is also generated, so that the external postprocessor @code{gbr960} (supplied by Intel) can locate all the counters. This table is always labelled @samp{__BRANCH_TABLE__}; this is a local symbol to permit collecting statistics for many separate object files. The table is word aligned, and begins with a two-word header. The first word, initialized to 0, is used in maintaining linked lists of branch tables. The second word is a count of the number of entries in the table, which follow immediately: each is a word, pointing to one of the labels illustrated above. @c TEXI2ROFF-KILL @ifinfo @c END TEXI2ROFF-KILL @example +------------+------------+------------+ ... +------------+ | | | | | | | *NEXT | COUNT: N | *BRLAB 1 | | *BRLAB N | | | | | | | +------------+------------+------------+ ... +------------+ __BRANCH_TABLE__ layout @end example @c TEXI2ROFF-KILL @end ifinfo @tex \vskip 1pc \line{\leftskip=0pt\hskip\tableindent \boxit{2cm}{\tt *NEXT}\boxit{2cm}{\tt COUNT: \it N}\boxit{2cm}{\tt *BRLAB 1}\ibox{1cm}{\quad\dots}\boxit{2cm}{\tt *BRLAB \it N}\hfil} \centerline{\it {\tt \_\_BRANCH\_TABLE\_\_} layout} @end tex @c END TEXI2ROFF-KILL The first word of the header is used to locate multiple branch tables, since each object file may contain one. Normally the links are maintained with a call to an initialization routine, placed at the beginning of each function in the file. The GNU C compiler will generate these calls automatically when you give it a @samp{-b} option. For further details, see the documentation of @samp{gbr960}. @item -norelax @cindex @code{-norelax} option, i960 Normally, Compare-and-Branch instructions with targets that require displacements greater than 13 bits (or that have external targets) are replaced with the corresponding compare (or @samp{chkbit}) and branch instructions. You can use the @samp{-norelax} option to specify that @code{as} should generate errors instead, if the target displacement is larger than 13 bits. This option does not affect the Compare-and-Jump instructions; the code emitted for them is @emph{always} adjusted when necessary (depending on displacement size), regardless of whether you use @samp{-norelax}. @end table @node Floating Point-i960, Directives-i960, Options-i960, i960-Dependent @subsection Floating Point @cindex floating point, i960 (@sc{ieee}) @cindex i960 floating point (@sc{ieee}) @code{as} generates @sc{ieee} floating-point numbers for the directives @samp{.float}, @samp{.double}, @samp{.extended}, and @samp{.single}. @node Directives-i960, Opcodes for i960, Floating Point-i960, i960-Dependent @subsection i960 Machine Directives @cindex machine directives, i960 @cindex i960 machine directives @table @code @cindex @code{bss} directive, i960 @item .bss @var{symbol}, @var{length}, @var{align} Reserve @var{length} bytes in the bss section for a local @var{symbol}, aligned to the power of two specified by @var{align}. @var{length} and @var{align} must be positive absolute expressions. This directive differs from @samp{.lcomm} only in that it permits you to specify an alignment. @xref{Lcomm,,@code{.lcomm}}. @end table @table @code @item .extended @var{flonums} @cindex @code{extended} directive, i960 @code{.extended} expects zero or more flonums, separated by commas; for each flonum, @samp{.extended} emits an @sc{ieee} extended-format (80-bit) floating-point number. @item .leafproc @var{call-lab}, @var{bal-lab} @cindex @code{leafproc} directive, i960 You can use the @samp{.leafproc} directive in conjunction with the optimized @code{callj} instruction to enable faster calls of leaf procedures. If a procedure is known to call no other procedures, you may define an entry point that skips procedure prolog code (and that does not depend on system-supplied saved context), and declare it as the @var{bal-lab} using @samp{.leafproc}. If the procedure also has an entry point that goes through the normal prolog, you can specify that entry point as @var{call-lab}. A @samp{.leafproc} declaration is meant for use in conjunction with the optimized call instruction @samp{callj}; the directive records the data needed later to choose between converting the @samp{callj} into a @code{bal} or a @code{call}. @var{call-lab} is optional; if only one argument is present, or if the two arguments are identical, the single argument is assumed to be the @code{bal} entry point. @item .sysproc @var{name}, @var{index} @cindex @code{sysproc} directive, i960 The @samp{.sysproc} directive defines a name for a system procedure. After you define it using @samp{.sysproc}, you can use @var{name} to refer to the system procedure identified by @var{index} when calling procedures with the optimized call instruction @samp{callj}. Both arguments are required; @var{index} must be between 0 and 31 (inclusive). @end table @node Opcodes for i960, , Directives-i960, i960-Dependent @subsection i960 Opcodes @cindex opcodes, i960 @cindex i960 opcodes All Intel 960 machine instructions are supported; @pxref{Options-i960,,i960 Command-line Options} for a discussion of selecting the instruction subset for a particular 960 architecture.@refill Some opcodes are processed beyond simply emitting a single corresponding instruction: @samp{callj}, and Compare-and-Branch or Compare-and-Jump instructions with target displacements larger than 13 bits. @menu * callj-i960:: @code{callj} * Compare-and-branch-i960:: Compare-and-Branch @end menu @node callj-i960, Compare-and-branch-i960, Opcodes for i960, Opcodes for i960 @subsubsection @code{callj} @cindex @code{callj}, i960 pseudo-opcode @cindex i960 @code{callj} pseudo-opcode You can write @code{callj} to have the assembler or the linker determine the most appropriate form of subroutine call: @samp{call}, @samp{bal}, or @samp{calls}. If the assembly source contains enough information---a @samp{.leafproc} or @samp{.sysproc} directive defining the operand---then @code{as} will translate the @code{callj}; if not, it will simply emit the @code{callj}, leaving it for the linker to resolve. @node Compare-and-branch-i960, , callj-i960, Opcodes for i960 @subsubsection Compare-and-Branch @cindex i960 compare/branch instructions @cindex compare/branch instructions, i960 The 960 architectures provide combined Compare-and-Branch instructions that permit you to store the branch target in the lower 13 bits of the instruction word itself. However, if you specify a branch target far enough away that its address won't fit in 13 bits, the assembler can either issue an error, or convert your Compare-and-Branch instruction into separate instructions to do the compare and the branch. @cindex compare and jump expansions, i960 @cindex i960 compare and jump expansions Whether @code{as} gives an error or expands the instruction depends on two choices you can make: whether you use the @samp{-norelax} option, and whether you use a ``Compare and Branch'' instruction or a ``Compare and Jump'' instruction. The ``Jump'' instructions are @emph{always} expanded if necessary; the ``Branch'' instructions are expanded when necessary @emph{unless} you specify @code{-norelax}---in which case @code{as} gives an error instead. These are the Compare-and-Branch instructions, their ``Jump'' variants, and the instruction pairs they may expand into: @c TEXI2ROFF-KILL @ifinfo @c END TEXI2ROFF-KILL @example Compare and Branch Jump Expanded to ------ ------ ------------ bbc chkbit; bno bbs chkbit; bo cmpibe cmpije cmpi; be cmpibg cmpijg cmpi; bg cmpibge cmpijge cmpi; bge cmpibl cmpijl cmpi; bl cmpible cmpijle cmpi; ble cmpibno cmpijno cmpi; bno cmpibne cmpijne cmpi; bne cmpibo cmpijo cmpi; bo cmpobe cmpoje cmpo; be cmpobg cmpojg cmpo; bg cmpobge cmpojge cmpo; bge cmpobl cmpojl cmpo; bl cmpoble cmpojle cmpo; ble cmpobne cmpojne cmpo; bne @end example @c TEXI2ROFF-KILL @end ifinfo @tex \hskip\tableindent \halign{\hfil {\tt #}\quad&\hfil {\tt #}\qquad&{\tt #}\hfil\cr \omit{\hfil\it Compare and\hfil}\span\omit&\cr {\it Branch}&{\it Jump}&{\it Expanded to}\cr bbc& & chkbit; bno\cr bbs& & chkbit; bo\cr cmpibe& cmpije& cmpi; be\cr cmpibg& cmpijg& cmpi; bg\cr cmpibge& cmpijge& cmpi; bge\cr cmpibl& cmpijl& cmpi; bl\cr cmpible& cmpijle& cmpi; ble\cr cmpibno& cmpijno& cmpi; bno\cr cmpibne& cmpijne& cmpi; bne\cr cmpibo& cmpijo& cmpi; bo\cr cmpobe& cmpoje& cmpo; be\cr cmpobg& cmpojg& cmpo; bg\cr cmpobge& cmpojge& cmpo; bge\cr cmpobl& cmpojl& cmpo; bl\cr cmpoble& cmpojle& cmpo; ble\cr cmpobne& cmpojne& cmpo; bne\cr} @end tex @c END TEXI2ROFF-KILL @c FIXME! node conds are only sufficient for m68k alone, all, and vintage @node M68K-Dependent, Sparc-Dependent, i960-Dependent, Machine Dependent @section M680x0 Dependent Features @cindex M680x0 support @menu * M68K-Opts:: M680x0 Options * M68K-Syntax:: Syntax * M68K-Float:: Floating Point * M68K-Directives:: 680x0 Machine Directives * M68K-opcodes:: Opcodes @end menu @node M68K-Opts, M68K-Syntax, M68K-Dependent, M68K-Dependent @subsection M680x0 Options @cindex options, M680x0 @cindex M680x0 options The Motorola 680x0 version of @code{as} has two machine dependent options. One shortens undefined references from 32 to 16 bits, while the other is used to tell @code{as} what kind of machine it is assembling for. @cindex @code{-l} option, M680x0 You can use the @kbd{-l} option to shorten the size of references to undefined symbols. If the @kbd{-l} option is not given, references to undefined symbols will be a full long (32 bits) wide. (Since @code{as} cannot know where these symbols will end up, @code{as} can only allocate space for the linker to fill in later. Since @code{as} doesn't know how far away these symbols will be, it allocates as much space as it can.) If this option is given, the references will only be one word wide (16 bits). This may be useful if you want the object file to be as small as possible, and you know that the relevant symbols will be less than 17 bits away. @cindex @code{-m68000} and related options @cindex architecture options, M680x0 @cindex M680x0 architecture options The 680x0 version of @code{as} is most frequently used to assemble programs for the Motorola MC68020 microprocessor. Occasionally it is used to assemble programs for the mostly similar, but slightly different MC68000 or MC68010 microprocessors. You can give @code{as} the options @samp{-m68000}, @samp{-mc68000}, @samp{-m68010}, @samp{-mc68010}, @samp{-m68020}, and @samp{-mc68020} to tell it what processor is the target. @node M68K-Syntax, M68K-Float, M68K-Opts, M68K-Dependent @subsection Syntax @cindex M680x0 syntax @cindex syntax, M680x0 @cindex M680x0 size modifiers @cindex size modifiers, M680x0 The 680x0 version of @code{as} uses syntax similar to the Sun assembler. Size modifiers are appended directly to the end of the opcode without an intervening period. For example, write @samp{movl} rather than @samp{move.l}. In the following table @dfn{apc} stands for any of the address registers (@samp{a0} through @samp{a7}), nothing, (@samp{}), the Program Counter (@samp{pc}), or the zero-address relative to the program counter (@samp{zpc}). @cindex M680x0 addressing modes @cindex addressing modes, M680x0 The following addressing modes are understood: @table @dfn @item Immediate @samp{#@var{digits}} @item Data Register @samp{d0} through @samp{d7} @item Address Register @samp{a0} through @samp{a7} @item Address Register Indirect @samp{a0@@} through @samp{a7@@} @item Address Register Postincrement @samp{a0@@+} through @samp{a7@@+} @item Address Register Predecrement @samp{a0@@-} through @samp{a7@@-} @item Indirect Plus Offset @samp{@var{apc}@@(@var{digits})} @item Index @samp{@var{apc}@@(@var{digits},@var{register}:@var{size}:@var{scale})} or @samp{@var{apc}@@(@var{register}:@var{size}:@var{scale})} @item Postindex @samp{@var{apc}@@(@var{digits})@@(@var{digits},@var{register}:@var{size}:@var{scale})} or @samp{@var{apc}@@(@var{digits})@@(@var{register}:@var{size}:@var{scale})} @item Preindex @samp{@var{apc}@@(@var{digits},@var{register}:@var{size}:@var{scale})@@(@var{digits})} or @samp{@var{apc}@@(@var{register}:@var{size}:@var{scale})@@(@var{digits})} @item Memory Indirect @samp{@var{apc}@@(@var{digits})@@(@var{digits})} @item Absolute @samp{@var{symbol}}, or @samp{@var{digits}} @ignore @c pesch@cygnus.com: gnu, rich concur the following needs careful @c research before documenting. , or either of the above followed by @samp{:b}, @samp{:w}, or @samp{:l}. @end ignore @end table @node M68K-Float, M68K-Directives, M68K-Syntax, M68K-Dependent @subsection Floating Point @cindex floating point, M680x0 @cindex M680x0 floating point @c FIXME is this "not too well tested" crud STILL true? The floating point code is not too well tested, and may have subtle bugs in it. Packed decimal (P) format floating literals are not supported. Feel free to add the code! The floating point formats generated by directives are these. @table @code @item .float @cindex @code{float} directive, M680x0 @code{Single} precision floating point constants. @item .double @cindex @code{double} directive, M680x0 @code{Double} precision floating point constants. @end table There is no directive to produce regions of memory holding extended precision numbers, however they can be used as immediate operands to floating-point instructions. Adding a directive to create extended precision numbers would not be hard, but it has not yet seemed necessary. @node M68K-Directives, M68K-opcodes, M68K-Float, M68K-Dependent @subsection 680x0 Machine Directives @cindex M680x0 directives @cindex directives, M680x0 In order to be compatible with the Sun assembler the 680x0 assembler understands the following directives. @table @code @item .data1 @cindex @code{data1} directive, M680x0 This directive is identical to a @code{.data 1} directive. @item .data2 @cindex @code{data2} directive, M680x0 This directive is identical to a @code{.data 2} directive. @item .even @cindex @code{even} directive, M680x0 This directive is identical to a @code{.align 1} directive. @c Is this true? does it work??? @item .skip @cindex @code{skip} directive, M680x0 This directive is identical to a @code{.space} directive. @end table @node M68K-opcodes, , M68K-Directives, M68K-Dependent @subsection Opcodes @cindex M680x0 opcodes @cindex opcodes, M680x0 @cindex instruction set, M680x0 @c pesch@cygnus.com: I don't see any point in the following @c paragraph. Bugs are bugs; how does saying this @c help anyone? @ignore Danger: Several bugs have been found in the opcode table (and fixed). More bugs may exist. Be careful when using obscure instructions. @end ignore @menu * M68K-Branch:: Branch Improvement * M68K-Chars:: Special Characters @end menu @node M68K-Branch, M68K-Chars, M68K-opcodes, M68K-opcodes @subsubsection Branch Improvement @cindex pseudo-opcodes, M680x0 @cindex M680x0 pseudo-opcodes @cindex branch improvement, M680x0 @cindex M680x0 branch improvement Certain pseudo opcodes are permitted for branch instructions. They expand to the shortest branch instruction that will reach the target. Generally these mnemonics are made by substituting @samp{j} for @samp{b} at the start of a Motorola mnemonic. The following table summarizes the pseudo-operations. A @code{*} flags cases that are more fully described after the table: @smallexample Displacement +------------------------------------------------- | 68020 68000/10 Pseudo-Op |BYTE WORD LONG LONG non-PC relative +------------------------------------------------- jbsr |bsrs bsr bsrl jsr jsr jra |bras bra bral jmp jmp * jXX |bXXs bXX bXXl bNXs;jmpl bNXs;jmp * dbXX |dbXX dbXX dbXX; bra; jmpl * fjXX |fbXXw fbXXw fbXXl fbNXw;jmp XX: condition NX: negative of condition XX @end smallexample @center @code{*}---see full description below @table @code @item jbsr @itemx jra These are the simplest jump pseudo-operations; they always map to one particular machine instruction, depending on the displacement to the branch target. @item j@var{XX} Here, @samp{j@var{XX}} stands for an entire family of pseudo-operations, where @var{XX} is a conditional branch or condition-code test. The full list of pseudo-ops in this family is: @smallexample jhi jls jcc jcs jne jeq jvc jvs jpl jmi jge jlt jgt jle @end smallexample For the cases of non-PC relative displacements and long displacements on the 68000 or 68010, @code{as} will issue a longer code fragment in terms of @var{NX}, the opposite condition to @var{XX}. For example, for the non-PC relative case: @smallexample j@var{XX} foo @end smallexample gives @smallexample b@var{NX}s oof jmp foo oof: @end smallexample @item db@var{XX} The full family of pseudo-operations covered here is @smallexample dbhi dbls dbcc dbcs dbne dbeq dbvc dbvs dbpl dbmi dbge dblt dbgt dble dbf dbra dbt @end smallexample Other than for word and byte displacements, when the source reads @samp{db@var{XX} foo}, @code{as} will emit @smallexample db@var{XX} oo1 bra oo2 oo1:jmpl foo oo2: @end smallexample @item fj@var{XX} This family includes @smallexample fjne fjeq fjge fjlt fjgt fjle fjf fjt fjgl fjgle fjnge fjngl fjngle fjngt fjnle fjnlt fjoge fjogl fjogt fjole fjolt fjor fjseq fjsf fjsne fjst fjueq fjuge fjugt fjule fjult fjun @end smallexample For branch targets that are not PC relative, @code{as} emits @smallexample fb@var{NX} oof jmp foo oof: @end smallexample when it encounters @samp{fj@var{XX} foo}. @end table @node M68K-Chars, , M68K-Branch, M68K-opcodes @subsubsection Special Characters @cindex special characters, M680x0 @cindex M680x0 immediate character @cindex immediate character, M680x0 @cindex M680x0 line comment character @cindex line comment character, M680x0 @cindex comments, M680x0 The immediate character is @samp{#} for Sun compatibility. The line-comment character is @samp{|}. If a @samp{#} appears at the beginning of a line, it is treated as a comment unless it looks like @samp{# line file}, in which case it is treated normally. @node Sparc-Dependent, i386-Dependent, M68K-Dependent, Machine Dependent @section SPARC Dependent Features @cindex SPARC support @menu * Sparc-Opts:: Options * Sparc-Float:: Floating Point * Sparc-Directives:: Sparc Machine Directives @end menu @node Sparc-Opts, Sparc-Float, Sparc-Dependent, Sparc-Dependent @subsection Options @cindex options for SPARC (none) @cindex SPARC options (none) The Sparc has no machine dependent options. @ignore @c FIXME: (sparc) Fill in "syntax" section! @c subsection syntax I don't know anything about Sparc syntax. Someone who does will have to write this section. @end ignore @node Sparc-Float, Sparc-Directives, Sparc-Opts, Sparc-Dependent @subsection Floating Point @cindex floating point, SPARC (@sc{ieee}) @cindex SPARC floating point (@sc{ieee}) The Sparc uses @sc{ieee} floating-point numbers. @node Sparc-Directives, , Sparc-Float, Sparc-Dependent @subsection Sparc Machine Directives @cindex SPARC machine directives @cindex machine directives, SPARC The Sparc version of @code{as} supports the following additional machine directives: @table @code @item .common @cindex @code{common} directive, SPARC This must be followed by a symbol name, a positive number, and @code{"bss"}. This behaves somewhat like @code{.comm}, but the syntax is different. @item .half @cindex @code{half} directive, SPARC This is functionally identical to @code{.short}. @item .proc @cindex @code{proc} directive, SPARC This directive is ignored. Any text following it on the same line is also ignored. @item .reserve @cindex @code{reserve} directive, SPARC This must be followed by a symbol name, a positive number, and @code{"bss"}. This behaves somewhat like @code{.lcomm}, but the syntax is different. @item .seg @cindex @code{seg} directive, SPARC This must be followed by @code{"text"}, @code{"data"}, or @code{"data1"}. It behaves like @code{.text}, @code{.data}, or @code{.data 1}. @item .skip @cindex @code{skip} directive, SPARC This is functionally identical to the @code{.space} directive. @item .word @cindex @code{word} directive, SPARC On the Sparc, the .word directive produces 32 bit values, instead of the 16 bit values it produces on many other machines. @end table @c FIXME! Conditionalize for all combinations in this section @node i386-Dependent, , Sparc-Dependent, Machine Dependent @section 80386 Dependent Features @cindex i386 support @cindex i80306 support @menu * i386-Options:: Options * i386-Syntax:: AT&T Syntax versus Intel Syntax * i386-Opcodes:: Opcode Naming * i386-Regs:: Register Naming * i386-prefixes:: Opcode Prefixes * i386-Memory:: Memory References * i386-jumps:: Handling of Jump Instructions * i386-Float:: Floating Point * i386-Notes:: Notes @end menu @node i386-Options, i386-Syntax, i386-Dependent, i386-Dependent @subsection Options @cindex options for i386 (none) @cindex i386 options (none) The 80386 has no machine dependent options. @node i386-Syntax, i386-Opcodes, i386-Options, i386-Dependent @subsection AT&T Syntax versus Intel Syntax @cindex i386 syntax compatibility @cindex syntax compatibility, i386 In order to maintain compatibility with the output of @code{gcc}, @code{as} supports AT&T System V/386 assembler syntax. This is quite different from Intel syntax. We mention these differences because almost all 80386 documents used only Intel syntax. Notable differences between the two syntaxes are: @itemize @bullet @item @cindex immediate operands, i386 @cindex i386 immediate operands @cindex register operands, i386 @cindex i386 register operands @cindex jump/call operands, i386 @cindex i386 jump/call operands @cindex operand delimiters, i386 AT&T immediate operands are preceded by @samp{$}; Intel immediate operands are undelimited (Intel @samp{push 4} is AT&T @samp{pushl $4}). AT&T register operands are preceded by @samp{%}; Intel register operands are undelimited. AT&T absolute (as opposed to PC relative) jump/call operands are prefixed by @samp{*}; they are undelimited in Intel syntax. @item @cindex i386 source, destination operands @cindex source, destination operands; i386 AT&T and Intel syntax use the opposite order for source and destination operands. Intel @samp{add eax, 4} is @samp{addl $4, %eax}. The @samp{source, dest} convention is maintained for compatibility with previous Unix assemblers. @item @cindex opcode suffixes, i386 @cindex sizes operands, i386 @cindex i386 size suffixes In AT&T syntax the size of memory operands is determined from the last character of the opcode name. Opcode suffixes of @samp{b}, @samp{w}, and @samp{l} specify byte (8-bit), word (16-bit), and long (32-bit) memory references. Intel syntax accomplishes this by prefixes memory operands (@emph{not} the opcodes themselves) with @samp{byte ptr}, @samp{word ptr}, and @samp{dword ptr}. Thus, Intel @samp{mov al, byte ptr @var{foo}} is @samp{movb @var{foo}, %al} in AT&T syntax. @item @cindex return instructions, i386 @cindex i386 jump, call, return Immediate form long jumps and calls are @samp{lcall/ljmp $@var{section}, $@var{offset}} in AT&T syntax; the Intel syntax is @samp{call/jmp far @var{section}:@var{offset}}. Also, the far return instruction is @samp{lret $@var{stack-adjust}} in AT&T syntax; Intel syntax is @samp{ret far @var{stack-adjust}}. @item @cindex sections, i386 @cindex i386 sections The AT&T assembler does not provide support for multiple section programs. Unix style systems expect all programs to be single sections. @end itemize @node i386-Opcodes, i386-Regs, i386-Syntax, i386-Dependent @subsection Opcode Naming @cindex i386 opcode naming @cindex opcode naming, i386 Opcode names are suffixed with one character modifiers which specify the size of operands. The letters @samp{b}, @samp{w}, and @samp{l} specify byte, word, and long operands. If no suffix is specified by an instruction and it contains no memory operands then @code{as} tries to fill in the missing suffix based on the destination register operand (the last one by convention). Thus, @samp{mov %ax, %bx} is equivalent to @samp{movw %ax, %bx}; also, @samp{mov $1, %bx} is equivalent to @samp{movw $1, %bx}. Note that this is incompatible with the AT&T Unix assembler which assumes that a missing opcode suffix implies long operand size. (This incompatibility does not affect compiler output since compilers always explicitly specify the opcode suffix.) Almost all opcodes have the same names in AT&T and Intel format. There are a few exceptions. The sign extend and zero extend instructions need two sizes to specify them. They need a size to sign/zero extend @emph{from} and a size to zero extend @emph{to}. This is accomplished by using two opcode suffixes in AT&T syntax. Base names for sign extend and zero extend are @samp{movs@dots{}} and @samp{movz@dots{}} in AT&T syntax (@samp{movsx} and @samp{movzx} in Intel syntax). The opcode suffixes are tacked on to this base name, the @emph{from} suffix before the @emph{to} suffix. Thus, @samp{movsbl %al, %edx} is AT&T syntax for ``move sign extend @emph{from} %al @emph{to} %edx.'' Possible suffixes, thus, are @samp{bl} (from byte to long), @samp{bw} (from byte to word), and @samp{wl} (from word to long). @cindex conversion instructions, i386 @cindex i386 conversion instructions The Intel-syntax conversion instructions @itemize @bullet @item @samp{cbw} --- sign-extend byte in @samp{%al} to word in @samp{%ax}, @item @samp{cwde} --- sign-extend word in @samp{%ax} to long in @samp{%eax}, @item @samp{cwd} --- sign-extend word in @samp{%ax} to long in @samp{%dx:%ax}, @item @samp{cdq} --- sign-extend dword in @samp{%eax} to quad in @samp{%edx:%eax}, @end itemize @noindent are called @samp{cbtw}, @samp{cwtl}, @samp{cwtd}, and @samp{cltd} in AT&T naming. @code{as} accepts either naming for these instructions. @cindex jump instructions, i386 @cindex call instructions, i386 Far call/jump instructions are @samp{lcall} and @samp{ljmp} in AT&T syntax, but are @samp{call far} and @samp{jump far} in Intel convention. @node i386-Regs, i386-prefixes, i386-Opcodes, i386-Dependent @subsection Register Naming @cindex i386 registers @cindex registers, i386 Register operands are always prefixes with @samp{%}. The 80386 registers consist of @itemize @bullet @item the 8 32-bit registers @samp{%eax} (the accumulator), @samp{%ebx}, @samp{%ecx}, @samp{%edx}, @samp{%edi}, @samp{%esi}, @samp{%ebp} (the frame pointer), and @samp{%esp} (the stack pointer). @item the 8 16-bit low-ends of these: @samp{%ax}, @samp{%bx}, @samp{%cx}, @samp{%dx}, @samp{%di}, @samp{%si}, @samp{%bp}, and @samp{%sp}. @item the 8 8-bit registers: @samp{%ah}, @samp{%al}, @samp{%bh}, @samp{%bl}, @samp{%ch}, @samp{%cl}, @samp{%dh}, and @samp{%dl} (These are the high-bytes and low-bytes of @samp{%ax}, @samp{%bx}, @samp{%cx}, and @samp{%dx}) @item the 6 section registers @samp{%cs} (code section), @samp{%ds} (data section), @samp{%ss} (stack section), @samp{%es}, @samp{%fs}, and @samp{%gs}. @item the 3 processor control registers @samp{%cr0}, @samp{%cr2}, and @samp{%cr3}. @item the 6 debug registers @samp{%db0}, @samp{%db1}, @samp{%db2}, @samp{%db3}, @samp{%db6}, and @samp{%db7}. @item the 2 test registers @samp{%tr6} and @samp{%tr7}. @item the 8 floating point register stack @samp{%st} or equivalently @samp{%st(0)}, @samp{%st(1)}, @samp{%st(2)}, @samp{%st(3)}, @samp{%st(4)}, @samp{%st(5)}, @samp{%st(6)}, and @samp{%st(7)}. @end itemize @node i386-prefixes, i386-Memory, i386-Regs, i386-Dependent @subsection Opcode Prefixes @cindex i386 opcode prefixes @cindex opcode prefixes, i386 @cindex prefixes, i386 Opcode prefixes are used to modify the following opcode. They are used to repeat string instructions, to provide section overrides, to perform bus lock operations, and to give operand and address size (16-bit operands are specified in an instruction by prefixing what would normally be 32-bit operands with a ``operand size'' opcode prefix). Opcode prefixes are usually given as single-line instructions with no operands, and must directly precede the instruction they act upon. For example, the @samp{scas} (scan string) instruction is repeated with: @smallexample repne scas @end smallexample Here is a list of opcode prefixes: @itemize @bullet @item @cindex section override prefixes, i386 Section override prefixes @samp{cs}, @samp{ds}, @samp{ss}, @samp{es}, @samp{fs}, @samp{gs}. These are automatically added by specifying using the @var{section}:@var{memory-operand} form for memory references. @item @cindex size prefixes, i386 Operand/Address size prefixes @samp{data16} and @samp{addr16} change 32-bit operands/addresses into 16-bit operands/addresses. Note that 16-bit addressing modes (i.e. 8086 and 80286 addressing modes) are not supported (yet). @item @cindex bus lock prefixes, i386 @cindex inhibiting interrupts, i386 The bus lock prefix @samp{lock} inhibits interrupts during execution of the instruction it precedes. (This is only valid with certain instructions; see a 80386 manual for details). @item @cindex coprocessor wait, i386 The wait for coprocessor prefix @samp{wait} waits for the coprocessor to complete the current instruction. This should never be needed for the 80386/80387 combination. @item @cindex repeat prefixes, i386 The @samp{rep}, @samp{repe}, and @samp{repne} prefixes are added to string instructions to make them repeat @samp{%ecx} times. @end itemize @node i386-Memory, i386-jumps, i386-prefixes, i386-Dependent @subsection Memory References @cindex i386 memory references @cindex memory references, i386 An Intel syntax indirect memory reference of the form @smallexample @var{section}:[@var{base} + @var{index}*@var{scale} + @var{disp}] @end smallexample @noindent is translated into the AT&T syntax @smallexample @var{section}:@var{disp}(@var{base}, @var{index}, @var{scale}) @end smallexample @noindent where @var{base} and @var{index} are the optional 32-bit base and index registers, @var{disp} is the optional displacement, and @var{scale}, taking the values 1, 2, 4, and 8, multiplies @var{index} to calculate the address of the operand. If no @var{scale} is specified, @var{scale} is taken to be 1. @var{section} specifies the optional section register for the memory operand, and may override the default section register (see a 80386 manual for section register defaults). Note that section overrides in AT&T syntax @emph{must} have be preceded by a @samp{%}. If you specify a section override which coincides with the default section register, @code{as} will @emph{not} output any section register override prefixes to assemble the given instruction. Thus, section overrides can be specified to emphasize which section register is used for a given memory operand. Here are some examples of Intel and AT&T style memory references: @table @asis @item AT&T: @samp{-4(%ebp)}, Intel: @samp{[ebp - 4]} @var{base} is @samp{%ebp}; @var{disp} is @samp{-4}. @var{section} is missing, and the default section is used (@samp{%ss} for addressing with @samp{%ebp} as the base register). @var{index}, @var{scale} are both missing. @item AT&T: @samp{foo(,%eax,4)}, Intel: @samp{[foo + eax*4]} @var{index} is @samp{%eax} (scaled by a @var{scale} 4); @var{disp} is @samp{foo}. All other fields are missing. The section register here defaults to @samp{%ds}. @item AT&T: @samp{foo(,1)}; Intel @samp{[foo]} This uses the value pointed to by @samp{foo} as a memory operand. Note that @var{base} and @var{index} are both missing, but there is only @emph{one} @samp{,}. This is a syntactic exception. @item AT&T: @samp{%gs:foo}; Intel @samp{gs:foo} This selects the contents of the variable @samp{foo} with section register @var{section} being @samp{%gs}. @end table Absolute (as opposed to PC relative) call and jump operands must be prefixed with @samp{*}. If no @samp{*} is specified, @code{as} will always choose PC relative addressing for jump/call labels. Any instruction that has a memory operand @emph{must} specify its size (byte, word, or long) with an opcode suffix (@samp{b}, @samp{w}, or @samp{l}, respectively). @node i386-jumps, i386-Float, i386-Memory, i386-Dependent @subsection Handling of Jump Instructions @cindex jump optimization, i386 @cindex i386 jump optimization Jump instructions are always optimized to use the smallest possible displacements. This is accomplished by using byte (8-bit) displacement jumps whenever the target is sufficiently close. If a byte displacement is insufficient a long (32-bit) displacement is used. We do not support word (16-bit) displacement jumps (i.e. prefixing the jump instruction with the @samp{addr16} opcode prefix), since the 80386 insists upon masking @samp{%eip} to 16 bits after the word displacement is added. Note that the @samp{jcxz}, @samp{jecxz}, @samp{loop}, @samp{loopz}, @samp{loope}, @samp{loopnz} and @samp{loopne} instructions only come in byte displacements, so that it is possible that use of these instructions (@code{gcc} does not use them) will cause the assembler to print an error message (and generate incorrect code). The AT&T 80386 assembler tries to get around this problem by expanding @samp{jcxz foo} to @smallexample jcxz cx_zero jmp cx_nonzero cx_zero: jmp foo cx_nonzero: @end smallexample @node i386-Float, i386-Notes, i386-jumps, i386-Dependent @subsection Floating Point @cindex i386 floating point @cindex floating point, i386 All 80387 floating point types except packed BCD are supported. (BCD support may be added without much difficulty). These data types are 16-, 32-, and 64- bit integers, and single (32-bit), double (64-bit), and extended (80-bit) precision floating point. Each supported type has an opcode suffix and a constructor associated with it. Opcode suffixes specify operand's data types. Constructors build these data types into memory. @itemize @bullet @item @cindex @code{float} directive, i386 @cindex @code{single} directive, i386 @cindex @code{double} directive, i386 @cindex @code{tfloat} directive, i386 Floating point constructors are @samp{.float} or @samp{.single}, @samp{.double}, and @samp{.tfloat} for 32-, 64-, and 80-bit formats. These correspond to opcode suffixes @samp{s}, @samp{l}, and @samp{t}. @samp{t} stands for temporary real, and that the 80387 only supports this format via the @samp{fldt} (load temporary real to stack top) and @samp{fstpt} (store temporary real and pop stack) instructions. @item @cindex @code{word} directive, i386 @cindex @code{long} directive, i386 @cindex @code{int} directive, i386 @cindex @code{quad} directive, i386 Integer constructors are @samp{.word}, @samp{.long} or @samp{.int}, and @samp{.quad} for the 16-, 32-, and 64-bit integer formats. The corresponding opcode suffixes are @samp{s} (single), @samp{l} (long), and @samp{q} (quad). As with the temporary real format the 64-bit @samp{q} format is only present in the @samp{fildq} (load quad integer to stack top) and @samp{fistpq} (store quad integer and pop stack) instructions. @end itemize Register to register operations do not require opcode suffixes, so that @samp{fst %st, %st(1)} is equivalent to @samp{fstl %st, %st(1)}. @cindex i386 @code{fwait} instruction @cindex @code{fwait instruction}, i386 Since the 80387 automatically synchronizes with the 80386 @samp{fwait} instructions are almost never needed (this is not the case for the 80286/80287 and 8086/8087 combinations). Therefore, @code{as} suppresses the @samp{fwait} instruction whenever it is implicitly selected by one of the @samp{fn@dots{}} instructions. For example, @samp{fsave} and @samp{fnsave} are treated identically. In general, all the @samp{fn@dots{}} instructions are made equivalent to @samp{f@dots{}} instructions. If @samp{fwait} is desired it must be explicitly coded. @node i386-Notes, , i386-Float, i386-Dependent @subsection Notes @cindex i386 @code{mul}, @code{imul} instructions @cindex @code{mul} instruction, i386 @cindex @code{imul} instruction, i386 There is some trickery concerning the @samp{mul} and @samp{imul} instructions that deserves mention. The 16-, 32-, and 64-bit expanding multiplies (base opcode @samp{0xf6}; extension 4 for @samp{mul} and 5 for @samp{imul}) can be output only in the one operand form. Thus, @samp{imul %ebx, %eax} does @emph{not} select the expanding multiply; the expanding multiply would clobber the @samp{%edx} register, and this would confuse @code{gcc} output. Use @samp{imul %ebx} to get the 64-bit product in @samp{%edx:%eax}. We have added a two operand form of @samp{imul} when the first operand is an immediate mode expression and the second operand is a register. This is just a shorthand, so that, multiplying @samp{%eax} by 69, for example, can be done with @samp{imul $69, %eax} rather than @samp{imul $69, %eax, %eax}. @node Copying, Index, Machine Dependent, Top @unnumbered GNU GENERAL PUBLIC LICENSE @cindex license @cindex GPL @cindex copying @code{as} @center Version 2, June 1991 @display Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. 675 Mass Ave, Cambridge, MA 02139, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. @end display @unnumberedsec Preamble The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software---to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too. When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things. To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it. For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights. We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software. Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations. Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all. The precise terms and conditions for copying, distribution and modification follow. @iftex @unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION @end iftex @ifinfo @center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION @end ifinfo @enumerate @item This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The ``Program'', below, refers to any such program or work, and a ``work based on the Program'' means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term ``modification''.) Each licensee is addressed as ``you''. Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does. @item You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program. You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee. @item You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions: @enumerate a @item You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change. @item You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License. @item If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.) @end enumerate These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it. Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program. In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License. @item You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following: @enumerate a @item Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, @item Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, @item Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.) @end enumerate The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable. If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code. @item You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance. @item You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it. @item Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License. @item If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program. If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances. It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice. This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License. @item If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License. @item The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and ``any later version'', you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation. @item If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally. @iftex @heading NO WARRANTY @end iftex @ifinfo @center NO WARRANTY @end ifinfo @item BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. @item IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. @end enumerate @iftex @heading END OF TERMS AND CONDITIONS @end iftex @ifinfo @center END OF TERMS AND CONDITIONS @end ifinfo @page @unnumberedsec Applying These Terms to Your New Programs If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the ``copyright'' line and a pointer to where the full notice is found. @smallexample @var{one line to give the program's name and an idea of what it does.} Copyright (C) 19@var{yy} @var{name of author} This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. @end smallexample Also add information on how to contact you by electronic and paper mail. If the program is interactive, make it output a short notice like this when it starts in an interactive mode: @smallexample Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author} Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. @end smallexample The hypothetical commands @samp{show w} and @samp{show c} should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than @samp{show w} and @samp{show c}; they could even be mouse-clicks or menu items---whatever suits your program. You should also get your employer (if you work as a programmer) or your school, if any, to sign a ``copyright disclaimer'' for the program, if necessary. Here is a sample; alter the names: @smallexample Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. @var{signature of Ty Coon}, 1 April 1989 Ty Coon, President of Vice @end smallexample This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License. @node Index, , Copying, Top @unnumbered Index @printindex cp @summarycontents @contents @bye