base/allocator/partition_allocator/partition_alloc_config.h - chromium/src - Git at Google

 // Copyright 2021 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.

 #ifndef BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_ALLOC_CONFIG_H_
 #define BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_ALLOC_CONFIG_H_

 #include "base/allocator/buildflags.h"
 #include "build/build_config.h"

 // ARCH_CPU_64_BITS implies 64-bit instruction set, but not necessarily 64-bit
 // address space. The only known case where address space is 32-bit is NaCl, so
 // eliminate it explicitly. static_assert below ensures that others won't slip
 // through.
 #if defined(ARCH_CPU_64_BITS) && !BUILDFLAG(IS_NACL)
 #define PA_HAS_64_BITS_POINTERS
 static_assert(sizeof(void*) == 8, "");
 #else
 static_assert(sizeof(void*) != 8, "");
 #endif

 // PCScan supports 64 bits only.
 #if defined(PA_HAS_64_BITS_POINTERS)
 #define PA_ALLOW_PCSCAN
 #endif

 #if defined(PA_HAS_64_BITS_POINTERS) && \
     (defined(__ARM_NEON) || defined(__ARM_NEON__)) && defined(__ARM_FP)
 #define PA_STARSCAN_NEON_SUPPORTED
 #endif

 #if BUILDFLAG(IS_IOS)
 // Use dynamically sized GigaCage. This allows to query the size at run-time,
 // before initialization, instead of using a hardcoded constexpr. This is needed
 // on iOS because iOS test processes can't handle a large cage (see
 // crbug.com/1250788).
 #define PA_USE_DYNAMICALLY_SIZED_GIGA_CAGE
 #endif

 #if defined(PA_HAS_64_BITS_POINTERS) && \
     (BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_ANDROID))
 #include <linux/version.h>
 // TODO(bikineev): Enable for ChromeOS.
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 8, 0)
 #define PA_STARSCAN_UFFD_WRITE_PROTECTOR_SUPPORTED
 #endif
 #endif  // defined(PA_HAS_64_BITS_POINTERS) &&
         // (BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_ANDROID))

 #if defined(PA_HAS_64_BITS_POINTERS)
 // Use card table to avoid races for PCScan configuration without safepoints.
 // The card table provides the guaranteee that for a marked card the underling
 // super-page is fully initialized.
 #define PA_STARSCAN_USE_CARD_TABLE 1
 #else
 // The card table is permanently disabled for 32-bit.
 #define PA_STARSCAN_USE_CARD_TABLE 0
 #endif  // defined(PA_HAS_64_BITS_POINTERS)

 #if PA_STARSCAN_USE_CARD_TABLE && !defined(PA_ALLOW_PCSCAN)
 #error "Card table can only be used when *Scan is allowed"
 #endif

 // Use batched freeing when sweeping pages. This builds up a freelist in the
 // scanner thread and appends to the slot-span's freelist only once.
 #define PA_STARSCAN_BATCHED_FREE 1

 // POSIX is not only UNIX, e.g. macOS and other OSes. We do use Linux-specific
 // features such as futex(2).
 #if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS) || BUILDFLAG(IS_ANDROID)
 #define PA_HAS_LINUX_KERNEL
 #endif

 // On some platforms, we implement locking by spinning in userspace, then going
 // into the kernel only if there is contention. This requires platform support,
 // namely:
 // - On Linux, futex(2)
 // - On Windows, a fast userspace "try" operation which is available
 //   with SRWLock
 // - Otherwise, a fast userspace pthread_mutex_trylock().
 //
 // On macOS, pthread_mutex_trylock() is fast by default starting with macOS
 // 10.14. Chromium targets an earlier version, so it cannot be known at
 // compile-time. So we use something different. On other POSIX systems, we
 // assume that pthread_mutex_trylock() is suitable.
 //
 // Otherwise, a userspace spinlock implementation is used.
 #if defined(PA_HAS_LINUX_KERNEL) || BUILDFLAG(IS_WIN) || \
     (BUILDFLAG(IS_POSIX) && !BUILDFLAG(IS_APPLE)) || BUILDFLAG(IS_FUCHSIA)
 #define PA_HAS_FAST_MUTEX
 #endif

 // If set to 1, enables zeroing memory on Free() with roughly 1% probability.
 // This applies only to normal buckets, as direct-map allocations are always
 // decommitted.
 // TODO(bartekn): Re-enable once PartitionAlloc-Everywhere evaluation is done.
 #if 0
 #define PA_ZERO_RANDOMLY_ON_FREE
 #endif

 // Need TLS support.
 #if BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_WIN) || BUILDFLAG(IS_FUCHSIA)
 #define PA_THREAD_CACHE_SUPPORTED
 #endif

 // Too expensive for official builds, as it adds cache misses to all
 // allocations. On the other hand, we want wide metrics coverage to get
 // realistic profiles.
 #if BUILDFLAG(USE_PARTITION_ALLOC_AS_MALLOC) && !defined(OFFICIAL_BUILD)
 #define PA_THREAD_CACHE_ALLOC_STATS
 #endif

 // Optional statistics collection. Lightweight, contrary to the ones above,
 // hence enabled by default.
 #define PA_THREAD_CACHE_ENABLE_STATISTICS

 // Enable free list shadow entry to strengthen hardening as much as possible.
 // The shadow entry is an inversion (bitwise-NOT) of the encoded `next` pointer.
 //
 // Disabled when ref-count is placed in the previous slot, as it will overlap
 // with the shadow for the smallest slots.
 //
 // Disabled on Big Endian CPUs, because encoding is also a bitwise-NOT there,
 // making the shadow entry equal to the original, valid pointer to the next
 // slot. In case Use-after-Free happens, we'd rather not hand out a valid,
 // ready-to-use pointer.
 #if !BUILDFLAG(PUT_REF_COUNT_IN_PREVIOUS_SLOT) && \
     defined(ARCH_CPU_LITTLE_ENDIAN)
 #define PA_HAS_FREELIST_SHADOW_ENTRY
 #endif

 // Specifies whether allocation extras need to be added.
 #if BUILDFLAG(PA_DCHECK_IS_ON) || BUILDFLAG(USE_BACKUP_REF_PTR)
 #define PA_EXTRAS_REQUIRED
 #endif

 // Count and total wall clock time spent in memory related system calls. This
 // doesn't cover all system calls, in particular the ones related to locking.
 //
 // Not enabled by default, as it has a runtime cost, and causes issues with some
 // builds (e.g. Windows).
 // However the total count is collected on all platforms.
 // #define PA_COUNT_SYSCALL_TIME

 // On Windows, |thread_local| variables cannot be marked "dllexport", see
 // compiler error C2492 at
 // https://docs.microsoft.com/en-us/cpp/error-messages/compiler-errors-1/compiler-error-c2492?view=msvc-160.
 // Don't use it there.
 //
 // On macOS and iOS:
 // - With PartitionAlloc-Everywhere, thread_local allocates, reentering the
 //   allocator.
 // - Component builds triggered a clang bug: crbug.com/1243375
 //
 // Regardless, the "normal" TLS access is fast on x86_64 (see partition_tls.h),
 // so don't bother with thread_local anywhere.
 #if !(BUILDFLAG(IS_WIN) && defined(COMPONENT_BUILD)) && !BUILDFLAG(IS_APPLE)
 #define PA_THREAD_LOCAL_TLS
 #endif

 // When PartitionAlloc is malloc(), detect malloc() becoming re-entrant by
 // calling malloc() again.
 //
 // Limitations:
 // - BUILDFLAG(PA_DCHECK_IS_ON) due to runtime cost
 // - thread_local TLS to simplify the implementation
 // - Not on Android due to bot failures
 #if BUILDFLAG(PA_DCHECK_IS_ON) && BUILDFLAG(USE_PARTITION_ALLOC_AS_MALLOC) && \
     defined(PA_THREAD_LOCAL_TLS) && !BUILDFLAG(IS_ANDROID)
 #define PA_HAS_ALLOCATION_GUARD
 #endif

 #if defined(ARCH_CPU_ARM64) && defined(__clang__) && \
     (BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_ANDROID))
 static_assert(sizeof(void*) == 8);
 #define PA_HAS_MEMORY_TAGGING
 #endif

 // Lazy commit should only be enabled on Windows, because commit charge is
 // only meaningful and limited on Windows. It affects performance on other
 // platforms and is simply not needed there due to OS supporting overcommit.
 #if BUILDFLAG(IS_WIN)
 constexpr bool kUseLazyCommit = true;
 #else
 constexpr bool kUseLazyCommit = false;
 #endif

 // On these platforms, lock all the partitions before fork(), and unlock after.
 // This may be required on more platforms in the future.
 #if BUILDFLAG(IS_APPLE) || BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
 #define PA_HAS_ATFORK_HANDLER
 #endif

 // PartitionAlloc uses PartitionRootEnumerator to acquire all
 // PartitionRoots at BeforeFork and to release at AfterFork.
 #if BUILDFLAG(USE_PARTITION_ALLOC_AS_MALLOC) && defined(PA_HAS_ATFORK_HANDLER)
 #define PA_USE_PARTITION_ROOT_ENUMERATOR
 #endif

 // Due to potential conflict with the free list pointer in the "previous slot"
 // mode in the smallest bucket, we can't check both the cookie and the dangling
 // raw_ptr at the same time.
 #if !(BUILDFLAG(ENABLE_DANGLING_RAW_PTR_CHECKS) &&  \
       BUILDFLAG(PUT_REF_COUNT_IN_PREVIOUS_SLOT)) && \
     (BUILDFLAG(PA_DCHECK_IS_ON) ||                  \
      BUILDFLAG(ENABLE_BACKUP_REF_PTR_SLOW_CHECKS))
 #define PA_REF_COUNT_CHECK_COOKIE
 #endif

 // Use available space in the reference count to store the initially requested
 // size from the application. This is used for debugging, hence disabled by
 // default.
 // #define PA_REF_COUNT_STORE_REQUESTED_SIZE

 #if defined(PA_REF_COUNT_STORE_REQUESTED_SIZE) && \
     defined(PA_REF_COUNT_CHECK_COOKIE)
 #error "Cannot use a cookie *and* store the allocation size"
 #endif

 // Prefer smaller slot spans.
 //
 // Smaller slot spans may improve dirty memory fragmentation, but may also
 // increase address space usage.
 //
 // This is intended to roll out more broadly, but only enabled on Linux for now
 // to get performance bot and real-world data pre-A/B experiment.
 //
 // Also enabled on ARM64 macOS, as the 16kiB pages on this platform lead to
 // larger slot spans.
 #if BUILDFLAG(IS_LINUX) || (BUILDFLAG(IS_MAC) && defined(ARCH_CPU_ARM64))
 #define PA_PREFER_SMALLER_SLOT_SPANS
 #endif  // BUILDFLAG(IS_LINUX)

 // Build MTECheckedPtr code.
 //
 // Only applicable to code with 64-bit pointers. Currently conflicts with true
 // hardware MTE.
 #if BUILDFLAG(USE_MTE_CHECKED_PTR) && defined(PA_HAS_64_BITS_POINTERS) && \
     !defined(PA_HAS_MEMORY_TAGGING)
 #define PA_USE_MTE_CHECKED_PTR_WITH_64_BITS_POINTERS
 #endif  // BUILDFLAG(USE_MTE_CHECKED_PTR) && defined(PA_HAS_64_BITS_POINTERS) &&
         // !defined(PA_HAS_MEMORY_TAGGING)

 #endif  // BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_ALLOC_CONFIG_H_
	// Copyright 2021 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.

	#ifndef BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_ALLOC_CONFIG_H_
	#define BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_ALLOC_CONFIG_H_

	#include "base/allocator/buildflags.h"
	#include "build/build_config.h"

	// ARCH_CPU_64_BITS implies 64-bit instruction set, but not necessarily 64-bit
	// address space. The only known case where address space is 32-bit is NaCl, so
	// eliminate it explicitly. static_assert below ensures that others won't slip
	// through.
	#if defined(ARCH_CPU_64_BITS) && !BUILDFLAG(IS_NACL)
	#define PA_HAS_64_BITS_POINTERS
	static_assert(sizeof(void*) == 8, "");
	#else
	static_assert(sizeof(void*) != 8, "");
	#endif

	// PCScan supports 64 bits only.
	#if defined(PA_HAS_64_BITS_POINTERS)
	#define PA_ALLOW_PCSCAN
	#endif

	#if defined(PA_HAS_64_BITS_POINTERS) && \
	(defined(__ARM_NEON) \|\| defined(__ARM_NEON__)) && defined(__ARM_FP)
	#define PA_STARSCAN_NEON_SUPPORTED
	#endif

	#if BUILDFLAG(IS_IOS)
	// Use dynamically sized GigaCage. This allows to query the size at run-time,
	// before initialization, instead of using a hardcoded constexpr. This is needed
	// on iOS because iOS test processes can't handle a large cage (see
	// crbug.com/1250788).
	#define PA_USE_DYNAMICALLY_SIZED_GIGA_CAGE
	#endif

	#if defined(PA_HAS_64_BITS_POINTERS) && \
	(BUILDFLAG(IS_LINUX) \|\| BUILDFLAG(IS_ANDROID))
	#include <linux/version.h>
	// TODO(bikineev): Enable for ChromeOS.
	#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 8, 0)
	#define PA_STARSCAN_UFFD_WRITE_PROTECTOR_SUPPORTED
	#endif
	#endif // defined(PA_HAS_64_BITS_POINTERS) &&
	// (BUILDFLAG(IS_LINUX) \|\| BUILDFLAG(IS_ANDROID))

	#if defined(PA_HAS_64_BITS_POINTERS)
	// Use card table to avoid races for PCScan configuration without safepoints.
	// The card table provides the guaranteee that for a marked card the underling
	// super-page is fully initialized.
	#define PA_STARSCAN_USE_CARD_TABLE 1
	#else
	// The card table is permanently disabled for 32-bit.
	#define PA_STARSCAN_USE_CARD_TABLE 0
	#endif // defined(PA_HAS_64_BITS_POINTERS)

	#if PA_STARSCAN_USE_CARD_TABLE && !defined(PA_ALLOW_PCSCAN)
	#error "Card table can only be used when *Scan is allowed"
	#endif

	// Use batched freeing when sweeping pages. This builds up a freelist in the
	// scanner thread and appends to the slot-span's freelist only once.
	#define PA_STARSCAN_BATCHED_FREE 1

	// POSIX is not only UNIX, e.g. macOS and other OSes. We do use Linux-specific
	// features such as futex(2).
	#if BUILDFLAG(IS_LINUX) \|\| BUILDFLAG(IS_CHROMEOS) \|\| BUILDFLAG(IS_ANDROID)
	#define PA_HAS_LINUX_KERNEL
	#endif

	// On some platforms, we implement locking by spinning in userspace, then going
	// into the kernel only if there is contention. This requires platform support,
	// namely:
	// - On Linux, futex(2)
	// - On Windows, a fast userspace "try" operation which is available
	// with SRWLock
	// - Otherwise, a fast userspace pthread_mutex_trylock().
	//
	// On macOS, pthread_mutex_trylock() is fast by default starting with macOS
	// 10.14. Chromium targets an earlier version, so it cannot be known at
	// compile-time. So we use something different. On other POSIX systems, we
	// assume that pthread_mutex_trylock() is suitable.
	//
	// Otherwise, a userspace spinlock implementation is used.
	#if defined(PA_HAS_LINUX_KERNEL) \|\| BUILDFLAG(IS_WIN) \|\| \
	(BUILDFLAG(IS_POSIX) && !BUILDFLAG(IS_APPLE)) \|\| BUILDFLAG(IS_FUCHSIA)
	#define PA_HAS_FAST_MUTEX
	#endif

	// If set to 1, enables zeroing memory on Free() with roughly 1% probability.
	// This applies only to normal buckets, as direct-map allocations are always
	// decommitted.
	// TODO(bartekn): Re-enable once PartitionAlloc-Everywhere evaluation is done.
	#if 0
	#define PA_ZERO_RANDOMLY_ON_FREE
	#endif

	// Need TLS support.
	#if BUILDFLAG(IS_POSIX) \|\| BUILDFLAG(IS_WIN) \|\| BUILDFLAG(IS_FUCHSIA)
	#define PA_THREAD_CACHE_SUPPORTED
	#endif

	// Too expensive for official builds, as it adds cache misses to all
	// allocations. On the other hand, we want wide metrics coverage to get
	// realistic profiles.
	#if BUILDFLAG(USE_PARTITION_ALLOC_AS_MALLOC) && !defined(OFFICIAL_BUILD)
	#define PA_THREAD_CACHE_ALLOC_STATS
	#endif

	// Optional statistics collection. Lightweight, contrary to the ones above,
	// hence enabled by default.
	#define PA_THREAD_CACHE_ENABLE_STATISTICS

	// Enable free list shadow entry to strengthen hardening as much as possible.
	// The shadow entry is an inversion (bitwise-NOT) of the encoded `next` pointer.
	//
	// Disabled when ref-count is placed in the previous slot, as it will overlap
	// with the shadow for the smallest slots.
	//
	// Disabled on Big Endian CPUs, because encoding is also a bitwise-NOT there,
	// making the shadow entry equal to the original, valid pointer to the next
	// slot. In case Use-after-Free happens, we'd rather not hand out a valid,
	// ready-to-use pointer.
	#if !BUILDFLAG(PUT_REF_COUNT_IN_PREVIOUS_SLOT) && \
	defined(ARCH_CPU_LITTLE_ENDIAN)
	#define PA_HAS_FREELIST_SHADOW_ENTRY
	#endif

	// Specifies whether allocation extras need to be added.
	#if BUILDFLAG(PA_DCHECK_IS_ON) \|\| BUILDFLAG(USE_BACKUP_REF_PTR)
	#define PA_EXTRAS_REQUIRED
	#endif

	// Count and total wall clock time spent in memory related system calls. This
	// doesn't cover all system calls, in particular the ones related to locking.
	//
	// Not enabled by default, as it has a runtime cost, and causes issues with some
	// builds (e.g. Windows).
	// However the total count is collected on all platforms.
	// #define PA_COUNT_SYSCALL_TIME

	// On Windows, \|thread_local\| variables cannot be marked "dllexport", see
	// compiler error C2492 at
	// https://docs.microsoft.com/en-us/cpp/error-messages/compiler-errors-1/compiler-error-c2492?view=msvc-160.
	// Don't use it there.
	//
	// On macOS and iOS:
	// - With PartitionAlloc-Everywhere, thread_local allocates, reentering the
	// allocator.
	// - Component builds triggered a clang bug: crbug.com/1243375
	//
	// Regardless, the "normal" TLS access is fast on x86_64 (see partition_tls.h),
	// so don't bother with thread_local anywhere.
	#if !(BUILDFLAG(IS_WIN) && defined(COMPONENT_BUILD)) && !BUILDFLAG(IS_APPLE)
	#define PA_THREAD_LOCAL_TLS
	#endif

	// When PartitionAlloc is malloc(), detect malloc() becoming re-entrant by
	// calling malloc() again.
	//
	// Limitations:
	// - BUILDFLAG(PA_DCHECK_IS_ON) due to runtime cost
	// - thread_local TLS to simplify the implementation
	// - Not on Android due to bot failures
	#if BUILDFLAG(PA_DCHECK_IS_ON) && BUILDFLAG(USE_PARTITION_ALLOC_AS_MALLOC) && \
	defined(PA_THREAD_LOCAL_TLS) && !BUILDFLAG(IS_ANDROID)
	#define PA_HAS_ALLOCATION_GUARD
	#endif

	#if defined(ARCH_CPU_ARM64) && defined(__clang__) && \
	(BUILDFLAG(IS_LINUX) \|\| BUILDFLAG(IS_ANDROID))
	static_assert(sizeof(void*) == 8);
	#define PA_HAS_MEMORY_TAGGING
	#endif

	// Lazy commit should only be enabled on Windows, because commit charge is
	// only meaningful and limited on Windows. It affects performance on other
	// platforms and is simply not needed there due to OS supporting overcommit.
	#if BUILDFLAG(IS_WIN)
	constexpr bool kUseLazyCommit = true;
	#else
	constexpr bool kUseLazyCommit = false;
	#endif

	// On these platforms, lock all the partitions before fork(), and unlock after.
	// This may be required on more platforms in the future.
	#if BUILDFLAG(IS_APPLE) \|\| BUILDFLAG(IS_LINUX) \|\| BUILDFLAG(IS_CHROMEOS)
	#define PA_HAS_ATFORK_HANDLER
	#endif

	// PartitionAlloc uses PartitionRootEnumerator to acquire all
	// PartitionRoots at BeforeFork and to release at AfterFork.
	#if BUILDFLAG(USE_PARTITION_ALLOC_AS_MALLOC) && defined(PA_HAS_ATFORK_HANDLER)
	#define PA_USE_PARTITION_ROOT_ENUMERATOR
	#endif

	// Due to potential conflict with the free list pointer in the "previous slot"
	// mode in the smallest bucket, we can't check both the cookie and the dangling
	// raw_ptr at the same time.
	#if !(BUILDFLAG(ENABLE_DANGLING_RAW_PTR_CHECKS) && \
	BUILDFLAG(PUT_REF_COUNT_IN_PREVIOUS_SLOT)) && \
	(BUILDFLAG(PA_DCHECK_IS_ON) \|\| \
	BUILDFLAG(ENABLE_BACKUP_REF_PTR_SLOW_CHECKS))
	#define PA_REF_COUNT_CHECK_COOKIE
	#endif

	// Use available space in the reference count to store the initially requested
	// size from the application. This is used for debugging, hence disabled by
	// default.
	// #define PA_REF_COUNT_STORE_REQUESTED_SIZE

	#if defined(PA_REF_COUNT_STORE_REQUESTED_SIZE) && \
	defined(PA_REF_COUNT_CHECK_COOKIE)
	#error "Cannot use a cookie and store the allocation size"
	#endif

	// Prefer smaller slot spans.
	//
	// Smaller slot spans may improve dirty memory fragmentation, but may also
	// increase address space usage.
	//
	// This is intended to roll out more broadly, but only enabled on Linux for now
	// to get performance bot and real-world data pre-A/B experiment.
	//
	// Also enabled on ARM64 macOS, as the 16kiB pages on this platform lead to
	// larger slot spans.
	#if BUILDFLAG(IS_LINUX) \|\| (BUILDFLAG(IS_MAC) && defined(ARCH_CPU_ARM64))
	#define PA_PREFER_SMALLER_SLOT_SPANS
	#endif // BUILDFLAG(IS_LINUX)

	// Build MTECheckedPtr code.
	//
	// Only applicable to code with 64-bit pointers. Currently conflicts with true
	// hardware MTE.
	#if BUILDFLAG(USE_MTE_CHECKED_PTR) && defined(PA_HAS_64_BITS_POINTERS) && \
	!defined(PA_HAS_MEMORY_TAGGING)
	#define PA_USE_MTE_CHECKED_PTR_WITH_64_BITS_POINTERS
	#endif // BUILDFLAG(USE_MTE_CHECKED_PTR) && defined(PA_HAS_64_BITS_POINTERS) &&
	// !defined(PA_HAS_MEMORY_TAGGING)

	#endif // BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_ALLOC_CONFIG_H_