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| <a name="AT_0026T-Syntax-bugs"></a> |
| <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> |
| <p>For example |
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| <div class="smallexample"> |
| <pre class="smallexample"> fsub %st,%st(3) |
| </pre></div> |
| <p>results in ‘<samp>%st(3)</samp>’ being updated to ‘<samp>%st - %st(3)</samp>’ rather |
| than the expected ‘<samp>%st(3) - %st</samp>’. This happens with all the |
| non-commutative arithmetic floating point operations with two register |
| operands where the source register is ‘<samp>%st</samp>’ and the destination |
| register is ‘<samp>%st(i)</samp>’. |
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