1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- This file documents the GNU Assembler "as". 4 5Copyright (C) 1991-2021 Free Software Foundation, Inc. 6 7Permission is granted to copy, distribute and/or modify this document 8under the terms of the GNU Free Documentation License, Version 1.3 9or any later version published by the Free Software Foundation; 10with no Invariant Sections, with no Front-Cover Texts, and with no 11Back-Cover Texts. A copy of the license is included in the 12section entitled "GNU Free Documentation License". 13 --> 14<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> 15<head> 16<title>Using as: Symver</title> 17 18<meta name="description" content="Using as: Symver"> 19<meta name="keywords" content="Using as: Symver"> 20<meta name="resource-type" content="document"> 21<meta name="distribution" content="global"> 22<meta name="Generator" content="makeinfo"> 23<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 24<link href="index.html#Top" rel="start" title="Top"> 25<link href="AS-Index.html#AS-Index" rel="index" title="AS Index"> 26<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> 27<link href="Pseudo-Ops.html#Pseudo-Ops" rel="up" title="Pseudo Ops"> 28<link href="Tag.html#Tag" rel="next" title="Tag"> 29<link href="SubSection.html#SubSection" rel="previous" title="SubSection"> 30<style type="text/css"> 31<!-- 32a.summary-letter {text-decoration: none} 33blockquote.smallquotation {font-size: smaller} 34div.display {margin-left: 3.2em} 35div.example {margin-left: 3.2em} 36div.indentedblock {margin-left: 3.2em} 37div.lisp {margin-left: 3.2em} 38div.smalldisplay {margin-left: 3.2em} 39div.smallexample {margin-left: 3.2em} 40div.smallindentedblock {margin-left: 3.2em; font-size: smaller} 41div.smalllisp {margin-left: 3.2em} 42kbd {font-style:oblique} 43pre.display {font-family: inherit} 44pre.format {font-family: inherit} 45pre.menu-comment {font-family: serif} 46pre.menu-preformatted {font-family: serif} 47pre.smalldisplay {font-family: inherit; font-size: smaller} 48pre.smallexample {font-size: smaller} 49pre.smallformat {font-family: inherit; font-size: smaller} 50pre.smalllisp {font-size: smaller} 51span.nocodebreak {white-space:nowrap} 52span.nolinebreak {white-space:nowrap} 53span.roman {font-family:serif; font-weight:normal} 54span.sansserif {font-family:sans-serif; font-weight:normal} 55ul.no-bullet {list-style: none} 56--> 57</style> 58 59 60</head> 61 62<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> 63<a name="Symver"></a> 64<div class="header"> 65<p> 66Next: <a href="Tag.html#Tag" accesskey="n" rel="next">Tag</a>, Previous: <a href="SubSection.html#SubSection" accesskey="p" rel="previous">SubSection</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p> 67</div> 68<hr> 69<a name="g_t_002esymver"></a> 70<h3 class="section">7.96 <code>.symver</code></h3> 71<a name="index-symver-directive"></a> 72<a name="index-symbol-versioning"></a> 73<a name="index-versions-of-symbols"></a> 74<p>Use the <code>.symver</code> directive to bind symbols to specific version nodes 75within a source file. This is only supported on ELF platforms, and is 76typically used when assembling files to be linked into a shared library. 77There are cases where it may make sense to use this in objects to be bound 78into an application itself so as to override a versioned symbol from a 79shared library. 80</p> 81<p>For ELF targets, the <code>.symver</code> directive can be used like this: 82</p><div class="smallexample"> 83<pre class="smallexample">.symver <var>name</var>, <var>name2@nodename</var>[ ,<var>visibility</var>] 84</pre></div> 85<p>If the original symbol <var>name</var> is defined within the file 86being assembled, the <code>.symver</code> directive effectively creates a symbol 87alias with the name <var>name2@nodename</var>, and in fact the main reason that we 88just don’t try and create a regular alias is that the <var>@</var> character isn’t 89permitted in symbol names. The <var>name2</var> part of the name is the actual name 90of the symbol by which it will be externally referenced. The name <var>name</var> 91itself is merely a name of convenience that is used so that it is possible to 92have definitions for multiple versions of a function within a single source 93file, and so that the compiler can unambiguously know which version of a 94function is being mentioned. The <var>nodename</var> portion of the alias should be 95the name of a node specified in the version script supplied to the linker when 96building a shared library. If you are attempting to override a versioned 97symbol from a shared library, then <var>nodename</var> should correspond to the 98nodename of the symbol you are trying to override. The optional argument 99<var>visibility</var> updates the visibility of the original symbol. The valid 100visibilities are <code>local</code>, <code>hidden</code>, and <code>remove</code>. The 101<code>local</code> visibility makes the original symbol a local symbol 102(see <a href="Local.html#Local">Local</a>). The <code>hidden</code> visibility sets the visibility of the 103original symbol to <code>hidden</code> (see <a href="Hidden.html#Hidden">Hidden</a>). The <code>remove</code> 104visibility removes the original symbol from the symbol table. If visibility 105isn’t specified, the original symbol is unchanged. 106</p> 107<p>If the symbol <var>name</var> is not defined within the file being assembled, all 108references to <var>name</var> will be changed to <var>name2@nodename</var>. If no 109reference to <var>name</var> is made, <var>name2@nodename</var> will be removed from the 110symbol table. 111</p> 112<p>Another usage of the <code>.symver</code> directive is: 113</p><div class="smallexample"> 114<pre class="smallexample">.symver <var>name</var>, <var>name2@@nodename</var> 115</pre></div> 116<p>In this case, the symbol <var>name</var> must exist and be defined within 117the file being assembled. It is similar to <var>name2@nodename</var>. The 118difference is <var>name2@@nodename</var> will also be used to resolve 119references to <var>name2</var> by the linker. 120</p> 121<p>The third usage of the <code>.symver</code> directive is: 122</p><div class="smallexample"> 123<pre class="smallexample">.symver <var>name</var>, <var>name2@@@nodename</var> 124</pre></div> 125<p>When <var>name</var> is not defined within the 126file being assembled, it is treated as <var>name2@nodename</var>. When 127<var>name</var> is defined within the file being assembled, the symbol 128name, <var>name</var>, will be changed to <var>name2@@nodename</var>. 129</p> 130<hr> 131<div class="header"> 132<p> 133Next: <a href="Tag.html#Tag" accesskey="n" rel="next">Tag</a>, Previous: <a href="SubSection.html#SubSection" accesskey="p" rel="previous">SubSection</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p> 134</div> 135 136 137 138</body> 139</html> 140