1/* ===---------- emutls.c - Implements __emutls_get_address ---------------===
2 *
3 *                     The LLVM Compiler Infrastructure
4 *
5 * This file is dual licensed under the MIT and the University of Illinois Open
6 * Source Licenses. See LICENSE.TXT for details.
7 *
8 * ===----------------------------------------------------------------------===
9 */
10#include <pthread.h>
11#include <stdint.h>
12#include <stdlib.h>
13#include <string.h>
14
15#include "int_lib.h"
16#include "int_util.h"
17
18/* Default is not to use posix_memalign, so systems like Android
19 * can use thread local data without heavier POSIX memory allocators.
20 */
21#ifndef EMUTLS_USE_POSIX_MEMALIGN
22#define EMUTLS_USE_POSIX_MEMALIGN 0
23#endif
24
25/* For every TLS variable xyz,
26 * there is one __emutls_control variable named __emutls_v.xyz.
27 * If xyz has non-zero initial value, __emutls_v.xyz's "value"
28 * will point to __emutls_t.xyz, which has the initial value.
29 */
30typedef struct __emutls_control {
31    size_t size;  /* size of the object in bytes */
32    size_t align;  /* alignment of the object in bytes */
33    union {
34        uintptr_t index;  /* data[index-1] is the object address */
35        void* address;  /* object address, when in single thread env */
36    } object;
37    void* value;  /* null or non-zero initial value for the object */
38} __emutls_control;
39
40static __inline void *emutls_memalign_alloc(size_t align, size_t size) {
41    void *base;
42#if EMUTLS_USE_POSIX_MEMALIGN
43    if (posix_memalign(&base, align, size) != 0)
44        abort();
45#else
46    #define EXTRA_ALIGN_PTR_BYTES (align - 1 + sizeof(void*))
47    char* object;
48    if ((object = malloc(EXTRA_ALIGN_PTR_BYTES + size)) == NULL)
49        abort();
50    base = (void*)(((uintptr_t)(object + EXTRA_ALIGN_PTR_BYTES))
51                    & ~(uintptr_t)(align - 1));
52
53    ((void**)base)[-1] = object;
54#endif
55    return base;
56}
57
58static __inline void emutls_memalign_free(void *base) {
59#if EMUTLS_USE_POSIX_MEMALIGN
60    free(base);
61#else
62    /* The mallocated address is in ((void**)base)[-1] */
63    free(((void**)base)[-1]);
64#endif
65}
66
67/* Emulated TLS objects are always allocated at run-time. */
68static __inline void *emutls_allocate_object(__emutls_control *control) {
69    /* Use standard C types, check with gcc's emutls.o. */
70    typedef unsigned int gcc_word __attribute__((mode(word)));
71    typedef unsigned int gcc_pointer __attribute__((mode(pointer)));
72    COMPILE_TIME_ASSERT(sizeof(size_t) == sizeof(gcc_word));
73    COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(gcc_pointer));
74    COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(void*));
75
76    size_t size = control->size;
77    size_t align = control->align;
78    if (align < sizeof(void*))
79        align = sizeof(void*);
80    /* Make sure that align is power of 2. */
81    if ((align & (align - 1)) != 0)
82        abort();
83
84    void* base = emutls_memalign_alloc(align, size);
85    if (control->value)
86        memcpy(base, control->value, size);
87    else
88        memset(base, 0, size);
89    return base;
90}
91
92static pthread_mutex_t emutls_mutex = PTHREAD_MUTEX_INITIALIZER;
93
94static size_t emutls_num_object = 0;  /* number of allocated TLS objects */
95
96typedef struct emutls_address_array {
97    uintptr_t size;  /* number of elements in the 'data' array */
98    void* data[];
99} emutls_address_array;
100
101static pthread_key_t emutls_pthread_key;
102
103static void emutls_key_destructor(void* ptr) {
104    emutls_address_array* array = (emutls_address_array*)ptr;
105    uintptr_t i;
106    for (i = 0; i < array->size; ++i) {
107        if (array->data[i])
108            emutls_memalign_free(array->data[i]);
109    }
110    free(ptr);
111}
112
113static void emutls_init(void) {
114    if (pthread_key_create(&emutls_pthread_key, emutls_key_destructor) != 0)
115        abort();
116}
117
118/* Returns control->object.index; set index if not allocated yet. */
119static __inline uintptr_t emutls_get_index(__emutls_control *control) {
120    uintptr_t index = __atomic_load_n(&control->object.index, __ATOMIC_ACQUIRE);
121    if (!index) {
122        static pthread_once_t once = PTHREAD_ONCE_INIT;
123        pthread_once(&once, emutls_init);
124        pthread_mutex_lock(&emutls_mutex);
125        index = control->object.index;
126        if (!index) {
127            index = ++emutls_num_object;
128            __atomic_store_n(&control->object.index, index, __ATOMIC_RELEASE);
129        }
130        pthread_mutex_unlock(&emutls_mutex);
131    }
132    return index;
133}
134
135/* Updates newly allocated thread local emutls_address_array. */
136static __inline void emutls_check_array_set_size(emutls_address_array *array,
137                                                 uintptr_t size) {
138    if (array == NULL)
139        abort();
140    array->size = size;
141    pthread_setspecific(emutls_pthread_key, (void*)array);
142}
143
144/* Returns the new 'data' array size, number of elements,
145 * which must be no smaller than the given index.
146 */
147static __inline uintptr_t emutls_new_data_array_size(uintptr_t index) {
148   /* Need to allocate emutls_address_array with one extra slot
149    * to store the data array size.
150    * Round up the emutls_address_array size to multiple of 16.
151    */
152    return ((index + 1 + 15) & ~((uintptr_t)15)) - 1;
153}
154
155/* Returns the thread local emutls_address_array.
156 * Extends its size if necessary to hold address at index.
157 */
158static __inline emutls_address_array *
159emutls_get_address_array(uintptr_t index) {
160    emutls_address_array* array = pthread_getspecific(emutls_pthread_key);
161    if (array == NULL) {
162        uintptr_t new_size = emutls_new_data_array_size(index);
163        array = calloc(new_size + 1, sizeof(void*));
164        emutls_check_array_set_size(array, new_size);
165    } else if (index > array->size) {
166        uintptr_t orig_size = array->size;
167        uintptr_t new_size = emutls_new_data_array_size(index);
168        array = realloc(array, (new_size + 1) * sizeof(void*));
169        if (array)
170            memset(array->data + orig_size, 0,
171                   (new_size - orig_size) * sizeof(void*));
172        emutls_check_array_set_size(array, new_size);
173    }
174    return array;
175}
176
177void* __emutls_get_address(__emutls_control* control) {
178    uintptr_t index = emutls_get_index(control);
179    emutls_address_array* array = emutls_get_address_array(index);
180    if (array->data[index - 1] == NULL)
181        array->data[index - 1] = emutls_allocate_object(control);
182    return array->data[index - 1];
183}
184