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- // Copyright 2020 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_TLS_H_
- #define BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_TLS_H_
- #include "base/allocator/partition_allocator/partition_alloc_base/compiler_specific.h"
- #include "base/allocator/partition_allocator/partition_alloc_base/component_export.h"
- #include "base/allocator/partition_allocator/partition_alloc_base/immediate_crash.h"
- #include "base/allocator/partition_allocator/partition_alloc_check.h"
- #include "build/build_config.h"
- #if BUILDFLAG(IS_POSIX)
- #include <pthread.h>
- #endif
- #if BUILDFLAG(IS_WIN)
- #include "base/allocator/partition_allocator/partition_alloc_base/win/windows_types.h"
- #endif
- // Barebones TLS implementation for use in PartitionAlloc. This doesn't use the
- // general chromium TLS handling to avoid dependencies, but more importantly
- // because it allocates memory.
- namespace partition_alloc::internal {
- #if BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
- using PartitionTlsKey = pthread_key_t;
- // Only on x86_64, the implementation is not stable on ARM64. For instance, in
- // macOS 11, the TPIDRRO_EL0 registers holds the CPU index in the low bits,
- // which is not the case in macOS 12. See libsyscall/os/tsd.h in XNU
- // (_os_tsd_get_direct() is used by pthread_getspecific() internally).
- #if BUILDFLAG(IS_MAC) && defined(ARCH_CPU_X86_64)
- namespace {
- PA_ALWAYS_INLINE void* FastTlsGet(PartitionTlsKey index) {
- // On macOS, pthread_getspecific() is in libSystem, so a call to it has to go
- // through PLT. However, and contrary to some other platforms, *all* TLS keys
- // are in a static array in the thread structure. So they are *always* at a
- // fixed offset from the segment register holding the thread structure
- // address.
- //
- // We could use _pthread_getspecific_direct(), but it is not
- // exported. However, on all macOS versions we support, the TLS array is at
- // %gs. This is used in V8 to back up InternalGetExistingThreadLocal(), and
- // can also be seen by looking at pthread_getspecific() disassembly:
- //
- // libsystem_pthread.dylib`pthread_getspecific:
- // libsystem_pthread.dylib[0x7ff800316099] <+0>: movq %gs:(,%rdi,8), %rax
- // libsystem_pthread.dylib[0x7ff8003160a2] <+9>: retq
- //
- // This function is essentially inlining the content of pthread_getspecific()
- // here.
- intptr_t result;
- static_assert(sizeof index <= sizeof(intptr_t));
- asm("movq %%gs:(,%1,8), %0;"
- : "=r"(result)
- : "r"(static_cast<intptr_t>(index)));
- return reinterpret_cast<void*>(result);
- }
- } // namespace
- #endif // BUILDFLAG(IS_MAC) && defined(ARCH_CPU_X86_64)
- PA_ALWAYS_INLINE bool PartitionTlsCreate(PartitionTlsKey* key,
- void (*destructor)(void*)) {
- return !pthread_key_create(key, destructor);
- }
- PA_ALWAYS_INLINE void* PartitionTlsGet(PartitionTlsKey key) {
- #if BUILDFLAG(IS_MAC) && defined(ARCH_CPU_X86_64)
- PA_DCHECK(pthread_getspecific(key) == FastTlsGet(key));
- return FastTlsGet(key);
- #else
- return pthread_getspecific(key);
- #endif
- }
- PA_ALWAYS_INLINE void PartitionTlsSet(PartitionTlsKey key, void* value) {
- int ret = pthread_setspecific(key, value);
- PA_DCHECK(!ret);
- }
- #elif BUILDFLAG(IS_WIN)
- // Note: supports only a single TLS key on Windows. Not a hard constraint, may
- // be lifted.
- using PartitionTlsKey = unsigned long;
- PA_COMPONENT_EXPORT(PARTITION_ALLOC)
- bool PartitionTlsCreate(PartitionTlsKey* key, void (*destructor)(void*));
- PA_ALWAYS_INLINE void* PartitionTlsGet(PartitionTlsKey key) {
- // Accessing TLS resets the last error, which then makes |GetLastError()|
- // return something misleading. While this means that properly using
- // |GetLastError()| is difficult, there is currently code in Chromium which
- // expects malloc() to *not* reset it. Meaning that we either have to fix this
- // code, or pay the cost of saving/restoring it.
- //
- // Source:
- // https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-tlsgetvalue
- // "Functions that return indications of failure call SetLastError() when they
- // fail. They generally do not call SetLastError() when they succeed. The
- // TlsGetValue() function is an exception to this general rule. The
- // TlsGetValue() function calls SetLastError() to clear a thread's last error
- // when it succeeds."
- DWORD saved_error = GetLastError();
- void* ret = TlsGetValue(key);
- // Only non-zero errors need to be restored.
- if (PA_UNLIKELY(saved_error))
- SetLastError(saved_error);
- return ret;
- }
- PA_ALWAYS_INLINE void PartitionTlsSet(PartitionTlsKey key, void* value) {
- BOOL ret = TlsSetValue(key, value);
- PA_DCHECK(ret);
- }
- // Registers a callback for DLL_PROCESS_DETACH events.
- void PartitionTlsSetOnDllProcessDetach(void (*callback)());
- #else
- // Not supported.
- using PartitionTlsKey = int;
- PA_ALWAYS_INLINE bool PartitionTlsCreate(PartitionTlsKey* key,
- void (*destructor)(void*)) {
- // NOTIMPLEMENTED() may allocate, crash instead.
- PA_IMMEDIATE_CRASH();
- }
- PA_ALWAYS_INLINE void* PartitionTlsGet(PartitionTlsKey key) {
- PA_IMMEDIATE_CRASH();
- }
- PA_ALWAYS_INLINE void PartitionTlsSet(PartitionTlsKey key, void* value) {
- PA_IMMEDIATE_CRASH();
- }
- #endif // BUILDFLAG(IS_WIN)
- } // namespace partition_alloc::internal
- #endif // BASE_ALLOCATOR_PARTITION_ALLOCATOR_PARTITION_TLS_H_
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