lib/builtins/emutls.c

/* ===---------- emutls.c - Implements __emutls_get_address ---------------===
 *
 *                     The LLVM Compiler Infrastructure
 *
 * This file is dual licensed under the MIT and the University of Illinois Open
 * Source Licenses. See LICENSE.TXT for details.
 *
 * ===----------------------------------------------------------------------===
 */
#include <pthread.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

#include "int_lib.h"
#include "int_util.h"

/* 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

/* 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 unsigned int gcc_word __attribute__((mode(word)));
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;

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 = 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
}

/* 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. */
    typedef unsigned int gcc_pointer __attribute__((mode(pointer)));
    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;
}

static pthread_mutex_t emutls_mutex = PTHREAD_MUTEX_INITIALIZER;

static size_t emutls_num_object = 0;  /* number of allocated TLS objects */

typedef struct emutls_address_array {
    uintptr_t size;  /* number of elements in the 'data' array */
    void* data[];
} emutls_address_array;

static pthread_key_t emutls_pthread_key;

static void emutls_key_destructor(void* ptr) {
    emutls_address_array* array = (emutls_address_array*)ptr;
    uintptr_t i;
    for (i = 0; i < array->size; ++i) {
        if (array->data[i])
            emutls_memalign_free(array->data[i]);
    }
    free(ptr);
}

static void emutls_init(void) {
    if (pthread_key_create(&emutls_pthread_key, emutls_key_destructor) != 0)
        abort();
}

/* 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) {
        static pthread_once_t once = PTHREAD_ONCE_INIT;
        pthread_once(&once, emutls_init);
        pthread_mutex_lock(&emutls_mutex);
        index = control->object.index;
        if (!index) {
            index = ++emutls_num_object;
            __atomic_store_n(&control->object.index, index, __ATOMIC_RELEASE);
        }
        pthread_mutex_unlock(&emutls_mutex);
    }
    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;
    pthread_setspecific(emutls_pthread_key, (void*)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 one extra slot
    * to store the data array size.
    * Round up the emutls_address_array size to multiple of 16.
    */
    return ((index + 1 + 15) & ~((uintptr_t)15)) - 1;
}

/* 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 = pthread_getspecific(emutls_pthread_key);
    if (array == NULL) {
        uintptr_t new_size = emutls_new_data_array_size(index);
        array = malloc(new_size * sizeof(void *) + sizeof(emutls_address_array));
        if (array)
            memset(array->data, 0, new_size * sizeof(void*));
        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 = realloc(array, new_size * sizeof(void *) + sizeof(emutls_address_array));
        if (array)
            memset(array->data + orig_size, 0,
                   (new_size - orig_size) * sizeof(void*));
        emutls_check_array_set_size(array, new_size);
    }
    return array;
}

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 - 1] == NULL)
        array->data[index - 1] = emutls_allocate_object(control);
    return array->data[index - 1];
}