[clang] 4fca7b0 - [LifetimeSafety] Detect expiry of loans to trivially destructed types (#168855)
via cfe-commits
cfe-commits at lists.llvm.org
Fri Nov 21 05:21:26 PST 2025
Author: Kashika Akhouri
Date: 2025-11-21T18:51:21+05:30
New Revision: 4fca7b05e397e381466d6943a56f8407349c7594
URL: https://github.com/llvm/llvm-project/commit/4fca7b05e397e381466d6943a56f8407349c7594
DIFF: https://github.com/llvm/llvm-project/commit/4fca7b05e397e381466d6943a56f8407349c7594.diff
LOG: [LifetimeSafety] Detect expiry of loans to trivially destructed types (#168855)
Handling Trivially Destructed Types
This PR uses `AddLifetime` to handle expiry of loans to trivially
destructed types.
Example:
```cpp
int * trivial_uar(){
int *ptr;
int x = 1;
ptr = &x;
return ptr;
}
```
The CFG created now has an Expire Fact for trivially destructed types:
```
Function: trivial_uar
Block B2:
End of Block
Block B1:
Issue (0 (Path: x), ToOrigin: 0 (Expr: DeclRefExpr))
OriginFlow (Dest: 1 (Expr: UnaryOperator), Src: 0 (Expr: DeclRefExpr))
Use (2 (Decl: ptr), Write)
OriginFlow (Dest: 2 (Decl: ptr), Src: 1 (Expr: UnaryOperator))
Use (2 (Decl: ptr), Read)
OriginFlow (Dest: 3 (Expr: ImplicitCastExpr), Src: 2 (Decl: ptr))
Expire (0 (Path: x))
OriginEscapes (3 (Expr: ImplicitCastExpr))
End of Block
Block B0:
End of Block
```
This Expire Fact issues UAR and UAF warnings.
Fixes https://github.com/llvm/llvm-project/issues/162862
Added:
Modified:
clang/include/clang/Analysis/Analyses/LifetimeSafety/FactsGenerator.h
clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
clang/lib/Sema/AnalysisBasedWarnings.cpp
clang/test/Sema/warn-lifetime-safety-dataflow.cpp
clang/test/Sema/warn-lifetime-safety.cpp
clang/unittests/Analysis/LifetimeSafetyTest.cpp
Removed:
################################################################################
diff --git a/clang/include/clang/Analysis/Analyses/LifetimeSafety/FactsGenerator.h b/clang/include/clang/Analysis/Analyses/LifetimeSafety/FactsGenerator.h
index 8ea37259c570b..878cb90b685f9 100644
--- a/clang/include/clang/Analysis/Analyses/LifetimeSafety/FactsGenerator.h
+++ b/clang/include/clang/Analysis/Analyses/LifetimeSafety/FactsGenerator.h
@@ -50,7 +50,7 @@ class FactsGenerator : public ConstStmtVisitor<FactsGenerator> {
void VisitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *MTE);
private:
- void handleDestructor(const CFGAutomaticObjDtor &DtorOpt);
+ void handleLifetimeEnds(const CFGLifetimeEnds &LifetimeEnds);
void handleGSLPointerConstruction(const CXXConstructExpr *CCE);
diff --git a/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp b/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
index cb9a202b08968..f7be472ed15b5 100644
--- a/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
+++ b/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
@@ -63,9 +63,9 @@ void FactsGenerator::run() {
const CFGElement &Element = Block->Elements[I];
if (std::optional<CFGStmt> CS = Element.getAs<CFGStmt>())
Visit(CS->getStmt());
- else if (std::optional<CFGAutomaticObjDtor> DtorOpt =
- Element.getAs<CFGAutomaticObjDtor>())
- handleDestructor(*DtorOpt);
+ else if (std::optional<CFGLifetimeEnds> LifetimeEnds =
+ Element.getAs<CFGLifetimeEnds>())
+ handleLifetimeEnds(*LifetimeEnds);
}
CurrentBlockFacts.append(EscapesInCurrentBlock.begin(),
EscapesInCurrentBlock.end());
@@ -229,25 +229,19 @@ void FactsGenerator::VisitMaterializeTemporaryExpr(
killAndFlowOrigin(*MTE, *MTE->getSubExpr());
}
-void FactsGenerator::handleDestructor(const CFGAutomaticObjDtor &DtorOpt) {
- /// TODO: Also handle trivial destructors (e.g., for `int`
- /// variables) which will never have a CFGAutomaticObjDtor node.
+void FactsGenerator::handleLifetimeEnds(const CFGLifetimeEnds &LifetimeEnds) {
/// TODO: Handle loans to temporaries.
- /// TODO: Consider using clang::CFG::BuildOptions::AddLifetime to reuse the
- /// lifetime ends.
- const VarDecl *DestructedVD = DtorOpt.getVarDecl();
- if (!DestructedVD)
+ const VarDecl *LifetimeEndsVD = LifetimeEnds.getVarDecl();
+ if (!LifetimeEndsVD)
return;
// Iterate through all loans to see if any expire.
- /// TODO(opt): Do better than a linear search to find loans associated with
- /// 'DestructedVD'.
- for (const Loan &L : FactMgr.getLoanMgr().getLoans()) {
- const AccessPath &LoanPath = L.Path;
+ for (const auto &Loan : FactMgr.getLoanMgr().getLoans()) {
+ const AccessPath &LoanPath = Loan.Path;
// Check if the loan is for a stack variable and if that variable
// is the one being destructed.
- if (LoanPath.D == DestructedVD)
+ if (LoanPath.D == LifetimeEndsVD)
CurrentBlockFacts.push_back(FactMgr.createFact<ExpireFact>(
- L.ID, DtorOpt.getTriggerStmt()->getEndLoc()));
+ Loan.ID, LifetimeEnds.getTriggerStmt()->getEndLoc()));
}
}
diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 0fa75a24db4f3..43d2b9a829545 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -2992,6 +2992,9 @@ void clang::sema::AnalysisBasedWarnings::IssueWarnings(
bool EnableLifetimeSafetyAnalysis = S.getLangOpts().EnableLifetimeSafety;
+ if (EnableLifetimeSafetyAnalysis)
+ AC.getCFGBuildOptions().AddLifetime = true;
+
// Force that certain expressions appear as CFGElements in the CFG. This
// is used to speed up various analyses.
// FIXME: This isn't the right factoring. This is here for initial
diff --git a/clang/test/Sema/warn-lifetime-safety-dataflow.cpp b/clang/test/Sema/warn-lifetime-safety-dataflow.cpp
index 11d3b836db3e7..7b6fc9201af6d 100644
--- a/clang/test/Sema/warn-lifetime-safety-dataflow.cpp
+++ b/clang/test/Sema/warn-lifetime-safety-dataflow.cpp
@@ -59,6 +59,7 @@ int return_int_val() {
int x = 10;
// CHECK: Block B{{[0-9]+}}:
// CHECK: Issue ([[L_X:[0-9]+]] (Path: x), ToOrigin: {{[0-9]+}} (Expr: DeclRefExpr))
+// CHECK: Expire ([[L_X:[0-9]+]] (Path: x))
return x;
}
// CHECK-NEXT: End of Block
@@ -77,7 +78,6 @@ void loan_expires_cpp() {
}
-// FIXME: No expire for Trivial Destructors
// CHECK-LABEL: Function: loan_expires_trivial
void loan_expires_trivial() {
int trivial_obj = 1;
@@ -86,11 +86,29 @@ void loan_expires_trivial() {
// CHECK: OriginFlow (Dest: [[O_ADDR_TRIVIAL_OBJ:[0-9]+]] (Expr: UnaryOperator), Src: [[O_DRE_TRIVIAL]] (Expr: DeclRefExpr))
int* pTrivialObj = &trivial_obj;
// CHECK: OriginFlow (Dest: {{[0-9]+}} (Decl: pTrivialObj), Src: [[O_ADDR_TRIVIAL_OBJ]] (Expr: UnaryOperator))
-// CHECK-NOT: Expire
+// CHECK: Expire ([[L_TRIVIAL_OBJ:[0-9]+]] (Path: trivial_obj))
// CHECK-NEXT: End of Block
- // FIXME: Add check for Expire once trivial destructors are handled for expiration.
}
+// Trivial Destructors
+// CHECK-LABEL: Function: return_int_pointer
+int* return_int_pointer() {
+ int* ptr;
+// CHECK: Block B{{[0-9]+}}:
+ int x = 1;
+// CHECK: Issue ([[L_X:[0-9]+]] (Path: x), ToOrigin: [[O_DRE_X:[0-9]+]] (Expr: DeclRefExpr))
+// CHECK: OriginFlow (Dest: [[O_ADDR_X:[0-9]+]] (Expr: UnaryOperator), Src: [[O_DRE_X]] (Expr: DeclRefExpr))
+ ptr = &x;
+// CHECK: Use ([[O_PTR:[0-9]+]] (Decl: ptr), Write)
+// CHECK: OriginFlow (Dest: [[O_PTR]] (Decl: ptr), Src: [[O_ADDR_X]] (Expr: UnaryOperator))
+// CHECK: Use ([[O_PTR]] (Decl: ptr), Read)
+// CHECK: OriginFlow (Dest: [[O_RET_VAL:[0-9]+]] (Expr: ImplicitCastExpr), Src: [[O_PTR]] (Decl: ptr))
+// CHECK: Expire ([[L_X]] (Path: x))
+// CHECK: OriginEscapes ([[O_RET_VAL]] (Expr: ImplicitCastExpr))
+ return ptr;
+}
+// CHECK-NEXT: End of Block
+
// CHECK-LABEL: Function: conditional
void conditional(bool condition) {
int a = 5;
diff --git a/clang/test/Sema/warn-lifetime-safety.cpp b/clang/test/Sema/warn-lifetime-safety.cpp
index 2803e73b5aee2..e80a05860389c 100644
--- a/clang/test/Sema/warn-lifetime-safety.cpp
+++ b/clang/test/Sema/warn-lifetime-safety.cpp
@@ -12,6 +12,10 @@ struct [[gsl::Pointer()]] View {
void use() const;
};
+class TriviallyDestructedClass {
+ View a, b;
+};
+
//===----------------------------------------------------------------------===//
// Basic Definite Use-After-Free (-W...permissive)
// These are cases where the pointer is guaranteed to be dangling at the use site.
@@ -396,6 +400,24 @@ void loan_from_previous_iteration(MyObj safe, bool condition) {
} // expected-note {{destroyed here}}
}
+void trivial_int_uaf() {
+ int * a;
+ {
+ int b = 1;
+ a = &b; // expected-warning {{object whose reference is captured does not live long enough}}
+ } // expected-note {{destroyed here}}
+ (void)*a; // expected-note {{later used here}}
+}
+
+void trivial_class_uaf() {
+ TriviallyDestructedClass* ptr;
+ {
+ TriviallyDestructedClass s;
+ ptr = &s; // expected-warning {{object whose reference is captured does not live long enough}}
+ } // expected-note {{destroyed here}}
+ (void)ptr; // expected-note {{later used here}}
+}
+
//===----------------------------------------------------------------------===//
// Basic Definite Use-After-Return (Return-Stack-Address) (-W...permissive)
// These are cases where the pointer is guaranteed to be dangling at the use site.
@@ -493,6 +515,43 @@ MyObj& reference_return_of_local() {
// expected-note at -1 {{returned here}}
}
+int* trivial_int_uar() {
+ int *a;
+ int b = 1;
+ a = &b; // expected-warning {{address of stack memory is returned later}}
+ return a; // expected-note {{returned here}}
+}
+
+TriviallyDestructedClass* trivial_class_uar () {
+ TriviallyDestructedClass *ptr;
+ TriviallyDestructedClass s;
+ ptr = &s; // expected-warning {{address of stack memory is returned later}}
+ return ptr; // expected-note {{returned here}}
+}
+
+// FIXME: No lifetime warning for this as no expire facts are generated for parameters
+const int& return_parameter(int a) {
+ return a;
+}
+
+// FIXME: No lifetime warning for this as no expire facts are generated for parameters
+int* return_pointer_to_parameter(int a) {
+ return &a;
+}
+
+const int& return_reference_to_parameter(int a)
+{
+ const int &b = a;
+ return b; // expected-warning {{address of stack memory is returned later}}
+ // expected-note at -1 {{returned here}}
+}
+
+const int& get_ref_to_local() {
+ int a = 42;
+ return a; // expected-warning {{address of stack memory is returned later}}
+ // expected-note at -1 {{returned here}}
+}
+
//===----------------------------------------------------------------------===//
// Use-After-Scope & Use-After-Return (Return-Stack-Address) Combined
// These are cases where the diagnostic kind is determined by location
@@ -688,7 +747,8 @@ void lifetimebound_partial_safety(bool cond) {
v.use(); // expected-note {{later used here}}
}
-// FIXME: Creating reference from lifetimebound call doesn't propagate loans.
+// FIXME: Warning should be on the 'GetObject' call, not the assignment to 'ptr'.
+// The loan from the lifetimebound argument is not propagated to the call expression itself.
const MyObj& GetObject(View v [[clang::lifetimebound]]);
void lifetimebound_return_reference() {
View v;
@@ -697,9 +757,9 @@ void lifetimebound_return_reference() {
MyObj obj;
View temp_v = obj;
const MyObj& ref = GetObject(temp_v);
- ptr = &ref;
- }
- (void)*ptr;
+ ptr = &ref; // expected-warning {{object whose reference is captured does not live long enough}}
+ } // expected-note {{destroyed here}}
+ (void)*ptr; // expected-note {{later used here}}
}
// FIXME: No warning for non gsl::Pointer types. Origin tracking is only supported for pointer types.
diff --git a/clang/unittests/Analysis/LifetimeSafetyTest.cpp b/clang/unittests/Analysis/LifetimeSafetyTest.cpp
index 558a22af72572..a895475013c98 100644
--- a/clang/unittests/Analysis/LifetimeSafetyTest.cpp
+++ b/clang/unittests/Analysis/LifetimeSafetyTest.cpp
@@ -59,6 +59,7 @@ class LifetimeTestRunner {
BuildOptions.setAllAlwaysAdd();
BuildOptions.AddImplicitDtors = true;
BuildOptions.AddTemporaryDtors = true;
+ BuildOptions.AddLifetime = true;
// Run the main analysis.
Analysis = std::make_unique<LifetimeSafetyAnalysis>(*AnalysisCtx, nullptr);
@@ -1307,6 +1308,42 @@ TEST_F(LifetimeAnalysisTest, LivenessOutsideLoop) {
EXPECT_THAT(Origins({"p"}), MaybeLiveAt("p1"));
}
+TEST_F(LifetimeAnalysisTest, TrivialDestructorsUAF) {
+ SetupTest(R"(
+ void target() {
+ int *ptr;
+ {
+ int s = 1;
+ ptr = &s;
+ }
+ POINT(p1);
+ (void)*ptr;
+ }
+ )");
+ EXPECT_THAT(Origin("ptr"), HasLoansTo({"s"}, "p1"));
+ EXPECT_THAT(Origins({"ptr"}), MustBeLiveAt("p1"));
+}
+
+TEST_F(LifetimeAnalysisTest, TrivialClassDestructorsUAF) {
+ SetupTest(R"(
+ class S {
+ View a, b;
+ };
+
+ void target() {
+ S* ptr;
+ {
+ S s;
+ ptr = &s;
+ }
+ POINT(p1);
+ (void)ptr;
+ }
+ )");
+ EXPECT_THAT(Origin("ptr"), HasLoansTo({"s"}, "p1"));
+ EXPECT_THAT(Origins({"ptr"}), MustBeLiveAt("p1"));
+}
+
TEST_F(LifetimeAnalysisTest, SimpleReturnStackAddress) {
SetupTest(R"(
MyObj* target() {
@@ -1506,5 +1543,34 @@ TEST_F(LifetimeAnalysisTest, ReturnBeforeUseAfterScope) {
EXPECT_THAT(Origins({"p"}), MustBeLiveAt("p1"));
}
+TEST_F(LifetimeAnalysisTest, TrivialDestructorsUAR) {
+ SetupTest(R"(
+ int* target() {
+ int s = 10;
+ int* p = &s;
+ POINT(p1);
+ return p;
+ }
+ )");
+ EXPECT_THAT("s", HasLiveLoanAtExpiry("p1"));
+}
+
+TEST_F(LifetimeAnalysisTest, TrivialClassDestructorsUAR) {
+ SetupTest(R"(
+ class S {
+ View a, b;
+ };
+
+ S* target() {
+ S *ptr;
+ S s;
+ ptr = &s;
+ POINT(p1);
+ return ptr;
+ }
+ )");
+ EXPECT_THAT("s", HasLiveLoanAtExpiry("p1"));
+}
+
} // anonymous namespace
} // namespace clang::lifetimes::internal
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