base/mac/scoped_mach_vm.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_MAC_SCOPED_MACH_VM_H_
   6 #define BASE_MAC_SCOPED_MACH_VM_H_
   7
   8 #include <mach/mach.h>
   9
  10 #include <algorithm>
  11
  12 #include "base/base_export.h"
  13 #include "base/basictypes.h"
  14 #include "base/logging.h"
  15
  16 // Use ScopedMachVM to supervise ownership of pages in the current process
  17 // through the Mach VM subsystem. Pages allocated with vm_allocate can be
  18 // released when exiting a scope with ScopedMachVM.
  19 //
  20 // The Mach VM subsystem operates on a page-by-page basis, and a single VM
  21 // allocation managed by a ScopedMachVM object may span multiple pages. As far
  22 // as Mach is concerned, allocated pages may be deallocated individually. This
  23 // is in contrast to higher-level allocators such as malloc, where the base
  24 // address of an allocation implies the size of an allocated block.
  25 // Consequently, it is not sufficient to just pass the base address of an
  26 // allocation to ScopedMachVM, it also needs to know the size of the
  27 // allocation. To avoid any confusion, both the base address and size must
  28 // be page-aligned.
  29 //
  30 // When dealing with Mach VM, base addresses will naturally be page-aligned,
  31 // but user-specified sizes may not be. If there's a concern that a size is
  32 // not page-aligned, use the mach_vm_round_page macro to correct it.
  33 //
  34 // Example:
  35 //
  36 //   vm_address_t address = 0;
  37 //   vm_size_t size = 12345;  // This requested size is not page-aligned.
  38 //   kern_return_t kr =
  39 //       vm_allocate(mach_task_self(), &address, size, VM_FLAGS_ANYWHERE);
  40 //   if (kr != KERN_SUCCESS) {
  41 //     return false;
  42 //   }
  43 //   ScopedMachVM vm_owner(address, mach_vm_round_page(size));
  44
  45 namespace base {
  46 namespace mac {
  47
  48 class BASE_EXPORT ScopedMachVM {
  49  public:
  50   explicit ScopedMachVM(vm_address_t address = 0, vm_size_t size = 0)
  51       : address_(address), size_(size) {
  52     DCHECK_EQ(address % PAGE_SIZE, 0u);
  53     DCHECK_EQ(size % PAGE_SIZE, 0u);
  54   }
  55
  56   ~ScopedMachVM() {
  57     if (size_) {
  58       vm_deallocate(mach_task_self(), address_, size_);
  59     }
  60   }
  61
  62   void reset(vm_address_t address = 0, vm_size_t size = 0);
  63
  64   vm_address_t address() const {
  65     return address_;
  66   }
  67
  68   vm_size_t size() const {
  69     return size_;
  70   }
  71
  72   void swap(ScopedMachVM& that) {
  73     std::swap(address_, that.address_);
  74     std::swap(size_, that.size_);
  75   }
  76
  77   void release() {
  78     address_ = 0;
  79     size_ = 0;
  80   }
  81
  82  private:
  83   vm_address_t address_;
  84   vm_size_t size_;
  85
  86   DISALLOW_COPY_AND_ASSIGN(ScopedMachVM);
  87 };
  88
  89 }  // namespace mac
  90 }  // namespace base
  91
  92 #endif  // BASE_MAC_SCOPED_MACH_VM_H_