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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#include "NonParamInsideFunctionDeclChecker.h"
#include "CustomMatchers.h"
#include "clang/Basic/TargetInfo.h"
class NonParamAnnotation : public CustomTypeAnnotation {
NonParamAnnotation() : CustomTypeAnnotation(moz_non_param, "non-param"){};
// Helper for checking if a Decl has an explicitly specified alignment.
// Returns the alignment, in char units, of the largest alignment attribute,
// if it exceeds pointer alignment, and 0 otherwise.
static unsigned checkExplicitAlignment(const Decl *D) {
ASTContext &Context = D->getASTContext();
unsigned PointerAlign = Context.getTargetInfo().getPointerAlign(LangAS::Default);
unsigned PointerAlign = Context.getTargetInfo().getPointerAlign(0);
// getMaxAlignment gets the largest alignment, in bits, specified by an
// alignment attribute directly on the declaration. If no alignment
// attribute is specified, it will return `0`.
unsigned MaxAlign = D->getMaxAlignment();
if (MaxAlign > PointerAlign) {
return Context.toCharUnitsFromBits(MaxAlign).getQuantity();
return 0;
// This is directly derived from the logic in Clang's `canPassInRegisters`
// function, from `SemaDeclCXX`. It is used instead of `canPassInRegisters` to
// behave consistently on 64-bit windows platforms which are overly
// permissive, allowing too many types to be passed in registers.
// Types which can be passed in registers will be re-aligned in the called
// function by clang, so aren't impacted by the win32 object passing ABI
// alignment issue.
static bool canPassAsTemporary(const CXXRecordDecl *D) {
// Per C++ [class.temporary]p3:
// When an object of class type X is passed to or returned from a function,
// if X has at least one eligible copy or move constructor ([special]), each
// such constructor is trivial, and the destructor of X is either trivial or
// deleted, implementations are permitted to create a temporary object to
// hold the function parameter or result object.
// The temporary object is constructed from the function argument or return
// value, respectively, and the function's parameter or return object is
// initialized as if by using the eligible trivial constructor to copy the
// temporary (even if that constructor is inaccessible or would not be
// selected by overload resolution to perform a copy or move of the object).
bool HasNonDeletedCopyOrMove = false;
if (D->needsImplicitCopyConstructor() &&
!D->defaultedCopyConstructorIsDeleted()) {
if (!D->hasTrivialCopyConstructorForCall())
return false;
HasNonDeletedCopyOrMove = true;
if (D->needsImplicitMoveConstructor() &&
!D->defaultedMoveConstructorIsDeleted()) {
if (!D->hasTrivialMoveConstructorForCall())
return false;
HasNonDeletedCopyOrMove = true;
if (D->needsImplicitDestructor() && !D->defaultedDestructorIsDeleted() &&
return false;
for (const CXXMethodDecl *MD : D->methods()) {
if (MD->isDeleted())
auto *CD = dyn_cast<CXXConstructorDecl>(MD);
if (CD && CD->isCopyOrMoveConstructor())
HasNonDeletedCopyOrMove = true;
else if (!isa<CXXDestructorDecl>(MD))
if (!MD->isTrivialForCall())
return false;
return HasNonDeletedCopyOrMove;
// Adding alignas(_) on a struct implicitly marks it as MOZ_NON_PARAM, due to
// MSVC limitations which prevent passing explcitly aligned types by value as
// parameters. This overload of hasFakeAnnotation injects fake MOZ_NON_PARAM
// annotations onto these types.
std::string getImplicitReason(const TagDecl *D,
VisitFlags &ToVisit) const override {
// Some stdlib types are known to have alignments over the pointer size on
// non-win32 platforms, but should not be linted against. Clear any
// annotations on those types.
if (!D->getASTContext().getTargetInfo().getCXXABI().isMicrosoft() &&
getDeclarationNamespace(D) == "std") {
StringRef Name = getNameChecked(D);
if (Name == "function") {
return "";
// If the type doesn't have a destructor and can be passed with a temporary,
// clang will handle re-aligning it for us automatically, and we don't need
// to worry about the passed alignment.
auto RD = dyn_cast<CXXRecordDecl>(D);
if (RD && RD->isCompleteDefinition() && canPassAsTemporary(RD)) {
return "";
// Check if the decl itself has an explicit alignment on it.
if (unsigned ExplicitAlign = checkExplicitAlignment(D)) {
return "it has an explicit alignment of '" +
std::to_string(ExplicitAlign) + "'";
// Check if any of the decl's fields have an explicit alignment on them.
if (auto RD = dyn_cast<RecordDecl>(D)) {
for (auto F : RD->fields()) {
if (unsigned ExplicitAlign = checkExplicitAlignment(F)) {
return ("member '" + F->getName() +
"' has an explicit alignment of '" +
std::to_string(ExplicitAlign) + "'")
// We don't need to check the types of fields, as the CustomTypeAnnotation
// infrastructure will handle that for us.
return "";
NonParamAnnotation NonParam;
void NonParamInsideFunctionDeclChecker::registerMatchers(
MatchFinder *AstMatcher) {
AstMatcher->addMatcher(lambdaExpr().bind("lambda"), this);
void NonParamInsideFunctionDeclChecker::check(
const MatchFinder::MatchResult &Result) {
static DenseSet<const FunctionDecl *> CheckedFunctionDecls;
const FunctionDecl *func = Result.Nodes.getNodeAs<FunctionDecl>("func");
if (!func) {
const LambdaExpr *lambda = Result.Nodes.getNodeAs<LambdaExpr>("lambda");
if (lambda) {
func = lambda->getCallOperator();
if (!func) {
if (func->isDeleted()) {
// We need to skip decls which have these types as parameters in system
// headers, because presumably those headers act like an assertion that the
// alignment will be preserved in that situation.
if (getDeclarationNamespace(func) == "std") {
if (inThirdPartyPath(func)) {
// Don't report errors on the same declarations more than once.
if (CheckedFunctionDecls.count(func)) {
const ClassTemplateSpecializationDecl *Spec =
for (ParmVarDecl *p : func->parameters()) {
QualType T = p->getType().withoutLocalFastQualifiers();
if (NonParam.hasEffectiveAnnotation(T)) {
diag(p->getLocation(), "Type %0 must not be used as parameter",
<< T;
"Please consider passing a const reference instead",
if (Spec) {
"The bad argument was passed to %0 here", DiagnosticIDs::Note)
<< Spec->getSpecializedTemplate();
NonParam.dumpAnnotationReason(*this, T, p->getLocation());