Refactor and cleanup VirtualMemory.

src/platform/virtual-memory.h

+// Copyright 2013 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_PLATFORM_VIRTUAL_MEMORY_H_
+#define V8_PLATFORM_VIRTUAL_MEMORY_H_
+
+#include "checks.h"
+#include "globals.h"
+
+namespace v8 {
+namespace internal {
+
+// -----------------------------------------------------------------------------
+// VirtualMemory
+//
+// This class represents and controls an area of reserved memory.
+// Control of the reserved memory can be assigned to another VirtualMemory
+// object by assignment or copy-contructing. This removes the reserved memory

[Toon Verwaest, 2013/09/10 15:11:41]

constructing

[Benedikt Meurer, 2013/09/11 09:38:08]

Done.

+// from the original object.
+class VirtualMemory V8_FINAL {
+ public:
+  // The executability of a memory region.
+  enum Executability { NOT_EXECUTABLE, EXECUTABLE };
+
+  // Empty VirtualMemory object, controlling no reserved memory.
+  VirtualMemory() : address_(NULL), size_(0) {}
+
+  // Reserves virtual memory with size.
+  explicit VirtualMemory(size_t size) : size_(0) {
+    address_ = ReserveRegion(size, &size_);
+  }
+
+  // Reserves virtual memory containing an area of the given size that
+  // is aligned per alignment. This may not be at the position returned
+  // by address().
+  VirtualMemory(size_t size, size_t alignment) : size_(0) {
+    address_ = ReserveRegion(size, &size_, alignment);
+  }
+
+  // Releases the reserved memory, if any, controlled by this VirtualMemory
+  // object.
+  ~VirtualMemory() {
+    if (IsReserved()) {
+      bool result = ReleaseRegion(address_, size_);
+      ASSERT(result);
+      USE(result);
+    }
+  }
+
+  // Returns whether the memory contains the specified address.
+  bool Contains(const void* address) const V8_WARN_UNUSED_RESULT {
+    if (!IsReserved()) return false;
+    if (address < address_) return false;
+    if (address >= reinterpret_cast<uint8_t*>(address_) + size_) return false;
+    return true;
+  }
+
+  // Returns whether the memory has been reserved.
+  bool IsReserved() const V8_WARN_UNUSED_RESULT {
+    return address_ != NULL;
+  }
+
+  // Initialize or resets an embedded VirtualMemory object.
+  void Reset() {
+    address_ = NULL;
+    size_ = 0;
+  }
+
+  // Returns the start address of the reserved memory. The returned value is
+  // only meaningful if |IsReserved()| returns true.
+  // 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.
+  void* address() const V8_WARN_UNUSED_RESULT { return address_; }
+
+  // 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 V8_WARN_UNUSED_RESULT { return size_; }
+
+  // Commits real memory. Returns whether the operation succeeded.
+  bool Commit(void* address,
+              size_t size,
+              Executability executability) V8_WARN_UNUSED_RESULT {
+    ASSERT(IsReserved());
+    ASSERT(Contains(address));
+    ASSERT(Contains(reinterpret_cast<uint8_t*>(address) + size - 1));
+    return CommitRegion(address, size, executability);
+  }
+
+  // Uncommit real memory.  Returns whether the operation succeeded.
+  bool Uncommit(void* address, size_t size) V8_WARN_UNUSED_RESULT {
+    ASSERT(IsReserved());
+    ASSERT(Contains(address));
+    ASSERT(Contains(reinterpret_cast<uint8_t*>(address) + size - 1));
+    return UncommitRegion(address, size);
+  }
+
+  // Creates guard pages at the given address.
+  bool Guard(void* address, size_t size) V8_WARN_UNUSED_RESULT {
+    // We can simply uncommit the specified pages. Any access
+    // to them will cause a processor exception then.

[Toon Verwaest, 2013/09/10 15:11:41]

remove "then" at the end. Reindent.

[Benedikt Meurer, 2013/09/11 09:38:08]

Done.

+    return Uncommit(address, size);
+  }
+
+  void Release() {
+    ASSERT(IsReserved());
+    // WARNING: Order is important here. The VirtualMemory
+    // object might live inside the allocated region.
+    void* address = address_;
+    size_t size = size_;
+    Reset();
+    bool result = ReleaseRegion(address, size);
+    USE(result);
+    ASSERT(result);
+  }
+
+  // Assign control of the reserved region to a different VirtualMemory object.
+  // The old object is no longer functional (IsReserved() returns false).
+  void TakeControl(VirtualMemory* from) {
+    ASSERT(!IsReserved());
+    address_ = from->address_;
+    size_ = from->size_;
+    from->Reset();
+  }
+
+  // Allocates a region of memory pages. The pages are readable/writable,
+  // but are not guaranteed to be executable unless explicitly requested.
+  // Returns the base address of the allocated memory region, or NULL in
+  // case of an error.
+  static void* AllocateRegion(size_t size,
+                              size_t* size_return,
+                              Executability executability)
+      V8_WARN_UNUSED_RESULT;
+
+  static void* ReserveRegion(size_t size,
+                             size_t* size_return) V8_WARN_UNUSED_RESULT;
+
+  static void* ReserveRegion(size_t size,
+                             size_t* size_return,
+                             size_t alignment) V8_WARN_UNUSED_RESULT;
+
+  static bool CommitRegion(void* address,
+                           size_t size,
+                           Executability executability) V8_WARN_UNUSED_RESULT;
+
+  static bool UncommitRegion(void* address, size_t size) V8_WARN_UNUSED_RESULT;
+
+  // Mark code segments non-writable.
+  static bool ProtectRegion(void* address, size_t size) V8_WARN_UNUSED_RESULT;
+
+  // Must be called with a base pointer that has been returned by ReserveRegion
+  // and the same size it was reserved with.
+  static bool ReleaseRegion(void* address, size_t size) V8_WARN_UNUSED_RESULT;
+
+  // The granularity for the starting address at which virtual memory can be
+  // reserved (or allocated in terms of the underlying operating system).
+  static size_t GetAllocationGranularity() V8_PURE;
+
+  // The maximum size of the virtual memory. 0 means there is no artificial
+  // limit.
+  static size_t GetLimit() V8_PURE;
+
+  // The page size and the granularity of page protection and commitment.
+  static size_t GetPageSize() V8_PURE;
+
+  // Returns true if OS performs lazy commits, i.e. the memory allocation call
+  // defers actual physical memory allocation till the first memory access.
+  // Otherwise returns false.
+  static V8_INLINE(bool HasLazyCommits()) {
+#if V8_OS_LINUX
+    return true;
+#else
+    return false;
+#endif
+  }
+
+ private:
+  void* address_;  // Start address of the virtual memory.
+  size_t size_;  // Size of the virtual memory.
+};
+
+} }  // namespace v8::internal
+
+#endif  // V8_PLATFORM_VIRTUAL_MEMORY_H_