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107 lines
5.8 KiB
HTML
107 lines
5.8 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Output Section Data - 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="SECTIONS.html#SECTIONS" title="SECTIONS">
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<link rel="prev" href="Input-Section.html#Input-Section" title="Input Section">
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<link rel="next" href="Output-Section-Keywords.html#Output-Section-Keywords" title="Output Section Keywords">
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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 Binutils)
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version 2.26.
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Copyright (C) 1991-2015 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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<meta http-equiv="Content-Style-Type" content="text/css">
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<style type="text/css"><!--
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pre.display { font-family:inherit }
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pre.format { font-family:inherit }
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pre.smalldisplay { font-family:inherit; font-size:smaller }
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pre.smallformat { font-family:inherit; font-size:smaller }
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pre.smallexample { font-size:smaller }
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pre.smalllisp { font-size:smaller }
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span.sc { font-variant:small-caps }
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span.roman { font-family:serif; font-weight:normal; }
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span.sansserif { font-family:sans-serif; font-weight:normal; }
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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="Output-Section-Data"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Output-Section-Keywords.html#Output-Section-Keywords">Output Section Keywords</a>,
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Previous: <a rel="previous" accesskey="p" href="Input-Section.html#Input-Section">Input Section</a>,
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Up: <a rel="up" accesskey="u" href="SECTIONS.html#SECTIONS">SECTIONS</a>
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<hr>
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</div>
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<h4 class="subsection">3.6.5 Output Section Data</h4>
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<p><a name="index-data-447"></a><a name="index-section-data-448"></a><a name="index-output-section-data-449"></a><a name="index-BYTE_0028_0040var_007bexpression_007d_0029-450"></a><a name="index-SHORT_0028_0040var_007bexpression_007d_0029-451"></a><a name="index-LONG_0028_0040var_007bexpression_007d_0029-452"></a><a name="index-QUAD_0028_0040var_007bexpression_007d_0029-453"></a><a name="index-SQUAD_0028_0040var_007bexpression_007d_0029-454"></a>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>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>For example, this will store the byte 1 followed by the four byte value
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of the symbol ‘<samp><span class="samp">addr</span></samp>’:
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<pre class="smallexample"> BYTE(1)
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LONG(addr)
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</pre>
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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>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>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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<pre class="smallexample"> SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } }</pre>
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<p>whereas this will work:
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<pre class="smallexample"> SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } }</pre>
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<p><a name="index-FILL_0028_0040var_007bexpression_007d_0029-455"></a><a name="index-holes_002c-filling-456"></a><a name="index-unspecified-memory-457"></a>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>This example shows how to fill unspecified regions of memory with the
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value ‘<samp><span class="samp">0x90</span></samp>’:
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<pre class="smallexample"> FILL(0x90909090)
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</pre>
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<p>The <code>FILL</code> command is similar to the ‘<samp><span class="samp">=</span><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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</body></html>
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