69 lines
2.9 KiB
HTML
69 lines
2.9 KiB
HTML
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<html lang="en">
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<title>Lazy Alien Resolution - SBCL Internals</title>
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<link rel="up" href="Foreign-Linkage.html#Foreign-Linkage" title="Foreign Linkage">
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<link rel="prev" href="Linkage_002dtable.html#Linkage_002dtable" title="Linkage-table">
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This manual is part of the SBCL software system. See the `README'
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This manual is in the public domain and is provided with
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<p>
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<a name="Lazy-Alien-Resolution"></a>
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Next: <a rel="next" accesskey="n" href="Callbacks.html#Callbacks">Callbacks</a>,
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Previous: <a rel="previous" accesskey="p" href="Linkage_002dtable.html#Linkage_002dtable">Linkage-table</a>,
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Up: <a rel="up" accesskey="u" href="Foreign-Linkage.html#Foreign-Linkage">Foreign Linkage</a>
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<!-- node-name, next, previous, up -->
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<h3 class="section">4.2 Lazy Alien Resolution</h3>
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<p>On linkage-table ports SBCL is able to deal with forward-references to
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aliens – which is to say, compile and load code referring to aliens
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before the shared object containing the alien in question has been
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loaded.
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<p>This is handled by <code>ENSURE-DYNAMIC-FOREIGN-SYMBOL-ADDRESS</code>, which
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first tries to resolve the address in the loaded shared objects, but
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failing that records the alien as undefined and returns the address of
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a read/write/execute protected guard page for variables, and address
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of <code>undefined_alien_function</code> for routines. These are in turn
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responsible for catching attempts to access the undefined alien, and
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signalling the appropriate error.
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<p>These placeholder addresses get recorded in the linkage-table.
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<p>When new shared objects are loaded <code>UPDATE-LINKAGE-TABLE</code> is
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called, which in turn attempts to resolve all currently undefined
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aliens, and registers the correct addresses for them in the
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linkage-table.
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</body></html>
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