85 lines
4.0 KiB
HTML
85 lines
4.0 KiB
HTML
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<html lang="en">
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<head>
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<title>PROVIDE - Untitled</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="Untitled">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Assignments.html#Assignments" title="Assignments">
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<link rel="prev" href="HIDDEN.html#HIDDEN" title="HIDDEN">
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<link rel="next" href="PROVIDE_005fHIDDEN.html#PROVIDE_005fHIDDEN" title="PROVIDE_HIDDEN">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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This file documents the GNU linker LD
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(GNU Toolchain for the A-profile Architecture 9.2-2019.12 (arm-9.10))
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version 2.33.1.
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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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<style type="text/css"><!--
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pre.display { font-family:inherit }
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="PROVIDE"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="PROVIDE_005fHIDDEN.html#PROVIDE_005fHIDDEN">PROVIDE_HIDDEN</a>,
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Previous: <a rel="previous" accesskey="p" href="HIDDEN.html#HIDDEN">HIDDEN</a>,
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Up: <a rel="up" accesskey="u" href="Assignments.html#Assignments">Assignments</a>
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<hr>
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</div>
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<h4 class="subsection">3.5.3 PROVIDE</h4>
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<p><a name="index-PROVIDE-448"></a>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><span class="samp">etext</span></samp>’. However, ANSI C requires that the user be able to use
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‘<samp><span class="samp">etext</span></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><span class="samp">etext</span></samp>’, only if it is referenced but not defined. The syntax is
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<code>PROVIDE(</code><var>symbol</var><code> = </code><var>expression</var><code>)</code>.
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<p>Here is an example of using <code>PROVIDE</code> to define ‘<samp><span class="samp">etext</span></samp>’:
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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>
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<p>In this example, if the program defines ‘<samp><span class="samp">_etext</span></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><span class="samp">etext</span></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><span class="samp">etext</span></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>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><span class="samp">__CTOR_LIST__</span></samp>’ as these are often defined as common symbols.
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</body></html>
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