src/side.c

   1 // SPDX-License-Identifier: MIT
   2 /*
   3  * Copyright 2022 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  */
   5
   6 #include <side/trace.h>
   7 #include <string.h>
   8
   9 #include "tracer.h"
  10 #include "rcu.h"
  11 #include "list.h"
  12
  13 /* Top 8 bits reserved for kernel tracer use. */
  14 #if SIDE_BITS_PER_LONG == 64
  15 # define SIDE_EVENT_ENABLED_KERNEL_MASK                 0xFF00000000000000ULL
  16 # define SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK      0x8000000000000000ULL
  17
  18 /* Allow 2^56 tracer references on an event. */
  19 # define SIDE_EVENT_ENABLED_USER_MASK                   0x00FFFFFFFFFFFFFFULL
  20 #else
  21 # define SIDE_EVENT_ENABLED_KERNEL_MASK                 0xFF000000UL
  22 # define SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK      0x80000000UL
  23
  24 /* Allow 2^24 tracer references on an event. */
  25 # define SIDE_EVENT_ENABLED_USER_MASK                   0x00FFFFFFUL
  26 #endif
  27
  28 struct side_events_register_handle {
  29         struct side_list_node node;
  30         struct side_event_description **events;
  31         uint32_t nr_events;
  32 };
  33
  34 struct side_tracer_handle {
  35         struct side_list_node node;
  36         void (*cb)(enum side_tracer_notification notif,
  37                 struct side_event_description **events, uint32_t nr_events, void *priv);
  38         void *priv;
  39 };
  40
  41 static struct side_rcu_gp_state rcu_gp;
  42
  43 /*
  44  * Lazy initialization for early use within library constructors.
  45  */
  46 static bool initialized;
  47 /*
  48  * Do not register/unregister any more events after destructor.
  49  */
  50 static bool finalized;
  51
  52 /*
  53  * Recursive mutex to allow tracer callbacks to use the side API.
  54  */
  55 static pthread_mutex_t side_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
  56
  57 static DEFINE_SIDE_LIST_HEAD(side_events_list);
  58 static DEFINE_SIDE_LIST_HEAD(side_tracer_list);
  59
  60 /*
  61  * The empty callback has a NULL function callback pointer, which stops
  62  * iteration on the array of callbacks immediately.
  63  */
  64 const struct side_callback side_empty_callback = { };
  65
  66 void side_init(void) __attribute__((constructor));
  67 void side_exit(void) __attribute__((destructor));
  68
  69 void side_call(const struct side_event_description *desc, const struct side_arg_vec *side_arg_vec)
  70 {
  71         struct side_rcu_read_state rcu_read_state;
  72         const struct side_callback *side_cb;
  73         uintptr_t enabled;
  74
  75         if (side_unlikely(finalized))
  76                 return;
  77         if (side_unlikely(!initialized))
  78                 side_init();
  79         if (side_unlikely(desc->flags & SIDE_EVENT_FLAG_VARIADIC)) {
  80                 printf("ERROR: unexpected variadic event description\n");
  81                 abort();
  82         }
  83         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
  84         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  85                 // TODO: call kernel write.
  86         }
  87         side_rcu_read_begin(&rcu_gp, &rcu_read_state);
  88         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call != NULL; side_cb++)
  89                 side_cb->u.call(desc, side_arg_vec, side_cb->priv);
  90         side_rcu_read_end(&rcu_gp, &rcu_read_state);
  91 }
  92
  93 void side_call_variadic(const struct side_event_description *desc,
  94         const struct side_arg_vec *side_arg_vec,
  95         const struct side_arg_dynamic_struct *var_struct)
  96 {
  97         struct side_rcu_read_state rcu_read_state;
  98         const struct side_callback *side_cb;
  99         uintptr_t enabled;
 100
 101         if (side_unlikely(finalized))
 102                 return;
 103         if (side_unlikely(!initialized))
 104                 side_init();
 105         if (side_unlikely(!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))) {
 106                 printf("ERROR: unexpected non-variadic event description\n");
 107                 abort();
 108         }
 109         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
 110         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
 111                 // TODO: call kernel write.
 112         }
 113         side_rcu_read_begin(&rcu_gp, &rcu_read_state);
 114         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
 115                 side_cb->u.call_variadic(desc, side_arg_vec, var_struct, side_cb->priv);
 116         side_rcu_read_end(&rcu_gp, &rcu_read_state);
 117 }
 118
 119 static
 120 const struct side_callback *side_tracer_callback_lookup(
 121                 const struct side_event_description *desc,
 122                 void *call, void *priv)
 123 {
 124         const struct side_callback *cb;
 125
 126         for (cb = desc->callbacks; cb->u.call != NULL; cb++) {
 127                 if ((void *) cb->u.call == call && cb->priv == priv)
 128                         return cb;
 129         }
 130         return NULL;
 131 }
 132
 133 static
 134 int _side_tracer_callback_register(struct side_event_description *desc,
 135                 void *call, void *priv)
 136 {
 137         struct side_callback *old_cb, *new_cb;
 138         int ret = SIDE_ERROR_OK;
 139         uint32_t old_nr_cb;
 140
 141         if (!call)
 142                 return SIDE_ERROR_INVAL;
 143         if (finalized)
 144                 return SIDE_ERROR_EXITING;
 145         if (!initialized)
 146                 side_init();
 147         pthread_mutex_lock(&side_lock);
 148         old_nr_cb = desc->nr_callbacks;
 149         if (old_nr_cb == UINT32_MAX) {
 150                 ret = SIDE_ERROR_INVAL;
 151                 goto unlock;
 152         }
 153         /* Reject duplicate (call, priv) tuples. */
 154         if (side_tracer_callback_lookup(desc, call, priv)) {
 155                 ret = SIDE_ERROR_EXIST;
 156                 goto unlock;
 157         }
 158         old_cb = (struct side_callback *) desc->callbacks;
 159         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 160         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 161         if (!new_cb) {
 162                 ret = SIDE_ERROR_NOMEM;
 163                 goto unlock;
 164         }
 165         memcpy(new_cb, old_cb, old_nr_cb);
 166         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 167                 new_cb[old_nr_cb].u.call_variadic =
 168                         (side_tracer_callback_variadic_func) call;
 169         else
 170                 new_cb[old_nr_cb].u.call =
 171                         (side_tracer_callback_func) call;
 172         new_cb[old_nr_cb].priv = priv;
 173         side_rcu_assign_pointer(desc->callbacks, new_cb);
 174         side_rcu_wait_grace_period(&rcu_gp);
 175         if (old_nr_cb)
 176                 free(old_cb);
 177         desc->nr_callbacks++;
 178         /* Increment concurrently with kernel setting the top bits. */
 179         if (!old_nr_cb)
 180                 (void) __atomic_add_fetch(desc->enabled, 1, __ATOMIC_RELAXED);
 181 unlock:
 182         pthread_mutex_unlock(&side_lock);
 183         return ret;
 184 }
 185
 186 int side_tracer_callback_register(struct side_event_description *desc,
 187                 side_tracer_callback_func call,
 188                 void *priv)
 189 {
 190         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 191                 return SIDE_ERROR_INVAL;
 192         return _side_tracer_callback_register(desc, (void *) call, priv);
 193 }
 194
 195 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 196                 side_tracer_callback_variadic_func call_variadic,
 197                 void *priv)
 198 {
 199         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 200                 return SIDE_ERROR_INVAL;
 201         return _side_tracer_callback_register(desc, (void *) call_variadic, priv);
 202 }
 203
 204 int _side_tracer_callback_unregister(struct side_event_description *desc,
 205                 void *call, void *priv)
 206 {
 207         struct side_callback *old_cb, *new_cb;
 208         const struct side_callback *cb_pos;
 209         uint32_t pos_idx;
 210         int ret = SIDE_ERROR_OK;
 211         uint32_t old_nr_cb;
 212
 213         if (!call)
 214                 return SIDE_ERROR_INVAL;
 215         if (finalized)
 216                 return SIDE_ERROR_EXITING;
 217         if (!initialized)
 218                 side_init();
 219         pthread_mutex_lock(&side_lock);
 220         cb_pos = side_tracer_callback_lookup(desc, call, priv);
 221         if (!cb_pos) {
 222                 ret = SIDE_ERROR_NOENT;
 223                 goto unlock;
 224         }
 225         old_nr_cb = desc->nr_callbacks;
 226         old_cb = (struct side_callback *) desc->callbacks;
 227         if (old_nr_cb == 1) {
 228                 new_cb = (struct side_callback *) &side_empty_callback;
 229         } else {
 230                 pos_idx = cb_pos - desc->callbacks;
 231                 /* Remove entry at pos_idx. */
 232                 /* old_nr_cb - 1 (removed cb) + 1 (NULL) */
 233                 new_cb = (struct side_callback *) calloc(old_nr_cb, sizeof(struct side_callback));
 234                 if (!new_cb) {
 235                         ret = SIDE_ERROR_NOMEM;
 236                         goto unlock;
 237                 }
 238                 memcpy(new_cb, old_cb, pos_idx);
 239                 memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
 240         }
 241         side_rcu_assign_pointer(desc->callbacks, new_cb);
 242         side_rcu_wait_grace_period(&rcu_gp);
 243         free(old_cb);
 244         desc->nr_callbacks--;
 245         /* Decrement concurrently with kernel setting the top bits. */
 246         if (old_nr_cb == 1)
 247                 (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 248 unlock:
 249         pthread_mutex_unlock(&side_lock);
 250         return ret;
 251 }
 252
 253 int side_tracer_callback_unregister(struct side_event_description *desc,
 254                 side_tracer_callback_func call,
 255                 void *priv)
 256 {
 257         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 258                 return SIDE_ERROR_INVAL;
 259         return _side_tracer_callback_unregister(desc, (void *) call, priv);
 260 }
 261
 262 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 263                 side_tracer_callback_variadic_func call_variadic,
 264                 void *priv)
 265 {
 266         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 267                 return SIDE_ERROR_INVAL;
 268         return _side_tracer_callback_unregister(desc, (void *) call_variadic, priv);
 269 }
 270
 271 struct side_events_register_handle *side_events_register(struct side_event_description **events, uint32_t nr_events)
 272 {
 273         struct side_events_register_handle *events_handle = NULL;
 274         struct side_tracer_handle *tracer_handle;
 275
 276         if (finalized)
 277                 return NULL;
 278         if (!initialized)
 279                 side_init();
 280         events_handle = (struct side_events_register_handle *)
 281                         calloc(1, sizeof(struct side_events_register_handle));
 282         if (!events_handle)
 283                 return NULL;
 284         events_handle->events = events;
 285         events_handle->nr_events = nr_events;
 286
 287         pthread_mutex_lock(&side_lock);
 288         side_list_insert_node_tail(&side_events_list, &events_handle->node);
 289         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 290                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 291                         events, nr_events, tracer_handle->priv);
 292         }
 293         pthread_mutex_unlock(&side_lock);
 294         //TODO: call event batch register ioctl
 295         return events_handle;
 296 }
 297
 298 static
 299 void side_event_remove_callbacks(struct side_event_description *desc)
 300 {
 301         uint32_t nr_cb = desc->nr_callbacks;
 302         struct side_callback *old_cb;
 303
 304         if (!nr_cb)
 305                 return;
 306         old_cb = (struct side_callback *) desc->callbacks;
 307         (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 308         /*
 309          * Setting the state back to 0 cb and empty callbacks out of
 310          * caution. This should not matter because instrumentation is
 311          * unreachable.
 312          */
 313         desc->nr_callbacks = 0;
 314         side_rcu_assign_pointer(desc->callbacks, &side_empty_callback);
 315         /*
 316          * No need to wait for grace period because instrumentation is
 317          * unreachable.
 318          */
 319         free(old_cb);
 320 }
 321
 322 /*
 323  * Unregister event handle. At this point, all side events in that
 324  * handle should be unreachable.
 325  */
 326 void side_events_unregister(struct side_events_register_handle *events_handle)
 327 {
 328         struct side_tracer_handle *tracer_handle;
 329         uint32_t i;
 330
 331         if (!events_handle)
 332                 return;
 333         if (finalized)
 334                 return;
 335         if (!initialized)
 336                 side_init();
 337         pthread_mutex_lock(&side_lock);
 338         side_list_remove_node(&events_handle->node);
 339         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 340                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 341                         events_handle->events, events_handle->nr_events,
 342                         tracer_handle->priv);
 343         }
 344         for (i = 0; i < events_handle->nr_events; i++) {
 345                 struct side_event_description *event = events_handle->events[i];
 346
 347                 /* Skip NULL pointers */
 348                 if (!event)
 349                         continue;
 350                 side_event_remove_callbacks(event);
 351         }
 352         pthread_mutex_unlock(&side_lock);
 353         //TODO: call event batch unregister ioctl
 354         free(events_handle);
 355 }
 356
 357 struct side_tracer_handle *side_tracer_event_notification_register(
 358                 void (*cb)(enum side_tracer_notification notif,
 359                         struct side_event_description **events, uint32_t nr_events, void *priv),
 360                 void *priv)
 361 {
 362         struct side_tracer_handle *tracer_handle;
 363         struct side_events_register_handle *events_handle;
 364
 365         if (finalized)
 366                 return NULL;
 367         if (!initialized)
 368                 side_init();
 369         tracer_handle = (struct side_tracer_handle *)
 370                                 calloc(1, sizeof(struct side_tracer_handle));
 371         if (!tracer_handle)
 372                 return NULL;
 373         pthread_mutex_lock(&side_lock);
 374         tracer_handle->cb = cb;
 375         tracer_handle->priv = priv;
 376         side_list_insert_node_tail(&side_tracer_list, &tracer_handle->node);
 377         side_list_for_each_entry(events_handle, &side_events_list, node) {
 378                 cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 379                         events_handle->events, events_handle->nr_events, priv);
 380         }
 381         pthread_mutex_unlock(&side_lock);
 382         return tracer_handle;
 383 }
 384
 385 void side_tracer_event_notification_unregister(struct side_tracer_handle *tracer_handle)
 386 {
 387         struct side_events_register_handle *events_handle;
 388
 389         if (finalized)
 390                 return;
 391         if (!initialized)
 392                 side_init();
 393         pthread_mutex_lock(&side_lock);
 394         side_list_for_each_entry(events_handle, &side_events_list, node) {
 395                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 396                         events_handle->events, events_handle->nr_events,
 397                         tracer_handle->priv);
 398         }
 399         side_list_remove_node(&tracer_handle->node);
 400         pthread_mutex_unlock(&side_lock);
 401 }
 402
 403 void side_init(void)
 404 {
 405         if (initialized)
 406                 return;
 407         side_rcu_gp_init(&rcu_gp);
 408         initialized = true;
 409 }
 410
 411 /*
 412  * side_exit() is executed from a library destructor. It can be called
 413  * explicitly at application exit as well. Concurrent side API use is
 414  * not expected at that point.
 415  */
 416 void side_exit(void)
 417 {
 418         struct side_events_register_handle *handle, *tmp;
 419
 420         if (finalized)
 421                 return;
 422         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 423                 side_events_unregister(handle);
 424         side_rcu_gp_exit(&rcu_gp);
 425         finalized = true;
 426 }