aarch64-linux-gnu-5.1/share/doc/gas/as.html/TIC54X_002dSubsyms.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) 1991-2014 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: TIC54X-Subsyms</title>

 <meta name="description" content="Using as: TIC54X-Subsyms">
 <meta name="keywords" content="Using as: TIC54X-Subsyms">
 <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="TIC54X_002dDependent.html#TIC54X_002dDependent" rel="up" title="TIC54X-Dependent">
 <link href="TIC54X_002dLocals.html#TIC54X_002dLocals" rel="next" title="TIC54X-Locals">
 <link href="TIC54X_002dConstants.html#TIC54X_002dConstants" rel="prev" title="TIC54X-Constants">
 <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="TIC54X_002dSubsyms"></a>
 <div class="header">
 <p>
 Next: <a href="TIC54X_002dLocals.html#TIC54X_002dLocals" accesskey="n" rel="next">TIC54X-Locals</a>, Previous: <a href="TIC54X_002dConstants.html#TIC54X_002dConstants" accesskey="p" rel="prev">TIC54X-Constants</a>, Up: <a href="TIC54X_002dDependent.html#TIC54X_002dDependent" accesskey="u" rel="up">TIC54X-Dependent</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="String-Substitution"></a>
 <h4 class="subsection">9.43.5 String Substitution</h4>
 <p>A subset of allowable symbols (which we&rsquo;ll call subsyms) may be assigned
 arbitrary string values.  This is roughly equivalent to C preprocessor
 #define macros.  When <code>as</code> encounters one of these
 symbols, the symbol is replaced in the input stream by its string value.
 Subsym names <strong>must</strong> begin with a letter.
 </p>
 <p>Subsyms may be defined using the <code>.asg</code> and <code>.eval</code> directives
 (See <a href="TIC54X_002dDirectives.html#TIC54X_002dDirectives"><code>.asg</code></a>,
 See <a href="TIC54X_002dDirectives.html#TIC54X_002dDirectives"><code>.eval</code></a>.
 </p>
 <p>Expansion is recursive until a previously encountered symbol is seen, at
 which point substitution stops.
 </p>
 <p>In this example, x is replaced with SYM2; SYM2 is replaced with SYM1, and SYM1
 is replaced with x.  At this point, x has already been encountered
 and the substitution stops.
 </p>
 <div class="smallexample">
 <pre class="smallexample"> .asg   &quot;x&quot;,SYM1
  .asg   &quot;SYM1&quot;,SYM2
  .asg   &quot;SYM2&quot;,x
  add    x,a             ; final code assembled is &quot;add  x, a&quot;
 </pre></div>

 <p>Macro parameters are converted to subsyms; a side effect of this is the normal
 <code>as</code> &rsquo;\ARG&rsquo; dereferencing syntax is unnecessary.  Subsyms
 defined within a macro will have global scope, unless the <code>.var</code>
 directive is used to identify the subsym as a local macro variable
 see <a href="TIC54X_002dDirectives.html#TIC54X_002dDirectives"><code>.var</code></a>.
 </p>
 <p>Substitution may be forced in situations where replacement might be
 ambiguous by placing colons on either side of the subsym.  The following
 code:
 </p>
 <div class="smallexample">
 <pre class="smallexample"> .eval  &quot;10&quot;,x
 LAB:X:  add     #x, a
 </pre></div>

 <p>When assembled becomes:
 </p>
 <div class="smallexample">
 <pre class="smallexample">LAB10  add     #10, a
 </pre></div>

 <p>Smaller parts of the string assigned to a subsym may be accessed with
 the following syntax:
 </p>
 <dl compact="compact">
 <dt><code><code>:<var>symbol</var>(<var>char_index</var>):</code></code></dt>
 <dd><p>Evaluates to a single-character string, the character at <var>char_index</var>.
 </p></dd>
 <dt><code><code>:<var>symbol</var>(<var>start</var>,<var>length</var>):</code></code></dt>
 <dd><p>Evaluates to a substring of <var>symbol</var> beginning at <var>start</var> with
 length <var>length</var>.
 </p></dd>
 </dl>

 <hr>
 <div class="header">
 <p>
 Next: <a href="TIC54X_002dLocals.html#TIC54X_002dLocals" accesskey="n" rel="next">TIC54X-Locals</a>, Previous: <a href="TIC54X_002dConstants.html#TIC54X_002dConstants" accesskey="p" rel="prev">TIC54X-Constants</a>, Up: <a href="TIC54X_002dDependent.html#TIC54X_002dDependent" accesskey="u" rel="up">TIC54X-Dependent</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) 1991-2014 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: TIC54X-Subsyms</title>

	<meta name="description" content="Using as: TIC54X-Subsyms">
	<meta name="keywords" content="Using as: TIC54X-Subsyms">
	<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="TIC54X_002dDependent.html#TIC54X_002dDependent" rel="up" title="TIC54X-Dependent">
	<link href="TIC54X_002dLocals.html#TIC54X_002dLocals" rel="next" title="TIC54X-Locals">
	<link href="TIC54X_002dConstants.html#TIC54X_002dConstants" rel="prev" title="TIC54X-Constants">
	<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="TIC54X_002dSubsyms"></a>
	<div class="header">
	<p>
	Next: <a href="TIC54X_002dLocals.html#TIC54X_002dLocals" accesskey="n" rel="next">TIC54X-Locals</a>, Previous: <a href="TIC54X_002dConstants.html#TIC54X_002dConstants" accesskey="p" rel="prev">TIC54X-Constants</a>, Up: <a href="TIC54X_002dDependent.html#TIC54X_002dDependent" accesskey="u" rel="up">TIC54X-Dependent</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="String-Substitution"></a>
	<h4 class="subsection">9.43.5 String Substitution</h4>
	<p>A subset of allowable symbols (which we’ll call subsyms) may be assigned
	arbitrary string values. This is roughly equivalent to C preprocessor
	#define macros. When <code>as</code> encounters one of these
	symbols, the symbol is replaced in the input stream by its string value.
	Subsym names <strong>must</strong> begin with a letter.
	</p>
	<p>Subsyms may be defined using the <code>.asg</code> and <code>.eval</code> directives
	(See <a href="TIC54X_002dDirectives.html#TIC54X_002dDirectives"><code>.asg</code></a>,
	See <a href="TIC54X_002dDirectives.html#TIC54X_002dDirectives"><code>.eval</code></a>.
	</p>
	<p>Expansion is recursive until a previously encountered symbol is seen, at
	which point substitution stops.
	</p>
	<p>In this example, x is replaced with SYM2; SYM2 is replaced with SYM1, and SYM1
	is replaced with x. At this point, x has already been encountered
	and the substitution stops.
	</p>
	<div class="smallexample">
	<pre class="smallexample"> .asg "x",SYM1
	.asg "SYM1",SYM2
	.asg "SYM2",x
	add x,a ; final code assembled is "add x, a"
	</pre></div>

	<p>Macro parameters are converted to subsyms; a side effect of this is the normal
	<code>as</code> ’\ARG’ dereferencing syntax is unnecessary. Subsyms
	defined within a macro will have global scope, unless the <code>.var</code>
	directive is used to identify the subsym as a local macro variable
	see <a href="TIC54X_002dDirectives.html#TIC54X_002dDirectives"><code>.var</code></a>.
	</p>
	<p>Substitution may be forced in situations where replacement might be
	ambiguous by placing colons on either side of the subsym. The following
	code:
	</p>
	<div class="smallexample">
	<pre class="smallexample"> .eval "10",x
	LAB:X: add #x, a
	</pre></div>

	<p>When assembled becomes:
	</p>
	<div class="smallexample">
	<pre class="smallexample">LAB10 add #10, a
	</pre></div>

	<p>Smaller parts of the string assigned to a subsym may be accessed with
	the following syntax:
	</p>
	<dl compact="compact">
	<dt><code><code>:<var>symbol</var>(<var>char_index</var>):</code></code></dt>
	<dd><p>Evaluates to a single-character string, the character at <var>char_index</var>.
	</p></dd>
	<dt><code><code>:<var>symbol</var>(<var>start</var>,<var>length</var>):</code></code></dt>
	<dd><p>Evaluates to a substring of <var>symbol</var> beginning at <var>start</var> with
	length <var>length</var>.
	</p></dd>
	</dl>

	<hr>
	<div class="header">
	<p>
	Next: <a href="TIC54X_002dLocals.html#TIC54X_002dLocals" accesskey="n" rel="next">TIC54X-Locals</a>, Previous: <a href="TIC54X_002dConstants.html#TIC54X_002dConstants" accesskey="p" rel="prev">TIC54X-Constants</a>, Up: <a href="TIC54X_002dDependent.html#TIC54X_002dDependent" accesskey="u" rel="up">TIC54X-Dependent</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>