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92 lines
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<title>MMIX-Symbols - Using as</title>
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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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<a name="MMIX-Symbols"></a>
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<a name="MMIX_002dSymbols"></a>
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<p>
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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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<h5 class="subsubsection">9.28.3.2 Symbols</h5>
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<p>The character ‘<samp><span class="samp">:</span></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><span class="samp">:</span></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_002dprefix.html#MMIX_002dprefix">MMIX-prefix</a>). The ‘<samp><span class="samp">:</span></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><span class="samp">:</span></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><span class="samp">:</span></samp>’, as with many other
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assembly formats.
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<p>The character ‘<samp><span class="samp">@</span></samp>’ in an expression, is a synonym for ‘<samp><span class="samp">.</span></samp>’, 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 ‘<samp><span class="samp">B</span></samp>’ and
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‘<samp><span class="samp">F</span></samp>’, as in ‘<samp><span class="samp">8B</span></samp>’ and ‘<samp><span class="samp">9F</span></samp>’. A local label defined for the
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current position is written with a ‘<samp><span class="samp">H</span></samp>’ 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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‘<samp><span class="samp">\003</span></samp>’ (control-C) and ‘<samp><span class="samp">\004</span></samp>’ (control-D) are used for the
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MMIX-specific local-symbol syntax.
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<p>The symbol ‘<samp><span class="samp">Main</span></samp>’ is handled specially; it is always global.
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<p>By defining the symbols ‘<samp><span class="samp">__.MMIX.start..text</span></samp>’ and
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‘<samp><span class="samp">__.MMIX.start..data</span></samp>’, the address of respectively the ‘<samp><span class="samp">.text</span></samp>’
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and ‘<samp><span class="samp">.data</span></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_002dloc.html#MMIX_002dloc">MMIX-loc</a>.
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</body></html>
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