[webkit.UncountedLambdaCapturesChecker] Ignore trivial functions and [[clang::noescape]]. #114374
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…[[clang::noescape]]. This PR makes webkit.UncountedLambdaCapturesChecker ignore trivial functions as well as the one being passed to an argument with [[clang::noescape]] attribute. This dramatically reduces the false positive rate for this checker. To do this, this PR replaces VisitLambdaExpr in favor of checking lambdas via VisitDeclRefExpr and VisitCallExpr. The idea is that if a lambda is defined but never called or stored somewhere, then capturing whatever variable in such a lambda is harmless. VisitCallExpr explicitly looks for direct invocation of lambdas and registers its DeclRefExpr to be ignored in VisitDeclRefExpr. If a lambda is being passed to a function, it checks whether its argument is annotated with [[clang::noescape]]. If it's not annotated such, it checks captures for their safety. Because WTF::switchOn could not be annotated with [[clang::noescape]] as function type parameters are variadic template function so we hard-code this function into the checker. In order to check whether "this" pointer is ref-counted type or not, we override TraverseDecl and record the most recent method's declaration. In addition, this PR fixes a bug in isUnsafePtr that it was erroneously checking whether std::nullopt was returned by isUncounted and isUnchecked as opposed to the actual boolean value. Finally, this PR also converts the accompanying test to use -verify and adds a bunch of tests.
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@llvm/pr-subscribers-clang @llvm/pr-subscribers-clang-static-analyzer-1 Author: Ryosuke Niwa (rniwa) ChangesThis PR makes webkit.UncountedLambdaCapturesChecker ignore trivial functions as well as the one being passed to an argument with [[clang::noescape]] attribute. This dramatically reduces the false positive rate for this checker. To do this, this PR replaces VisitLambdaExpr in favor of checking lambdas via VisitDeclRefExpr and VisitCallExpr. The idea is that if a lambda is defined but never called or stored somewhere, then capturing whatever variable in such a lambda is harmless. VisitCallExpr explicitly looks for direct invocation of lambdas and registers its DeclRefExpr to be ignored in VisitDeclRefExpr. If a lambda is being passed to a function, it checks whether its argument is annotated with [[clang::noescape]]. If it's not annotated such, it checks captures for their safety. Because WTF::switchOn could not be annotated with [[clang::noescape]] as function type parameters are variadic template function so we hard-code this function into the checker. In order to check whether "this" pointer is ref-counted type or not, we override TraverseDecl and record the most recent method's declaration. In addition, this PR fixes a bug in isUnsafePtr that it was erroneously checking whether std::nullopt was returned by isUncounted and isUnchecked as opposed to the actual boolean value. Finally, this PR also converts the accompanying test to use -verify and adds a bunch of tests. Full diff: https://github.com/llvm/llvm-project/pull/114374.diff 5 Files Affected:
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
index 2293dcf1d4bd64..2ef93b2855e237 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
@@ -203,7 +203,13 @@ std::optional<bool> isUncountedPtr(const QualType T) {
std::optional<bool> isUnsafePtr(const QualType T) {
if (T->isPointerType() || T->isReferenceType()) {
if (auto *CXXRD = T->getPointeeCXXRecordDecl()) {
- return isUncounted(CXXRD) || isUnchecked(CXXRD);
+ auto isUncountedPtr = isUncounted(CXXRD);
+ auto isUncheckedPtr = isUnchecked(CXXRD);
+ if (isUncountedPtr && isUncheckedPtr)
+ return *isUncountedPtr || *isUncheckedPtr;
+ if (isUncountedPtr)
+ return *isUncountedPtr;
+ return isUncheckedPtr;
}
}
return false;
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.h b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.h
index 4b41ca96e1df1d..814015c311d61e 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.h
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.h
@@ -63,6 +63,10 @@ std::optional<bool> isUncounted(const clang::CXXRecordDecl* Class);
/// class, false if not, std::nullopt if inconclusive.
std::optional<bool> isUncountedPtr(const clang::QualType T);
+/// \returns true if \p T is either a raw pointer or reference to an uncounted
+/// or unchecked class, false if not, std::nullopt if inconclusive.
+std::optional<bool> isUnsafePtr(const QualType T);
+
/// \returns true if \p T is a RefPtr, Ref, CheckedPtr, CheckedRef, or its
/// variant, false if not.
bool isSafePtrType(const clang::QualType T);
diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp
index 998bd4ccee07db..021d00f3ec579a 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLambdaCapturesChecker.cpp
@@ -6,6 +6,7 @@
//
//===----------------------------------------------------------------------===//
+#include "ASTUtils.h"
#include "DiagOutputUtils.h"
#include "PtrTypesSemantics.h"
#include "clang/AST/CXXInheritance.h"
@@ -26,6 +27,7 @@ class UncountedLambdaCapturesChecker
BugType Bug{this, "Lambda capture of uncounted variable",
"WebKit coding guidelines"};
mutable BugReporter *BR = nullptr;
+ TrivialFunctionAnalysis TFA;
public:
void checkASTDecl(const TranslationUnitDecl *TUD, AnalysisManager &MGR,
@@ -37,6 +39,11 @@ class UncountedLambdaCapturesChecker
// want to visit those, so we make our own RecursiveASTVisitor.
struct LocalVisitor : public RecursiveASTVisitor<LocalVisitor> {
const UncountedLambdaCapturesChecker *Checker;
+ llvm::DenseSet<const DeclRefExpr *> DeclRefExprsToIgnore;
+ QualType ClsType;
+
+ using Base = RecursiveASTVisitor<LocalVisitor>;
+
explicit LocalVisitor(const UncountedLambdaCapturesChecker *Checker)
: Checker(Checker) {
assert(Checker);
@@ -45,32 +52,117 @@ class UncountedLambdaCapturesChecker
bool shouldVisitTemplateInstantiations() const { return true; }
bool shouldVisitImplicitCode() const { return false; }
- bool VisitLambdaExpr(LambdaExpr *L) {
- Checker->visitLambdaExpr(L);
+ bool TraverseDecl(Decl *D) {
+ if (auto *CXXMD = dyn_cast<CXXMethodDecl>(D)) {
+ llvm::SaveAndRestore SavedDecl(ClsType);
+ ClsType = CXXMD->getThisType();
+ return Base::TraverseDecl(D);
+ }
+ return Base::TraverseDecl(D);
+ }
+
+ bool shouldCheckThis() {
+ auto result = !ClsType.isNull() ? isUnsafePtr(ClsType) : std::nullopt;
+ return result && *result;
+ }
+
+ bool VisitDeclRefExpr(DeclRefExpr *DRE) {
+ if (DeclRefExprsToIgnore.contains(DRE))
+ return true;
+ auto *VD = dyn_cast_or_null<VarDecl>(DRE->getDecl());
+ if (!VD)
+ return true;
+ auto *Init = VD->getInit()->IgnoreParenCasts();
+ auto *L = dyn_cast_or_null<LambdaExpr>(Init);
+ if (!L)
+ return true;
+ Checker->visitLambdaExpr(L, shouldCheckThis());
+ return true;
+ }
+
+ // WTF::switchOn(T, F... f) is a variadic template function and couldn't
+ // be annotated with NOESCAPE. We hard code it here to workaround that.
+ bool shouldTreatAllArgAsNoEscape(FunctionDecl *Decl) {
+ auto *NsDecl = Decl->getParent();
+ if (!NsDecl || !isa<NamespaceDecl>(NsDecl))
+ return false;
+ return safeGetName(NsDecl) == "WTF" && safeGetName(Decl) == "switchOn";
+ }
+
+ bool VisitCallExpr(CallExpr *CE) {
+ checkCalleeLambda(CE);
+ if (auto *Callee = CE->getDirectCallee()) {
+ bool TreatAllArgsAsNoEscape = shouldTreatAllArgAsNoEscape(Callee);
+ unsigned ArgIndex = 0;
+ for (auto *Param : Callee->parameters()) {
+ if (ArgIndex >= CE->getNumArgs())
+ break;
+ auto *Arg = CE->getArg(ArgIndex)->IgnoreParenCasts();
+ if (!Param->hasAttr<NoEscapeAttr>() && !TreatAllArgsAsNoEscape) {
+ if (auto *L = dyn_cast_or_null<LambdaExpr>(Arg)) {
+ Checker->visitLambdaExpr(L, shouldCheckThis());
+ }
+ }
+ ++ArgIndex;
+ }
+ }
return true;
}
+
+ void checkCalleeLambda(CallExpr *CE) {
+ auto *Callee = CE->getCallee();
+ if (!Callee)
+ return;
+ auto *DRE = dyn_cast<DeclRefExpr>(Callee->IgnoreParenCasts());
+ if (!DRE)
+ return;
+ auto *MD = dyn_cast_or_null<CXXMethodDecl>(DRE->getDecl());
+ if (!MD || CE->getNumArgs() != 1)
+ return;
+ auto *Arg = CE->getArg(0)->IgnoreParenCasts();
+ auto *ArgRef = dyn_cast<DeclRefExpr>(Arg);
+ if (!ArgRef)
+ return;
+ auto *VD = dyn_cast_or_null<VarDecl>(ArgRef->getDecl());
+ if (!VD)
+ return;
+ auto *Init = VD->getInit()->IgnoreParenCasts();
+ auto *L = dyn_cast_or_null<LambdaExpr>(Init);
+ if (!L)
+ return;
+ DeclRefExprsToIgnore.insert(ArgRef);
+ Checker->visitLambdaExpr(L, shouldCheckThis(),
+ /* ignoreParamVarDecl */ true);
+ }
};
LocalVisitor visitor(this);
visitor.TraverseDecl(const_cast<TranslationUnitDecl *>(TUD));
}
- void visitLambdaExpr(LambdaExpr *L) const {
+ void visitLambdaExpr(LambdaExpr *L, bool shouldCheckThis,
+ bool ignoreParamVarDecl = false) const {
+ if (TFA.isTrivial(L->getBody()))
+ return;
for (const LambdaCapture &C : L->captures()) {
if (C.capturesVariable()) {
ValueDecl *CapturedVar = C.getCapturedVar();
+ if (ignoreParamVarDecl && isa<ParmVarDecl>(CapturedVar))
+ continue;
QualType CapturedVarQualType = CapturedVar->getType();
- if (auto *CapturedVarType = CapturedVarQualType.getTypePtrOrNull()) {
- auto IsUncountedPtr = isUncountedPtr(CapturedVarQualType);
- if (IsUncountedPtr && *IsUncountedPtr)
- reportBug(C, CapturedVar, CapturedVarType);
- }
+ auto IsUncountedPtr = isUnsafePtr(CapturedVar->getType());
+ if (IsUncountedPtr && *IsUncountedPtr)
+ reportBug(C, CapturedVar, CapturedVarQualType);
+ } else if (C.capturesThis() && shouldCheckThis) {
+ if (ignoreParamVarDecl) // this is always a parameter to this function.
+ continue;
+ reportBugOnThisPtr(C);
}
}
}
void reportBug(const LambdaCapture &Capture, ValueDecl *CapturedVar,
- const Type *T) const {
+ const QualType T) const {
assert(CapturedVar);
SmallString<100> Buf;
@@ -89,7 +181,25 @@ class UncountedLambdaCapturesChecker
}
printQuotedQualifiedName(Os, Capture.getCapturedVar());
- Os << " to uncounted type is unsafe.";
+ Os << " to ref-counted / CheckedPtr capable type is unsafe.";
+
+ PathDiagnosticLocation BSLoc(Capture.getLocation(), BR->getSourceManager());
+ auto Report = std::make_unique<BasicBugReport>(Bug, Os.str(), BSLoc);
+ BR->emitReport(std::move(Report));
+ }
+
+ void reportBugOnThisPtr(const LambdaCapture &Capture) const {
+ SmallString<100> Buf;
+ llvm::raw_svector_ostream Os(Buf);
+
+ if (Capture.isExplicit()) {
+ Os << "Captured ";
+ } else {
+ Os << "Implicitly captured ";
+ }
+
+ Os << "raw-pointer 'this' to ref-counted / CheckedPtr capable type is "
+ "unsafe.";
PathDiagnosticLocation BSLoc(Capture.getLocation(), BR->getSourceManager());
auto Report = std::make_unique<BasicBugReport>(Bug, Os.str(), BSLoc);
diff --git a/clang/test/Analysis/Checkers/WebKit/mock-types.h b/clang/test/Analysis/Checkers/WebKit/mock-types.h
index 82c79c97a83de6..30ea7839a223d9 100644
--- a/clang/test/Analysis/Checkers/WebKit/mock-types.h
+++ b/clang/test/Analysis/Checkers/WebKit/mock-types.h
@@ -135,7 +135,9 @@ struct RefCountable {
void ref() {}
void deref() {}
void method();
+ void constMethod() const;
int trivial() { return 123; }
+ RefCountable* next();
};
template <typename T> T *downcast(T *t) { return t; }
diff --git a/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp b/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp
index 27e0a74d583cd3..5d6941aee71aec 100644
--- a/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp
+++ b/clang/test/Analysis/Checkers/WebKit/uncounted-lambda-captures.cpp
@@ -1,39 +1,73 @@
-// RUN: %clang_analyze_cc1 -analyzer-checker=webkit.UncountedLambdaCapturesChecker %s 2>&1 | FileCheck %s --strict-whitespace
-#include "mock-types.h"
+// RUN: %clang_analyze_cc1 -analyzer-checker=webkit.UncountedLambdaCapturesChecker -verify %s
+//#include "mock-types.h"
+
+struct RefCountable {
+// static Ref<RefCountable> create();
+ void ref() {}
+ void deref() {}
+ void method();
+ void constMethod() const;
+ int trivial() { return 123; }
+ RefCountable* next();
+};
+
+RefCountable* make_obj();
+
+void someFunction();
+template <typename Callback> void call(Callback callback) {
+ someFunction();
+ callback();
+}
void raw_ptr() {
- RefCountable* ref_countable = nullptr;
- auto foo1 = [ref_countable](){};
- // CHECK: warning: Captured raw-pointer 'ref_countable' to uncounted type is unsafe [webkit.UncountedLambdaCapturesChecker]
- // CHECK-NEXT:{{^ 6 | }} auto foo1 = [ref_countable](){};
- // CHECK-NEXT:{{^ | }} ^
- auto foo2 = [&ref_countable](){};
- // CHECK: warning: Captured raw-pointer 'ref_countable' to uncounted type is unsafe [webkit.UncountedLambdaCapturesChecker]
- auto foo3 = [&](){ ref_countable = nullptr; };
- // CHECK: warning: Implicitly captured raw-pointer 'ref_countable' to uncounted type is unsafe [webkit.UncountedLambdaCapturesChecker]
- // CHECK-NEXT:{{^ 12 | }} auto foo3 = [&](){ ref_countable = nullptr; };
- // CHECK-NEXT:{{^ | }} ^
- auto foo4 = [=](){ (void) ref_countable; };
- // CHECK: warning: Implicitly captured raw-pointer 'ref_countable' to uncounted type is unsafe [webkit.UncountedLambdaCapturesChecker]
+ RefCountable* ref_countable = make_obj();
+ auto foo1 = [ref_countable](){
+ // expected-warning@-1{{Captured raw-pointer 'ref_countable' to ref-counted / CheckedPtr capable type is unsafe [webkit.UncountedLambdaCapturesChecker]}}
+ ref_countable->method();
+ };
+ auto foo2 = [&ref_countable](){
+ // expected-warning@-1{{Captured raw-pointer 'ref_countable' to ref-counted / CheckedPtr capable type is unsafe [webkit.UncountedLambdaCapturesChecker]}}
+ ref_countable->method();
+ };
+ auto foo3 = [&](){
+ ref_countable->method();
+ // expected-warning@-1{{Implicitly captured raw-pointer 'ref_countable' to ref-counted / CheckedPtr capable type is unsafe [webkit.UncountedLambdaCapturesChecker]}}
+ ref_countable = nullptr;
+ };
+
+ auto foo4 = [=](){
+ ref_countable->method();
+ // expected-warning@-1{{Implicitly captured raw-pointer 'ref_countable' to ref-counted / CheckedPtr capable type is unsafe [webkit.UncountedLambdaCapturesChecker]}}
+ };
+
+ call(foo1);
+ call(foo2);
+ call(foo3);
+ call(foo4);
// Confirm that the checker respects [[clang::suppress]].
RefCountable* suppressed_ref_countable = nullptr;
[[clang::suppress]] auto foo5 = [suppressed_ref_countable](){};
- // CHECK-NOT: warning: Captured raw-pointer 'suppressed_ref_countable' to uncounted type is unsafe [webkit.UncountedLambdaCapturesChecker]
+ // no warning.
+ call(foo5);
}
void references() {
RefCountable automatic;
RefCountable& ref_countable_ref = automatic;
+ auto foo1 = [ref_countable_ref](){ ref_countable_ref.constMethod(); };
+ // expected-warning@-1{{Captured reference 'ref_countable_ref' to ref-counted / CheckedPtr capable type is unsafe [webkit.UncountedLambdaCapturesChecker]}}
+ auto foo2 = [&ref_countable_ref](){ ref_countable_ref.method(); };
+ // expected-warning@-1{{Captured reference 'ref_countable_ref' to ref-counted / CheckedPtr capable type is unsafe [webkit.UncountedLambdaCapturesChecker]}}
+ auto foo3 = [&](){ ref_countable_ref.method(); };
+ // expected-warning@-1{{Implicitly captured reference 'ref_countable_ref' to ref-counted / CheckedPtr capable type is unsafe [webkit.UncountedLambdaCapturesChecker]}}
+ auto foo4 = [=](){ ref_countable_ref.constMethod(); };
+ // expected-warning@-1{{Implicitly captured reference 'ref_countable_ref' to ref-counted / CheckedPtr capable type is unsafe [webkit.UncountedLambdaCapturesChecker]}}
- auto foo1 = [ref_countable_ref](){};
- // CHECK: warning: Captured reference 'ref_countable_ref' to uncounted type is unsafe [webkit.UncountedLambdaCapturesChecker]
- auto foo2 = [&ref_countable_ref](){};
- // CHECK: warning: Captured reference 'ref_countable_ref' to uncounted type is unsafe [webkit.UncountedLambdaCapturesChecker]
- auto foo3 = [&](){ (void) ref_countable_ref; };
- // CHECK: warning: Implicitly captured reference 'ref_countable_ref' to uncounted type is unsafe [webkit.UncountedLambdaCapturesChecker]
- auto foo4 = [=](){ (void) ref_countable_ref; };
- // CHECK: warning: Implicitly captured reference 'ref_countable_ref' to uncounted type is unsafe [webkit.UncountedLambdaCapturesChecker]
+ call(foo1);
+ call(foo2);
+ call(foo3);
+ call(foo4);
}
void quiet() {
@@ -45,5 +79,100 @@ void quiet() {
auto foo3 = [&]() {};
auto foo4 = [=]() {};
+
+ call(foo3);
+ call(foo4);
+
RefCountable *ref_countable = nullptr;
}
+
+template <typename Callback>
+void map(RefCountable* start, [[clang::noescape]] Callback&& callback)
+{
+ while (start) {
+ callback(*start);
+ start = start->next();
+ }
+}
+
+template <typename Callback1, typename Callback2>
+void doubleMap(RefCountable* start, [[clang::noescape]] Callback1&& callback1, Callback2&& callback2)
+{
+ while (start) {
+ callback1(*start);
+ callback2(*start);
+ start = start->next();
+ }
+}
+
+void noescape_lambda() {
+ RefCountable* someObj = make_obj();
+ RefCountable* otherObj = make_obj();
+ map(make_obj(), [&](RefCountable& obj) {
+ otherObj->method();
+ });
+ doubleMap(make_obj(), [&](RefCountable& obj) {
+ otherObj->method();
+ }, [&](RefCountable& obj) {
+ otherObj->method();
+ // expected-warning@-1{{Implicitly captured raw-pointer 'otherObj' to ref-counted / CheckedPtr capable type is unsafe [webkit.UncountedLambdaCapturesChecker]}}
+ });
+ ([&] {
+ someObj->method();
+ })();
+}
+
+void lambda_capture_param(RefCountable* obj) {
+ auto someLambda = [&] {
+ obj->method();
+ };
+ someLambda();
+ someLambda();
+}
+
+struct RefCountableWithLambdaCapturingThis {
+ void ref() const;
+ void deref() const;
+ void nonTrivial();
+
+ void method_captures_this_safe() {
+ auto lambda = [&]() {
+ nonTrivial();
+ };
+ lambda();
+ }
+
+ void method_captures_this_unsafe() {
+ auto lambda = [&]() {
+ nonTrivial();
+ // expected-warning@-1{{Implicitly captured raw-pointer 'this' to ref-counted / CheckedPtr capable type is unsafe [webkit.UncountedLambdaCapturesChecker]}}
+ };
+ call(lambda);
+ }
+};
+
+struct NonRefCountableWithLambdaCapturingThis {
+ void nonTrivial();
+
+ void method_captures_this_safe() {
+ auto lambda = [&]() {
+ nonTrivial();
+ };
+ lambda();
+ }
+
+ void method_captures_this_unsafe() {
+ auto lambda = [&]() {
+ nonTrivial();
+ };
+ call(lambda);
+ }
+};
+
+void trivial_lambda() {
+ RefCountable* ref_countable = make_obj();
+ auto trivial_lambda = [&]() {
+ return ref_countable->trivial();
+ };
+ trivial_lambda();
+}
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Closing this in favor of #114897. |
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This PR makes webkit.UncountedLambdaCapturesChecker ignore trivial functions as well as the one being passed to an argument with [[clang::noescape]] attribute. This dramatically reduces the false positive rate for this checker.
To do this, this PR replaces VisitLambdaExpr in favor of checking lambdas via VisitDeclRefExpr and VisitCallExpr. The idea is that if a lambda is defined but never called or stored somewhere, then capturing whatever variable in such a lambda is harmless.
VisitCallExpr explicitly looks for direct invocation of lambdas and registers its DeclRefExpr to be ignored in VisitDeclRefExpr. If a lambda is being passed to a function, it checks whether its argument is annotated with [[clang::noescape]]. If it's not annotated such, it checks captures for their safety.
Because WTF::switchOn could not be annotated with [[clang::noescape]] as function type parameters are variadic template function so we hard-code this function into the checker.
In order to check whether "this" pointer is ref-counted type or not, we override TraverseDecl and record the most recent method's declaration.
In addition, this PR fixes a bug in isUnsafePtr that it was erroneously checking whether std::nullopt was returned by isUncounted and isUnchecked as opposed to the actual boolean value.
Finally, this PR also converts the accompanying test to use -verify and adds a bunch of tests.