181 lines
8.8 KiB
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181 lines
8.8 KiB
HTML
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<title>Section - Using as</title>
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<link rel="up" href="Pseudo-Ops.html#Pseudo-Ops" title="Pseudo Ops">
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 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 1.1
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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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</head>
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<body>
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<div class="node">
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<p>
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<a name="Section"></a>Next: <a rel="next" accesskey="n" href="Set.html#Set">Set</a>,
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Previous: <a rel="previous" accesskey="p" href="Scl.html#Scl">Scl</a>,
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Up: <a rel="up" accesskey="u" href="Pseudo-Ops.html#Pseudo-Ops">Pseudo Ops</a>
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<hr><br>
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</div>
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<h3 class="section">7.95 <code>.section </code><var>name</var></h3>
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<p><a name="index-named-section-440"></a>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>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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<!-- only print the extra heading if both COFF and ELF are set -->
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<h4 class="subheading">COFF Version</h4>
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<p><a name="index-_0040code_007bsection_007d-directive-_0028COFF-version_0029-441"></a>For COFF targets, the <code>.section</code> directive is used in one of the following
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ways:
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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>
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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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<dl>
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<dt><code>b</code><dd>bss section (uninitialized data)
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<br><dt><code>n</code><dd>section is not loaded
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<br><dt><code>w</code><dd>writable section
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<br><dt><code>d</code><dd>data section
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<br><dt><code>r</code><dd>read-only section
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<br><dt><code>x</code><dd>executable section
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<br><dt><code>s</code><dd>shared section (meaningful for PE targets)
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<br><dt><code>a</code><dd>ignored. (For compatibility with the ELF version)
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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>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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<!-- only print the extra heading if both COFF and ELF are set -->
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<h4 class="subheading">ELF Version</h4>
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<p><a name="index-Section-Stack-442"></a>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><a name="index-_0040code_007bsection_007d-directive-_0028ELF-version_0029-443"></a>For ELF targets, the <code>.section</code> directive is used like this:
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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>
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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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<dl>
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<dt><code>a</code><dd>section is allocatable
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<br><dt><code>w</code><dd>section is writable
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<br><dt><code>x</code><dd>section is executable
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<br><dt><code>M</code><dd>section is mergeable
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<br><dt><code>S</code><dd>section contains zero terminated strings
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<br><dt><code>G</code><dd>section is a member of a section group
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<br><dt><code>T</code><dd>section is used for thread-local-storage
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</dl>
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<p>The optional <var>type</var> argument may contain one of the following constants:
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<dl>
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<dt><code>@progbits</code><dd>section contains data
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<br><dt><code>@nobits</code><dd>section does not contain data (i.e., section only occupies space)
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<br><dt><code>@note</code><dd>section contains data which is used by things other than the program
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<br><dt><code>@init_array</code><dd>section contains an array of pointers to init functions
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<br><dt><code>@fini_array</code><dd>section contains an array of pointers to finish functions
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<br><dt><code>@preinit_array</code><dd>section contains an array of pointers to pre-init functions
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</dl>
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<p>Many targets only support the first three section types.
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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>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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<pre class="smallexample"> .section <var>name</var> , "<var>flags</var>"M, @<var>type</var>, <var>entsize</var>
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</pre>
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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.
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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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<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>
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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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<dl>
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<dt><code>comdat</code><dd>indicates that only one copy of this section should be retained
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<br><dt><code>.gnu.linkonce</code><dd>an alias for comdat
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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
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the Merge flag should come first, like this:
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<pre class="smallexample"> .section <var>name</var> , "<var>flags</var>"MG, @<var>type</var>, <var>entsize</var>, <var>GroupName</var>[, <var>linkage</var>]
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</pre>
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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 have
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none of the above flags: it will not be allocated in memory, nor writable, nor
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executable. The section will contain data.
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<p>For ELF targets, the assembler supports another type of <code>.section</code>
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directive for compatibility with the Solaris assembler:
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<pre class="smallexample"> .section "<var>name</var>"[, <var>flags</var>...]
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</pre>
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<p>Note that the section name is quoted. There may be a sequence of comma
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separated flags:
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<dl>
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<dt><code>#alloc</code><dd>section is allocatable
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<br><dt><code>#write</code><dd>section is writable
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<br><dt><code>#execinstr</code><dd>section is executable
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<br><dt><code>#tls</code><dd>section is used for thread local storage
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</dl>
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<p>This directive replaces the current section and subsection. See the
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contents of the gas testsuite directory <code>gas/testsuite/gas/elf</code> for
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some examples of how this directive and the other section stack directives
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work.
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</body></html>
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