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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - baremetal DWARF leaves dso_base uninitialized"
href="https://bugs.llvm.org/show_bug.cgi?id=47335">47335</a>
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<th>Summary</th>
<td>baremetal DWARF leaves dso_base uninitialized
</td>
</tr>
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<th>Product</th>
<td>Runtime Libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>libunwind
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>rprichard@google.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>For a -DLIBUNWIND_IS_BAREMETAL=ON configuration that uses DWARF EH (rather than
ARM EHABI), the UnwindInfoSections::dso_base field is read, but never
initialized.
The uninitialized field is copied to unw_proc_info_t::extra, which is also
exposed via _Unwind_Find_FDE's dwarf_eh_bases::tbase field.
dso_base is also used as the key to DwarfFDECache (as the "mh" value -- "mach
header").
An obvious fix is to set dso_base to 0, but then the first
DwarfFDECache::findFDE call ("otherwise, search cache of previously found
FDEs.") will search the entire cache (whereas dynamically-registered are
expected to be searched in a later pass). We could change the full-search
sentinel value to ~0, or add a parameter instead of a sentinel value.
After I make unrelated changes, gcc (but not clang) is able to detect the
uninitialized field:
/x/llvm-upstream/llvm-project/libunwind/src/UnwindCursor.hpp: In member
function ‘void libunwind::UnwindCursor<A, R>::setInfoBasedOnIPRegister(bool)
[with A = libunwind::LocalAddressSpace; R = libunwind::Registers_x86_64]’:
/x/llvm-upstream/llvm-project/libunwind/src/UnwindCursor.hpp:1924:9: warning:
‘sects.libunwind::UnwindInfoSections::dso_base’ may be used uninitialized in
this function [-Wmaybe-uninitialized]
1924 | if (getInfoFromFdeCie(fdeInfo, cieInfo, pc, sects.dso_base))
| ^~</pre>
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