base/allocator/partition_allocator/src/partition_alloc/shim/malloc_zone_functions_apple.cc

// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "partition_alloc/shim/malloc_zone_functions_apple.h"

#include <atomic>
#include <type_traits>

#include "partition_alloc/partition_alloc_base/check.h"
#include "partition_alloc/partition_lock.h"

namespace allocator_shim {

MallocZoneFunctions g_malloc_zones[kMaxZoneCount];
static_assert(std::is_trivial_v<MallocZoneFunctions> &&
                  std::is_standard_layout_v<MallocZoneFunctions>,
              "MallocZoneFunctions must be POD");

void StoreZoneFunctions(const ChromeMallocZone* zone,
                        MallocZoneFunctions* functions) {
  memset(functions, 0, sizeof(MallocZoneFunctions));
  functions->malloc = zone->malloc;
  functions->calloc = zone->calloc;
  functions->valloc = zone->valloc;
  functions->free = zone->free;
  functions->realloc = zone->realloc;
  functions->size = zone->size;
  functions->good_size = zone->introspect->good_size;
  PA_BASE_CHECK(functions->malloc && functions->calloc && functions->valloc &&
                functions->free && functions->realloc && functions->size &&
                functions->good_size);

  // These functions might be nullptr.
  functions->batch_malloc = zone->batch_malloc;
  functions->batch_free = zone->batch_free;

  if (zone->version >= 5) {
    // Not all custom malloc zones have a memalign.
    functions->memalign = zone->memalign;
  }
  if (zone->version >= 6) {
    // This may be nullptr.
    functions->free_definite_size = zone->free_definite_size;
  }
  if (zone->version >= 10) {
    functions->claimed_address = zone->claimed_address;
  }
  if (zone->version >= 13) {
    functions->try_free_default = zone->try_free_default;
  }

  // Note that zone version 8 introduced a pressure relief callback, and version
  // 10 introduced a claimed address callback, but neither are allocation or
  // deallocation callbacks and so aren't important to intercept.

  functions->context = zone;
}

namespace {

// All modifications to g_malloc_zones are gated behind this lock.
// Dispatch to a malloc zone does not need to acquire this lock.
partition_alloc::internal::Lock& GetLock() {
  static partition_alloc::internal::Lock s_lock;
  return s_lock;
}

void EnsureMallocZonesInitializedLocked() {
  GetLock().AssertAcquired();
}

int g_zone_count = 0;

bool IsMallocZoneAlreadyStoredLocked(ChromeMallocZone* zone) {
  EnsureMallocZonesInitializedLocked();
  for (int i = 0; i < g_zone_count; ++i) {
    if (g_malloc_zones[i].context == reinterpret_cast<void*>(zone)) {
      return true;
    }
  }
  return false;
}

}  // namespace

bool StoreMallocZone(ChromeMallocZone* zone) {
  partition_alloc::internal::ScopedGuard guard(GetLock());
  if (IsMallocZoneAlreadyStoredLocked(zone)) {
    return false;
  }

  if (g_zone_count == kMaxZoneCount) {
    return false;
  }

  StoreZoneFunctions(zone, &g_malloc_zones[g_zone_count]);
  ++g_zone_count;

  // No other thread can possibly see these stores at this point. The code that
  // reads these values is triggered after this function returns. so we want to
  // guarantee that they are committed at this stage"
  std::atomic_thread_fence(std::memory_order_seq_cst);
  return true;
}

bool IsMallocZoneAlreadyStored(ChromeMallocZone* zone) {
  partition_alloc::internal::ScopedGuard guard(GetLock());
  return IsMallocZoneAlreadyStoredLocked(zone);
}

bool DoesMallocZoneNeedReplacing(ChromeMallocZone* zone,
                                 const MallocZoneFunctions* functions) {
  return IsMallocZoneAlreadyStored(zone) && zone->malloc != functions->malloc;
}

int GetMallocZoneCountForTesting() {
  partition_alloc::internal::ScopedGuard guard(GetLock());
  return g_zone_count;
}

void ClearAllMallocZonesForTesting() {
  partition_alloc::internal::ScopedGuard guard(GetLock());
  memset(g_malloc_zones, 0, kMaxZoneCount * sizeof(MallocZoneFunctions));
  g_zone_count = 0;
}

}  // namespace allocator_shim