blob: 3d4cc022b4b6deef5cbfc13057ec5e7ae62a6f04 [file] [log] [blame]
// Copyright 2014 The Chromium 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 <mach/mach.h>
#include <stddef.h>
#include <algorithm>
#include "base/base_export.h"
#include "base/logging.h"
#include "base/macros.h"
// Use ScopedMachVM to supervise ownership of pages in the current process
// through the Mach VM subsystem. Pages allocated with vm_allocate can be
// released when exiting a scope with ScopedMachVM.
// The Mach VM subsystem operates on a page-by-page basis, and a single VM
// allocation managed by a ScopedMachVM object may span multiple pages. As far
// as Mach is concerned, allocated pages may be deallocated individually. This
// is in contrast to higher-level allocators such as malloc, where the base
// address of an allocation implies the size of an allocated block.
// Consequently, it is not sufficient to just pass the base address of an
// allocation to ScopedMachVM, it also needs to know the size of the
// allocation. To avoid any confusion, both the base address and size must
// be page-aligned.
// When dealing with Mach VM, base addresses will naturally be page-aligned,
// but user-specified sizes may not be. If there's a concern that a size is
// not page-aligned, use the mach_vm_round_page macro to correct it.
// Example:
// vm_address_t address = 0;
// vm_size_t size = 12345; // This requested size is not page-aligned.
// kern_return_t kr =
// vm_allocate(mach_task_self(), &address, size, VM_FLAGS_ANYWHERE);
// if (kr != KERN_SUCCESS) {
// return false;
// }
// ScopedMachVM vm_owner(address, mach_vm_round_page(size));
namespace base {
namespace mac {
class BASE_EXPORT ScopedMachVM {
explicit ScopedMachVM(vm_address_t address = 0, vm_size_t size = 0)
: address_(address), size_(size) {
DCHECK_EQ(address % PAGE_SIZE, 0u);
DCHECK_EQ(size % PAGE_SIZE, 0u);
~ScopedMachVM() {
if (size_) {
vm_deallocate(mach_task_self(), address_, size_);
// Resets the scoper to manage a new memory region. Both |address| and |size|
// must be page-aligned. If the new region is a smaller subset of the
// existing region (i.e. the new and old regions overlap), the non-
// overlapping part of the old region is deallocated.
void reset(vm_address_t address = 0, vm_size_t size = 0);
// Like reset() but does not DCHECK that |address| and |size| are page-
// aligned.
void reset_unaligned(vm_address_t address, vm_size_t size);
vm_address_t address() const {
return address_;
vm_size_t size() const {
return size_;
void swap(ScopedMachVM& that) {
std::swap(address_, that.address_);
std::swap(size_, that.size_);
void release() {
address_ = 0;
size_ = 0;
vm_address_t address_;
vm_size_t size_;
} // namespace mac
} // namespace base