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         rcu_period = side_rcu_read_begin(&rcu_gp);
  85         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call != NULL; side_cb++)
  86                 side_cb->u.call(desc, sav_desc, side_cb->priv);
  87         side_rcu_read_end(&rcu_gp, rcu_period);
  88 }
  89
  90 void side_call_variadic(const struct side_event_description *desc,
  91         const struct side_arg_vec_description *sav_desc,
  92         const struct side_arg_dynamic_event_struct *var_struct)
  93 {
  94         const struct side_callback *side_cb;
  95         unsigned int rcu_period;
  96         uintptr_t enabled;
  97
  98         if (side_unlikely(finalized))
  99                 return;
 100         if (side_unlikely(!initialized))
 101                 side_init();
 102         if (side_unlikely(!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))) {
 103                 printf("ERROR: unexpected non-variadic event description\n");
 104                 abort();
 105         }
 106         enabled = __atomic_load_n(desc->enabled, __ATOMIC_RELAXED);
 107         if (side_unlikely(enabled & SIDE_EVENT_ENABLED_KERNEL_USER_EVENT_MASK)) {
 108                 // TODO: call kernel write.
 109         }
 110         rcu_period = side_rcu_read_begin(&rcu_gp);
 111         for (side_cb = side_rcu_dereference(desc->callbacks); side_cb->u.call_variadic != NULL; side_cb++)
 112                 side_cb->u.call_variadic(desc, sav_desc, var_struct, side_cb->priv);
 113         side_rcu_read_end(&rcu_gp, rcu_period);
 114 }
 115
 116 static
 117 const struct side_callback *side_tracer_callback_lookup(
 118                 const struct side_event_description *desc,
 119                 void (*call)(), void *priv)
 120 {
 121         const struct side_callback *cb;
 122
 123         for (cb = desc->callbacks; cb->u.call != NULL; cb++) {
 124                 if (cb->u.call == call && cb->priv == priv)
 125                         return cb;
 126         }
 127         return NULL;
 128 }
 129
 130 static
 131 int _side_tracer_callback_register(struct side_event_description *desc,
 132                 void (*call)(), void *priv)
 133 {
 134         struct side_callback *old_cb, *new_cb;
 135         int ret = SIDE_ERROR_OK;
 136         uint32_t old_nr_cb;
 137
 138         if (!call)
 139                 return SIDE_ERROR_INVAL;
 140         if (finalized)
 141                 return SIDE_ERROR_EXITING;
 142         if (!initialized)
 143                 side_init();
 144         pthread_mutex_lock(&side_lock);
 145         old_nr_cb = desc->nr_callbacks;
 146         if (old_nr_cb == UINT32_MAX) {
 147                 ret = SIDE_ERROR_INVAL;
 148                 goto unlock;
 149         }
 150         /* Reject duplicate (call, priv) tuples. */
 151         if (side_tracer_callback_lookup(desc, call, priv)) {
 152                 ret = SIDE_ERROR_EXIST;
 153                 goto unlock;
 154         }
 155         old_cb = (struct side_callback *) desc->callbacks;
 156         /* old_nr_cb + 1 (new cb) + 1 (NULL) */
 157         new_cb = (struct side_callback *) calloc(old_nr_cb + 2, sizeof(struct side_callback));
 158         if (!new_cb) {
 159                 ret = SIDE_ERROR_NOMEM;
 160                 goto unlock;
 161         }
 162         memcpy(new_cb, old_cb, old_nr_cb);
 163         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 164                 new_cb[old_nr_cb].u.call_variadic = call;
 165         else
 166                 new_cb[old_nr_cb].u.call = call;
 167         new_cb[old_nr_cb].priv = priv;
 168         side_rcu_assign_pointer(desc->callbacks, new_cb);
 169         side_rcu_wait_grace_period(&rcu_gp);
 170         if (old_nr_cb)
 171                 free(old_cb);
 172         desc->nr_callbacks++;
 173         /* Increment concurrently with kernel setting the top bits. */
 174         if (!old_nr_cb)
 175                 (void) __atomic_add_fetch(desc->enabled, 1, __ATOMIC_RELAXED);
 176 unlock:
 177         pthread_mutex_unlock(&side_lock);
 178         return ret;
 179 }
 180
 181 int side_tracer_callback_register(struct side_event_description *desc,
 182                 void (*call)(const struct side_event_description *desc,
 183                         const struct side_arg_vec_description *sav_desc,
 184                         void *priv),
 185                 void *priv)
 186 {
 187         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 188                 return SIDE_ERROR_INVAL;
 189         return _side_tracer_callback_register(desc, call, priv);
 190 }
 191
 192 int side_tracer_callback_variadic_register(struct side_event_description *desc,
 193                 void (*call_variadic)(const struct side_event_description *desc,
 194                         const struct side_arg_vec_description *sav_desc,
 195                         const struct side_arg_dynamic_event_struct *var_struct,
 196                         void *priv),
 197                 void *priv)
 198 {
 199         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 200                 return SIDE_ERROR_INVAL;
 201         return _side_tracer_callback_register(desc, 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                 void (*call)(const struct side_event_description *desc,
 255                         const struct side_arg_vec_description *sav_desc,
 256                         void *priv),
 257                 void *priv)
 258 {
 259         if (desc->flags & SIDE_EVENT_FLAG_VARIADIC)
 260                 return SIDE_ERROR_INVAL;
 261         return _side_tracer_callback_unregister(desc, call, priv);
 262 }
 263
 264 int side_tracer_callback_variadic_unregister(struct side_event_description *desc,
 265                 void (*call_variadic)(const struct side_event_description *desc,
 266                         const struct side_arg_vec_description *sav_desc,
 267                         const struct side_arg_dynamic_event_struct *var_struct,
 268                         void *priv),
 269                 void *priv)
 270 {
 271         if (!(desc->flags & SIDE_EVENT_FLAG_VARIADIC))
 272                 return SIDE_ERROR_INVAL;
 273         return _side_tracer_callback_unregister(desc, call_variadic, priv);
 274 }
 275
 276 struct side_events_register_handle *side_events_register(struct side_event_description **events, uint32_t nr_events)
 277 {
 278         struct side_events_register_handle *events_handle = NULL;
 279         struct side_tracer_handle *tracer_handle;
 280
 281         if (finalized)
 282                 return NULL;
 283         if (!initialized)
 284                 side_init();
 285         events_handle = calloc(1, sizeof(struct side_events_register_handle));
 286         if (!events_handle)
 287                 return NULL;
 288         events_handle->events = events;
 289         events_handle->nr_events = nr_events;
 290
 291         pthread_mutex_lock(&side_lock);
 292         side_list_insert_node_tail(&side_events_list, &events_handle->node);
 293         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 294                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 295                         events, nr_events, tracer_handle->priv);
 296         }
 297         pthread_mutex_unlock(&side_lock);
 298         //TODO: call event batch register ioctl
 299         return events_handle;
 300 }
 301
 302 static
 303 void side_event_remove_callbacks(struct side_event_description *desc)
 304 {
 305         uint32_t nr_cb = desc->nr_callbacks;
 306         struct side_callback *old_cb;
 307
 308         if (!nr_cb)
 309                 return;
 310         old_cb = (struct side_callback *) desc->callbacks;
 311         (void) __atomic_add_fetch(desc->enabled, -1, __ATOMIC_RELAXED);
 312         /*
 313          * Setting the state back to 0 cb and empty callbacks out of
 314          * caution. This should not matter because instrumentation is
 315          * unreachable.
 316          */
 317         desc->nr_callbacks = 0;
 318         side_rcu_assign_pointer(desc->callbacks, &side_empty_callback);
 319         /*
 320          * No need to wait for grace period because instrumentation is
 321          * unreachable.
 322          */
 323         free(old_cb);
 324 }
 325
 326 /*
 327  * Unregister event handle. At this point, all side events in that
 328  * handle should be unreachable.
 329  */
 330 void side_events_unregister(struct side_events_register_handle *events_handle)
 331 {
 332         struct side_tracer_handle *tracer_handle;
 333         uint32_t i;
 334
 335         if (!events_handle)
 336                 return;
 337         if (finalized)
 338                 return;
 339         if (!initialized)
 340                 side_init();
 341         pthread_mutex_lock(&side_lock);
 342         side_list_remove_node(&events_handle->node);
 343         side_list_for_each_entry(tracer_handle, &side_tracer_list, node) {
 344                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 345                         events_handle->events, events_handle->nr_events,
 346                         tracer_handle->priv);
 347         }
 348         for (i = 0; i < events_handle->nr_events; i++) {
 349                 struct side_event_description *event = events_handle->events[i];
 350
 351                 /* Skip NULL pointers */
 352                 if (!event)
 353                         continue;
 354                 side_event_remove_callbacks(event);
 355         }
 356         pthread_mutex_unlock(&side_lock);
 357         //TODO: call event batch unregister ioctl
 358         free(events_handle);
 359 }
 360
 361 struct side_tracer_handle *side_tracer_event_notification_register(
 362                 void (*cb)(enum side_tracer_notification notif,
 363                         struct side_event_description **events, uint32_t nr_events, void *priv),
 364                 void *priv)
 365 {
 366         struct side_tracer_handle *tracer_handle;
 367         struct side_events_register_handle *events_handle;
 368
 369         if (finalized)
 370                 return NULL;
 371         if (!initialized)
 372                 side_init();
 373         tracer_handle = calloc(1, sizeof(struct side_tracer_handle));
 374         if (!tracer_handle)
 375                 return NULL;
 376         pthread_mutex_lock(&side_lock);
 377         tracer_handle->cb = cb;
 378         tracer_handle->priv = priv;
 379         side_list_insert_node_tail(&side_tracer_list, &tracer_handle->node);
 380         side_list_for_each_entry(events_handle, &side_events_list, node) {
 381                 cb(SIDE_TRACER_NOTIFICATION_INSERT_EVENTS,
 382                         events_handle->events, events_handle->nr_events, priv);
 383         }
 384         pthread_mutex_unlock(&side_lock);
 385         return tracer_handle;
 386 }
 387
 388 void side_tracer_event_notification_unregister(struct side_tracer_handle *tracer_handle)
 389 {
 390         struct side_events_register_handle *events_handle;
 391
 392         if (finalized)
 393                 return;
 394         if (!initialized)
 395                 side_init();
 396         pthread_mutex_lock(&side_lock);
 397         side_list_for_each_entry(events_handle, &side_events_list, node) {
 398                 tracer_handle->cb(SIDE_TRACER_NOTIFICATION_REMOVE_EVENTS,
 399                         events_handle->events, events_handle->nr_events,
 400                         tracer_handle->priv);
 401         }
 402         side_list_remove_node(&tracer_handle->node);
 403         pthread_mutex_unlock(&side_lock);
 404 }
 405
 406 void side_init(void)
 407 {
 408         if (initialized)
 409                 return;
 410         side_rcu_gp_init(&rcu_gp);
 411         initialized = true;
 412 }
 413
 414 /*
 415  * side_exit() is executed from a library destructor. It can be called
 416  * explicitly at application exit as well. Concurrent side API use is
 417  * not expected at that point.
 418  */
 419 void side_exit(void)
 420 {
 421         struct side_events_register_handle *handle, *tmp;
 422
 423         if (finalized)
 424                 return;
 425         side_rcu_gp_exit(&rcu_gp);
 426         side_list_for_each_entry_safe(handle, tmp, &side_events_list, node)
 427                 side_events_unregister(handle);
 428         finalized = true;
 429 }