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212 lines
9.8 KiB
HTML
212 lines
9.8 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>Input Section Basics (LD)</title>
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<meta name="description" content="Input Section Basics (LD)">
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<meta name="keywords" content="Input Section Basics (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="Input-Section.html#Input-Section" rel="up" title="Input Section">
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<link href="Input-Section-Wildcards.html#Input-Section-Wildcards" rel="next" title="Input Section Wildcards">
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<link href="Input-Section.html#Input-Section" rel="prev" title="Input Section">
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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="Input-Section-Basics"></a>
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<div class="header">
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<p>
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Next: <a href="Input-Section-Wildcards.html#Input-Section-Wildcards" accesskey="n" rel="next">Input Section Wildcards</a>, Up: <a href="Input-Section.html#Input-Section" accesskey="u" rel="up">Input Section</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="Input-Section-Basics-1"></a>
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<h4 class="subsubsection">3.6.4.1 Input Section Basics</h4>
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<a name="index-input-section-basics"></a>
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<p>An input section description consists of a file name optionally followed
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by a list of section names in parentheses.
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</p>
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<p>The file name and the section name may be wildcard patterns, which we
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describe further below (see <a href="Input-Section-Wildcards.html#Input-Section-Wildcards">Input Section Wildcards</a>).
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</p>
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<p>The most common input section description is to include all input
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sections with a particular name in the output section. For example, to
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include all input ‘<samp>.text</samp>’ sections, you would write:
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</p><div class="smallexample">
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<pre class="smallexample">*(.text)
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</pre></div>
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<p>Here the ‘<samp>*</samp>’ is a wildcard which matches any file name. To exclude a list
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<a name="index-EXCLUDE_005fFILE"></a>
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of files from matching the file name wildcard, EXCLUDE_FILE may be used to
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match all files except the ones specified in the EXCLUDE_FILE list. For
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example:
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</p><div class="smallexample">
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<pre class="smallexample">EXCLUDE_FILE (*crtend.o *otherfile.o) *(.ctors)
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</pre></div>
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<p>will cause all .ctors sections from all files except <samp>crtend.o</samp>
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and <samp>otherfile.o</samp> to be included. The EXCLUDE_FILE can also be
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placed inside the section list, for example:
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</p><div class="smallexample">
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<pre class="smallexample">*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)
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</pre></div>
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<p>The result of this is identically to the previous example. Supporting
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two syntaxes for EXCLUDE_FILE is useful if the section list contains
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more than one section, as described below.
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</p>
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<p>There are two ways to include more than one section:
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</p><div class="smallexample">
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<pre class="smallexample">*(.text .rdata)
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*(.text) *(.rdata)
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</pre></div>
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<p>The difference between these is the order in which the ‘<samp>.text</samp>’ and
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‘<samp>.rdata</samp>’ input sections will appear in the output section. In the
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first example, they will be intermingled, appearing in the same order as
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they are found in the linker input. In the second example, all
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‘<samp>.text</samp>’ input sections will appear first, followed by all
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‘<samp>.rdata</samp>’ input sections.
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</p>
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<p>When using EXCLUDE_FILE with more than one section, if the exclusion
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is within the section list then the exclusion only applies to the
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immediately following section, for example:
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</p><div class="smallexample">
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<pre class="smallexample">*(EXCLUDE_FILE (*somefile.o) .text .rdata)
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</pre></div>
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<p>will cause all ‘<samp>.text</samp>’ sections from all files except
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<samp>somefile.o</samp> to be included, while all ‘<samp>.rdata</samp>’ sections
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from all files, including <samp>somefile.o</samp>, will be included. To
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exclude the ‘<samp>.rdata</samp>’ sections from <samp>somefile.o</samp> the example
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could be modified to:
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</p><div class="smallexample">
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<pre class="smallexample">*(EXCLUDE_FILE (*somefile.o) .text EXCLUDE_FILE (*somefile.o) .rdata)
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</pre></div>
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<p>Alternatively, placing the EXCLUDE_FILE outside of the section list,
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before the input file selection, will cause the exclusion to apply for
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all sections. Thus the previous example can be rewritten as:
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</p><div class="smallexample">
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<pre class="smallexample">EXCLUDE_FILE (*somefile.o) *(.text .rdata)
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</pre></div>
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<p>You can specify a file name to include sections from a particular file.
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You would do this if one or more of your files contain special data that
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needs to be at a particular location in memory. For example:
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</p><div class="smallexample">
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<pre class="smallexample">data.o(.data)
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</pre></div>
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<p>To refine the sections that are included based on the section flags
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of an input section, INPUT_SECTION_FLAGS may be used.
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</p>
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<p>Here is a simple example for using Section header flags for ELF sections:
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</p>
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<div class="smallexample">
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<pre class="smallexample">SECTIONS {
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.text : { INPUT_SECTION_FLAGS (SHF_MERGE & SHF_STRINGS) *(.text) }
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.text2 : { INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) }
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}
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</pre></div>
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<p>In this example, the output section ‘<samp>.text</samp>’ will be comprised of any
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input section matching the name *(.text) whose section header flags
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<code>SHF_MERGE</code> and <code>SHF_STRINGS</code> are set. The output section
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‘<samp>.text2</samp>’ will be comprised of any input section matching the name *(.text)
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whose section header flag <code>SHF_WRITE</code> is clear.
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</p>
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<p>You can also specify files within archives by writing a pattern
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matching the archive, a colon, then the pattern matching the file,
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with no whitespace around the colon.
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</p>
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<dl compact="compact">
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<dt>‘<samp>archive:file</samp>’</dt>
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<dd><p>matches file within archive
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</p></dd>
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<dt>‘<samp>archive:</samp>’</dt>
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<dd><p>matches the whole archive
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</p></dd>
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<dt>‘<samp>:file</samp>’</dt>
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<dd><p>matches file but not one in an archive
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</p></dd>
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</dl>
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<p>Either one or both of ‘<samp>archive</samp>’ and ‘<samp>file</samp>’ can contain shell
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wildcards. On DOS based file systems, the linker will assume that a
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single letter followed by a colon is a drive specifier, so
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‘<samp>c:myfile.o</samp>’ is a simple file specification, not ‘<samp>myfile.o</samp>’
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within an archive called ‘<samp>c</samp>’. ‘<samp>archive:file</samp>’ filespecs may
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also be used within an <code>EXCLUDE_FILE</code> list, but may not appear in
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other linker script contexts. For instance, you cannot extract a file
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from an archive by using ‘<samp>archive:file</samp>’ in an <code>INPUT</code>
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command.
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</p>
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<p>If you use a file name without a list of sections, then all sections in
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the input file will be included in the output section. This is not
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commonly done, but it may by useful on occasion. For example:
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</p><div class="smallexample">
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<pre class="smallexample">data.o
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</pre></div>
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<p>When you use a file name which is not an ‘<samp>archive:file</samp>’ specifier
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and does not contain any wild card
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characters, the linker will first see if you also specified the file
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name on the linker command line or in an <code>INPUT</code> command. If you
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did not, the linker will attempt to open the file as an input file, as
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though it appeared on the command line. Note that this differs from an
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<code>INPUT</code> command, because the linker will not search for the file in
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the archive search path.
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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="Input-Section-Wildcards.html#Input-Section-Wildcards" accesskey="n" rel="next">Input Section Wildcards</a>, Up: <a href="Input-Section.html#Input-Section" accesskey="u" rel="up">Input Section</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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</body>
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</html>
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