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| <title>Using the GNU Compiler Collection (GCC): Using Assembly Language with C</title> |
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| <a name="How-to-Use-Inline-Assembly-Language-in-C-Code"></a> |
| <h3 class="section">6.43 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. |
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| <tr><td align="left" valign="top">• <a href="Basic-Asm.html#Basic-Asm" accesskey="1">Basic Asm</a>:</td><td> </td><td align="left" valign="top">Inline assembler without operands. |
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| <tr><td align="left" valign="top">• <a href="Extended-Asm.html#Extended-Asm" accesskey="2">Extended Asm</a>:</td><td> </td><td align="left" valign="top">Inline assembler with operands. |
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| <tr><td align="left" valign="top">• <a href="Constraints.html#Constraints" accesskey="3">Constraints</a>:</td><td> </td><td align="left" valign="top">Constraints for <code>asm</code> operands |
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| <tr><td align="left" valign="top">• <a href="Asm-Labels.html#Asm-Labels" accesskey="4">Asm Labels</a>:</td><td> </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">• <a href="Explicit-Reg-Vars.html#Explicit-Reg-Vars" accesskey="5">Explicit Reg Vars</a>:</td><td> </td><td align="left" valign="top">Defining variables residing in specified registers. |
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| <tr><td align="left" valign="top">• <a href="Size-of-an-asm.html#Size-of-an-asm" accesskey="6">Size of an asm</a>:</td><td> </td><td align="left" valign="top">How GCC calculates the size of an <code>asm</code> block. |
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