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 #include <assert.h>
   9
  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_call(const struct side_event_state *event_state, const struct side_arg_vec *side_arg_vec)
  67 {
  68         struct side_rcu_read_state rcu_read_state;
  69         const struct side_event_state_0 *es0;
  70         const struct side_callback *side_cb;
  71         uintptr_t enabled;
  72
  73         if (side_unlikely(finalized))
  74                 return;
  75         if (side_unlikely(!initialized))
  76                 side_init();
  77         if (side_unlikely(event_state->version != 0))
  78                 abort();
  79         es0 = side_container_of(event_state, const struct side_event_state_0, p);
  80         assert(!(es0->desc->flags & SIDE_EVENT_FLAG_VARIADIC));
  81         enabled = __atomic_load_n(&es0->enabled, __ATOMIC_RELAXED);
  82         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  83                 // TODO: call kernel write.
  84         }
  85         side_rcu_read_begin(&rcu_gp, &rcu_read_state);
  86         for (side_cb = side_rcu_dereference(es0->callbacks); side_cb->u.call != NULL; side_cb++)
  87                 side_cb->u.call(es0->desc, side_arg_vec, side_cb->priv);
  88         side_rcu_read_end(&rcu_gp, &rcu_read_state);
  89 }
  90
  91 void side_call_variadic(const struct side_event_state *event_state,
  92         const struct side_arg_vec *side_arg_vec,
  93         const struct side_arg_dynamic_struct *var_struct)
  94 {
  95         struct side_rcu_read_state rcu_read_state;
  96         const struct side_event_state_0 *es0;
  97         const struct side_callback *side_cb;
  98         uintptr_t enabled;
  99
 100         if (side_unlikely(finalized))
 101                 return;
 102         if (side_unlikely(!initialized))
 103                 side_init();
 104         if (side_unlikely(event_state->version != 0))
 105                 abort();
 106         es0 = side_container_of(event_state, const struct side_event_state_0, p);
 107         assert(es0->desc->flags & SIDE_EVENT_FLAG_VARIADIC);
 108         enabled = __atomic_load_n(&es0->enabled, __ATOMIC_RELAXED);
 109         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
 110                 // TODO: call kernel write.
 111         }
 112         side_rcu_read_begin(&rcu_gp, &rcu_read_state);
 113         for (side_cb = side_rcu_dereference(es0->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
 114                 side_cb->u.call_variadic(es0->desc, side_arg_vec, var_struct, side_cb->priv);
 115         side_rcu_read_end(&rcu_gp, &rcu_read_state);
 116 }
 117
 118 static
 119 const struct side_callback *side_tracer_callback_lookup(
 120                 const struct side_event_description *desc,
 121                 void *call, void *priv)
 122 {
 123         struct side_event_state *event_state = side_ptr_get(desc->state);
 124         const struct side_event_state_0 *es0;
 125         const struct side_callback *cb;
 126
 127         if (side_unlikely(event_state->version != 0))
 128                 abort();
 129         es0 = side_container_of(event_state, const struct side_event_state_0, p);
 130         for (cb = es0->callbacks; cb->u.call != NULL; cb++) {
 131                 if ((void *) cb->u.call == call && cb->priv == priv)
 132                         return cb;
 133         }
 134         return NULL;
 135 }
 136
 137 static
 138 int _side_tracer_callback_register(struct side_event_description *desc,
 139                 void *call, void *priv)
 140 {
 141         struct side_event_state *event_state;
 142         struct side_callback *old_cb, *new_cb;
 143         struct side_event_state_0 *es0;
 144         int ret = SIDE_ERROR_OK;
 145         uint32_t old_nr_cb;
 146
 147         if (!call)
 148                 return SIDE_ERROR_INVAL;
 149         if (finalized)
 150                 return SIDE_ERROR_EXITING;
 151         if (!initialized)
 152                 side_init();
 153         pthread_mutex_lock(&side_lock);
 154         event_state = side_ptr_get(desc->state);
 155         if (side_unlikely(event_state->version != 0))
 156                 abort();
 157         es0 = side_container_of(event_state, struct side_event_state_0, p);
 158         old_nr_cb = desc->nr_callbacks;
 159         if (old_nr_cb == UINT32_MAX) {
 160                 ret = SIDE_ERROR_INVAL;
 161                 goto unlock;
 162         }
 163         /* Reject duplicate (call, priv) tuples. */
 164         if (side_tracer_callback_lookup(desc, call, priv)) {
 165                 ret = SIDE_ERROR_EXIST;
 166                 goto unlock;
 167         }
 168         old_cb = (struct side_callback *) es0->callbacks;
 169         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 170         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 171         if (!new_cb) {
 172                 ret = SIDE_ERROR_NOMEM;
 173                 goto unlock;
 174         }
 175         memcpy(new_cb, old_cb, old_nr_cb);
 176         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 177                 new_cb[old_nr_cb].u.call_variadic =
 178                         (side_tracer_callback_variadic_func) call;
 179         else
 180                 new_cb[old_nr_cb].u.call =
 181                         (side_tracer_callback_func) call;
 182         new_cb[old_nr_cb].priv = priv;
 183         /* High order bits are already zeroed. */
 184         side_rcu_assign_pointer(es0->callbacks, new_cb);
 185         side_rcu_wait_grace_period(&rcu_gp);
 186         if (old_nr_cb)
 187                 free(old_cb);
 188         desc->nr_callbacks++;
 189         /* Increment concurrently with kernel setting the top bits. */
 190         if (!old_nr_cb)
 191                 (void) __atomic_add_fetch(&es0->enabled, 1, __ATOMIC_RELAXED);
 192 unlock:
 193         pthread_mutex_unlock(&side_lock);
 194         return ret;
 195 }
 196
 197 int side_tracer_callback_register(struct side_event_description *desc,
 198                 side_tracer_callback_func call,
 199                 void *priv)
 200 {
 201         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 202                 return SIDE_ERROR_INVAL;
 203         return _side_tracer_callback_register(desc, (void *) call, priv);
 204 }
 205
 206 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 207                 side_tracer_callback_variadic_func call_variadic,
 208                 void *priv)
 209 {
 210         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 211                 return SIDE_ERROR_INVAL;
 212         return _side_tracer_callback_register(desc, (void *) call_variadic, priv);
 213 }
 214
 215 static int _side_tracer_callback_unregister(struct side_event_description *desc,
 216                 void *call, void *priv)
 217 {
 218         struct side_event_state *event_state;
 219         struct side_callback *old_cb, *new_cb;
 220         const struct side_callback *cb_pos;
 221         struct side_event_state_0 *es0;
 222         uint32_t pos_idx;
 223         int ret = SIDE_ERROR_OK;
 224         uint32_t old_nr_cb;
 225
 226         if (!call)
 227                 return SIDE_ERROR_INVAL;
 228         if (finalized)
 229                 return SIDE_ERROR_EXITING;
 230         if (!initialized)
 231                 side_init();
 232         pthread_mutex_lock(&side_lock);
 233         event_state = side_ptr_get(desc->state);
 234         if (side_unlikely(event_state->version != 0))
 235                 abort();
 236         es0 = side_container_of(event_state, struct side_event_state_0, p);
 237         cb_pos = side_tracer_callback_lookup(desc, call, priv);
 238         if (!cb_pos) {
 239                 ret = SIDE_ERROR_NOENT;
 240                 goto unlock;
 241         }
 242         old_nr_cb = desc->nr_callbacks;
 243         old_cb = (struct side_callback *) es0->callbacks;
 244         if (old_nr_cb == 1) {
 245                 new_cb = (struct side_callback *) &side_empty_callback;
 246         } else {
 247                 pos_idx = cb_pos - es0->callbacks;
 248                 /* Remove entry at pos_idx. */
 249                 /* old_nr_cb - 1 (removed cb) + 1 (NULL) */
 250                 new_cb = (struct side_callback *) calloc(old_nr_cb, sizeof(struct side_callback));
 251                 if (!new_cb) {
 252                         ret = SIDE_ERROR_NOMEM;
 253                         goto unlock;
 254                 }
 255                 memcpy(new_cb, old_cb, pos_idx);
 256                 memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
 257         }
 258         /* High order bits are already zeroed. */
 259         side_rcu_assign_pointer(es0->callbacks, new_cb);
 260         side_rcu_wait_grace_period(&rcu_gp);
 261         free(old_cb);
 262         desc->nr_callbacks--;
 263         /* Decrement concurrently with kernel setting the top bits. */
 264         if (old_nr_cb == 1)
 265                 (void) __atomic_add_fetch(&es0->enabled, -1, __ATOMIC_RELAXED);
 266 unlock:
 267         pthread_mutex_unlock(&side_lock);
 268         return ret;
 269 }
 270
 271 int side_tracer_callback_unregister(struct side_event_description *desc,
 272                 side_tracer_callback_func call,
 273                 void *priv)
 274 {
 275         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 276                 return SIDE_ERROR_INVAL;
 277         return _side_tracer_callback_unregister(desc, (void *) call, priv);
 278 }
 279
 280 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 281                 side_tracer_callback_variadic_func call_variadic,
 282                 void *priv)
 283 {
 284         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 285                 return SIDE_ERROR_INVAL;
 286         return _side_tracer_callback_unregister(desc, (void *) call_variadic, priv);
 287 }
 288
 289 struct side_events_register_handle *side_events_register(struct side_event_description **events, uint32_t nr_events)
 290 {
 291         struct side_events_register_handle *events_handle = NULL;
 292         struct side_tracer_handle *tracer_handle;
 293
 294         if (finalized)
 295                 return NULL;
 296         if (!initialized)
 297                 side_init();
 298         events_handle = (struct side_events_register_handle *)
 299                         calloc(1, sizeof(struct side_events_register_handle));
 300         if (!events_handle)
 301                 return NULL;
 302         events_handle->events = events;
 303         events_handle->nr_events = nr_events;
 304
 305         pthread_mutex_lock(&side_lock);
 306         side_list_insert_node_tail(&side_events_list, &events_handle->node);
 307         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 308                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 309                         events, nr_events, tracer_handle->priv);
 310         }
 311         pthread_mutex_unlock(&side_lock);
 312         //TODO: call event batch register ioctl
 313         return events_handle;
 314 }
 315
 316 static
 317 void side_event_remove_callbacks(struct side_event_description *desc)
 318 {
 319         struct side_event_state *event_state = side_ptr_get(desc->state);
 320         uint32_t nr_cb = desc->nr_callbacks;
 321         struct side_event_state_0 *es0;
 322         struct side_callback *old_cb;
 323
 324         if (!nr_cb)
 325                 return;
 326         if (side_unlikely(event_state->version != 0))
 327                 abort();
 328         es0 = side_container_of(event_state, struct side_event_state_0, p);
 329         old_cb = (struct side_callback *) es0->callbacks;
 330         (void) __atomic_add_fetch(&es0->enabled, -1, __ATOMIC_RELAXED);
 331         /*
 332          * Setting the state back to 0 cb and empty callbacks out of
 333          * caution. This should not matter because instrumentation is
 334          * unreachable.
 335          */
 336         desc->nr_callbacks = 0;
 337         side_rcu_assign_pointer(es0->callbacks, &side_empty_callback);
 338         /*
 339          * No need to wait for grace period because instrumentation is
 340          * unreachable.
 341          */
 342         free(old_cb);
 343 }
 344
 345 /*
 346  * Unregister event handle. At this point, all side events in that
 347  * handle should be unreachable.
 348  */
 349 void side_events_unregister(struct side_events_register_handle *events_handle)
 350 {
 351         struct side_tracer_handle *tracer_handle;
 352         uint32_t i;
 353
 354         if (!events_handle)
 355                 return;
 356         if (finalized)
 357                 return;
 358         if (!initialized)
 359                 side_init();
 360         pthread_mutex_lock(&side_lock);
 361         side_list_remove_node(&events_handle->node);
 362         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 363                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 364                         events_handle->events, events_handle->nr_events,
 365                         tracer_handle->priv);
 366         }
 367         for (i = 0; i < events_handle->nr_events; i++) {
 368                 struct side_event_description *event = events_handle->events[i];
 369
 370                 /* Skip NULL pointers */
 371                 if (!event)
 372                         continue;
 373                 side_event_remove_callbacks(event);
 374         }
 375         pthread_mutex_unlock(&side_lock);
 376         //TODO: call event batch unregister ioctl
 377         free(events_handle);
 378 }
 379
 380 struct side_tracer_handle *side_tracer_event_notification_register(
 381                 void (*cb)(enum side_tracer_notification notif,
 382                         struct side_event_description **events, uint32_t nr_events, void *priv),
 383                 void *priv)
 384 {
 385         struct side_tracer_handle *tracer_handle;
 386         struct side_events_register_handle *events_handle;
 387
 388         if (finalized)
 389                 return NULL;
 390         if (!initialized)
 391                 side_init();
 392         tracer_handle = (struct side_tracer_handle *)
 393                                 calloc(1, sizeof(struct side_tracer_handle));
 394         if (!tracer_handle)
 395                 return NULL;
 396         pthread_mutex_lock(&side_lock);
 397         tracer_handle->cb = cb;
 398         tracer_handle->priv = priv;
 399         side_list_insert_node_tail(&side_tracer_list, &tracer_handle->node);
 400         side_list_for_each_entry(events_handle, &side_events_list, node) {
 401                 cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 402                         events_handle->events, events_handle->nr_events, priv);
 403         }
 404         pthread_mutex_unlock(&side_lock);
 405         return tracer_handle;
 406 }
 407
 408 void side_tracer_event_notification_unregister(struct side_tracer_handle *tracer_handle)
 409 {
 410         struct side_events_register_handle *events_handle;
 411
 412         if (finalized)
 413                 return;
 414         if (!initialized)
 415                 side_init();
 416         pthread_mutex_lock(&side_lock);
 417         side_list_for_each_entry(events_handle, &side_events_list, node) {
 418                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 419                         events_handle->events, events_handle->nr_events,
 420                         tracer_handle->priv);
 421         }
 422         side_list_remove_node(&tracer_handle->node);
 423         pthread_mutex_unlock(&side_lock);
 424         free(tracer_handle);
 425 }
 426
 427 void side_init(void)
 428 {
 429         if (initialized)
 430                 return;
 431         side_rcu_gp_init(&rcu_gp);
 432         initialized = true;
 433 }
 434
 435 /*
 436  * side_exit() is executed from a library destructor. It can be called
 437  * explicitly at application exit as well. Concurrent side API use is
 438  * not expected at that point.
 439  */
 440 void side_exit(void)
 441 {
 442         struct side_events_register_handle *handle, *tmp;
 443
 444         if (finalized)
 445                 return;
 446         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 447                 side_events_unregister(handle);
 448         side_rcu_gp_exit(&rcu_gp);
 449         finalized = true;
 450 }