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//===--- InferAlloc.cpp - Allocation type inference -----------------------===//
//
// 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 implements allocation-related type inference.
//
//===----------------------------------------------------------------------===//
#include "clang/AST/InferAlloc.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/Expr.h"
#include "clang/AST/Type.h"
#include "clang/Basic/IdentifierTable.h"
#include "llvm/ADT/SmallPtrSet.h"
using namespace clang;
using namespace infer_alloc;
static bool
typeContainsPointer(QualType T,
llvm::SmallPtrSet<const RecordDecl *, 4> &VisitedRD,
bool &IncompleteType) {
QualType CanonicalType = T.getCanonicalType();
if (CanonicalType->isPointerType())
return true; // base case
// Look through typedef chain to check for special types.
for (QualType CurrentT = T; const auto *TT = CurrentT->getAs<TypedefType>();
CurrentT = TT->getDecl()->getUnderlyingType()) {
const IdentifierInfo *II = TT->getDecl()->getIdentifier();
// Special Case: Syntactically uintptr_t is not a pointer; semantically,
// however, very likely used as such. Therefore, classify uintptr_t as a
// pointer, too.
if (II && II->isStr("uintptr_t"))
return true;
}
// The type is an array; check the element type.
if (const ArrayType *AT = dyn_cast<ArrayType>(CanonicalType))
return typeContainsPointer(AT->getElementType(), VisitedRD, IncompleteType);
// The type is a struct, class, or union.
if (const RecordDecl *RD = CanonicalType->getAsRecordDecl()) {
if (!RD->isCompleteDefinition()) {
IncompleteType = true;
return false;
}
if (!VisitedRD.insert(RD).second)
return false; // already visited
// Check all fields.
for (const FieldDecl *Field : RD->fields()) {
if (typeContainsPointer(Field->getType(), VisitedRD, IncompleteType))
return true;
}
// For C++ classes, also check base classes.
if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
// Polymorphic types require a vptr.
if (CXXRD->isDynamicClass())
return true;
for (const CXXBaseSpecifier &Base : CXXRD->bases()) {
if (typeContainsPointer(Base.getType(), VisitedRD, IncompleteType))
return true;
}
}
}
return false;
}
/// Infer type from a simple sizeof expression.
static QualType inferTypeFromSizeofExpr(const Expr *E) {
const Expr *Arg = E->IgnoreParenImpCasts();
if (const auto *UET = dyn_cast<UnaryExprOrTypeTraitExpr>(Arg)) {
if (UET->getKind() == UETT_SizeOf) {
if (UET->isArgumentType())
return UET->getArgumentTypeInfo()->getType();
else
return UET->getArgumentExpr()->getType();
}
}
return QualType();
}
/// Infer type from an arithmetic expression involving a sizeof. For example:
///
/// malloc(sizeof(MyType) + padding); // infers 'MyType'
/// malloc(sizeof(MyType) * 32); // infers 'MyType'
/// malloc(32 * sizeof(MyType)); // infers 'MyType'
/// malloc(sizeof(MyType) << 1); // infers 'MyType'
/// ...
///
/// More complex arithmetic expressions are supported, but are a heuristic, e.g.
/// when considering allocations for structs with flexible array members:
///
/// malloc(sizeof(HasFlexArray) + sizeof(int) * 32); // infers 'HasFlexArray'
///
static QualType inferPossibleTypeFromArithSizeofExpr(const Expr *E) {
const Expr *Arg = E->IgnoreParenImpCasts();
// The argument is a lone sizeof expression.
if (QualType T = inferTypeFromSizeofExpr(Arg); !T.isNull())
return T;
if (const auto *BO = dyn_cast<BinaryOperator>(Arg)) {
// Argument is an arithmetic expression. Cover common arithmetic patterns
// involving sizeof.
switch (BO->getOpcode()) {
case BO_Add:
case BO_Div:
case BO_Mul:
case BO_Shl:
case BO_Shr:
case BO_Sub:
if (QualType T = inferPossibleTypeFromArithSizeofExpr(BO->getLHS());
!T.isNull())
return T;
if (QualType T = inferPossibleTypeFromArithSizeofExpr(BO->getRHS());
!T.isNull())
return T;
break;
default:
break;
}
}
return QualType();
}
/// If the expression E is a reference to a variable, infer the type from a
/// variable's initializer if it contains a sizeof. Beware, this is a heuristic
/// and ignores if a variable is later reassigned. For example:
///
/// size_t my_size = sizeof(MyType);
/// void *x = malloc(my_size); // infers 'MyType'
///
static QualType inferPossibleTypeFromVarInitSizeofExpr(const Expr *E) {
const Expr *Arg = E->IgnoreParenImpCasts();
if (const auto *DRE = dyn_cast<DeclRefExpr>(Arg)) {
if (const auto *VD = dyn_cast<VarDecl>(DRE->getDecl())) {
if (const Expr *Init = VD->getInit())
return inferPossibleTypeFromArithSizeofExpr(Init);
}
}
return QualType();
}
/// Deduces the allocated type by checking if the allocation call's result
/// is immediately used in a cast expression. For example:
///
/// MyType *x = (MyType *)malloc(4096); // infers 'MyType'
///
static QualType inferPossibleTypeFromCastExpr(const CallExpr *CallE,
const CastExpr *CastE) {
if (!CastE)
return QualType();
QualType PtrType = CastE->getType();
if (PtrType->isPointerType())
return PtrType->getPointeeType();
return QualType();
}
QualType infer_alloc::inferPossibleType(const CallExpr *E,
const ASTContext &Ctx,
const CastExpr *CastE) {
QualType AllocType;
// First check arguments.
for (const Expr *Arg : E->arguments()) {
AllocType = inferPossibleTypeFromArithSizeofExpr(Arg);
if (AllocType.isNull())
AllocType = inferPossibleTypeFromVarInitSizeofExpr(Arg);
if (!AllocType.isNull())
break;
}
// Then check later casts.
if (AllocType.isNull())
AllocType = inferPossibleTypeFromCastExpr(E, CastE);
return AllocType;
}
std::optional<llvm::AllocTokenMetadata>
infer_alloc::getAllocTokenMetadata(QualType T, const ASTContext &Ctx) {
llvm::AllocTokenMetadata ATMD;
// Get unique type name.
PrintingPolicy Policy(Ctx.getLangOpts());
Policy.SuppressTagKeyword = true;
Policy.FullyQualifiedName = true;
llvm::raw_svector_ostream TypeNameOS(ATMD.TypeName);
T.getCanonicalType().print(TypeNameOS, Policy);
// Check if QualType contains a pointer. Implements a simple DFS to
// recursively check if a type contains a pointer type.
llvm::SmallPtrSet<const RecordDecl *, 4> VisitedRD;
bool IncompleteType = false;
ATMD.ContainsPointer = typeContainsPointer(T, VisitedRD, IncompleteType);
if (!ATMD.ContainsPointer && IncompleteType)
return std::nullopt;
return ATMD;
}
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