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// Copyright 2012 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 "include/v8-platform.h"
#include "src/base/address-region.h"
#include "src/base/compiler-specific.h"
#include "src/base/platform/platform.h"
#include "src/common/globals.h"
#include "src/init/v8.h"
namespace v8 {
namespace internal {
class Isolate;
// This file defines memory allocation functions. If a first attempt at an
// allocation fails, these functions call back into the embedder, then attempt
// the allocation a second time. The embedder callback must not reenter V8.
// Called when allocation routines fail to allocate, even with a possible retry.
// This function should not return, but should terminate the current processing.
[[noreturn]] V8_EXPORT_PRIVATE void FatalProcessOutOfMemory(
Isolate* isolate, const char* message);
// Superclass for classes managed with new & delete.
class V8_EXPORT_PRIVATE Malloced {
static void* operator new(size_t size);
static void operator delete(void* p);
template <typename T>
T* NewArray(size_t size) {
T* result = new (std::nothrow) T[size];
if (result == nullptr) {
result = new (std::nothrow) T[size];
if (result == nullptr) FatalProcessOutOfMemory(nullptr, "NewArray");
return result;
template <typename T, typename = typename std::enable_if<
T* NewArray(size_t size, T default_val) {
T* result = reinterpret_cast<T*>(NewArray<uint8_t>(sizeof(T) * size));
for (size_t i = 0; i < size; ++i) result[i] = default_val;
return result;
template <typename T>
void DeleteArray(T* array) {
delete[] array;
// The normal strdup functions use malloc. These versions of StrDup
// and StrNDup uses new and calls the FatalProcessOutOfMemory handler
// if allocation fails.
V8_EXPORT_PRIVATE char* StrDup(const char* str);
char* StrNDup(const char* str, int n);
// Allocation policy for allocating in the C free store using malloc
// and free. Used as the default policy for lists.
class FreeStoreAllocationPolicy {
V8_INLINE void* New(size_t size) { return Malloced::operator new(size); }
V8_INLINE static void Delete(void* p) { Malloced::operator delete(p); }
// Performs a malloc, with retry logic on failure. Returns nullptr on failure.
// Call free to release memory allocated with this function.
void* AllocWithRetry(size_t size);
V8_EXPORT_PRIVATE void* AlignedAlloc(size_t size, size_t alignment);
V8_EXPORT_PRIVATE void AlignedFree(void* ptr);
// Returns platfrom page allocator instance. Guaranteed to be a valid pointer.
V8_EXPORT_PRIVATE v8::PageAllocator* GetPlatformPageAllocator();
// Sets the given page allocator as the platform page allocator and returns
// the current one. This function *must* be used only for testing purposes.
// It is not thread-safe and the testing infrastructure should ensure that
// the tests do not modify the value simultaneously.
V8_EXPORT_PRIVATE v8::PageAllocator* SetPlatformPageAllocatorForTesting(
v8::PageAllocator* page_allocator);
// Gets the page granularity for AllocatePages and FreePages. Addresses returned
// by AllocatePages are aligned to this size.
V8_EXPORT_PRIVATE size_t AllocatePageSize();
// Gets the granularity at which the permissions and release calls can be made.
V8_EXPORT_PRIVATE size_t CommitPageSize();
// Sets the random seed so that GetRandomMmapAddr() will generate repeatable
// sequences of random mmap addresses.
V8_EXPORT_PRIVATE void SetRandomMmapSeed(int64_t seed);
// Generate a random address to be used for hinting allocation calls.
V8_EXPORT_PRIVATE void* GetRandomMmapAddr();
// Allocates memory. Permissions are set according to the access argument.
// |address| is a hint. |size| and |alignment| must be multiples of
// AllocatePageSize(). Returns the address of the allocated memory, with the
// specified size and alignment, or nullptr on failure.
V8_WARN_UNUSED_RESULT void* AllocatePages(v8::PageAllocator* page_allocator,
void* address, size_t size,
size_t alignment,
PageAllocator::Permission access);
// Frees memory allocated by a call to AllocatePages. |address| and |size| must
// be multiples of AllocatePageSize(). Returns true on success, otherwise false.
V8_WARN_UNUSED_RESULT bool FreePages(v8::PageAllocator* page_allocator,
void* address, const size_t size);
// Releases memory that is no longer needed. The range specified by |address|
// and |size| must be an allocated memory region. |size| and |new_size| must be
// multiples of CommitPageSize(). Memory from |new_size| to |size| is released.
// Released memory is left in an undefined state, so it should not be accessed.
// Returns true on success, otherwise false.
V8_WARN_UNUSED_RESULT bool ReleasePages(v8::PageAllocator* page_allocator,
void* address, size_t size,
size_t new_size);
// Sets permissions according to |access|. |address| and |size| must be
// multiples of CommitPageSize(). Setting permission to kNoAccess may
// cause the memory contents to be lost. Returns true on success, otherwise
// false.
V8_WARN_UNUSED_RESULT bool SetPermissions(v8::PageAllocator* page_allocator,
void* address, size_t size,
PageAllocator::Permission access);
inline bool SetPermissions(v8::PageAllocator* page_allocator, Address address,
size_t size, PageAllocator::Permission access) {
return SetPermissions(page_allocator, reinterpret_cast<void*>(address), size,
// Function that may release reserved memory regions to allow failed allocations
// to succeed. |length| is the amount of memory needed. Returns |true| if memory
// could be released, false otherwise.
V8_EXPORT_PRIVATE bool OnCriticalMemoryPressure(size_t length);
// Represents and controls an area of reserved memory.
class VirtualMemory final {
// Empty VirtualMemory object, controlling no reserved memory.
V8_EXPORT_PRIVATE VirtualMemory();
// Reserves virtual memory containing an area of the given size that is
// aligned per |alignment| rounded up to the |page_allocator|'s allocate page
// size. The |size| must be aligned with |page_allocator|'s commit page size.
// This may not be at the position returned by address().
V8_EXPORT_PRIVATE VirtualMemory(v8::PageAllocator* page_allocator,
size_t size, void* hint,
size_t alignment = 1);
// Construct a virtual memory by assigning it some already mapped address
// and size.
VirtualMemory(v8::PageAllocator* page_allocator, Address address, size_t size)
: page_allocator_(page_allocator), region_(address, size) {
DCHECK(IsAligned(address, page_allocator->AllocatePageSize()));
DCHECK(IsAligned(size, page_allocator->CommitPageSize()));
// Releases the reserved memory, if any, controlled by this VirtualMemory
// object.
V8_EXPORT_PRIVATE ~VirtualMemory();
// Move constructor.
VirtualMemory(VirtualMemory&& other) V8_NOEXCEPT { *this = std::move(other); }
// Move assignment operator.
VirtualMemory& operator=(VirtualMemory&& other) V8_NOEXCEPT {
page_allocator_ = other.page_allocator_;
region_ = other.region_;
return *this;
// Returns whether the memory has been reserved.
bool IsReserved() const { return region_.begin() != kNullAddress; }
// Initialize or resets an embedded VirtualMemory object.
V8_EXPORT_PRIVATE void Reset();
v8::PageAllocator* page_allocator() { return page_allocator_; }
base::AddressRegion region() const { return region_; }
// Returns the start address of the reserved memory.
// If the memory was reserved with an alignment, this address is not
// necessarily aligned. The user might need to round it up to a multiple of
// the alignment to get the start of the aligned block.
Address address() const {
return region_.begin();
Address end() const {
return region_.end();
// Returns the size of the reserved memory. The returned value is only
// meaningful when IsReserved() returns true.
// If the memory was reserved with an alignment, this size may be larger
// than the requested size.
size_t size() const { return region_.size(); }
// Sets permissions according to the access argument. address and size must be
// multiples of CommitPageSize(). Returns true on success, otherwise false.
V8_EXPORT_PRIVATE bool SetPermissions(Address address, size_t size,
PageAllocator::Permission access);
// Releases memory after |free_start|. Returns the number of bytes released.
V8_EXPORT_PRIVATE size_t Release(Address free_start);
// Frees all memory.
V8_EXPORT_PRIVATE void Free();
bool InVM(Address address, size_t size) {
return region_.contains(address, size);
// Page allocator that controls the virtual memory.
v8::PageAllocator* page_allocator_ = nullptr;
base::AddressRegion region_;
} // namespace internal
} // namespace v8