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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 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#ifndef wasm_module_types_h
#define wasm_module_types_h
#include "mozilla/RefPtr.h"
#include "mozilla/Span.h"
#include "js/AllocPolicy.h"
#include "js/HashTable.h"
#include "js/RefCounted.h"
#include "js/Utility.h"
#include "js/Vector.h"
#include "wasm/WasmCompileArgs.h"
#include "wasm/WasmConstants.h"
#include "wasm/WasmExprType.h"
#include "wasm/WasmInitExpr.h"
#include "wasm/WasmMemory.h"
#include "wasm/WasmSerialize.h"
#include "wasm/WasmShareable.h"
#include "wasm/WasmTypeDecls.h"
#include "wasm/WasmValType.h"
#include "wasm/WasmValue.h"
namespace js {
namespace wasm {
using mozilla::Maybe;
using mozilla::Nothing;
using mozilla::Span;
class FuncType;
// A Module can either be asm.js or wasm.
enum ModuleKind { Wasm, AsmJS };
// CacheableChars is used to cacheably store UniqueChars.
struct CacheableChars : UniqueChars {
CacheableChars() = default;
explicit CacheableChars(char* ptr) : UniqueChars(ptr) {}
MOZ_IMPLICIT CacheableChars(UniqueChars&& rhs)
: UniqueChars(std::move(rhs)) {}
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
using CacheableCharsVector = Vector<CacheableChars, 0, SystemAllocPolicy>;
// CacheableName is used to cacheably store a UTF-8 string that may contain
// null terminators in sequence.
struct CacheableName {
UTF8Bytes bytes_;
const char* begin() const { return (const char*)bytes_.begin(); }
size_t length() const { return bytes_.length(); }
CacheableName() = default;
MOZ_IMPLICIT CacheableName(UTF8Bytes&& rhs) : bytes_(std::move(rhs)) {}
bool isEmpty() const { return bytes_.length() == 0; }
Span<char> utf8Bytes() { return Span<char>(bytes_); }
Span<const char> utf8Bytes() const { return Span<const char>(bytes_); }
static CacheableName fromUTF8Chars(UniqueChars&& utf8Chars);
[[nodiscard]] static bool fromUTF8Chars(const char* utf8Chars,
CacheableName* name);
[[nodiscard]] JSAtom* toAtom(JSContext* cx) const;
[[nodiscard]] bool toPropertyKey(JSContext* cx,
MutableHandleId propertyKey) const;
[[nodiscard]] UniqueChars toQuotedString(JSContext* cx) const;
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
using CacheableNameVector = Vector<CacheableName, 0, SystemAllocPolicy>;
// A hash policy for names.
struct NameHasher {
using Key = Span<const char>;
using Lookup = Span<const char>;
static HashNumber hash(const Lookup& aLookup) {
return mozilla::HashString(, aLookup.Length());
static bool match(const Key& aKey, const Lookup& aLookup) {
return aKey == aLookup;
// Import describes a single wasm import. An ImportVector describes all
// of a single module's imports.
// ImportVector is built incrementally by ModuleGenerator and then stored
// immutably by Module.
struct Import {
CacheableName module;
CacheableName field;
DefinitionKind kind;
Import() = default;
Import(CacheableName&& module, CacheableName&& field, DefinitionKind kind)
: module(std::move(module)), field(std::move(field)), kind(kind) {}
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
using ImportVector = Vector<Import, 0, SystemAllocPolicy>;
// Export describes the export of a definition in a Module to a field in the
// export object. The Export stores the index of the exported item in the
// appropriate type-specific module data structure (function table, global
// table, table table, and - eventually - memory table).
// Note a single definition can be exported by multiple Exports in the
// ExportVector.
// ExportVector is built incrementally by ModuleGenerator and then stored
// immutably by Module.
class Export {
struct CacheablePod {
DefinitionKind kind_;
uint32_t index_;
CacheableName fieldName_;
CacheablePod pod;
Export() = default;
explicit Export(CacheableName&& fieldName, uint32_t index,
DefinitionKind kind);
const CacheableName& fieldName() const { return fieldName_; }
DefinitionKind kind() const { return pod.kind_; }
uint32_t funcIndex() const;
uint32_t tagIndex() const;
uint32_t memoryIndex() const;
uint32_t globalIndex() const;
uint32_t tableIndex() const;
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
using ExportVector = Vector<Export, 0, SystemAllocPolicy>;
// FuncFlags provides metadata for a function definition.
enum class FuncFlags : uint8_t {
None = 0x0,
// The function maybe be accessible by JS and needs thunks generated for it.
// See `[SMDOC] Exported wasm functions and the jit-entry stubs` in
// WasmJS.cpp for more information.
Exported = 0x1,
// The function should have thunks generated upon instantiation, not upon
// first call. May only be set if `Exported` is set.
Eager = 0x2,
// The function can be the target of a ref.func instruction in the code
// section. May only be set if `Exported` is set.
CanRefFunc = 0x4,
// A FuncDesc describes a single function definition.
struct FuncDesc {
const FuncType* type;
// Bit pack to keep this struct small on 32-bit systems
uint32_t typeIndex : 24;
FuncFlags flags : 8;
// Assert that the bit packing scheme is viable
static_assert(MaxTypes <= (1 << 24) - 1);
static_assert(sizeof(FuncFlags) == sizeof(uint8_t));
FuncDesc() = default;
FuncDesc(const FuncType* type, uint32_t typeIndex)
: type(type), typeIndex(typeIndex), flags(FuncFlags::None) {}
bool isExported() const {
return uint8_t(flags) & uint8_t(FuncFlags::Exported);
bool isEager() const { return uint8_t(flags) & uint8_t(FuncFlags::Eager); }
bool canRefFunc() const {
return uint8_t(flags) & uint8_t(FuncFlags::CanRefFunc);
using FuncDescVector = Vector<FuncDesc, 0, SystemAllocPolicy>;
enum class BranchHint : uint8_t { Unlikely = 0, Likely = 1, Invalid = 2 };
// Stores pairs of <BranchOffset, BranchHint>
struct BranchHintEntry {
uint32_t branchOffset;
BranchHint value;
BranchHintEntry() = default;
BranchHintEntry(uint32_t branchOffset, BranchHint value)
: branchOffset(branchOffset), value(value) {}
// Branch hint sorted vector for a function,
// stores tuples of <BranchOffset, BranchHint>
using BranchHintVector = Vector<BranchHintEntry, 0, SystemAllocPolicy>;
struct BranchHintCollection {
// Map from function index to their collection of branch hints
HashMap<uint32_t, BranchHintVector, DefaultHasher<uint32_t>,
// Used for lookups into the collection if a function
// doesn't contain any hints.
static BranchHintVector invalidVector;
// Add all the branch hints for a function
[[nodiscard]] bool addHintsForFunc(uint32_t functionIndex,
BranchHintVector&& branchHints) {
return branchHintsMap.put(functionIndex, std::move(branchHints));
// Return the vector with branch hints for a funcIndex.
// If this function doesn't contain any hints, return an empty vector.
BranchHintVector& getHintVector(uint32_t funcIndex) const {
if (auto hintsVector = branchHintsMap.readonlyThreadsafeLookup(funcIndex)) {
return hintsVector->value();
// If not found, return the empty invalid Vector
return invalidVector;
bool isEmpty() const { return branchHintsMap.empty(); }
enum class GlobalKind { Import, Constant, Variable };
// A GlobalDesc describes a single global variable.
// wasm can import and export mutable and immutable globals.
// asm.js can import mutable and immutable globals, but a mutable global has a
// location that is private to the module, and its initial value is copied into
// that cell from the environment. asm.js cannot export globals.
class GlobalDesc {
GlobalKind kind_;
// Stores the value type of this global for all kinds, and the initializer
// expression when `constant` or `variable`.
InitExpr initial_;
// Metadata for the global when `variable` or `import`.
unsigned offset_;
bool isMutable_;
bool isWasm_;
bool isExport_;
// Metadata for the global when `import`.
uint32_t importIndex_;
// Private, as they have unusual semantics.
bool isExport() const { return !isConstant() && isExport_; }
bool isWasm() const { return !isConstant() && isWasm_; }
GlobalDesc() = default;
explicit GlobalDesc(InitExpr&& initial, bool isMutable,
ModuleKind kind = ModuleKind::Wasm)
: kind_((!isMutable && initial.isLiteral()) ? GlobalKind::Constant
: GlobalKind::Variable) {
initial_ = std::move(initial);
if (isVariable()) {
isMutable_ = isMutable;
isWasm_ = kind == Wasm;
isExport_ = false;
offset_ = UINT32_MAX;
explicit GlobalDesc(ValType type, bool isMutable, uint32_t importIndex,
ModuleKind kind = ModuleKind::Wasm)
: kind_(GlobalKind::Import) {
initial_ = InitExpr(LitVal(type));
importIndex_ = importIndex;
isMutable_ = isMutable;
isWasm_ = kind == Wasm;
isExport_ = false;
offset_ = UINT32_MAX;
void setOffset(unsigned offset) {
MOZ_ASSERT(offset_ == UINT32_MAX);
offset_ = offset;
unsigned offset() const {
MOZ_ASSERT(offset_ != UINT32_MAX);
return offset_;
void setIsExport() {
if (!isConstant()) {
isExport_ = true;
GlobalKind kind() const { return kind_; }
bool isVariable() const { return kind_ == GlobalKind::Variable; }
bool isConstant() const { return kind_ == GlobalKind::Constant; }
bool isImport() const { return kind_ == GlobalKind::Import; }
bool isMutable() const { return !isConstant() && isMutable_; }
const InitExpr& initExpr() const {
return initial_;
uint32_t importIndex() const {
return importIndex_;
LitVal constantValue() const { return initial_.literal(); }
// If isIndirect() is true then storage for the value is not in the
// instance's global area, but in a WasmGlobalObject::Cell hanging off a
// WasmGlobalObject; the global area contains a pointer to the Cell.
// We don't want to indirect unless we must, so only mutable, exposed
// globals are indirected - in all other cases we copy values into and out
// of their module.
// Note that isIndirect() isn't equivalent to getting a WasmGlobalObject:
// an immutable exported global will still get an object, but will not be
// indirect.
bool isIndirect() const {
return isMutable() && isWasm() && (isImport() || isExport());
ValType type() const { return initial_.type(); }
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
using GlobalDescVector = Vector<GlobalDesc, 0, SystemAllocPolicy>;
// A TagDesc represents fresh per-instance tags that are used for the
// exception handling proposal and potentially other future proposals.
// The TagOffsetVector represents the offsets in the layout of the
// data buffer stored in a Wasm exception.
using TagOffsetVector = Vector<uint32_t, 2, SystemAllocPolicy>;
class TagType : public AtomicRefCounted<TagType> {
ValTypeVector argTypes_;
TagOffsetVector argOffsets_;
uint32_t size_;
TagType() : size_(0) {}
const ValTypeVector& argTypes() const { return argTypes_; }
const TagOffsetVector& argOffsets() const { return argOffsets_; }
ResultType resultType() const { return ResultType::Vector(argTypes_); }
uint32_t tagSize() const { return size_; }
[[nodiscard]] bool initialize(ValTypeVector&& argTypes);
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
using MutableTagType = RefPtr<TagType>;
using SharedTagType = RefPtr<const TagType>;
struct TagDesc {
TagKind kind;
SharedTagType type;
bool isExport;
TagDesc() : isExport(false) {}
TagDesc(TagKind kind, const SharedTagType& type, bool isExport = false)
: kind(kind), type(type), isExport(isExport) {}
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
using TagDescVector = Vector<TagDesc, 0, SystemAllocPolicy>;
using ElemExprOffsetVector = Vector<size_t, 0, SystemAllocPolicy>;
struct ModuleElemSegment {
enum class Kind {
// The type of encoding used by this element segment. 0 is an invalid value to
// make sure we notice if we fail to correctly initialize the element segment
// - reading from the wrong representation could be a bad time.
enum class Encoding {
Indices = 1,
struct Expressions {
size_t count = 0;
Bytes exprBytes;
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
Kind kind;
uint32_t tableIndex;
RefType elemType;
Maybe<InitExpr> offsetIfActive;
// We store either an array of indices or the full bytecode of the element
// expressions, depending on the encoding used for the element segment.
Encoding encoding;
Uint32Vector elemIndices;
Expressions elemExpressions;
bool active() const { return kind == Kind::Active; }
const InitExpr& offset() const { return *offsetIfActive; }
size_t numElements() const {
switch (encoding) {
case Encoding::Indices:
return elemIndices.length();
case Encoding::Expressions:
return elemExpressions.count;
MOZ_CRASH("unknown element segment encoding");
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
using ModuleElemSegmentVector = Vector<ModuleElemSegment, 0, SystemAllocPolicy>;
using InstanceElemSegment = GCVector<HeapPtr<AnyRef>, 0, SystemAllocPolicy>;
using InstanceElemSegmentVector =
GCVector<InstanceElemSegment, 0, SystemAllocPolicy>;
// DataSegmentEnv holds the initial results of decoding a data segment from the
// bytecode and is stored in the ModuleEnvironment during compilation. When
// compilation completes, (non-Env) DataSegments are created and stored in
// the wasm::Module which contain copies of the data segment payload. This
// allows non-compilation uses of wasm validation to avoid expensive copies.
// When a DataSegment is "passive" it is shared between a wasm::Module and its
// wasm::Instances. To allow each segment to be released as soon as the last
// Instance mem.drops it and the Module is destroyed, each DataSegment is
// individually atomically ref-counted.
constexpr uint32_t InvalidMemoryIndex = UINT32_MAX;
static_assert(InvalidMemoryIndex > MaxMemories, "Invariant");
struct DataSegmentEnv {
uint32_t memoryIndex;
Maybe<InitExpr> offsetIfActive;
uint32_t bytecodeOffset;
uint32_t length;
using DataSegmentEnvVector = Vector<DataSegmentEnv, 0, SystemAllocPolicy>;
struct DataSegment : AtomicRefCounted<DataSegment> {
uint32_t memoryIndex;
Maybe<InitExpr> offsetIfActive;
Bytes bytes;
DataSegment() = default;
bool active() const { return !!offsetIfActive; }
const InitExpr& offset() const { return *offsetIfActive; }
[[nodiscard]] bool init(const ShareableBytes& bytecode,
const DataSegmentEnv& src) {
memoryIndex = src.memoryIndex;
if (src.offsetIfActive) {
if (!offsetIfActive->clone(*src.offsetIfActive)) {
return false;
return bytes.append(bytecode.begin() + src.bytecodeOffset, src.length);
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
using MutableDataSegment = RefPtr<DataSegment>;
using SharedDataSegment = RefPtr<const DataSegment>;
using DataSegmentVector = Vector<SharedDataSegment, 0, SystemAllocPolicy>;
// The CustomSection(Env) structs are like DataSegment(Env): CustomSectionEnv is
// stored in the ModuleEnvironment and CustomSection holds a copy of the payload
// and is stored in the wasm::Module.
struct CustomSectionEnv {
uint32_t nameOffset;
uint32_t nameLength;
uint32_t payloadOffset;
uint32_t payloadLength;
using CustomSectionEnvVector = Vector<CustomSectionEnv, 0, SystemAllocPolicy>;
struct CustomSection {
Bytes name;
SharedBytes payload;
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
using CustomSectionVector = Vector<CustomSection, 0, SystemAllocPolicy>;
// A Name represents a string of utf8 chars embedded within the name custom
// section. The offset of a name is expressed relative to the beginning of the
// name section's payload so that Names can stored in wasm::Code, which only
// holds the name section's bytes, not the whole bytecode.
struct Name {
// All fields are treated as cacheable POD:
uint32_t offsetInNamePayload;
uint32_t length;
WASM_CHECK_CACHEABLE_POD(offsetInNamePayload, length);
Name() : offsetInNamePayload(UINT32_MAX), length(0) {}
using NameVector = Vector<Name, 0, SystemAllocPolicy>;
// The kind of limits to decode or convert from JS.
enum class LimitsKind {
// Represents the resizable limits of memories and tables.
struct Limits {
// `indexType` will always be I32 for tables, but may be I64 for memories
// when memory64 is enabled.
IndexType indexType;
// The initial and maximum limit. The unit is pages for memories and elements
// for tables.
uint64_t initial;
Maybe<uint64_t> maximum;
// `shared` is Shareable::False for tables but may be Shareable::True for
// memories.
Shareable shared;
WASM_CHECK_CACHEABLE_POD(indexType, initial, maximum, shared);
Limits() = default;
explicit Limits(uint64_t initial, const Maybe<uint64_t>& maximum = Nothing(),
Shareable shared = Shareable::False)
: indexType(IndexType::I32),
shared(shared) {}
// MemoryDesc describes a memory.
struct MemoryDesc {
Limits limits;
bool isShared() const { return limits.shared == Shareable::True; }
// Whether a backing store for this memory may move when grown.
bool canMovingGrow() const { return limits.maximum.isNothing(); }
// Whether the bounds check limit (see the doc comment in
// ArrayBufferObject.cpp regarding linear memory structure) can ever be
// larger than 32-bits.
bool boundsCheckLimitIs32Bits() const {
return limits.maximum.isSome() &&
limits.maximum.value() < (0x100000000 / PageSize);
IndexType indexType() const { return limits.indexType; }
// The initial length of this memory in pages.
Pages initialPages() const { return Pages(limits.initial); }
// The maximum length of this memory in pages.
Maybe<Pages> maximumPages() const {
return[](uint64_t x) { return Pages(x); });
// The initial length of this memory in bytes. Only valid for memory32.
uint64_t initialLength32() const {
MOZ_ASSERT(indexType() == IndexType::I32);
// See static_assert after MemoryDesc for why this is safe.
return limits.initial * PageSize;
uint64_t initialLength64() const {
MOZ_ASSERT(indexType() == IndexType::I64);
return limits.initial * PageSize;
MemoryDesc() {}
explicit MemoryDesc(Limits limits) : limits(limits) {}
using MemoryDescVector = Vector<MemoryDesc, 1, SystemAllocPolicy>;
// We don't need to worry about overflow with a Memory32 field when
// using a uint64_t.
static_assert(MaxMemory32LimitField <= UINT64_MAX / PageSize);
// TableDesc describes a table as well as the offset of the table's base pointer
// in global memory.
// A TableDesc contains the element type and whether the table is for asm.js,
// which determines the table representation.
// - ExternRef: a wasm anyref word (wasm::AnyRef)
// - FuncRef: a two-word FunctionTableElem (wasm indirect call ABI)
// - FuncRef (if `isAsmJS`): a two-word FunctionTableElem (asm.js ABI)
// Eventually there should be a single unified AnyRef representation.
struct TableDesc {
RefType elemType;
bool isImported;
bool isExported;
bool isAsmJS;
uint32_t initialLength;
Maybe<uint32_t> maximumLength;
Maybe<InitExpr> initExpr;
TableDesc() = default;
TableDesc(RefType elemType, uint32_t initialLength,
Maybe<uint32_t> maximumLength, Maybe<InitExpr>&& initExpr,
bool isAsmJS, bool isImported = false, bool isExported = false)
: elemType(elemType),
initExpr(std::move(initExpr)) {}
using TableDescVector = Vector<TableDesc, 0, SystemAllocPolicy>;
} // namespace wasm
} // namespace js
#endif // wasm_module_types_h