v8-fast-api-calls.h

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// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#ifndef INCLUDE_V8_FAST_API_CALLS_H_
#define INCLUDE_V8_FAST_API_CALLS_H_
 
#include <stddef.h>
#include <stdint.h>
 
#include "v8config.h"  // NOLINT(build/include_directory)
 
namespace v8 {
 
class CTypeInfo {
 public:
  enum class Type : char {
    kVoid,
    kBool,
    kInt32,
    kUint32,
    kInt64,
    kUint64,
    kFloat32,
    kFloat64,
    kUnwrappedApiObject,
  };
 
  enum class ArgFlags : uint8_t {
    kNone = 0,
    kIsArrayBit = 1 << 0,  // This argument is first in an array of values.
  };
 
  static CTypeInfo FromWrapperType(const void* wrapper_type_info,
                                   ArgFlags flags = ArgFlags::kNone) {
    uintptr_t wrapper_type_info_ptr =
        reinterpret_cast<uintptr_t>(wrapper_type_info);
    // Check that the lower kIsWrapperTypeBit bits are 0's.
    CHECK_EQ(
        wrapper_type_info_ptr & ~(static_cast<uintptr_t>(~0)
                                  << static_cast<uintptr_t>(kIsWrapperTypeBit)),
        0u);
    // TODO(mslekova): Refactor the manual bit manipulations to use
    // PointerWithPayload instead.
    return CTypeInfo(wrapper_type_info_ptr | static_cast<int>(flags) |
                     kIsWrapperTypeBit);
  }
 
  static constexpr CTypeInfo FromCType(Type ctype,
                                       ArgFlags flags = ArgFlags::kNone) {
    // ctype cannot be Type::kUnwrappedApiObject.
    return CTypeInfo(
        ((static_cast<uintptr_t>(ctype) << kTypeOffset) & kTypeMask) |
        static_cast<int>(flags));
  }
 
  const void* GetWrapperInfo() const;
 
  constexpr Type GetType() const {
    if (payload_ & kIsWrapperTypeBit) {
      return Type::kUnwrappedApiObject;
    }
    return static_cast<Type>((payload_ & kTypeMask) >> kTypeOffset);
  }
 
  constexpr bool IsArray() const {
    return payload_ & static_cast<int>(ArgFlags::kIsArrayBit);
  }
 
 private:
  explicit constexpr CTypeInfo(uintptr_t payload) : payload_(payload) {}
 
  // That must be the last bit after ArgFlags.
  static constexpr uintptr_t kIsWrapperTypeBit = 1 << 1;
  static constexpr uintptr_t kWrapperTypeInfoMask = static_cast<uintptr_t>(~0)
                                                    << 2;
 
  static constexpr unsigned int kTypeOffset = kIsWrapperTypeBit;
  static constexpr unsigned int kTypeSize = 8 - kTypeOffset;
  static constexpr uintptr_t kTypeMask =
      (~(static_cast<uintptr_t>(~0) << kTypeSize)) << kTypeOffset;
 
  const uintptr_t payload_;
};
 
class CFunctionInfo {
 public:
  virtual const CTypeInfo& ReturnInfo() const = 0;
  virtual unsigned int ArgumentCount() const = 0;
  virtual const CTypeInfo& ArgumentInfo(unsigned int index) const = 0;
};
 
template <typename T>
class WrapperTraits {
 public:
  static const void* GetTypeInfo() {
    static_assert(sizeof(T) != sizeof(T),
                  "WrapperTraits must be specialized for this type.");
    return nullptr;
  }
};
 
namespace internal {
 
template <typename T>
struct GetCType {
  static_assert(sizeof(T) != sizeof(T), "Unsupported CType");
};
 
#define SPECIALIZE_GET_C_TYPE_FOR(ctype, ctypeinfo)            \
  template <>                                                  \
  struct GetCType<ctype> {                                     \
    static constexpr CTypeInfo Get() {                         \
      return CTypeInfo::FromCType(CTypeInfo::Type::ctypeinfo); \
    }                                                          \
  };
 
#define SUPPORTED_C_TYPES(V) \
  V(void, kVoid)             \
  V(bool, kBool)             \
  V(int32_t, kInt32)         \
  V(uint32_t, kUint32)       \
  V(int64_t, kInt64)         \
  V(uint64_t, kUint64)       \
  V(float, kFloat32)         \
  V(double, kFloat64)
 
SUPPORTED_C_TYPES(SPECIALIZE_GET_C_TYPE_FOR)
 
template <typename T, typename = void>
struct EnableIfHasWrapperTypeInfo {};
 
template <typename T>
struct EnableIfHasWrapperTypeInfo<T, decltype(WrapperTraits<T>::GetTypeInfo(),
                                              void())> {
  typedef void type;
};
 
// T* where T is a primitive (array of primitives).
template <typename T, typename = void>
struct GetCTypePointerImpl {
  static constexpr CTypeInfo Get() {
    return CTypeInfo::FromCType(GetCType<T>::Get().GetType(),
                                CTypeInfo::ArgFlags::kIsArrayBit);
  }
};
 
// T* where T is an API object.
template <typename T>
struct GetCTypePointerImpl<T, typename EnableIfHasWrapperTypeInfo<T>::type> {
  static constexpr CTypeInfo Get() {
    return CTypeInfo::FromWrapperType(WrapperTraits<T>::GetTypeInfo());
  }
};
 
// T** where T is a primitive. Not allowed.
template <typename T, typename = void>
struct GetCTypePointerPointerImpl {
  static_assert(sizeof(T**) != sizeof(T**), "Unsupported type");
};
 
// T** where T is an API object (array of API objects).
template <typename T>
struct GetCTypePointerPointerImpl<
    T, typename EnableIfHasWrapperTypeInfo<T>::type> {
  static constexpr CTypeInfo Get() {
    return CTypeInfo::FromWrapperType(WrapperTraits<T>::GetTypeInfo(),
                                      CTypeInfo::ArgFlags::kIsArrayBit);
  }
};
 
template <typename T>
struct GetCType<T**> : public GetCTypePointerPointerImpl<T> {};
 
template <typename T>
struct GetCType<T*> : public GetCTypePointerImpl<T> {};
 
template <typename R, typename... Args>
class CFunctionInfoImpl : public CFunctionInfo {
 public:
  CFunctionInfoImpl()
      : return_info_(internal::GetCType<R>::Get()),
        arg_count_(sizeof...(Args)),
        arg_info_{internal::GetCType<Args>::Get()...} {
    static_assert(
        internal::GetCType<R>::Get().GetType() == CTypeInfo::Type::kVoid,
        "Only void return types are currently supported.");
  }
 
  const CTypeInfo& ReturnInfo() const override { return return_info_; }
  unsigned int ArgumentCount() const override { return arg_count_; }
  const CTypeInfo& ArgumentInfo(unsigned int index) const override {
    CHECK_LT(index, ArgumentCount());
    return arg_info_[index];
  }
 
 private:
  CTypeInfo return_info_;
  const unsigned int arg_count_;
  CTypeInfo arg_info_[sizeof...(Args)];
};
 
}  // namespace internal
 
class V8_EXPORT CFunction {
 public:
  constexpr CFunction() : address_(nullptr), type_info_(nullptr) {}
 
  const CTypeInfo& ReturnInfo() const { return type_info_->ReturnInfo(); }
 
  const CTypeInfo& ArgumentInfo(unsigned int index) const {
    return type_info_->ArgumentInfo(index);
  }
 
  unsigned int ArgumentCount() const { return type_info_->ArgumentCount(); }
 
  const void* GetAddress() const { return address_; }
  const CFunctionInfo* GetTypeInfo() const { return type_info_; }
 
  template <typename F>
  static CFunction Make(F* func) {
    return ArgUnwrap<F*>::Make(func);
  }
 
 private:
  const void* address_;
  const CFunctionInfo* type_info_;
 
  CFunction(const void* address, const CFunctionInfo* type_info);
 
  template <typename R, typename... Args>
  static CFunctionInfo* GetCFunctionInfo() {
    static internal::CFunctionInfoImpl<R, Args...> instance;
    return &instance;
  }
 
  template <typename F>
  class ArgUnwrap {
    static_assert(sizeof(F) != sizeof(F),
                  "CFunction must be created from a function pointer.");
  };
 
  template <typename R, typename... Args>
  class ArgUnwrap<R (*)(Args...)> {
   public:
    static CFunction Make(R (*func)(Args...)) {
      return CFunction(reinterpret_cast<const void*>(func),
                       GetCFunctionInfo<R, Args...>());
    }
  };
};
 
}  // namespace v8
 
#endif  // INCLUDE_V8_FAST_API_CALLS_H_