read-only-heap.cc

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// Copyright 2019 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#include "src/heap/read-only-heap.h"
 
#include <cstddef>
#include <cstring>
 
#include "src/common/globals.h"
#include "src/common/ptr-compr-inl.h"
#include "src/heap/heap-write-barrier-inl.h"
#include "src/heap/memory-chunk-metadata.h"
#include "src/heap/mutable-page-metadata.h"
#include "src/heap/read-only-spaces.h"
#include "src/init/isolate-group.h"
#include "src/objects/heap-object-inl.h"
#include "src/objects/objects-inl.h"
#include "src/objects/smi.h"
#include "src/sandbox/js-dispatch-table-inl.h"
#include "src/snapshot/read-only-deserializer.h"
#include "src/utils/allocation.h"
 
namespace v8 {
namespace internal {
 
ReadOnlyHeap::~ReadOnlyHeap() {
#ifdef V8_ENABLE_SANDBOX
  IsolateGroup::current()->code_pointer_table()->TearDownSpace(
      &code_pointer_space_);
#endif
#ifdef V8_ENABLE_LEAPTIERING
  JSDispatchTable* jdt = IsolateGroup::current()->js_dispatch_table();
#if V8_STATIC_DISPATCH_HANDLES_BOOL
  jdt->DetachSpaceFromReadOnlySegment(&js_dispatch_table_space_);
#endif  // V8_STATIC_DISPATCH_HANDLES_BOOL
  jdt->TearDownSpace(&js_dispatch_table_space_);
#endif
}
 
// static
void ReadOnlyHeap::SetUp(Isolate* isolate,
                         SnapshotData* read_only_snapshot_data,
                         bool can_rehash) {
  DCHECK_NOT_NULL(isolate);
  IsolateGroup* group = isolate->isolate_group();
  group->mutex()->AssertHeld();
  if (read_only_snapshot_data != nullptr) {
    bool read_only_heap_created = false;
    ReadOnlyArtifacts* artifacts = group->read_only_artifacts();
    if (!artifacts) {
      artifacts = group->InitializeReadOnlyArtifacts();
      artifacts->InitializeChecksum(read_only_snapshot_data);
      CreateInitialHeapForBootstrapping(isolate, artifacts);
      artifacts->read_only_heap()->DeserializeIntoIsolate(
          isolate, read_only_snapshot_data, can_rehash);
      artifacts->set_initial_next_unique_sfi_id(isolate->next_unique_sfi_id());
      read_only_heap_created = true;
    } else {
      isolate->SetUpFromReadOnlyArtifacts(artifacts);
#ifdef V8_COMPRESS_POINTERS
      isolate->external_pointer_table().SetUpFromReadOnlyArtifacts(
          isolate->heap()->read_only_external_pointer_space(), artifacts);
#endif  // V8_COMPRESS_POINTERS
    }
    artifacts->VerifyChecksum(read_only_snapshot_data, read_only_heap_created);
    artifacts->read_only_heap()->InitializeIsolateRoots(isolate);
  } else {
    // This path should only be taken in mksnapshot, should only be run once
    // before tearing down the Isolate that holds this ReadOnlyArtifacts and
    // is not thread-safe.
    ReadOnlyArtifacts* artifacts = group->read_only_artifacts();
    CHECK(!artifacts);
    artifacts = group->InitializeReadOnlyArtifacts();
    CreateInitialHeapForBootstrapping(isolate, artifacts);
 
    // Ensure the first read-only page ends up first in the cage.
    artifacts->read_only_heap()->read_only_space()->EnsurePage();
    artifacts->VerifyChecksum(read_only_snapshot_data, true);
  }
}
 
void ReadOnlyHeap::DeserializeIntoIsolate(Isolate* isolate,
                                          SnapshotData* read_only_snapshot_data,
                                          bool can_rehash) {
  DCHECK_NOT_NULL(read_only_snapshot_data);
 
  ReadOnlyDeserializer des(isolate, read_only_snapshot_data, can_rehash);
  des.DeserializeIntoIsolate();
  OnCreateRootsComplete(isolate);
 
  if (V8_UNLIKELY(v8_flags.extensible_ro_snapshot &&
                  isolate->serializer_enabled())) {
    // If this isolate will be serialized, leave RO space unfinalized and
    // allocatable s.t. it can be extended (e.g. by future Context::New calls).
    // We reach this scenario when creating custom snapshots - these initially
    // create the isolate from the default V8 snapshot, create new customized
    // contexts, and finally reserialize.
  } else {
    InitFromIsolate(isolate);
  }
}
 
void ReadOnlyHeap::OnCreateRootsComplete(Isolate* isolate) {
  DCHECK_NOT_NULL(isolate);
  DCHECK(!roots_init_complete_);
  InitializeFromIsolateRoots(isolate);
  roots_init_complete_ = true;
}
 
void ReadOnlyHeap::OnCreateHeapObjectsComplete(Isolate* isolate) {
  DCHECK_NOT_NULL(isolate);
 
  // InitFromIsolate mutates MemoryChunk flags which would race with any
  // concurrently-running sweeper tasks. Ensure that sweeping has been
  // completed, i.e. no sweeper tasks are currently running.
  isolate->heap()->EnsureSweepingCompleted(
      Heap::SweepingForcedFinalizationMode::kV8Only);
 
  InitFromIsolate(isolate);
 
#ifdef VERIFY_HEAP
  if (v8_flags.verify_heap) {
    HeapVerifier::VerifyReadOnlyHeap(isolate->heap());
    HeapVerifier::VerifyHeap(isolate->heap());
  }
#endif
}
 
// static
void ReadOnlyHeap::CreateInitialHeapForBootstrapping(
    Isolate* isolate, ReadOnlyArtifacts* artifacts) {
  ReadOnlySpace* ro_space = new ReadOnlySpace(isolate->heap());
  std::unique_ptr<ReadOnlyHeap> shared_ro_heap(new ReadOnlyHeap(ro_space));
  isolate->isolate_group()->set_shared_read_only_heap(shared_ro_heap.get());
  artifacts->set_read_only_heap(std::move(shared_ro_heap));
  isolate->SetUpFromReadOnlyArtifacts(artifacts);
}
 
void ReadOnlyHeap::InitializeIsolateRoots(Isolate* isolate) {
  void* const isolate_ro_roots =
      isolate->roots_table().read_only_roots_begin().location();
  std::memcpy(isolate_ro_roots, read_only_roots_,
              kEntriesCount * sizeof(Address));
}
 
void ReadOnlyHeap::InitializeFromIsolateRoots(Isolate* isolate) {
  void* const isolate_ro_roots =
      isolate->roots_table().read_only_roots_begin().location();
  std::memcpy(read_only_roots_, isolate_ro_roots,
              kEntriesCount * sizeof(Address));
}
 
void ReadOnlyHeap::InitFromIsolate(Isolate* isolate) {
  DCHECK(roots_init_complete_);
  read_only_space_->ShrinkPages();
  ReadOnlyArtifacts* artifacts =
      isolate->isolate_group()->read_only_artifacts();
  read_only_space()->DetachPagesAndAddToArtifacts(artifacts);
  artifacts->ReinstallReadOnlySpace(isolate);
 
  read_only_space_ = artifacts->shared_read_only_space();
 
#ifdef DEBUG
  artifacts->VerifyHeapAndSpaceRelationships(isolate);
#endif
}
 
ReadOnlyHeap::ReadOnlyHeap(ReadOnlySpace* ro_space)
    : read_only_space_(ro_space) {
#ifdef V8_ENABLE_SANDBOX
  IsolateGroup::current()->code_pointer_table()->InitializeSpace(
      &code_pointer_space_);
#endif  // V8_ENABLE_SANDBOX
#ifdef V8_ENABLE_LEAPTIERING
  JSDispatchTable* jdt = IsolateGroup::current()->js_dispatch_table();
  jdt->InitializeSpace(&js_dispatch_table_space_);
  // To avoid marking trying to write to these read-only cells they are
  // allocated black. Target code objects in the read-only dispatch table are
  // read-only code objects.
  js_dispatch_table_space_.set_allocate_black(true);
#if V8_STATIC_DISPATCH_HANDLES_BOOL
  jdt->AttachSpaceToReadOnlySegment(&js_dispatch_table_space_);
  jdt->PreAllocateEntries(&js_dispatch_table_space_,
                          JSBuiltinDispatchHandleRoot::kCount, true);
#endif  // V8_STATIC_DISPATCH_HANDLES_BOOL
#endif  // V8_ENABLE_LEAPTIERING
}
 
// static
void ReadOnlyHeap::PopulateReadOnlySpaceStatistics(
    SharedMemoryStatistics* statistics) {
  statistics->read_only_space_size_ = 0;
  statistics->read_only_space_used_size_ = 0;
  statistics->read_only_space_physical_size_ = 0;
  ReadOnlyArtifacts* artifacts = IsolateGroup::current()->read_only_artifacts();
  if (artifacts) {
    SharedReadOnlySpace* ro_space = artifacts->shared_read_only_space();
    statistics->read_only_space_size_ = ro_space->CommittedMemory();
    statistics->read_only_space_used_size_ = ro_space->Size();
    statistics->read_only_space_physical_size_ =
        ro_space->CommittedPhysicalMemory();
  }
}
 
// static
bool ReadOnlyHeap::Contains(Address address) {
  return MemoryChunk::FromAddress(address)->InReadOnlySpace();
}
 
// static
bool ReadOnlyHeap::Contains(Tagged<HeapObject> object) {
  return Contains(object.address());
}
 
// static
bool ReadOnlyHeap::SandboxSafeContains(Tagged<HeapObject> object) {
#ifdef V8_ENABLE_SANDBOX
  return MemoryChunk::FromHeapObject(object)->SandboxSafeInReadOnlySpace();
#else
  return Contains(object);
#endif
}
 
ReadOnlyHeapObjectIterator::ReadOnlyHeapObjectIterator(
    const ReadOnlyHeap* ro_heap)
    : ReadOnlyHeapObjectIterator(ro_heap->read_only_space()) {}
 
ReadOnlyHeapObjectIterator::ReadOnlyHeapObjectIterator(
    const ReadOnlySpace* ro_space)
    : ro_space_(ro_space),
      current_page_(ro_space->pages().begin()),
      page_iterator_(
          current_page_ == ro_space->pages().end() ? nullptr : *current_page_) {
}
 
Tagged<HeapObject> ReadOnlyHeapObjectIterator::Next() {
  while (current_page_ != ro_space_->pages().end()) {
    Tagged<HeapObject> obj = page_iterator_.Next();
    if (!obj.is_null()) return obj;
 
    ++current_page_;
    if (current_page_ == ro_space_->pages().end()) return Tagged<HeapObject>();
    page_iterator_.Reset(*current_page_);
  }
 
  DCHECK_EQ(current_page_, ro_space_->pages().end());
  return Tagged<HeapObject>();
}
 
ReadOnlyPageObjectIterator::ReadOnlyPageObjectIterator(
    const ReadOnlyPageMetadata* page,
    SkipFreeSpaceOrFiller skip_free_space_or_filler)
    : ReadOnlyPageObjectIterator(
          page, page == nullptr ? kNullAddress : page->GetAreaStart(),
          skip_free_space_or_filler) {}
 
ReadOnlyPageObjectIterator::ReadOnlyPageObjectIterator(
    const ReadOnlyPageMetadata* page, Address current_addr,
    SkipFreeSpaceOrFiller skip_free_space_or_filler)
    : page_(page),
      current_addr_(current_addr),
      skip_free_space_or_filler_(skip_free_space_or_filler) {
  DCHECK_GE(current_addr, page->GetAreaStart());
  DCHECK_LT(current_addr, page->GetAreaStart() + page->area_size());
}
 
Tagged<HeapObject> ReadOnlyPageObjectIterator::Next() {
  if (page_ == nullptr) return HeapObject();
 
  Address end = page_->GetAreaStart() + page_->area_size();
  for (;;) {
    DCHECK_LE(current_addr_, end);
    if (current_addr_ == end) return HeapObject();
 
    Tagged<HeapObject> object = HeapObject::FromAddress(current_addr_);
    const int object_size = object->Size();
    current_addr_ += ALIGN_TO_ALLOCATION_ALIGNMENT(object_size);
 
    if (skip_free_space_or_filler_ == SkipFreeSpaceOrFiller::kYes &&
        IsFreeSpaceOrFiller(object)) {
      continue;
    }
 
    DCHECK_OBJECT_SIZE(object_size);
    return object;
  }
}
 
void ReadOnlyPageObjectIterator::Reset(const ReadOnlyPageMetadata* page) {
  page_ = page;
  current_addr_ = page->GetAreaStart();
}
 
}  // namespace internal
}  // namespace v8