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 unsigned int gcc_word __attribute__((mode(word)));
31typedef struct __emutls_control {
32    /* Must use gcc_word here, instead of size_t, to match GCC.  When
33       gcc_word is larger than size_t, the upper extra bits are all
34       zeros.  We can use variables of size_t to operate on size and
35       align.  */
36    gcc_word size;  /* size of the object in bytes */
37    gcc_word align;  /* alignment of the object in bytes */
38    union {
39        uintptr_t index;  /* data[index-1] is the object address */
40        void* address;  /* object address, when in single thread env */
41    } object;
42    void* value;  /* null or non-zero initial value for the object */
43} __emutls_control;
44
45static __inline void *emutls_memalign_alloc(size_t align, size_t size) {
46    void *base;
47#if EMUTLS_USE_POSIX_MEMALIGN
48    if (posix_memalign(&base, align, size) != 0)
49        abort();
50#else
51    #define EXTRA_ALIGN_PTR_BYTES (align - 1 + sizeof(void*))
52    char* object;
53    if ((object = malloc(EXTRA_ALIGN_PTR_BYTES + size)) == NULL)
54        abort();
55    base = (void*)(((uintptr_t)(object + EXTRA_ALIGN_PTR_BYTES))
56                    & ~(uintptr_t)(align - 1));
57
58    ((void**)base)[-1] = object;
59#endif
60    return base;
61}
62
63static __inline void emutls_memalign_free(void *base) {
64#if EMUTLS_USE_POSIX_MEMALIGN
65    free(base);
66#else
67    /* The mallocated address is in ((void**)base)[-1] */
68    free(((void**)base)[-1]);
69#endif
70}
71
72/* Emulated TLS objects are always allocated at run-time. */
73static __inline void *emutls_allocate_object(__emutls_control *control) {
74    /* Use standard C types, check with gcc's emutls.o. */
75    typedef unsigned int gcc_pointer __attribute__((mode(pointer)));
76    COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(gcc_pointer));
77    COMPILE_TIME_ASSERT(sizeof(uintptr_t) == sizeof(void*));
78
79    size_t size = control->size;
80    size_t align = control->align;
81    void* base;
82    if (align < sizeof(void*))
83        align = sizeof(void*);
84    /* Make sure that align is power of 2. */
85    if ((align & (align - 1)) != 0)
86        abort();
87
88    base = emutls_memalign_alloc(align, size);
89    if (control->value)
90        memcpy(base, control->value, size);
91    else
92        memset(base, 0, size);
93    return base;
94}
95
96static pthread_mutex_t emutls_mutex = PTHREAD_MUTEX_INITIALIZER;
97
98static size_t emutls_num_object = 0;  /* number of allocated TLS objects */
99
100typedef struct emutls_address_array {
101    uintptr_t size;  /* number of elements in the 'data' array */
102    void* data[];
103} emutls_address_array;
104
105static pthread_key_t emutls_pthread_key;
106
107static void emutls_key_destructor(void* ptr) {
108    emutls_address_array* array = (emutls_address_array*)ptr;
109    uintptr_t i;
110    for (i = 0; i < array->size; ++i) {
111        if (array->data[i])
112            emutls_memalign_free(array->data[i]);
113    }
114    free(ptr);
115}
116
117static void emutls_init(void) {
118    if (pthread_key_create(&emutls_pthread_key, emutls_key_destructor) != 0)
119        abort();
120}
121
122/* Returns control->object.index; set index if not allocated yet. */
123static __inline uintptr_t emutls_get_index(__emutls_control *control) {
124    uintptr_t index = __atomic_load_n(&control->object.index, __ATOMIC_ACQUIRE);
125    if (!index) {
126        static pthread_once_t once = PTHREAD_ONCE_INIT;
127        pthread_once(&once, emutls_init);
128        pthread_mutex_lock(&emutls_mutex);
129        index = control->object.index;
130        if (!index) {
131            index = ++emutls_num_object;
132            __atomic_store_n(&control->object.index, index, __ATOMIC_RELEASE);
133        }
134        pthread_mutex_unlock(&emutls_mutex);
135    }
136    return index;
137}
138
139/* Updates newly allocated thread local emutls_address_array. */
140static __inline void emutls_check_array_set_size(emutls_address_array *array,
141                                                 uintptr_t size) {
142    if (array == NULL)
143        abort();
144    array->size = size;
145    pthread_setspecific(emutls_pthread_key, (void*)array);
146}
147
148/* Returns the new 'data' array size, number of elements,
149 * which must be no smaller than the given index.
150 */
151static __inline uintptr_t emutls_new_data_array_size(uintptr_t index) {
152   /* Need to allocate emutls_address_array with one extra slot
153    * to store the data array size.
154    * Round up the emutls_address_array size to multiple of 16.
155    */
156    return ((index + 1 + 15) & ~((uintptr_t)15)) - 1;
157}
158
159/* Returns the thread local emutls_address_array.
160 * Extends its size if necessary to hold address at index.
161 */
162static __inline emutls_address_array *
163emutls_get_address_array(uintptr_t index) {
164    emutls_address_array* array = pthread_getspecific(emutls_pthread_key);
165    if (array == NULL) {
166        uintptr_t new_size = emutls_new_data_array_size(index);
167        array = calloc(new_size + 1, sizeof(void*));
168        emutls_check_array_set_size(array, new_size);
169    } else if (index > array->size) {
170        uintptr_t orig_size = array->size;
171        uintptr_t new_size = emutls_new_data_array_size(index);
172        array = realloc(array, (new_size + 1) * sizeof(void*));
173        if (array)
174            memset(array->data + orig_size, 0,
175                   (new_size - orig_size) * sizeof(void*));
176        emutls_check_array_set_size(array, new_size);
177    }
178    return array;
179}
180
181void* __emutls_get_address(__emutls_control* control) {
182    uintptr_t index = emutls_get_index(control);
183    emutls_address_array* array = emutls_get_address_array(index);
184    if (array->data[index - 1] == NULL)
185        array->data[index - 1] = emutls_allocate_object(control);
186    return array->data[index - 1];
187}
188