1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- Copyright (C) 1992-2021 Free Software Foundation, Inc. 4Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon, 5and David MacKenzie. 6 7Permission is granted to copy, distribute and/or modify this document 8under the terms of the GNU Free Documentation License, Version 1.3 or 9any later version published by the Free Software Foundation; with no 10Invariant Sections, with no Front-Cover Texts, and with no Back-Cover 11Texts. A copy of the license is included in the section entitled "GNU 12Free Documentation License". --> 13<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> 14<head> 15<title>STABS: Common Blocks</title> 16 17<meta name="description" content="STABS: Common Blocks"> 18<meta name="keywords" content="STABS: Common Blocks"> 19<meta name="resource-type" content="document"> 20<meta name="distribution" content="global"> 21<meta name="Generator" content="makeinfo"> 22<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 23<link href="index.html#Top" rel="start" title="Top"> 24<link href="Symbol-Types-Index.html#Symbol-Types-Index" rel="index" title="Symbol Types Index"> 25<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> 26<link href="Variables.html#Variables" rel="up" title="Variables"> 27<link href="Statics.html#Statics" rel="next" title="Statics"> 28<link href="Register-Variables.html#Register-Variables" rel="previous" title="Register Variables"> 29<style type="text/css"> 30<!-- 31a.summary-letter {text-decoration: none} 32blockquote.smallquotation {font-size: smaller} 33div.display {margin-left: 3.2em} 34div.example {margin-left: 3.2em} 35div.indentedblock {margin-left: 3.2em} 36div.lisp {margin-left: 3.2em} 37div.smalldisplay {margin-left: 3.2em} 38div.smallexample {margin-left: 3.2em} 39div.smallindentedblock {margin-left: 3.2em; font-size: smaller} 40div.smalllisp {margin-left: 3.2em} 41kbd {font-style:oblique} 42pre.display {font-family: inherit} 43pre.format {font-family: inherit} 44pre.menu-comment {font-family: serif} 45pre.menu-preformatted {font-family: serif} 46pre.smalldisplay {font-family: inherit; font-size: smaller} 47pre.smallexample {font-size: smaller} 48pre.smallformat {font-family: inherit; font-size: smaller} 49pre.smalllisp {font-size: smaller} 50span.nocodebreak {white-space:nowrap} 51span.nolinebreak {white-space:nowrap} 52span.roman {font-family:serif; font-weight:normal} 53span.sansserif {font-family:sans-serif; font-weight:normal} 54ul.no-bullet {list-style: none} 55--> 56</style> 57 58 59</head> 60 61<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> 62<a name="Common-Blocks"></a> 63<div class="header"> 64<p> 65Next: <a href="Statics.html#Statics" accesskey="n" rel="next">Statics</a>, Previous: <a href="Register-Variables.html#Register-Variables" accesskey="p" rel="previous">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> 66</div> 67<hr> 68<a name="Common-Blocks-1"></a> 69<h3 class="section">4.4 Common Blocks</h3> 70 71<p>A common block is a statically allocated section of memory which can be 72referred to by several source files. It may contain several variables. 73I believe Fortran is the only language with this feature. 74</p> 75<a name="index-N_005fBCOMM"></a> 76<a name="index-N_005fECOMM"></a> 77<a name="index-C_005fBCOMM"></a> 78<a name="index-C_005fECOMM"></a> 79<p>A <code>N_BCOMM</code> stab begins a common block and an <code>N_ECOMM</code> stab 80ends it. The only field that is significant in these two stabs is the 81string, which names a normal (non-debugging) symbol that gives the 82address of the common block. According to IBM documentation, only the 83<code>N_BCOMM</code> has the name of the common block (even though their 84compiler actually puts it both places). 85</p> 86<a name="index-N_005fECOML"></a> 87<a name="index-C_005fECOML"></a> 88<p>The stabs for the members of the common block are between the 89<code>N_BCOMM</code> and the <code>N_ECOMM</code>; the value of each stab is the 90offset within the common block of that variable. IBM uses the 91<code>C_ECOML</code> stab type, and there is a corresponding <code>N_ECOML</code> 92stab type, but Sun’s Fortran compiler uses <code>N_GSYM</code> instead. The 93variables within a common block use the ‘<samp>V</samp>’ symbol descriptor (I 94believe this is true of all Fortran variables). Other stabs (at least 95type declarations using <code>C_DECL</code>) can also be between the 96<code>N_BCOMM</code> and the <code>N_ECOMM</code>. 97</p> 98 99 100 101</body> 102</html> 103