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 #include <optional>
13
14 using namespace clang::ast_matchers;
15
16 namespace clang::tidy::bugprone {
17
tryEvaluateSizeExpr(const Expr * SizeExpr,const ASTContext & Ctx)18 static std::optional<uint64_t> tryEvaluateSizeExpr(const Expr *SizeExpr,
19 const ASTContext &Ctx) {
20 Expr::EvalResult Result;
21 if (SizeExpr->EvaluateAsRValue(Result, Ctx))
22 return Ctx.toBits(
23 CharUnits::fromQuantity(Result.Val.getInt().getExtValue()));
24 return std::nullopt;
25 }
26
registerMatchers(MatchFinder * Finder)27 void SuspiciousMemoryComparisonCheck::registerMatchers(MatchFinder *Finder) {
28 Finder->addMatcher(
29 callExpr(callee(namedDecl(
30 anyOf(hasName("::memcmp"), hasName("::std::memcmp")))),
31 unless(isInstantiationDependent()))
32 .bind("call"),
33 this);
34 }
35
check(const MatchFinder::MatchResult & Result)36 void SuspiciousMemoryComparisonCheck::check(
37 const MatchFinder::MatchResult &Result) {
38 const ASTContext &Ctx = *Result.Context;
39 const auto *CE = Result.Nodes.getNodeAs<CallExpr>("call");
40
41 const Expr *SizeExpr = CE->getArg(2);
42 assert(SizeExpr != nullptr && "Third argument of memcmp is mandatory.");
43 std::optional<uint64_t> ComparedBits = tryEvaluateSizeExpr(SizeExpr, Ctx);
44
45 for (unsigned int ArgIndex = 0; ArgIndex < 2; ++ArgIndex) {
46 const Expr *ArgExpr = CE->getArg(ArgIndex);
47 QualType ArgType = ArgExpr->IgnoreImplicit()->getType();
48 const Type *PointeeType = ArgType->getPointeeOrArrayElementType();
49 assert(PointeeType != nullptr && "PointeeType should always be available.");
50 QualType PointeeQualifiedType(PointeeType, 0);
51
52 if (PointeeType->isRecordType()) {
53 if (const RecordDecl *RD =
54 PointeeType->getAsRecordDecl()->getDefinition()) {
55 if (const auto *CXXDecl = dyn_cast<CXXRecordDecl>(RD)) {
56 if (!CXXDecl->isStandardLayout()) {
57 diag(CE->getBeginLoc(),
58 "comparing object representation of non-standard-layout type "
59 "%0; consider using a comparison operator instead")
60 << PointeeQualifiedType;
61 break;
62 }
63 }
64 }
65 }
66
67 if (!PointeeType->isIncompleteType()) {
68 uint64_t PointeeSize = Ctx.getTypeSize(PointeeType);
69 if (ComparedBits && *ComparedBits >= PointeeSize &&
70 !Ctx.hasUniqueObjectRepresentations(PointeeQualifiedType)) {
71 diag(CE->getBeginLoc(),
72 "comparing object representation of type %0 which does not have a "
73 "unique object representation; consider comparing %select{the "
74 "values|the members of the object}1 manually")
75 << PointeeQualifiedType << (PointeeType->isRecordType() ? 1 : 0);
76 break;
77 }
78 }
79 }
80 }
81
82 } // namespace clang::tidy::bugprone
83