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| <h5 class="subsubsection">9.25.3.2 Symbols</h5> |
| |
| <p>The character ‘<samp><span class="samp">:</span></samp>’ is permitted in identifiers. There are two |
| exceptions to it being treated as any other symbol character: if a symbol |
| begins with ‘<samp><span class="samp">:</span></samp>’, it means that the symbol is in the global namespace |
| and that the current prefix should not be prepended to that symbol |
| (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 |
| symbol. For a symbol in the label position (first on a line), a ‘<samp><span class="samp">:</span></samp>’ |
| at the end of a symbol is silently stripped off. A label is permitted, |
| but not required, to be followed by a ‘<samp><span class="samp">:</span></samp>’, as with many other |
| assembly formats. |
| |
| <p>The character ‘<samp><span class="samp">@</span></samp>’ in an expression, is a synonym for ‘<samp><span class="samp">.</span></samp>’, the |
| current location. |
| |
| <p>In addition to the common forward and backward local symbol formats |
| (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 |
| ‘<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 |
| current position is written with a ‘<samp><span class="samp">H</span></samp>’ appended to the number: |
| <pre class="smallexample"> 3H LDB $0,$1,2 |
| </pre> |
| <p>This and traditional local-label formats cannot be mixed: a label must be |
| defined and referred to using the same format. |
| |
| <p>There's a minor caveat: just as for the ordinary local symbols, the local |
| symbols are translated into ordinary symbols using control characters are |
| to hide the ordinal number of the symbol. Unfortunately, these symbols |
| are not translated back in error messages. Thus you may see confusing |
| error messages when local symbols are used. Control characters |
| ‘<samp><span class="samp">\003</span></samp>’ (control-C) and ‘<samp><span class="samp">\004</span></samp>’ (control-D) are used for the |
| MMIX-specific local-symbol syntax. |
| |
| <p>The symbol ‘<samp><span class="samp">Main</span></samp>’ is handled specially; it is always global. |
| |
| <p>By defining the symbols ‘<samp><span class="samp">__.MMIX.start..text</span></samp>’ and |
| ‘<samp><span class="samp">__.MMIX.start..data</span></samp>’, the address of respectively the ‘<samp><span class="samp">.text</span></samp>’ |
| and ‘<samp><span class="samp">.data</span></samp>’ segments of the final program can be defined, though when |
| linking more than one object file, the code or data in the object file |
| containing the symbol is not guaranteed to be start at that position; just |
| the final executable. See <a href="MMIX_002dloc.html#MMIX_002dloc">MMIX-loc</a>. |
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