[Tracing] Add allocation register for heap profiling

base/trace_event/memory_profiler_allocation_register_posix.cc

+// Copyright 2015 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 "base/trace_event/memory_profiler_allocation_register.h"
+
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "base/basictypes.h"
+#include "base/bits.h"
+#include "base/logging.h"
+#include "base/process/process_metrics.h"
+
+namespace base {
+namespace trace_event {
+
+// static
+void* AllocationRegister::AllocateVirtualMemory(size_t min_size) {
+  size_t size = bits::Align(min_size, GetPageSize());
+
+  // Add space for a guard page at the end.
+  size_t map_size = size + GetPageSize();
+
+  void* addr = mmap(nullptr, map_size, PROT_READ | PROT_WRITE,
+                    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

[Primiano Tucci (use gerrit), 2015/10/06 13:34:44]

I think you need some ifdef guard here, IIRC MAP_ANONYMOUS is not posix and mac
will be unhappy

[Ruud van Asseldonk, 2015/10/06 15:44:35]

Yep, found that out via the trybots. PartitionAlloc solved it by #defining it to
MAP_ANON if not defined, so did that here as well (see patchset 6).

+
+  PCHECK(addr != MAP_FAILED);
+
+  // Mark the last page of the allocated address space as inaccessible
+  // (PROT_NONE). The read/write accessible space is still at least |min_size|
+  // bytes.
+  void* guard_addr = static_cast<void*>(static_cast<uint8_t*>(addr) + size);

[Primiano Tucci (use gerrit), 2015/10/06 13:34:44]

s/uint8_t/uintptr_t/ (and use reinterpret_cast).
afaik that is the one you want to do pointer arith with void*

P.S. Let me guess: you did that but preferred to use static_Cast because
reinterpret_cast wouldn't fit in one line, eh? :P

[Ruud van Asseldonk, 2015/10/06 15:44:35]

Done. I casted to |uint8_t| because this is really counting bytes, and |uint8_t|
is a byte. My OCD was unhappier about the |AllocationRegister| constructor (the
comments don’t line up, and moving the colon before the comment makes it even
worse ...)

+  size_t guard_size = map_size - size;

[Primiano Tucci (use gerrit), 2015/10/06 13:34:44]

probably the code here would be a bit more readable if you:
make guard_size a constatnt in the anonymous namespace:
size_t GetGuardSize() { return GetPageSize(); }
(Ideally it would be a const but you cannot write const kGuardSize =
GetPageSize() as it would cause a static initializer and our checkers will barf)

then say
const size_t map_size = size + GetGuardSize()

and use GetGuardSize() below

[Ruud van Asseldonk, 2015/10/06 15:44:35]

As you wish.

+  int result = mprotect(guard_addr, guard_size, PROT_NONE);
+  PCHECK(result == 0);
+
+  return addr;
+}
+
+// static
+void AllocationRegister::FreeVirtualMemory(void* address,
+                                           size_t allocated_min_size) {
+  size_t size = bits::Align(allocated_min_size, GetPageSize()) + GetPageSize();
+  munmap(address, size);
+}
+
+}  // namespace trace_event
+}  // namespace base