runtime/vm/virtual_memory.cc

// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#include "vm/virtual_memory.h"

#include "platform/assert.h"
#include "platform/utils.h"

namespace dart {

bool VirtualMemory::InSamePage(uword address0, uword address1) {
  return (Utils::RoundDown(address0, PageSize()) ==
          Utils::RoundDown(address1, PageSize()));
}

void VirtualMemory::Truncate(intptr_t new_size) {
  ASSERT(Utils::IsAligned(new_size, PageSize()));
  ASSERT(new_size <= size());
  // We are not expected to call this with executable pages.
  ASSERT(OffsetToExecutableAlias() == 0);
  if (!InCage()) {
    if (reserved_.size() ==
        region_.size()) {  // Don't create holes in reservation.
      if (FreeSubSegment(reinterpret_cast<void*>(start() + new_size),
                         size() - new_size)) {
        reserved_.set_size(new_size);
      }
    }
  }
  region_.Subregion(region_, 0, new_size);
}

VirtualMemory* VirtualMemory::ForImagePage(void* pointer, uword size) {
  // Memory for precompilated instructions was allocated by the embedder, so
  // create a VirtualMemory without allocating.
  MemoryRegion region(pointer, size);
  MemoryRegion reserved(nullptr, 0);  // null reservation indicates VM should
                                      // not attempt to free this memory.
  VirtualMemory* memory = new VirtualMemory(region, reserved);
  ASSERT(!memory->vm_owns_region());
  return memory;
}

VirtualMemory* VirtualMemory::Adopt(void* pointer, uword size) {
  MemoryRegion region(pointer, size);
  VirtualMemory* memory = new VirtualMemory(region, region);
  ASSERT(memory->vm_owns_region());
  return memory;
}

}  // namespace dart