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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [x86 disassembler] prefix ordering may ignores opsize and rep[n]e prefixes"
href="http://llvm.org/bugs/show_bug.cgi?id=19251">19251</a>
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<th>Summary</th>
<td>[x86 disassembler] prefix ordering may ignores opsize and rep[n]e prefixes
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>aaron@lintile.com
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>echo "0x66 0xF2 0xAF 0xF2 0x66 0xAF" | ./llvm-mc --disassemble
--triple=x86_64-linux-none
.text
scasl %es:(%rdi), %eax
repne
scasw %es:(%rdi), %ax
The first instruction decoding has the wrong operand size and ignores the repne
prefix. The second disassembly is what I would expect.
According to IDA (and a couple other disassemblers) they are equivalent.
seg000:00000000 66 F2 AF repne scasw
seg000:00000003 F2 66 AF repne scasw</pre>
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