Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 907 insertions, 0 deletions

diff --git a/js/src/wasm/WasmBinary.h b/js/src/wasm/WasmBinary.h
new file mode 100644
index 0000000000..2d41528157
--- /dev/null
+++ b/js/src/wasm/WasmBinary.h
@@ -0,0 +1,907 @@
+/* -*- 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 2021 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_binary_h
+#define wasm_binary_h
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Maybe.h"
+
+#include <type_traits>
+
+#include "js/WasmFeatures.h"
+
+#include "wasm/WasmCompile.h"
+#include "wasm/WasmCompileArgs.h"
+#include "wasm/WasmConstants.h"
+#include "wasm/WasmTypeDecls.h"
+#include "wasm/WasmTypeDef.h"
+#include "wasm/WasmValType.h"
+
+namespace js {
+namespace wasm {
+
+using mozilla::DebugOnly;
+using mozilla::Maybe;
+
+struct ModuleEnvironment;
+
+// The Opcode compactly and safely represents the primary opcode plus any
+// extension, with convenient predicates and accessors.
+
+class Opcode {
+  uint32_t bits_;
+
+ public:
+  MOZ_IMPLICIT Opcode(Op op) : bits_(uint32_t(op)) {
+    static_assert(size_t(Op::Limit) == 256, "fits");
+    MOZ_ASSERT(size_t(op) < size_t(Op::Limit));
+  }
+  MOZ_IMPLICIT Opcode(MiscOp op)
+      : bits_((uint32_t(op) << 8) | uint32_t(Op::MiscPrefix)) {
+    static_assert(size_t(MiscOp::Limit) <= 0xFFFFFF, "fits");
+    MOZ_ASSERT(size_t(op) < size_t(MiscOp::Limit));
+  }
+  MOZ_IMPLICIT Opcode(ThreadOp op)
+      : bits_((uint32_t(op) << 8) | uint32_t(Op::ThreadPrefix)) {
+    static_assert(size_t(ThreadOp::Limit) <= 0xFFFFFF, "fits");
+    MOZ_ASSERT(size_t(op) < size_t(ThreadOp::Limit));
+  }
+  MOZ_IMPLICIT Opcode(MozOp op)
+      : bits_((uint32_t(op) << 8) | uint32_t(Op::MozPrefix)) {
+    static_assert(size_t(MozOp::Limit) <= 0xFFFFFF, "fits");
+    MOZ_ASSERT(size_t(op) < size_t(MozOp::Limit));
+  }
+  MOZ_IMPLICIT Opcode(SimdOp op)
+      : bits_((uint32_t(op) << 8) | uint32_t(Op::SimdPrefix)) {
+    static_assert(size_t(SimdOp::Limit) <= 0xFFFFFF, "fits");
+    MOZ_ASSERT(size_t(op) < size_t(SimdOp::Limit));
+  }
+
+  bool isOp() const { return bits_ < uint32_t(Op::FirstPrefix); }
+  bool isMisc() const { return (bits_ & 255) == uint32_t(Op::MiscPrefix); }
+  bool isThread() const { return (bits_ & 255) == uint32_t(Op::ThreadPrefix); }
+  bool isMoz() const { return (bits_ & 255) == uint32_t(Op::MozPrefix); }
+  bool isSimd() const { return (bits_ & 255) == uint32_t(Op::SimdPrefix); }
+
+  Op asOp() const {
+    MOZ_ASSERT(isOp());
+    return Op(bits_);
+  }
+  MiscOp asMisc() const {
+    MOZ_ASSERT(isMisc());
+    return MiscOp(bits_ >> 8);
+  }
+  ThreadOp asThread() const {
+    MOZ_ASSERT(isThread());
+    return ThreadOp(bits_ >> 8);
+  }
+  MozOp asMoz() const {
+    MOZ_ASSERT(isMoz());
+    return MozOp(bits_ >> 8);
+  }
+  SimdOp asSimd() const {
+    MOZ_ASSERT(isSimd());
+    return SimdOp(bits_ >> 8);
+  }
+
+  uint32_t bits() const { return bits_; }
+
+  bool operator==(const Opcode& that) const { return bits_ == that.bits_; }
+  bool operator!=(const Opcode& that) const { return bits_ != that.bits_; }
+};
+
+// This struct captures the bytecode offset of a section's payload (so not
+// including the header) and the size of the payload.
+
+struct SectionRange {
+  uint32_t start;
+  uint32_t size;
+
+  uint32_t end() const { return start + size; }
+  bool operator==(const SectionRange& rhs) const {
+    return start == rhs.start && size == rhs.size;
+  }
+};
+
+using MaybeSectionRange = Maybe<SectionRange>;
+
+// The Encoder class appends bytes to the Bytes object it is given during
+// construction. The client is responsible for the Bytes's lifetime and must
+// keep the Bytes alive as long as the Encoder is used.
+
+class Encoder {
+  Bytes& bytes_;
+
+  template <class T>
+  [[nodiscard]] bool write(const T& v) {
+    return bytes_.append(reinterpret_cast<const uint8_t*>(&v), sizeof(T));
+  }
+
+  template <typename UInt>
+  [[nodiscard]] bool writeVarU(UInt i) {
+    do {
+      uint8_t byte = i & 0x7f;
+      i >>= 7;
+      if (i != 0) {
+        byte |= 0x80;
+      }
+      if (!bytes_.append(byte)) {
+        return false;
+      }
+    } while (i != 0);
+    return true;
+  }
+
+  template <typename SInt>
+  [[nodiscard]] bool writeVarS(SInt i) {
+    bool done;
+    do {
+      uint8_t byte = i & 0x7f;
+      i >>= 7;
+      done = ((i == 0) && !(byte & 0x40)) || ((i == -1) && (byte & 0x40));
+      if (!done) {
+        byte |= 0x80;
+      }
+      if (!bytes_.append(byte)) {
+        return false;
+      }
+    } while (!done);
+    return true;
+  }
+
+  void patchVarU32(size_t offset, uint32_t patchBits, uint32_t assertBits) {
+    do {
+      uint8_t assertByte = assertBits & 0x7f;
+      uint8_t patchByte = patchBits & 0x7f;
+      assertBits >>= 7;
+      patchBits >>= 7;
+      if (assertBits != 0) {
+        assertByte |= 0x80;
+        patchByte |= 0x80;
+      }
+      MOZ_ASSERT(assertByte == bytes_[offset]);
+      (void)assertByte;
+      bytes_[offset] = patchByte;
+      offset++;
+    } while (assertBits != 0);
+  }
+
+  void patchFixedU7(size_t offset, uint8_t patchBits, uint8_t assertBits) {
+    MOZ_ASSERT(patchBits <= uint8_t(INT8_MAX));
+    patchFixedU8(offset, patchBits, assertBits);
+  }
+
+  void patchFixedU8(size_t offset, uint8_t patchBits, uint8_t assertBits) {
+    MOZ_ASSERT(bytes_[offset] == assertBits);
+    bytes_[offset] = patchBits;
+  }
+
+  uint32_t varU32ByteLength(size_t offset) const {
+    size_t start = offset;
+    while (bytes_[offset] & 0x80) {
+      offset++;
+    }
+    return offset - start + 1;
+  }
+
+ public:
+  explicit Encoder(Bytes& bytes) : bytes_(bytes) { MOZ_ASSERT(empty()); }
+
+  size_t currentOffset() const { return bytes_.length(); }
+  bool empty() const { return currentOffset() == 0; }
+
+  // Fixed-size encoding operations simply copy the literal bytes (without
+  // attempting to align).
+
+  [[nodiscard]] bool writeFixedU7(uint8_t i) {
+    MOZ_ASSERT(i <= uint8_t(INT8_MAX));
+    return writeFixedU8(i);
+  }
+  [[nodiscard]] bool writeFixedU8(uint8_t i) { return write<uint8_t>(i); }
+  [[nodiscard]] bool writeFixedU32(uint32_t i) { return write<uint32_t>(i); }
+  [[nodiscard]] bool writeFixedF32(float f) { return write<float>(f); }
+  [[nodiscard]] bool writeFixedF64(double d) { return write<double>(d); }
+
+  // Variable-length encodings that all use LEB128.
+
+  [[nodiscard]] bool writeVarU32(uint32_t i) { return writeVarU<uint32_t>(i); }
+  [[nodiscard]] bool writeVarS32(int32_t i) { return writeVarS<int32_t>(i); }
+  [[nodiscard]] bool writeVarU64(uint64_t i) { return writeVarU<uint64_t>(i); }
+  [[nodiscard]] bool writeVarS64(int64_t i) { return writeVarS<int64_t>(i); }
+  [[nodiscard]] bool writeValType(ValType type) {
+    static_assert(size_t(TypeCode::Limit) <= UINT8_MAX, "fits");
+    // writeValType is only used by asm.js, which doesn't use type
+    // references
+    MOZ_RELEASE_ASSERT(!type.isTypeRef(), "NYI");
+    TypeCode tc = type.packed().typeCode();
+    MOZ_ASSERT(size_t(tc) < size_t(TypeCode::Limit));
+    return writeFixedU8(uint8_t(tc));
+  }
+  [[nodiscard]] bool writeOp(Opcode opcode) {
+    // The Opcode constructor has asserted that `opcode` is meaningful, so no
+    // further correctness checking is necessary here.
+    uint32_t bits = opcode.bits();
+    if (!writeFixedU8(bits & 255)) {
+      return false;
+    }
+    if (opcode.isOp()) {
+      return true;
+    }
+    return writeVarU32(bits >> 8);
+  }
+
+  // Fixed-length encodings that allow back-patching.
+
+  [[nodiscard]] bool writePatchableFixedU7(size_t* offset) {
+    *offset = bytes_.length();
+    return writeFixedU8(UINT8_MAX);
+  }
+  void patchFixedU7(size_t offset, uint8_t patchBits) {
+    return patchFixedU7(offset, patchBits, UINT8_MAX);
+  }
+
+  // Variable-length encodings that allow back-patching.
+
+  [[nodiscard]] bool writePatchableVarU32(size_t* offset) {
+    *offset = bytes_.length();
+    return writeVarU32(UINT32_MAX);
+  }
+  void patchVarU32(size_t offset, uint32_t patchBits) {
+    return patchVarU32(offset, patchBits, UINT32_MAX);
+  }
+
+  // Byte ranges start with an LEB128 length followed by an arbitrary sequence
+  // of bytes. When used for strings, bytes are to be interpreted as utf8.
+
+  [[nodiscard]] bool writeBytes(const void* bytes, uint32_t numBytes) {
+    return writeVarU32(numBytes) &&
+           bytes_.append(reinterpret_cast<const uint8_t*>(bytes), numBytes);
+  }
+
+  // A "section" is a contiguous range of bytes that stores its own size so
+  // that it may be trivially skipped without examining the payload. Sections
+  // require backpatching since the size of the section is only known at the
+  // end while the size's varU32 must be stored at the beginning. Immediately
+  // after the section length is the string id of the section.
+
+  [[nodiscard]] bool startSection(SectionId id, size_t* offset) {
+    MOZ_ASSERT(uint32_t(id) < 128);
+    return writeVarU32(uint32_t(id)) && writePatchableVarU32(offset);
+  }
+  void finishSection(size_t offset) {
+    return patchVarU32(offset,
+                       bytes_.length() - offset - varU32ByteLength(offset));
+  }
+};
+
+// The Decoder class decodes the bytes in the range it is given during
+// construction. The client is responsible for keeping the byte range alive as
+// long as the Decoder is used.
+
+class Decoder {
+  const uint8_t* const beg_;
+  const uint8_t* const end_;
+  const uint8_t* cur_;
+  const size_t offsetInModule_;
+  UniqueChars* error_;
+  UniqueCharsVector* warnings_;
+  bool resilientMode_;
+
+  template <class T>
+  [[nodiscard]] bool read(T* out) {
+    if (bytesRemain() < sizeof(T)) {
+      return false;
+    }
+    memcpy((void*)out, cur_, sizeof(T));
+    cur_ += sizeof(T);
+    return true;
+  }
+
+  template <class T>
+  T uncheckedRead() {
+    MOZ_ASSERT(bytesRemain() >= sizeof(T));
+    T ret;
+    memcpy(&ret, cur_, sizeof(T));
+    cur_ += sizeof(T);
+    return ret;
+  }
+
+  template <class T>
+  void uncheckedRead(T* ret) {
+    MOZ_ASSERT(bytesRemain() >= sizeof(T));
+    memcpy(ret, cur_, sizeof(T));
+    cur_ += sizeof(T);
+  }
+
+  template <typename UInt>
+  [[nodiscard]] bool readVarU(UInt* out) {
+    DebugOnly<const uint8_t*> before = cur_;
+    const unsigned numBits = sizeof(UInt) * CHAR_BIT;
+    const unsigned remainderBits = numBits % 7;
+    const unsigned numBitsInSevens = numBits - remainderBits;
+    UInt u = 0;
+    uint8_t byte;
+    UInt shift = 0;
+    do {
+      if (!readFixedU8(&byte)) {
+        return false;
+      }
+      if (!(byte & 0x80)) {
+        *out = u | UInt(byte) << shift;
+        return true;
+      }
+      u |= UInt(byte & 0x7F) << shift;
+      shift += 7;
+    } while (shift != numBitsInSevens);
+    if (!readFixedU8(&byte) || (byte & (unsigned(-1) << remainderBits))) {
+      return false;
+    }
+    *out = u | (UInt(byte) << numBitsInSevens);
+    MOZ_ASSERT_IF(sizeof(UInt) == 4,
+                  unsigned(cur_ - before) <= MaxVarU32DecodedBytes);
+    return true;
+  }
+
+  template <typename SInt>
+  [[nodiscard]] bool readVarS(SInt* out) {
+    using UInt = std::make_unsigned_t<SInt>;
+    const unsigned numBits = sizeof(SInt) * CHAR_BIT;
+    const unsigned remainderBits = numBits % 7;
+    const unsigned numBitsInSevens = numBits - remainderBits;
+    SInt s = 0;
+    uint8_t byte;
+    unsigned shift = 0;
+    do {
+      if (!readFixedU8(&byte)) {
+        return false;
+      }
+      s |= SInt(byte & 0x7f) << shift;
+      shift += 7;
+      if (!(byte & 0x80)) {
+        if (byte & 0x40) {
+          s |= UInt(-1) << shift;
+        }
+        *out = s;
+        return true;
+      }
+    } while (shift < numBitsInSevens);
+    if (!remainderBits || !readFixedU8(&byte) || (byte & 0x80)) {
+      return false;
+    }
+    uint8_t mask = 0x7f & (uint8_t(-1) << remainderBits);
+    if ((byte & mask) != ((byte & (1 << (remainderBits - 1))) ? mask : 0)) {
+      return false;
+    }
+    *out = s | UInt(byte) << shift;
+    return true;
+  }
+
+ public:
+  Decoder(const uint8_t* begin, const uint8_t* end, size_t offsetInModule,
+          UniqueChars* error, UniqueCharsVector* warnings = nullptr,
+          bool resilientMode = false)
+      : beg_(begin),
+        end_(end),
+        cur_(begin),
+        offsetInModule_(offsetInModule),
+        error_(error),
+        warnings_(warnings),
+        resilientMode_(resilientMode) {
+    MOZ_ASSERT(begin <= end);
+  }
+  explicit Decoder(const Bytes& bytes, size_t offsetInModule = 0,
+                   UniqueChars* error = nullptr,
+                   UniqueCharsVector* warnings = nullptr)
+      : beg_(bytes.begin()),
+        end_(bytes.end()),
+        cur_(bytes.begin()),
+        offsetInModule_(offsetInModule),
+        error_(error),
+        warnings_(warnings),
+        resilientMode_(false) {}
+
+  // These convenience functions use currentOffset() as the errorOffset.
+  bool fail(const char* msg) { return fail(currentOffset(), msg); }
+  bool failf(const char* msg, ...) MOZ_FORMAT_PRINTF(2, 3);
+  void warnf(const char* msg, ...) MOZ_FORMAT_PRINTF(2, 3);
+
+  // Report an error at the given offset (relative to the whole module).
+  bool fail(size_t errorOffset, const char* msg);
+
+  UniqueChars* error() { return error_; }
+
+  void clearError() {
+    if (error_) {
+      error_->reset();
+    }
+  }
+
+  bool done() const {
+    MOZ_ASSERT(cur_ <= end_);
+    return cur_ == end_;
+  }
+  bool resilientMode() const { return resilientMode_; }
+
+  size_t bytesRemain() const {
+    MOZ_ASSERT(end_ >= cur_);
+    return size_t(end_ - cur_);
+  }
+  // pos must be a value previously returned from currentPosition.
+  void rollbackPosition(const uint8_t* pos) { cur_ = pos; }
+  const uint8_t* currentPosition() const { return cur_; }
+  size_t beginOffset() const { return offsetInModule_; }
+  size_t currentOffset() const { return offsetInModule_ + (cur_ - beg_); }
+  const uint8_t* begin() const { return beg_; }
+  const uint8_t* end() const { return end_; }
+
+  // Peek at the next byte, if it exists, without advancing the position.
+
+  bool peekByte(uint8_t* byte) {
+    if (done()) {
+      return false;
+    }
+    *byte = *cur_;
+    return true;
+  }
+
+  // Fixed-size encoding operations simply copy the literal bytes (without
+  // attempting to align).
+
+  [[nodiscard]] bool readFixedU8(uint8_t* i) { return read<uint8_t>(i); }
+  [[nodiscard]] bool readFixedU32(uint32_t* u) { return read<uint32_t>(u); }
+  [[nodiscard]] bool readFixedF32(float* f) { return read<float>(f); }
+  [[nodiscard]] bool readFixedF64(double* d) { return read<double>(d); }
+#ifdef ENABLE_WASM_SIMD
+  [[nodiscard]] bool readFixedV128(V128* d) {
+    for (unsigned i = 0; i < 16; i++) {
+      if (!read<uint8_t>(d->bytes + i)) {
+        return false;
+      }
+    }
+    return true;
+  }
+#endif
+
+  // Variable-length encodings that all use LEB128.
+
+  [[nodiscard]] bool readVarU32(uint32_t* out) {
+    return readVarU<uint32_t>(out);
+  }
+  [[nodiscard]] bool readVarS32(int32_t* out) { return readVarS<int32_t>(out); }
+  [[nodiscard]] bool readVarU64(uint64_t* out) {
+    return readVarU<uint64_t>(out);
+  }
+  [[nodiscard]] bool readVarS64(int64_t* out) { return readVarS<int64_t>(out); }
+
+  // Value and reference types
+
+  [[nodiscard]] ValType uncheckedReadValType(const TypeContext& types);
+
+  template <class T>
+  [[nodiscard]] bool readPackedType(const TypeContext& types,
+                                    const FeatureArgs& features, T* type);
+
+  [[nodiscard]] bool readValType(const TypeContext& types,
+                                 const FeatureArgs& features, ValType* type);
+
+  [[nodiscard]] bool readStorageType(const TypeContext& types,
+                                     const FeatureArgs& features,
+                                     StorageType* type);
+
+  [[nodiscard]] bool readHeapType(const TypeContext& types,
+                                  const FeatureArgs& features, bool nullable,
+                                  RefType* type);
+
+  [[nodiscard]] bool readRefType(const TypeContext& types,
+                                 const FeatureArgs& features, RefType* type);
+
+  // Instruction opcode
+
+  [[nodiscard]] bool readOp(OpBytes* op);
+
+  // Instruction immediates for constant instructions
+
+  [[nodiscard]] bool readBinary() { return true; }
+  [[nodiscard]] bool readTypeIndex(uint32_t* typeIndex);
+  [[nodiscard]] bool readGlobalIndex(uint32_t* globalIndex);
+  [[nodiscard]] bool readFuncIndex(uint32_t* funcIndex);
+  [[nodiscard]] bool readI32Const(int32_t* i32);
+  [[nodiscard]] bool readI64Const(int64_t* i64);
+  [[nodiscard]] bool readF32Const(float* f32);
+  [[nodiscard]] bool readF64Const(double* f64);
+#ifdef ENABLE_WASM_SIMD
+  [[nodiscard]] bool readV128Const(V128* value);
+#endif
+  [[nodiscard]] bool readRefNull(const TypeContext& types,
+                                 const FeatureArgs& features, RefType* type);
+
+  // See writeBytes comment.
+
+  [[nodiscard]] bool readBytes(uint32_t numBytes,
+                               const uint8_t** bytes = nullptr) {
+    if (bytes) {
+      *bytes = cur_;
+    }
+    if (bytesRemain() < numBytes) {
+      return false;
+    }
+    cur_ += numBytes;
+    return true;
+  }
+
+  // See "section" description in Encoder.
+
+  [[nodiscard]] bool readSectionHeader(uint8_t* id, SectionRange* range);
+
+  [[nodiscard]] bool startSection(SectionId id, ModuleEnvironment* env,
+                                  MaybeSectionRange* range,
+                                  const char* sectionName);
+  [[nodiscard]] bool finishSection(const SectionRange& range,
+                                   const char* sectionName);
+
+  // Custom sections do not cause validation errors unless the error is in
+  // the section header itself.
+
+  [[nodiscard]] bool startCustomSection(const char* expected,
+                                        size_t expectedLength,
+                                        ModuleEnvironment* env,
+                                        MaybeSectionRange* range);
+
+  template <size_t NameSizeWith0>
+  [[nodiscard]] bool startCustomSection(const char (&name)[NameSizeWith0],
+                                        ModuleEnvironment* env,
+                                        MaybeSectionRange* range) {
+    MOZ_ASSERT(name[NameSizeWith0 - 1] == '\0');
+    return startCustomSection(name, NameSizeWith0 - 1, env, range);
+  }
+
+  void finishCustomSection(const char* name, const SectionRange& range);
+  void skipAndFinishCustomSection(const SectionRange& range);
+
+  [[nodiscard]] bool skipCustomSection(ModuleEnvironment* env);
+
+  // The Name section has its own optional subsections.
+
+  [[nodiscard]] bool startNameSubsection(NameType nameType,
+                                         Maybe<uint32_t>* endOffset);
+  [[nodiscard]] bool finishNameSubsection(uint32_t endOffset);
+  [[nodiscard]] bool skipNameSubsection();
+
+  // The infallible "unchecked" decoding functions can be used when we are
+  // sure that the bytes are well-formed (by construction or due to previous
+  // validation).
+
+  uint8_t uncheckedReadFixedU8() { return uncheckedRead<uint8_t>(); }
+  uint32_t uncheckedReadFixedU32() { return uncheckedRead<uint32_t>(); }
+  void uncheckedReadFixedF32(float* out) { uncheckedRead<float>(out); }
+  void uncheckedReadFixedF64(double* out) { uncheckedRead<double>(out); }
+  template <typename UInt>
+  UInt uncheckedReadVarU() {
+    static const unsigned numBits = sizeof(UInt) * CHAR_BIT;
+    static const unsigned remainderBits = numBits % 7;
+    static const unsigned numBitsInSevens = numBits - remainderBits;
+    UInt decoded = 0;
+    uint32_t shift = 0;
+    do {
+      uint8_t byte = *cur_++;
+      if (!(byte & 0x80)) {
+        return decoded | (UInt(byte) << shift);
+      }
+      decoded |= UInt(byte & 0x7f) << shift;
+      shift += 7;
+    } while (shift != numBitsInSevens);
+    uint8_t byte = *cur_++;
+    MOZ_ASSERT(!(byte & 0xf0));
+    return decoded | (UInt(byte) << numBitsInSevens);
+  }
+  uint32_t uncheckedReadVarU32() { return uncheckedReadVarU<uint32_t>(); }
+  int32_t uncheckedReadVarS32() {
+    int32_t i32 = 0;
+    MOZ_ALWAYS_TRUE(readVarS32(&i32));
+    return i32;
+  }
+  uint64_t uncheckedReadVarU64() { return uncheckedReadVarU<uint64_t>(); }
+  int64_t uncheckedReadVarS64() {
+    int64_t i64 = 0;
+    MOZ_ALWAYS_TRUE(readVarS64(&i64));
+    return i64;
+  }
+  Op uncheckedReadOp() {
+    static_assert(size_t(Op::Limit) == 256, "fits");
+    uint8_t u8 = uncheckedReadFixedU8();
+    return u8 != UINT8_MAX ? Op(u8) : Op(uncheckedReadFixedU8() + UINT8_MAX);
+  }
+};
+
+// Value and reference types
+
+inline ValType Decoder::uncheckedReadValType(const TypeContext& types) {
+  uint8_t code = uncheckedReadFixedU8();
+  switch (code) {
+    case uint8_t(TypeCode::FuncRef):
+    case uint8_t(TypeCode::ExternRef):
+    case uint8_t(TypeCode::ExnRef):
+      return RefType::fromTypeCode(TypeCode(code), true);
+    case uint8_t(TypeCode::Ref):
+    case uint8_t(TypeCode::NullableRef): {
+      bool nullable = code == uint8_t(TypeCode::NullableRef);
+
+      uint8_t nextByte;
+      peekByte(&nextByte);
+
+      if ((nextByte & SLEB128SignMask) == SLEB128SignBit) {
+        uint8_t code = uncheckedReadFixedU8();
+        return RefType::fromTypeCode(TypeCode(code), nullable);
+      }
+
+      int32_t x = uncheckedReadVarS32();
+      const TypeDef* typeDef = &types.type(x);
+      return RefType::fromTypeDef(typeDef, nullable);
+    }
+    default:
+      return ValType::fromNonRefTypeCode(TypeCode(code));
+  }
+}
+
+template <class T>
+inline bool Decoder::readPackedType(const TypeContext& types,
+                                    const FeatureArgs& features, T* type) {
+  static_assert(uint8_t(TypeCode::Limit) <= UINT8_MAX, "fits");
+  uint8_t code;
+  if (!readFixedU8(&code)) {
+    return fail("expected type code");
+  }
+  switch (code) {
+    case uint8_t(TypeCode::V128): {
+#ifdef ENABLE_WASM_SIMD
+      if (!features.simd) {
+        return fail("v128 not enabled");
+      }
+      *type = T::fromNonRefTypeCode(TypeCode(code));
+      return true;
+#else
+      break;
+#endif
+    }
+    case uint8_t(TypeCode::FuncRef):
+    case uint8_t(TypeCode::ExternRef): {
+      *type = RefType::fromTypeCode(TypeCode(code), true);
+      return true;
+    }
+    case uint8_t(TypeCode::ExnRef): {
+      if (!features.exnref) {
+        return fail("exnref not enabled");
+      }
+      *type = RefType::fromTypeCode(TypeCode(code), true);
+      return true;
+    }
+    case uint8_t(TypeCode::Ref):
+    case uint8_t(TypeCode::NullableRef): {
+#ifdef ENABLE_WASM_FUNCTION_REFERENCES
+      if (!features.functionReferences) {
+        return fail("(ref T) types not enabled");
+      }
+      bool nullable = code == uint8_t(TypeCode::NullableRef);
+      RefType refType;
+      if (!readHeapType(types, features, nullable, &refType)) {
+        return false;
+      }
+      *type = refType;
+      return true;
+#else
+      break;
+#endif
+    }
+    case uint8_t(TypeCode::AnyRef):
+    case uint8_t(TypeCode::I31Ref):
+    case uint8_t(TypeCode::EqRef):
+    case uint8_t(TypeCode::StructRef):
+    case uint8_t(TypeCode::ArrayRef):
+    case uint8_t(TypeCode::NullFuncRef):
+    case uint8_t(TypeCode::NullExternRef):
+    case uint8_t(TypeCode::NullAnyRef): {
+#ifdef ENABLE_WASM_GC
+      if (!features.gc) {
+        return fail("gc types not enabled");
+      }
+      *type = RefType::fromTypeCode(TypeCode(code), true);
+      return true;
+#else
+      break;
+#endif
+    }
+    default: {
+      if (!T::isValidTypeCode(TypeCode(code))) {
+        break;
+      }
+      *type = T::fromNonRefTypeCode(TypeCode(code));
+      return true;
+    }
+  }
+  return fail("bad type");
+}
+
+inline bool Decoder::readValType(const TypeContext& types,
+                                 const FeatureArgs& features, ValType* type) {
+  return readPackedType<ValType>(types, features, type);
+}
+
+inline bool Decoder::readStorageType(const TypeContext& types,
+                                     const FeatureArgs& features,
+                                     StorageType* type) {
+  return readPackedType<StorageType>(types, features, type);
+}
+
+inline bool Decoder::readHeapType(const TypeContext& types,
+                                  const FeatureArgs& features, bool nullable,
+                                  RefType* type) {
+  uint8_t nextByte;
+  if (!peekByte(&nextByte)) {
+    return fail("expected heap type code");
+  }
+
+  if ((nextByte & SLEB128SignMask) == SLEB128SignBit) {
+    uint8_t code;
+    if (!readFixedU8(&code)) {
+      return false;
+    }
+
+    switch (code) {
+      case uint8_t(TypeCode::FuncRef):
+      case uint8_t(TypeCode::ExternRef):
+        *type = RefType::fromTypeCode(TypeCode(code), nullable);
+        return true;
+      case uint8_t(TypeCode::ExnRef): {
+        if (!features.exnref) {
+          return fail("exnref not enabled");
+        }
+        *type = RefType::fromTypeCode(TypeCode(code), nullable);
+        return true;
+      }
+#ifdef ENABLE_WASM_GC
+      case uint8_t(TypeCode::AnyRef):
+      case uint8_t(TypeCode::I31Ref):
+      case uint8_t(TypeCode::EqRef):
+      case uint8_t(TypeCode::StructRef):
+      case uint8_t(TypeCode::ArrayRef):
+      case uint8_t(TypeCode::NullFuncRef):
+      case uint8_t(TypeCode::NullExternRef):
+      case uint8_t(TypeCode::NullAnyRef):
+        if (!features.gc) {
+          return fail("gc types not enabled");
+        }
+        *type = RefType::fromTypeCode(TypeCode(code), nullable);
+        return true;
+#endif
+      default:
+        return fail("invalid heap type");
+    }
+  }
+
+#ifdef ENABLE_WASM_FUNCTION_REFERENCES
+  if (features.functionReferences) {
+    int32_t x;
+    if (!readVarS32(&x) || x < 0 || uint32_t(x) >= types.length()) {
+      return fail("invalid heap type index");
+    }
+    const TypeDef* typeDef = &types.type(x);
+    *type = RefType::fromTypeDef(typeDef, nullable);
+    return true;
+  }
+#endif
+  return fail("invalid heap type");
+}
+
+inline bool Decoder::readRefType(const TypeContext& types,
+                                 const FeatureArgs& features, RefType* type) {
+  ValType valType;
+  if (!readValType(types, features, &valType)) {
+    return false;
+  }
+  if (!valType.isRefType()) {
+    return fail("bad type");
+  }
+  *type = valType.refType();
+  return true;
+}
+
+// Instruction opcode
+
+inline bool Decoder::readOp(OpBytes* op) {
+  static_assert(size_t(Op::Limit) == 256, "fits");
+  uint8_t u8;
+  if (!readFixedU8(&u8)) {
+    return false;
+  }
+  op->b0 = u8;
+  if (MOZ_LIKELY(!IsPrefixByte(u8))) {
+    return true;
+  }
+  return readVarU32(&op->b1);
+}
+
+// Instruction immediates for constant instructions
+
+inline bool Decoder::readTypeIndex(uint32_t* typeIndex) {
+  if (!readVarU32(typeIndex)) {
+    return fail("unable to read type index");
+  }
+  return true;
+}
+
+inline bool Decoder::readGlobalIndex(uint32_t* globalIndex) {
+  if (!readVarU32(globalIndex)) {
+    return fail("unable to read global index");
+  }
+  return true;
+}
+
+inline bool Decoder::readFuncIndex(uint32_t* funcIndex) {
+  if (!readVarU32(funcIndex)) {
+    return fail("unable to read function index");
+  }
+  return true;
+}
+
+inline bool Decoder::readI32Const(int32_t* i32) {
+  if (!readVarS32(i32)) {
+    return fail("failed to read I32 constant");
+  }
+  return true;
+}
+
+inline bool Decoder::readI64Const(int64_t* i64) {
+  if (!readVarS64(i64)) {
+    return fail("failed to read I64 constant");
+  }
+  return true;
+}
+
+inline bool Decoder::readF32Const(float* f32) {
+  if (!readFixedF32(f32)) {
+    return fail("failed to read F32 constant");
+  }
+  return true;
+}
+
+inline bool Decoder::readF64Const(double* f64) {
+  if (!readFixedF64(f64)) {
+    return fail("failed to read F64 constant");
+  }
+  return true;
+}
+
+#ifdef ENABLE_WASM_SIMD
+inline bool Decoder::readV128Const(V128* value) {
+  if (!readFixedV128(value)) {
+    return fail("unable to read V128 constant");
+  }
+  return true;
+}
+#endif
+
+inline bool Decoder::readRefNull(const TypeContext& types,
+                                 const FeatureArgs& features, RefType* type) {
+  return readHeapType(types, features, true, type);
+}
+
+}  // namespace wasm
+}  // namespace js
+
+#endif  // namespace wasm_binary_h