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The SwitchStmt::FirstCase member is not initialized when the AST is
built by the ASTStmtReader. See the below code of
ASTStmtReader::VisitSwitchStmt in the case where the for loop does not
have any iterations:
// ... more code ...
SwitchCase *PrevSC = nullptr;
for (auto E = Record.size(); Record.getIdx() != E; ) {
SwitchCase *SC = Record.getSwitchCaseWithID(Record.readInt());
if (PrevSC)
PrevSC->setNextSwitchCase(SC);
else
S->setSwitchCaseList(SC); // Sets FirstCase !!!
PrevSC = SC;
}
} // return
Later, in ASTNodeImporter::VisitSwitchStmt,
we have a condition that depends on this uninited value:
for (SwitchCase *SC = S->getSwitchCaseList(); SC != nullptr;
SC = SC->getNextSwitchCase()) {
// ... more code ...
}
This is clearly an UB. This causes non-deterministic crashes when
ClangSA analyzes some code with CTU. See the below report by valgrind
(the whole valgrind output is attached):
==31019== Conditional jump or move depends on uninitialised value(s)
==31019== at 0x12ED1983:
clang::ASTNodeImporter::VisitSwitchStmt(clang::SwitchStmt*)
(ASTImporter.cpp:6195)
==31019== by 0x12F1D509: clang::StmtVisitorBase<std::add_pointer,
clang::ASTNodeImporter, llvm::Expected<clang::Stmt*>>::Visit(clang::Stmt*)
(StmtNodes.inc:591)
==31019== by 0x12EE4FDF: clang::ASTImporter::Import(clang::Stmt*)
(ASTImporter.cpp:8484)
==31019== by 0x12F09498: llvm::Expected<clang::Stmt*>
clang::ASTNodeImporter::import<clang::Stmt>(clang::Stmt*) (ASTImporter.cpp:164)
==31019== by 0x12F3A1F5: llvm::Error
clang::ASTNodeImporter::ImportArrayChecked<clang::Stmt**,
clang::Stmt**>(clang::Stmt**, clang::Stmt**, clang::Stmt**)
(ASTImporter.cpp:653)
==31019== by 0x12F13152: llvm::Error
clang::ASTNodeImporter::ImportContainerChecked<llvm::iterator_range<clang::Stmt**>,
llvm::SmallVector<clang::Stmt*, 8u> >(llvm::iterator_range<clang::Stmt**>
const&, llvm::SmallVector<clang::Stmt*, 8u>&) (ASTImporter.cpp:669)
==31019== by 0x12ED099F:
clang::ASTNodeImporter::VisitCompoundStmt(clang::CompoundStmt*)
(ASTImporter.cpp:6077)
==31019== by 0x12F1CC2D: clang::StmtVisitorBase<std::add_pointer,
clang::ASTNodeImporter, llvm::Expected<clang::Stmt*>>::Visit(clang::Stmt*)
(StmtNodes.inc:73)
==31019== by 0x12EE4FDF: clang::ASTImporter::Import(clang::Stmt*)
(ASTImporter.cpp:8484)
==31019== by 0x12F09498: llvm::Expected<clang::Stmt*>
clang::ASTNodeImporter::import<clang::Stmt>(clang::Stmt*) (ASTImporter.cpp:164)
==31019== by 0x12F13275: clang::Stmt*
clang::ASTNodeImporter::importChecked<clang::Stmt*>(llvm::Error&, clang::Stmt*
const&) (ASTImporter.cpp:197)
==31019== by 0x12ED0CE6:
clang::ASTNodeImporter::VisitCaseStmt(clang::CaseStmt*) (ASTImporter.cpp:6098)
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D97849
Files:
clang/include/clang/AST/Stmt.h
Index: clang/include/clang/AST/Stmt.h
===================================================================
--- clang/include/clang/AST/Stmt.h
+++ clang/include/clang/AST/Stmt.h
@@ -2119,7 +2119,7 @@
friend TrailingObjects;
/// Points to a linked list of case and default statements.
- SwitchCase *FirstCase;
+ SwitchCase *FirstCase = nullptr;
// SwitchStmt is followed by several trailing objects,
// some of which optional. Note that it would be more convenient to
Index: clang/include/clang/AST/Stmt.h
===================================================================
--- clang/include/clang/AST/Stmt.h
+++ clang/include/clang/AST/Stmt.h
@@ -2119,7 +2119,7 @@
friend TrailingObjects;
/// Points to a linked list of case and default statements.
- SwitchCase *FirstCase;
+ SwitchCase *FirstCase = nullptr;
// SwitchStmt is followed by several trailing objects,
// some of which optional. Note that it would be more convenient to
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