Adding upstream version 86.0.1.upstream/86.0.1upstream

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

1 files changed, 774 insertions, 0 deletions

diff --git a/js/src/gc/Heap.h b/js/src/gc/Heap.h
new file mode 100644
index 0000000000..daa20cbf0f
--- /dev/null
+++ b/js/src/gc/Heap.h
@@ -0,0 +1,774 @@
+/* -*- 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 gc_Heap_h
+#define gc_Heap_h
+
+#include "mozilla/DebugOnly.h"
+
+#include "ds/BitArray.h"
+#include "gc/AllocKind.h"
+#include "gc/GCEnum.h"
+#include "js/HeapAPI.h"
+#include "js/TypeDecls.h"
+#include "util/Poison.h"
+
+namespace js {
+
+class AutoLockGC;
+class AutoLockGCBgAlloc;
+class NurseryDecommitTask;
+
+namespace gc {
+
+class Arena;
+class ArenaCellSet;
+class ArenaList;
+class GCRuntime;
+class MarkingValidator;
+class SortedArenaList;
+class StoreBuffer;
+class TenuredCell;
+
+// Cells are aligned to CellAlignShift, so the largest tagged null pointer is:
+const uintptr_t LargestTaggedNullCellPointer = (1 << CellAlignShift) - 1;
+
+/*
+ * The minimum cell size ends up as twice the cell alignment because the mark
+ * bitmap contains one bit per CellBytesPerMarkBit bytes (which is equal to
+ * CellAlignBytes) and we need two mark bits per cell.
+ */
+const size_t MinCellSize = CellBytesPerMarkBit * MarkBitsPerCell;
+
+static_assert(ArenaSize % CellAlignBytes == 0,
+              "Arena size must be a multiple of cell alignment");
+
+/*
+ * A FreeSpan represents a contiguous sequence of free cells in an Arena. It
+ * can take two forms.
+ *
+ * - In an empty span, |first| and |last| are both zero.
+ *
+ * - In a non-empty span, |first| is the address of the first free thing in the
+ *   span, and |last| is the address of the last free thing in the span.
+ *   Furthermore, the memory pointed to by |last| holds a FreeSpan structure
+ *   that points to the next span (which may be empty); this works because
+ *   sizeof(FreeSpan) is less than the smallest thingSize.
+ */
+class FreeSpan {
+  friend class Arena;
+  friend class ArenaCellIter;
+  friend class ArenaFreeCellIter;
+
+  uint16_t first;
+  uint16_t last;
+
+ public:
+  // This inits just |first| and |last|; if the span is non-empty it doesn't
+  // do anything with the next span stored at |last|.
+  void initBounds(uintptr_t firstArg, uintptr_t lastArg, const Arena* arena) {
+    checkRange(firstArg, lastArg, arena);
+    first = firstArg;
+    last = lastArg;
+  }
+
+  void initAsEmpty() {
+    first = 0;
+    last = 0;
+  }
+
+  // This sets |first| and |last|, and also sets the next span stored at
+  // |last| as empty. (As a result, |firstArg| and |lastArg| cannot represent
+  // an empty span.)
+  void initFinal(uintptr_t firstArg, uintptr_t lastArg, const Arena* arena) {
+    initBounds(firstArg, lastArg, arena);
+    FreeSpan* last = nextSpanUnchecked(arena);
+    last->initAsEmpty();
+    checkSpan(arena);
+  }
+
+  bool isEmpty() const { return !first; }
+
+  Arena* getArenaUnchecked() { return reinterpret_cast<Arena*>(this); }
+  inline Arena* getArena();
+
+  static size_t offsetOfFirst() { return offsetof(FreeSpan, first); }
+
+  static size_t offsetOfLast() { return offsetof(FreeSpan, last); }
+
+  // Like nextSpan(), but no checking of the following span is done.
+  FreeSpan* nextSpanUnchecked(const Arena* arena) const {
+    MOZ_ASSERT(arena && !isEmpty());
+    return reinterpret_cast<FreeSpan*>(uintptr_t(arena) + last);
+  }
+
+  const FreeSpan* nextSpan(const Arena* arena) const {
+    checkSpan(arena);
+    return nextSpanUnchecked(arena);
+  }
+
+  MOZ_ALWAYS_INLINE TenuredCell* allocate(size_t thingSize) {
+    // Eschew the usual checks, because this might be the placeholder span.
+    // If this is somehow an invalid, non-empty span, checkSpan() will catch it.
+    Arena* arena = getArenaUnchecked();
+    checkSpan(arena);
+    uintptr_t thing = uintptr_t(arena) + first;
+    if (first < last) {
+      // We have space for at least two more things, so do a simple
+      // bump-allocate.
+      first += thingSize;
+    } else if (MOZ_LIKELY(first)) {
+      // The last space points to the next free span (which may be empty).
+      const FreeSpan* next = nextSpan(arena);
+      first = next->first;
+      last = next->last;
+    } else {
+      return nullptr;  // The span is empty.
+    }
+    checkSpan(arena);
+    DebugOnlyPoison(reinterpret_cast<void*>(thing),
+                    JS_ALLOCATED_TENURED_PATTERN, thingSize,
+                    MemCheckKind::MakeUndefined);
+    return reinterpret_cast<TenuredCell*>(thing);
+  }
+
+  inline void checkSpan(const Arena* arena) const;
+  inline void checkRange(uintptr_t first, uintptr_t last,
+                         const Arena* arena) const;
+};
+
+/*
+ * Arenas are the allocation units of the tenured heap in the GC. An arena
+ * is 4kiB in size and 4kiB-aligned. It starts with several header fields
+ * followed by some bytes of padding. The remainder of the arena is filled
+ * with GC things of a particular AllocKind. The padding ensures that the
+ * GC thing array ends exactly at the end of the arena:
+ *
+ * <----------------------------------------------> = ArenaSize bytes
+ * +---------------+---------+----+----+-----+----+
+ * | header fields | padding | T0 | T1 | ... | Tn |
+ * +---------------+---------+----+----+-----+----+
+ * <-------------------------> = first thing offset
+ */
+class alignas(ArenaSize) Arena {
+  static JS_FRIEND_DATA const uint8_t ThingSizes[];
+  static JS_FRIEND_DATA const uint8_t FirstThingOffsets[];
+  static JS_FRIEND_DATA const uint8_t ThingsPerArena[];
+  /*
+   * The first span of free things in the arena. Most of these spans are
+   * stored as offsets in free regions of the data array, and most operations
+   * on FreeSpans take an Arena pointer for safety. However, the FreeSpans
+   * used for allocation are stored here, at the start of an Arena, and use
+   * their own address to grab the next span within the same Arena.
+   */
+  FreeSpan firstFreeSpan;
+
+ public:
+  /*
+   * The zone that this Arena is contained within, when allocated. The offset
+   * of this field must match the ArenaZoneOffset stored in js/HeapAPI.h,
+   * as is statically asserted below.
+   */
+  JS::Zone* zone;
+
+  /*
+   * Arena::next has two purposes: when unallocated, it points to the next
+   * available Arena. When allocated, it points to the next Arena in the same
+   * zone and with the same alloc kind.
+   */
+  Arena* next;
+
+ private:
+  /*
+   * One of the AllocKind constants or AllocKind::LIMIT when the arena does
+   * not contain any GC things and is on the list of empty arenas in the GC
+   * chunk.
+   *
+   * We use 8 bits for the alloc kind so the compiler can use byte-level
+   * memory instructions to access it.
+   */
+  size_t allocKind : 8;
+
+ private:
+  /*
+   * When recursive marking uses too much stack we delay marking of
+   * arenas and link them into a list for later processing. This
+   * uses the following fields.
+   */
+  static const size_t DELAYED_MARKING_FLAG_BITS = 3;
+  static const size_t DELAYED_MARKING_ARENA_BITS =
+      JS_BITS_PER_WORD - 8 - DELAYED_MARKING_FLAG_BITS;
+  size_t onDelayedMarkingList_ : 1;
+  size_t hasDelayedBlackMarking_ : 1;
+  size_t hasDelayedGrayMarking_ : 1;
+  size_t nextDelayedMarkingArena_ : DELAYED_MARKING_ARENA_BITS;
+  static_assert(
+      DELAYED_MARKING_ARENA_BITS >= JS_BITS_PER_WORD - ArenaShift,
+      "Arena::nextDelayedMarkingArena_ packing assumes that ArenaShift has "
+      "enough bits to cover allocKind and delayed marking state.");
+
+  union {
+    /*
+     * For arenas in zones other than the atoms zone, if non-null, points
+     * to an ArenaCellSet that represents the set of cells in this arena
+     * that are in the nursery's store buffer.
+     */
+    ArenaCellSet* bufferedCells_;
+
+    /*
+     * For arenas in the atoms zone, the starting index into zone atom
+     * marking bitmaps (see AtomMarking.h) of the things in this zone.
+     * Atoms never refer to nursery things, so no store buffer index is
+     * needed.
+     */
+    size_t atomBitmapStart_;
+  };
+
+ public:
+  /*
+   * The size of data should be |ArenaSize - offsetof(data)|, but the offset
+   * is not yet known to the compiler, so we do it by hand. |firstFreeSpan|
+   * takes up 8 bytes on 64-bit due to alignment requirements; the rest are
+   * obvious. This constant is stored in js/HeapAPI.h.
+   */
+  uint8_t data[ArenaSize - ArenaHeaderSize];
+
+  void init(JS::Zone* zoneArg, AllocKind kind, const AutoLockGC& lock);
+
+  // Sets |firstFreeSpan| to the Arena's entire valid range, and
+  // also sets the next span stored at |firstFreeSpan.last| as empty.
+  void setAsFullyUnused() {
+    AllocKind kind = getAllocKind();
+    firstFreeSpan.first = firstThingOffset(kind);
+    firstFreeSpan.last = lastThingOffset(kind);
+    FreeSpan* last = firstFreeSpan.nextSpanUnchecked(this);
+    last->initAsEmpty();
+  }
+
+  // Initialize an arena to its unallocated state. For arenas that were
+  // previously allocated for some zone, use release() instead.
+  void setAsNotAllocated() {
+    firstFreeSpan.initAsEmpty();
+
+    // Poison zone pointer to highlight UAF on released arenas in crash data.
+    AlwaysPoison(&zone, JS_FREED_ARENA_PATTERN, sizeof(zone),
+                 MemCheckKind::MakeNoAccess);
+
+    allocKind = size_t(AllocKind::LIMIT);
+    onDelayedMarkingList_ = 0;
+    hasDelayedBlackMarking_ = 0;
+    hasDelayedGrayMarking_ = 0;
+    nextDelayedMarkingArena_ = 0;
+    bufferedCells_ = nullptr;
+  }
+
+  // Return an allocated arena to its unallocated state.
+  inline void release(const AutoLockGC& lock);
+
+  uintptr_t address() const {
+    checkAddress();
+    return uintptr_t(this);
+  }
+
+  inline void checkAddress() const;
+
+  inline TenuredChunk* chunk() const;
+
+  bool allocated() const {
+    MOZ_ASSERT(IsAllocKind(AllocKind(allocKind)));
+    return IsValidAllocKind(AllocKind(allocKind));
+  }
+
+  AllocKind getAllocKind() const {
+    MOZ_ASSERT(allocated());
+    return AllocKind(allocKind);
+  }
+
+  FreeSpan* getFirstFreeSpan() { return &firstFreeSpan; }
+
+  static size_t thingSize(AllocKind kind) { return ThingSizes[size_t(kind)]; }
+  static size_t thingsPerArena(AllocKind kind) {
+    return ThingsPerArena[size_t(kind)];
+  }
+  static size_t thingsSpan(AllocKind kind) {
+    return thingsPerArena(kind) * thingSize(kind);
+  }
+
+  static size_t firstThingOffset(AllocKind kind) {
+    return FirstThingOffsets[size_t(kind)];
+  }
+  static size_t lastThingOffset(AllocKind kind) {
+    return ArenaSize - thingSize(kind);
+  }
+
+  size_t getThingSize() const { return thingSize(getAllocKind()); }
+  size_t getThingsPerArena() const { return thingsPerArena(getAllocKind()); }
+  size_t getThingsSpan() const { return getThingsPerArena() * getThingSize(); }
+  size_t getFirstThingOffset() const {
+    return firstThingOffset(getAllocKind());
+  }
+
+  uintptr_t thingsStart() const { return address() + getFirstThingOffset(); }
+  uintptr_t thingsEnd() const { return address() + ArenaSize; }
+
+  bool isEmpty() const {
+    // Arena is empty if its first span covers the whole arena.
+    firstFreeSpan.checkSpan(this);
+    AllocKind kind = getAllocKind();
+    return firstFreeSpan.first == firstThingOffset(kind) &&
+           firstFreeSpan.last == lastThingOffset(kind);
+  }
+
+  bool hasFreeThings() const { return !firstFreeSpan.isEmpty(); }
+
+  size_t numFreeThings(size_t thingSize) const {
+    firstFreeSpan.checkSpan(this);
+    size_t numFree = 0;
+    const FreeSpan* span = &firstFreeSpan;
+    for (; !span->isEmpty(); span = span->nextSpan(this)) {
+      numFree += (span->last - span->first) / thingSize + 1;
+    }
+    return numFree;
+  }
+
+  size_t countFreeCells() { return numFreeThings(getThingSize()); }
+  size_t countUsedCells() { return getThingsPerArena() - countFreeCells(); }
+
+  bool inFreeList(uintptr_t thing) {
+    uintptr_t base = address();
+    const FreeSpan* span = &firstFreeSpan;
+    for (; !span->isEmpty(); span = span->nextSpan(this)) {
+      /* If the thing comes before the current span, it's not free. */
+      if (thing < base + span->first) {
+        return false;
+      }
+
+      /* If we find it before the end of the span, it's free. */
+      if (thing <= base + span->last) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  static bool isAligned(uintptr_t thing, size_t thingSize) {
+    /* Things ends at the arena end. */
+    uintptr_t tailOffset = ArenaSize - (thing & ArenaMask);
+    return tailOffset % thingSize == 0;
+  }
+
+  bool onDelayedMarkingList() const { return onDelayedMarkingList_; }
+
+  Arena* getNextDelayedMarking() const {
+    MOZ_ASSERT(onDelayedMarkingList_);
+    return reinterpret_cast<Arena*>(nextDelayedMarkingArena_ << ArenaShift);
+  }
+
+  void setNextDelayedMarkingArena(Arena* arena) {
+    MOZ_ASSERT(!(uintptr_t(arena) & ArenaMask));
+    MOZ_ASSERT(!onDelayedMarkingList_);
+    MOZ_ASSERT(!hasDelayedBlackMarking_);
+    MOZ_ASSERT(!hasDelayedGrayMarking_);
+    MOZ_ASSERT(!nextDelayedMarkingArena_);
+    onDelayedMarkingList_ = 1;
+    if (arena) {
+      nextDelayedMarkingArena_ = arena->address() >> ArenaShift;
+    }
+  }
+
+  void updateNextDelayedMarkingArena(Arena* arena) {
+    MOZ_ASSERT(!(uintptr_t(arena) & ArenaMask));
+    MOZ_ASSERT(onDelayedMarkingList_);
+    nextDelayedMarkingArena_ = arena ? arena->address() >> ArenaShift : 0;
+  }
+
+  bool hasDelayedMarking(MarkColor color) const {
+    MOZ_ASSERT(onDelayedMarkingList_);
+    return color == MarkColor::Black ? hasDelayedBlackMarking_
+                                     : hasDelayedGrayMarking_;
+  }
+
+  bool hasAnyDelayedMarking() const {
+    MOZ_ASSERT(onDelayedMarkingList_);
+    return hasDelayedBlackMarking_ || hasDelayedGrayMarking_;
+  }
+
+  void setHasDelayedMarking(MarkColor color, bool value) {
+    MOZ_ASSERT(onDelayedMarkingList_);
+    if (color == MarkColor::Black) {
+      hasDelayedBlackMarking_ = value;
+    } else {
+      hasDelayedGrayMarking_ = value;
+    }
+  }
+
+  void clearDelayedMarkingState() {
+    MOZ_ASSERT(onDelayedMarkingList_);
+    onDelayedMarkingList_ = 0;
+    hasDelayedBlackMarking_ = 0;
+    hasDelayedGrayMarking_ = 0;
+    nextDelayedMarkingArena_ = 0;
+  }
+
+  inline ArenaCellSet*& bufferedCells();
+  inline size_t& atomBitmapStart();
+
+  template <typename T>
+  size_t finalize(JSFreeOp* fop, AllocKind thingKind, size_t thingSize);
+
+  static void staticAsserts();
+  static void checkLookupTables();
+
+  void unmarkAll();
+  void unmarkPreMarkedFreeCells();
+
+  void arenaAllocatedDuringGC();
+
+#ifdef DEBUG
+  void checkNoMarkedFreeCells();
+  void checkAllCellsMarkedBlack();
+#endif
+
+#if defined(DEBUG) || defined(JS_GC_ZEAL)
+  void checkNoMarkedCells();
+#endif
+};
+
+static_assert(ArenaZoneOffset == offsetof(Arena, zone),
+              "The hardcoded API zone offset must match the actual offset.");
+
+static_assert(sizeof(Arena) == ArenaSize,
+              "ArenaSize must match the actual size of the Arena structure.");
+
+static_assert(
+    offsetof(Arena, data) == ArenaHeaderSize,
+    "ArenaHeaderSize must match the actual size of the header fields.");
+
+inline Arena* FreeSpan::getArena() {
+  Arena* arena = getArenaUnchecked();
+  arena->checkAddress();
+  return arena;
+}
+
+inline void FreeSpan::checkSpan(const Arena* arena) const {
+#ifdef DEBUG
+  if (!first) {
+    MOZ_ASSERT(!first && !last);
+    return;
+  }
+
+  arena->checkAddress();
+  checkRange(first, last, arena);
+
+  // If there's a following span, it must have a higher address,
+  // and the gap must be at least 2 * thingSize.
+  const FreeSpan* next = nextSpanUnchecked(arena);
+  if (next->first) {
+    checkRange(next->first, next->last, arena);
+    size_t thingSize = arena->getThingSize();
+    MOZ_ASSERT(last + 2 * thingSize <= next->first);
+  }
+#endif
+}
+
+inline void FreeSpan::checkRange(uintptr_t first, uintptr_t last,
+                                 const Arena* arena) const {
+#ifdef DEBUG
+  MOZ_ASSERT(arena);
+  MOZ_ASSERT(first <= last);
+  AllocKind thingKind = arena->getAllocKind();
+  MOZ_ASSERT(first >= Arena::firstThingOffset(thingKind));
+  MOZ_ASSERT(last <= Arena::lastThingOffset(thingKind));
+  MOZ_ASSERT((last - first) % Arena::thingSize(thingKind) == 0);
+#endif
+}
+
+// Mark bitmap API:
+
+MOZ_ALWAYS_INLINE bool MarkBitmap::markBit(const TenuredCell* cell,
+                                           ColorBit colorBit) {
+  MarkBitmapWord* word;
+  uintptr_t mask;
+  getMarkWordAndMask(cell, colorBit, &word, &mask);
+  return *word & mask;
+}
+
+MOZ_ALWAYS_INLINE bool MarkBitmap::isMarkedAny(const TenuredCell* cell) {
+  return markBit(cell, ColorBit::BlackBit) ||
+         markBit(cell, ColorBit::GrayOrBlackBit);
+}
+
+MOZ_ALWAYS_INLINE bool MarkBitmap::isMarkedBlack(const TenuredCell* cell) {
+  return markBit(cell, ColorBit::BlackBit);
+}
+
+MOZ_ALWAYS_INLINE bool MarkBitmap::isMarkedGray(const TenuredCell* cell) {
+  return !markBit(cell, ColorBit::BlackBit) &&
+         markBit(cell, ColorBit::GrayOrBlackBit);
+}
+
+// The return value indicates if the cell went from unmarked to marked.
+MOZ_ALWAYS_INLINE bool MarkBitmap::markIfUnmarked(const TenuredCell* cell,
+                                                  MarkColor color) {
+  MarkBitmapWord* word;
+  uintptr_t mask;
+  getMarkWordAndMask(cell, ColorBit::BlackBit, &word, &mask);
+  if (*word & mask) {
+    return false;
+  }
+  if (color == MarkColor::Black) {
+    *word |= mask;
+  } else {
+    /*
+     * We use getMarkWordAndMask to recalculate both mask and word as
+     * doing just mask << color may overflow the mask.
+     */
+    getMarkWordAndMask(cell, ColorBit::GrayOrBlackBit, &word, &mask);
+    if (*word & mask) {
+      return false;
+    }
+    *word |= mask;
+  }
+  return true;
+}
+
+MOZ_ALWAYS_INLINE void MarkBitmap::markBlack(const TenuredCell* cell) {
+  MarkBitmapWord* word;
+  uintptr_t mask;
+  getMarkWordAndMask(cell, ColorBit::BlackBit, &word, &mask);
+  *word |= mask;
+}
+
+MOZ_ALWAYS_INLINE void MarkBitmap::copyMarkBit(TenuredCell* dst,
+                                               const TenuredCell* src,
+                                               ColorBit colorBit) {
+  TenuredChunkBase* srcChunk = detail::GetCellChunkBase(src);
+  MarkBitmapWord* srcWord;
+  uintptr_t srcMask;
+  srcChunk->markBits.getMarkWordAndMask(src, colorBit, &srcWord, &srcMask);
+
+  MarkBitmapWord* dstWord;
+  uintptr_t dstMask;
+  getMarkWordAndMask(dst, colorBit, &dstWord, &dstMask);
+
+  *dstWord &= ~dstMask;
+  if (*srcWord & srcMask) {
+    *dstWord |= dstMask;
+  }
+}
+
+MOZ_ALWAYS_INLINE void MarkBitmap::unmark(const TenuredCell* cell) {
+  MarkBitmapWord* word;
+  uintptr_t mask;
+  getMarkWordAndMask(cell, ColorBit::BlackBit, &word, &mask);
+  *word &= ~mask;
+  getMarkWordAndMask(cell, ColorBit::GrayOrBlackBit, &word, &mask);
+  *word &= ~mask;
+}
+
+inline void MarkBitmap::clear() {
+  for (size_t i = 0; i < MarkBitmap::WordCount; i++) {
+    bitmap[i] = 0;
+  }
+}
+
+inline MarkBitmapWord* MarkBitmap::arenaBits(Arena* arena) {
+  static_assert(
+      ArenaBitmapBits == ArenaBitmapWords * JS_BITS_PER_WORD,
+      "We assume that the part of the bitmap corresponding to the arena "
+      "has the exact number of words so we do not need to deal with a word "
+      "that covers bits from two arenas.");
+
+  MarkBitmapWord* word;
+  uintptr_t unused;
+  getMarkWordAndMask(reinterpret_cast<TenuredCell*>(arena->address()),
+                     ColorBit::BlackBit, &word, &unused);
+  return word;
+}
+
+/*
+ * A chunk in the tenured heap. TenuredChunks contain arenas and associated data
+ * structures (mark bitmap, delayed marking state).
+ */
+class TenuredChunk : public TenuredChunkBase {
+  Arena arenas[ArenasPerChunk];
+
+  friend class GCRuntime;
+  friend class MarkingValidator;
+
+ public:
+  static TenuredChunk* fromAddress(uintptr_t addr) {
+    addr &= ~ChunkMask;
+    return reinterpret_cast<TenuredChunk*>(addr);
+  }
+
+  static bool withinValidRange(uintptr_t addr) {
+    uintptr_t offset = addr & ChunkMask;
+    if (TenuredChunk::fromAddress(addr)->isNurseryChunk()) {
+      return offset >= sizeof(ChunkBase) && offset < ChunkSize;
+    }
+    return offset >= offsetof(TenuredChunk, arenas) && offset < ChunkSize;
+  }
+
+  static size_t arenaIndex(uintptr_t addr) {
+    MOZ_ASSERT(!TenuredChunk::fromAddress(addr)->isNurseryChunk());
+    MOZ_ASSERT(withinValidRange(addr));
+    uintptr_t offset = addr & ChunkMask;
+    return (offset - offsetof(TenuredChunk, arenas)) >> ArenaShift;
+  }
+
+  explicit TenuredChunk(JSRuntime* runtime) : TenuredChunkBase(runtime) {}
+
+  uintptr_t address() const {
+    uintptr_t addr = reinterpret_cast<uintptr_t>(this);
+    MOZ_ASSERT(!(addr & ChunkMask));
+    return addr;
+  }
+
+  bool unused() const { return info.numArenasFree == ArenasPerChunk; }
+
+  bool hasAvailableArenas() const { return info.numArenasFree != 0; }
+
+  bool isNurseryChunk() const { return storeBuffer; }
+
+  Arena* allocateArena(GCRuntime* gc, JS::Zone* zone, AllocKind kind,
+                       const AutoLockGC& lock);
+
+  void releaseArena(GCRuntime* gc, Arena* arena, const AutoLockGC& lock);
+  void recycleArena(Arena* arena, SortedArenaList& dest, size_t thingsPerArena);
+
+  MOZ_MUST_USE bool decommitOneFreeArena(GCRuntime* gc, AutoLockGC& lock);
+  void decommitAllArenas();
+
+  // This will decommit each unused not-already decommitted arena. It performs a
+  // system call for each arena but is only used during OOM.
+  void decommitFreeArenasWithoutUnlocking(const AutoLockGC& lock);
+
+  static TenuredChunk* allocate(GCRuntime* gc);
+  void init(GCRuntime* gc);
+
+  /* Unlink and return the freeArenasHead. */
+  Arena* fetchNextFreeArena(GCRuntime* gc);
+
+ private:
+  /* Search for a decommitted arena to allocate. */
+  unsigned findDecommittedArenaOffset();
+  Arena* fetchNextDecommittedArena();
+
+  void addArenaToFreeList(GCRuntime* gc, Arena* arena);
+  void addArenaToDecommittedList(const Arena* arena);
+
+  void updateChunkListAfterAlloc(GCRuntime* gc, const AutoLockGC& lock);
+  void updateChunkListAfterFree(GCRuntime* gc, const AutoLockGC& lock);
+};
+
+inline void Arena::checkAddress() const {
+  mozilla::DebugOnly<uintptr_t> addr = uintptr_t(this);
+  MOZ_ASSERT(addr);
+  MOZ_ASSERT(!(addr & ArenaMask));
+  MOZ_ASSERT(TenuredChunk::withinValidRange(addr));
+}
+
+inline TenuredChunk* Arena::chunk() const {
+  return TenuredChunk::fromAddress(address());
+}
+
+inline bool InFreeList(Arena* arena, void* thing) {
+  uintptr_t addr = reinterpret_cast<uintptr_t>(thing);
+  MOZ_ASSERT(Arena::isAligned(addr, arena->getThingSize()));
+  return arena->inFreeList(addr);
+}
+
+static const int32_t ChunkStoreBufferOffsetFromLastByte =
+    int32_t(gc::ChunkStoreBufferOffset) - int32_t(gc::ChunkMask);
+
+// Cell header stored before all nursery cells.
+struct alignas(gc::CellAlignBytes) NurseryCellHeader {
+  // Store zone pointer with the trace kind in the lowest three bits.
+  const uintptr_t zoneAndTraceKind;
+
+  // We only need to store a subset of trace kinds so this doesn't cover the
+  // full range.
+  static const uintptr_t TraceKindMask = 3;
+
+  static uintptr_t MakeValue(JS::Zone* const zone, JS::TraceKind kind) {
+    MOZ_ASSERT(uintptr_t(kind) < TraceKindMask);
+    MOZ_ASSERT((uintptr_t(zone) & TraceKindMask) == 0);
+    return uintptr_t(zone) | uintptr_t(kind);
+  }
+
+  NurseryCellHeader(JS::Zone* const zone, JS::TraceKind kind)
+      : zoneAndTraceKind(MakeValue(zone, kind)) {}
+
+  JS::Zone* zone() const {
+    return reinterpret_cast<JS::Zone*>(zoneAndTraceKind & ~TraceKindMask);
+  }
+
+  JS::TraceKind traceKind() const {
+    return JS::TraceKind(zoneAndTraceKind & TraceKindMask);
+  }
+
+  static const NurseryCellHeader* from(const Cell* cell) {
+    MOZ_ASSERT(IsInsideNursery(cell));
+    return reinterpret_cast<const NurseryCellHeader*>(
+        uintptr_t(cell) - sizeof(NurseryCellHeader));
+  }
+};
+
+static_assert(uintptr_t(JS::TraceKind::Object) <=
+              NurseryCellHeader::TraceKindMask);
+static_assert(uintptr_t(JS::TraceKind::String) <=
+              NurseryCellHeader::TraceKindMask);
+static_assert(uintptr_t(JS::TraceKind::BigInt) <=
+              NurseryCellHeader::TraceKindMask);
+
+} /* namespace gc */
+
+namespace debug {
+
+// Utility functions meant to be called from an interactive debugger.
+enum class MarkInfo : int {
+  BLACK = 0,
+  GRAY = 1,
+  UNMARKED = -1,
+  NURSERY = -2,
+};
+
+// Get the mark color for a cell, in a way easily usable from a debugger.
+MOZ_NEVER_INLINE MarkInfo GetMarkInfo(js::gc::Cell* cell);
+
+// Sample usage from gdb:
+//
+//   (gdb) p $word = js::debug::GetMarkWordAddress(obj)
+//   $1 = (uintptr_t *) 0x7fa56d5fe360
+//   (gdb) p/x $mask = js::debug::GetMarkMask(obj, js::gc::GRAY)
+//   $2 = 0x200000000
+//   (gdb) watch *$word
+//   Hardware watchpoint 7: *$word
+//   (gdb) cond 7 *$word & $mask
+//   (gdb) cont
+//
+// Note that this is *not* a watchpoint on a single bit. It is a watchpoint on
+// the whole word, which will trigger whenever the word changes and the
+// selected bit is set after the change.
+//
+// So if the bit changing is the desired one, this is exactly what you want.
+// But if a different bit changes (either set or cleared), you may still stop
+// execution if the $mask bit happened to already be set. gdb does not expose
+// enough information to restrict the watchpoint to just a single bit.
+
+// Return the address of the word containing the mark bits for the given cell,
+// or nullptr if the cell is in the nursery.
+MOZ_NEVER_INLINE uintptr_t* GetMarkWordAddress(js::gc::Cell* cell);
+
+// Return the mask for the given cell and color bit, or 0 if the cell is in the
+// nursery.
+MOZ_NEVER_INLINE uintptr_t GetMarkMask(js::gc::Cell* cell, uint32_t colorBit);
+
+} /* namespace debug */
+} /* namespace js */
+
+#endif /* gc_Heap_h */