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79 lines
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79 lines
4.0 KiB
HTML
4 years ago
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<title>Constraints - 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 title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C" title="Using Assembly Language with C">
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<link rel="prev" href="Extended-Asm.html#Extended-Asm" title="Extended Asm">
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<link rel="next" href="Asm-Labels.html#Asm-Labels" title="Asm Labels">
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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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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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</head>
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<body>
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<div class="node">
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<a name="Constraints"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Asm-Labels.html#Asm-Labels">Asm Labels</a>,
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Previous: <a rel="previous" accesskey="p" href="Extended-Asm.html#Extended-Asm">Extended Asm</a>,
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Up: <a rel="up" accesskey="u" href="Using-Assembly-Language-with-C.html#Using-Assembly-Language-with-C">Using Assembly Language with C</a>
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<hr>
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</div>
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<h4 class="subsection">6.43.3 Constraints for <code>asm</code> Operands</h4>
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<p><a name="index-operand-constraints_002c-_0040code_007basm_007d-3433"></a><a name="index-constraints_002c-_0040code_007basm_007d-3434"></a><a name="index-g_t_0040code_007basm_007d-constraints-3435"></a>
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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><span class="samp"><</span></samp>’ or ‘<samp><span class="samp">></span></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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<ul class="menu">
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<li><a accesskey="1" href="Simple-Constraints.html#Simple-Constraints">Simple Constraints</a>: Basic use of constraints.
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<li><a accesskey="2" href="Multi_002dAlternative.html#Multi_002dAlternative">Multi-Alternative</a>: When an insn has two alternative constraint-patterns.
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<li><a accesskey="3" href="Modifiers.html#Modifiers">Modifiers</a>: More precise control over effects of constraints.
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<li><a accesskey="4" href="Machine-Constraints.html#Machine-Constraints">Machine Constraints</a>: Special constraints for some particular machines.
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</ul>
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</body></html>
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