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//===--- NonNullParamChecker.cpp - Undefined arguments checker -*- C++ -*--===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This defines NonNullParamChecker, which checks for arguments expected not to
// be null due to:
// - the corresponding parameters being declared to have nonnull attribute
// - the corresponding parameters being references; since the call would form
// a reference to a null pointer
#include "ClangSACheckers.h"
#include "clang/AST/Attr.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
using namespace clang;
using namespace ento;
namespace {
class NonNullParamChecker
: public Checker< check::PreCall, EventDispatcher<ImplicitNullDerefEvent> > {
mutable std::unique_ptr<BugType> BTAttrNonNull;
mutable std::unique_ptr<BugType> BTNullRefArg;
void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
genReportNullAttrNonNull(const ExplodedNode *ErrorN, const Expr *ArgE) const;
genReportReferenceToNullPointer(const ExplodedNode *ErrorN,
const Expr *ArgE) const;
} // end anonymous namespace
/// \return Bitvector marking non-null attributes.
static llvm::SmallBitVector getNonNullAttrs(const CallEvent &Call) {
const Decl *FD = Call.getDecl();
unsigned NumArgs = Call.getNumArgs();
llvm::SmallBitVector AttrNonNull(NumArgs);
for (const auto *NonNull : FD->specific_attrs<NonNullAttr>()) {
if (!NonNull->args_size()) {
AttrNonNull.set(0, NumArgs);
for (const ParamIdx &Idx : NonNull->args()) {
unsigned IdxAST = Idx.getASTIndex();
if (IdxAST >= NumArgs)
return AttrNonNull;
void NonNullParamChecker::checkPreCall(const CallEvent &Call,
CheckerContext &C) const {
if (!Call.getDecl())
llvm::SmallBitVector AttrNonNull = getNonNullAttrs(Call);
unsigned NumArgs = Call.getNumArgs();
ProgramStateRef state = C.getState();
ArrayRef<ParmVarDecl*> parms = Call.parameters();
for (unsigned idx = 0; idx < NumArgs; ++idx) {
// For vararg functions, a corresponding parameter decl may not exist.
bool HasParam = idx < parms.size();
// Check if the parameter is a reference. We want to report when reference
// to a null pointer is passed as a parameter.
bool haveRefTypeParam =
HasParam ? parms[idx]->getType()->isReferenceType() : false;
bool haveAttrNonNull = AttrNonNull[idx];
// Check if the parameter is also marked 'nonnull'.
if (!haveAttrNonNull && HasParam)
haveAttrNonNull = parms[idx]->hasAttr<NonNullAttr>();
if (!haveAttrNonNull && !haveRefTypeParam)
// If the value is unknown or undefined, we can't perform this check.
const Expr *ArgE = Call.getArgExpr(idx);
SVal V = Call.getArgSVal(idx);
auto DV = V.getAs<DefinedSVal>();
if (!DV)
assert(!haveRefTypeParam || DV->getAs<Loc>());
// Process the case when the argument is not a location.
if (haveAttrNonNull && !DV->getAs<Loc>()) {
// If the argument is a union type, we want to handle a potential
// transparent_union GCC extension.
if (!ArgE)
QualType T = ArgE->getType();
const RecordType *UT = T->getAsUnionType();
if (!UT || !UT->getDecl()->hasAttr<TransparentUnionAttr>())
auto CSV = DV->getAs<nonloc::CompoundVal>();
// FIXME: Handle LazyCompoundVals?
if (!CSV)
V = *(CSV->begin());
DV = V.getAs<DefinedSVal>();
assert(++CSV->begin() == CSV->end());
// FIXME: Handle (some_union){ some_other_union_val }, which turns into
// a LazyCompoundVal inside a CompoundVal.
if (!V.getAs<Loc>())
// Retrieve the corresponding expression.
if (const auto *CE = dyn_cast<CompoundLiteralExpr>(ArgE))
if (const auto *IE = dyn_cast<InitListExpr>(CE->getInitializer()))
ArgE = dyn_cast<Expr>(*(IE->begin()));
ConstraintManager &CM = C.getConstraintManager();
ProgramStateRef stateNotNull, stateNull;
std::tie(stateNotNull, stateNull) = CM.assumeDual(state, *DV);
// Generate an error node. Check for a null node in case
// we cache out.
if (stateNull && !stateNotNull) {
if (ExplodedNode *errorNode = C.generateErrorNode(stateNull)) {
std::unique_ptr<BugReport> R;
if (haveAttrNonNull)
R = genReportNullAttrNonNull(errorNode, ArgE);
else if (haveRefTypeParam)
R = genReportReferenceToNullPointer(errorNode, ArgE);
// Highlight the range of the argument that was null.
// Emit the bug report.
// Always return. Either we cached out or we just emitted an error.
if (stateNull) {
if (ExplodedNode *N = C.generateSink(stateNull, C.getPredecessor())) {
ImplicitNullDerefEvent event = {
V, false, N, &C.getBugReporter(),
// If a pointer value passed the check we should assume that it is
// indeed not null from this point forward.
state = stateNotNull;
// If we reach here all of the arguments passed the nonnull check.
// If 'state' has been updated generated a new node.
NonNullParamChecker::genReportNullAttrNonNull(const ExplodedNode *ErrorNode,
const Expr *ArgE) const {
// Lazily allocate the BugType object if it hasn't already been
// created. Ownership is transferred to the BugReporter object once
// the BugReport is passed to 'EmitWarning'.
if (!BTAttrNonNull)
BTAttrNonNull.reset(new BugType(
this, "Argument with 'nonnull' attribute passed null", "API"));
auto R = llvm::make_unique<BugReport>(
"Null pointer passed as an argument to a 'nonnull' parameter", ErrorNode);
if (ArgE)
bugreporter::trackNullOrUndefValue(ErrorNode, ArgE, *R);
return R;
std::unique_ptr<BugReport> NonNullParamChecker::genReportReferenceToNullPointer(
const ExplodedNode *ErrorNode, const Expr *ArgE) const {
if (!BTNullRefArg)
BTNullRefArg.reset(new BuiltinBug(this, "Dereference of null pointer"));
auto R = llvm::make_unique<BugReport>(
*BTNullRefArg, "Forming reference to null pointer", ErrorNode);
if (ArgE) {
const Expr *ArgEDeref = bugreporter::getDerefExpr(ArgE);
if (!ArgEDeref)
ArgEDeref = ArgE;
return R;
void ento::registerNonNullParamChecker(CheckerManager &mgr) {