Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 296 insertions, 0 deletions

diff --git a/js/src/wasm/WasmSerialize.h b/js/src/wasm/WasmSerialize.h
new file mode 100644
index 0000000000..918e50b42d
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+++ b/js/src/wasm/WasmSerialize.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ *
+ * Copyright 2022 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef wasm_serialize_h
+#define wasm_serialize_h
+
+#include "mozilla/CheckedInt.h"
+#include "mozilla/MacroForEach.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/Result.h"
+
+#include <cstdint>
+#include <cstring>
+#include <type_traits>
+
+namespace js {
+namespace wasm {
+
+class TypeContext;
+
+// [SMDOC] "Module serialization"
+//
+// A wasm::Module may be serialized to a binary format that allows for quick
+// reloads of a previous compiled wasm binary.
+//
+// The binary format is optimized for encoding/decoding speed, not size. There
+// is no formal specification, and no backwards/forwards compatibility
+// guarantees. The prelude of the encoding contains a 'build ID' which must be
+// used when reading from a cache entry to determine if it is valid.
+//
+// Module serialization and deserialization are performed using templated
+// functions that allow for (imperfect) abstraction over whether we are decoding
+// or encoding the module. It can be viewed as a specialization of the visitor
+// pattern.
+//
+// Each module data structure is visited by a function parameterized by the
+// "mode", which may be either:
+//  1. MODE_SIZE - We are computing the final encoding size, before encoding it
+//  2. MODE_ENCODE - We are actually encoding the module to bytes
+//  3. MODE_DECODE - We are decoding the module from bytes
+//
+// These functions are called "coding" functions, as they are generic to whether
+// we are "encoding" or "decoding". The verb tense "code" is used for the
+// prefix.
+//
+// Each coding function takes the item being visited, along with a "Coder"
+// which contains the state needed for each mode. This is either a buffer span
+// or an accumulated length. The coding function either manipulates the Coder
+// directly or delegates to its field's coding functions.
+//
+// Leaf data types are usually just copied directly to and from memory using a
+// generic "CodePod" function. See the "cacheable POD" documentation in this
+// file for more information.
+//
+// Non-leaf data types need an explicit coding function. This function can
+// usually be completely generic to decoding/encoding, and delegate to the
+// coding functions for each field. Separate decoding/encoding functions may
+// be needed when decoding requires initialization logic, such as constructors.
+// In this case, it is critical that both functions agree on the fields to be
+// coded, and the order they are coded in.
+//
+// Coding functions are defined as free functions in "WasmSerialize.cpp". When
+// they require access to protected state in a type, they may use the
+// WASM_DECLARE_FRIEND_SERIALIZE macro.
+
+// Signal an out of memory condition
+struct OutOfMemory {};
+
+// The result of serialization, either OK or OOM
+using CoderResult = mozilla::Result<mozilla::Ok, OutOfMemory>;
+
+// CoderMode parameterizes the coding functions
+enum CoderMode {
+  // We are computing the final size of the encoded buffer. This is a discrete
+  // pass that runs before encoding.
+  MODE_SIZE,
+  // We are encoding the module to bytes.
+  MODE_ENCODE,
+  // We are decoding the module from bytes.
+  MODE_DECODE,
+};
+
+// Coding functions take a different argument depending on which CoderMode
+// they are invoked with:
+//   * MODE_SIZE - const T*
+//   * MODE_ENCODE - const T*
+//   * MODE_DECODE - T*
+//
+// The CoderArg<mode, T> type alias is used to acquire the proper type for
+// coding function arguments.
+template <CoderMode mode, typename V>
+struct CoderArgT;
+
+template <typename V>
+struct CoderArgT<MODE_SIZE, V> {
+  using T = const V*;
+};
+
+template <typename V>
+struct CoderArgT<MODE_DECODE, V> {
+  using T = V*;
+};
+
+template <typename V>
+struct CoderArgT<MODE_ENCODE, V> {
+  using T = const V*;
+};
+
+template <CoderMode mode, typename T>
+using CoderArg = typename CoderArgT<mode, T>::T;
+
+// Coder is the state provided to all coding functions during module traversal.
+template <CoderMode mode>
+struct Coder;
+
+// A Coder<MODE_SIZE> computes the total encoded size of a module
+template <>
+struct Coder<MODE_SIZE> {
+  explicit Coder(const TypeContext* types) : types_(types), size_(0) {}
+
+  // The types of the module that we're going to encode. This is required in
+  // order to encode the original index of types that we encounter.
+  const TypeContext* types_;
+
+  // The current size of buffer required to serialize this module.
+  mozilla::CheckedInt<size_t> size_;
+
+  // This function shares a signature with MODE_ENCODE to allow functions to be
+  // generic across MODE_SIZE/MODE_ENCODE, even though the src pointer is not
+  // needed for MODE_SIZE.
+  CoderResult writeBytes(const void* unusedSrc, size_t length);
+};
+
+// A Coder<MODE_ENCODE> holds the buffer being written to
+template <>
+struct Coder<MODE_ENCODE> {
+  Coder(const TypeContext* types, uint8_t* start, size_t length)
+      : types_(types), buffer_(start), end_(start + length) {}
+
+  // The types of the module that we're encoding. This is required in
+  // order to encode the original index of types that we encounter.
+  const TypeContext* types_;
+
+  // The current position in the buffer we're writing to.
+  uint8_t* buffer_;
+  // The end position in the buffer we're writing to.
+  const uint8_t* end_;
+
+  CoderResult writeBytes(const void* src, size_t length);
+};
+
+// A Coder<MODE_DECODE> holds the buffer being read from
+template <>
+struct Coder<MODE_DECODE> {
+  Coder(const uint8_t* start, size_t length)
+      : types_(nullptr), buffer_(start), end_(start + length) {}
+
+  // The types of the module that we're decoding. This is null until the types
+  // of this module are decoded.
+  const TypeContext* types_;
+
+  // The current position in the buffer we're reading from.
+  const uint8_t* buffer_;
+  // The end position in the buffer we're reading from.
+  const uint8_t* end_;
+
+  CoderResult readBytes(void* dest, size_t length);
+};
+
+// Macros to help types declare friendship with a coding function
+
+#define WASM_DECLARE_FRIEND_SERIALIZE(TYPE) \
+  template <CoderMode mode>                 \
+  friend CoderResult Code##TYPE(Coder<mode>&, CoderArg<mode, TYPE>);
+
+#define WASM_DECLARE_FRIEND_SERIALIZE_ARGS(TYPE, ARGS...) \
+  template <CoderMode mode>                               \
+  friend CoderResult Code##TYPE(Coder<mode>&, CoderArg<mode, TYPE>, ARGS);
+
+// [SMDOC] "Cacheable POD"
+//
+// Module serialization relies on copying simple structs to and from the
+// cache format. We need a way to ensure that we only do this on types that are
+// "safe". We call this "cacheable POD". Note: this is not the same thing as
+// "POD" as that may contain pointers, which are not cacheable.
+//
+// We define cacheable POD (C-POD) recursively upon types:
+//   1. any integer type is C-POD
+//   2. any floating point type is C-POD
+//   3. any enum type is C-POD
+//   4. any mozilla::Maybe<T> with T: C-POD is C-POD
+//   5. any T[N] with T: C-POD is C-POD
+//   6. any union where all fields are C-POD is C-POD
+//   7. any struct with the following conditions must is C-POD
+//      * every field's type must be C-POD
+//      * the parent type, if it exists, must also be C-POD
+//      * there must be no virtual methods
+//
+// There are no combination of C++ type traits at this time that can
+// automatically meet these criteria, so we are rolling our own system.
+//
+// We define a "IsCacheablePod" type trait, with builtin rules for cases (1-5).
+// The complex cases (6-7) are handled using manual declaration and checking
+// macros that must be used upon structs and unions that are considered
+// cacheable POD.
+//
+// See the following macros for details:
+//   - WASM_DECLARE_CACHEABLE_POD
+//   - WASM_CHECK_CACHEABLE_POD[_WITH_PARENT]
+
+// The IsCacheablePod type trait primary template. Contains the rules for
+// (cases 1-3).
+template <typename T>
+struct IsCacheablePod
+    : public std::conditional_t<std::is_arithmetic_v<T> || std::is_enum_v<T>,
+                                std::true_type, std::false_type> {};
+
+// Partial specialization for (case 4).
+template <typename T>
+struct IsCacheablePod<mozilla::Maybe<T>>
+    : public std::conditional_t<IsCacheablePod<T>::value, std::true_type,
+                                std::false_type> {};
+
+// Partial specialization for (case 5).
+template <typename T, size_t N>
+struct IsCacheablePod<T[N]>
+    : public std::conditional_t<IsCacheablePod<T>::value, std::true_type,
+                                std::false_type> {};
+
+template <class T>
+inline constexpr bool is_cacheable_pod = IsCacheablePod<T>::value;
+
+// Checks if derrived class will not use the structure alignment for its
+// next field. It used when pod is a base class.
+#define WASM_CHECK_CACHEABLE_POD_PADDING(Type)                \
+  class __CHECK_PADING_##Type : public Type {                 \
+   public:                                                    \
+    char c;                                                   \
+  };                                                          \
+  static_assert(sizeof(__CHECK_PADING_##Type) > sizeof(Type), \
+                #Type " will overlap with next field if inherited");
+
+// Declare the type 'Type' to be cacheable POD. The definition of the type must
+// contain a WASM_CHECK_CACHEABLE_POD[_WITH_PARENT] to ensure all fields of the
+// type are cacheable POD.
+#define WASM_DECLARE_CACHEABLE_POD(Type)                                      \
+  static_assert(!std::is_polymorphic_v<Type>,                                 \
+                #Type "must not have virtual methods");                       \
+  } /* namespace wasm */                                                      \
+  } /* namespace js */                                                        \
+  template <>                                                                 \
+  struct js::wasm::IsCacheablePod<js::wasm::Type> : public std::true_type {}; \
+  namespace js {                                                              \
+  namespace wasm {
+
+// Helper: check each field's type to be cacheable POD
+#define WASM_CHECK_CACHEABLE_POD_FIELD_(Field)                    \
+  static_assert(js::wasm::IsCacheablePod<decltype(Field)>::value, \
+                #Field " must be cacheable pod");
+
+// Check every field in a type definition to ensure they are cacheable POD.
+#define WASM_CHECK_CACHEABLE_POD(Fields...) \
+  MOZ_FOR_EACH(WASM_CHECK_CACHEABLE_POD_FIELD_, (), (Fields))
+
+// Check every field in a type definition to ensure they are cacheable POD, and
+// check that the parent class is also cacheable POD.
+#define WASM_CHECK_CACHEABLE_POD_WITH_PARENT(Parent, Fields...) \
+  static_assert(js::wasm::IsCacheablePod<Parent>::value,        \
+                #Parent " must be cacheable pod");              \
+  MOZ_FOR_EACH(WASM_CHECK_CACHEABLE_POD_FIELD_, (), (Fields))
+
+// Allow fields that are not cacheable POD but are believed to be safe for
+// serialization due to some justification.
+#define WASM_ALLOW_NON_CACHEABLE_POD_FIELD(Field, Reason)          \
+  static_assert(!js::wasm::IsCacheablePod<decltype(Field)>::value, \
+                #Field " is not cacheable due to " Reason);
+
+}  // namespace wasm
+}  // namespace js
+
+#endif  // wasm_serialize_h