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 static pthread_mutex_t side_lock = PTHREAD_MUTEX_INITIALIZER;
  53
  54 static DEFINE_SIDE_LIST_HEAD(side_events_list);
  55 static DEFINE_SIDE_LIST_HEAD(side_tracer_list);
  56
  57 /*
  58  * The empty callback has a NULL function callback pointer, which stops
  59  * iteration on the array of callbacks immediately.
  60  */
  61 const struct side_callback side_empty_callback;
  62
  63 void side_init(void) __attribute__((constructor));
  64 void side_exit(void) __attribute__((destructor));
  65
  66 void side_call(const struct side_event_description *desc, const struct side_arg_vec_description *sav_desc)
  67 {
  68         const struct side_callback *side_cb;
  69         unsigned int rcu_period;
  70         uintptr_t enabled;
  71
  72         if (side_unlikely(finalized))
  73                 return;
  74         if (side_unlikely(!initialized))
  75                 side_init();
  76         if (side_unlikely(desc->flags & SIDE_EVENT_FLAG_VARIADIC)) {
  77                 printf("ERROR: unexpected variadic event description\n");
  78                 abort();
  79         }
  80         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
  81         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
  82                 // TODO: call kernel write.
  83         }
  84         if (side_unlikely(!(enabled & SIDE_EVENT_ENABLED_USER_MASK)))
  85                 return;
  86
  87         rcu_period = side_rcu_read_begin(&rcu_gp);
  88         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call != NULL; side_cb++)
  89                 side_cb->u.call(desc, sav_desc, side_cb->priv);
  90         side_rcu_read_end(&rcu_gp, rcu_period);
  91 }
  92
  93 void side_call_variadic(const struct side_event_description *desc,
  94         const struct side_arg_vec_description *sav_desc,
  95         const struct side_arg_dynamic_event_struct *var_struct)
  96 {
  97         const struct side_callback *side_cb;
  98         unsigned int rcu_period;
  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         if (side_unlikely(!(enabled & SIDE_EVENT_ENABLED_USER_MASK)))
 114                 return;
 115
 116         rcu_period = side_rcu_read_begin(&rcu_gp);
 117         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
 118                 side_cb->u.call_variadic(desc, sav_desc, var_struct, side_cb->priv);
 119         side_rcu_read_end(&rcu_gp, rcu_period);
 120 }
 121
 122 static
 123 const struct side_callback *side_tracer_callback_lookup(
 124                 const struct side_event_description *desc,
 125                 void (*call)(), void *priv)
 126 {
 127         const struct side_callback *cb;
 128
 129         for (cb = desc->callbacks; cb->u.call != NULL; cb++) {
 130                 if (cb->u.call == call && cb->priv == priv)
 131                         return cb;
 132         }
 133         return NULL;
 134 }
 135
 136 static
 137 int _side_tracer_callback_register(struct side_event_description *desc,
 138                 void (*call)(), void *priv)
 139 {
 140         struct side_callback *old_cb, *new_cb;
 141         int ret = SIDE_ERROR_OK;
 142         uint32_t old_nr_cb;
 143
 144         if (!call)
 145                 return SIDE_ERROR_INVAL;
 146         if (finalized)
 147                 return SIDE_ERROR_EXITING;
 148         if (!initialized)
 149                 side_init();
 150         pthread_mutex_lock(&side_lock);
 151         old_nr_cb = desc->nr_callbacks;
 152         if (old_nr_cb == UINT32_MAX) {
 153                 ret = SIDE_ERROR_INVAL;
 154                 goto unlock;
 155         }
 156         /* Reject duplicate (call, priv) tuples. */
 157         if (side_tracer_callback_lookup(desc, call, priv)) {
 158                 ret = SIDE_ERROR_EXIST;
 159                 goto unlock;
 160         }
 161         old_cb = (struct side_callback *) desc->callbacks;
 162         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 163         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 164         if (!new_cb) {
 165                 ret = SIDE_ERROR_NOMEM;
 166                 goto unlock;
 167         }
 168         memcpy(new_cb, old_cb, old_nr_cb);
 169         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 170                 new_cb[old_nr_cb].u.call_variadic = call;
 171         else
 172                 new_cb[old_nr_cb].u.call = call;
 173         new_cb[old_nr_cb].priv = priv;
 174         side_rcu_assign_pointer(desc->callbacks, new_cb);
 175         side_rcu_wait_grace_period(&rcu_gp);
 176         if (old_nr_cb)
 177                 free(old_cb);
 178         desc->nr_callbacks++;
 179         /* Increment concurrently with kernel setting the top bits. */
 180         if (!old_nr_cb)
 181                 (void) __atomic_add_fetch(desc->enabled, 1, __ATOMIC_RELAXED);
 182 unlock:
 183         pthread_mutex_unlock(&side_lock);
 184         return ret;
 185 }
 186
 187 int side_tracer_callback_register(struct side_event_description *desc,
 188                 void (*call)(const struct side_event_description *desc,
 189                         const struct side_arg_vec_description *sav_desc,
 190                         void *priv),
 191                 void *priv)
 192 {
 193         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 194                 return SIDE_ERROR_INVAL;
 195         return _side_tracer_callback_register(desc, call, priv);
 196 }
 197
 198 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 199                 void (*call_variadic)(const struct side_event_description *desc,
 200                         const struct side_arg_vec_description *sav_desc,
 201                         const struct side_arg_dynamic_event_struct *var_struct,
 202                         void *priv),
 203                 void *priv)
 204 {
 205         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 206                 return SIDE_ERROR_INVAL;
 207         return _side_tracer_callback_register(desc, call_variadic, priv);
 208 }
 209
 210 int _side_tracer_callback_unregister(struct side_event_description *desc,
 211                 void (*call)(), void *priv)
 212 {
 213         struct side_callback *old_cb, *new_cb;
 214         const struct side_callback *cb_pos;
 215         uint32_t pos_idx;
 216         int ret = SIDE_ERROR_OK;
 217         uint32_t old_nr_cb;
 218
 219         if (!call)
 220                 return SIDE_ERROR_INVAL;
 221         if (finalized)
 222                 return SIDE_ERROR_EXITING;
 223         if (!initialized)
 224                 side_init();
 225         pthread_mutex_lock(&side_lock);
 226         cb_pos = side_tracer_callback_lookup(desc, call, priv);
 227         if (!cb_pos) {
 228                 ret = SIDE_ERROR_NOENT;
 229                 goto unlock;
 230         }
 231         old_nr_cb = desc->nr_callbacks;
 232         old_cb = (struct side_callback *) desc->callbacks;
 233         if (old_nr_cb == 1) {
 234                 new_cb = (struct side_callback *) &side_empty_callback;
 235         } else {
 236                 pos_idx = cb_pos - desc->callbacks;
 237                 /* Remove entry at pos_idx. */
 238                 /* old_nr_cb - 1 (removed cb) + 1 (NULL) */
 239                 new_cb = (struct side_callback *) calloc(old_nr_cb, sizeof(struct side_callback));
 240                 if (!new_cb) {
 241                         ret = SIDE_ERROR_NOMEM;
 242                         goto unlock;
 243                 }
 244                 memcpy(new_cb, old_cb, pos_idx);
 245                 memcpy(&new_cb[pos_idx], &old_cb[pos_idx + 1], old_nr_cb - pos_idx - 1);
 246         }
 247         side_rcu_assign_pointer(desc->callbacks, new_cb);
 248         side_rcu_wait_grace_period(&rcu_gp);
 249         free(old_cb);
 250         desc->nr_callbacks--;
 251         /* Decrement concurrently with kernel setting the top bits. */
 252         if (old_nr_cb == 1)
 253                 (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 254 unlock:
 255         pthread_mutex_unlock(&side_lock);
 256         return ret;
 257 }
 258
 259 int side_tracer_callback_unregister(struct side_event_description *desc,
 260                 void (*call)(const struct side_event_description *desc,
 261                         const struct side_arg_vec_description *sav_desc,
 262                         void *priv),
 263                 void *priv)
 264 {
 265         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 266                 return SIDE_ERROR_INVAL;
 267         return _side_tracer_callback_unregister(desc, call, priv);
 268 }
 269
 270 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 271                 void (*call_variadic)(const struct side_event_description *desc,
 272                         const struct side_arg_vec_description *sav_desc,
 273                         const struct side_arg_dynamic_event_struct *var_struct,
 274                         void *priv),
 275                 void *priv)
 276 {
 277         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 278                 return SIDE_ERROR_INVAL;
 279         return _side_tracer_callback_unregister(desc, call_variadic, priv);
 280 }
 281
 282 struct side_events_register_handle *side_events_register(struct side_event_description **events, uint32_t nr_events)
 283 {
 284         struct side_events_register_handle *events_handle = NULL;
 285         struct side_tracer_handle *tracer_handle;
 286
 287         if (finalized)
 288                 return NULL;
 289         if (!initialized)
 290                 side_init();
 291         events_handle = calloc(1, sizeof(struct side_events_register_handle));
 292         if (!events_handle)
 293                 return NULL;
 294         events_handle->events = events;
 295         events_handle->nr_events = nr_events;
 296
 297         pthread_mutex_lock(&side_lock);
 298         side_list_insert_node_tail(&side_events_list, &events_handle->node);
 299         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 300                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 301                         events, nr_events, tracer_handle->priv);
 302         }
 303         pthread_mutex_unlock(&side_lock);
 304         //TODO: call event batch register ioctl
 305         return events_handle;
 306 }
 307
 308 static
 309 void side_event_remove_callbacks(struct side_event_description *desc)
 310 {
 311         uint32_t nr_cb = desc->nr_callbacks;
 312         struct side_callback *old_cb;
 313
 314         if (!nr_cb)
 315                 return;
 316         old_cb = (struct side_callback *) desc->callbacks;
 317         (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 318         /*
 319          * Setting the state back to 0 cb and empty callbacks out of
 320          * caution. This should not matter because instrumentation is
 321          * unreachable.
 322          */
 323         desc->nr_callbacks = 0;
 324         side_rcu_assign_pointer(desc->callbacks, &side_empty_callback);
 325         /*
 326          * No need to wait for grace period because instrumentation is
 327          * unreachable.
 328          */
 329         free(old_cb);
 330 }
 331
 332 /*
 333  * Unregister event handle. At this point, all side events in that
 334  * handle should be unreachable.
 335  */
 336 void side_events_unregister(struct side_events_register_handle *events_handle)
 337 {
 338         struct side_tracer_handle *tracer_handle;
 339         uint32_t i;
 340
 341         if (!events_handle)
 342                 return;
 343         if (finalized)
 344                 return;
 345         if (!initialized)
 346                 side_init();
 347         pthread_mutex_lock(&side_lock);
 348         side_list_remove_node(&events_handle->node);
 349         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 350                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 351                         events_handle->events, events_handle->nr_events,
 352                         tracer_handle->priv);
 353         }
 354         for (i = 0; i < events_handle->nr_events; i++) {
 355                 struct side_event_description *event = events_handle->events[i];
 356
 357                 /* Skip NULL pointers */
 358                 if (!event)
 359                         continue;
 360                 side_event_remove_callbacks(event);
 361         }
 362         pthread_mutex_unlock(&side_lock);
 363         //TODO: call event batch unregister ioctl
 364         free(events_handle);
 365 }
 366
 367 struct side_tracer_handle *side_tracer_event_notification_register(
 368                 void (*cb)(enum side_tracer_notification notif,
 369                         struct side_event_description **events, uint32_t nr_events, void *priv),
 370                 void *priv)
 371 {
 372         struct side_tracer_handle *tracer_handle;
 373         struct side_events_register_handle *events_handle;
 374
 375         if (finalized)
 376                 return NULL;
 377         if (!initialized)
 378                 side_init();
 379         tracer_handle = calloc(1, sizeof(struct side_tracer_handle));
 380         if (!tracer_handle)
 381                 return NULL;
 382         pthread_mutex_lock(&side_lock);
 383         tracer_handle->cb = cb;
 384         tracer_handle->priv = priv;
 385         side_list_insert_node_tail(&side_tracer_list, &tracer_handle->node);
 386         side_list_for_each_entry(events_handle, &side_events_list, node) {
 387                 cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 388                         events_handle->events, events_handle->nr_events, priv);
 389         }
 390         pthread_mutex_unlock(&side_lock);
 391         return tracer_handle;
 392 }
 393
 394 void side_tracer_event_notification_unregister(struct side_tracer_handle *tracer_handle)
 395 {
 396         struct side_events_register_handle *events_handle;
 397
 398         if (finalized)
 399                 return;
 400         if (!initialized)
 401                 side_init();
 402         pthread_mutex_lock(&side_lock);
 403         side_list_for_each_entry(events_handle, &side_events_list, node) {
 404                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 405                         events_handle->events, events_handle->nr_events,
 406                         tracer_handle->priv);
 407         }
 408         side_list_remove_node(&tracer_handle->node);
 409         pthread_mutex_unlock(&side_lock);
 410 }
 411
 412 void side_init(void)
 413 {
 414         if (initialized)
 415                 return;
 416         side_rcu_gp_init(&rcu_gp);
 417         initialized = true;
 418 }
 419
 420 /*
 421  * side_exit() is executed from a library destructor. It can be called
 422  * explicitly at application exit as well. Concurrent side API use is
 423  * not expected at that point.
 424  */
 425 void side_exit(void)
 426 {
 427         struct side_events_register_handle *handle, *tmp;
 428
 429         if (finalized)
 430                 return;
 431         side_rcu_gp_exit(&rcu_gp);
 432         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 433                 side_events_unregister(handle);
 434         finalized = true;
 435 }