374 lines
15 KiB
HTML
374 lines
15 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 Assembler "as".
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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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-->
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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>Using as: Section</title>
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<meta name="description" content="Using as: Section">
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<meta name="keywords" content="Using as: Section">
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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="AS-Index.html#AS-Index" rel="index" title="AS Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Pseudo-Ops.html#Pseudo-Ops" rel="up" title="Pseudo Ops">
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<link href="Set.html#Set" rel="next" title="Set">
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<link href="Scl.html#Scl" rel="prev" title="Scl">
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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="Section"></a>
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<div class="header">
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<p>
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Next: <a href="Set.html#Set" accesskey="n" rel="next">Set</a>, Previous: <a href="Scl.html#Scl" accesskey="p" rel="prev">Scl</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="g_t_002esection-name"></a>
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<h3 class="section">7.78 <code>.section <var>name</var></code></h3>
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<a name="index-named-section"></a>
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<p>Use the <code>.section</code> directive to assemble the following code into a section
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named <var>name</var>.
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</p>
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<p>This directive is only supported for targets that actually support arbitrarily
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named sections; on <code>a.out</code> targets, for example, it is not accepted, even
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with a standard <code>a.out</code> section name.
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</p>
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<a name="COFF-Version"></a>
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<h4 class="subheading">COFF Version</h4>
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<a name="index-section-directive-_0028COFF-version_0029"></a>
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<p>For COFF targets, the <code>.section</code> directive is used in one of the following
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ways:
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</p>
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<div class="smallexample">
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<pre class="smallexample">.section <var>name</var>[, "<var>flags</var>"]
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.section <var>name</var>[, <var>subsection</var>]
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</pre></div>
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<p>If the optional argument is quoted, it is taken as flags to use for the
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section. Each flag is a single character. The following flags are recognized:
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</p>
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<dl compact="compact">
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<dt><code>b</code></dt>
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<dd><p>bss section (uninitialized data)
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</p></dd>
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<dt><code>n</code></dt>
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<dd><p>section is not loaded
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</p></dd>
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<dt><code>w</code></dt>
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<dd><p>writable section
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</p></dd>
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<dt><code>d</code></dt>
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<dd><p>data section
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</p></dd>
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<dt><code>e</code></dt>
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<dd><p>exclude section from linking
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</p></dd>
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<dt><code>r</code></dt>
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<dd><p>read-only section
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</p></dd>
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<dt><code>x</code></dt>
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<dd><p>executable section
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</p></dd>
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<dt><code>s</code></dt>
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<dd><p>shared section (meaningful for PE targets)
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</p></dd>
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<dt><code>a</code></dt>
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<dd><p>ignored. (For compatibility with the ELF version)
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</p></dd>
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<dt><code>y</code></dt>
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<dd><p>section is not readable (meaningful for PE targets)
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</p></dd>
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<dt><code>0-9</code></dt>
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<dd><p>single-digit power-of-two section alignment (GNU extension)
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</p></dd>
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</dl>
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<p>If no flags are specified, the default flags depend upon the section name. If
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the section name is not recognized, the default will be for the section to be
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loaded and writable. Note the <code>n</code> and <code>w</code> flags remove attributes
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from the section, rather than adding them, so if they are used on their own it
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will be as if no flags had been specified at all.
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</p>
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<p>If the optional argument to the <code>.section</code> directive is not quoted, it is
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taken as a subsection number (see <a href="Sub_002dSections.html#Sub_002dSections">Sub-Sections</a>).
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</p>
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<a name="ELF-Version"></a>
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<h4 class="subheading">ELF Version</h4>
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<a name="index-Section-Stack-3"></a>
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<p>This is one of the ELF section stack manipulation directives. The others are
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<code>.subsection</code> (see <a href="SubSection.html#SubSection">SubSection</a>), <code>.pushsection</code>
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(see <a href="PushSection.html#PushSection">PushSection</a>), <code>.popsection</code> (see <a href="PopSection.html#PopSection">PopSection</a>), and
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<code>.previous</code> (see <a href="Previous.html#Previous">Previous</a>).
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</p>
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<a name="index-section-directive-_0028ELF-version_0029"></a>
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<p>For ELF targets, the <code>.section</code> directive is used like this:
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</p>
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<div class="smallexample">
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<pre class="smallexample">.section <var>name</var> [, "<var>flags</var>"[, @<var>type</var>[,<var>flag_specific_arguments</var>]]]
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</pre></div>
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<a name="Section-Name-Substitutions"></a><a name="index-_002d_002dsectname_002dsubst"></a>
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<a name="index-section-name-substitution"></a>
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<p>If the ‘<samp>--sectname-subst</samp>’ command-line option is provided, the <var>name</var>
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argument may contain a substitution sequence. Only <code>%S</code> is supported
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at the moment, and substitutes the current section name. For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">.macro exception_code
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.section %S.exception
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[exception code here]
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.previous
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.endm
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.text
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[code]
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exception_code
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[...]
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.section .init
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[init code]
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exception_code
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[...]
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</pre></div>
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<p>The two <code>exception_code</code> invocations above would create the
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<code>.text.exception</code> and <code>.init.exception</code> sections respectively.
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This is useful e.g. to discriminate between anciliary sections that are
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tied to setup code to be discarded after use from anciliary sections that
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need to stay resident without having to define multiple <code>exception_code</code>
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macros just for that purpose.
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</p>
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<p>The optional <var>flags</var> argument is a quoted string which may contain any
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combination of the following characters:
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</p>
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<dl compact="compact">
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<dt><code>a</code></dt>
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<dd><p>section is allocatable
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</p></dd>
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<dt><code>e</code></dt>
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<dd><p>section is excluded from executable and shared library.
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</p></dd>
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<dt><code>w</code></dt>
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<dd><p>section is writable
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</p></dd>
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<dt><code>x</code></dt>
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<dd><p>section is executable
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</p></dd>
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<dt><code>M</code></dt>
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<dd><p>section is mergeable
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</p></dd>
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<dt><code>S</code></dt>
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<dd><p>section contains zero terminated strings
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</p></dd>
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<dt><code>G</code></dt>
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<dd><p>section is a member of a section group
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</p></dd>
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<dt><code>T</code></dt>
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<dd><p>section is used for thread-local-storage
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</p></dd>
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<dt><code>?</code></dt>
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<dd><p>section is a member of the previously-current section’s group, if any
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</p></dd>
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<dt><code><code><number></code></code></dt>
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<dd><p>a numeric value indicating the bits to be set in the ELF section header’s flags
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field. Note - if one or more of the alphabetic characters described above is
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also included in the flags field, their bit values will be ORed into the
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resulting value.
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</p></dd>
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<dt><code><code><target specific></code></code></dt>
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<dd><p>some targets extend this list with their own flag characters
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</p></dd>
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</dl>
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<p>Note - once a section’s flags have been set they cannot be changed. There are
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a few exceptions to this rule however. Processor and application specific
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flags can be added to an already defined section. The <code>.interp</code>,
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<code>.strtab</code> and <code>.symtab</code> sections can have the allocate flag
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(<code>a</code>) set after they are initially defined, and the <code>.note-GNU-stack</code>
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section may have the executable (<code>x</code>) flag added.
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</p>
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<p>The optional <var>type</var> argument may contain one of the following constants:
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</p>
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<dl compact="compact">
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<dt><code>@progbits</code></dt>
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<dd><p>section contains data
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</p></dd>
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<dt><code>@nobits</code></dt>
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<dd><p>section does not contain data (i.e., section only occupies space)
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</p></dd>
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<dt><code>@note</code></dt>
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<dd><p>section contains data which is used by things other than the program
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</p></dd>
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<dt><code>@init_array</code></dt>
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<dd><p>section contains an array of pointers to init functions
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</p></dd>
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<dt><code>@fini_array</code></dt>
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<dd><p>section contains an array of pointers to finish functions
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</p></dd>
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<dt><code>@preinit_array</code></dt>
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<dd><p>section contains an array of pointers to pre-init functions
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</p></dd>
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<dt><code>@<code><number></code></code></dt>
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<dd><p>a numeric value to be set as the ELF section header’s type field.
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</p></dd>
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<dt><code>@<code><target specific></code></code></dt>
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<dd><p>some targets extend this list with their own types
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</p></dd>
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</dl>
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<p>Many targets only support the first three section types. The type may be
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enclosed in double quotes if necessary.
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</p>
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<p>Note on targets where the <code>@</code> character is the start of a comment (eg
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ARM) then another character is used instead. For example the ARM port uses the
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<code>%</code> character.
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</p>
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<p>Note - some sections, eg <code>.text</code> and <code>.data</code> are considered to be
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special and have fixed types. Any attempt to declare them with a different
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type will generate an error from the assembler.
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</p>
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<p>If <var>flags</var> contains the <code>M</code> symbol then the <var>type</var> argument must
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be specified as well as an extra argument—<var>entsize</var>—like this:
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</p>
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<div class="smallexample">
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<pre class="smallexample">.section <var>name</var> , "<var>flags</var>"M, @<var>type</var>, <var>entsize</var>
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</pre></div>
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<p>Sections with the <code>M</code> flag but not <code>S</code> flag must contain fixed size
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constants, each <var>entsize</var> octets long. Sections with both <code>M</code> and
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<code>S</code> must contain zero terminated strings where each character is
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<var>entsize</var> bytes long. The linker may remove duplicates within sections with
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the same name, same entity size and same flags. <var>entsize</var> must be an
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absolute expression. For sections with both <code>M</code> and <code>S</code>, a string
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which is a suffix of a larger string is considered a duplicate. Thus
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<code>"def"</code> will be merged with <code>"abcdef"</code>; A reference to the first
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<code>"def"</code> will be changed to a reference to <code>"abcdef"+3</code>.
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</p>
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<p>If <var>flags</var> contains the <code>G</code> symbol then the <var>type</var> argument must
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be present along with an additional field like this:
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</p>
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<div class="smallexample">
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<pre class="smallexample">.section <var>name</var> , "<var>flags</var>"G, @<var>type</var>, <var>GroupName</var>[, <var>linkage</var>]
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</pre></div>
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<p>The <var>GroupName</var> field specifies the name of the section group to which this
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particular section belongs. The optional linkage field can contain:
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</p>
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<dl compact="compact">
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<dt><code>comdat</code></dt>
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<dd><p>indicates that only one copy of this section should be retained
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</p></dd>
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<dt><code>.gnu.linkonce</code></dt>
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||
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<dd><p>an alias for comdat
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</p></dd>
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||
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</dl>
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<p>Note: if both the <var>M</var> and <var>G</var> flags are present then the fields for
|
||
|
|
the Merge flag should come first, like this:
|
||
|
|
</p>
|
||
|
|
<div class="smallexample">
|
||
|
|
<pre class="smallexample">.section <var>name</var> , "<var>flags</var>"MG, @<var>type</var>, <var>entsize</var>, <var>GroupName</var>[, <var>linkage</var>]
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>If <var>flags</var> contains the <code>?</code> symbol then it may not also contain the
|
||
|
|
<code>G</code> symbol and the <var>GroupName</var> or <var>linkage</var> fields should not be
|
||
|
|
present. Instead, <code>?</code> says to consider the section that’s current before
|
||
|
|
this directive. If that section used <code>G</code>, then the new section will use
|
||
|
|
<code>G</code> with those same <var>GroupName</var> and <var>linkage</var> fields implicitly.
|
||
|
|
If not, then the <code>?</code> symbol has no effect.
|
||
|
|
</p>
|
||
|
|
<p>If no flags are specified, the default flags depend upon the section name. If
|
||
|
|
the section name is not recognized, the default will be for the section to have
|
||
|
|
none of the above flags: it will not be allocated in memory, nor writable, nor
|
||
|
|
executable. The section will contain data.
|
||
|
|
</p>
|
||
|
|
<p>For ELF targets, the assembler supports another type of <code>.section</code>
|
||
|
|
directive for compatibility with the Solaris assembler:
|
||
|
|
</p>
|
||
|
|
<div class="smallexample">
|
||
|
|
<pre class="smallexample">.section "<var>name</var>"[, <var>flags</var>...]
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>Note that the section name is quoted. There may be a sequence of comma
|
||
|
|
separated flags:
|
||
|
|
</p>
|
||
|
|
<dl compact="compact">
|
||
|
|
<dt><code>#alloc</code></dt>
|
||
|
|
<dd><p>section is allocatable
|
||
|
|
</p></dd>
|
||
|
|
<dt><code>#write</code></dt>
|
||
|
|
<dd><p>section is writable
|
||
|
|
</p></dd>
|
||
|
|
<dt><code>#execinstr</code></dt>
|
||
|
|
<dd><p>section is executable
|
||
|
|
</p></dd>
|
||
|
|
<dt><code>#exclude</code></dt>
|
||
|
|
<dd><p>section is excluded from executable and shared library.
|
||
|
|
</p></dd>
|
||
|
|
<dt><code>#tls</code></dt>
|
||
|
|
<dd><p>section is used for thread local storage
|
||
|
|
</p></dd>
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<p>This directive replaces the current section and subsection. See the
|
||
|
|
contents of the gas testsuite directory <code>gas/testsuite/gas/elf</code> for
|
||
|
|
some examples of how this directive and the other section stack directives
|
||
|
|
work.
|
||
|
|
</p>
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Set.html#Set" accesskey="n" rel="next">Set</a>, Previous: <a href="Scl.html#Scl" accesskey="p" rel="prev">Scl</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|