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 
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 
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 
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.hasValue() && *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