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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - PowerPC - bug in generation of @ha/@l pair for symbol+addend"
href="https://llvm.org/bugs/show_bug.cgi?id=28727">28727</a>
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<th>Summary</th>
<td>PowerPC - bug in generation of @ha/@l pair for symbol+addend
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>3.8
</td>
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<th>Hardware</th>
<td>Other
</td>
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<th>OS</th>
<td>Linux
</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>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>eric.schweitz@pgroup.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=16815" name="attach_16815" title="reduced bitcode file">attachment 16815</a> <a href="attachment.cgi?id=16815&action=edit" title="reduced bitcode file">[details]</a></span>
reduced bitcode file
When the attached example is assembled by llc, as in,
% llc -O2 -disable-ppc-vsx-fma-mutation reduced.bc -o buggy.s
We can look at the high-adjusted and low relocation notations in the assembly
and see that some of the pairings do not match. In this partial list,
addis 14, 2, z00cb@toc@ha
lwa 4, z00cb@toc@l+8(14)
stw 5, z00cb@toc@l+20(14)
lwz 5, z00cb@toc@l+20(14)
we see that the high adjusted value of z00cb has no addend, but there are
several low subsequent notations that do have addends (of 8 and 20). This has
resulted in some hard to diagnose, hard to reproduce failures on OpenPOWER.
We believe, after reviewing "Power Architecture 64-Bit ELF V2 ABI
Specification", that this code-gen pattern is simply incorrect. The linker
cannot correctly generate a high adjusted value near a 16-bit boundary without
also knowing and accounting for all used addend values. Some may wrap and some
may not. Specifically then, the @ha and @l notations must be exactly paired.</pre>
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