You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
73 lines
3.5 KiB
HTML
73 lines
3.5 KiB
HTML
<html lang="en">
|
|
<head>
|
|
<title>Comm - Using as</title>
|
|
<meta http-equiv="Content-Type" content="text/html">
|
|
<meta name="description" content="Using as">
|
|
<meta name="generator" content="makeinfo 4.7">
|
|
<link title="Top" rel="start" href="index.html#Top">
|
|
<link rel="up" href="Pseudo-Ops.html#Pseudo-Ops" title="Pseudo Ops">
|
|
<link rel="prev" href="Byte.html#Byte" title="Byte">
|
|
<link rel="next" href="CFI-directives.html#CFI-directives" title="CFI directives">
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
|
<!--
|
|
This file documents the GNU Assembler "as".
|
|
|
|
Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
|
|
2006, 2007 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 1.1
|
|
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''.
|
|
|
|
man end-->
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
|
<style type="text/css"><!--
|
|
pre.display { font-family:inherit }
|
|
pre.format { font-family:inherit }
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
|
pre.smallexample { font-size:smaller }
|
|
pre.smalllisp { font-size:smaller }
|
|
span.sc { font-variant:small-caps }
|
|
span.roman { font-family: serif; font-weight: normal; }
|
|
--></style>
|
|
</head>
|
|
<body>
|
|
<div class="node">
|
|
<p>
|
|
<a name="Comm"></a>Next: <a rel="next" accesskey="n" href="CFI-directives.html#CFI-directives">CFI directives</a>,
|
|
Previous: <a rel="previous" accesskey="p" href="Byte.html#Byte">Byte</a>,
|
|
Up: <a rel="up" accesskey="u" href="Pseudo-Ops.html#Pseudo-Ops">Pseudo Ops</a>
|
|
<hr><br>
|
|
</div>
|
|
|
|
<h3 class="section">7.8 <code>.comm </code><var>symbol</var><code> , </code><var>length</var> </h3>
|
|
|
|
<p><a name="index-_0040code_007bcomm_007d-directive-288"></a><a name="index-symbol_002c-common-289"></a><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>When using ELF, the <code>.comm</code> directive takes an optional third argument.
|
|
This is the desired alignment of the symbol, specified as a byte boundary (for
|
|
example, an alignment of 16 means that the least significant 4 bits of the
|
|
address should be zero). 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, <span class="command">as</span> 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.
|
|
|
|
<p>The syntax for <code>.comm</code> differs slightly on the HPPA. The syntax is
|
|
<var>symbol</var><span class="samp"> .comm, </span><var>length</var>; <var>symbol</var> is optional.
|
|
|
|
</body></html>
|
|
|