[clang] [clang] Implement function pointer type discrimination (PR #96992)
Daniil Kovalev via cfe-commits
cfe-commits at lists.llvm.org
Fri Jun 28 08:14:24 PDT 2024
================
@@ -3140,6 +3140,269 @@ ASTContext::getPointerAuthVTablePointerDiscriminator(const CXXRecordDecl *RD) {
return llvm::getPointerAuthStableSipHash(Str);
}
+/// Encode a function type for use in the discriminator of a function pointer
+/// type. We can't use the itanium scheme for this since C has quite permissive
+/// rules for type compatibility that we need to be compatible with.
+///
+/// Formally, this function associates every function pointer type T with an
+/// encoded string E(T). Let the equivalence relation T1 ~ T2 be defined as
+/// E(T1) == E(T2). E(T) is part of the ABI of values of type T. C type
+/// compatibility requires equivalent treatment under the ABI, so
+/// CCompatible(T1, T2) must imply E(T1) == E(T2), that is, CCompatible must be
+/// a subset of ~. Crucially, however, it must be a proper subset because
+/// CCompatible is not an equivalence relation: for example, int[] is compatible
+/// with both int[1] and int[2], but the latter are not compatible with each
+/// other. Therefore this encoding function must be careful to only distinguish
+/// types if there is no third type with which they are both required to be
+/// compatible.
+static void encodeTypeForFunctionPointerAuth(ASTContext &Ctx, raw_ostream &OS,
+ QualType QT) {
+ // FIXME: Consider address space qualifiers.
+ const Type *T = QT.getCanonicalType().getTypePtr();
+
+ // FIXME: Consider using the C++ type mangling when we encounter a construct
+ // that is incompatible with C.
+
+ switch (T->getTypeClass()) {
+ case Type::Atomic:
+ return encodeTypeForFunctionPointerAuth(
+ Ctx, OS, cast<AtomicType>(T)->getValueType());
+
+ case Type::LValueReference:
+ OS << "R";
+ encodeTypeForFunctionPointerAuth(Ctx, OS,
+ cast<ReferenceType>(T)->getPointeeType());
+ return;
+ case Type::RValueReference:
+ OS << "O";
+ encodeTypeForFunctionPointerAuth(Ctx, OS,
+ cast<ReferenceType>(T)->getPointeeType());
+ return;
+
+ case Type::Pointer:
+ // C11 6.7.6.1p2:
+ // For two pointer types to be compatible, both shall be identically
+ // qualified and both shall be pointers to compatible types.
+ // FIXME: we should also consider pointee types.
+ OS << "P";
+ return;
+
+ case Type::ObjCObjectPointer:
+ case Type::BlockPointer:
+ OS << "P";
+ return;
+
+ case Type::Complex:
+ OS << "C";
+ return encodeTypeForFunctionPointerAuth(
+ Ctx, OS, cast<ComplexType>(T)->getElementType());
+
+ case Type::VariableArray:
+ case Type::ConstantArray:
+ case Type::IncompleteArray:
+ case Type::ArrayParameter:
+ // C11 6.7.6.2p6:
+ // For two array types to be compatible, both shall have compatible
+ // element types, and if both size specifiers are present, and are integer
+ // constant expressions, then both size specifiers shall have the same
+ // constant value [...]
+ //
+ // So since ElemType[N] has to be compatible ElemType[], we can't encode the
+ // width of the array.
+ OS << "A";
+ return encodeTypeForFunctionPointerAuth(
+ Ctx, OS, cast<ArrayType>(T)->getElementType());
+
+ case Type::ObjCInterface:
+ case Type::ObjCObject:
+ OS << "<objc_object>";
+ return;
+
+ case Type::Enum:
+ // C11 6.7.2.2p4:
+ // Each enumerated type shall be compatible with char, a signed integer
+ // type, or an unsigned integer type.
+ //
+ // So we have to treat enum types as integers.
+ OS << "i";
+ return;
+
+ case Type::FunctionNoProto:
+ case Type::FunctionProto: {
+ // C11 6.7.6.3p15:
+ // For two function types to be compatible, both shall specify compatible
+ // return types. Moreover, the parameter type lists, if both are present,
+ // shall agree in the number of parameters and in the use of the ellipsis
+ // terminator; corresponding parameters shall have compatible types.
+ //
+ // That paragraph goes on to describe how unprototyped functions are to be
+ // handled, which we ignore here. Unprototyped function pointers are hashed
+ // as though they were prototyped nullary functions since thats probably
+ // what the user meant. This behavior is non-conforming.
+ // FIXME: If we add a "custom discriminator" function type attribute we
+ // should encode functions as their discriminators.
+ OS << "F";
+ auto *FuncType = cast<FunctionType>(T);
+ encodeTypeForFunctionPointerAuth(Ctx, OS, FuncType->getReturnType());
+ if (auto *FPT = dyn_cast<FunctionProtoType>(FuncType)) {
+ for (QualType Param : FPT->param_types()) {
+ Param = Ctx.getSignatureParameterType(Param);
+ encodeTypeForFunctionPointerAuth(Ctx, OS, Param);
+ }
+ if (FPT->isVariadic())
+ OS << "z";
+ }
+ OS << "E";
+ return;
+ }
+
+ case Type::MemberPointer: {
+ OS << "M";
+ auto *MPT = T->getAs<MemberPointerType>();
+ encodeTypeForFunctionPointerAuth(Ctx, OS, QualType(MPT->getClass(), 0));
+ encodeTypeForFunctionPointerAuth(Ctx, OS, MPT->getPointeeType());
+ return;
+ }
+ case Type::ExtVector:
+ case Type::Vector:
+ OS << "Dv" << Ctx.getTypeSizeInChars(T).getQuantity();
+ break;
+
+ // Don't bother discriminating based on these types.
+ case Type::Pipe:
+ case Type::BitInt:
+ case Type::ConstantMatrix:
+ OS << "?";
+ return;
+
+ case Type::Builtin: {
+ const BuiltinType *BTy = T->getAs<BuiltinType>();
+ switch (BTy->getKind()) {
+#define SIGNED_TYPE(Id, SingletonId) \
+ case BuiltinType::Id: \
+ OS << "i"; \
+ return;
+#define UNSIGNED_TYPE(Id, SingletonId) \
+ case BuiltinType::Id: \
+ OS << "i"; \
+ return;
+#define PLACEHOLDER_TYPE(Id, SingletonId) case BuiltinType::Id:
+#define BUILTIN_TYPE(Id, SingletonId)
+#include "clang/AST/BuiltinTypes.def"
+ llvm_unreachable("placeholder types should not appear here.");
+
+ case BuiltinType::Half:
+ OS << "Dh";
+ return;
+ case BuiltinType::Float:
+ OS << "f";
+ return;
+ case BuiltinType::Double:
+ OS << "d";
+ return;
+ case BuiltinType::LongDouble:
+ OS << "e";
+ return;
+ case BuiltinType::Float16:
+ OS << "DF16_";
+ return;
+ case BuiltinType::Float128:
+ OS << "g";
+ return;
+
+ case BuiltinType::Void:
+ OS << "v";
+ return;
+
+ case BuiltinType::ObjCId:
+ case BuiltinType::ObjCClass:
+ case BuiltinType::ObjCSel:
+ case BuiltinType::NullPtr:
+ OS << "P";
+ return;
+
+ // Don't bother discriminating based on OpenCL types.
+ case BuiltinType::OCLSampler:
+ case BuiltinType::OCLEvent:
+ case BuiltinType::OCLClkEvent:
+ case BuiltinType::OCLQueue:
+ case BuiltinType::OCLReserveID:
+ case BuiltinType::BFloat16:
+ case BuiltinType::VectorQuad:
+ case BuiltinType::VectorPair:
+ OS << "?";
+ return;
+
+ // Don't bother discriminating based on these seldom-used types.
+ case BuiltinType::Ibm128:
+ return;
+#define IMAGE_TYPE(ImgType, Id, SingletonId, Access, Suffix) \
+ case BuiltinType::Id: \
+ return;
+#include "clang/Basic/OpenCLImageTypes.def"
+#define EXT_OPAQUE_TYPE(ExtType, Id, Ext) \
+ case BuiltinType::Id: \
+ return;
+#include "clang/Basic/OpenCLExtensionTypes.def"
+#define SVE_TYPE(Name, Id, SingletonId) \
+ case BuiltinType::Id: \
+ return;
+#include "clang/Basic/AArch64SVEACLETypes.def"
+ case BuiltinType::Dependent:
+ llvm_unreachable("should never get here");
+ case BuiltinType::AMDGPUBufferRsrc:
+ case BuiltinType::WasmExternRef:
+#define RVV_TYPE(Name, Id, SingletonId) case BuiltinType::Id:
+#include "clang/Basic/RISCVVTypes.def"
+ llvm_unreachable("not yet implemented");
+ }
+ }
+ case Type::Record: {
+ RecordDecl *RD = T->getAs<RecordType>()->getDecl();
+ IdentifierInfo *II = RD->getIdentifier();
+ if (!II)
+ if (const TypedefNameDecl *Typedef = RD->getTypedefNameForAnonDecl())
+ II = Typedef->getDeclName().getAsIdentifierInfo();
+
+ if (!II) {
+ OS << "<anonymous_record>";
+ return;
+ }
+ OS << II->getLength() << II->getName();
+ return;
+ }
+ case Type::DeducedTemplateSpecialization:
+ case Type::Auto:
+#define NON_CANONICAL_TYPE(Class, Base) case Type::Class:
+#define DEPENDENT_TYPE(Class, Base) case Type::Class:
+#define NON_CANONICAL_UNLESS_DEPENDENT_TYPE(Class, Base) case Type::Class:
+#define ABSTRACT_TYPE(Class, Base)
+#define TYPE(Class, Base)
+#include "clang/AST/TypeNodes.inc"
+ llvm_unreachable("unexpected non-canonical or dependent type!");
+ return;
+ }
+}
+
+uint16_t ASTContext::getPointerAuthTypeDiscriminator(QualType T) {
----------------
kovdan01 wrote:
```suggestion
uint16_t ASTContext::getPointerAuthTypeDiscriminator(QualType T) const {
```
https://github.com/llvm/llvm-project/pull/96992
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