//==- CheckSizeofPointer.cpp - Check for sizeof on pointers ------*- C++ -*-==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  This file defines a check for unintended use of sizeof() on pointer
//  expressions.
//
//===----------------------------------------------------------------------===//

#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"

using namespace clang;
using namespace ento;

namespace {
class WalkAST : public StmtVisitor<WalkAST> {
  BugReporter &BR;
  const CheckerBase *Checker;
  AnalysisDeclContext* AC;

public:
  WalkAST(BugReporter &br, const CheckerBase *checker, AnalysisDeclContext *ac)
      : BR(br), Checker(checker), AC(ac) {}
  void VisitUnaryExprOrTypeTraitExpr(UnaryExprOrTypeTraitExpr *E);
  void VisitStmt(Stmt *S) { VisitChildren(S); }
  void VisitChildren(Stmt *S);
};
}

void WalkAST::VisitChildren(Stmt *S) {
  for (Stmt *Child : S->children())
    if (Child)
      Visit(Child);
}

// CWE-467: Use of sizeof() on a Pointer Type
void WalkAST::VisitUnaryExprOrTypeTraitExpr(UnaryExprOrTypeTraitExpr *E) {
  if (E->getKind() != UETT_SizeOf)
    return;

  // If an explicit type is used in the code, usually the coder knows what they are
  // doing.
  if (E->isArgumentType())
    return;

  QualType T = E->getTypeOfArgument();
  if (T->isPointerType()) {

    // Many false positives have the form 'sizeof *p'. This is reasonable
    // because people know what they are doing when they intentionally
    // dereference the pointer.
    Expr *ArgEx = E->getArgumentExpr();
    if (!isa<DeclRefExpr>(ArgEx->IgnoreParens()))
      return;

    PathDiagnosticLocation ELoc =
      PathDiagnosticLocation::createBegin(E, BR.getSourceManager(), AC);
    BR.EmitBasicReport(AC->getDecl(), Checker,
                       "Potential unintended use of sizeof() on pointer type",
                       categories::LogicError,
                       "The code calls sizeof() on a pointer type. "
                       "This can produce an unexpected result.",
                       ELoc, ArgEx->getSourceRange());
  }
}

//===----------------------------------------------------------------------===//
// SizeofPointerChecker
//===----------------------------------------------------------------------===//

namespace {
class SizeofPointerChecker : public Checker<check::ASTCodeBody> {
public:
  void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
                        BugReporter &BR) const {
    WalkAST walker(BR, this, mgr.getAnalysisDeclContext(D));
    walker.Visit(D->getBody());
  }
};
}

void ento::registerSizeofPointerChecker(CheckerManager &mgr) {
  mgr.registerChecker<SizeofPointerChecker>();
}

bool ento::shouldRegisterSizeofPointerChecker(const LangOptions &LO) {
  return true;
}