aarch64-linux-gnu-4.9/share/doc/as.html/Comm.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 Assembler "as".

 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>Using as: Comm</title>

 <meta name="description" content="Using as: Comm">
 <meta name="keywords" content="Using as: Comm">
 <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="AS-Index.html#AS-Index" rel="index" title="AS Index">
 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
 <link href="Pseudo-Ops.html#Pseudo-Ops" rel="up" title="Pseudo Ops">
 <link href="Data.html#Data" rel="next" title="Data">
 <link href="CFI-directives.html#CFI-directives" rel="prev" title="CFI directives">
 <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="Comm"></a>
 <div class="header">
 <p>
 Next: <a href="Data.html#Data" accesskey="n" rel="next">Data</a>, Previous: <a href="CFI-directives.html#CFI-directives" accesskey="p" rel="prev">CFI directives</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> &nbsp; [<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>
 <hr>
 <a name="g_t_002ecomm-symbol-_002c-length-"></a>
 <h3 class="section">7.32 <code>.comm <var>symbol</var> , <var>length</var> </code></h3>

 <a name="index-comm-directive"></a>
 <a name="index-symbol_002c-common"></a>
 <p><code>.comm</code> declares a common symbol named <var>symbol</var>.  When linking, a
 common symbol in one object file may be merged with a defined or common symbol
 of the same name in another object file.  If <code>ld</code> does not see a
 definition for the symbol&ndash;just one or more common symbols&ndash;then it will
 allocate <var>length</var> bytes of uninitialized memory.  <var>length</var> must be an
 absolute expression.  If <code>ld</code> sees multiple common symbols with
 the same name, and they do not all have the same size, it will allocate space
 using the largest size.
 </p>
 <p>When using ELF or (as a GNU extension) PE, the <code>.comm</code> directive takes
 an optional third argument.  This is the desired alignment of the symbol,
 specified for ELF as a byte boundary (for example, an alignment of 16 means
 that the least significant 4 bits of the address should be zero), and for PE
 as a power of two (for example, an alignment of 5 means aligned to a 32-byte
 boundary).  The alignment must be an absolute expression, and it must be a
 power of two.  If <code>ld</code> allocates uninitialized memory for the
 common symbol, it will use the alignment when placing the symbol.  If no
 alignment is specified, <code>as</code> will set the alignment to the
 largest power of two less than or equal to the size of the symbol, up to a
 maximum of 16 on ELF, or the default section alignment of 4 on PE<a name="DOCF1" href="#FOOT1"><sup>1</sup></a>.
 </p>
 <p>The syntax for <code>.comm</code> differs slightly on the HPPA.  The syntax is
 &lsquo;<samp><var>symbol</var> .comm, <var>length</var></samp>&rsquo;; <var>symbol</var> is optional.
 </p>
 <div class="footnote">
 <hr>
 <h4 class="footnotes-heading">Footnotes</h4>

 <h3><a name="FOOT1" href="#DOCF1">(1)</a></h3>
 <p>This
 is not the same as the executable image file alignment controlled by <code>ld</code>&rsquo;s
 &lsquo;<samp>--section-alignment</samp>&rsquo; option; image file sections in PE are aligned to
 multiples of 4096, which is far too large an alignment for ordinary variables.
 It is rather the default alignment for (non-debug) sections within object
 (&lsquo;<samp>*.o</samp>&rsquo;) files, which are less strictly aligned.</p>
 </div>
 <hr>
 <div class="header">
 <p>
 Next: <a href="Data.html#Data" accesskey="n" rel="next">Data</a>, Previous: <a href="CFI-directives.html#CFI-directives" accesskey="p" rel="prev">CFI directives</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> &nbsp; [<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>
	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
	<html>
	<!-- This file documents the GNU Assembler "as".

	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>Using as: Comm</title>

	<meta name="description" content="Using as: Comm">
	<meta name="keywords" content="Using as: Comm">
	<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="AS-Index.html#AS-Index" rel="index" title="AS Index">
	<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
	<link href="Pseudo-Ops.html#Pseudo-Ops" rel="up" title="Pseudo Ops">
	<link href="Data.html#Data" rel="next" title="Data">
	<link href="CFI-directives.html#CFI-directives" rel="prev" title="CFI directives">
	<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="Comm"></a>
	<div class="header">
	<p>
	Next: <a href="Data.html#Data" accesskey="n" rel="next">Data</a>, Previous: <a href="CFI-directives.html#CFI-directives" accesskey="p" rel="prev">CFI directives</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>
	<hr>
	<a name="g_t_002ecomm-symbol-_002c-length-"></a>
	<h3 class="section">7.32 <code>.comm <var>symbol</var> , <var>length</var> </code></h3>

	<a name="index-comm-directive"></a>
	<a name="index-symbol_002c-common"></a>
	<p><code>.comm</code> declares a common symbol named <var>symbol</var>. When linking, a
	common symbol in one object file may be merged with a defined or common symbol
	of the same name in another object file. If <code>ld</code> does not see a
	definition for the symbol–just one or more common symbols–then it will
	allocate <var>length</var> bytes of uninitialized memory. <var>length</var> must be an
	absolute expression. If <code>ld</code> sees multiple common symbols with
	the same name, and they do not all have the same size, it will allocate space
	using the largest size.
	</p>
	<p>When using ELF or (as a GNU extension) PE, the <code>.comm</code> directive takes
	an optional third argument. This is the desired alignment of the symbol,
	specified for ELF as a byte boundary (for example, an alignment of 16 means
	that the least significant 4 bits of the address should be zero), and for PE
	as a power of two (for example, an alignment of 5 means aligned to a 32-byte
	boundary). The alignment must be an absolute expression, and it must be a
	power of two. If <code>ld</code> allocates uninitialized memory for the
	common symbol, it will use the alignment when placing the symbol. If no
	alignment is specified, <code>as</code> will set the alignment to the
	largest power of two less than or equal to the size of the symbol, up to a
	maximum of 16 on ELF, or the default section alignment of 4 on PE<a name="DOCF1" href="#FOOT1"><sup>1</sup></a>.
	</p>
	<p>The syntax for <code>.comm</code> differs slightly on the HPPA. The syntax is
	‘<samp><var>symbol</var> .comm, <var>length</var></samp>’; <var>symbol</var> is optional.
	</p>
	<div class="footnote">
	<hr>
	<h4 class="footnotes-heading">Footnotes</h4>

	<h3><a name="FOOT1" href="#DOCF1">(1)</a></h3>
	<p>This
	is not the same as the executable image file alignment controlled by <code>ld</code>’s
	‘<samp>--section-alignment</samp>’ option; image file sections in PE are aligned to
	multiples of 4096, which is far too large an alignment for ordinary variables.
	It is rather the default alignment for (non-debug) sections within object
	(‘<samp>*.o</samp>’) files, which are less strictly aligned.</p>
	</div>
	<hr>
	<div class="header">
	<p>
	Next: <a href="Data.html#Data" accesskey="n" rel="next">Data</a>, Previous: <a href="CFI-directives.html#CFI-directives" accesskey="p" rel="prev">CFI directives</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>