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81 lines
4.2 KiB
HTML
81 lines
4.2 KiB
HTML
4 years ago
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<title>Using Assembly Language with C - Using the GNU Compiler Collection (GCC)</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<link rel="up" href="C-Extensions.html#C-Extensions" title="C Extensions">
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<link rel="prev" href="Volatiles.html#Volatiles" title="Volatiles">
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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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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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<body>
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<div class="node">
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<a name="Using-Assembly-Language-with-C"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Alternate-Keywords.html#Alternate-Keywords">Alternate Keywords</a>,
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Previous: <a rel="previous" accesskey="p" href="Volatiles.html#Volatiles">Volatiles</a>,
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Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a>
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<hr>
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</div>
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<h3 class="section">6.43 How to Use Inline Assembly Language in C Code</h3>
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<p><a name="index-g_t_0040code_007basm_007d-keyword-3417"></a><a name="index-assembly-language-in-C-3418"></a><a name="index-inline-assembly-language-3419"></a><a name="index-mixing-assembly-language-and-C-3420"></a>
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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 <dfn>basic </dfn><code>asm</code> statement is one with no
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operands (see <a href="Basic-Asm.html#Basic-Asm">Basic Asm</a>), while an <dfn>extended </dfn><code>asm</code>
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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>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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<ul class="menu">
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<li><a accesskey="1" href="Basic-Asm.html#Basic-Asm">Basic Asm</a>: Inline assembler without operands.
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<li><a accesskey="2" href="Extended-Asm.html#Extended-Asm">Extended Asm</a>: Inline assembler with operands.
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<li><a accesskey="3" href="Constraints.html#Constraints">Constraints</a>: Constraints for <code>asm</code> operands
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<li><a accesskey="4" href="Asm-Labels.html#Asm-Labels">Asm Labels</a>: Specifying the assembler name to use for a C symbol.
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<li><a accesskey="5" href="Explicit-Reg-Vars.html#Explicit-Reg-Vars">Explicit Reg Vars</a>: Defining variables residing in specified registers.
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<li><a accesskey="6" href="Size-of-an-asm.html#Size-of-an-asm">Size of an asm</a>: How GCC calculates the size of an <code>asm</code> block.
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</ul>
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</body></html>
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