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96 lines
4.5 KiB
HTML
96 lines
4.5 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Asm Labels - Using the GNU Compiler Collection (GCC)</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C" title="Using Assembly Language with C">
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<link rel="prev" href="Constraints.html#Constraints" title="Constraints">
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<link rel="next" href="Explicit-Reg-Vars.html#Explicit-Reg-Vars" title="Explicit Reg Vars">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1988-2015 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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<style type="text/css"><!--
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pre.display { font-family:inherit }
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span.sansserif { font-family:sans-serif; font-weight:normal; }
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Asm-Labels"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Explicit-Reg-Vars.html#Explicit-Reg-Vars">Explicit Reg Vars</a>,
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Previous: <a rel="previous" accesskey="p" href="Constraints.html#Constraints">Constraints</a>,
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Up: <a rel="up" accesskey="u" href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C">Using Assembly Language with C</a>
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<hr>
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</div>
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<h4 class="subsection">6.43.4 Controlling Names Used in Assembler Code</h4>
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<p><a name="index-assembler-names-for-identifiers-3489"></a><a name="index-names-used-in-assembler-code-3490"></a><a name="index-identifiers_002c-names-in-assembler-code-3491"></a>
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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 as follows:
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<pre class="smallexample"> int foo asm ("myfoo") = 2;
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</pre>
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<p class="noindent">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><span class="samp">myfoo</span></samp>’ rather than the usual
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‘<samp><span class="samp">_foo</span></samp>’.
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<p>On systems where an underscore is normally prepended to the name of a C
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function or 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>It does not make sense to use this feature with a non-static local
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variable 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 <a href="Explicit-Reg-Vars.html#Explicit-Reg-Vars">Explicit Reg Vars</a>. GCC presently accepts such code with a warning, but will
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probably be changed to issue an error, rather than a warning, in the
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future.
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<p>You cannot use <code>asm</code> in this way in a function <em>definition</em>; but
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you can get the same effect by writing a declaration for the function
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before its definition and putting <code>asm</code> there, like this:
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<pre class="smallexample"> extern func () asm ("FUNC");
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func (x, y)
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int x, y;
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/* <span class="roman">...</span> */
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</pre>
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<p>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. Also, you must not use a
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register name; that would produce completely invalid assembler code. GCC
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does not as yet have the ability to store static variables in registers.
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Perhaps that will be added.
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</body></html>
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