[Wasm][Runtime] Interpret absolute function pointer in runtime structures

When SWIFT_COMPACT_ABSOLUTE_FUNCTION_POINTER is enabled, relative direct
pointers whose pointees are functions will be turned into absolute
pointer at compile-time.

Author: kateinoigakukun

include/swift/ABI/CompactFunctionPointer.h

@@ -0,0 +1,62 @@
+//===--- CompactFunctionPointer.h - Compact Function Pointers ---*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// Swift's runtime structures often use relative function pointers to reduce the
+// size of metadata and also to minimize load-time overhead in PIC.
+// This file defines pointer types whose size and interface are compatible with
+// the relative pointer types for targets that do not support relative references
+// to code from data.
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_ABI_COMPACTFUNCTIONPOINTER_H
+#define SWIFT_ABI_COMPACTFUNCTIONPOINTER_H
+
+namespace swift {
+
+/// A compact unconditional absolute function pointer that can fit in a 32-bit
+/// integer.
+/// As a trade-off compared to relative pointers, this has load-time overhead in PIC
+/// and is only available on 32-bit targets.
+template <typename T>
+class AbsoluteFunctionPointer {
+  T *Pointer;
+  static_assert(sizeof(T *) == sizeof(int32_t),
+                "Function pointer must be 32-bit when using compact absolute pointer");
+
+public:
+  using PointerTy = T *;
+
+  PointerTy get() const & { return Pointer; }
+
+  operator PointerTy() const & { return this->get(); }
+
+  bool isNull() const & { return Pointer == nullptr; }
+
+  /// Resolve a pointer from a `base` pointer and a value loaded from `base`.
+  template <typename BasePtrTy, typename Value>
+  static PointerTy resolve(BasePtrTy *base, Value value) {
+    return reinterpret_cast<PointerTy>(value);
+  }
+
+  template <typename... ArgTy>
+  typename std::result_of<T *(ArgTy...)>::type operator()(ArgTy... arg) const {
+    static_assert(std::is_function<T>::value,
+                  "T must be an explicit function type");
+    return this->get()(std::forward<ArgTy>(arg)...);
+  }
+};
+
+// TODO(katei): Add another pointer structure for 64-bit targets and for efficiency on PIC
+
+} // namespace swift
+
+#endif // SWIFT_ABI_COMPACTFUNCTIONPOINTER_H

include/swift/ABI/Executor.h

@@ -241,7 +241,7 @@ template <class AsyncSignature>
 class AsyncFunctionPointer {
 public:
   /// The function to run.
-  RelativeDirectPointer<AsyncFunctionType<AsyncSignature>,
+  TargetCompactFunctionPointer<InProcess, AsyncFunctionType<AsyncSignature>,
                         /*nullable*/ false,
                         int32_t> Function;
 

include/swift/ABI/Metadata.h

@@ -506,9 +506,20 @@ struct TargetMethodDescriptor {
   MethodDescriptorFlags Flags;
 
   /// The method implementation.
-  TargetRelativeDirectPointer<Runtime, void> Impl;
+  union {
+    TargetCompactFunctionPointer<Runtime, void> Impl;
+    TargetRelativeDirectPointer<Runtime, void> AsyncImpl;
+  };
 
   // TODO: add method types or anything else needed for reflection.
+
+  void *getImpl() const {
+    if (Flags.isAsync()) {
+      return AsyncImpl.get();
+    } else {
+      return Impl.get();
+    }
+  }
 };
 
 using MethodDescriptor = TargetMethodDescriptor<InProcess>;
@@ -578,7 +589,20 @@ struct TargetMethodOverrideDescriptor {
   TargetRelativeMethodDescriptorPointer<Runtime> Method;
 
   /// The implementation of the override.
-  TargetRelativeDirectPointer<Runtime, void, /*nullable*/ true> Impl;
+  union {
+    TargetCompactFunctionPointer<Runtime, void, /*nullable*/ true> Impl;
+    TargetRelativeDirectPointer<Runtime, void, /*nullable*/ true> AsyncImpl;
+  };
+
+  void *getImpl() const {
+    auto *baseMethod = Method.get();
+    assert(baseMethod && "no base method");
+    if (baseMethod->Flags.isAsync()) {
+      return AsyncImpl.get();
+    } else {
+      return Impl.get();
+    }
+  }
 };
 
 /// Header for a class vtable override descriptor. This is a variable-sized
@@ -1523,7 +1547,18 @@ struct TargetProtocolRequirement {
   // TODO: name, type
 
   /// The optional default implementation of the protocol.
-  RelativeDirectPointer<void, /*nullable*/ true> DefaultImplementation;
+  union {
+    TargetCompactFunctionPointer<Runtime, void, /*nullable*/ true> DefaultFuncImplementation;
+    TargetRelativeDirectPointer<Runtime, void, /*nullable*/ true> DefaultImplementation;
+  };
+
+  void *getDefaultImplementation() const {
+    if (Flags.isFunctionImpl()) {
+      return DefaultFuncImplementation.get();
+    } else {
+      return DefaultImplementation.get();
+    }
+  }
 };
 
 using ProtocolRequirement = TargetProtocolRequirement<InProcess>;
@@ -2170,7 +2205,18 @@ using GenericBoxHeapMetadata = TargetGenericBoxHeapMetadata<InProcess>;
 template <typename Runtime>
 struct TargetResilientWitness {
   TargetRelativeProtocolRequirementPointer<Runtime> Requirement;
-  RelativeDirectPointer<void> Witness;
+  union {
+    TargetRelativeDirectPointer<Runtime, void> Impl;
+    TargetCompactFunctionPointer<Runtime, void> FuncImpl;
+  };
+
+  void *getWitness(ProtocolRequirementFlags flags) const {
+    if (flags.isFunctionImpl()) {
+      return FuncImpl.get();
+    } else {
+      return Impl.get();
+    }
+  }
 };
 using ResilientWitness = TargetResilientWitness<InProcess>;
 
@@ -2233,10 +2279,13 @@ struct TargetGenericWitnessTable {
   uint16_t WitnessTablePrivateSizeInWordsAndRequiresInstantiation;
 
   /// The instantiation function, which is called after the template is copied.
-  RelativeDirectPointer<void(TargetWitnessTable<Runtime> *instantiatedTable,
-                             const TargetMetadata<Runtime> *type,
-                             const void * const *instantiationArgs),
-                        /*nullable*/ true> Instantiator;
+  TargetCompactFunctionPointer<
+      Runtime,
+      void(TargetWitnessTable<Runtime> *instantiatedTable,
+           const TargetMetadata<Runtime> *type,
+           const void *const *instantiationArgs),
+      /*nullable*/ true>
+      Instantiator;
 
   using PrivateDataType = void *[swift::NumGenericMetadataPrivateDataWords];
 
@@ -2968,12 +3017,12 @@ using MetadataCompleter =
 template <typename Runtime>
 struct TargetGenericMetadataPattern {
   /// The function to call to instantiate the template.
-  TargetRelativeDirectPointer<Runtime, MetadataInstantiator>
+  TargetCompactFunctionPointer<Runtime, MetadataInstantiator>
     InstantiationFunction;
 
   /// The function to call to complete the instantiation.  If this is null,
   /// the instantiation function must always generate complete metadata.
-  TargetRelativeDirectPointer<Runtime, MetadataCompleter, /*nullable*/ true>
+  TargetCompactFunctionPointer<Runtime, MetadataCompleter, /*nullable*/ true>
     CompletionFunction;
 
   /// Flags describing the layout of this instantiation pattern.
@@ -3080,10 +3129,10 @@ struct TargetGenericClassMetadataPattern final :
   using TargetGenericMetadataPattern<Runtime>::PatternFlags;
 
   /// The heap-destructor function.
-  TargetRelativeDirectPointer<Runtime, HeapObjectDestroyer> Destroy;
+  TargetCompactFunctionPointer<Runtime, HeapObjectDestroyer> Destroy;
 
   /// The ivar-destructor function.
-  TargetRelativeDirectPointer<Runtime, ClassIVarDestroyer, /*nullable*/ true>
+  TargetCompactFunctionPointer<Runtime, ClassIVarDestroyer, /*nullable*/ true>
     IVarDestroyer;
 
   /// The class flags.
@@ -3284,7 +3333,7 @@ class MetadataAccessFunction {
 template <typename Runtime>
 struct TargetForeignMetadataInitialization {
   /// The completion function.  The pattern will always be null.
-  TargetRelativeDirectPointer<Runtime, MetadataCompleter, /*nullable*/ true>
+  TargetCompactFunctionPointer<Runtime, MetadataCompleter, /*nullable*/ true>
     CompletionFunction;
 };
 
@@ -3329,14 +3378,14 @@ struct TargetResilientClassMetadataPattern {
   ///
   /// If this is null, the runtime instead calls swift_relocateClassMetadata(),
   /// passing in the class descriptor and this pattern.
-  TargetRelativeDirectPointer<Runtime, MetadataRelocator, /*nullable*/ true>
+  TargetCompactFunctionPointer<Runtime, MetadataRelocator, /*nullable*/ true>
     RelocationFunction;
 
   /// The heap-destructor function.
-  TargetRelativeDirectPointer<Runtime, HeapObjectDestroyer> Destroy;
+  TargetCompactFunctionPointer<Runtime, HeapObjectDestroyer> Destroy;
 
   /// The ivar-destructor function.
-  TargetRelativeDirectPointer<Runtime, ClassIVarDestroyer, /*nullable*/ true>
+  TargetCompactFunctionPointer<Runtime, ClassIVarDestroyer, /*nullable*/ true>
     IVarDestroyer;
 
   /// The class flags.
@@ -3380,7 +3429,7 @@ struct TargetSingletonMetadataInitialization {
 
   /// The completion function.  The pattern will always be null, even
   /// for a resilient class.
-  TargetRelativeDirectPointer<Runtime, MetadataCompleter>
+  TargetCompactFunctionPointer<Runtime, MetadataCompleter>
     CompletionFunction;
 
   bool hasResilientClassPattern(
@@ -3409,7 +3458,7 @@ struct TargetCanonicalSpecializedMetadatasListEntry {
 
 template <typename Runtime>
 struct TargetCanonicalSpecializedMetadataAccessorsListEntry {
-  TargetRelativeDirectPointer<Runtime, MetadataResponse(MetadataRequest), /*Nullable*/ false> accessor;
+  TargetCompactFunctionPointer<Runtime, MetadataResponse(MetadataRequest), /*Nullable*/ false> accessor;
 };
 
 template <typename Runtime>
@@ -3429,7 +3478,7 @@ class TargetTypeContextDescriptor
   /// The function type here is a stand-in. You should use getAccessFunction()
   /// to wrap the function pointer in an accessor that uses the proper calling
   /// convention for a given number of arguments.
-  TargetRelativeDirectPointer<Runtime, MetadataResponse(...),
+  TargetCompactFunctionPointer<Runtime, MetadataResponse(...),
                               /*Nullable*/ true> AccessFunctionPtr;
 
   /// A pointer to the field descriptor for the type, if any.
@@ -3694,7 +3743,7 @@ class TargetClassDescriptor final
   using MetadataListEntry = 
     TargetCanonicalSpecializedMetadatasListEntry<Runtime>;
   using MetadataAccessor = 
-    TargetRelativeDirectPointer<Runtime, MetadataResponse(MetadataRequest), /*Nullable*/ false>;
+    TargetCompactFunctionPointer<Runtime, MetadataResponse(MetadataRequest), /*Nullable*/ false>;
   using MetadataAccessorListEntry =
       TargetCanonicalSpecializedMetadataAccessorsListEntry<Runtime>;
   using MetadataCachingOnceToken =
@@ -4495,12 +4544,23 @@ class DynamicReplacementDescriptor {
                           DynamicReplacementKey *
                               __ptrauth_swift_dynamic_replacement_key>>
       replacedFunctionKey;
-  RelativeDirectPointer<void, false> replacementFunction;
+  union {
+    TargetCompactFunctionPointer<InProcess, void, false> replacementFunction;
+    TargetRelativeDirectPointer<InProcess, void, false> replacementAsyncFunction;
+  };
   RelativeDirectPointer<DynamicReplacementChainEntry, false> chainEntry;
   uint32_t flags;
 
   enum : uint32_t { EnableChainingMask = 0x1 };
 
+  void *getReplacementFunction() const {
+    if (replacedFunctionKey->isAsync()) {
+      return replacementAsyncFunction.get();
+    } else {
+      return replacementFunction.get();
+    }
+  }
+
 public:
   /// Enable this replacement by changing the function's replacement chain's
   /// root entry.

include/swift/ABI/MetadataValues.h

@@ -611,6 +611,21 @@ class ProtocolRequirementFlags {
 
   int_type getIntValue() const { return Value; }
 
+  /// Is the method implementation is represented as a native function pointer?
+  bool isFunctionImpl() const {
+    switch (getKind()) {
+    case ProtocolRequirementFlags::Kind::Method:
+    case ProtocolRequirementFlags::Kind::Init:
+    case ProtocolRequirementFlags::Kind::Getter:
+    case ProtocolRequirementFlags::Kind::Setter:
+    case ProtocolRequirementFlags::Kind::ReadCoroutine:
+    case ProtocolRequirementFlags::Kind::ModifyCoroutine:
+      return !isAsync();
+    default:
+      return false;
+    }
+  }
+
   enum : uintptr_t {
     /// Bit used to indicate that an associated type witness is a pointer to
     /// a mangled name (vs. a pointer to metadata).

include/swift/ABI/TargetLayout.h

@@ -31,6 +31,7 @@
 
 #include "swift/Runtime/Config.h"
 #include "swift/Basic/RelativePointer.h"
+#include "swift/ABI/CompactFunctionPointer.h"
 
 namespace swift {
 
@@ -101,6 +102,14 @@ struct InProcess {
   template <typename T, bool Nullable = true>
   using RelativeDirectPointer = RelativeDirectPointer<T, Nullable>;
 
+  template <typename T, bool Nullable = true, typename Offset = int32_t>
+#if SWIFT_COMPACT_ABSOLUTE_FUNCTION_POINTER
+  using CompactFunctionPointer = AbsoluteFunctionPointer<T>;
+#else
+  using CompactFunctionPointer =
+      swift::RelativeDirectPointer<T, Nullable, Offset>;
+#endif
+
   template<typename T>
   T *getStrippedSignedPointer(const T *pointer) const {
     return swift_ptrauth_strip(pointer);
@@ -163,6 +172,9 @@ struct External {
   template <typename T, bool Nullable = true>
   using RelativeDirectPointer = int32_t;
 
+  template <typename T, bool Nullable = true, typename Offset = int32_t>
+  using CompactFunctionPointer = int32_t;
+
   StoredPointer getStrippedSignedPointer(const StoredSignedPointer pointer) const {
     return swift_ptrauth_strip(pointer);
   }
@@ -191,6 +203,12 @@ template <typename Runtime, typename Pointee, bool Nullable = true>
 using TargetRelativeIndirectablePointer
   = typename Runtime::template RelativeIndirectablePointer<Pointee,Nullable>;
 
+template <typename Runtime, typename Pointee, bool Nullable = true,
+          typename Offset = int32_t>
+using TargetCompactFunctionPointer =
+    typename Runtime::template CompactFunctionPointer<Pointee, Nullable,
+                                                      Offset>;
+
 } // end namespace swift
 
 #endif