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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * 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 js_HeapAPI_h
#define js_HeapAPI_h

#include <limits.h>

#include "jspubtd.h"

#include "js/TraceKind.h"
#include "js/Utility.h"

/* These values are private to the JS engine. */
namespace js {

JS_FRIEND_API bool CurrentThreadCanAccessZone(JS::Zone* zone);

namespace gc {

struct Cell;

/*
 * The low bit is set so this should never equal a normal pointer, and the high
 * bit is set so this should never equal the upper 32 bits of a 64-bit pointer.
 */
const uint32_t Relocated = uintptr_t(0xbad0bad1);

const size_t ArenaShift = 12;
const size_t ArenaSize = size_t(1) << ArenaShift;
const size_t ArenaMask = ArenaSize - 1;

#ifdef JS_GC_SMALL_CHUNK_SIZE
const size_t ChunkShift = 18;
#else
const size_t ChunkShift = 20;
#endif
const size_t ChunkSize = size_t(1) << ChunkShift;
const size_t ChunkMask = ChunkSize - 1;

const size_t CellAlignShift = 3;
const size_t CellAlignBytes = size_t(1) << CellAlignShift;
const size_t CellAlignMask = CellAlignBytes - 1;

const size_t CellBytesPerMarkBit = CellAlignBytes;

/*
 * We sometimes use an index to refer to a cell in an arena. The index for a
 * cell is found by dividing by the cell alignment so not all indicies refer to
 * valid cells.
 */
const size_t ArenaCellIndexBytes = CellAlignBytes;
const size_t MaxArenaCellIndex = ArenaSize / CellAlignBytes;

/* These are magic constants derived from actual offsets in gc/Heap.h. */
#ifdef JS_GC_SMALL_CHUNK_SIZE
const size_t ChunkMarkBitmapOffset = 258104;
const size_t ChunkMarkBitmapBits = 31744;
#else
const size_t ChunkMarkBitmapOffset = 1032352;
const size_t ChunkMarkBitmapBits = 129024;
#endif
const size_t ChunkRuntimeOffset = ChunkSize - sizeof(void*);
const size_t ChunkTrailerSize = 2 * sizeof(uintptr_t) + sizeof(uint64_t);
const size_t ChunkLocationOffset = ChunkSize - ChunkTrailerSize;
const size_t ChunkStoreBufferOffset =
    ChunkSize - ChunkTrailerSize + sizeof(uint64_t);
const size_t ArenaZoneOffset = sizeof(size_t);
const size_t ArenaHeaderSize =
    sizeof(size_t) + 2 * sizeof(uintptr_t) + sizeof(size_t) + sizeof(uintptr_t);

/*
 * Live objects are marked black or gray. Everything reachable from a JS root is
 * marked black. Objects marked gray are eligible for cycle collection.
 *
 *    BlackBit:     GrayOrBlackBit:  Color:
 *       0               0           white
 *       0               1           gray
 *       1               0           black
 *       1               1           black
 */
enum class ColorBit : uint32_t { BlackBit = 0, GrayOrBlackBit = 1 };

/*
 * The "location" field in the Chunk trailer is a enum indicating various roles
 * of the chunk.
 */
enum class ChunkLocation : uint32_t {
  Invalid = 0,
  Nursery = 1,
  TenuredHeap = 2
};

#ifdef JS_DEBUG
/* When downcasting, ensure we are actually the right type. */
extern JS_FRIEND_API void AssertGCThingHasType(js::gc::Cell* cell,
                                               JS::TraceKind kind);
#else
inline void AssertGCThingHasType(js::gc::Cell* cell, JS::TraceKind kind) {}
#endif

MOZ_ALWAYS_INLINE bool IsInsideNursery(const js::gc::Cell* cell);

} /* namespace gc */
} /* namespace js */

namespace JS {

/*
 * This list enumerates the different types of conceptual stacks we have in
 * SpiderMonkey. In reality, they all share the C stack, but we allow different
 * stack limits depending on the type of code running.
 */
enum StackKind {
  StackForSystemCode,       // C++, such as the GC, running on behalf of the VM.
  StackForTrustedScript,    // Script running with trusted principals.
  StackForUntrustedScript,  // Script running with untrusted principals.
  StackKindCount
};

/*
 * Default size for the generational nursery in bytes.
 * This is the initial nursery size, when running in the browser this is
 * updated by JS_SetGCParameter().
 */
const uint32_t DefaultNurseryBytes = 16 * js::gc::ChunkSize;

/* Default maximum heap size in bytes to pass to JS_NewContext(). */
const uint32_t DefaultHeapMaxBytes = 32 * 1024 * 1024;

namespace shadow {

struct Zone {
  enum GCState : uint8_t { NoGC, Mark, MarkGray, Sweep, Finished, Compact };

 protected:
  JSRuntime* const runtime_;
  JSTracer* const barrierTracer_;  // A pointer to the JSRuntime's |gcMarker|.
  uint32_t needsIncrementalBarrier_;
  GCState gcState_;

  Zone(JSRuntime* runtime, JSTracer* barrierTracerArg)
      : runtime_(runtime),
        barrierTracer_(barrierTracerArg),
        needsIncrementalBarrier_(0),
        gcState_(NoGC) {}

 public:
  bool needsIncrementalBarrier() const { return needsIncrementalBarrier_; }

  JSTracer* barrierTracer() {
    MOZ_ASSERT(needsIncrementalBarrier_);
    MOZ_ASSERT(js::CurrentThreadCanAccessRuntime(runtime_));
    return barrierTracer_;
  }

  JSRuntime* runtimeFromActiveCooperatingThread() const {
    MOZ_ASSERT(js::CurrentThreadCanAccessRuntime(runtime_));
    return runtime_;
  }

  // Note: Unrestricted access to the zone's runtime from an arbitrary
  // thread can easily lead to races. Use this method very carefully.
  JSRuntime* runtimeFromAnyThread() const { return runtime_; }

  GCState gcState() const { return gcState_; }
  bool wasGCStarted() const { return gcState_ != NoGC; }
  bool isGCMarkingBlack() const { return gcState_ == Mark; }
  bool isGCMarkingGray() const { return gcState_ == MarkGray; }
  bool isGCSweeping() const { return gcState_ == Sweep; }
  bool isGCFinished() const { return gcState_ == Finished; }
  bool isGCCompacting() const { return gcState_ == Compact; }
  bool isGCMarking() const { return gcState_ == Mark || gcState_ == MarkGray; }
  bool isGCSweepingOrCompacting() const {
    return gcState_ == Sweep || gcState_ == Compact;
  }

  static MOZ_ALWAYS_INLINE JS::shadow::Zone* asShadowZone(JS::Zone* zone) {
    return reinterpret_cast<JS::shadow::Zone*>(zone);
  }
};

} /* namespace shadow */

/**
 * A GC pointer, tagged with the trace kind.
 *
 * In general, a GC pointer should be stored with an exact type. This class
 * is for use when that is not possible because a single pointer must point
 * to several kinds of GC thing.
 */
class JS_FRIEND_API GCCellPtr {
 public:
  // Construction from a void* and trace kind.
  GCCellPtr(void* gcthing, JS::TraceKind traceKind)
      : ptr(checkedCast(gcthing, traceKind)) {}

  // Automatically construct a null GCCellPtr from nullptr.
  MOZ_IMPLICIT GCCellPtr(decltype(nullptr))
      : ptr(checkedCast(nullptr, JS::TraceKind::Null)) {}

  // Construction from an explicit type.
  template <typename T>
  explicit GCCellPtr(T* p)
      : ptr(checkedCast(p, JS::MapTypeToTraceKind<T>::kind)) {}
  explicit GCCellPtr(JSFunction* p)
      : ptr(checkedCast(p, JS::TraceKind::Object)) {}
  explicit GCCellPtr(JSFlatString* str)
      : ptr(checkedCast(str, JS::TraceKind::String)) {}
  explicit GCCellPtr(const Value& v);

  JS::TraceKind kind() const {
    JS::TraceKind traceKind = JS::TraceKind(ptr & OutOfLineTraceKindMask);
    if (uintptr_t(traceKind) != OutOfLineTraceKindMask) return traceKind;
    return outOfLineKind();
  }

  // Allow GCCellPtr to be used in a boolean context.
  explicit operator bool() const {
    MOZ_ASSERT(bool(asCell()) == (kind() != JS::TraceKind::Null));
    return asCell();
  }

  // Simplify checks to the kind.
  template <typename T>
  bool is() const {
    return kind() == JS::MapTypeToTraceKind<T>::kind;
  }

  // Conversions to more specific types must match the kind. Access to
  // further refined types is not allowed directly from a GCCellPtr.
  template <typename T>
  T& as() const {
    MOZ_ASSERT(kind() == JS::MapTypeToTraceKind<T>::kind);
    // We can't use static_cast here, because the fact that JSObject
    // inherits from js::gc::Cell is not part of the public API.
    return *reinterpret_cast<T*>(asCell());
  }

  // Return a pointer to the cell this |GCCellPtr| refers to, or |nullptr|.
  // (It would be more symmetrical with |to| for this to return a |Cell&|, but
  // the result can be |nullptr|, and null references are undefined behavior.)
  js::gc::Cell* asCell() const {
    return reinterpret_cast<js::gc::Cell*>(ptr & ~OutOfLineTraceKindMask);
  }

  // The CC's trace logger needs an identity that is XPIDL serializable.
  uint64_t unsafeAsInteger() const {
    return static_cast<uint64_t>(unsafeAsUIntPtr());
  }
  // Inline mark bitmap access requires direct pointer arithmetic.
  uintptr_t unsafeAsUIntPtr() const {
    MOZ_ASSERT(asCell());
    MOZ_ASSERT(!js::gc::IsInsideNursery(asCell()));
    return reinterpret_cast<uintptr_t>(asCell());
  }

  MOZ_ALWAYS_INLINE bool mayBeOwnedByOtherRuntime() const {
    if (is<JSString>() || is<JS::Symbol>())
      return mayBeOwnedByOtherRuntimeSlow();
    return false;
  }

 private:
  static uintptr_t checkedCast(void* p, JS::TraceKind traceKind) {
    js::gc::Cell* cell = static_cast<js::gc::Cell*>(p);
    MOZ_ASSERT((uintptr_t(p) & OutOfLineTraceKindMask) == 0);
    AssertGCThingHasType(cell, traceKind);
    // Note: the OutOfLineTraceKindMask bits are set on all out-of-line kinds
    // so that we can mask instead of branching.
    MOZ_ASSERT_IF(uintptr_t(traceKind) >= OutOfLineTraceKindMask,
                  (uintptr_t(traceKind) & OutOfLineTraceKindMask) ==
                      OutOfLineTraceKindMask);
    return uintptr_t(p) | (uintptr_t(traceKind) & OutOfLineTraceKindMask);
  }

  bool mayBeOwnedByOtherRuntimeSlow() const;

  JS::TraceKind outOfLineKind() const;

  uintptr_t ptr;
};

inline bool operator==(const GCCellPtr& ptr1, const GCCellPtr& ptr2) {
  return ptr1.asCell() == ptr2.asCell();
}

inline bool operator!=(const GCCellPtr& ptr1, const GCCellPtr& ptr2) {
  return !(ptr1 == ptr2);
}

// Unwraps the given GCCellPtr and calls the given functor with a template
// argument of the actual type of the pointer.
template <typename F, typename... Args>
auto DispatchTyped(F f, GCCellPtr thing, Args&&... args)
    -> decltype(f(static_cast<JSObject*>(nullptr),
                  mozilla::Forward<Args>(args)...)) {
  switch (thing.kind()) {
#define JS_EXPAND_DEF(name, type, _) \
  case JS::TraceKind::name:          \
    return f(&thing.as<type>(), mozilla::Forward<Args>(args)...);
    JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
#undef JS_EXPAND_DEF
    default:
      MOZ_CRASH("Invalid trace kind in DispatchTyped for GCCellPtr.");
  }
}

} /* namespace JS */

namespace js {
namespace gc {
namespace detail {

static MOZ_ALWAYS_INLINE uintptr_t* GetGCThingMarkBitmap(const uintptr_t addr) {
  // Note: the JIT pre-barrier trampolines inline this code. Update that
  // code too when making changes here!
  MOZ_ASSERT(addr);
  const uintptr_t bmap_addr = (addr & ~ChunkMask) | ChunkMarkBitmapOffset;
  return reinterpret_cast<uintptr_t*>(bmap_addr);
}

static MOZ_ALWAYS_INLINE void GetGCThingMarkWordAndMask(const uintptr_t addr,
                                                        ColorBit colorBit,
                                                        uintptr_t** wordp,
                                                        uintptr_t* maskp) {
  // Note: the JIT pre-barrier trampolines inline this code. Update that
  // code too when making changes here!
  MOZ_ASSERT(addr);
  const size_t bit = (addr & js::gc::ChunkMask) / js::gc::CellBytesPerMarkBit +
                     static_cast<uint32_t>(colorBit);
  MOZ_ASSERT(bit < js::gc::ChunkMarkBitmapBits);
  uintptr_t* bitmap = GetGCThingMarkBitmap(addr);
  const uintptr_t nbits = sizeof(*bitmap) * CHAR_BIT;
  *maskp = uintptr_t(1) << (bit % nbits);
  *wordp = &bitmap[bit / nbits];
}

static MOZ_ALWAYS_INLINE JS::Zone* GetGCThingZone(const uintptr_t addr) {
  MOZ_ASSERT(addr);
  const uintptr_t zone_addr = (addr & ~ArenaMask) | ArenaZoneOffset;
  return *reinterpret_cast<JS::Zone**>(zone_addr);
}

static MOZ_ALWAYS_INLINE bool TenuredCellIsMarkedGray(const Cell* cell) {
  // Return true if GrayOrBlackBit is set and BlackBit is not set.
  MOZ_ASSERT(cell);
  MOZ_ASSERT(!js::gc::IsInsideNursery(cell));

  uintptr_t *grayWord, grayMask;
  js::gc::detail::GetGCThingMarkWordAndMask(
      uintptr_t(cell), js::gc::ColorBit::GrayOrBlackBit, &grayWord, &grayMask);
  if (!(*grayWord & grayMask)) return false;

  uintptr_t *blackWord, blackMask;
  js::gc::detail::GetGCThingMarkWordAndMask(
      uintptr_t(cell), js::gc::ColorBit::BlackBit, &blackWord, &blackMask);
  return !(*blackWord & blackMask);
}

static MOZ_ALWAYS_INLINE bool CellIsMarkedGray(const Cell* cell) {
  MOZ_ASSERT(cell);
  if (js::gc::IsInsideNursery(cell)) return false;
  return TenuredCellIsMarkedGray(cell);
}

extern JS_PUBLIC_API bool CellIsMarkedGrayIfKnown(const Cell* cell);

#ifdef DEBUG
extern JS_PUBLIC_API bool CellIsNotGray(const Cell* cell);

extern JS_PUBLIC_API bool ObjectIsMarkedBlack(const JSObject* obj);
#endif

MOZ_ALWAYS_INLINE ChunkLocation GetCellLocation(const void* cell) {
  uintptr_t addr = uintptr_t(cell);
  addr &= ~js::gc::ChunkMask;
  addr |= js::gc::ChunkLocationOffset;
  return *reinterpret_cast<ChunkLocation*>(addr);
}

MOZ_ALWAYS_INLINE bool NurseryCellHasStoreBuffer(const void* cell) {
  uintptr_t addr = uintptr_t(cell);
  addr &= ~js::gc::ChunkMask;
  addr |= js::gc::ChunkStoreBufferOffset;
  return *reinterpret_cast<void**>(addr) != nullptr;
}

} /* namespace detail */

MOZ_ALWAYS_INLINE bool IsInsideNursery(const js::gc::Cell* cell) {
  if (!cell) return false;
  auto location = detail::GetCellLocation(cell);
  MOZ_ASSERT(location == ChunkLocation::Nursery ||
             location == ChunkLocation::TenuredHeap);
  return location == ChunkLocation::Nursery;
}

MOZ_ALWAYS_INLINE bool IsCellPointerValid(const void* cell) {
  auto addr = uintptr_t(cell);
  if (addr < ChunkSize || addr % CellAlignBytes != 0) return false;
  auto location = detail::GetCellLocation(cell);
  if (location == ChunkLocation::TenuredHeap)
    return !!detail::GetGCThingZone(addr);
  if (location == ChunkLocation::Nursery)
    return detail::NurseryCellHasStoreBuffer(cell);
  return false;
}

MOZ_ALWAYS_INLINE bool IsCellPointerValidOrNull(const void* cell) {
  if (!cell) return true;
  return IsCellPointerValid(cell);
}

} /* namespace gc */
} /* namespace js */

namespace JS {

static MOZ_ALWAYS_INLINE Zone* GetTenuredGCThingZone(GCCellPtr thing) {
  MOZ_ASSERT(!js::gc::IsInsideNursery(thing.asCell()));
  return js::gc::detail::GetGCThingZone(thing.unsafeAsUIntPtr());
}

extern JS_PUBLIC_API Zone* GetNurseryStringZone(JSString* str);

static MOZ_ALWAYS_INLINE Zone* GetStringZone(JSString* str) {
  if (!js::gc::IsInsideNursery(reinterpret_cast<js::gc::Cell*>(str)))
    return js::gc::detail::GetGCThingZone(reinterpret_cast<uintptr_t>(str));
  return GetNurseryStringZone(str);
}

extern JS_PUBLIC_API Zone* GetObjectZone(JSObject* obj);

extern JS_PUBLIC_API Zone* GetValueZone(const Value& value);

static MOZ_ALWAYS_INLINE bool GCThingIsMarkedGray(GCCellPtr thing) {
  if (thing.mayBeOwnedByOtherRuntime()) return false;
  return js::gc::detail::CellIsMarkedGrayIfKnown(thing.asCell());
}

extern JS_PUBLIC_API JS::TraceKind GCThingTraceKind(void* thing);

extern JS_PUBLIC_API void EnableNurseryStrings(JSContext* cx);

extern JS_PUBLIC_API void DisableNurseryStrings(JSContext* cx);

/*
 * Returns true when writes to GC thing pointers (and reads from weak pointers)
 * must call an incremental barrier. This is generally only true when running
 * mutator code in-between GC slices. At other times, the barrier may be elided
 * for performance.
 */
extern JS_PUBLIC_API bool IsIncrementalBarrierNeeded(JSContext* cx);

/*
 * Notify the GC that a reference to a JSObject is about to be overwritten.
 * This method must be called if IsIncrementalBarrierNeeded.
 */
extern JS_PUBLIC_API void IncrementalPreWriteBarrier(JSObject* obj);

/*
 * Notify the GC that a weak reference to a GC thing has been read.
 * This method must be called if IsIncrementalBarrierNeeded.
 */
extern JS_PUBLIC_API void IncrementalReadBarrier(GCCellPtr thing);

/**
 * Unsets the gray bit for anything reachable from |thing|. |kind| should not be
 * JS::TraceKind::Shape. |thing| should be non-null. The return value indicates
 * if anything was unmarked.
 */
extern JS_FRIEND_API bool UnmarkGrayGCThingRecursively(GCCellPtr thing);

}  // namespace JS

namespace js {
namespace gc {

static MOZ_ALWAYS_INLINE bool IsIncrementalBarrierNeededOnTenuredGCThing(
    const JS::GCCellPtr thing) {
  MOZ_ASSERT(thing);
  MOZ_ASSERT(!js::gc::IsInsideNursery(thing.asCell()));

  // TODO: I'd like to assert !CurrentThreadIsHeapBusy() here but this gets
  // called while we are tracing the heap, e.g. during memory reporting
  // (see bug 1313318).
  MOZ_ASSERT(!JS::CurrentThreadIsHeapCollecting());

  JS::Zone* zone = JS::GetTenuredGCThingZone(thing);
  return JS::shadow::Zone::asShadowZone(zone)->needsIncrementalBarrier();
}

static MOZ_ALWAYS_INLINE void ExposeGCThingToActiveJS(JS::GCCellPtr thing) {
  // GC things residing in the nursery cannot be gray: they have no mark bits.
  // All live objects in the nursery are moved to tenured at the beginning of
  // each GC slice, so the gray marker never sees nursery things.
  if (IsInsideNursery(thing.asCell())) return;

  // There's nothing to do for permanent GC things that might be owned by
  // another runtime.
  if (thing.mayBeOwnedByOtherRuntime()) return;

  if (IsIncrementalBarrierNeededOnTenuredGCThing(thing))
    JS::IncrementalReadBarrier(thing);
  else if (js::gc::detail::TenuredCellIsMarkedGray(thing.asCell()))
    JS::UnmarkGrayGCThingRecursively(thing);

  MOZ_ASSERT(!js::gc::detail::TenuredCellIsMarkedGray(thing.asCell()));
}

template <typename T>
extern JS_PUBLIC_API bool EdgeNeedsSweepUnbarrieredSlow(T* thingp);

static MOZ_ALWAYS_INLINE bool EdgeNeedsSweepUnbarriered(JSObject** objp) {
  // This function does not handle updating nursery pointers. Raw JSObject
  // pointers should be updated separately or replaced with
  // JS::Heap<JSObject*> which handles this automatically.
  MOZ_ASSERT(!JS::CurrentThreadIsHeapMinorCollecting());
  if (IsInsideNursery(reinterpret_cast<Cell*>(*objp))) return false;

  auto zone =
      JS::shadow::Zone::asShadowZone(detail::GetGCThingZone(uintptr_t(*objp)));
  if (!zone->isGCSweepingOrCompacting()) return false;

  return EdgeNeedsSweepUnbarrieredSlow(objp);
}

}  // namespace gc
}  // namespace js

namespace JS {

/*
 * This should be called when an object that is marked gray is exposed to the JS
 * engine (by handing it to running JS code or writing it into live JS
 * data). During incremental GC, since the gray bits haven't been computed yet,
 * we conservatively mark the object black.
 */
static MOZ_ALWAYS_INLINE void ExposeObjectToActiveJS(JSObject* obj) {
  MOZ_ASSERT(obj);
  MOZ_ASSERT(!js::gc::EdgeNeedsSweepUnbarrieredSlow(&obj));
  js::gc::ExposeGCThingToActiveJS(GCCellPtr(obj));
}

static MOZ_ALWAYS_INLINE void ExposeScriptToActiveJS(JSScript* script) {
  MOZ_ASSERT(!js::gc::EdgeNeedsSweepUnbarrieredSlow(&script));
  js::gc::ExposeGCThingToActiveJS(GCCellPtr(script));
}

} /* namespace JS */

#endif /* js_HeapAPI_h */