66 lines
2.8 KiB
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66 lines
2.8 KiB
HTML
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<title>i386-Bugs - Using as</title>
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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or any later version published by the Free Software Foundation;
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<p>
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<a name="i386_002dBugs"></a>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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<h4 class="subsection">9.13.13 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 <span class="samp">%st(3)</span> being updated to <span class="samp">%st - %st(3)</span> rather
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than the expected <span class="samp">%st(3) - %st</span>. 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 <span class="samp">%st</span> and the destination
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register is <span class="samp">%st(i)</span>.
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</body></html>
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