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106 lines
4.6 KiB
HTML
106 lines
4.6 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Output Section Address - 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="Output-Section-Name.html#Output-Section-Name" title="Output Section Name">
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<link rel="next" href="Input-Section.html#Input-Section" title="Input Section">
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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-Address"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Input-Section.html#Input-Section">Input Section</a>,
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Previous: <a rel="previous" accesskey="p" href="Output-Section-Name.html#Output-Section-Name">Output Section Name</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">3.6.3 Output Section Address</h4>
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<p><a name="index-address_002c-section-426"></a><a name="index-section-address-427"></a>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>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>The output section address heuristic is as follows:
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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>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>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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</ul>
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<p class="noindent">For example:
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<pre class="smallexample"> .text . : { *(.text) }
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</pre>
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<p class="noindent">and
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<pre class="smallexample"> .text : { *(.text) }
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</pre>
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<p class="noindent">are subtly different. The first will set the address of the
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‘<samp><span class="samp">.text</span></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><span class="samp">.text</span></samp>’
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input sections.
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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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<pre class="smallexample"> .text ALIGN(0x10) : { *(.text) }
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</pre>
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<p class="noindent">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>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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</body></html>
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