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120 lines
6.1 KiB
HTML
120 lines
6.1 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This file documents the GNU Assembler "as".
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Copyright (C) 1991-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled "GNU Free Documentation License".
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-->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>MMIX-Symbols (Using as)</title>
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<meta name="description" content="MMIX-Symbols (Using as)">
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<meta name="keywords" content="MMIX-Symbols (Using as)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="AS-Index.html#AS-Index" rel="index" title="AS Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="MMIX_002dSyntax.html#MMIX_002dSyntax" rel="up" title="MMIX-Syntax">
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<link href="MMIX_002dRegs.html#MMIX_002dRegs" rel="next" title="MMIX-Regs">
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<link href="MMIX_002dChars.html#MMIX_002dChars" rel="prev" title="MMIX-Chars">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="MMIX_002dSymbols"></a>
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<div class="header">
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<p>
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Next: <a href="MMIX_002dRegs.html#MMIX_002dRegs" accesskey="n" rel="next">MMIX-Regs</a>, Previous: <a href="MMIX_002dChars.html#MMIX_002dChars" accesskey="p" rel="prev">MMIX-Chars</a>, Up: <a href="MMIX_002dSyntax.html#MMIX_002dSyntax" accesskey="u" rel="up">MMIX-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>
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</div>
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<hr>
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<a name="Symbols-4"></a>
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<h4 class="subsubsection">9.27.3.2 Symbols</h4>
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<p>The character ‘<samp>:</samp>’ is permitted in identifiers. There are two
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exceptions to it being treated as any other symbol character: if a symbol
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begins with ‘<samp>:</samp>’, it means that the symbol is in the global namespace
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and that the current prefix should not be prepended to that symbol
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(see <a href="MMIX_002dPseudos.html#MMIX_002dprefix">MMIX-prefix</a>). The ‘<samp>:</samp>’ is then not considered part of the
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symbol. For a symbol in the label position (first on a line), a ‘<samp>:</samp>’
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at the end of a symbol is silently stripped off. A label is permitted,
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but not required, to be followed by a ‘<samp>:</samp>’, as with many other
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assembly formats.
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</p>
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<p>The character ‘<samp>@</samp>’ in an expression, is a synonym for ‘<samp>.</samp>’, the
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current location.
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</p>
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<p>In addition to the common forward and backward local symbol formats
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(see <a href="Symbol-Names.html#Symbol-Names">Symbol Names</a>), they can be specified with upper-case ‘<samp>B</samp>’ and
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‘<samp>F</samp>’, as in ‘<samp>8B</samp>’ and ‘<samp>9F</samp>’. A local label defined for the
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current position is written with a ‘<samp>H</samp>’ appended to the number:
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</p><div class="smallexample">
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<pre class="smallexample">3H LDB $0,$1,2
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</pre></div>
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<p>This and traditional local-label formats cannot be mixed: a label must be
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defined and referred to using the same format.
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</p>
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<p>There’s a minor caveat: just as for the ordinary local symbols, the local
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symbols are translated into ordinary symbols using control characters are
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to hide the ordinal number of the symbol. Unfortunately, these symbols
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are not translated back in error messages. Thus you may see confusing
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error messages when local symbols are used. Control characters
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‘<samp>\003</samp>’ (control-C) and ‘<samp>\004</samp>’ (control-D) are used for the
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MMIX-specific local-symbol syntax.
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</p>
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<p>The symbol ‘<samp>Main</samp>’ is handled specially; it is always global.
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</p>
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<p>By defining the symbols ‘<samp>__.MMIX.start..text</samp>’ and
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‘<samp>__.MMIX.start..data</samp>’, the address of respectively the ‘<samp>.text</samp>’
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and ‘<samp>.data</samp>’ segments of the final program can be defined, though when
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linking more than one object file, the code or data in the object file
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containing the symbol is not guaranteed to be start at that position; just
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the final executable. See <a href="MMIX_002dPseudos.html#MMIX_002dloc">MMIX-loc</a>.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="MMIX_002dRegs.html#MMIX_002dRegs" accesskey="n" rel="next">MMIX-Regs</a>, Previous: <a href="MMIX_002dChars.html#MMIX_002dChars" accesskey="p" rel="prev">MMIX-Chars</a>, Up: <a href="MMIX_002dSyntax.html#MMIX_002dSyntax" accesskey="u" rel="up">MMIX-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>
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</div>
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</body>
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</html>
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