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//===---------- emutls.c - Implements __emutls_get_address ---------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include "int_lib.h"
#ifdef __BIONIC__
// There are 4 pthread key cleanup rounds on Bionic. Delay emutls deallocation
// to round 2. We need to delay deallocation because:
// - Android versions older than M lack __cxa_thread_atexit_impl, so apps
// use a pthread key destructor to call C++ destructors.
// - Apps might use __thread/thread_local variables in pthread destructors.
// We can't wait until the final two rounds, because jemalloc needs two rounds
// after the final malloc/free call to free its thread-specific data (see
// https://reviews.llvm.org/D46978#1107507).
#define EMUTLS_SKIP_DESTRUCTOR_ROUNDS 1
#else
#define EMUTLS_SKIP_DESTRUCTOR_ROUNDS 0
#endif
#if defined(_MSC_VER) && !defined(__clang__)
// MSVC raises a warning about a nonstandard extension being used for the 0
// sized element in this array. Disable this for warn-as-error builds.
#pragma warning(push)
#pragma warning(disable : 4200)
#endif
typedef struct emutls_address_array {
uintptr_t skip_destructor_rounds;
uintptr_t size; // number of elements in the 'data' array
void *data[];
} emutls_address_array;
#if defined(_MSC_VER) && !defined(__clang__)
#pragma warning(pop)
#endif
static void emutls_shutdown(emutls_address_array *array);
#ifndef _WIN32
#include <pthread.h>
static pthread_mutex_t emutls_mutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_key_t emutls_pthread_key;
static bool emutls_key_created = false;
typedef unsigned int gcc_word __attribute__((mode(word)));
typedef unsigned int gcc_pointer __attribute__((mode(pointer)));
// Default is not to use posix_memalign, so systems like Android
// can use thread local data without heavier POSIX memory allocators.
#ifndef EMUTLS_USE_POSIX_MEMALIGN
#define EMUTLS_USE_POSIX_MEMALIGN 0
#endif
static __inline void *emutls_memalign_alloc(size_t align, size_t size) {
void *base;
#if EMUTLS_USE_POSIX_MEMALIGN
if (posix_memalign(&base, align, size) != 0)
abort();
#else
#define EXTRA_ALIGN_PTR_BYTES (align - 1 + sizeof(void *))
char *object;
if ((object = (char *)malloc(EXTRA_ALIGN_PTR_BYTES + size)) == NULL)
abort();
base = (void *)(((uintptr_t)(object + EXTRA_ALIGN_PTR_BYTES)) &
~(uintptr_t)(align - 1));
((void **)base)[-1] = object;
#endif
return base;
}
static __inline void emutls_memalign_free(void *base) {
#if EMUTLS_USE_POSIX_MEMALIGN
free(base);
#else
// The mallocated address is in ((void**)base)[-1]
free(((void **)base)[-1]);
#endif
}
static __inline void emutls_setspecific(emutls_address_array *value) {
pthread_setspecific(emutls_pthread_key, (void *)value);
}
static __inline emutls_address_array *emutls_getspecific(void) {
return (emutls_address_array *)pthread_getspecific(emutls_pthread_key);
}
static void emutls_key_destructor(void *ptr) {
emutls_address_array *array = (emutls_address_array *)ptr;
if (array->skip_destructor_rounds > 0) {
// emutls is deallocated using a pthread key destructor. These
// destructors are called in several rounds to accommodate destructor
// functions that (re)initialize key values with pthread_setspecific.
// Delay the emutls deallocation to accommodate other end-of-thread
// cleanup tasks like calling thread_local destructors (e.g. the
// __cxa_thread_atexit fallback in libc++abi).
array->skip_destructor_rounds--;
emutls_setspecific(array);
} else {
emutls_shutdown(array);
free(ptr);
}
}
static __inline void emutls_init(void) {
if (pthread_key_create(&emutls_pthread_key, emutls_key_destructor) != 0)
abort();
emutls_key_created = true;
}
static __inline void emutls_init_once(void) {
static pthread_once_t once = PTHREAD_ONCE_INIT;
pthread_once(&once, emutls_init);
}
static __inline void emutls_lock(void) { pthread_mutex_lock(&emutls_mutex); }
static __inline void emutls_unlock(void) { pthread_mutex_unlock(&emutls_mutex); }
#else // _WIN32
#include <assert.h>
#include <malloc.h>
#include <stdio.h>
#include <windows.h>
static LPCRITICAL_SECTION emutls_mutex;
static DWORD emutls_tls_index = TLS_OUT_OF_INDEXES;
typedef uintptr_t gcc_word;
typedef void *gcc_pointer;
static void win_error(DWORD last_err, const char *hint) {
char *buffer = NULL;
if (FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM |
FORMAT_MESSAGE_MAX_WIDTH_MASK,
NULL, last_err, 0, (LPSTR)&buffer, 1, NULL)) {
fprintf(stderr, "Windows error: %s\n", buffer);
} else {
fprintf(stderr, "Unknown Windows error: %s\n", hint);
}
LocalFree(buffer);
}
static __inline void win_abort(DWORD last_err, const char *hint) {
win_error(last_err, hint);
abort();
}
static __inline void *emutls_memalign_alloc(size_t align, size_t size) {
void *base = _aligned_malloc(size, align);
if (!base)
win_abort(GetLastError(), "_aligned_malloc");
return base;
}
static __inline void emutls_memalign_free(void *base) { _aligned_free(base); }
static void emutls_exit(void) {
if (emutls_mutex) {
DeleteCriticalSection(emutls_mutex);
_aligned_free(emutls_mutex);
emutls_mutex = NULL;
}
if (emutls_tls_index != TLS_OUT_OF_INDEXES) {
emutls_shutdown((emutls_address_array *)TlsGetValue(emutls_tls_index));
TlsFree(emutls_tls_index);
emutls_tls_index = TLS_OUT_OF_INDEXES;
}
}
static BOOL CALLBACK emutls_init(PINIT_ONCE p0, PVOID p1, PVOID *p2) {
(void)p0;
(void)p1;
(void)p2;
emutls_mutex =
(LPCRITICAL_SECTION)_aligned_malloc(sizeof(CRITICAL_SECTION), 16);
if (!emutls_mutex) {
win_error(GetLastError(), "_aligned_malloc");
return FALSE;
}
InitializeCriticalSection(emutls_mutex);
emutls_tls_index = TlsAlloc();
if (emutls_tls_index == TLS_OUT_OF_INDEXES) {
emutls_exit();
win_error(GetLastError(), "TlsAlloc");
return FALSE;
}
atexit(&emutls_exit);
return TRUE;
}
static __inline void emutls_init_once(void) {
static INIT_ONCE once;
InitOnceExecuteOnce(&once, emutls_init, NULL, NULL);
}
static __inline void emutls_lock(void) { EnterCriticalSection(emutls_mutex); }
static __inline void emutls_unlock(void) { LeaveCriticalSection(emutls_mutex); }
static __inline void emutls_setspecific(emutls_address_array *value) {
if (TlsSetValue(emutls_tls_index, (LPVOID)value) == 0)
win_abort(GetLastError(), "TlsSetValue");
}
static __inline emutls_address_array *emutls_getspecific(void) {
LPVOID value = TlsGetValue(emutls_tls_index);
if (value == NULL) {
const DWORD err = GetLastError();
if (err != ERROR_SUCCESS)
win_abort(err, "TlsGetValue");
}
return (emutls_address_array *)value;
}
// Provide atomic load/store functions for emutls_get_index if built with MSVC.
#if !defined(__ATOMIC_RELEASE)
#include <intrin.h>
enum { __ATOMIC_ACQUIRE = 2, __ATOMIC_RELEASE = 3 };
static __inline uintptr_t __atomic_load_n(void *ptr, unsigned type) {
assert(type == __ATOMIC_ACQUIRE);
// These return the previous value - but since we do an OR with 0,
// it's equivalent to a plain load.
#ifdef _WIN64
return InterlockedOr64(ptr, 0);
#else
return InterlockedOr(ptr, 0);
#endif
}
static __inline void __atomic_store_n(void *ptr, uintptr_t val, unsigned type) {
assert(type == __ATOMIC_RELEASE);
InterlockedExchangePointer((void *volatile *)ptr, (void *)val);
}
#endif // __ATOMIC_RELEASE
#endif // _WIN32
static size_t emutls_num_object = 0; // number of allocated TLS objects
// Free the allocated TLS data
static void emutls_shutdown(emutls_address_array *array) {
if (array) {
uintptr_t i;
for (i = 0; i < array->size; ++i) {
if (array->data[i])
emutls_memalign_free(array->data[i]);
}
}
}
// For every TLS variable xyz,
// there is one __emutls_control variable named __emutls_v.xyz.
// If xyz has non-zero initial value, __emutls_v.xyz's "value"
// will point to __emutls_t.xyz, which has the initial value.
typedef struct __emutls_control {
// Must use gcc_word here, instead of size_t, to match GCC. When
// gcc_word is larger than size_t, the upper extra bits are all
// zeros. We can use variables of size_t to operate on size and
// align.
gcc_word size; // size of the object in bytes
gcc_word align; // alignment of the object in bytes
union {
uintptr_t index; // data[index-1] is the object address
void *address; // object address, when in single thread env
} object;
void *value; // null or non-zero initial value for the object
} __emutls_control;
// Emulated TLS objects are always allocated at run-time.
static __inline void *emutls_allocate_object(__emutls_control *control) {
// Use standard C types, check with gcc's emutls.o.
COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(gcc_pointer));
COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(void *));
size_t size = control->size;
size_t align = control->align;
void *base;
if (align < sizeof(void *))
align = sizeof(void *);
// Make sure that align is power of 2.
if ((align & (align - 1)) != 0)
abort();
base = emutls_memalign_alloc(align, size);
if (control->value)
memcpy(base, control->value, size);
else
memset(base, 0, size);
return base;
}
// Returns control->object.index; set index if not allocated yet.
static __inline uintptr_t emutls_get_index(__emutls_control *control) {
uintptr_t index = __atomic_load_n(&control->object.index, __ATOMIC_ACQUIRE);
if (!index) {
emutls_init_once();
emutls_lock();
index = control->object.index;
if (!index) {
index = ++emutls_num_object;
__atomic_store_n(&control->object.index, index, __ATOMIC_RELEASE);
}
emutls_unlock();
}
return index;
}
// Updates newly allocated thread local emutls_address_array.
static __inline void emutls_check_array_set_size(emutls_address_array *array,
uintptr_t size) {
if (array == NULL)
abort();
array->size = size;
emutls_setspecific(array);
}
// Returns the new 'data' array size, number of elements,
// which must be no smaller than the given index.
static __inline uintptr_t emutls_new_data_array_size(uintptr_t index) {
// Need to allocate emutls_address_array with extra slots
// to store the header.
// Round up the emutls_address_array size to multiple of 16.
uintptr_t header_words = sizeof(emutls_address_array) / sizeof(void *);
return ((index + header_words + 15) & ~((uintptr_t)15)) - header_words;
}
// Returns the size in bytes required for an emutls_address_array with
// N number of elements for data field.
static __inline uintptr_t emutls_asize(uintptr_t N) {
return N * sizeof(void *) + sizeof(emutls_address_array);
}
// Returns the thread local emutls_address_array.
// Extends its size if necessary to hold address at index.
static __inline emutls_address_array *
emutls_get_address_array(uintptr_t index) {
emutls_address_array *array = emutls_getspecific();
if (array == NULL) {
uintptr_t new_size = emutls_new_data_array_size(index);
array = (emutls_address_array *)malloc(emutls_asize(new_size));
if (array) {
memset(array->data, 0, new_size * sizeof(void *));
array->skip_destructor_rounds = EMUTLS_SKIP_DESTRUCTOR_ROUNDS;
}
emutls_check_array_set_size(array, new_size);
} else if (index > array->size) {
uintptr_t orig_size = array->size;
uintptr_t new_size = emutls_new_data_array_size(index);
array = (emutls_address_array *)realloc(array, emutls_asize(new_size));
if (array)
memset(array->data + orig_size, 0,
(new_size - orig_size) * sizeof(void *));
emutls_check_array_set_size(array, new_size);
}
return array;
}
#ifndef _WIN32
// Our emulated TLS implementation relies on local state (e.g. for the pthread
// key), and if we duplicate this state across different shared libraries,
// accesses to the same TLS variable from different shared libraries will yield
// different results (see https://github.com/android/ndk/issues/1551 for an
// example). __emutls_get_address is the only external entry point for emulated
// TLS, and by making it default visibility and weak, we can rely on the dynamic
// linker to coalesce multiple copies at runtime and ensure a single unique copy
// of TLS state. This is a best effort; it won't work if the user is linking
// with -Bsymbolic or -Bsymbolic-functions, and it also won't work on Windows,
// where the dynamic linker has no notion of coalescing weak symbols at runtime.
// A more robust solution would be to create a separate shared library for
// emulated TLS, to ensure a single copy of its state.
__attribute__((visibility("default"), weak))
#endif
void *__emutls_get_address(__emutls_control *control) {
uintptr_t index = emutls_get_index(control);
emutls_address_array *array = emutls_get_address_array(index--);
if (array->data[index] == NULL)
array->data[index] = emutls_allocate_object(control);
return array->data[index];
}
#ifdef __BIONIC__
// Called by Bionic on dlclose to delete the emutls pthread key.
__attribute__((visibility("hidden"))) void __emutls_unregister_key(void) {
if (emutls_key_created) {
pthread_key_delete(emutls_pthread_key);
emutls_key_created = false;
}
}
#endif