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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - clang generates illegal ARM STR opcode with FlexOffset"
href="http://llvm.org/bugs/show_bug.cgi?id=20323">20323</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>clang generates illegal ARM STR opcode with FlexOffset
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.4
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Other
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>max@duempel.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=12776" name="attach_12776" title="Demo program">attachment 12776</a> <a href="attachment.cgi?id=12776&action=edit" title="Demo program">[details]</a></span>
Demo program
Compile the attached program on an ARM (e.g. Raspberry Pi, Cubieboard) with:
clang++ -std=c++11 -O2 -S str_flexoffset.cpp
The resulting assembly file contains the following opcode:
str r2, [r2], #4
Some CPUs crash with SIGILL (e.g. Qualcomm QSD8250, Allwinner A20), while
others ignore the problem (e.g. Qualcomm MSM7200A, Allwinner A10, Exynos 4210).
Documentation on STR:
<a href="http://infocenter.arm.com/help/topic/com.arm.doc.dui0068b/Bcfihdhj.html#Chdjhhhe">http://infocenter.arm.com/help/topic/com.arm.doc.dui0068b/Bcfihdhj.html#Chdjhhhe</a>
"Rn must not be the same as Rd, if the instruction:
is pre-indexed with writeback (the ! suffix);
is post-indexed;
uses the T suffix;"
Here, Rn and Rd are the same, and the ", #4" is a post-indexed FlexOffset. This
combination is illegal.
I could observe this problem with clang 3.5 (Debian 1:3.5~svn211669-1), clang
3.4 (Android NDK r9d) and clang 3.0 (Debian 1:3.0-6.2).
Link to the original bug report: <a href="http://bugs.xcsoar.org/ticket/3356">http://bugs.xcsoar.org/ticket/3356</a></pre>
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