117 lines
6.0 KiB
HTML
117 lines
6.0 KiB
HTML
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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) 1988-2016 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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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Using the GNU Compiler Collection (GCC): Using Assembly Language with C</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC): Using Assembly Language with C">
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<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Using Assembly Language with C">
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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="C-Extensions.html#C-Extensions" rel="up" title="C Extensions">
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<link href="Basic-Asm.html#Basic-Asm" rel="next" title="Basic Asm">
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<link href="Volatiles.html#Volatiles" rel="prev" title="Volatiles">
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Using-Assembly-Language-with-C"></a>
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<div class="header">
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<p>
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Next: <a href="Alternate-Keywords.html#Alternate-Keywords" accesskey="n" rel="next">Alternate Keywords</a>, Previous: <a href="Volatiles.html#Volatiles" accesskey="p" rel="prev">Volatiles</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</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="How-to-Use-Inline-Assembly-Language-in-C-Code"></a>
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<h3 class="section">6.44 How to Use Inline Assembly Language in C Code</h3>
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<a name="index-asm-keyword"></a>
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<a name="index-assembly-language-in-C"></a>
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<a name="index-inline-assembly-language"></a>
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<a name="index-mixing-assembly-language-and-C"></a>
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<p>The <code>asm</code> keyword allows you to embed assembler instructions
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within C code. GCC provides two forms of inline <code>asm</code>
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statements. A <em>basic <code>asm</code></em> statement is one with no
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operands (see <a href="Basic-Asm.html#Basic-Asm">Basic Asm</a>), while an <em>extended <code>asm</code></em>
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statement (see <a href="Extended-Asm.html#Extended-Asm">Extended Asm</a>) includes one or more operands.
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The extended form is preferred for mixing C and assembly language
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within a function, but to include assembly language at
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top level you must use basic <code>asm</code>.
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</p>
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<p>You can also use the <code>asm</code> keyword to override the assembler name
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for a C symbol, or to place a C variable in a specific register.
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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="Basic-Asm.html#Basic-Asm" accesskey="1">Basic Asm</a>:</td><td> </td><td align="left" valign="top">Inline assembler without operands.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Extended-Asm.html#Extended-Asm" accesskey="2">Extended Asm</a>:</td><td> </td><td align="left" valign="top">Inline assembler with operands.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Constraints.html#Constraints" accesskey="3">Constraints</a>:</td><td> </td><td align="left" valign="top">Constraints for <code>asm</code> operands
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Asm-Labels.html#Asm-Labels" accesskey="4">Asm Labels</a>:</td><td> </td><td align="left" valign="top">Specifying the assembler name to use for a C symbol.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Explicit-Register-Variables.html#Explicit-Register-Variables" accesskey="5">Explicit Register Variables</a>:</td><td> </td><td align="left" valign="top">Defining variables residing in specified
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registers.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Size-of-an-asm.html#Size-of-an-asm" accesskey="6">Size of an asm</a>:</td><td> </td><td align="left" valign="top">How GCC calculates the size of an <code>asm</code> block.
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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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