<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1992-2019 Free Software Foundation, Inc.
Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon,
and David MacKenzie.
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 6.4, http://www.gnu.org/software/texinfo/ -->
<head>
<title>Common Blocks (STABS)</title>
<meta name="description" content="Common Blocks (STABS)">
<meta name="keywords" content="Common Blocks (STABS)">
<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="Symbol-Types-Index.html#Symbol-Types-Index" rel="index" title="Symbol Types Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Variables.html#Variables" rel="up" title="Variables">
<link href="Statics.html#Statics" rel="next" title="Statics">
<link href="Register-Variables.html#Register-Variables" rel="prev" title="Register Variables">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
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.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>
</head>
<body lang="en">
<a name="Common-Blocks"></a>
<div class="header">
<p>
Next: <a href="Statics.html#Statics" accesskey="n" rel="next">Statics</a>, Previous: <a href="Register-Variables.html#Register-Variables" accesskey="p" rel="prev">Register Variables</a>, Up: <a href="Variables.html#Variables" accesskey="u" rel="up">Variables</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Common-Blocks-1"></a>
<h3 class="section">4.4 Common Blocks</h3>
<p>A common block is a statically allocated section of memory which can be
referred to by several source files. It may contain several variables.
I believe Fortran is the only language with this feature.
</p>
<a name="index-N_005fBCOMM"></a>
<a name="index-N_005fECOMM"></a>
<a name="index-C_005fBCOMM"></a>
<a name="index-C_005fECOMM"></a>
<p>A <code>N_BCOMM</code> stab begins a common block and an <code>N_ECOMM</code> stab
ends it. The only field that is significant in these two stabs is the
string, which names a normal (non-debugging) symbol that gives the
address of the common block. According to IBM documentation, only the
<code>N_BCOMM</code> has the name of the common block (even though their
compiler actually puts it both places).
</p>
<a name="index-N_005fECOML"></a>
<a name="index-C_005fECOML"></a>
<p>The stabs for the members of the common block are between the
<code>N_BCOMM</code> and the <code>N_ECOMM</code>; the value of each stab is the
offset within the common block of that variable. IBM uses the
<code>C_ECOML</code> stab type, and there is a corresponding <code>N_ECOML</code>
stab type, but Sun’s Fortran compiler uses <code>N_GSYM</code> instead. The
variables within a common block use the ‘<samp>V</samp>’ symbol descriptor (I
believe this is true of all Fortran variables). Other stabs (at least
type declarations using <code>C_DECL</code>) can also be between the
<code>N_BCOMM</code> and the <code>N_ECOMM</code>.
</p>
</body>
</html>