chromium/v8/src/heap/cppgc/globals.h

// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_HEAP_CPPGC_GLOBALS_H_
#define V8_HEAP_CPPGC_GLOBALS_H_

#include <stddef.h>
#include <stdint.h>

#include "include/cppgc/internal/gc-info.h"
#include "src/base/build_config.h"

namespace cppgc {
namespace internal {

Address;
ConstAddress;

constexpr size_t kKB = …;
constexpr size_t kMB = …;
constexpr size_t kGB = …;

// AccessMode used for choosing between atomic and non-atomic accesses.
enum class AccessMode : uint8_t { … };

// See 6.7.6 (http://eel.is/c++draft/basic.align) for alignment restrictions. We
// do not fully support all alignment restrictions (following
// alignof(std​::​max_­align_­t)) but limit to alignof(double).
//
// This means that any scalar type with stricter alignment requirements (in
// practice: long double) cannot be used unrestricted in garbage-collected
// objects.
#if defined(V8_HOST_ARCH_64_BIT)
constexpr size_t kAllocationGranularity = …;
#else   // !V8_HOST_ARCH_64_BIT
constexpr size_t kAllocationGranularity = 4;
#endif  // !V8_HOST_ARCH_64_BIT
constexpr size_t kAllocationMask = …;

constexpr size_t kPageSizeLog2 = …;
constexpr size_t kPageSize = …;
constexpr size_t kPageOffsetMask = …;
constexpr size_t kPageBaseMask = …;

#if defined(V8_HOST_ARCH_ARM64) && defined(V8_OS_DARWIN)
// No guard pages on ARM64 macOS. This target has 16 kiB pages, meaning that
// the guard pages do not protect anything, since there is no inaccessible
// region surrounding the allocation.
//
// However, with a 4k guard page size (as below), we avoid putting any data
// inside the "guard pages" region. Effectively, this wastes 2 * 4kiB of memory
// for each 128kiB page, since this is memory we pay for (since accounting as at
// the OS page level), but never use.
//
// The layout of pages is broadly:
// | guard page | header | payload | guard page |
// <---  4k --->                    <---  4k --->
// <------------------ 128k -------------------->
//
// Since this is aligned on an OS page boundary (16k), the guard pages are part
// of the first and last OS page, respectively. So they are really private dirty
// memory which we never use.
constexpr size_t kGuardPageSize = 0;
#elif defined(V8_HOST_ARCH_PPC64)
// PPC has 64K pages.
constexpr size_t kGuardPageSize = 0;
#elif defined(V8_HOST_ARCH_LOONG64) || defined(V8_HOST_ARCH_MIPS64)
// LoongArch64 and MIPS64 have 16K pages.
constexpr size_t kGuardPageSize = 0;
#else
// Guard pages are always put into memory. Whether they are actually protected
// depends on the allocator provided to the garbage collector.
constexpr size_t kGuardPageSize = …;
#endif

constexpr size_t kLargeObjectSizeThreshold = …;

constexpr GCInfoIndex kFreeListGCInfoIndex = …;
constexpr size_t kFreeListEntrySize = …;

#if defined(CPPGC_POINTER_COMPRESSION)
constexpr size_t kSlotSize = …;
#else   // !defined(CPPGC_POINTER_COMPRESSION)
constexpr size_t kSlotSize = sizeof(uintptr_t);
#endif  // !defined(CPPGC_POINTER_COMPRESSION)

}  // namespace internal
}  // namespace cppgc

#endif  // V8_HEAP_CPPGC_GLOBALS_H_