llvm-project/compiler-rt/lib/builtins/emutls.c

/* ===---------- 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"
#include "int_util.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

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;

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() {
    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() {
    pthread_mutex_lock(&emutls_mutex);
}

static __inline void emutls_unlock() {
    pthread_mutex_unlock(&emutls_mutex);
}

#else /* _WIN32 */

#include <windows.h>
#include <malloc.h>
#include <stdio.h>
#include <assert.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, "Unkown 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;
    }
}

#pragma warning (push)
#pragma warning (disable : 4100)
static BOOL CALLBACK emutls_init(PINIT_ONCE p0, PVOID p1, PVOID *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() {
    EnterCriticalSection(emutls_mutex);
}

static __inline void emutls_unlock() {
    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() {
    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 */

#pragma warning (pop)

#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;
}

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