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97 lines
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97 lines
4.8 KiB
HTML
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<title>Symver - Using as</title>
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<link rel="up" href="Pseudo-Ops.html#Pseudo-Ops" title="Pseudo Ops">
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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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or any later version published by the Free Software Foundation;
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<body>
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<div class="node">
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<p>
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<a name="Symver"></a>Next: <a rel="next" accesskey="n" href="Tag.html#Tag">Tag</a>,
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Previous: <a rel="previous" accesskey="p" href="SubSection.html#SubSection">SubSection</a>,
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Up: <a rel="up" accesskey="u" href="Pseudo-Ops.html#Pseudo-Ops">Pseudo Ops</a>
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<hr><br>
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</div>
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<h3 class="section">7.107 <code>.symver</code></h3>
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<p><a name="index-_0040code_007bsymver_007d-directive-474"></a><a name="index-symbol-versioning-475"></a><a name="index-versions-of-symbols-476"></a>Use the <code>.symver</code> directive to bind symbols to specific version nodes
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within a source file. This is only supported on ELF platforms, and is
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typically used when assembling files to be linked into a shared library.
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There are cases where it may make sense to use this in objects to be bound
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into an application itself so as to override a versioned symbol from a
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shared library.
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<p>For ELF targets, the <code>.symver</code> directive can be used like this:
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<pre class="smallexample"> .symver <var>name</var>, <var>name2@nodename</var>
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</pre>
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<p>If the symbol <var>name</var> is defined within the file
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being assembled, the <code>.symver</code> directive effectively creates a symbol
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alias with the name <var>name2@nodename</var>, and in fact the main reason that we
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just don't try and create a regular alias is that the <var>@</var> character isn't
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permitted in symbol names. The <var>name2</var> part of the name is the actual name
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of the symbol by which it will be externally referenced. The name <var>name</var>
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itself is merely a name of convenience that is used so that it is possible to
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have definitions for multiple versions of a function within a single source
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file, and so that the compiler can unambiguously know which version of a
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function is being mentioned. The <var>nodename</var> portion of the alias should be
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the name of a node specified in the version script supplied to the linker when
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building a shared library. If you are attempting to override a versioned
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symbol from a shared library, then <var>nodename</var> should correspond to the
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nodename of the symbol you are trying to override.
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<p>If the symbol <var>name</var> is not defined within the file being assembled, all
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references to <var>name</var> will be changed to <var>name2@nodename</var>. If no
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reference to <var>name</var> is made, <var>name2@nodename</var> will be removed from the
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symbol table.
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<p>Another usage of the <code>.symver</code> directive is:
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<pre class="smallexample"> .symver <var>name</var>, <var>name2@@nodename</var>
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</pre>
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<p>In this case, the symbol <var>name</var> must exist and be defined within
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the file being assembled. It is similar to <var>name2@nodename</var>. The
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difference is <var>name2@@nodename</var> will also be used to resolve
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references to <var>name2</var> by the linker.
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<p>The third usage of the <code>.symver</code> directive is:
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<pre class="smallexample"> .symver <var>name</var>, <var>name2@@@nodename</var>
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</pre>
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<p>When <var>name</var> is not defined within the
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file being assembled, it is treated as <var>name2@nodename</var>. When
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<var>name</var> is defined within the file being assembled, the symbol
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name, <var>name</var>, will be changed to <var>name2@@nodename</var>.
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</body></html>
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