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109 lines
4.5 KiB
HTML
109 lines
4.5 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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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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Texts. A copy of the license is included in the section entitled "GNU
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Free Documentation License". -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Global Variables (STABS)</title>
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<meta name="description" content="Global Variables (STABS)">
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<meta name="keywords" content="Global Variables (STABS)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Symbol-Types-Index.html#Symbol-Types-Index" rel="index" title="Symbol Types Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Variables.html#Variables" rel="up" title="Variables">
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<link href="Register-Variables.html#Register-Variables" rel="next" title="Register Variables">
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<link href="Stack-Variables.html#Stack-Variables" rel="prev" title="Stack Variables">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Global-Variables"></a>
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<div class="header">
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<p>
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Next: <a href="Register-Variables.html#Register-Variables" accesskey="n" rel="next">Register Variables</a>, Previous: <a href="Stack-Variables.html#Stack-Variables" accesskey="p" rel="prev">Stack 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>
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</div>
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<hr>
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<a name="Global-Variables-1"></a>
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<h3 class="section">4.2 Global Variables</h3>
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<a name="index-N_005fGSYM"></a>
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<a name="index-C_005fGSYM"></a>
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<p>A variable whose scope is not specific to just one source file is
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represented by the ‘<samp>G</samp>’ symbol descriptor. These stabs use the
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<code>N_GSYM</code> stab type (C_GSYM for XCOFF). The type information for
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the stab (see <a href="String-Field.html#String-Field">String Field</a>) gives the type of the variable.
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</p>
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<p>For example, the following source code:
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</p>
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<div class="example">
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<pre class="example">char g_foo = 'c';
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</pre></div>
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<p>yields the following assembly code:
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</p>
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<div class="example">
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<pre class="example">.stabs "g_foo:G2",32,0,0,0 # <span class="roman">32 is N_GSYM</span>
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.global _g_foo
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.data
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_g_foo:
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.byte 99
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</pre></div>
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<p>The address of the variable represented by the <code>N_GSYM</code> is not
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contained in the <code>N_GSYM</code> stab. The debugger gets this information
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from the external symbol for the global variable. In the example above,
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the <code>.global _g_foo</code> and <code>_g_foo:</code> lines tell the assembler to
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produce an external symbol.
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</p>
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<p>Some compilers, like GCC, output <code>N_GSYM</code> stabs only once, where
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the variable is defined. Other compilers, like SunOS4 /bin/cc, output a
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<code>N_GSYM</code> stab for each compilation unit which references the
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variable.
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</p>
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</body>
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</html>
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