in_slot_metadata.h | Explore in Territory

// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef PARTITION_ALLOC_IN_SLOT_METADATA_H_
#define PARTITION_ALLOC_IN_SLOT_METADATA_H_

#include <atomic>
#include <cstddef>
#include <cstdint>
#include <limits>

#include "partition_alloc/build_config.h"
#include "partition_alloc/buildflags.h"
#include "partition_alloc/dangling_raw_ptr_checks.h"
#include "partition_alloc/partition_alloc_base/bits.h"
#include "partition_alloc/partition_alloc_base/compiler_specific.h"
#include "partition_alloc/partition_alloc_base/component_export.h"
#include "partition_alloc/partition_alloc_base/immediate_crash.h"
#include "partition_alloc/partition_alloc_check.h"
#include "partition_alloc/partition_alloc_config.h"
#include "partition_alloc/partition_alloc_constants.h"
#include "partition_alloc/partition_alloc_forward.h"
#include "partition_alloc/tagging.h"

namespace partition_alloc::internal {

// Aligns up (on 8B boundary) `in_slot_metadata_size` on Mac as a workaround for
// crash. Workaround was introduced for MacOS 13: https://crbug.com/1378822. But
// it has been enabled by default because MacOS 14 and later seems to need it
// too. https://crbug.com/1457756
// Enabled on iOS as a workaround for a speculative bug in Swift's
// __StringStorage.create https://crbug.com/327804972
//
// Placed outside `PA_BUILDFLAG(ENABLE_BACKUP_REF_PTR_SUPPORT)`
// intentionally to accommodate usage in contexts also outside
// this gating.
PA_ALWAYS_INLINE constexpr size_t AlignUpInSlotMetadataSizeForApple(
    size_t in_slot_metadata_size) { … }

#if PA_BUILDFLAG(ENABLE_BACKUP_REF_PTR_SUPPORT)

namespace {
// Utility functions to define a bit field.
template <typename CountType>
static constexpr CountType SafeShift(CountType lhs, int rhs) { … }
template <typename CountType>
struct BitField { … };
}  // namespace

// Special-purpose atomic bit field class mainly used by RawPtrBackupRefImpl.
// Formerly known as `PartitionRefCount`, but renamed to support usage that is
// unrelated to BRP.
class PA_COMPONENT_EXPORT(PARTITION_ALLOC) InSlotMetadata { … };

PA_ALWAYS_INLINE InSlotMetadata::InSlotMetadata(
    bool needs_mac11_malloc_size_hack)
    : … { … }

static_assert …;

#if PA_BUILDFLAG(ENABLE_DANGLING_RAW_PTR_CHECKS)

#if PA_CONFIG(IN_SLOT_METADATA_CHECK_COOKIE) || \
    PA_CONFIG(IN_SLOT_METADATA_STORE_REQUESTED_SIZE)
static constexpr size_t kInSlotMetadataSizeShift = 4;
#else
static constexpr size_t kInSlotMetadataSizeShift = …;
#endif

#else  // PA_BUILDFLAG(ENABLE_DANGLING_RAW_PTR_CHECKS)

#if PA_CONFIG(IN_SLOT_METADATA_CHECK_COOKIE) && \
    PA_CONFIG(IN_SLOT_METADATA_STORE_REQUESTED_SIZE)
static constexpr size_t kInSlotMetadataSizeShift = 4;
#elif PA_CONFIG(IN_SLOT_METADATA_CHECK_COOKIE) || \
    PA_CONFIG(IN_SLOT_METADATA_STORE_REQUESTED_SIZE)
static constexpr size_t kInSlotMetadataSizeShift = 3;
#else
static constexpr size_t kInSlotMetadataSizeShift = 2;
#endif

#endif  // PA_CONFIG(ENABLE_DANGLING_RAW_PTR_CHECKS)
static_assert …;

// The in-slot metadata table is tucked in the metadata region of the super
// page, and spans a single system page.
//
// We need one InSlotMetadata for each data system page in a super page. They
// take `x = sizeof(InSlotMetadata) * (kSuperPageSize / SystemPageSize())`
// space. They need to fit into a system page of metadata as sparsely as
// possible to minimize cache line sharing, hence we calculate a multiplier as
// `SystemPageSize() / x` which is equal to
// `SystemPageSize()^2 / kSuperPageSize / sizeof(InSlotMetadata)`.
//
// The multiplier is expressed as a bitshift to optimize the code generation.
// SystemPageSize() isn't always a constrexpr, in which case the compiler
// wouldn't know it's a power of two. The equivalence of these calculations is
// checked in PartitionAllocGlobalInit().
PA_ALWAYS_INLINE static PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
GetInSlotMetadataIndexMultiplierShift() { … }

PA_ALWAYS_INLINE InSlotMetadata* InSlotMetadataPointer(uintptr_t slot_start,
                                                       size_t slot_size) { … }

#endif  // PA_BUILDFLAG(ENABLE_BACKUP_REF_PTR_SUPPORT)

static inline constexpr size_t kInSlotMetadataSizeAdjustment = …;
#else
    0ul;
#endif

}  // namespace partition_alloc::internal

#endif  // PARTITION_ALLOC_IN_SLOT_METADATA_H_
chromium/base/allocator/partition_allocator/src/partition_alloc/in_slot_metadata.h
