base/allocator/allocator.gni

# Copyright 2019 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.

import("//build/config/chromecast_build.gni")
import("//build/config/sanitizers/sanitizers.gni")

if (is_ios) {
  import("//build/config/ios/ios_sdk.gni")
}

# Sanitizers replace the allocator, don't use our own.
_is_using_sanitizers = is_asan || is_hwasan || is_lsan || is_tsan || is_msan

# - Component build support is disabled on all platforms. It is known to cause
#   issues on some (e.g. Windows with shims, Android with non-universal symbol
#   wrapping), and has not been validated on others.
# - Windows: debug CRT is not compatible, see below.
_disable_partition_alloc = is_component_build || (is_win && is_debug)
_is_partition_alloc_platform = is_android || is_win || is_linux || is_chromeos

# The debug CRT on Windows has some debug features that are incompatible with
# the shim. NaCl in particular does seem to link some binaries statically
# against the debug CRT with "is_nacl=false".
if ((is_linux || is_chromeos || is_android || is_apple ||
     (is_win && !is_component_build && !is_debug)) && !_is_using_sanitizers) {
  _default_use_allocator_shim = true
} else {
  _default_use_allocator_shim = false
}

if (_default_use_allocator_shim && _is_partition_alloc_platform &&
    !_disable_partition_alloc) {
  _default_allocator = "partition"
} else {
  _default_allocator = "none"
}

declare_args() {
  # Memory allocator to use. Set to "none" to use default allocator.
  use_allocator = _default_allocator

  # Causes all the allocations to be routed via allocator_shim.cc.
  use_allocator_shim = _default_use_allocator_shim

  # Whether PartitionAlloc should be available for use or not.
  # true makes PartitionAlloc linked to the executable or shared library and
  # makes it available for use, but it doesn't mean that the default allocator
  # is PartitionAlloc.  PartitionAlloc may or may not be the default allocator.
  #
  # |use_allocator = "partition"| makes PartitionAlloc the default allocator
  # but it's effective only when |use_partition_alloc = true|.
  #
  # TODO(lizeb, yukishiino): Determine if |use_partition_alloc| is necessary or
  # not, and redesign or remove the flag accordingly.  We may want to assert a
  # possible conflict between |use_allocator = "partition"| and
  # |use_partition_alloc = true| rather than prioritizing use_partition_alloc.
  # TODO(crbug.com/1250788): Enable use_partition_alloc on iOS device builds.
  use_partition_alloc = !is_ios || target_environment == "simulator"

  # Set use_backup_ref_ptr true to use BackupRefPtr (BRP) as the implementation
  # of raw_ptr<T>, and enable PartitionAlloc support for it. The _fake option
  # doesn't enable BRP, but pretends it's enabled for the syntethic field trial
  #(for testing purposes only).
  use_backup_ref_ptr = false
  use_backup_ref_ptr_fake = false

  # If BRP is enabled, additional options are available:
  # - put_ref_count_in_previous_slot: place the ref-count at the end of the
  #   previous slot (or in metadata if a slot starts on the page boundary), as
  #   opposed to the beginning of the slot.
  # - never_remove_from_brp_pool_blocklist: never remove super-pages from the
  #   BRP-pool block list
  # - enable_backup_ref_ptr_slow_checks: enable additional safety checks that
  #   are too expensive to have on by default.
  put_ref_count_in_previous_slot = false
  never_remove_from_brp_pool_blocklist = false
  enable_backup_ref_ptr_slow_checks = false
}

if (!use_partition_alloc && use_allocator == "partition") {
  # If there is a conflict, prioritize |use_partition_alloc| over
  # |use_allocator|.
  use_allocator = "none"
}

# No longer the default on any platform, but still supported through GN args on Linux.
assert(use_allocator != "tcmalloc" || is_linux,
       "tcmalloc is only supported on Linux")
assert(use_allocator == "none" || use_allocator == "partition" ||
       use_allocator == "tcmalloc")

assert(
    !use_allocator_shim || is_linux || is_chromeos || is_android || is_win ||
        is_fuchsia || is_apple,
    "use_allocator_shim works only on Android, iOS, Linux, macOS, Fuchsia, " +
        "and Windows.")

if (is_win && use_allocator_shim) {
  # TODO(crbug.com/1245317): Add a comment indicating why the shim doesn't work.
  assert(!is_component_build,
         "The allocator shim doesn't work for the component build on Windows.")
}

# Prevent using BackupRefPtr when PartitionAlloc-Everywhere isn't used.
# In theory, such a configuration is possible, but its scope would be limited to
# only Blink partitions, which is currently not tested. Better to trigger an
# error, than have BackupRefPtr silently disabled while believing it is enabled.
if (!is_nacl) {
  assert(!use_backup_ref_ptr || use_allocator == "partition",
         "Can't use BackupRefPtr without PartitionAlloc-Everywhere")
}

# put_ref_count_in_previous_slot can only be used if use_backup_ref_ptr
# is true.
assert(
    use_backup_ref_ptr || !put_ref_count_in_previous_slot,
    "Can't put ref count in the previous slot if BackupRefPtr isn't enabled at all")

# never_remove_from_brp_pool_blocklist can only be used if use_backup_ref_ptr
# is true.
assert(
    use_backup_ref_ptr || !never_remove_from_brp_pool_blocklist,
    "never_remove_from_brp_pool_blocklist requires BackupRefPtr to be enabled")

# enable_backup_ref_ptr_slow_checks can only be used if use_backup_ref_ptr
# is true.
assert(use_backup_ref_ptr || !enable_backup_ref_ptr_slow_checks,
       "Can't enable additional BackupRefPtr checks if it isn't enabled at all")