<html lang="en">
<head>
<title>Symver - Using as</title>
<meta http-equiv="Content-Type" content="text/html">
<meta name="description" content="Using as">
<meta name="generator" content="makeinfo 4.13">
<link title="Top" rel="start" href="index.html#Top">
<link rel="up" href="Pseudo-Ops.html#Pseudo-Ops" title="Pseudo Ops">
<link rel="prev" href="SubSection.html#SubSection" title="SubSection">
<link rel="next" href="Tag.html#Tag" title="Tag">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
This file documents the GNU Assembler "as".
Copyright (C) 1991-2015 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, with no Front-Cover Texts, and with no
Back-Cover Texts. A copy of the license is included in the
section entitled ``GNU Free Documentation License''.
-->
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
pre.display { font-family:inherit }
pre.format { font-family:inherit }
pre.smalldisplay { font-family:inherit; font-size:smaller }
pre.smallformat { font-family:inherit; font-size:smaller }
pre.smallexample { font-size:smaller }
pre.smalllisp { font-size:smaller }
span.sc { font-variant:small-caps }
span.roman { font-family:serif; font-weight:normal; }
span.sansserif { font-family:sans-serif; font-weight:normal; }
--></style>
</head>
<body>
<div class="node">
<a name="Symver"></a>
<p>
Next: <a rel="next" accesskey="n" href="Tag.html#Tag">Tag</a>,
Previous: <a rel="previous" accesskey="p" href="SubSection.html#SubSection">SubSection</a>,
Up: <a rel="up" accesskey="u" href="Pseudo-Ops.html#Pseudo-Ops">Pseudo Ops</a>
<hr>
</div>
<h3 class="section">7.90 <code>.symver</code></h3>
<p><a name="index-g_t_0040code_007bsymver_007d-directive-488"></a><a name="index-symbol-versioning-489"></a><a name="index-versions-of-symbols-490"></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>.
</body></html>