1 //===--- SuspiciousMemoryComparisonCheck.cpp - clang-tidy -----------------===//
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 #include "SuspiciousMemoryComparisonCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12
13 using namespace clang::ast_matchers;
14
15 namespace clang {
16 namespace tidy {
17 namespace bugprone {
18
tryEvaluateSizeExpr(const Expr * SizeExpr,const ASTContext & Ctx)19 static llvm::Optional<uint64_t> tryEvaluateSizeExpr(const Expr *SizeExpr,
20 const ASTContext &Ctx) {
21 Expr::EvalResult Result;
22 if (SizeExpr->EvaluateAsRValue(Result, Ctx))
23 return Ctx.toBits(
24 CharUnits::fromQuantity(Result.Val.getInt().getExtValue()));
25 return None;
26 }
27
registerMatchers(MatchFinder * Finder)28 void SuspiciousMemoryComparisonCheck::registerMatchers(MatchFinder *Finder) {
29 Finder->addMatcher(
30 callExpr(allOf(callee(namedDecl(
31 anyOf(hasName("::memcmp"), hasName("::std::memcmp")))),
32 unless(isInstantiationDependent())))
33 .bind("call"),
34 this);
35 }
36
check(const MatchFinder::MatchResult & Result)37 void SuspiciousMemoryComparisonCheck::check(
38 const MatchFinder::MatchResult &Result) {
39 const ASTContext &Ctx = *Result.Context;
40 const auto *CE = Result.Nodes.getNodeAs<CallExpr>("call");
41
42 const Expr *SizeExpr = CE->getArg(2);
43 assert(SizeExpr != nullptr && "Third argument of memcmp is mandatory.");
44 llvm::Optional<uint64_t> ComparedBits = tryEvaluateSizeExpr(SizeExpr, Ctx);
45
46 for (unsigned int ArgIndex = 0; ArgIndex < 2; ++ArgIndex) {
47 const Expr *ArgExpr = CE->getArg(ArgIndex);
48 QualType ArgType = ArgExpr->IgnoreImplicit()->getType();
49 const Type *PointeeType = ArgType->getPointeeOrArrayElementType();
50 assert(PointeeType != nullptr && "PointeeType should always be available.");
51 QualType PointeeQualifiedType(PointeeType, 0);
52
53 if (PointeeType->isRecordType()) {
54 if (const RecordDecl *RD =
55 PointeeType->getAsRecordDecl()->getDefinition()) {
56 if (const auto *CXXDecl = dyn_cast<CXXRecordDecl>(RD)) {
57 if (!CXXDecl->isStandardLayout()) {
58 diag(CE->getBeginLoc(),
59 "comparing object representation of non-standard-layout type "
60 "%0; consider using a comparison operator instead")
61 << PointeeQualifiedType;
62 break;
63 }
64 }
65 }
66 }
67
68 if (!PointeeType->isIncompleteType()) {
69 uint64_t PointeeSize = Ctx.getTypeSize(PointeeType);
70 if (ComparedBits && *ComparedBits >= PointeeSize &&
71 !Ctx.hasUniqueObjectRepresentations(PointeeQualifiedType)) {
72 diag(CE->getBeginLoc(),
73 "comparing object representation of type %0 which does not have a "
74 "unique object representation; consider comparing %select{the "
75 "values|the members of the object}1 manually")
76 << PointeeQualifiedType << (PointeeType->isRecordType() ? 1 : 0);
77 break;
78 }
79 }
80 }
81 }
82
83 } // namespace bugprone
84 } // namespace tidy
85 } // namespace clang
86