1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- This file documents the GNU Assembler "as". 4 5Copyright (C) 1991-2021 Free Software Foundation, Inc. 6 7Permission is granted to copy, distribute and/or modify this document 8under the terms of the GNU Free Documentation License, Version 1.3 9or any later version published by the Free Software Foundation; 10with no Invariant Sections, with no Front-Cover Texts, and with no 11Back-Cover Texts. A copy of the license is included in the 12section entitled "GNU Free Documentation License". 13 --> 14<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> 15<head> 16<title>Using as: S12Z Register Notation</title> 17 18<meta name="description" content="Using as: S12Z Register Notation"> 19<meta name="keywords" content="Using as: S12Z Register Notation"> 20<meta name="resource-type" content="document"> 21<meta name="distribution" content="global"> 22<meta name="Generator" content="makeinfo"> 23<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 24<link href="index.html#Top" rel="start" title="Top"> 25<link href="AS-Index.html#AS-Index" rel="index" title="AS Index"> 26<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> 27<link href="S12Z-Syntax.html#S12Z-Syntax" rel="up" title="S12Z Syntax"> 28<link href="Meta_002dDependent.html#Meta_002dDependent" rel="next" title="Meta-Dependent"> 29<link href="S12Z-Addressing-Modes.html#S12Z-Addressing-Modes" rel="previous" title="S12Z Addressing Modes"> 30<style type="text/css"> 31<!-- 32a.summary-letter {text-decoration: none} 33blockquote.smallquotation {font-size: smaller} 34div.display {margin-left: 3.2em} 35div.example {margin-left: 3.2em} 36div.indentedblock {margin-left: 3.2em} 37div.lisp {margin-left: 3.2em} 38div.smalldisplay {margin-left: 3.2em} 39div.smallexample {margin-left: 3.2em} 40div.smallindentedblock {margin-left: 3.2em; font-size: smaller} 41div.smalllisp {margin-left: 3.2em} 42kbd {font-style:oblique} 43pre.display {font-family: inherit} 44pre.format {font-family: inherit} 45pre.menu-comment {font-family: serif} 46pre.menu-preformatted {font-family: serif} 47pre.smalldisplay {font-family: inherit; font-size: smaller} 48pre.smallexample {font-size: smaller} 49pre.smallformat {font-family: inherit; font-size: smaller} 50pre.smalllisp {font-size: smaller} 51span.nocodebreak {white-space:nowrap} 52span.nolinebreak {white-space:nowrap} 53span.roman {font-family:serif; font-weight:normal} 54span.sansserif {font-family:sans-serif; font-weight:normal} 55ul.no-bullet {list-style: none} 56--> 57</style> 58 59 60</head> 61 62<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> 63<a name="S12Z-Register-Notation"></a> 64<div class="header"> 65<p> 66Previous: <a href="S12Z-Addressing-Modes.html#S12Z-Addressing-Modes" accesskey="p" rel="previous">S12Z Addressing Modes</a>, Up: <a href="S12Z-Syntax.html#S12Z-Syntax" accesskey="u" rel="up">S12Z Syntax</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> 67</div> 68<hr> 69<a name="Register-Notation"></a> 70<h4 class="subsubsection">9.24.2.3 Register Notation</h4> 71 72<a name="index-register-notation_002c-S12Z"></a> 73<p>Without a register prefix (see <a href="S12Z-Options.html#S12Z-Options">S12Z Options</a>), S12Z assembler code is expected in the traditional 74format like this: 75</p><div class="smallexample"> 76<pre class="smallexample">lea s, (-2,s) 77st d2, (0,s) 78ld x, symbol 79tfr d2, d6 80cmp d6, #1532 81</pre></div> 82 83<p>However, if <code>as</code> is started with (for example) ‘<samp>-mreg-prefix=%</samp>’ 84then all register names must be prefixed with ‘<samp>%</samp>’ as follows: 85</p><div class="smallexample"> 86<pre class="smallexample">lea %s, (-2,%s) 87st %d2, (0,%s) 88ld %x, symbol 89tfr %d2, %d6 90cmp %d6, #1532 91</pre></div> 92 93<p>The register prefix feature is intended to be used by compilers 94to avoid ambiguity between symbols and register names. 95Consider the following assembler instruction: 96</p><div class="smallexample"> 97<pre class="smallexample">st d0, d1 98</pre></div> 99<p>The destination operand of this instruction could either refer to the register 100‘<samp>D1</samp>’, or it could refer to the symbol named “d1”. 101If the latter is intended then <code>as</code> must be invoked with 102‘<samp>-mreg-prefix=<var>pfx</var></samp>’ and the code written as 103</p><div class="smallexample"> 104<pre class="smallexample">st <var>pfx</var>d0, d1 105</pre></div> 106<p>where <var>pfx</var> is the chosen register prefix. 107For this reason, compiler back-ends should choose a register prefix which 108cannot be confused with a symbol name. 109</p> 110 111 112 113 114</body> 115</html> 116