89 lines
4.5 KiB
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89 lines
4.5 KiB
HTML
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<title>MMIX-Symbols - Using as</title>
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 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 1.1
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or any later version published by the Free Software Foundation;
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<p>
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<a name="MMIX_002dSymbols"></a>Next: <a rel="next" accesskey="n" href="MMIX_002dRegs.html#MMIX_002dRegs">MMIX-Regs</a>,
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Previous: <a rel="previous" accesskey="p" href="MMIX_002dChars.html#MMIX_002dChars">MMIX-Chars</a>,
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Up: <a rel="up" accesskey="u" href="MMIX_002dSyntax.html#MMIX_002dSyntax">MMIX-Syntax</a>
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<hr><br>
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</div>
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<h5 class="subsubsection">9.23.3.2 Symbols</h5>
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<p>The character <span class="samp">:</span> 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 <span class="samp">:</span>, 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_002dprefix.html#MMIX_002dprefix">MMIX-prefix</a>). The <span class="samp">:</span> is then not considered part of the
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symbol. For a symbol in the label position (first on a line), a <span class="samp">:</span>
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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 <span class="samp">:</span>, as with many other
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assembly formats.
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<p>The character <span class="samp">@</span> in an expression, is a synonym for <span class="samp">.</span>, the
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current location.
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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 <span class="samp">B</span> and
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<span class="samp">F</span>, as in <span class="samp">8B</span> and <span class="samp">9F</span>. A local label defined for the
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current position is written with a <span class="samp">H</span> appended to the number:
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<pre class="smallexample"> 3H LDB $0,$1,2
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</pre>
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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>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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<span class="samp">\003</span> (control-C) and <span class="samp">\004</span> (control-D) are used for the
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MMIX-specific local-symbol syntax.
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<p>The symbol <span class="samp">Main</span> is handled specially; it is always global.
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<p>By defining the symbols <span class="samp">__.MMIX.start..text</span> and
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<span class="samp">__.MMIX.start..data</span>, the address of respectively the <span class="samp">.text</span>
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and <span class="samp">.data</span> 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_002dloc.html#MMIX_002dloc">MMIX-loc</a>.
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</body></html>
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