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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - Wrong code for saving registers on ARM" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D24331&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=fq2w5YOuqvLDi3kLrra-cww86PhPkBVshbjrBclaD1A&s=Xhbn9x5A_OHpazs0e7ieDCc4AVmb0JOW60jCqsmNDCw&e=">24331</a>
</td>
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<th>Summary</th>
<td>Wrong code for saving registers on ARM
</td>
</tr>
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<th>Product</th>
<td>libc++abi
</td>
</tr>
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<th>Version</th>
<td>3.7
</td>
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<th>Hardware</th>
<td>Other
</td>
</tr>
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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>All Bugs
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>manuel.freiberger@gmx.at
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu, mclow.lists@gmail.com
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Hello,
The function unw_getcontext() implemented in the file UnwindRegistersSave.S has
a wrong instruction in line 304:
stm r0!, {r0-r7}
As a write-back on R0 is used here, the offsets for the instructions in line
307-309 are wrong. The code should be changed to
stm r0, {r0-r7}
i.e. register R0 should not be modified, similar to the code in the lines
314--317.
I have tested this on a Cortex-M4. Before making the modification, backtraces
with libunwind were not working because the PC register was always zero when
unw_step() was called. After the modification everything was fine.
/Manuel
--- UnwindRegistersSave.S 2015-08-01 15:35:38.847465964 +0200
+++ UnwindRegistersSave.S_modified 2015-08-01 15:35:57.105379894 +0200
@@ -301,7 +301,7 @@
.p2align 2
DEFINE_LIBUNWIND_FUNCTION(unw_getcontext)
#if !defined(__ARM_ARCH_ISA_ARM)
- stm r0!, {r0-r7}
+ stm r0, {r0-r7}
mov r2, sp
mov r3, lr
str r2, [r0, #52]</pre>
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