<html lang="en"> <head> <title>i386-Bugs - Using as</title> <meta http-equiv="Content-Type" content="text/html"> <meta name="description" content="Using as"> <meta name="generator" content="makeinfo 4.13"> <link title="Top" rel="start" href="index.html#Top"> <link rel="up" href="i386_002dDependent.html#i386_002dDependent" title="i386-Dependent"> <link rel="prev" href="i386_002dArch.html#i386_002dArch" title="i386-Arch"> <link rel="next" href="i386_002dNotes.html#i386_002dNotes" title="i386-Notes"> <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> <!-- This file documents the GNU Assembler "as". Copyright (C) 1991-2015 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. --> <meta http-equiv="Content-Style-Type" content="text/css"> <style type="text/css"><!-- pre.display { font-family:inherit } pre.format { font-family:inherit } pre.smalldisplay { font-family:inherit; font-size:smaller } pre.smallformat { font-family:inherit; font-size:smaller } pre.smallexample { font-size:smaller } pre.smalllisp { font-size:smaller } span.sc { font-variant:small-caps } span.roman { font-family:serif; font-weight:normal; } span.sansserif { font-family:sans-serif; font-weight:normal; } --></style> </head> <body> <div class="node"> <a name="i386-Bugs"></a> <a name="i386_002dBugs"></a> <p> Next: <a rel="next" accesskey="n" href="i386_002dNotes.html#i386_002dNotes">i386-Notes</a>, Previous: <a rel="previous" accesskey="p" href="i386_002dArch.html#i386_002dArch">i386-Arch</a>, Up: <a rel="up" accesskey="u" href="i386_002dDependent.html#i386_002dDependent">i386-Dependent</a> <hr> </div> <h4 class="subsection">9.15.16 AT&T Syntax bugs</h4> <p>The UnixWare assembler, and probably other AT&T derived ix86 Unix assemblers, generate floating point instructions with reversed source and destination registers in certain cases. Unfortunately, gcc and possibly many other programs use this reversed syntax, so we're stuck with it. <p>For example <pre class="smallexample"> fsub %st,%st(3) </pre> <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 than the expected ‘<samp><span class="samp">%st(3) - %st</span></samp>’. This happens with all the non-commutative arithmetic floating point operations with two register operands where the source register is ‘<samp><span class="samp">%st</span></samp>’ and the destination register is ‘<samp><span class="samp">%st(i)</span></samp>’. </body></html>