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<h3 class="section">6.43 How to Use Inline Assembly Language in C Code</h3>
<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>
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 <dfn>basic </dfn><code>asm</code> statement is one with no
operands (see <a href="Basic-Asm.html#Basic-Asm">Basic Asm</a>), while an <dfn>extended </dfn><code>asm</code>
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>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.
<ul class="menu">
<li><a accesskey="1" href="Basic-Asm.html#Basic-Asm">Basic Asm</a>: Inline assembler without operands.
<li><a accesskey="2" href="Extended-Asm.html#Extended-Asm">Extended Asm</a>: Inline assembler with operands.
<li><a accesskey="3" href="Constraints.html#Constraints">Constraints</a>: Constraints for <code>asm</code> operands
<li><a accesskey="4" href="Asm-Labels.html#Asm-Labels">Asm Labels</a>: Specifying the assembler name to use for a C symbol.
<li><a accesskey="5" href="Explicit-Reg-Vars.html#Explicit-Reg-Vars">Explicit Reg Vars</a>: Defining variables residing in specified registers.
<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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