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// 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 "platform/utils.h"
#include "vm/globals.h"
#include "vm/memory_region.h"
namespace dart {
class VirtualMemory {
enum Protection {
// The reserved memory is unmapped on destruction.
uword start() const { return region_.start(); }
uword end() const { return region_.end(); }
void* address() const { return region_.pointer(); }
intptr_t size() const { return region_.size(); }
intptr_t AliasOffset() const { return alias_.start() - region_.start(); }
static void Init();
bool Contains(uword addr) const { return region_.Contains(addr); }
bool ContainsAlias(uword addr) const {
return (AliasOffset() != 0) && alias_.Contains(addr);
// Changes the protection of the virtual memory area.
static void Protect(void* address, intptr_t size, Protection mode);
void Protect(Protection mode) { return Protect(address(), size(), mode); }
// Reserves and commits a virtual memory segment with size. If a segment of
// the requested size cannot be allocated, NULL is returned.
static VirtualMemory* Allocate(intptr_t size,
bool is_executable,
const char* name) {
return AllocateAligned(size, PageSize(), is_executable, name);
static VirtualMemory* AllocateAligned(intptr_t size,
intptr_t alignment,
bool is_executable,
const char* name);
static intptr_t PageSize() {
ASSERT(page_size_ != 0);
return page_size_;
static bool InSamePage(uword address0, uword address1);
// Truncate this virtual memory segment.
void Truncate(intptr_t new_size);
// False for a part of a snapshot added directly to the Dart heap, which
// belongs to the embedder and must not be deallocated or have its
// protection status changed by the VM.
bool vm_owns_region() const { return reserved_.pointer() != NULL; }
static VirtualMemory* ForImagePage(void* pointer, uword size);
// Free a sub segment. On operating systems that support it this
// can give back the virtual memory to the system. Returns true on success.
static void FreeSubSegment(void* address, intptr_t size);
// These constructors are only used internally when reserving new virtual
// spaces. They do not reserve any virtual address space on their own.
VirtualMemory(const MemoryRegion& region,
const MemoryRegion& alias,
const MemoryRegion& reserved)
: region_(region), alias_(alias), reserved_(reserved) {}
VirtualMemory(const MemoryRegion& region, const MemoryRegion& reserved)
: region_(region), alias_(region), reserved_(reserved) {}
MemoryRegion region_;
// Optional secondary mapping of region_ to a virtual space with different
// protection, e.g. allowing code execution.
MemoryRegion alias_;
// The underlying reservation not yet given back to the OS.
// Its address might disagree with region_ due to aligned allocations.
// Its size might disagree with region_ due to Truncate.
MemoryRegion reserved_;
static uword page_size_;
#if defined(HOST_OS_FUCHSIA)
static uword base_; // Cached base of root vmar.
} // namespace dart