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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Removal of AArch64II::MO_CONSTPOOL breaks booting the FreeBSD kernel"
href="https://llvm.org/bugs/show_bug.cgi?id=30848">30848</a>
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<th>Summary</th>
<td>Removal of AArch64II::MO_CONSTPOOL breaks booting the FreeBSD kernel
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>3.9
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>FreeBSD
</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: AArch64
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>andrew@fubar.geek.nz
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<th>CC</th>
<td>dimitry@andric.com, emaste@freebsd.org, llvm-bugs@lists.llvm.org, rafael.espindola@gmail.com
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<th>Classification</th>
<td>Unclassified
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<div>
<pre>In r271311 AArch64II::MO_CONSTPOOL was removed as it produces the same
instruction sequence as with accessing via the got. There is a difference
between the two however within the FreeBSD kernel. This is built as a dynamic
ELF binary, but doesn't have a run time linker.
FreeBSD makes extensive use of linker set, where it may iterate over all
objects within a named section. For this it has an weak extern pointer to the
__start and __stop variables the linker generates. Moving from llvm 3.8 to 3.9
there is a change in behaviour with weak extern pointers where they now always
pass through the got, however there is no dynamic linker to perform the needed
relocation so these become a NULL pointer dereference.
I can work around this by returning AArch64II::MO_NO_FLAG from
AArch64Subtarget::ClassifyGlobalReference, however I don't know if this is a
correct fix.</pre>
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