text: // 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.
  
  #ifndef V8_EXECUTION_ISOLATE_UTILS_INL_H_
  #define V8_EXECUTION_ISOLATE_UTILS_INL_H_
  
  #include "src/common/ptr-compr-inl.h"
  #include "src/execution/isolate-utils.h"
  #include "src/execution/isolate.h"
  #include "src/heap/heap-write-barrier-inl.h"
  
  namespace v8 {
  namespace internal {
  
  #ifdef V8_COMPRESS_POINTERS_IN_ISOLATE_CAGE
  
  // Aliases for GetPtrComprCageBase when
  // V8_COMPRESS_POINTERS_IN_ISOLATE_CAGE. Each Isolate has its own cage, whose
  // base address is also the Isolate root.
  V8_INLINE constexpr Address GetIsolateRootAddress(Address on_heap_addr) {
    return GetPtrComprCageBaseAddress(on_heap_addr);
  }
  
  V8_INLINE Address GetIsolateRootAddress(PtrComprCageBase cage_base) {
    return cage_base.address();
  }
  
  #else
  
  V8_INLINE Address GetIsolateRootAddress(Address on_heap_addr) { UNREACHABLE(); }
  
  V8_INLINE Address GetIsolateRootAddress(PtrComprCageBase cage_base) {
    UNREACHABLE();
  }
  
  #endif  // V8_COMPRESS_POINTERS_IN_ISOLATE_CAGE
  
  V8_INLINE Heap* GetHeapFromWritableObject(HeapObject object) {
    // Avoid using the below GetIsolateFromWritableObject because we want to be
    // able to get the heap, but not the isolate, for off-thread objects.
  
  #if defined V8_ENABLE_THIRD_PARTY_HEAP
    return Heap::GetIsolateFromWritableObject(object)->heap();
  #elif defined V8_COMPRESS_POINTERS_IN_ISOLATE_CAGE
    Isolate* isolate =
        Isolate::FromRootAddress(GetIsolateRootAddress(object.ptr()));
    DCHECK_NOT_NULL(isolate);
    return isolate->heap();
  #else
    heap_internals::MemoryChunk* chunk =
        heap_internals::MemoryChunk::FromHeapObject(object);
    return chunk->GetHeap();
  #endif  // V8_COMPRESS_POINTERS_IN_ISOLATE_CAGE, V8_ENABLE_THIRD_PARTY_HEAP
  }
  
  V8_INLINE Isolate* GetIsolateFromWritableObject(HeapObject object) {
  #ifdef V8_ENABLE_THIRD_PARTY_HEAP
    return Heap::GetIsolateFromWritableObject(object);
  #elif defined V8_COMPRESS_POINTERS_IN_ISOLATE_CAGE
    Isolate* isolate =
        Isolate::FromRootAddress(GetIsolateRootAddress(object.ptr()));
    DCHECK_NOT_NULL(isolate);
    return isolate;
  #else
    return Isolate::FromHeap(GetHeapFromWritableObject(object));
  #endif  // V8_COMPRESS_POINTERS_IN_ISOLATE_CAGE, V8_ENABLE_THIRD_PARTY_HEAP
  }
  
  V8_INLINE bool GetIsolateFromHeapObject(HeapObject object, Isolate** isolate) {
  #ifdef V8_ENABLE_THIRD_PARTY_HEAP
    *isolate = Heap::GetIsolateFromWritableObject(object);
    return true;
  #elif defined V8_COMPRESS_POINTERS_IN_ISOLATE_CAGE
    *isolate = GetIsolateFromWritableObject(object);
    return true;
  #else
    heap_internals::MemoryChunk* chunk =
        heap_internals::MemoryChunk::FromHeapObject(object);
    if (chunk->InReadOnlySpace()) {
      *isolate = nullptr;
      return false;
    }
    *isolate = Isolate::FromHeap(chunk->GetHeap());
    return true;
  #endif  // V8_COMPRESS_POINTERS_IN_ISOLATE_CAGE, V8_ENABLE_THIRD_PARTY_HEAP
  }
  
  // Use this function instead of Internals::GetIsolateForSandbox for internal
  // code, as this function is fully inlinable.
  V8_INLINE static Isolate* GetIsolateForSandbox(HeapObject object) {
  #ifdef V8_SANDBOXED_EXTERNAL_POINTERS
    return GetIsolateFromWritableObject(object);
  #else
    // Not used in non-sandbox mode.
    return nullptr;
  #endif
  }
  
  // This is an external code space friendly version of GetPtrComprCageBase(..)
  // which also works for objects located in external code space.
  //
  // NOTE: it's supposed to be used only for the cases where performance doesn't
  // matter. For example, in debug only code or in debugging macros.
  // In production code the preferred way is to use precomputed cage base value
  // which is a result of PtrComprCageBase{isolate} or GetPtrComprCageBase()
  // applied to a heap object which is known to not be a part of external code
  // space.
  V8_INLINE PtrComprCageBase GetPtrComprCageBaseSlow(HeapObject object) {
    if (V8_EXTERNAL_CODE_SPACE_BOOL) {
      Isolate* isolate;
      if (GetIsolateFromHeapObject(object, &isolate)) {
        return PtrComprCageBase{isolate};
      }
      // If the Isolate can't be obtained then the heap object is a read-only
      // one and therefore not a Code object, so fallback to auto-computing cage
      // base value.
    }
    return GetPtrComprCageBase(object);
  }
  
  }  // namespace internal
  }  // namespace v8
  
  #endif  // V8_EXECUTION_ISOLATE_UTILS_INL_H_
  