chromium/base/allocator/partition_allocator/src/partition_alloc/page_allocator_constants.h

// Copyright 2018 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_PAGE_ALLOCATOR_CONSTANTS_H_
#define PARTITION_ALLOC_PAGE_ALLOCATOR_CONSTANTS_H_

#include <cstddef>

#include "partition_alloc/build_config.h"
#include "partition_alloc/partition_alloc_base/compiler_specific.h"
#include "partition_alloc/partition_alloc_base/component_export.h"

#if PA_BUILDFLAG(IS_APPLE) && PA_BUILDFLAG(PA_ARCH_CPU_64_BITS)

#include <mach/vm_page_size.h>

// Although page allocator constants are not constexpr, they are run-time
// constant. Because the underlying variables they access, such as vm_page_size,
// are not marked const, the compiler normally has no way to know that they
// don’t change and must obtain their values whenever it can't prove that they
// haven't been modified, even if they had already been obtained previously.
// Attaching __attribute__((const)) to these declarations allows these redundant
// accesses to be omitted under optimization such as common subexpression
// elimination.
#define PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR …

#elif (PA_BUILDFLAG(IS_ANDROID) && PA_BUILDFLAG(PA_ARCH_CPU_64_BITS)) || \
    (PA_BUILDFLAG(IS_LINUX) && PA_BUILDFLAG(PA_ARCH_CPU_ARM64)) || \
    (PA_BUILDFLAG(IS_LINUX) && PA_BUILDFLAG(PA_ARCH_CPU_PPC64))
// This should work for all POSIX (if needed), but currently all other
// supported OS/architecture combinations use either hard-coded values
// (such as x86) or have means to determine these values without needing
// atomics (such as macOS on arm64).

#define PARTITION_ALLOCATOR_CONSTANTS_POSIX_NONCONST_PAGE_SIZE

// Page allocator constants are run-time constant
#define PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR …

#include <unistd.h>
#include <atomic>

namespace partition_alloc::internal {

// Holds the current page size and shift, where size = 1 << shift
// Use PageAllocationGranularity(), PageAllocationGranularityShift()
// to initialize and retrieve these values safely.
struct PageCharacteristics {
  std::atomic<size_t> size;
  std::atomic<size_t> shift;
};
PA_COMPONENT_EXPORT(PARTITION_ALLOC)
extern PageCharacteristics page_characteristics;

}  // namespace partition_alloc::internal

#else

// When defined, page size constants are fixed at compile time. When not
// defined, they may vary at run time.
#define PAGE_ALLOCATOR_CONSTANTS_ARE_CONSTEXPR …

// Use this macro to declare a function as constexpr or not based on whether
// PAGE_ALLOCATOR_CONSTANTS_ARE_CONSTEXPR is defined.
#define PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR …

#endif

// Ability to name anonymous VMAs is available on some, but not all Linux-based
// systems.
#if PA_BUILDFLAG(IS_ANDROID) || PA_BUILDFLAG(IS_LINUX)
#include <sys/prctl.h>

#if defined(PR_SET_VMA) && defined(PR_SET_VMA_ANON_NAME)
#define LINUX_NAME_REGION …
#endif

#endif  // PA_BUILDFLAG(IS_ANDROID) || PA_BUILDFLAG(IS_LINUX)

namespace partition_alloc {
namespace internal {

// Forward declaration, implementation below
PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
PageAllocationGranularity();

PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
PageAllocationGranularityShift() { … }

PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
PageAllocationGranularity() { … }

PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
PageAllocationGranularityOffsetMask() { … }

PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
PageAllocationGranularityBaseMask() { … }

PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
SystemPageShift() { … }

PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
SystemPageSize() { … }

PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
SystemPageOffsetMask() { … }

PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
SystemPageBaseMask() { … }

constexpr size_t kPageMetadataShift = …;  // 32 bytes per partition page.
constexpr size_t kPageMetadataSize = …;

}  // namespace internal

PA_ALWAYS_INLINE PAGE_ALLOCATOR_CONSTANTS_DECLARE_CONSTEXPR size_t
SystemPageSize() { … }

}  // namespace partition_alloc

#endif  // PARTITION_ALLOC_PAGE_ALLOCATOR_CONSTANTS_H_