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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - A null pointer dereference error in DWARFLinker::loadClangModule"
href="https://bugs.llvm.org/show_bug.cgi?id=48118">48118</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>A null pointer dereference error in DWARFLinker::loadClangModule
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Linker
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>alansnape3058@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>According to the bug reports of my clang static analyzer fork, in function
`DWARFLinker::loadClangModule`, the local variable `Unit` may not be
initialized and will trigger a null pointer dereference problem when
dereferencing it.
1. call function DWARFLinker::loadClangModule
llvm/lib/DWARFLinker/DWARFLinker.cpp
2012 Error DWARFLinker::loadClangModule(
2. create local variable std::unique_ptr<CompileUnit> Unit
llvm/lib/DWARFLinker/DWARFLinker.cpp
2033 std::unique_ptr<CompileUnit> Unit;
3. skip the initialization of Unit in the loop from 2035 to 2080
llvm/lib/DWARFLinker/DWARFLinker.cpp
2035 for (const auto &CU : ErrOrObj->Dwarf->compile_units()) {
2036 updateDwarfVersion(CU->getVersion());
2037 // Recursively get all modules imported by this one.
2038 auto CUDie = CU->getUnitDIE(false);
2039 if (!CUDie)
2040 continue;
2041 if (!registerModuleReference(
2042 CUDie, *CU, File, StringPool, UniquingStringPool, ODRContexts,
2043 ModulesEndOffset, UnitID, IsLittleEndian, Indent, Quiet)) {
2044 if (Unit) {
2045 std::string Err =
2046 (Filename +
2047 ": Clang modules are expected to have exactly 1 compile
unit.\n")
2048 .str();
2049 reportError(Err, File);
2050 return make_error<StringError>(Err, inconvertibleErrorCode());
2051 }
2052 // FIXME: Until PR27449
(<a href="https://llvm.org/bugs/show_bug.cgi?id=27449">https://llvm.org/bugs/show_bug.cgi?id=27449</a>) is
2053 // fixed in clang, only warn about DWO_id mismatches in verbose
mode.
2054 // ASTFileSignatures will change randomly when a module is rebuilt.
2055 uint64_t PCMDwoId = getDwoId(CUDie, *CU);
2056 if (PCMDwoId != DwoId) {
2057 if (!Quiet && Options.Verbose)
2058 reportWarning(
2059 Twine("hash mismatch: this object file was built against a "
2060 "different version of the module ") +
2061 Filename,
2062 File);
2063 // Update the cache entry with the DwoId of the module loaded from
disk.
2064 ClangModules[Filename] = PCMDwoId;
2065 }
2066
Assume the initialization of the variable `Unit` is not executed. {{{
2067 // Add this module.
2068 Unit = std::make_unique<CompileUnit>(*CU, UnitID++, !Options.NoODR,
2069 ModuleName);
}}}
2070 Unit->setHasInterestingContent();
2071 analyzeContextInfo(CUDie, 0, *Unit, &ODRContexts.getRoot(),
2072 UniquingStringPool, ODRContexts,
ModulesEndOffset,
2073 Options.ParseableSwiftInterfaces,
2074 [&](const Twine &Warning, const DWARFDie &DIE) {
2075 reportWarning(Warning, File, &DIE);
2076 });
2077 // Keep everything.
2078 Unit->markEverythingAsKept();
2079 }
2080 }
3. dereference on null smart pointer
llvm/lib/DWARFLinker/DWARFLinker.cpp
2081 if (!Unit->getOrigUnit().getUnitDIE().hasChildren())
Although the problem will not be triggered by the path presented, the problem
still worth noting.
See the HTML report for more details:
<a href="http://lcs.ios.ac.cn/~maxt/SPelton/reports/llvm/report-dc3dc4.html#EndPath">http://lcs.ios.ac.cn/~maxt/SPelton/reports/llvm/report-dc3dc4.html#EndPath</a></pre>
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