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8.8 KiB
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159 lines
8.8 KiB
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<html lang="en">
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<head>
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<title>Input Section Basics - Untitled</title>
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<meta name="description" content="Untitled">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Input-Section.html#Input-Section" title="Input Section">
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<link rel="next" href="Input-Section-Wildcards.html#Input-Section-Wildcards" title="Input Section Wildcards">
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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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</head>
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<body>
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<div class="node">
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<a name="Input-Section-Basics"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Input-Section-Wildcards.html#Input-Section-Wildcards">Input Section Wildcards</a>,
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Up: <a rel="up" accesskey="u" href="Input-Section.html#Input-Section">Input Section</a>
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<hr>
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</div>
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<h5 class="subsubsection">3.6.4.1 Input Section Basics</h5>
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<p><a name="index-input-section-basics-457"></a>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>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>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><span class="samp">.text</span></samp>’ sections, you would write:
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<pre class="smallexample"> *(.text)
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</pre>
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<p class="noindent">Here the ‘<samp><span class="samp">*</span></samp>’ is a wildcard which matches any file name. To exclude a list
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<a name="index-EXCLUDE_005fFILE-458"></a>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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<pre class="smallexample"> EXCLUDE_FILE (*crtend.o *otherfile.o) *(.ctors)
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</pre>
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<p class="noindent">will cause all .ctors sections from all files except <samp><span class="file">crtend.o</span></samp>
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and <samp><span class="file">otherfile.o</span></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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<pre class="smallexample"> *(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)
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</pre>
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<p class="noindent">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>There are two ways to include more than one section:
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<pre class="smallexample"> *(.text .rdata)
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*(.text) *(.rdata)
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</pre>
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<p class="noindent">The difference between these is the order in which the ‘<samp><span class="samp">.text</span></samp>’ and
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‘<samp><span class="samp">.rdata</span></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><span class="samp">.text</span></samp>’ input sections will appear first, followed by all
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‘<samp><span class="samp">.rdata</span></samp>’ input sections.
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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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<pre class="smallexample"> *(EXCLUDE_FILE (*somefile.o) .text .rdata)
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</pre>
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<p class="noindent">will cause all ‘<samp><span class="samp">.text</span></samp>’ sections from all files except
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<samp><span class="file">somefile.o</span></samp> to be included, while all ‘<samp><span class="samp">.rdata</span></samp>’ sections
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from all files, including <samp><span class="file">somefile.o</span></samp>, will be included. To
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exclude the ‘<samp><span class="samp">.rdata</span></samp>’ sections from <samp><span class="file">somefile.o</span></samp> the example
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could be modified to:
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<pre class="smallexample"> *(EXCLUDE_FILE (*somefile.o) .text EXCLUDE_FILE (*somefile.o) .rdata)
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</pre>
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<p class="noindent">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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<pre class="smallexample"> EXCLUDE_FILE (*somefile.o) *(.text .rdata)
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</pre>
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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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<pre class="smallexample"> data.o(.data)
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</pre>
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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>Here is a simple example for using Section header flags for ELF sections:
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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>
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<p>In this example, the output section ‘<samp><span class="samp">.text</span></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><span class="samp">.text2</span></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>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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<dl>
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<dt>‘<samp><span class="samp">archive:file</span></samp>’<dd>matches file within archive
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<br><dt>‘<samp><span class="samp">archive:</span></samp>’<dd>matches the whole archive
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<br><dt>‘<samp><span class="samp">:file</span></samp>’<dd>matches file but not one in an archive
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</dl>
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<p>Either one or both of ‘<samp><span class="samp">archive</span></samp>’ and ‘<samp><span class="samp">file</span></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><span class="samp">c:myfile.o</span></samp>’ is a simple file specification, not ‘<samp><span class="samp">myfile.o</span></samp>’
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within an archive called ‘<samp><span class="samp">c</span></samp>’. ‘<samp><span class="samp">archive:file</span></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><span class="samp">archive:file</span></samp>’ in an <code>INPUT</code>
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command.
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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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<pre class="smallexample"> data.o
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</pre>
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<p>When you use a file name which is not an ‘<samp><span class="samp">archive:file</span></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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</body></html>
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