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<h3 class="section">7.107 <code>.symver</code></h3>
<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
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>For ELF targets, the <code>.symver</code> directive can be used like this:
<pre class="smallexample"> .symver <var>name</var>, <var>name2@nodename</var>
</pre>
<p>If the 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't try and create a regular alias is that the <var>@</var> character isn'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.
<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>Another usage of the <code>.symver</code> directive is:
<pre class="smallexample"> .symver <var>name</var>, <var>name2@@nodename</var>
</pre>
<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>The third usage of the <code>.symver</code> directive is:
<pre class="smallexample"> .symver <var>name</var>, <var>name2@@@nodename</var>
</pre>
<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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