clang 18.0.0git
UndefBranchChecker.cpp
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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"
21#include <optional>
22#include <utility>
23
24using namespace clang;
25using namespace ento;
26
27namespace {
28
29class UndefBranchChecker : public Checker<check::BranchCondition> {
30 mutable std::unique_ptr<BugType> BT;
31
32 struct FindUndefExpr {
34 const LocationContext *LCtx;
35
36 FindUndefExpr(ProgramStateRef S, const LocationContext *L)
37 : St(std::move(S)), LCtx(L) {}
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>(SubStmt))
45 if (const Expr *E2 = FindExpr(ExI))
46 return E2;
47
48 return Ex;
49 }
50
51 bool MatchesCriteria(const Expr *Ex) {
52 return St->getSVal(Ex, LCtx).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>(Condition))
66 return;
67 SVal X = Ctx.getSVal(Condition);
68 if (X.isUndef()) {
69 // Generate a sink node, which implicitly marks both outgoing branches as
70 // infeasible.
72 if (N) {
73 if (!BT)
74 BT.reset(
75 new BugType(this, "Branch condition evaluates to a garbage value"));
76
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 const Expr *Ex = cast<Expr>(Condition);
93 ExplodedNode *PrevN = *N->pred_begin();
94 ProgramPoint P = PrevN->getLocation();
95 ProgramStateRef St = N->getState();
96
97 if (std::optional<PostStmt> PS = P.getAs<PostStmt>())
98 if (PS->getStmt() == Ex)
99 St = PrevN->getState();
100
101 FindUndefExpr FindIt(St, Ctx.getLocationContext());
102 Ex = FindIt.FindExpr(Ex);
103
104 // Emit the bug report.
105 auto R = std::make_unique<PathSensitiveBugReport>(
106 *BT, BT->getDescription(), N);
108 R->addRange(Ex->getSourceRange());
109
110 Ctx.emitReport(std::move(R));
111 }
112 }
113}
114
115void ento::registerUndefBranchChecker(CheckerManager &mgr) {
116 mgr.registerChecker<UndefBranchChecker>();
117}
118
119bool ento::shouldRegisterUndefBranchChecker(const CheckerManager &mgr) {
120 return true;
121}
StringRef P
#define X(type, name)
Definition: Value.h:142
Defines the Objective-C statement AST node classes.
C Language Family Type Representation.
This represents one expression.
Definition: Expr.h:110
It wraps the AnalysisDeclContext to represent both the call stack with the help of StackFrameContext ...
Stmt - This represents one statement.
Definition: Stmt.h:84
child_range children()
Definition: Stmt.cpp:286
SourceRange getSourceRange() const LLVM_READONLY
SourceLocation tokens are not useful in isolation - they are low level value objects created/interpre...
Definition: Stmt.cpp:325
SVal getSVal(const Stmt *S) const
Get the value of arbitrary expressions at this point in the path.
ExplodedNode * generateErrorNode(ProgramStateRef State=nullptr, const ProgramPointTag *Tag=nullptr)
Generate a transition to a node that will be used to report an error.
const LocationContext * getLocationContext() const
void emitReport(std::unique_ptr< BugReport > R)
Emit the diagnostics report.
CHECKER * registerChecker(AT &&... Args)
Used to register checkers.
const ProgramStateRef & getState() const
pred_iterator pred_begin()
ProgramPoint getLocation() const
getLocation - Returns the edge associated with the given node.
SVal - This represents a symbolic expression, which can be either an L-value or an R-value.
Definition: SVals.h:55
bool trackExpressionValue(const ExplodedNode *N, const Expr *E, PathSensitiveBugReport &R, TrackingOptions Opts={})
Attempts to add visitors to track expression value back to its point of origin.
Definition: Format.h:5226