69 lines
3.0 KiB
HTML
69 lines
3.0 KiB
HTML
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<html lang="en">
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<head>
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<title>i386-Bugs - Using as</title>
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<meta name="description" content="Using as">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="i386_002dDependent.html#i386_002dDependent" title="i386-Dependent">
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<link rel="prev" href="i386_002dArch.html#i386_002dArch" title="i386-Arch">
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<link rel="next" href="i386_002dNotes.html#i386_002dNotes" title="i386-Notes">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991-2019 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
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled ``GNU Free Documentation License''.
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</head>
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<body>
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<div class="node">
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<a name="i386-Bugs"></a>
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<a name="i386_002dBugs"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="i386_002dNotes.html#i386_002dNotes">i386-Notes</a>,
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Previous: <a rel="previous" accesskey="p" href="i386_002dArch.html#i386_002dArch">i386-Arch</a>,
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Up: <a rel="up" accesskey="u" href="i386_002dDependent.html#i386_002dDependent">i386-Dependent</a>
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<hr>
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</div>
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<h4 class="subsection">9.16.16 AT&T Syntax bugs</h4>
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<p>The UnixWare assembler, and probably other AT&T derived ix86 Unix
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assemblers, generate floating point instructions with reversed source
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and destination registers in certain cases. Unfortunately, gcc and
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possibly many other programs use this reversed syntax, so we're stuck
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with it.
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<p>For example
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<pre class="smallexample"> fsub %st,%st(3)
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</pre>
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<p class="noindent">results in ‘<samp><span class="samp">%st(3)</span></samp>’ being updated to ‘<samp><span class="samp">%st - %st(3)</span></samp>’ rather
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than the expected ‘<samp><span class="samp">%st(3) - %st</span></samp>’. This happens with all the
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non-commutative arithmetic floating point operations with two register
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operands where the source register is ‘<samp><span class="samp">%st</span></samp>’ and the destination
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register is ‘<samp><span class="samp">%st(i)</span></samp>’.
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</body></html>
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