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154 lines
7.4 KiB
HTML
154 lines
7.4 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>Output Section Data (LD)</title>
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<meta name="description" content="Output Section Data (LD)">
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<meta name="keywords" content="Output Section Data (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="SECTIONS.html#SECTIONS" rel="up" title="SECTIONS">
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<link href="Output-Section-Keywords.html#Output-Section-Keywords" rel="next" title="Output Section Keywords">
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<link href="Input-Section-Example.html#Input-Section-Example" rel="prev" title="Input Section Example">
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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="Output-Section-Data"></a>
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<div class="header">
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<p>
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Next: <a href="Output-Section-Keywords.html#Output-Section-Keywords" accesskey="n" rel="next">Output Section Keywords</a>, Previous: <a href="Input-Section.html#Input-Section" accesskey="p" rel="prev">Input Section</a>, Up: <a href="SECTIONS.html#SECTIONS" accesskey="u" rel="up">SECTIONS</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="Output-Section-Data-1"></a>
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<h4 class="subsection">3.6.5 Output Section Data</h4>
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<a name="index-data"></a>
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<a name="index-section-data"></a>
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<a name="index-output-section-data"></a>
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<a name="index-BYTE_0028expression_0029"></a>
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<a name="index-SHORT_0028expression_0029"></a>
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<a name="index-LONG_0028expression_0029"></a>
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<a name="index-QUAD_0028expression_0029"></a>
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<a name="index-SQUAD_0028expression_0029"></a>
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<p>You can include explicit bytes of data in an output section by using
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<code>BYTE</code>, <code>SHORT</code>, <code>LONG</code>, <code>QUAD</code>, or <code>SQUAD</code> as
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an output section command. Each keyword is followed by an expression in
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parentheses providing the value to store (see <a href="Expressions.html#Expressions">Expressions</a>). The
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value of the expression is stored at the current value of the location
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counter.
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</p>
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<p>The <code>BYTE</code>, <code>SHORT</code>, <code>LONG</code>, and <code>QUAD</code> commands
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store one, two, four, and eight bytes (respectively). After storing the
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bytes, the location counter is incremented by the number of bytes
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stored.
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</p>
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<p>For example, this will store the byte 1 followed by the four byte value
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of the symbol ‘<samp>addr</samp>’:
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</p><div class="smallexample">
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<pre class="smallexample">BYTE(1)
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LONG(addr)
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</pre></div>
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<p>When using a 64 bit host or target, <code>QUAD</code> and <code>SQUAD</code> are the
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same; they both store an 8 byte, or 64 bit, value. When both host and
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target are 32 bits, an expression is computed as 32 bits. In this case
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<code>QUAD</code> stores a 32 bit value zero extended to 64 bits, and
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<code>SQUAD</code> stores a 32 bit value sign extended to 64 bits.
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</p>
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<p>If the object file format of the output file has an explicit endianness,
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which is the normal case, the value will be stored in that endianness.
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When the object file format does not have an explicit endianness, as is
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true of, for example, S-records, the value will be stored in the
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endianness of the first input object file.
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</p>
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<p>Note—these commands only work inside a section description and not
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between them, so the following will produce an error from the linker:
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</p><div class="smallexample">
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<pre class="smallexample">SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } } </pre></div>
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<p>whereas this will work:
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</p><div class="smallexample">
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<pre class="smallexample">SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } } </pre></div>
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<a name="index-FILL_0028expression_0029"></a>
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<a name="index-holes_002c-filling"></a>
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<a name="index-unspecified-memory"></a>
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<p>You may use the <code>FILL</code> command to set the fill pattern for the
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current section. It is followed by an expression in parentheses. Any
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otherwise unspecified regions of memory within the section (for example,
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gaps left due to the required alignment of input sections) are filled
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with the value of the expression, repeated as
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necessary. A <code>FILL</code> statement covers memory locations after the
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point at which it occurs in the section definition; by including more
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than one <code>FILL</code> statement, you can have different fill patterns in
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different parts of an output section.
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</p>
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<p>This example shows how to fill unspecified regions of memory with the
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value ‘<samp>0x90</samp>’:
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</p><div class="smallexample">
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<pre class="smallexample">FILL(0x90909090)
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</pre></div>
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<p>The <code>FILL</code> command is similar to the ‘<samp>=<var>fillexp</var></samp>’ output
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section attribute, but it only affects the
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part of the section following the <code>FILL</code> command, rather than the
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entire section. If both are used, the <code>FILL</code> command takes
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precedence. See <a href="Output-Section-Fill.html#Output-Section-Fill">Output Section Fill</a>, for details on the fill
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expression.
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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="Output-Section-Keywords.html#Output-Section-Keywords" accesskey="n" rel="next">Output Section Keywords</a>, Previous: <a href="Input-Section.html#Input-Section" accesskey="p" rel="prev">Input Section</a>, Up: <a href="SECTIONS.html#SECTIONS" accesskey="u" rel="up">SECTIONS</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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