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| <h4 class="subsection">9.13.14 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>’. |
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