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<a name="Symver"></a>
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<a name="g_t_002esymver"></a>
<h3 class="section">7.95 <code>.symver</code></h3>
<a name="index-symver-directive"></a>
<a name="index-symbol-versioning"></a>
<a name="index-versions-of-symbols"></a>
<p>Use the <code>.symver</code> directive to bind symbols to specific version nodes
within a source file.  This is only supported on ELF platforms, and is
typically used when assembling files to be linked into a shared library.
There are cases where it may make sense to use this in objects to be bound
into an application itself so as to override a versioned symbol from a
shared library.
</p>
<p>For ELF targets, the <code>.symver</code> directive can be used like this:
</p><div class="smallexample">
<pre class="smallexample">.symver <var>name</var>, <var>name2@nodename</var>[ ,<var>visibility</var>]
</pre></div>
<p>If the original symbol <var>name</var> is defined within the file
being assembled, the <code>.symver</code> directive effectively creates a symbol
alias with the name <var>name2@nodename</var>, and in fact the main reason that we
just don&rsquo;t try and create a regular alias is that the <var>@</var> character isn&rsquo;t
permitted in symbol names.  The <var>name2</var> part of the name is the actual name
of the symbol by which it will be externally referenced.  The name <var>name</var>
itself is merely a name of convenience that is used so that it is possible to
have definitions for multiple versions of a function within a single source
file, and so that the compiler can unambiguously know which version of a
function is being mentioned.  The <var>nodename</var> portion of the alias should be
the name of a node specified in the version script supplied to the linker when
building a shared library.  If you are attempting to override a versioned
symbol from a shared library, then <var>nodename</var> should correspond to the
nodename of the symbol you are trying to override.  The optional argument
<var>visibility</var> updates the visibility of the original symbol.  The valid
visibilities are <code>local</code>, <code>hidden</code>, and <code>remove</code>.  The
<code>local</code> visibility makes the original symbol a local symbol
(see <a href="Local.html#Local">Local</a>).  The <code>hidden</code> visibility sets the visibility of the
original symbol to <code>hidden</code> (see <a href="Hidden.html#Hidden">Hidden</a>).  The <code>remove</code>
visibility removes the original symbol from the symbol table.  If visibility
isn&rsquo;t specified, the original symbol is unchanged.
</p>
<p>If the symbol <var>name</var> is not defined within the file being assembled, all
references to <var>name</var> will be changed to <var>name2@nodename</var>.  If no
reference to <var>name</var> is made, <var>name2@nodename</var> will be removed from the
symbol table.
</p>
<p>Another usage of the <code>.symver</code> directive is:
</p><div class="smallexample">
<pre class="smallexample">.symver <var>name</var>, <var>name2@@nodename</var>
</pre></div>
<p>In this case, the symbol <var>name</var> must exist and be defined within
the file being assembled. It is similar to <var>name2@nodename</var>. The
difference is <var>name2@@nodename</var> will also be used to resolve
references to <var>name2</var> by the linker.
</p>
<p>The third usage of the <code>.symver</code> directive is:
</p><div class="smallexample">
<pre class="smallexample">.symver <var>name</var>, <var>name2@@@nodename</var>
</pre></div>
<p>When <var>name</var> is not defined within the
file being assembled, it is treated as <var>name2@nodename</var>. When
<var>name</var> is defined within the file being assembled, the symbol
name, <var>name</var>, will be changed to <var>name2@@nodename</var>.
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