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137 lines
6.2 KiB
HTML
137 lines
6.2 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>Asm Labels (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Asm Labels (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Asm Labels (Using the GNU Compiler Collection (GCC))">
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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="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="Explicit-Register-Variables.html#Explicit-Register-Variables" rel="next" title="Explicit Register Variables">
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<link href="Machine-Constraints.html#Machine-Constraints" rel="prev" title="Machine Constraints">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smallexample {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: 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="Asm-Labels"></a>
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<div class="header">
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<p>
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Next: <a href="Explicit-Register-Variables.html#Explicit-Register-Variables" accesskey="n" rel="next">Explicit Register Variables</a>, Previous: <a href="Constraints.html#Constraints" accesskey="p" rel="prev">Constraints</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="Controlling-Names-Used-in-Assembler-Code"></a>
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<h4 class="subsection">6.45.4 Controlling Names Used in Assembler Code</h4>
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<a name="index-assembler-names-for-identifiers"></a>
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<a name="index-names-used-in-assembler-code"></a>
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<a name="index-identifiers_002c-names-in-assembler-code"></a>
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<p>You can specify the name to be used in the assembler code for a C
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function or variable by writing the <code>asm</code> (or <code>__asm__</code>)
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keyword after the declarator.
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It is up to you to make sure that the assembler names you choose do not
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conflict with any other assembler symbols, or reference registers.
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</p>
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<a name="Assembler-names-for-data_003a"></a>
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<h4 class="subsubheading">Assembler names for data:</h4>
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<p>This sample shows how to specify the assembler name for data:
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</p>
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<div class="smallexample">
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<pre class="smallexample">int foo asm ("myfoo") = 2;
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</pre></div>
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<p>This specifies that the name to be used for the variable <code>foo</code> in
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the assembler code should be ‘<samp>myfoo</samp>’ rather than the usual
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‘<samp>_foo</samp>’.
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</p>
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<p>On systems where an underscore is normally prepended to the name of a C
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variable, this feature allows you to define names for the
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linker that do not start with an underscore.
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</p>
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<p>GCC does not support using this feature with a non-static local variable
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since such variables do not have assembler names. If you are
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trying to put the variable in a particular register, see
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<a href="Explicit-Register-Variables.html#Explicit-Register-Variables">Explicit Register Variables</a>.
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</p>
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<a name="Assembler-names-for-functions_003a"></a>
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<h4 class="subsubheading">Assembler names for functions:</h4>
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<p>To specify the assembler name for functions, write a declaration for the
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function before its definition and put <code>asm</code> there, like this:
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</p>
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<div class="smallexample">
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<pre class="smallexample">int func (int x, int y) asm ("MYFUNC");
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int func (int x, int y)
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{
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/* <span class="roman">…</span> */
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</pre></div>
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<p>This specifies that the name to be used for the function <code>func</code> in
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the assembler code should be <code>MYFUNC</code>.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Explicit-Register-Variables.html#Explicit-Register-Variables" accesskey="n" rel="next">Explicit Register Variables</a>, Previous: <a href="Constraints.html#Constraints" accesskey="p" rel="prev">Constraints</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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</body>
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</html>
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