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//===--- ThrowByValueCatchByReferenceCheck.cpp - clang-tidy----------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "ThrowByValueCatchByReferenceCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/OperationKinds.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
using namespace clang::ast_matchers;
namespace clang::tidy::misc {
ThrowByValueCatchByReferenceCheck::ThrowByValueCatchByReferenceCheck(
StringRef Name, ClangTidyContext *Context)
: ClangTidyCheck(Name, Context),
CheckAnonymousTemporaries(Options.get("CheckThrowTemporaries", true)),
WarnOnLargeObject(Options.get("WarnOnLargeObject", false)),
// Cannot access `ASTContext` from here so set it to an extremal value.
MaxSizeOptions(
Options.get("MaxSize", std::numeric_limits<uint64_t>::max())),
MaxSize(MaxSizeOptions) {}
void ThrowByValueCatchByReferenceCheck::registerMatchers(MatchFinder *Finder) {
Finder->addMatcher(cxxThrowExpr().bind("throw"), this);
Finder->addMatcher(cxxCatchStmt().bind("catch"), this);
}
void ThrowByValueCatchByReferenceCheck::storeOptions(
ClangTidyOptions::OptionMap &Opts) {
Options.store(Opts, "CheckThrowTemporaries", true);
Options.store(Opts, "WarnOnLargeObjects", WarnOnLargeObject);
Options.store(Opts, "MaxSize", MaxSizeOptions);
}
void ThrowByValueCatchByReferenceCheck::check(
const MatchFinder::MatchResult &Result) {
diagnoseThrowLocations(Result.Nodes.getNodeAs<CXXThrowExpr>("throw"));
diagnoseCatchLocations(Result.Nodes.getNodeAs<CXXCatchStmt>("catch"),
*Result.Context);
}
bool ThrowByValueCatchByReferenceCheck::isFunctionParameter(
const DeclRefExpr *DeclRefExpr) {
return isa<ParmVarDecl>(DeclRefExpr->getDecl());
}
bool ThrowByValueCatchByReferenceCheck::isCatchVariable(
const DeclRefExpr *DeclRefExpr) {
auto *ValueDecl = DeclRefExpr->getDecl();
if (auto *VarDecl = dyn_cast<clang::VarDecl>(ValueDecl))
return VarDecl->isExceptionVariable();
return false;
}
bool ThrowByValueCatchByReferenceCheck::isFunctionOrCatchVar(
const DeclRefExpr *DeclRefExpr) {
return isFunctionParameter(DeclRefExpr) || isCatchVariable(DeclRefExpr);
}
void ThrowByValueCatchByReferenceCheck::diagnoseThrowLocations(
const CXXThrowExpr *ThrowExpr) {
if (!ThrowExpr)
return;
auto *SubExpr = ThrowExpr->getSubExpr();
if (!SubExpr)
return;
auto QualType = SubExpr->getType();
if (QualType->isPointerType()) {
// The code is throwing a pointer.
// In case it is string literal, it is safe and we return.
auto *Inner = SubExpr->IgnoreParenImpCasts();
if (isa<StringLiteral>(Inner))
return;
// If it's a variable from a catch statement, we return as well.
auto *DeclRef = dyn_cast<DeclRefExpr>(Inner);
if (DeclRef && isCatchVariable(DeclRef)) {
return;
}
diag(SubExpr->getBeginLoc(), "throw expression throws a pointer; it should "
"throw a non-pointer value instead");
}
// If the throw statement does not throw by pointer then it throws by value
// which is ok.
// There are addition checks that emit diagnosis messages if the thrown value
// is not an RValue. See:
// https://www.securecoding.cert.org/confluence/display/cplusplus/ERR09-CPP.+Throw+anonymous+temporaries
// This behavior can be influenced by an option.
// If we encounter a CXXThrowExpr, we move through all casts until you either
// encounter a DeclRefExpr or a CXXConstructExpr.
// If it's a DeclRefExpr, we emit a message if the referenced variable is not
// a catch variable or function parameter.
// When encountering a CopyOrMoveConstructor: emit message if after casts,
// the expression is a LValue
if (CheckAnonymousTemporaries) {
bool Emit = false;
auto *CurrentSubExpr = SubExpr->IgnoreImpCasts();
const auto *VariableReference = dyn_cast<DeclRefExpr>(CurrentSubExpr);
const auto *ConstructorCall = dyn_cast<CXXConstructExpr>(CurrentSubExpr);
// If we have a DeclRefExpr, we flag for emitting a diagnosis message in
// case the referenced variable is neither a function parameter nor a
// variable declared in the catch statement.
if (VariableReference)
Emit = !isFunctionOrCatchVar(VariableReference);
else if (ConstructorCall &&
ConstructorCall->getConstructor()->isCopyOrMoveConstructor()) {
// If we have a copy / move construction, we emit a diagnosis message if
// the object that we copy construct from is neither a function parameter
// nor a variable declared in a catch statement
auto ArgIter =
ConstructorCall
->arg_begin(); // there's only one for copy constructors
auto *CurrentSubExpr = (*ArgIter)->IgnoreImpCasts();
if (CurrentSubExpr->isLValue()) {
if (auto *Tmp = dyn_cast<DeclRefExpr>(CurrentSubExpr))
Emit = !isFunctionOrCatchVar(Tmp);
else if (isa<CallExpr>(CurrentSubExpr))
Emit = true;
}
}
if (Emit)
diag(SubExpr->getBeginLoc(),
"throw expression should throw anonymous temporary values instead");
}
}
void ThrowByValueCatchByReferenceCheck::diagnoseCatchLocations(
const CXXCatchStmt *CatchStmt, ASTContext &Context) {
if (!CatchStmt)
return;
auto CaughtType = CatchStmt->getCaughtType();
if (CaughtType.isNull())
return;
auto *VarDecl = CatchStmt->getExceptionDecl();
if (const auto *PT = CaughtType.getCanonicalType()->getAs<PointerType>()) {
const char *DiagMsgCatchReference =
"catch handler catches a pointer value; "
"should throw a non-pointer value and "
"catch by reference instead";
// We do not diagnose when catching pointer to strings since we also allow
// throwing string literals.
if (!PT->getPointeeType()->isAnyCharacterType())
diag(VarDecl->getBeginLoc(), DiagMsgCatchReference);
} else if (!CaughtType->isReferenceType()) {
const char *DiagMsgCatchReference = "catch handler catches by value; "
"should catch by reference instead";
// If it's not a pointer and not a reference then it must be caught "by
// value". In this case we should emit a diagnosis message unless the type
// is trivial.
if (!CaughtType.isTrivialType(Context)) {
diag(VarDecl->getBeginLoc(), DiagMsgCatchReference);
} else if (WarnOnLargeObject) {
// If the type is trivial, then catching it by reference is not dangerous.
// However, catching large objects by value decreases the performance.
// We can now access `ASTContext` so if `MaxSize` is an extremal value
// then set it to the size of `size_t`.
if (MaxSize == std::numeric_limits<uint64_t>::max())
MaxSize = Context.getTypeSize(Context.getSizeType());
if (Context.getTypeSize(CaughtType) > MaxSize)
diag(VarDecl->getBeginLoc(), DiagMsgCatchReference);
}
}
}
} // namespace clang::tidy::misc
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