aarch64-linux-gnu-4.9/share/doc/ld.html/Output-Section-Keywords.html - toolchains/linux-x86/gcc - Git at Google

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <!-- This file documents the GNU linker LD
 (Linaro_Binutils-2017.01)
 version 2.24.0.

 Copyright (C) 1991-2013 Free Software Foundation, Inc.

 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3
 or any later version published by the Free Software Foundation;
 with no Invariant Sections, with no Front-Cover Texts, and with no
 Back-Cover Texts.  A copy of the license is included in the
 section entitled "GNU Free Documentation License". -->
 <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
 <head>
 <title>LD: Output Section Keywords</title>

 <meta name="description" content="LD: Output Section Keywords">
 <meta name="keywords" content="LD: Output Section Keywords">
 <meta name="resource-type" content="document">
 <meta name="distribution" content="global">
 <meta name="Generator" content="makeinfo">
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 <link href="index.html#Top" rel="start" title="Top">
 <link href="LD-Index.html#LD-Index" rel="index" title="LD Index">
 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
 <link href="SECTIONS.html#SECTIONS" rel="up" title="SECTIONS">
 <link href="Output-Section-Discarding.html#Output-Section-Discarding" rel="next" title="Output Section Discarding">
 <link href="Output-Section-Data.html#Output-Section-Data" rel="prev" title="Output Section Data">
 <style type="text/css">
 <!--
 a.summary-letter {text-decoration: none}
 blockquote.smallquotation {font-size: smaller}
 div.display {margin-left: 3.2em}
 div.example {margin-left: 3.2em}
 div.indentedblock {margin-left: 3.2em}
 div.lisp {margin-left: 3.2em}
 div.smalldisplay {margin-left: 3.2em}
 div.smallexample {margin-left: 3.2em}
 div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
 div.smalllisp {margin-left: 3.2em}
 kbd {font-style:oblique}
 pre.display {font-family: inherit}
 pre.format {font-family: inherit}
 pre.menu-comment {font-family: serif}
 pre.menu-preformatted {font-family: serif}
 pre.smalldisplay {font-family: inherit; font-size: smaller}
 pre.smallexample {font-size: smaller}
 pre.smallformat {font-family: inherit; font-size: smaller}
 pre.smalllisp {font-size: smaller}
 span.nocodebreak {white-space:nowrap}
 span.nolinebreak {white-space:nowrap}
 span.roman {font-family:serif; font-weight:normal}
 span.sansserif {font-family:sans-serif; font-weight:normal}
 ul.no-bullet {list-style: none}
 -->
 </style>


 </head>

 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
 <a name="Output-Section-Keywords"></a>
 <div class="header">
 <p>
 Next: <a href="Output-Section-Discarding.html#Output-Section-Discarding" accesskey="n" rel="next">Output Section Discarding</a>, Previous: <a href="Output-Section-Data.html#Output-Section-Data" accesskey="p" rel="prev">Output Section Data</a>, Up: <a href="SECTIONS.html#SECTIONS" accesskey="u" rel="up">SECTIONS</a> &nbsp; [<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>
 </div>
 <hr>
 <a name="Output-Section-Keywords-1"></a>
 <h4 class="subsection">3.6.6 Output Section Keywords</h4>
 <p>There are a couple of keywords which can appear as output section
 commands.
 </p>
 <dl compact="compact">
 <dd><a name="index-CREATE_005fOBJECT_005fSYMBOLS"></a>
 <a name="index-input-filename-symbols"></a>
 <a name="index-filename-symbols"></a>
 </dd>
 <dt><code>CREATE_OBJECT_SYMBOLS</code></dt>
 <dd><p>The command tells the linker to create a symbol for each input file.
 The name of each symbol will be the name of the corresponding input
 file.  The section of each symbol will be the output section in which
 the <code>CREATE_OBJECT_SYMBOLS</code> command appears.
 </p>
 <p>This is conventional for the a.out object file format.  It is not
 normally used for any other object file format.
 </p>
 <a name="index-CONSTRUCTORS"></a>
 <a name="index-C_002b_002b-constructors_002c-arranging-in-link"></a>
 <a name="index-constructors_002c-arranging-in-link"></a>
 </dd>
 <dt><code>CONSTRUCTORS</code></dt>
 <dd><p>When linking using the a.out object file format, the linker uses an
 unusual set construct to support C++ global constructors and
 destructors.  When linking object file formats which do not support
 arbitrary sections, such as ECOFF and XCOFF, the linker will
 automatically recognize C++ global constructors and destructors by name.
 For these object file formats, the <code>CONSTRUCTORS</code> command tells the
 linker to place constructor information in the output section where the
 <code>CONSTRUCTORS</code> command appears.  The <code>CONSTRUCTORS</code> command is
 ignored for other object file formats.
 </p>
 <p>The symbol <code><span class="nolinebreak">__CTOR_LIST__</span></code><!-- /@w --> marks the start of the global
 constructors, and the symbol <code><span class="nolinebreak">__CTOR_END__</span></code><!-- /@w --> marks the end.
 Similarly, <code><span class="nolinebreak">__DTOR_LIST__</span></code><!-- /@w --> and <code><span class="nolinebreak">__DTOR_END__</span></code><!-- /@w --> mark
 the start and end of the global destructors.  The
 first word in the list is the number of entries, followed by the address
 of each constructor or destructor, followed by a zero word.  The
 compiler must arrange to actually run the code.  For these object file
 formats <small>GNU</small> C++ normally calls constructors from a subroutine
 <code>__main</code>; a call to <code>__main</code> is automatically inserted into
 the startup code for <code>main</code>.  <small>GNU</small> C++ normally runs
 destructors either by using <code>atexit</code>, or directly from the function
 <code>exit</code>.
 </p>
 <p>For object file formats such as <code>COFF</code> or <code>ELF</code> which support
 arbitrary section names, <small>GNU</small> C++ will normally arrange to put the
 addresses of global constructors and destructors into the <code>.ctors</code>
 and <code>.dtors</code> sections.  Placing the following sequence into your
 linker script will build the sort of table which the <small>GNU</small> C++
 runtime code expects to see.
 </p>
 <div class="smallexample">
 <pre class="smallexample">      __CTOR_LIST__ = .;
       LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)
       *(.ctors)
       LONG(0)
       __CTOR_END__ = .;
       __DTOR_LIST__ = .;
       LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)
       *(.dtors)
       LONG(0)
       __DTOR_END__ = .;
 </pre></div>

 <p>If you are using the <small>GNU</small> C++ support for initialization priority,
 which provides some control over the order in which global constructors
 are run, you must sort the constructors at link time to ensure that they
 are executed in the correct order.  When using the <code>CONSTRUCTORS</code>
 command, use &lsquo;<samp>SORT_BY_NAME(CONSTRUCTORS)</samp>&rsquo; instead.  When using the
 <code>.ctors</code> and <code>.dtors</code> sections, use &lsquo;<samp>*(SORT_BY_NAME(.ctors))</samp>&rsquo; and
 &lsquo;<samp>*(SORT_BY_NAME(.dtors))</samp>&rsquo; instead of just &lsquo;<samp>*(.ctors)</samp>&rsquo; and
 &lsquo;<samp>*(.dtors)</samp>&rsquo;.
 </p>
 <p>Normally the compiler and linker will handle these issues automatically,
 and you will not need to concern yourself with them.  However, you may
 need to consider this if you are using C++ and writing your own linker
 scripts.
 </p>
 </dd>
 </dl>

 <hr>
 <div class="header">
 <p>
 Next: <a href="Output-Section-Discarding.html#Output-Section-Discarding" accesskey="n" rel="next">Output Section Discarding</a>, Previous: <a href="Output-Section-Data.html#Output-Section-Data" accesskey="p" rel="prev">Output Section Data</a>, Up: <a href="SECTIONS.html#SECTIONS" accesskey="u" rel="up">SECTIONS</a> &nbsp; [<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>
 </div>


 </body>
 </html>
	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
	<html>
	<!-- This file documents the GNU linker LD
	(Linaro_Binutils-2017.01)
	version 2.24.0.

	Copyright (C) 1991-2013 Free Software Foundation, Inc.

	Permission is granted to copy, distribute and/or modify this document
	under the terms of the GNU Free Documentation License, Version 1.3
	or any later version published by the Free Software Foundation;
	with no Invariant Sections, with no Front-Cover Texts, and with no
	Back-Cover Texts. A copy of the license is included in the
	section entitled "GNU Free Documentation License". -->
	<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
	<head>
	<title>LD: Output Section Keywords</title>

	<meta name="description" content="LD: Output Section Keywords">
	<meta name="keywords" content="LD: Output Section Keywords">
	<meta name="resource-type" content="document">
	<meta name="distribution" content="global">
	<meta name="Generator" content="makeinfo">
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
	<link href="index.html#Top" rel="start" title="Top">
	<link href="LD-Index.html#LD-Index" rel="index" title="LD Index">
	<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
	<link href="SECTIONS.html#SECTIONS" rel="up" title="SECTIONS">
	<link href="Output-Section-Discarding.html#Output-Section-Discarding" rel="next" title="Output Section Discarding">
	<link href="Output-Section-Data.html#Output-Section-Data" rel="prev" title="Output Section Data">
	<style type="text/css">
	<!--
	a.summary-letter {text-decoration: none}
	blockquote.smallquotation {font-size: smaller}
	div.display {margin-left: 3.2em}
	div.example {margin-left: 3.2em}
	div.indentedblock {margin-left: 3.2em}
	div.lisp {margin-left: 3.2em}
	div.smalldisplay {margin-left: 3.2em}
	div.smallexample {margin-left: 3.2em}
	div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
	div.smalllisp {margin-left: 3.2em}
	kbd {font-style:oblique}
	pre.display {font-family: inherit}
	pre.format {font-family: inherit}
	pre.menu-comment {font-family: serif}
	pre.menu-preformatted {font-family: serif}
	pre.smalldisplay {font-family: inherit; font-size: smaller}
	pre.smallexample {font-size: smaller}
	pre.smallformat {font-family: inherit; font-size: smaller}
	pre.smalllisp {font-size: smaller}
	span.nocodebreak {white-space:nowrap}
	span.nolinebreak {white-space:nowrap}
	span.roman {font-family:serif; font-weight:normal}
	span.sansserif {font-family:sans-serif; font-weight:normal}
	ul.no-bullet {list-style: none}
	-->
	</style>


	</head>

	<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
	<a name="Output-Section-Keywords"></a>
	<div class="header">
	<p>
	Next: <a href="Output-Section-Discarding.html#Output-Section-Discarding" accesskey="n" rel="next">Output Section Discarding</a>, Previous: <a href="Output-Section-Data.html#Output-Section-Data" accesskey="p" rel="prev">Output Section Data</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>
	</div>
	<hr>
	<a name="Output-Section-Keywords-1"></a>
	<h4 class="subsection">3.6.6 Output Section Keywords</h4>
	<p>There are a couple of keywords which can appear as output section
	commands.
	</p>
	<dl compact="compact">
	<dd><a name="index-CREATE_005fOBJECT_005fSYMBOLS"></a>
	<a name="index-input-filename-symbols"></a>
	<a name="index-filename-symbols"></a>
	</dd>
	<dt><code>CREATE_OBJECT_SYMBOLS</code></dt>
	<dd><p>The command tells the linker to create a symbol for each input file.
	The name of each symbol will be the name of the corresponding input
	file. The section of each symbol will be the output section in which
	the <code>CREATE_OBJECT_SYMBOLS</code> command appears.
	</p>
	<p>This is conventional for the a.out object file format. It is not
	normally used for any other object file format.
	</p>
	<a name="index-CONSTRUCTORS"></a>
	<a name="index-C_002b_002b-constructors_002c-arranging-in-link"></a>
	<a name="index-constructors_002c-arranging-in-link"></a>
	</dd>
	<dt><code>CONSTRUCTORS</code></dt>
	<dd><p>When linking using the a.out object file format, the linker uses an
	unusual set construct to support C++ global constructors and
	destructors. When linking object file formats which do not support
	arbitrary sections, such as ECOFF and XCOFF, the linker will
	automatically recognize C++ global constructors and destructors by name.
	For these object file formats, the <code>CONSTRUCTORS</code> command tells the
	linker to place constructor information in the output section where the
	<code>CONSTRUCTORS</code> command appears. The <code>CONSTRUCTORS</code> command is
	ignored for other object file formats.
	</p>
	<p>The symbol <code><span class="nolinebreak">__CTOR_LIST__</span></code><!-- /@w --> marks the start of the global
	constructors, and the symbol <code><span class="nolinebreak">__CTOR_END__</span></code><!-- /@w --> marks the end.
	Similarly, <code><span class="nolinebreak">__DTOR_LIST__</span></code><!-- /@w --> and <code><span class="nolinebreak">__DTOR_END__</span></code><!-- /@w --> mark
	the start and end of the global destructors. The
	first word in the list is the number of entries, followed by the address
	of each constructor or destructor, followed by a zero word. The
	compiler must arrange to actually run the code. For these object file
	formats <small>GNU</small> C++ normally calls constructors from a subroutine
	<code>__main</code>; a call to <code>__main</code> is automatically inserted into
	the startup code for <code>main</code>. <small>GNU</small> C++ normally runs
	destructors either by using <code>atexit</code>, or directly from the function
	<code>exit</code>.
	</p>
	<p>For object file formats such as <code>COFF</code> or <code>ELF</code> which support
	arbitrary section names, <small>GNU</small> C++ will normally arrange to put the
	addresses of global constructors and destructors into the <code>.ctors</code>
	and <code>.dtors</code> sections. Placing the following sequence into your
	linker script will build the sort of table which the <small>GNU</small> C++
	runtime code expects to see.
	</p>
	<div class="smallexample">
	<pre class="smallexample"> __CTOR_LIST__ = .;
	LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)
	*(.ctors)
	LONG(0)
	__CTOR_END__ = .;
	__DTOR_LIST__ = .;
	LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)
	*(.dtors)
	LONG(0)
	__DTOR_END__ = .;
	</pre></div>

	<p>If you are using the <small>GNU</small> C++ support for initialization priority,
	which provides some control over the order in which global constructors
	are run, you must sort the constructors at link time to ensure that they
	are executed in the correct order. When using the <code>CONSTRUCTORS</code>
	command, use ‘<samp>SORT_BY_NAME(CONSTRUCTORS)</samp>’ instead. When using the
	<code>.ctors</code> and <code>.dtors</code> sections, use ‘<samp>*(SORT_BY_NAME(.ctors))</samp>’ and
	‘<samp>(SORT_BY_NAME(.dtors))</samp>’ instead of just ‘<samp>(.ctors)</samp>’ and
	‘<samp>*(.dtors)</samp>’.
	</p>
	<p>Normally the compiler and linker will handle these issues automatically,
	and you will not need to concern yourself with them. However, you may
	need to consider this if you are using C++ and writing your own linker
	scripts.
	</p>
	</dd>
	</dl>

	<hr>
	<div class="header">
	<p>
	Next: <a href="Output-Section-Discarding.html#Output-Section-Discarding" accesskey="n" rel="next">Output Section Discarding</a>, Previous: <a href="Output-Section-Data.html#Output-Section-Data" accesskey="p" rel="prev">Output Section Data</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>
	</div>



	</body>
	</html>