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<title>Using Assembly Language with C (Using the GNU Compiler Collection (GCC))</title>

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<a name="Using-Assembly-Language-with-C"></a>
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<a name="How-to-Use-Inline-Assembly-Language-in-C-Code"></a>
<h3 class="section">6.47 How to Use Inline Assembly Language in C Code</h3>
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<p>The <code>asm</code> keyword allows you to embed assembler instructions
within C code.  GCC provides two forms of inline <code>asm</code>
statements.  A <em>basic <code>asm</code></em> statement is one with no
operands (see <a href="Basic-Asm.html#Basic-Asm">Basic Asm</a>), while an <em>extended <code>asm</code></em>
statement (see <a href="Extended-Asm.html#Extended-Asm">Extended Asm</a>) includes one or more operands.  
The extended form is preferred for mixing C and assembly language
within a function, but to include assembly language at
top level you must use basic <code>asm</code>.
</p>
<p>You can also use the <code>asm</code> keyword to override the assembler name
for a C symbol, or to place a C variable in a specific register.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="Basic-Asm.html#Basic-Asm" accesskey="1">Basic Asm</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Inline assembler without operands.
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<tr><td align="left" valign="top">&bull; <a href="Extended-Asm.html#Extended-Asm" accesskey="2">Extended Asm</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Inline assembler with operands.
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<tr><td align="left" valign="top">&bull; <a href="Constraints.html#Constraints" accesskey="3">Constraints</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Constraints for <code>asm</code> operands
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<tr><td align="left" valign="top">&bull; <a href="Asm-Labels.html#Asm-Labels" accesskey="4">Asm Labels</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Specifying the assembler name to use for a C symbol.
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<tr><td align="left" valign="top">&bull; <a href="Explicit-Register-Variables.html#Explicit-Register-Variables" accesskey="5">Explicit Register Variables</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining variables residing in specified 
                       registers.
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<tr><td align="left" valign="top">&bull; <a href="Size-of-an-asm.html#Size-of-an-asm" accesskey="6">Size of an asm</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">How GCC calculates the size of an <code>asm</code> block.
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