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104 lines
4.8 KiB
HTML
104 lines
4.8 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) 1988-2018 Free Software Foundation, Inc.
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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 the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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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>Explicit Register Variables (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Explicit Register Variables (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Explicit Register Variables (Using the GNU Compiler Collection (GCC))">
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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="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C" rel="up" title="Using Assembly Language with C">
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<link href="Global-Register-Variables.html#Global-Register-Variables" rel="next" title="Global Register Variables">
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<link href="Asm-Labels.html#Asm-Labels" rel="prev" title="Asm Labels">
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</style>
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</head>
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<body lang="en">
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<a name="Explicit-Register-Variables"></a>
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<div class="header">
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<p>
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Next: <a href="Size-of-an-asm.html#Size-of-an-asm" accesskey="n" rel="next">Size of an asm</a>, Previous: <a href="Asm-Labels.html#Asm-Labels" accesskey="p" rel="prev">Asm Labels</a>, Up: <a href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C" accesskey="u" rel="up">Using Assembly Language with C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Variables-in-Specified-Registers"></a>
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<h4 class="subsection">6.45.5 Variables in Specified Registers</h4>
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<a name="Explicit-Reg-Vars"></a><a name="index-explicit-register-variables"></a>
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<a name="index-variables-in-specified-registers"></a>
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<a name="index-specified-registers"></a>
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<p>GNU C allows you to associate specific hardware registers with C
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variables. In almost all cases, allowing the compiler to assign
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registers produces the best code. However under certain unusual
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circumstances, more precise control over the variable storage is
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required.
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</p>
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<p>Both global and local variables can be associated with a register. The
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consequences of performing this association are very different between
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the two, as explained in the sections below.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="Global-Register-Variables.html#Global-Register-Variables" accesskey="1">Global Register Variables</a>:</td><td> </td><td align="left" valign="top">Variables declared at global scope.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Local-Register-Variables.html#Local-Register-Variables" accesskey="2">Local Register Variables</a>:</td><td> </td><td align="left" valign="top">Variables declared within a function.
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</td></tr>
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</table>
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</body>
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</html>
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