aarch64-linux-gnu-5.1/share/doc/as.html/Word.html - toolchains/linux-x86/gcc - Git at Google

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <!-- This file documents the GNU Assembler "as".

 Copyright (C) 1991-2015 Free Software Foundation, Inc.

 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3
 or any later version published by the Free Software Foundation;
 with no Invariant Sections, with no Front-Cover Texts, and with no
 Back-Cover Texts.  A copy of the license is included in the
 section entitled "GNU Free Documentation License".
  -->
 <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
 <head>
 <title>Using as: Word</title>

 <meta name="description" content="Using as: Word">
 <meta name="keywords" content="Using as: Word">
 <meta name="resource-type" content="document">
 <meta name="distribution" content="global">
 <meta name="Generator" content="makeinfo">
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 <link href="index.html#Top" rel="start" title="Top">
 <link href="AS-Index.html#AS-Index" rel="index" title="AS Index">
 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
 <link href="Pseudo-Ops.html#Pseudo-Ops" rel="up" title="Pseudo Ops">
 <link href="Zero.html#Zero" rel="next" title="Zero">
 <link href="Weakref.html#Weakref" rel="prev" title="Weakref">
 <style type="text/css">
 <!--
 a.summary-letter {text-decoration: none}
 blockquote.smallquotation {font-size: smaller}
 div.display {margin-left: 3.2em}
 div.example {margin-left: 3.2em}
 div.indentedblock {margin-left: 3.2em}
 div.lisp {margin-left: 3.2em}
 div.smalldisplay {margin-left: 3.2em}
 div.smallexample {margin-left: 3.2em}
 div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
 div.smalllisp {margin-left: 3.2em}
 kbd {font-style:oblique}
 pre.display {font-family: inherit}
 pre.format {font-family: inherit}
 pre.menu-comment {font-family: serif}
 pre.menu-preformatted {font-family: serif}
 pre.smalldisplay {font-family: inherit; font-size: smaller}
 pre.smallexample {font-size: smaller}
 pre.smallformat {font-family: inherit; font-size: smaller}
 pre.smalllisp {font-size: smaller}
 span.nocodebreak {white-space:nowrap}
 span.nolinebreak {white-space:nowrap}
 span.roman {font-family:serif; font-weight:normal}
 span.sansserif {font-family:sans-serif; font-weight:normal}
 ul.no-bullet {list-style: none}
 -->
 </style>


 </head>

 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
 <a name="Word"></a>
 <div class="header">
 <p>
 Next: <a href="Zero.html#Zero" accesskey="n" rel="next">Zero</a>, Previous: <a href="Weakref.html#Weakref" accesskey="p" rel="prev">Weakref</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="g_t_002eword-expressions"></a>
 <h3 class="section">7.103 <code>.word <var>expressions</var></code></h3>

 <a name="index-word-directive"></a>
 <p>This directive expects zero or more <var>expressions</var>, of any section,
 separated by commas.
 </p>
 <p>The size of the number emitted, and its byte order,
 depend on what target computer the assembly is for.
 </p>
 <a name="index-difference-tables-altered"></a>
 <a name="index-altered-difference-tables"></a>
 <blockquote>
 <p><em>Warning: Special Treatment to support Compilers</em>
 </p></blockquote>

 <p>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&rsquo;t require it;
 see <a href="Machine-Dependencies.html#Machine-Dependencies">Machine Dependencies</a>), you can ignore this issue.
 </p>
 <p>In order to assemble compiler output into something that works,
 <code>as</code> occasionally does strange things to &lsquo;<samp>.word</samp>&rsquo; directives.
 Directives of the form &lsquo;<samp>.word sym1-sym2</samp>&rsquo; are often emitted by
 compilers as part of jump tables.  Therefore, when <code>as</code> assembles a
 directive of the form &lsquo;<samp>.word sym1-sym2</samp>&rsquo;, and the difference between
 <code>sym1</code> and <code>sym2</code> does not fit in 16 bits, <code>as</code>
 creates a <em>secondary jump table</em>, immediately before the next label.
 This secondary jump table is 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 is a long-jump to <code>sym2</code>.  The original &lsquo;<samp>.word</samp>&rsquo;
 contains <code>sym1</code> minus the address of the long-jump to
 <code>sym2</code>.
 </p>
 <p>If there were several occurrences of &lsquo;<samp>.word sym1-sym2</samp>&rsquo; before the
 secondary jump table, all of them are adjusted.  If there was a
 &lsquo;<samp>.word sym3-sym4</samp>&rsquo;, that also did not fit in sixteen bits, a
 long-jump to <code>sym4</code> is included in the secondary jump table,
 and the <code>.word</code> directives are adjusted to contain <code>sym3</code>
 minus the address of the long-jump to <code>sym4</code>; and so on, for as many
 entries in the original jump table as necessary.
 </p>

 <hr>
 <div class="header">
 <p>
 Next: <a href="Zero.html#Zero" accesskey="n" rel="next">Zero</a>, Previous: <a href="Weakref.html#Weakref" accesskey="p" rel="prev">Weakref</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
 </div>


 </body>
 </html>
	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
	<html>
	<!-- This file documents the GNU Assembler "as".

	Copyright (C) 1991-2015 Free Software Foundation, Inc.

	Permission is granted to copy, distribute and/or modify this document
	under the terms of the GNU Free Documentation License, Version 1.3
	or any later version published by the Free Software Foundation;
	with no Invariant Sections, with no Front-Cover Texts, and with no
	Back-Cover Texts. A copy of the license is included in the
	section entitled "GNU Free Documentation License".
	-->
	<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
	<head>
	<title>Using as: Word</title>

	<meta name="description" content="Using as: Word">
	<meta name="keywords" content="Using as: Word">
	<meta name="resource-type" content="document">
	<meta name="distribution" content="global">
	<meta name="Generator" content="makeinfo">
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
	<link href="index.html#Top" rel="start" title="Top">
	<link href="AS-Index.html#AS-Index" rel="index" title="AS Index">
	<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
	<link href="Pseudo-Ops.html#Pseudo-Ops" rel="up" title="Pseudo Ops">
	<link href="Zero.html#Zero" rel="next" title="Zero">
	<link href="Weakref.html#Weakref" rel="prev" title="Weakref">
	<style type="text/css">
	<!--
	a.summary-letter {text-decoration: none}
	blockquote.smallquotation {font-size: smaller}
	div.display {margin-left: 3.2em}
	div.example {margin-left: 3.2em}
	div.indentedblock {margin-left: 3.2em}
	div.lisp {margin-left: 3.2em}
	div.smalldisplay {margin-left: 3.2em}
	div.smallexample {margin-left: 3.2em}
	div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
	div.smalllisp {margin-left: 3.2em}
	kbd {font-style:oblique}
	pre.display {font-family: inherit}
	pre.format {font-family: inherit}
	pre.menu-comment {font-family: serif}
	pre.menu-preformatted {font-family: serif}
	pre.smalldisplay {font-family: inherit; font-size: smaller}
	pre.smallexample {font-size: smaller}
	pre.smallformat {font-family: inherit; font-size: smaller}
	pre.smalllisp {font-size: smaller}
	span.nocodebreak {white-space:nowrap}
	span.nolinebreak {white-space:nowrap}
	span.roman {font-family:serif; font-weight:normal}
	span.sansserif {font-family:sans-serif; font-weight:normal}
	ul.no-bullet {list-style: none}
	-->
	</style>


	</head>

	<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
	<a name="Word"></a>
	<div class="header">
	<p>
	Next: <a href="Zero.html#Zero" accesskey="n" rel="next">Zero</a>, Previous: <a href="Weakref.html#Weakref" accesskey="p" rel="prev">Weakref</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="g_t_002eword-expressions"></a>
	<h3 class="section">7.103 <code>.word <var>expressions</var></code></h3>

	<a name="index-word-directive"></a>
	<p>This directive expects zero or more <var>expressions</var>, of any section,
	separated by commas.
	</p>
	<p>The size of the number emitted, and its byte order,
	depend on what target computer the assembly is for.
	</p>
	<a name="index-difference-tables-altered"></a>
	<a name="index-altered-difference-tables"></a>
	<blockquote>
	<p><em>Warning: Special Treatment to support Compilers</em>
	</p></blockquote>

	<p>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;
	see <a href="Machine-Dependencies.html#Machine-Dependencies">Machine Dependencies</a>), you can ignore this issue.
	</p>
	<p>In order to assemble compiler output into something that works,
	<code>as</code> occasionally does strange things to ‘<samp>.word</samp>’ directives.
	Directives of the form ‘<samp>.word sym1-sym2</samp>’ are often emitted by
	compilers as part of jump tables. Therefore, when <code>as</code> assembles a
	directive of the form ‘<samp>.word sym1-sym2</samp>’, and the difference between
	<code>sym1</code> and <code>sym2</code> does not fit in 16 bits, <code>as</code>
	creates a <em>secondary jump table</em>, immediately before the next label.
	This secondary jump table is 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 is a long-jump to <code>sym2</code>. The original ‘<samp>.word</samp>’
	contains <code>sym1</code> minus the address of the long-jump to
	<code>sym2</code>.
	</p>
	<p>If there were several occurrences of ‘<samp>.word sym1-sym2</samp>’ before the
	secondary jump table, all of them are adjusted. If there was a
	‘<samp>.word sym3-sym4</samp>’, that also did not fit in sixteen bits, a
	long-jump to <code>sym4</code> is included in the secondary jump table,
	and the <code>.word</code> directives are adjusted to contain <code>sym3</code>
	minus the address of the long-jump to <code>sym4</code>; and so on, for as many
	entries in the original jump table as necessary.
	</p>

	<hr>
	<div class="header">
	<p>
	Next: <a href="Zero.html#Zero" accesskey="n" rel="next">Zero</a>, Previous: <a href="Weakref.html#Weakref" accesskey="p" rel="prev">Weakref</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
	</div>



	</body>
	</html>