UndefBranchChecker.cpp
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//=== UndefBranchChecker.cpp -----------------------------------*- C++ -*--===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines UndefBranchChecker, which checks for undefined branch
// condition.
//
//===----------------------------------------------------------------------===//
#include "clang/AST/StmtObjC.h"
#include "clang/AST/Type.h"
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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/CheckerContext.h"
#include <utility>
using namespace clang;
using namespace ento;
namespace {
class UndefBranchChecker : public Checker<check::BranchCondition> {
mutable std::unique_ptr<BuiltinBug> BT;
struct FindUndefExpr {
ProgramStateRef St;
const LocationContext *LCtx;
FindUndefExpr(ProgramStateRef S, const LocationContext *L)
: St(std::move(S)), LCtx(L) {}
const Expr *FindExpr(const Expr *Ex) {
if (!MatchesCriteria(Ex))
return nullptr;
for (const Stmt *SubStmt : Ex->children())
if (const Expr *ExI = dyn_cast_or_null<Expr>(SubStmt))
if (const Expr *E2 = FindExpr(ExI))
return E2;
return Ex;
}
bool MatchesCriteria(const Expr *Ex) {
return St->getSVal(Ex, LCtx).isUndef();
}
};
public:
void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const;
};
} // namespace
void UndefBranchChecker::checkBranchCondition(const Stmt *Condition,
CheckerContext &Ctx) const {
// ObjCForCollection is a loop, but has no actual condition.
if (isa<ObjCForCollectionStmt>(Condition))
return;
SVal X = Ctx.getSVal(Condition);
if (X.isUndef()) {
// Generate a sink node, which implicitly marks both outgoing branches as
// infeasible.
ExplodedNode *N = Ctx.generateErrorNode();
if (N) {
if (!BT)
BT.reset(new BuiltinBug(
this, "Branch condition evaluates to a garbage value"));
// What's going on here: we want to highlight the subexpression of the
// condition that is the most likely source of the "uninitialized
// branch condition." We do a recursive walk of the condition's
// subexpressions and roughly look for the most nested subexpression
// that binds to Undefined. We then highlight that expression's range.
// Get the predecessor node and check if is a PostStmt with the Stmt
// being the terminator condition. We want to inspect the state
// of that node instead because it will contain main information about
// the subexpressions.
// Note: any predecessor will do. They should have identical state,
// since all the BlockEdge did was act as an error sink since the value
// had to already be undefined.
assert (!N->pred_empty());
const Expr *Ex = cast<Expr>(Condition);
ExplodedNode *PrevN = *N->pred_begin();
ProgramPoint P = PrevN->getLocation();
ProgramStateRef St = N->getState();
if (Optional<PostStmt> PS = P.getAs<PostStmt>())
if (PS->getStmt() == Ex)
St = PrevN->getState();
FindUndefExpr FindIt(St, Ctx.getLocationContext());
Ex = FindIt.FindExpr(Ex);
// Emit the bug report.
auto R = std::make_unique<PathSensitiveBugReport>(
*BT, BT->getDescription(), N);
bugreporter::trackExpressionValue(N, Ex, *R);
R->addRange(Ex->getSourceRange());
Ctx.emitReport(std::move(R));
}
}
}
void ento::registerUndefBranchChecker(CheckerManager &mgr) {
mgr.registerChecker<UndefBranchChecker>();
}
bool ento::shouldRegisterUndefBranchChecker(const CheckerManager &mgr) {
return true;
}