143 lines
6.2 KiB
HTML
143 lines
6.2 KiB
HTML
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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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(Linaro_Binutils-2017.02)
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version 2.27.0.
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Copyright (C) 1991-2016 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 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>LD: Output Section Address</title>
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<meta name="description" content="LD: Output Section Address">
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<meta name="keywords" content="LD: Output Section Address">
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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="Input-Section.html#Input-Section" rel="next" title="Input Section">
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<link href="Output-Section-Name.html#Output-Section-Name" rel="prev" title="Output Section Name">
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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.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.indentedblock {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.smallindentedblock {margin-left: 3.2em; font-size: smaller}
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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.nocodebreak {white-space:nowrap}
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span.nolinebreak {white-space:nowrap}
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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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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" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Output-Section-Address"></a>
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<div class="header">
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<p>
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Next: <a href="Input-Section.html#Input-Section" accesskey="n" rel="next">Input Section</a>, Previous: <a href="Output-Section-Name.html#Output-Section-Name" accesskey="p" rel="prev">Output Section Name</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-Address-1"></a>
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<h4 class="subsection">3.6.3 Output Section Address</h4>
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<a name="index-address_002c-section"></a>
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<a name="index-section-address"></a>
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<p>The <var>address</var> is an expression for the VMA (the virtual memory
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address) of the output section. This address is optional, but if it
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is provided then the output address will be set exactly as specified.
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</p>
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<p>If the output address is not specified then one will be chosen for the
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section, based on the heuristic below. This address will be adjusted
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to fit the alignment requirement of the output section. The
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alignment requirement is the strictest alignment of any input section
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contained within the output section.
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</p>
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<p>The output section address heuristic is as follows:
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</p>
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<ul>
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<li> If an output memory <var>region</var> is set for the section then it
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is added to this region and its address will be the next free address
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in that region.
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</li><li> If the MEMORY command has been used to create a list of memory
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regions then the first region which has attributes compatible with the
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section is selected to contain it. The section’s output address will
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be the next free address in that region; <a href="MEMORY.html#MEMORY">MEMORY</a>.
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</li><li> If no memory regions were specified, or none match the section then
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the output address will be based on the current value of the location
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counter.
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</li></ul>
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<p>For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">.text . : { *(.text) }
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</pre></div>
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<p>and
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</p>
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<div class="smallexample">
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<pre class="smallexample">.text : { *(.text) }
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</pre></div>
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<p>are subtly different. The first will set the address of the
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‘<samp>.text</samp>’ output section to the current value of the location
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counter. The second will set it to the current value of the location
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counter aligned to the strictest alignment of any of the ‘<samp>.text</samp>’
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input sections.
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</p>
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<p>The <var>address</var> may be an arbitrary expression; <a href="Expressions.html#Expressions">Expressions</a>.
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For example, if you want to align the section on a 0x10 byte boundary,
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so that the lowest four bits of the section address are zero, you could
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do something like this:
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</p><div class="smallexample">
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<pre class="smallexample">.text ALIGN(0x10) : { *(.text) }
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</pre></div>
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<p>This works because <code>ALIGN</code> returns the current location counter
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aligned upward to the specified value.
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</p>
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<p>Specifying <var>address</var> for a section will change the value of the
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location counter, provided that the section is non-empty. (Empty
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sections are ignored).
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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.html#Input-Section" accesskey="n" rel="next">Input Section</a>, Previous: <a href="Output-Section-Name.html#Output-Section-Name" accesskey="p" rel="prev">Output Section Name</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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