112 lines
5.5 KiB
HTML
112 lines
5.5 KiB
HTML
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<head>
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<title>Using the GNU Compiler Collection (GCC): Constraints</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC): Constraints">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C" rel="up" title="Using Assembly Language with C">
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<link href="Simple-Constraints.html#Simple-Constraints" rel="next" title="Simple Constraints">
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<a name="Constraints"></a>
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<p>
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Next: <a href="Asm-Labels.html#Asm-Labels" accesskey="n" rel="next">Asm Labels</a>, Previous: <a href="Extended-Asm.html#Extended-Asm" accesskey="p" rel="prev">Extended Asm</a>, Up: <a href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C" accesskey="u" rel="up">Using Assembly Language with C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Constraints-for-asm-Operands"></a>
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<h4 class="subsection">6.44.3 Constraints for <code>asm</code> Operands</h4>
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<a name="index-operand-constraints_002c-asm"></a>
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<a name="index-constraints_002c-asm"></a>
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<a name="index-asm-constraints"></a>
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<p>Here are specific details on what constraint letters you can use with
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<code>asm</code> operands.
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Constraints can say whether
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an operand may be in a register, and which kinds of register; whether the
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operand can be a memory reference, and which kinds of address; whether the
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operand may be an immediate constant, and which possible values it may
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have. Constraints can also require two operands to match.
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Side-effects aren’t allowed in operands of inline <code>asm</code>, unless
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‘<samp><</samp>’ or ‘<samp>></samp>’ constraints are used, because there is no guarantee
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that the side-effects will happen exactly once in an instruction that can update
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the addressing register.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="Simple-Constraints.html#Simple-Constraints" accesskey="1">Simple Constraints</a>:</td><td> </td><td align="left" valign="top">Basic use of constraints.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Multi_002dAlternative.html#Multi_002dAlternative" accesskey="2">Multi-Alternative</a>:</td><td> </td><td align="left" valign="top">When an insn has two alternative constraint-patterns.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Modifiers.html#Modifiers" accesskey="3">Modifiers</a>:</td><td> </td><td align="left" valign="top">More precise control over effects of constraints.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Machine-Constraints.html#Machine-Constraints" accesskey="4">Machine Constraints</a>:</td><td> </td><td align="left" valign="top">Special constraints for some particular machines.
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</td></tr>
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</table>
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</body>
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