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132 lines
6.3 KiB
HTML
132 lines
6.3 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This file documents the GNU Assembler "as".
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Copyright (C) 1991-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled "GNU Free Documentation License".
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-->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Symver (Using as)</title>
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<meta name="description" content="Symver (Using as)">
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<meta name="keywords" content="Symver (Using as)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="AS-Index.html#AS-Index" rel="index" title="AS Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Pseudo-Ops.html#Pseudo-Ops" rel="up" title="Pseudo Ops">
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<link href="Tag.html#Tag" rel="next" title="Tag">
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<link href="SubSection.html#SubSection" rel="prev" title="SubSection">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smallexample {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Symver"></a>
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<div class="header">
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<p>
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Next: <a href="Tag.html#Tag" accesskey="n" rel="next">Tag</a>, Previous: <a href="SubSection.html#SubSection" accesskey="p" rel="prev">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>
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</div>
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<hr>
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<a name="g_t_002esymver"></a>
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<h3 class="section">7.94 <code>.symver</code></h3>
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<a name="index-symver-directive"></a>
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<a name="index-symbol-versioning"></a>
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<a name="index-versions-of-symbols"></a>
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<p>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>
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<p>For ELF targets, the <code>.symver</code> directive can be used like this:
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</p><div class="smallexample">
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<pre class="smallexample">.symver <var>name</var>, <var>name2@nodename</var>
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</pre></div>
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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>
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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>
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<p>Another usage of the <code>.symver</code> directive is:
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</p><div class="smallexample">
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<pre class="smallexample">.symver <var>name</var>, <var>name2@@nodename</var>
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</pre></div>
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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>
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<p>The third usage of the <code>.symver</code> directive is:
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</p><div class="smallexample">
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<pre class="smallexample">.symver <var>name</var>, <var>name2@@@nodename</var>
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</pre></div>
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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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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Tag.html#Tag" accesskey="n" rel="next">Tag</a>, Previous: <a href="SubSection.html#SubSection" accesskey="p" rel="prev">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>
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</div>
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</body>
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</html>
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