1//=== UndefBranchChecker.cpp -----------------------------------*- C++ -*--===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines UndefBranchChecker, which checks for undefined branch
10// condition.
11//
12//===----------------------------------------------------------------------===//
13
14#include "clang/AST/StmtObjC.h"
15#include "clang/AST/Type.h"
16#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
17#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
18#include "clang/StaticAnalyzer/Core/Checker.h"
19#include "clang/StaticAnalyzer/Core/CheckerManager.h"
20#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
21#include <optional>
22#include <utility>
23
24using namespace clang;
25using namespace ento;
26
27namespace {
28
29class UndefBranchChecker : public Checker<check::BranchCondition> {
30 const BugType BT{this, "Branch condition evaluates to a garbage value"};
31
32 struct FindUndefExpr {
33 ProgramStateRef St;
34 const StackFrame *SF;
35
36 FindUndefExpr(ProgramStateRef S, const StackFrame *SF)
37 : St(std::move(S)), SF(SF) {}
38
39 const Expr *FindExpr(const Expr *Ex) {
40 if (!MatchesCriteria(Ex))
41 return nullptr;
42
43 for (const Stmt *SubStmt : Ex->children())
44 if (const Expr *ExI = dyn_cast_or_null<Expr>(Val: SubStmt))
45 if (const Expr *E2 = FindExpr(Ex: ExI))
46 return E2;
47
48 return Ex;
49 }
50
51 bool MatchesCriteria(const Expr *Ex) {
52 return St->getSVal(E: Ex, SF).isUndef();
53 }
54 };
55
56public:
57 void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const;
58};
59
60} // namespace
61
62void UndefBranchChecker::checkBranchCondition(const Stmt *Condition,
63 CheckerContext &Ctx) const {
64 // ObjCForCollection is a loop, but has no actual condition.
65 if (isa<ObjCForCollectionStmt>(Val: Condition))
66 return;
67
68 const auto *Ex = cast<Expr>(Val: Condition);
69 if (!Ctx.getSVal(E: Ex).isUndef())
70 return;
71
72 // Generate a sink node, which implicitly marks both outgoing branches as
73 // infeasible.
74 ExplodedNode *N = Ctx.generateErrorNode();
75 if (!N)
76 return;
77 // What's going on here: we want to highlight the subexpression of the
78 // condition that is the most likely source of the "uninitialized
79 // branch condition." We do a recursive walk of the condition's
80 // subexpressions and roughly look for the most nested subexpression
81 // that binds to Undefined. We then highlight that expression's range.
82
83 // Get the predecessor node and check if is a PostStmt with the Stmt
84 // being the terminator condition. We want to inspect the state
85 // of that node instead because it will contain main information about
86 // the subexpressions.
87
88 // Note: any predecessor will do. They should have identical state,
89 // since all the BlockEdge did was act as an error sink since the value
90 // had to already be undefined.
91 assert(!N->pred_empty());
92 ExplodedNode *PrevN = *N->pred_begin();
93 ProgramPoint P = PrevN->getLocation();
94 ProgramStateRef St = N->getState();
95
96 if (std::optional<PostStmt> PS = P.getAs<PostStmt>())
97 if (PS->getStmt() == Ex)
98 St = PrevN->getState();
99
100 FindUndefExpr FindIt(St, Ctx.getStackFrame());
101 Ex = FindIt.FindExpr(Ex);
102
103 // Emit the bug report.
104 auto R = std::make_unique<PathSensitiveBugReport>(args: BT, args: BT.getDescription(), args&: N);
105 bugreporter::trackExpressionValue(N, E: Ex, R&: *R);
106 R->addRange(R: Ex->getSourceRange());
107
108 Ctx.emitReport(R: std::move(R));
109}
110
111void ento::registerUndefBranchChecker(CheckerManager &mgr) {
112 mgr.registerChecker<UndefBranchChecker>();
113}
114
115bool ento::shouldRegisterUndefBranchChecker(const CheckerManager &mgr) {
116 return true;
117}
118