libgcc/config/gthr-vxworks-tls.c

   1 /* Copyright (C) 2002-2020 Free Software Foundation, Inc.
   2    Contributed by Zack Weinberg <zack@codesourcery.com>
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 Under Section 7 of GPL version 3, you are granted additional
  17 permissions described in the GCC Runtime Library Exception, version
  18 3.1, as published by the Free Software Foundation.
  19
  20 You should have received a copy of the GNU General Public License and
  21 a copy of the GCC Runtime Library Exception along with this program;
  22 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 <http://www.gnu.org/licenses/>.  */
  24
  25 /* Threads compatibility routines for libgcc2 for VxWorks.
  26    These are out-of-line routines called from gthr-vxworks.h.
  27
  28    This file provides the TLS related support routines, calling specific
  29    VxWorks kernel entry points for this purpose.  */
  30
  31 #include "tconfig.h"
  32 #include "tsystem.h"
  33 #include "gthr.h"
  34
  35 #if defined(__GTHREADS)
  36
  37 #include <vxWorks.h>
  38 #ifndef __RTP__
  39 #include <vxLib.h>
  40 #endif
  41 #include <taskLib.h>
  42 #ifndef __RTP__
  43 #include <taskHookLib.h>
  44 #else
  45 #include <errno.h>
  46 #endif
  47
  48 #include <_vxworks-versions.h>
  49
  50 /* Thread-local storage.
  51
  52    A gthread TLS key is simply an offset in an array, the address of which
  53    we store in a single pointer field associated with the current task.
  54
  55    On VxWorks 7, we have direct support for __thread variables and use
  56    such a variable as the pointer "field".  On other versions, we resort
  57    to __gthread_get_tls_data and __gthread_set_tls_data functions provided
  58    by the kernel.
  59
  60    There is also a global array which records which keys are valid and
  61    which have destructors.
  62
  63    A task delete hook is installed to execute key destructors.  The routines
  64    __gthread_enter_tls_dtor_context and __gthread_leave_tls_dtor_context,
  65    which are also provided by the kernel, ensure that it is safe to call
  66    free() on memory allocated by the task being deleted.  This is a no-op on
  67    VxWorks 5, but a major undertaking on AE.
  68
  69    The task delete hook is only installed when at least one thread
  70    has TLS data.  This is a necessary precaution, to allow this module
  71    to be unloaded - a module with a hook can not be removed.
  72
  73    Since this interface is used to allocate only a small number of
  74    keys, the table size is small and static, which simplifies the
  75    code quite a bit.  Revisit this if and when it becomes necessary.  */
  76
  77 #define MAX_KEYS 4
  78
  79 /* This is the structure pointed to by the pointer returned
  80    by __gthread_get_tls_data.  */
  81 struct tls_data
  82 {
  83   int *owner;
  84   void *values[MAX_KEYS];
  85   unsigned int generation[MAX_KEYS];
  86 };
  87
  88 /* To make sure we only delete TLS data associated with this object,
  89    include a pointer to a local variable in the TLS data object.  */
  90 static int self_owner;
  91
  92 /* Flag to check whether the delete hook is installed.  Once installed
  93    it is only removed when unloading this module.  */
  94 static volatile int delete_hook_installed;
  95
  96 /* TLS data access internal API.  A straight __thread variable starting with
  97    VxWorks 7, a pointer returned by kernel provided routines otherwise.  And
  98    on VxWorks 6, the kernel expects us to notify entry/exit of regions
  99    handling such variables by calls to kernel provided __gthread routines.  */
 100
 101 #if _VXWORKS_MAJOR_GE(7)
 102
 103 static __thread struct tls_data *__gthread_tls_data;
 104
 105 #define VX_GET_TLS_DATA() __gthread_tls_data
 106 #define VX_SET_TLS_DATA(x) __gthread_tls_data = (x)
 107
 108 #else
 109
 110 extern void *__gthread_get_tls_data (void);
 111 extern void __gthread_set_tls_data (void *data);
 112
 113 #define VX_GET_TLS_DATA() __gthread_get_tls_data()
 114 #define VX_SET_TLS_DATA(x) __gthread_set_tls_data(x)
 115
 116 #endif
 117
 118 #if _VXWORKS_MAJOR_EQ(6)
 119
 120 extern void __gthread_enter_tls_dtor_context (void);
 121 extern void __gthread_leave_tls_dtor_context (void);
 122
 123 #define VX_ENTER_TLS_DTOR() __gthread_enter_tls_dtor_context ()
 124 #define VX_LEAVE_TLS_DTOR() __gthread_leave_tls_dtor_context ()
 125
 126 #else
 127
 128 #define VX_ENTER_TLS_DTOR()
 129 #define VX_LEAVE_TLS_DTOR()
 130
 131 #endif
 132
 133 /* This is a global structure which records all of the active keys.
 134
 135    A key is potentially valid (i.e. has been handed out by
 136    __gthread_key_create) iff its generation count in this structure is
 137    even.  In that case, the matching entry in the dtors array is a
 138    routine to be called when a thread terminates with a valid,
 139    non-NULL specific value for that key.
 140
 141    A key is actually valid in a thread T iff the generation count
 142    stored in this structure is equal to the generation count stored in
 143    T's specific-value structure.  */
 144
 145 typedef void (*tls_dtor) (void *);
 146
 147 struct tls_keys
 148 {
 149   tls_dtor dtor[MAX_KEYS];
 150   unsigned int generation[MAX_KEYS];
 151 };
 152
 153 #define KEY_VALID_P(key) !(tls_keys.generation[key] & 1)
 154
 155 /* Note: if MAX_KEYS is increased, this initializer must be updated
 156    to match.  All the generation counts begin at 1, which means no
 157    key is valid.  */
 158 static struct tls_keys tls_keys =
 159 {
 160   { NULL, NULL, NULL, NULL },
 161   { 1, 1, 1, 1 }
 162 };
 163
 164 /* This lock protects the tls_keys structure.  */
 165 static __gthread_mutex_t tls_lock;
 166
 167 static __gthread_once_t tls_init_guard = __GTHREAD_ONCE_INIT;
 168
 169 /* Internal routines.  */
 170
 171 /* The task TCB has just been deleted.  Call the destructor
 172    function for each TLS key that has both a destructor and
 173    a non-NULL specific value in this thread.
 174
 175    This routine does not need to take tls_lock; the generation
 176    count protects us from calling a stale destructor.  It does
 177    need to read tls_keys.dtor[key] atomically.  */
 178
 179 void
 180 tls_delete_hook (void *tcb ATTRIBUTE_UNUSED)
 181 {
 182   struct tls_data *data;
 183   __gthread_key_t key;
 184
 185   data = VX_GET_TLS_DATA();
 186
 187   if (data && data->owner == &self_owner)
 188     {
 189       VX_ENTER_TLS_DTOR();
 190       for (key = 0; key < MAX_KEYS; key++)
 191         {
 192           if (data->generation[key] == tls_keys.generation[key])
 193             {
 194               tls_dtor dtor = tls_keys.dtor[key];
 195
 196               if (dtor)
 197                 dtor (data->values[key]);
 198             }
 199         }
 200       free (data);
 201
 202       VX_LEAVE_TLS_DTOR();
 203       VX_SET_TLS_DATA(NULL);
 204     }
 205 }
 206
 207 /* Initialize global data used by the TLS system.  */
 208 static void
 209 tls_init (void)
 210 {
 211   __GTHREAD_MUTEX_INIT_FUNCTION (&tls_lock);
 212 }
 213
 214 static void tls_destructor (void) __attribute__ ((destructor));
 215 static void
 216 tls_destructor (void)
 217 {
 218 #ifdef __RTP__
 219   /* All threads but this one should have exited by now.  */
 220   tls_delete_hook (NULL);
 221 #endif
 222   /* Unregister the hook.  */
 223   if (delete_hook_installed)
 224     taskDeleteHookDelete ((FUNCPTR)tls_delete_hook);
 225
 226   if (tls_init_guard.done && __gthread_mutex_lock (&tls_lock) != ERROR)
 227     semDelete (tls_lock);
 228 }
 229
 230 /* External interface */
 231
 232 /* Store in KEYP a value which can be passed to __gthread_setspecific/
 233    __gthread_getspecific to store and retrieve a value which is
 234    specific to each calling thread.  If DTOR is not NULL, it will be
 235    called when a thread terminates with a non-NULL specific value for
 236    this key, with the value as its sole argument.  */
 237
 238 int
 239 __gthread_key_create (__gthread_key_t *keyp, tls_dtor dtor)
 240 {
 241   __gthread_key_t key;
 242
 243   __gthread_once (&tls_init_guard, tls_init);
 244
 245   if (__gthread_mutex_lock (&tls_lock) == ERROR)
 246     return errno;
 247
 248   for (key = 0; key < MAX_KEYS; key++)
 249     if (!KEY_VALID_P (key))
 250       goto found_slot;
 251
 252   /* no room */
 253   __gthread_mutex_unlock (&tls_lock);
 254   return EAGAIN;
 255
 256  found_slot:
 257   tls_keys.generation[key]++;  /* making it even */
 258   tls_keys.dtor[key] = dtor;
 259   *keyp = key;
 260   __gthread_mutex_unlock (&tls_lock);
 261   return 0;
 262 }
 263
 264 /* Invalidate KEY; it can no longer be used as an argument to
 265    setspecific/getspecific.  Note that this does NOT call destructor
 266    functions for any live values for this key.  */
 267 int
 268 __gthread_key_delete (__gthread_key_t key)
 269 {
 270   if (key >= MAX_KEYS)
 271     return EINVAL;
 272
 273   __gthread_once (&tls_init_guard, tls_init);
 274
 275   if (__gthread_mutex_lock (&tls_lock) == ERROR)
 276     return errno;
 277
 278   if (!KEY_VALID_P (key))
 279     {
 280       __gthread_mutex_unlock (&tls_lock);
 281       return EINVAL;
 282     }
 283
 284   tls_keys.generation[key]++;  /* making it odd */
 285   tls_keys.dtor[key] = 0;
 286
 287   __gthread_mutex_unlock (&tls_lock);
 288   return 0;
 289 }
 290
 291 /* Retrieve the thread-specific value for KEY.  If it has never been
 292    set in this thread, or KEY is invalid, returns NULL.
 293
 294    It does not matter if this function races with key_create or
 295    key_delete; the worst that can happen is you get a value other than
 296    the one that a serialized implementation would have provided.  */
 297
 298 void *
 299 __gthread_getspecific (__gthread_key_t key)
 300 {
 301   struct tls_data *data;
 302
 303   if (key >= MAX_KEYS)
 304     return 0;
 305
 306   data = VX_GET_TLS_DATA();
 307
 308   if (!data)
 309     return 0;
 310
 311   if (data->generation[key] != tls_keys.generation[key])
 312     return 0;
 313
 314   return data->values[key];
 315 }
 316
 317 /* Set the thread-specific value for KEY.  If KEY is invalid, or
 318    memory allocation fails, returns -1, otherwise 0.
 319
 320    The generation count protects this function against races with
 321    key_create/key_delete; the worst thing that can happen is that a
 322    value is successfully stored into a dead generation (and then
 323    immediately becomes invalid).  However, we do have to make sure
 324    to read tls_keys.generation[key] atomically.  */
 325
 326 int
 327 __gthread_setspecific (__gthread_key_t key, void *value)
 328 {
 329   struct tls_data *data;
 330   unsigned int generation;
 331
 332   if (key >= MAX_KEYS)
 333     return EINVAL;
 334
 335   data = VX_GET_TLS_DATA();
 336
 337   if (!data)
 338     {
 339       if (!delete_hook_installed)
 340         {
 341           /* Install the delete hook.  */
 342           if (__gthread_mutex_lock (&tls_lock) == ERROR)
 343             return ENOMEM;
 344           if (!delete_hook_installed)
 345             {
 346               taskDeleteHookAdd ((FUNCPTR)tls_delete_hook);
 347               delete_hook_installed = 1;
 348             }
 349           __gthread_mutex_unlock (&tls_lock);
 350         }
 351
 352       data = malloc (sizeof (struct tls_data));
 353       if (!data)
 354         return ENOMEM;
 355
 356       memset (data, 0, sizeof (struct tls_data));
 357       data->owner = &self_owner;
 358
 359       VX_SET_TLS_DATA(data);
 360     }
 361
 362   generation = tls_keys.generation[key];
 363
 364   if (generation & 1)
 365     return EINVAL;
 366
 367   data->generation[key] = generation;
 368   data->values[key] = value;
 369
 370   return 0;
 371 }
 372 #endif /* __GTHREADS */