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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - ARM disassembler ignores negative offset bit for ldrht, ldrsht, strht, and ldrsbt"
href="http://llvm.org/bugs/show_bug.cgi?id=19362">19362</a>
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<th>Summary</th>
<td>ARM disassembler ignores negative offset bit for ldrht, ldrsht, strht, and ldrsbt
</td>
</tr>
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<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>3.4
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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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>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>dpmiller@cmu.edu
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Disassembling ldrht, ldrsht, strht, and ldrsbt with llvm-mc produces
instructions without the optional negative sign in front of the optional
offset. All offsets are disassembled as a positive offset, regardless of the
sign bit.
Code to reproduce:
$ echo "ldrht r1, [r2], -r3" | llvm-mc -arch=arm -show-inst
.text
ldrht r1, [r2], -r3 @ <MCInst #217 LDRHTr
@ <MCOperand Reg:67>
@ <MCOperand Reg:68>
@ <MCOperand Reg:68>
@ <MCOperand Reg:69>
@ <MCOperand Imm:0>
@ <MCOperand Imm:14>
@ <MCOperand Reg:0>>
Notice that the Imm is 0. Compare with the disassembly for ldrh in which bit 8
of the immediate is properly set:
$ echo "ldrh r1, [r2], -r3" | llvm-mc -arch=arm -show-inst
.text
ldrh r1, [r2], -r3 @ <MCInst #218 LDRH_POST
@ <MCOperand Reg:67>
@ <MCOperand Reg:68>
@ <MCOperand Reg:68>
@ <MCOperand Reg:69>
@ <MCOperand Imm:256>
@ <MCOperand Imm:14>
@ <MCOperand Reg:0>></pre>
</div>
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