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| -rw-r--r-- | js/src/vm/SharedStencil.h | 631 |
1 files changed, 631 insertions, 0 deletions
diff --git a/js/src/vm/SharedStencil.h b/js/src/vm/SharedStencil.h new file mode 100644 index 0000000000..14d7272489 --- /dev/null +++ b/js/src/vm/SharedStencil.h @@ -0,0 +1,631 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- + * vim: set ts=8 sts=2 et sw=2 tw=80: + * This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +#ifndef vm_SharedStencil_h +#define vm_SharedStencil_h + +#include "mozilla/Assertions.h" // MOZ_ASSERT, MOZ_CRASH +#include "mozilla/Atomics.h" // mozilla::{Atomic, SequentiallyConsistent} +#include "mozilla/Attributes.h" // MOZ_MUST_USE +#include "mozilla/HashFunctions.h" // mozilla::HahNumber, mozilla::HashBytes +#include "mozilla/HashTable.h" // mozilla::HashSet +#include "mozilla/MemoryReporting.h" // mozilla::MallocSizeOf +#include "mozilla/RefPtr.h" // RefPtr +#include "mozilla/Span.h" // mozilla::Span + +#include <stddef.h> // size_t +#include <stdint.h> // uint8_t, uint16_t, uint32_t + +#include "frontend/SourceNotes.h" // js::SrcNote +#include "frontend/TypedIndex.h" // js::frontend::TypedIndex + +#include "js/AllocPolicy.h" // js::SystemAllocPolicy +#include "js/TypeDecls.h" // JSContext,jsbytecode +#include "js/UniquePtr.h" // js::UniquePtr +#include "util/TrailingArray.h" // js::TrailingArray +#include "vm/StencilEnums.h" // js::{TryNoteKind,ImmutableScriptFlagsEnum,MutableScriptFlagsEnum} + +// +// Data structures shared between Stencil and the VM. +// + +namespace js { + +namespace frontend { +class StencilXDR; +} // namespace frontend + +// Index into gcthings array. +class GCThingIndexType; +class GCThingIndex : public frontend::TypedIndex<GCThingIndexType> { + // Delegate constructors; + using Base = frontend::TypedIndex<GCThingIndexType>; + using Base::Base; + + public: + static constexpr GCThingIndex outermostScopeIndex() { + return GCThingIndex(0); + } + + static constexpr GCThingIndex invalid() { return GCThingIndex(UINT32_MAX); } + + GCThingIndex next() const { return GCThingIndex(index + 1); } +}; + +/* + * Exception handling record. + */ +struct TryNote { + uint32_t kind_; /* one of TryNoteKind */ + uint32_t stackDepth; /* stack depth upon exception handler entry */ + uint32_t start; /* start of the try statement or loop relative + to script->code() */ + uint32_t length; /* length of the try statement or loop */ + + TryNote(uint32_t kind, uint32_t stackDepth, uint32_t start, uint32_t length) + : kind_(kind), stackDepth(stackDepth), start(start), length(length) {} + + TryNote() = default; + + TryNoteKind kind() const { return TryNoteKind(kind_); } + + bool isLoop() const { + switch (kind()) { + case TryNoteKind::Loop: + case TryNoteKind::ForIn: + case TryNoteKind::ForOf: + return true; + case TryNoteKind::Catch: + case TryNoteKind::Finally: + case TryNoteKind::ForOfIterClose: + case TryNoteKind::Destructuring: + return false; + } + MOZ_CRASH("Unexpected try note kind"); + } +}; + +// A block scope has a range in bytecode: it is entered at some offset, and left +// at some later offset. Scopes can be nested. Given an offset, the +// ScopeNote containing that offset whose with the highest start value +// indicates the block scope. The block scope list is sorted by increasing +// start value. +// +// It is possible to leave a scope nonlocally, for example via a "break" +// statement, so there may be short bytecode ranges in a block scope in which we +// are popping the block chain in preparation for a goto. These exits are also +// nested with respect to outer scopes. The scopes in these exits are indicated +// by the "index" field, just like any other block. If a nonlocal exit pops the +// last block scope, the index will be NoScopeIndex. +// +struct ScopeNote { + // Sentinel index for no Scope. + static constexpr GCThingIndex NoScopeIndex = GCThingIndex::invalid(); + + // Sentinel index for no ScopeNote. + static const uint32_t NoScopeNoteIndex = UINT32_MAX; + + // Index of the js::Scope in the script's gcthings array, or NoScopeIndex if + // there is no block scope in this range. + GCThingIndex index; + + // Bytecode offset at which this scope starts relative to script->code(). + uint32_t start = 0; + + // Length of bytecode span this scope covers. + uint32_t length = 0; + + // Index of parent block scope in notes, or NoScopeNoteIndex. + uint32_t parent = 0; +}; + +// Range of characters in scriptSource which contains a script's source, +// that is, the range used by the Parser to produce a script. +// +// For most functions the fields point to the following locations. +// +// function * foo(a, b) { return a + b; } +// ^ ^ ^ +// | | | +// | sourceStart sourceEnd +// | | +// toStringStart toStringEnd +// +// For the special case of class constructors, the spec requires us to use an +// alternate definition of toStringStart / toStringEnd. +// +// class C { constructor() { this.field = 42; } } +// ^ ^ ^ ^ +// | | | | +// | sourceStart sourceEnd | +// | | +// toStringStart toStringEnd +// +// Implicit class constructors use the following definitions. +// +// class C { someMethod() { } } +// ^ ^ +// | | +// sourceStart sourceEnd +// | | +// toStringStart toStringEnd +// +// Field initializer lambdas are internal details of the engine, but we still +// provide a sensible definition of these values. +// +// class C { static field = 1 } +// class C { field = 1 } +// class C { somefield } +// ^ ^ +// | | +// sourceStart sourceEnd +// +// The non-static private class methods (including getters and setters) ALSO +// create a hidden initializer lambda in addition to the method itself. These +// lambdas are not exposed directly to script. +// +// class C { #field() { } } +// class C { get #field() { } } +// class C { async #field() { } } +// class C { * #field() { } } +// ^ ^ +// | | +// sourceStart sourceEnd +// +// NOTE: These are counted in Code Units from the start of the script source. +// +// Also included in the SourceExtent is the line and column numbers of the +// sourceStart position. Compilation options may specify the initial line and +// column number. +// +// NOTE: Column number may saturate and must not be used as unique identifier. +struct SourceExtent { + SourceExtent() = default; + + SourceExtent(uint32_t sourceStart, uint32_t sourceEnd, uint32_t toStringStart, + uint32_t toStringEnd, uint32_t lineno, uint32_t column) + : sourceStart(sourceStart), + sourceEnd(sourceEnd), + toStringStart(toStringStart), + toStringEnd(toStringEnd), + lineno(lineno), + column(column) {} + + static SourceExtent makeGlobalExtent(uint32_t len) { + return SourceExtent(0, len, 0, len, 1, 0); + } + + static SourceExtent makeGlobalExtent(uint32_t len, uint32_t lineno, + uint32_t column) { + return SourceExtent(0, len, 0, len, lineno, column); + } + + static SourceExtent makeClassExtent(uint32_t start, uint32_t end, + uint32_t lineno, uint32_t column) { + return SourceExtent(start, end, start, end, lineno, column); + } + + uint32_t sourceStart = 0; + uint32_t sourceEnd = 0; + uint32_t toStringStart = 0; + uint32_t toStringEnd = 0; + + // Line and column of |sourceStart_| position. + uint32_t lineno = 1; // 1-indexed. + uint32_t column = 0; // Count of Code Points +}; + +// These are wrapper types around the flag enums to provide a more appropriate +// abstraction of the bitfields. +template <typename EnumType> +class ScriptFlagBase { + protected: + // Stored as a uint32_t to make access more predictable from + // JIT code. + uint32_t flags_ = 0; + + public: + ScriptFlagBase() = default; + explicit ScriptFlagBase(uint32_t rawFlags) : flags_(rawFlags) {} + + MOZ_MUST_USE bool hasFlag(EnumType flag) const { + return flags_ & static_cast<uint32_t>(flag); + } + void setFlag(EnumType flag) { flags_ |= static_cast<uint32_t>(flag); } + void clearFlag(EnumType flag) { flags_ &= ~static_cast<uint32_t>(flag); } + void setFlag(EnumType flag, bool b) { + if (b) { + setFlag(flag); + } else { + clearFlag(flag); + } + } + + operator uint32_t() const { return flags_; } + + ScriptFlagBase& operator|=(const uint32_t rhs) { + flags_ |= rhs; + return *this; + } +}; + +class ImmutableScriptFlags : public ScriptFlagBase<ImmutableScriptFlagsEnum> { + public: + using ScriptFlagBase<ImmutableScriptFlagsEnum>::ScriptFlagBase; + + void operator=(uint32_t flag) { flags_ = flag; } +}; + +class MutableScriptFlags : public ScriptFlagBase<MutableScriptFlagsEnum> { + public: + MutableScriptFlags() = default; + + MutableScriptFlags& operator&=(const uint32_t rhs) { + flags_ &= rhs; + return *this; + } +}; + +// [SMDOC] JSScript data layout (immutable) +// +// ImmutableScriptData stores variable-length script data that may be shared +// between scripts with the same bytecode, even across different GC Zones. +// Abstractly this structure consists of multiple (optional) arrays that are +// exposed as mozilla::Span<T>. These arrays exist in a single heap allocation. +// +// Under the hood, ImmutableScriptData is a fixed-size header class followed +// the various array bodies interleaved with metadata to compactly encode the +// bounds. These arrays have varying requirements for alignment, performance, +// and jit-friendliness which leads to the complex indexing system below. +// +// Note: The '----' separators are for readability only. +// +// ---- +// <ImmutableScriptData itself> +// ---- +// (REQUIRED) Flags structure +// (REQUIRED) Array of jsbytecode constituting code() +// (REQUIRED) Array of SrcNote constituting notes() +// ---- +// (OPTIONAL) Array of uint32_t optional-offsets +// optArrayOffset: +// ---- +// L0: +// (OPTIONAL) Array of uint32_t constituting resumeOffsets() +// L1: +// (OPTIONAL) Array of ScopeNote constituting scopeNotes() +// L2: +// (OPTIONAL) Array of TryNote constituting tryNotes() +// L3: +// ---- +// +// NOTE: The notes() array must have been null-padded such that +// flags/code/notes together have uint32_t alignment. +// +// The labels shown are recorded as byte-offsets relative to 'this'. This is to +// reduce memory as well as make ImmutableScriptData easier to share across +// processes. +// +// The L0/L1/L2/L3 labels indicate the start and end of the optional arrays. +// Some of these labels may refer to the same location if the array between +// them is empty. Each unique label position has an offset stored in the +// optional-offsets table. Note that we also avoid entries for labels that +// match 'optArrayOffset'. This saves memory when arrays are empty. +// +// The flags() data indicates (for each optional array) which entry from the +// optional-offsets table marks the *end* of array. The array starts where the +// previous array ends (with the first array beginning at 'optArrayOffset'). +// The optional-offset table is addressed at negative indices from +// 'optArrayOffset'. +// +// In general, the length of each array is computed from subtracting the start +// offset of the array from the start offset of the subsequent array. The +// notable exception is that bytecode length is stored explicitly. +class alignas(uint32_t) ImmutableScriptData final : public TrailingArray { + private: + Offset optArrayOffset_ = 0; + + // Length of bytecode + uint32_t codeLength_ = 0; + + public: + // Offset of main entry point from code, after predef'ing prologue. + uint32_t mainOffset = 0; + + // Fixed frame slots. + uint32_t nfixed = 0; + + // Slots plus maximum stack depth. + uint32_t nslots = 0; + + // Index into the gcthings array of the body scope. + GCThingIndex bodyScopeIndex; + + // Number of IC entries to allocate in JitScript for Baseline ICs. + uint32_t numICEntries = 0; + + // ES6 function length. + uint16_t funLength = 0; + + // NOTE: The raw bytes of this structure are used for hashing so use explicit + // padding values as needed for predicatable results across compilers. + uint16_t padding = 0; + + private: + struct Flags { + uint8_t resumeOffsetsEndIndex : 2; + uint8_t scopeNotesEndIndex : 2; + uint8_t tryNotesEndIndex : 2; + uint8_t _unused : 2; + }; + static_assert(sizeof(Flags) == sizeof(uint8_t), + "Structure packing is broken"); + + // Offsets (in bytes) from 'this' to each component array. The delta between + // each offset and the next offset is the size of each array and is defined + // even if an array is empty. + Offset flagOffset() const { return offsetOfCode() - sizeof(Flags); } + Offset codeOffset() const { return offsetOfCode(); } + Offset noteOffset() const { return offsetOfCode() + codeLength_; } + Offset optionalOffsetsOffset() const { + // Determine the location to beginning of optional-offsets array by looking + // at index for try-notes. + // + // optionalOffsetsOffset(): + // (OPTIONAL) tryNotesEndOffset + // (OPTIONAL) scopeNotesEndOffset + // (OPTIONAL) resumeOffsetsEndOffset + // optArrayOffset_: + // .... + unsigned numOffsets = flags().tryNotesEndIndex; + MOZ_ASSERT(numOffsets >= flags().scopeNotesEndIndex); + MOZ_ASSERT(numOffsets >= flags().resumeOffsetsEndIndex); + + return optArrayOffset_ - (numOffsets * sizeof(Offset)); + } + Offset resumeOffsetsOffset() const { return optArrayOffset_; } + Offset scopeNotesOffset() const { + return getOptionalOffset(flags().resumeOffsetsEndIndex); + } + Offset tryNotesOffset() const { + return getOptionalOffset(flags().scopeNotesEndIndex); + } + Offset endOffset() const { + return getOptionalOffset(flags().tryNotesEndIndex); + } + + void initOptionalArrays(Offset* cursor, uint32_t numResumeOffsets, + uint32_t numScopeNotes, uint32_t numTryNotes); + + // Initialize to GC-safe state + ImmutableScriptData(uint32_t codeLength, uint32_t noteLength, + uint32_t numResumeOffsets, uint32_t numScopeNotes, + uint32_t numTryNotes); + + void setOptionalOffset(int index, Offset offset) { + MOZ_ASSERT(index > 0); + MOZ_ASSERT(offset != optArrayOffset_, "Do not store implicit offset"); + offsetToPointer<Offset>(optArrayOffset_)[-index] = offset; + } + Offset getOptionalOffset(int index) const { + // The index 0 represents (implicitly) the offset 'optArrayOffset_'. + if (index == 0) { + return optArrayOffset_; + } + + ImmutableScriptData* this_ = const_cast<ImmutableScriptData*>(this); + return this_->offsetToPointer<Offset>(optArrayOffset_)[-index]; + } + + public: + static js::UniquePtr<ImmutableScriptData> new_( + JSContext* cx, uint32_t mainOffset, uint32_t nfixed, uint32_t nslots, + GCThingIndex bodyScopeIndex, uint32_t numICEntries, bool isFunction, + uint16_t funLength, mozilla::Span<const jsbytecode> code, + mozilla::Span<const SrcNote> notes, + mozilla::Span<const uint32_t> resumeOffsets, + mozilla::Span<const ScopeNote> scopeNotes, + mozilla::Span<const TryNote> tryNotes); + + static js::UniquePtr<ImmutableScriptData> new_( + JSContext* cx, uint32_t codeLength, uint32_t noteLength, + uint32_t numResumeOffsets, uint32_t numScopeNotes, uint32_t numTryNotes); + + // The code() and note() arrays together maintain an target alignment by + // padding the source notes with null. This allows arrays with stricter + // alignment requirements to follow them. + static constexpr size_t CodeNoteAlign = sizeof(uint32_t); + + // Compute number of null notes to pad out source notes with. + static uint32_t ComputeNotePadding(uint32_t codeLength, uint32_t noteLength) { + uint32_t flagLength = sizeof(Flags); + uint32_t nullLength = + CodeNoteAlign - (flagLength + codeLength + noteLength) % CodeNoteAlign; + + // The source notes must have at least one null-terminator. + MOZ_ASSERT(nullLength >= 1); + + return nullLength; + } + + // Span over all raw bytes in this struct and its trailing arrays. + mozilla::Span<const uint8_t> immutableData() const { + size_t allocSize = endOffset(); + return mozilla::Span{reinterpret_cast<const uint8_t*>(this), allocSize}; + } + + private: + Flags& flagsRef() { return *offsetToPointer<Flags>(flagOffset()); } + const Flags& flags() const { + return const_cast<ImmutableScriptData*>(this)->flagsRef(); + } + + public: + uint32_t codeLength() const { return codeLength_; } + jsbytecode* code() { return offsetToPointer<jsbytecode>(codeOffset()); } + mozilla::Span<jsbytecode> codeSpan() { return {code(), codeLength()}; } + + uint32_t noteLength() const { + return numElements<SrcNote>(noteOffset(), optionalOffsetsOffset()); + } + SrcNote* notes() { return offsetToPointer<SrcNote>(noteOffset()); } + mozilla::Span<SrcNote> notesSpan() { return {notes(), noteLength()}; } + + mozilla::Span<uint32_t> resumeOffsets() { + return mozilla::Span{offsetToPointer<uint32_t>(resumeOffsetsOffset()), + offsetToPointer<uint32_t>(scopeNotesOffset())}; + } + mozilla::Span<ScopeNote> scopeNotes() { + return mozilla::Span{offsetToPointer<ScopeNote>(scopeNotesOffset()), + offsetToPointer<ScopeNote>(tryNotesOffset())}; + } + mozilla::Span<TryNote> tryNotes() { + return mozilla::Span{offsetToPointer<TryNote>(tryNotesOffset()), + offsetToPointer<TryNote>(endOffset())}; + } + + // Expose offsets to the JITs. + static constexpr size_t offsetOfCode() { + return sizeof(ImmutableScriptData) + sizeof(Flags); + } + static constexpr size_t offsetOfResumeOffsetsOffset() { + // Resume-offsets are the first optional array if they exist. Locate the + // array with the 'optArrayOffset_' field. + static_assert(sizeof(Offset) == sizeof(uint32_t), + "JIT expect Offset to be uint32_t"); + return offsetof(ImmutableScriptData, optArrayOffset_); + } + static constexpr size_t offsetOfNfixed() { + return offsetof(ImmutableScriptData, nfixed); + } + static constexpr size_t offsetOfNslots() { + return offsetof(ImmutableScriptData, nslots); + } + static constexpr size_t offsetOfFunLength() { + return offsetof(ImmutableScriptData, funLength); + } + + // ImmutableScriptData has trailing data so isn't copyable or movable. + ImmutableScriptData(const ImmutableScriptData&) = delete; + ImmutableScriptData& operator=(const ImmutableScriptData&) = delete; +}; + +// Wrapper type for ImmutableScriptData to allow sharing across a JSRuntime. +// +// Note: This is distinct from ImmutableScriptData because it contains a mutable +// ref-count while the ImmutableScriptData may live in read-only memory. +// +// Note: This is *not* directly inlined into the SharedImmutableScriptDataTable +// because scripts point directly to object and table resizing moves +// entries. This allows for fast finalization by decrementing the +// ref-count directly without doing a hash-table lookup. +class SharedImmutableScriptData { + // This class is reference counted as follows: each pointer from a JSScript + // counts as one reference plus there may be one reference from the shared + // script data table. + mozilla::Atomic<uint32_t, mozilla::SequentiallyConsistent> refCount_ = {}; + + js::UniquePtr<ImmutableScriptData> isd_ = nullptr; + + // End of fields. + + friend class ::JSScript; + friend class js::frontend::StencilXDR; + + public: + SharedImmutableScriptData() = default; + + // Hash over the contents of SharedImmutableScriptData and its + // ImmutableScriptData. + struct Hasher; + + uint32_t refCount() const { return refCount_; } + void AddRef() { refCount_++; } + void Release() { + MOZ_ASSERT(refCount_ != 0); + uint32_t remain = --refCount_; + if (remain == 0) { + isd_ = nullptr; + js_free(this); + } + } + + static constexpr size_t offsetOfISD() { + return offsetof(SharedImmutableScriptData, isd_); + } + + private: + static SharedImmutableScriptData* create(JSContext* cx); + + public: + static SharedImmutableScriptData* createWith( + JSContext* cx, js::UniquePtr<ImmutableScriptData>&& isd); + + size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) { + return mallocSizeOf(this) + mallocSizeOf(isd_.get()); + } + + // SharedImmutableScriptData has trailing data so isn't copyable or movable. + SharedImmutableScriptData(const SharedImmutableScriptData&) = delete; + SharedImmutableScriptData& operator=(const SharedImmutableScriptData&) = + delete; + + static bool shareScriptData(JSContext* cx, + RefPtr<SharedImmutableScriptData>& sisd); + + size_t immutableDataLength() const { return isd_->immutableData().Length(); } + uint32_t nfixed() const { return isd_->nfixed; } +}; + +// Matches SharedImmutableScriptData objects that have the same atoms as well as +// contain the same bytes in their ImmutableScriptData. +struct SharedImmutableScriptData::Hasher { + using Lookup = RefPtr<SharedImmutableScriptData>; + + static mozilla::HashNumber hash(const Lookup& l) { + mozilla::Span<const uint8_t> immutableData = l->isd_->immutableData(); + return mozilla::HashBytes(immutableData.data(), immutableData.size()); + } + + static bool match(SharedImmutableScriptData* entry, const Lookup& lookup) { + return (entry->isd_->immutableData() == lookup->isd_->immutableData()); + } +}; + +using SharedImmutableScriptDataTable = + mozilla::HashSet<SharedImmutableScriptData*, + SharedImmutableScriptData::Hasher, SystemAllocPolicy>; + +struct MemberInitializers { + static constexpr uint32_t MaxInitializers = INT32_MAX; + +#ifdef DEBUG + bool valid = false; +#endif + + // This struct will eventually have a vector of constant values for optimizing + // field initializers. + uint32_t numMemberInitializers = 0; + + explicit MemberInitializers(uint32_t numMemberInitializers) + : +#ifdef DEBUG + valid(true), +#endif + numMemberInitializers(numMemberInitializers) { + } + + static MemberInitializers Invalid() { return MemberInitializers(); } + + uint32_t serialize() const { return numMemberInitializers; } + + private: + MemberInitializers() = default; +}; + +} // namespace js + +#endif /* vm_SharedStencil_h */ |