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112 lines
4.7 KiB
HTML
112 lines
4.7 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 linker LD
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(SiFive Binutils 2.32.0-2020.04.1)
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version 2.32.
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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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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>PROVIDE (LD)</title>
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<meta name="description" content="PROVIDE (LD)">
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<meta name="keywords" content="PROVIDE (LD)">
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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="LD-Index.html#LD-Index" rel="index" title="LD Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Assignments.html#Assignments" rel="up" title="Assignments">
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<link href="PROVIDE_005fHIDDEN.html#PROVIDE_005fHIDDEN" rel="next" title="PROVIDE_HIDDEN">
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<link href="HIDDEN.html#HIDDEN" rel="prev" title="HIDDEN">
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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="PROVIDE"></a>
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<div class="header">
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<p>
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Next: <a href="PROVIDE_005fHIDDEN.html#PROVIDE_005fHIDDEN" accesskey="n" rel="next">PROVIDE_HIDDEN</a>, Previous: <a href="HIDDEN.html#HIDDEN" accesskey="p" rel="prev">HIDDEN</a>, Up: <a href="Assignments.html#Assignments" accesskey="u" rel="up">Assignments</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LD-Index.html#LD-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="PROVIDE-1"></a>
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<h4 class="subsection">3.5.3 PROVIDE</h4>
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<a name="index-PROVIDE"></a>
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<p>In some cases, it is desirable for a linker script to define a symbol
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only if it is referenced and is not defined by any object included in
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the link. For example, traditional linkers defined the symbol
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‘<samp>etext</samp>’. However, ANSI C requires that the user be able to use
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‘<samp>etext</samp>’ as a function name without encountering an error. The
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<code>PROVIDE</code> keyword may be used to define a symbol, such as
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‘<samp>etext</samp>’, only if it is referenced but not defined. The syntax is
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<code>PROVIDE(<var>symbol</var> = <var>expression</var>)</code>.
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</p>
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<p>Here is an example of using <code>PROVIDE</code> to define ‘<samp>etext</samp>’:
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</p><div class="smallexample">
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<pre class="smallexample">SECTIONS
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{
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.text :
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{
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*(.text)
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_etext = .;
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PROVIDE(etext = .);
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}
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}
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</pre></div>
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<p>In this example, if the program defines ‘<samp>_etext</samp>’ (with a leading
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underscore), the linker will give a multiple definition error. If, on
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the other hand, the program defines ‘<samp>etext</samp>’ (with no leading
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underscore), the linker will silently use the definition in the program.
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If the program references ‘<samp>etext</samp>’ but does not define it, the
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linker will use the definition in the linker script.
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</p>
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<p>Note - the <code>PROVIDE</code> directive considers a common symbol to be
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defined, even though such a symbol could be combined with the symbol
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that the <code>PROVIDE</code> would create. This is particularly important
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when considering constructor and destructor list symbols such as
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‘<samp>__CTOR_LIST__</samp>’ as these are often defined as common symbols.
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</p>
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</body>
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</html>
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