llvm/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"

#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 …
#else
#define EMUTLS_SKIP_DESTRUCTOR_ROUNDS …
#endif

#if defined(_MSC_VER) && !defined(__clang__)
// MSVC raises a warning about a nonstandard extension being used for the 0
// sized element in this array. Disable this for warn-as-error builds.
#pragma warning(push)
#pragma warning(disable : 4200)
#endif

emutls_address_array;

#if defined(_MSC_VER) && !defined(__clang__)
#pragma warning(pop)
#endif

static void emutls_shutdown(emutls_address_array *array);

#ifndef _WIN32

#include <pthread.h>

static pthread_mutex_t emutls_mutex = …;
static pthread_key_t emutls_pthread_key;
static bool emutls_key_created = …;

gcc_word __attribute__((mode …));
gcc_pointer __attribute__((mode …));

// 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 …
#endif

static __inline void *emutls_memalign_alloc(size_t align, size_t size) { … }

static __inline void emutls_memalign_free(void *base) { … }

static __inline void emutls_setspecific(emutls_address_array *value) { … }

static __inline emutls_address_array *emutls_getspecific(void) { … }

static void emutls_key_destructor(void *ptr) { … }

static __inline void emutls_init(void) { … }

static __inline void emutls_init_once(void) { … }

static __inline void emutls_lock(void) { … }

static __inline void emutls_unlock(void) { … }

#else // _WIN32

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

static BOOL CALLBACK emutls_init(PINIT_ONCE p0, PVOID p1, PVOID *p2) {
  (void)p0;
  (void)p1;
  (void)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(void) { EnterCriticalSection(emutls_mutex); }

static __inline void emutls_unlock(void) { 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(void) {
  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

#endif // _WIN32

static size_t emutls_num_object = …; // number of allocated TLS objects

// Free the allocated TLS data
static void emutls_shutdown(emutls_address_array *array) { … }

// 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.
__emutls_control;

// Emulated TLS objects are always allocated at run-time.
static __inline void *emutls_allocate_object(__emutls_control *control) { … }

// Returns control->object.index; set index if not allocated yet.
static __inline uintptr_t emutls_get_index(__emutls_control *control) { … }

// Updates newly allocated thread local emutls_address_array.
static __inline void emutls_check_array_set_size(emutls_address_array *array,
                                                 uintptr_t size) { … }

// 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) { … }

// 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) { … }

// 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) { … }

#ifndef _WIN32
// Our emulated TLS implementation relies on local state (e.g. for the pthread
// key), and if we duplicate this state across different shared libraries,
// accesses to the same TLS variable from different shared libraries will yield
// different results (see https://github.com/android/ndk/issues/1551 for an
// example). __emutls_get_address is the only external entry point for emulated
// TLS, and by making it default visibility and weak, we can rely on the dynamic
// linker to coalesce multiple copies at runtime and ensure a single unique copy
// of TLS state. This is a best effort; it won't work if the user is linking
// with -Bsymbolic or -Bsymbolic-functions, and it also won't work on Windows,
// where the dynamic linker has no notion of coalescing weak symbols at runtime.
// A more robust solution would be to create a separate shared library for
// emulated TLS, to ensure a single copy of its state.
__attribute__((visibility("default"), weak))
#endif
void *__emutls_get_address(__emutls_control *control) { … }

#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