libgcc/config/vxlib-tls.c

   1 /* Copyright (C) 2002-2018 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.  The base VxWorks 5.x kernels
  30    don't feature these entry points, and we provide gthr_supp_vxw_5x.c as an
  31    option to fill this gap.  Asking users to rebuild a kernel is not to be
  32    taken lightly, still, so we have isolated these routines from the rest of
  33    vxlib to ensure that the kernel dependencies are only dragged when really
  34    necessary.  */
  35
  36 #include "tconfig.h"
  37 #include "tsystem.h"
  38 #include "gthr.h"
  39
  40 #if defined(__GTHREADS)
  41 #include <vxWorks.h>
  42 #ifndef __RTP__
  43 #include <vxLib.h>
  44 #endif
  45 #include <taskLib.h>
  46 #ifndef __RTP__
  47 #include <taskHookLib.h>
  48 #else
  49 # include <errno.h>
  50 #endif
  51
  52 /* Thread-local storage.
  53
  54    We reserve a field in the TCB to point to a dynamically allocated
  55    array which is used to store TLS values.  A TLS key is simply an
  56    offset in this array.  The exact location of the TCB field is not
  57    known to this code nor to vxlib.c -- all access to it indirects
  58    through the routines __gthread_get_tls_data and
  59    __gthread_set_tls_data, which are provided by the VxWorks kernel.
  60
  61    There is also a global array which records which keys are valid and
  62    which have destructors.
  63
  64    A task delete hook is installed to execute key destructors.  The
  65    routines __gthread_enter_tls_dtor_context and
  66    __gthread_leave_tls_dtor_context, which are also provided by the
  67    kernel, ensure that it is safe to call free() on memory allocated
  68    by the task being deleted.  (This is a no-op on VxWorks 5, but
  69    a major undertaking on AE.)
  70
  71    The task delete hook is only installed when at least one thread
  72    has TLS data.  This is a necessary precaution, to allow this module
  73    to be unloaded - a module with a hook can not be removed.
  74
  75    Since this interface is used to allocate only a small number of
  76    keys, the table size is small and static, which simplifies the
  77    code quite a bit.  Revisit this if and when it becomes necessary.  */
  78
  79 #define MAX_KEYS 4
  80
  81 /* This is the structure pointed to by the pointer returned
  82    by __gthread_get_tls_data.  */
  83 struct tls_data
  84 {
  85   int *owner;
  86   void *values[MAX_KEYS];
  87   unsigned int generation[MAX_KEYS];
  88 };
  89
  90 /* To make sure we only delete TLS data associated with this object,
  91    include a pointer to a local variable in the TLS data object.  */
  92 static int self_owner;
  93
  94 /* Flag to check whether the delete hook is installed.  Once installed
  95    it is only removed when unloading this module.  */
  96 static volatile int delete_hook_installed;
  97
  98 /* kernel provided routines */
  99 extern void *__gthread_get_tls_data (void);
 100 extern void __gthread_set_tls_data (void *data);
 101
 102 extern void __gthread_enter_tls_dtor_context (void);
 103 extern void __gthread_leave_tls_dtor_context (void);
 104
 105 #ifndef __RTP__
 106
 107 extern void *__gthread_get_tsd_data (WIND_TCB *tcb);
 108 extern void __gthread_set_tsd_data (WIND_TCB *tcb, void *data);
 109 extern void __gthread_enter_tsd_dtor_context (WIND_TCB *tcb);
 110 extern void __gthread_leave_tsd_dtor_context (WIND_TCB *tcb);
 111
 112 #endif /* __RTP__ */
 113
 114 /* This is a global structure which records all of the active keys.
 115
 116    A key is potentially valid (i.e. has been handed out by
 117    __gthread_key_create) iff its generation count in this structure is
 118    even.  In that case, the matching entry in the dtors array is a
 119    routine to be called when a thread terminates with a valid,
 120    non-NULL specific value for that key.
 121
 122    A key is actually valid in a thread T iff the generation count
 123    stored in this structure is equal to the generation count stored in
 124    T's specific-value structure.  */
 125
 126 typedef void (*tls_dtor) (void *);
 127
 128 struct tls_keys
 129 {
 130   tls_dtor dtor[MAX_KEYS];
 131   unsigned int generation[MAX_KEYS];
 132 };
 133
 134 #define KEY_VALID_P(key) !(tls_keys.generation[key] & 1)
 135
 136 /* Note: if MAX_KEYS is increased, this initializer must be updated
 137    to match.  All the generation counts begin at 1, which means no
 138    key is valid.  */
 139 static struct tls_keys tls_keys =
 140 {
 141   { 0, 0, 0, 0 },
 142   { 1, 1, 1, 1 }
 143 };
 144
 145 /* This lock protects the tls_keys structure.  */
 146 static __gthread_mutex_t tls_lock;
 147
 148 static __gthread_once_t tls_init_guard = __GTHREAD_ONCE_INIT;
 149
 150 /* Internal routines.  */
 151
 152 /* The task TCB has just been deleted.  Call the destructor
 153    function for each TLS key that has both a destructor and
 154    a non-NULL specific value in this thread.
 155
 156    This routine does not need to take tls_lock; the generation
 157    count protects us from calling a stale destructor.  It does
 158    need to read tls_keys.dtor[key] atomically.  */
 159
 160 static void
 161 tls_delete_hook (void *tcb ATTRIBUTE_UNUSED)
 162 {
 163   struct tls_data *data;
 164   __gthread_key_t key;
 165
 166 #ifdef __RTP__
 167   data = __gthread_get_tls_data ();
 168 #else
 169   /* In kernel mode, we can be called in the context of the thread
 170      doing the killing, so must use the TCB to determine the data of
 171      the thread being killed.  */
 172   data = __gthread_get_tsd_data (tcb);
 173 #endif
 174
 175   if (data && data->owner == &self_owner)
 176     {
 177 #ifdef __RTP__
 178       __gthread_enter_tls_dtor_context ();
 179 #else
 180       __gthread_enter_tsd_dtor_context (tcb);
 181 #endif
 182       for (key = 0; key < MAX_KEYS; key++)
 183         {
 184           if (data->generation[key] == tls_keys.generation[key])
 185             {
 186               tls_dtor dtor = tls_keys.dtor[key];
 187
 188               if (dtor)
 189                 dtor (data->values[key]);
 190             }
 191         }
 192       free (data);
 193 #ifdef __RTP__
 194       __gthread_leave_tls_dtor_context ();
 195 #else
 196       __gthread_leave_tsd_dtor_context (tcb);
 197 #endif
 198
 199 #ifdef __RTP__
 200       __gthread_set_tls_data (0);
 201 #else
 202       __gthread_set_tsd_data (tcb, 0);
 203 #endif
 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 = __gthread_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 = __gthread_get_tls_data ();
 336   if (!data)
 337     {
 338       if (!delete_hook_installed)
 339         {
 340           /* Install the delete hook.  */
 341           if (__gthread_mutex_lock (&tls_lock) == ERROR)
 342             return ENOMEM;
 343           if (!delete_hook_installed)
 344             {
 345               taskDeleteHookAdd ((FUNCPTR)tls_delete_hook);
 346               delete_hook_installed = 1;
 347             }
 348           __gthread_mutex_unlock (&tls_lock);
 349         }
 350
 351       data = malloc (sizeof (struct tls_data));
 352       if (!data)
 353         return ENOMEM;
 354
 355       memset (data, 0, sizeof (struct tls_data));
 356       data->owner = &self_owner;
 357       __gthread_set_tls_data (data);
 358     }
 359
 360   generation = tls_keys.generation[key];
 361
 362   if (generation & 1)
 363     return EINVAL;
 364
 365   data->generation[key] = generation;
 366   data->values[key] = value;
 367
 368   return 0;
 369 }
 370 #endif /* __GTHREADS */