71 lines
3.5 KiB
HTML
71 lines
3.5 KiB
HTML
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<html lang="en">
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<head>
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<title>Common Blocks - STABS</title>
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<meta name="description" content="STABS">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Variables.html#Variables" title="Variables">
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<link rel="prev" href="Register-Variables.html#Register-Variables" title="Register Variables">
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<link rel="next" href="Statics.html#Statics" title="Statics">
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<!--
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Copyright (C) 1992-2019 Free Software Foundation, Inc.
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Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon,
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and David MacKenzie.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
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</head>
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<body>
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<div class="node">
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<a name="Common-Blocks"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Statics.html#Statics">Statics</a>,
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Previous: <a rel="previous" accesskey="p" href="Register-Variables.html#Register-Variables">Register Variables</a>,
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Up: <a rel="up" accesskey="u" href="Variables.html#Variables">Variables</a>
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<hr>
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</div>
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<h3 class="section">4.4 Common Blocks</h3>
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<p>A common block is a statically allocated section of memory which can be
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referred to by several source files. It may contain several variables.
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I believe Fortran is the only language with this feature.
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<p><a name="index-N_005fBCOMM-31"></a><a name="index-N_005fECOMM-32"></a><a name="index-C_005fBCOMM-33"></a><a name="index-C_005fECOMM-34"></a>A <code>N_BCOMM</code> stab begins a common block and an <code>N_ECOMM</code> stab
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ends it. The only field that is significant in these two stabs is the
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string, which names a normal (non-debugging) symbol that gives the
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address of the common block. According to IBM documentation, only the
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<code>N_BCOMM</code> has the name of the common block (even though their
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compiler actually puts it both places).
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<p><a name="index-N_005fECOML-35"></a><a name="index-C_005fECOML-36"></a>The stabs for the members of the common block are between the
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<code>N_BCOMM</code> and the <code>N_ECOMM</code>; the value of each stab is the
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offset within the common block of that variable. IBM uses the
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<code>C_ECOML</code> stab type, and there is a corresponding <code>N_ECOML</code>
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stab type, but Sun's Fortran compiler uses <code>N_GSYM</code> instead. The
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variables within a common block use the ‘<samp><span class="samp">V</span></samp>’ symbol descriptor (I
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believe this is true of all Fortran variables). Other stabs (at least
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type declarations using <code>C_DECL</code>) can also be between the
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<code>N_BCOMM</code> and the <code>N_ECOMM</code>.
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</body></html>
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