1//===---------- emutls.c - Implements __emutls_get_address ---------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include <stdint.h>
10#include <stdlib.h>
11#include <string.h>
12
13#include "int_lib.h"
14
15#ifdef __BIONIC__
16// There are 4 pthread key cleanup rounds on Bionic. Delay emutls deallocation
17// to round 2. We need to delay deallocation because:
18// - Android versions older than M lack __cxa_thread_atexit_impl, so apps
19// use a pthread key destructor to call C++ destructors.
20// - Apps might use __thread/thread_local variables in pthread destructors.
21// We can't wait until the final two rounds, because jemalloc needs two rounds
22// after the final malloc/free call to free its thread-specific data (see
23// https://reviews.llvm.org/D46978#1107507).
24#define EMUTLS_SKIP_DESTRUCTOR_ROUNDS 1
25#else
26#define EMUTLS_SKIP_DESTRUCTOR_ROUNDS 0
27#endif
28
29#if defined(_MSC_VER) && !defined(__clang__)
30// MSVC raises a warning about a nonstandard extension being used for the 0
31// sized element in this array. Disable this for warn-as-error builds.
32#pragma warning(push)
33#pragma warning(disable : 4200)
34#endif
35
36typedef struct emutls_address_array {
37 uintptr_t skip_destructor_rounds;
38 uintptr_t size; // number of elements in the 'data' array
39 void *data[];
40} emutls_address_array;
41
42#if defined(_MSC_VER) && !defined(__clang__)
43#pragma warning(pop)
44#endif
45
46static void emutls_shutdown(emutls_address_array *array);
47
48#ifndef _WIN32
49
50#include <pthread.h>
51
52static pthread_mutex_t emutls_mutex = PTHREAD_MUTEX_INITIALIZER;
53static pthread_key_t emutls_pthread_key;
54static bool emutls_key_created = false;
55
56typedef unsigned int gcc_word __attribute__((mode(word)));
57typedef unsigned int gcc_pointer __attribute__((mode(pointer)));
58
59// Default is not to use posix_memalign, so systems like Android
60// can use thread local data without heavier POSIX memory allocators.
61#ifndef EMUTLS_USE_POSIX_MEMALIGN
62#define EMUTLS_USE_POSIX_MEMALIGN 0
63#endif
64
65static __inline void *emutls_memalign_alloc(size_t align, size_t size) {
66 void *base;
67#if EMUTLS_USE_POSIX_MEMALIGN
68 if (posix_memalign(&base, align, size) != 0)
69 abort();
70#else
71#define EXTRA_ALIGN_PTR_BYTES (align - 1 + sizeof(void *))
72 char *object;
73 if ((object = (char *)malloc(EXTRA_ALIGN_PTR_BYTES + size)) == NULL)
74 abort();
75 base = (void *)(((uintptr_t)(object + EXTRA_ALIGN_PTR_BYTES)) &
76 ~(uintptr_t)(align - 1));
77
78 ((void **)base)[-1] = object;
79#endif
80 return base;
81}
82
83static __inline void emutls_memalign_free(void *base) {
84#if EMUTLS_USE_POSIX_MEMALIGN
85 free(base);
86#else
87 // The mallocated address is in ((void**)base)[-1]
88 free(ptr: ((void **)base)[-1]);
89#endif
90}
91
92static __inline void emutls_setspecific(emutls_address_array *value) {
93 pthread_setspecific(key: emutls_pthread_key, pointer: (void *)value);
94}
95
96static __inline emutls_address_array *emutls_getspecific(void) {
97 return (emutls_address_array *)pthread_getspecific(key: emutls_pthread_key);
98}
99
100static void emutls_key_destructor(void *ptr) {
101 emutls_address_array *array = (emutls_address_array *)ptr;
102 if (array->skip_destructor_rounds > 0) {
103 // emutls is deallocated using a pthread key destructor. These
104 // destructors are called in several rounds to accommodate destructor
105 // functions that (re)initialize key values with pthread_setspecific.
106 // Delay the emutls deallocation to accommodate other end-of-thread
107 // cleanup tasks like calling thread_local destructors (e.g. the
108 // __cxa_thread_atexit fallback in libc++abi).
109 array->skip_destructor_rounds--;
110 emutls_setspecific(value: array);
111 } else {
112 emutls_shutdown(array);
113 free(ptr: ptr);
114 }
115}
116
117static __inline void emutls_init(void) {
118 if (pthread_key_create(key: &emutls_pthread_key, destr_function: emutls_key_destructor) != 0)
119 abort();
120 emutls_key_created = true;
121}
122
123static __inline void emutls_init_once(void) {
124 static pthread_once_t once = PTHREAD_ONCE_INIT;
125 pthread_once(once_control: &once, init_routine: emutls_init);
126}
127
128static __inline void emutls_lock(void) { pthread_mutex_lock(mutex: &emutls_mutex); }
129
130static __inline void emutls_unlock(void) { pthread_mutex_unlock(mutex: &emutls_mutex); }
131
132#else // _WIN32
133
134#include <assert.h>
135#include <malloc.h>
136#include <stdio.h>
137#include <windows.h>
138
139static LPCRITICAL_SECTION emutls_mutex;
140static DWORD emutls_tls_index = TLS_OUT_OF_INDEXES;
141
142typedef uintptr_t gcc_word;
143typedef void *gcc_pointer;
144
145static void win_error(DWORD last_err, const char *hint) {
146 char *buffer = NULL;
147 if (FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER |
148 FORMAT_MESSAGE_FROM_SYSTEM |
149 FORMAT_MESSAGE_MAX_WIDTH_MASK,
150 NULL, last_err, 0, (LPSTR)&buffer, 1, NULL)) {
151 fprintf(stderr, "Windows error: %s\n", buffer);
152 } else {
153 fprintf(stderr, "Unknown Windows error: %s\n", hint);
154 }
155 LocalFree(buffer);
156}
157
158static __inline void win_abort(DWORD last_err, const char *hint) {
159 win_error(last_err, hint);
160 abort();
161}
162
163static __inline void *emutls_memalign_alloc(size_t align, size_t size) {
164 void *base = _aligned_malloc(size, align);
165 if (!base)
166 win_abort(GetLastError(), "_aligned_malloc");
167 return base;
168}
169
170static __inline void emutls_memalign_free(void *base) { _aligned_free(base); }
171
172static void emutls_exit(void) {
173 if (emutls_mutex) {
174 DeleteCriticalSection(emutls_mutex);
175 _aligned_free(emutls_mutex);
176 emutls_mutex = NULL;
177 }
178 if (emutls_tls_index != TLS_OUT_OF_INDEXES) {
179 emutls_shutdown((emutls_address_array *)TlsGetValue(emutls_tls_index));
180 TlsFree(emutls_tls_index);
181 emutls_tls_index = TLS_OUT_OF_INDEXES;
182 }
183}
184
185static BOOL CALLBACK emutls_init(PINIT_ONCE p0, PVOID p1, PVOID *p2) {
186 (void)p0;
187 (void)p1;
188 (void)p2;
189 emutls_mutex =
190 (LPCRITICAL_SECTION)_aligned_malloc(sizeof(CRITICAL_SECTION), 16);
191 if (!emutls_mutex) {
192 win_error(GetLastError(), "_aligned_malloc");
193 return FALSE;
194 }
195 InitializeCriticalSection(emutls_mutex);
196
197 emutls_tls_index = TlsAlloc();
198 if (emutls_tls_index == TLS_OUT_OF_INDEXES) {
199 emutls_exit();
200 win_error(GetLastError(), "TlsAlloc");
201 return FALSE;
202 }
203 atexit(&emutls_exit);
204 return TRUE;
205}
206
207static __inline void emutls_init_once(void) {
208 static INIT_ONCE once;
209 InitOnceExecuteOnce(&once, emutls_init, NULL, NULL);
210}
211
212static __inline void emutls_lock(void) { EnterCriticalSection(emutls_mutex); }
213
214static __inline void emutls_unlock(void) { LeaveCriticalSection(emutls_mutex); }
215
216static __inline void emutls_setspecific(emutls_address_array *value) {
217 if (TlsSetValue(emutls_tls_index, (LPVOID)value) == 0)
218 win_abort(GetLastError(), "TlsSetValue");
219}
220
221static __inline emutls_address_array *emutls_getspecific(void) {
222 LPVOID value = TlsGetValue(emutls_tls_index);
223 if (value == NULL) {
224 const DWORD err = GetLastError();
225 if (err != ERROR_SUCCESS)
226 win_abort(err, "TlsGetValue");
227 }
228 return (emutls_address_array *)value;
229}
230
231// Provide atomic load/store functions for emutls_get_index if built with MSVC.
232#if !defined(__ATOMIC_RELEASE)
233#include <intrin.h>
234
235enum { __ATOMIC_ACQUIRE = 2, __ATOMIC_RELEASE = 3 };
236
237static __inline uintptr_t __atomic_load_n(void *ptr, unsigned type) {
238 assert(type == __ATOMIC_ACQUIRE);
239 // These return the previous value - but since we do an OR with 0,
240 // it's equivalent to a plain load.
241#ifdef _WIN64
242 return InterlockedOr64(ptr, 0);
243#else
244 return InterlockedOr(ptr, 0);
245#endif
246}
247
248static __inline void __atomic_store_n(void *ptr, uintptr_t val, unsigned type) {
249 assert(type == __ATOMIC_RELEASE);
250 InterlockedExchangePointer((void *volatile *)ptr, (void *)val);
251}
252
253#endif // __ATOMIC_RELEASE
254
255#endif // _WIN32
256
257static size_t emutls_num_object = 0; // number of allocated TLS objects
258
259// Free the allocated TLS data
260static void emutls_shutdown(emutls_address_array *array) {
261 if (array) {
262 uintptr_t i;
263 for (i = 0; i < array->size; ++i) {
264 if (array->data[i])
265 emutls_memalign_free(base: array->data[i]);
266 }
267 }
268}
269
270// For every TLS variable xyz,
271// there is one __emutls_control variable named __emutls_v.xyz.
272// If xyz has non-zero initial value, __emutls_v.xyz's "value"
273// will point to __emutls_t.xyz, which has the initial value.
274typedef struct __emutls_control {
275 // Must use gcc_word here, instead of size_t, to match GCC. When
276 // gcc_word is larger than size_t, the upper extra bits are all
277 // zeros. We can use variables of size_t to operate on size and
278 // align.
279 gcc_word size; // size of the object in bytes
280 gcc_word align; // alignment of the object in bytes
281 union {
282 uintptr_t index; // data[index-1] is the object address
283 void *address; // object address, when in single thread env
284 } object;
285 void *value; // null or non-zero initial value for the object
286} __emutls_control;
287
288// Emulated TLS objects are always allocated at run-time.
289static __inline void *emutls_allocate_object(__emutls_control *control) {
290 // Use standard C types, check with gcc's emutls.o.
291 COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(gcc_pointer));
292 COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(void *));
293
294 size_t size = control->size;
295 size_t align = control->align;
296 void *base;
297 if (align < sizeof(void *))
298 align = sizeof(void *);
299 // Make sure that align is power of 2.
300 if ((align & (align - 1)) != 0)
301 abort();
302
303 base = emutls_memalign_alloc(align, size);
304 if (control->value)
305 memcpy(dest: base, src: control->value, n: size);
306 else
307 memset(s: base, c: 0, n: size);
308 return base;
309}
310
311// Returns control->object.index; set index if not allocated yet.
312static __inline uintptr_t emutls_get_index(__emutls_control *control) {
313 uintptr_t index = __atomic_load_n(&control->object.index, __ATOMIC_ACQUIRE);
314 if (!index) {
315 emutls_init_once();
316 emutls_lock();
317 index = control->object.index;
318 if (!index) {
319 index = ++emutls_num_object;
320 __atomic_store_n(&control->object.index, index, __ATOMIC_RELEASE);
321 }
322 emutls_unlock();
323 }
324 return index;
325}
326
327// Updates newly allocated thread local emutls_address_array.
328static __inline void emutls_check_array_set_size(emutls_address_array *array,
329 uintptr_t size) {
330 if (array == NULL)
331 abort();
332 array->size = size;
333 emutls_setspecific(value: array);
334}
335
336// Returns the new 'data' array size, number of elements,
337// which must be no smaller than the given index.
338static __inline uintptr_t emutls_new_data_array_size(uintptr_t index) {
339 // Need to allocate emutls_address_array with extra slots
340 // to store the header.
341 // Round up the emutls_address_array size to multiple of 16.
342 uintptr_t header_words = sizeof(emutls_address_array) / sizeof(void *);
343 return ((index + header_words + 15) & ~((uintptr_t)15)) - header_words;
344}
345
346// Returns the size in bytes required for an emutls_address_array with
347// N number of elements for data field.
348static __inline uintptr_t emutls_asize(uintptr_t N) {
349 return N * sizeof(void *) + sizeof(emutls_address_array);
350}
351
352// Returns the thread local emutls_address_array.
353// Extends its size if necessary to hold address at index.
354static __inline emutls_address_array *
355emutls_get_address_array(uintptr_t index) {
356 emutls_address_array *array = emutls_getspecific();
357 if (array == NULL) {
358 uintptr_t new_size = emutls_new_data_array_size(index);
359 array = (emutls_address_array *)malloc(size: emutls_asize(N: new_size));
360 if (array) {
361 memset(s: array->data, c: 0, n: new_size * sizeof(void *));
362 array->skip_destructor_rounds = EMUTLS_SKIP_DESTRUCTOR_ROUNDS;
363 }
364 emutls_check_array_set_size(array, size: new_size);
365 } else if (index > array->size) {
366 uintptr_t orig_size = array->size;
367 uintptr_t new_size = emutls_new_data_array_size(index);
368 array = (emutls_address_array *)realloc(ptr: array, size: emutls_asize(N: new_size));
369 if (array)
370 memset(s: array->data + orig_size, c: 0,
371 n: (new_size - orig_size) * sizeof(void *));
372 emutls_check_array_set_size(array, size: new_size);
373 }
374 return array;
375}
376
377#ifndef _WIN32
378// Our emulated TLS implementation relies on local state (e.g. for the pthread
379// key), and if we duplicate this state across different shared libraries,
380// accesses to the same TLS variable from different shared libraries will yield
381// different results (see https://github.com/android/ndk/issues/1551 for an
382// example). __emutls_get_address is the only external entry point for emulated
383// TLS, and by making it default visibility and weak, we can rely on the dynamic
384// linker to coalesce multiple copies at runtime and ensure a single unique copy
385// of TLS state. This is a best effort; it won't work if the user is linking
386// with -Bsymbolic or -Bsymbolic-functions, and it also won't work on Windows,
387// where the dynamic linker has no notion of coalescing weak symbols at runtime.
388// A more robust solution would be to create a separate shared library for
389// emulated TLS, to ensure a single copy of its state.
390__attribute__((visibility("default"), weak))
391#endif
392void *__emutls_get_address(__emutls_control *control) {
393 uintptr_t index = emutls_get_index(control);
394 emutls_address_array *array = emutls_get_address_array(index: index--);
395 if (array->data[index] == NULL)
396 array->data[index] = emutls_allocate_object(control);
397 return array->data[index];
398}
399
400#ifdef __BIONIC__
401// Called by Bionic on dlclose to delete the emutls pthread key.
402__attribute__((visibility("hidden"))) void __emutls_unregister_key(void) {
403 if (emutls_key_created) {
404 pthread_key_delete(emutls_pthread_key);
405 emutls_key_created = false;
406 }
407}
408#endif
409

source code of compiler-rt/lib/builtins/emutls.c