| 1 | /* |
| 2 | * Simple trace backend |
| 3 | * |
| 4 | * Copyright IBM, Corp. 2010 |
| 5 | * |
| 6 | * This work is licensed under the terms of the GNU GPL, version 2. See |
| 7 | * the COPYING file in the top-level directory. |
| 8 | * |
| 9 | */ |
| 10 | |
| 11 | #include "qemu/osdep.h" |
| 12 | #ifndef _WIN32 |
| 13 | #include <pthread.h> |
| 14 | #endif |
| 15 | #include "qemu/timer.h" |
| 16 | #include "trace/control.h" |
| 17 | #include "trace/simple.h" |
| 18 | #include "qemu/error-report.h" |
| 19 | #include "qemu/qemu-print.h" |
| 20 | |
| 21 | /** Trace file header event ID, picked to avoid conflict with real event IDs */ |
| 22 | #define HEADER_EVENT_ID (~(uint64_t)0) |
| 23 | |
| 24 | /** Trace file magic number */ |
| 25 | #define HEADER_MAGIC 0xf2b177cb0aa429b4ULL |
| 26 | |
| 27 | /** Trace file version number, bump if format changes */ |
| 28 | #define HEADER_VERSION 4 |
| 29 | |
| 30 | /** Records were dropped event ID */ |
| 31 | #define DROPPED_EVENT_ID (~(uint64_t)0 - 1) |
| 32 | |
| 33 | /** Trace record is valid */ |
| 34 | #define TRACE_RECORD_VALID ((uint64_t)1 << 63) |
| 35 | |
| 36 | /* |
| 37 | * Trace records are written out by a dedicated thread. The thread waits for |
| 38 | * records to become available, writes them out, and then waits again. |
| 39 | */ |
| 40 | static GMutex trace_lock; |
| 41 | static GCond trace_available_cond; |
| 42 | static GCond trace_empty_cond; |
| 43 | |
| 44 | static bool trace_available; |
| 45 | static bool trace_writeout_enabled; |
| 46 | |
| 47 | enum { |
| 48 | TRACE_BUF_LEN = 4096 * 64, |
| 49 | TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4, |
| 50 | }; |
| 51 | |
| 52 | uint8_t trace_buf[TRACE_BUF_LEN]; |
| 53 | static volatile gint trace_idx; |
| 54 | static unsigned int writeout_idx; |
| 55 | static volatile gint dropped_events; |
| 56 | static uint32_t trace_pid; |
| 57 | static FILE *trace_fp; |
| 58 | static char *trace_file_name; |
| 59 | |
| 60 | #define TRACE_RECORD_TYPE_MAPPING 0 |
| 61 | #define TRACE_RECORD_TYPE_EVENT 1 |
| 62 | |
| 63 | /* * Trace buffer entry */ |
| 64 | typedef struct { |
| 65 | uint64_t event; /* event ID value */ |
| 66 | uint64_t timestamp_ns; |
| 67 | uint32_t length; /* in bytes */ |
| 68 | uint32_t pid; |
| 69 | uint64_t arguments[]; |
| 70 | } TraceRecord; |
| 71 | |
| 72 | typedef struct { |
| 73 | uint64_t header_event_id; /* HEADER_EVENT_ID */ |
| 74 | uint64_t header_magic; /* HEADER_MAGIC */ |
| 75 | uint64_t header_version; /* HEADER_VERSION */ |
| 76 | } TraceLogHeader; |
| 77 | |
| 78 | |
| 79 | static void read_from_buffer(unsigned int idx, void *dataptr, size_t size); |
| 80 | static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size); |
| 81 | |
| 82 | static void clear_buffer_range(unsigned int idx, size_t len) |
| 83 | { |
| 84 | uint32_t num = 0; |
| 85 | while (num < len) { |
| 86 | if (idx >= TRACE_BUF_LEN) { |
| 87 | idx = idx % TRACE_BUF_LEN; |
| 88 | } |
| 89 | trace_buf[idx++] = 0; |
| 90 | num++; |
| 91 | } |
| 92 | } |
| 93 | /** |
| 94 | * Read a trace record from the trace buffer |
| 95 | * |
| 96 | * @idx Trace buffer index |
| 97 | * @record Trace record to fill |
| 98 | * |
| 99 | * Returns false if the record is not valid. |
| 100 | */ |
| 101 | static bool get_trace_record(unsigned int idx, TraceRecord **recordptr) |
| 102 | { |
| 103 | uint64_t event_flag = 0; |
| 104 | TraceRecord record; |
| 105 | /* read the event flag to see if its a valid record */ |
| 106 | read_from_buffer(idx, &record, sizeof(event_flag)); |
| 107 | |
| 108 | if (!(record.event & TRACE_RECORD_VALID)) { |
| 109 | return false; |
| 110 | } |
| 111 | |
| 112 | smp_rmb(); /* read memory barrier before accessing record */ |
| 113 | /* read the record header to know record length */ |
| 114 | read_from_buffer(idx, &record, sizeof(TraceRecord)); |
| 115 | *recordptr = malloc(record.length); /* don't use g_malloc, can deadlock when traced */ |
| 116 | /* make a copy of record to avoid being overwritten */ |
| 117 | read_from_buffer(idx, *recordptr, record.length); |
| 118 | smp_rmb(); /* memory barrier before clearing valid flag */ |
| 119 | (*recordptr)->event &= ~TRACE_RECORD_VALID; |
| 120 | /* clear the trace buffer range for consumed record otherwise any byte |
| 121 | * with its MSB set may be considered as a valid event id when the writer |
| 122 | * thread crosses this range of buffer again. |
| 123 | */ |
| 124 | clear_buffer_range(idx, record.length); |
| 125 | return true; |
| 126 | } |
| 127 | |
| 128 | /** |
| 129 | * Kick writeout thread |
| 130 | * |
| 131 | * @wait Whether to wait for writeout thread to complete |
| 132 | */ |
| 133 | static void flush_trace_file(bool wait) |
| 134 | { |
| 135 | g_mutex_lock(&trace_lock); |
| 136 | trace_available = true; |
| 137 | g_cond_signal(&trace_available_cond); |
| 138 | |
| 139 | if (wait) { |
| 140 | g_cond_wait(&trace_empty_cond, &trace_lock); |
| 141 | } |
| 142 | |
| 143 | g_mutex_unlock(&trace_lock); |
| 144 | } |
| 145 | |
| 146 | static void wait_for_trace_records_available(void) |
| 147 | { |
| 148 | g_mutex_lock(&trace_lock); |
| 149 | while (!(trace_available && trace_writeout_enabled)) { |
| 150 | g_cond_signal(&trace_empty_cond); |
| 151 | g_cond_wait(&trace_available_cond, &trace_lock); |
| 152 | } |
| 153 | trace_available = false; |
| 154 | g_mutex_unlock(&trace_lock); |
| 155 | } |
| 156 | |
| 157 | static gpointer writeout_thread(gpointer opaque) |
| 158 | { |
| 159 | TraceRecord *recordptr; |
| 160 | union { |
| 161 | TraceRecord rec; |
| 162 | uint8_t bytes[sizeof(TraceRecord) + sizeof(uint64_t)]; |
| 163 | } dropped; |
| 164 | unsigned int idx = 0; |
| 165 | int dropped_count; |
| 166 | size_t unused __attribute__ ((unused)); |
| 167 | uint64_t type = TRACE_RECORD_TYPE_EVENT; |
| 168 | |
| 169 | for (;;) { |
| 170 | wait_for_trace_records_available(); |
| 171 | |
| 172 | if (g_atomic_int_get(&dropped_events)) { |
| 173 | dropped.rec.event = DROPPED_EVENT_ID; |
| 174 | dropped.rec.timestamp_ns = get_clock(); |
| 175 | dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t); |
| 176 | dropped.rec.pid = trace_pid; |
| 177 | do { |
| 178 | dropped_count = g_atomic_int_get(&dropped_events); |
| 179 | } while (!g_atomic_int_compare_and_exchange(&dropped_events, |
| 180 | dropped_count, 0)); |
| 181 | dropped.rec.arguments[0] = dropped_count; |
| 182 | unused = fwrite(&type, sizeof(type), 1, trace_fp); |
| 183 | unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp); |
| 184 | } |
| 185 | |
| 186 | while (get_trace_record(idx, &recordptr)) { |
| 187 | unused = fwrite(&type, sizeof(type), 1, trace_fp); |
| 188 | unused = fwrite(recordptr, recordptr->length, 1, trace_fp); |
| 189 | writeout_idx += recordptr->length; |
| 190 | free(recordptr); /* don't use g_free, can deadlock when traced */ |
| 191 | idx = writeout_idx % TRACE_BUF_LEN; |
| 192 | } |
| 193 | |
| 194 | fflush(trace_fp); |
| 195 | } |
| 196 | return NULL; |
| 197 | } |
| 198 | |
| 199 | void trace_record_write_u64(TraceBufferRecord *rec, uint64_t val) |
| 200 | { |
| 201 | rec->rec_off = write_to_buffer(rec->rec_off, &val, sizeof(uint64_t)); |
| 202 | } |
| 203 | |
| 204 | void trace_record_write_str(TraceBufferRecord *rec, const char *s, uint32_t slen) |
| 205 | { |
| 206 | /* Write string length first */ |
| 207 | rec->rec_off = write_to_buffer(rec->rec_off, &slen, sizeof(slen)); |
| 208 | /* Write actual string now */ |
| 209 | rec->rec_off = write_to_buffer(rec->rec_off, (void*)s, slen); |
| 210 | } |
| 211 | |
| 212 | int trace_record_start(TraceBufferRecord *rec, uint32_t event, size_t datasize) |
| 213 | { |
| 214 | unsigned int idx, rec_off, old_idx, new_idx; |
| 215 | uint32_t rec_len = sizeof(TraceRecord) + datasize; |
| 216 | uint64_t event_u64 = event; |
| 217 | uint64_t timestamp_ns = get_clock(); |
| 218 | |
| 219 | do { |
| 220 | old_idx = g_atomic_int_get(&trace_idx); |
| 221 | smp_rmb(); |
| 222 | new_idx = old_idx + rec_len; |
| 223 | |
| 224 | if (new_idx - writeout_idx > TRACE_BUF_LEN) { |
| 225 | /* Trace Buffer Full, Event dropped ! */ |
| 226 | g_atomic_int_inc(&dropped_events); |
| 227 | return -ENOSPC; |
| 228 | } |
| 229 | } while (!g_atomic_int_compare_and_exchange(&trace_idx, old_idx, new_idx)); |
| 230 | |
| 231 | idx = old_idx % TRACE_BUF_LEN; |
| 232 | |
| 233 | rec_off = idx; |
| 234 | rec_off = write_to_buffer(rec_off, &event_u64, sizeof(event_u64)); |
| 235 | rec_off = write_to_buffer(rec_off, ×tamp_ns, sizeof(timestamp_ns)); |
| 236 | rec_off = write_to_buffer(rec_off, &rec_len, sizeof(rec_len)); |
| 237 | rec_off = write_to_buffer(rec_off, &trace_pid, sizeof(trace_pid)); |
| 238 | |
| 239 | rec->tbuf_idx = idx; |
| 240 | rec->rec_off = (idx + sizeof(TraceRecord)) % TRACE_BUF_LEN; |
| 241 | return 0; |
| 242 | } |
| 243 | |
| 244 | static void read_from_buffer(unsigned int idx, void *dataptr, size_t size) |
| 245 | { |
| 246 | uint8_t *data_ptr = dataptr; |
| 247 | uint32_t x = 0; |
| 248 | while (x < size) { |
| 249 | if (idx >= TRACE_BUF_LEN) { |
| 250 | idx = idx % TRACE_BUF_LEN; |
| 251 | } |
| 252 | data_ptr[x++] = trace_buf[idx++]; |
| 253 | } |
| 254 | } |
| 255 | |
| 256 | static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size) |
| 257 | { |
| 258 | uint8_t *data_ptr = dataptr; |
| 259 | uint32_t x = 0; |
| 260 | while (x < size) { |
| 261 | if (idx >= TRACE_BUF_LEN) { |
| 262 | idx = idx % TRACE_BUF_LEN; |
| 263 | } |
| 264 | trace_buf[idx++] = data_ptr[x++]; |
| 265 | } |
| 266 | return idx; /* most callers wants to know where to write next */ |
| 267 | } |
| 268 | |
| 269 | void trace_record_finish(TraceBufferRecord *rec) |
| 270 | { |
| 271 | TraceRecord record; |
| 272 | read_from_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord)); |
| 273 | smp_wmb(); /* write barrier before marking as valid */ |
| 274 | record.event |= TRACE_RECORD_VALID; |
| 275 | write_to_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord)); |
| 276 | |
| 277 | if (((unsigned int)g_atomic_int_get(&trace_idx) - writeout_idx) |
| 278 | > TRACE_BUF_FLUSH_THRESHOLD) { |
| 279 | flush_trace_file(false); |
| 280 | } |
| 281 | } |
| 282 | |
| 283 | static int st_write_event_mapping(TraceEventIter *iter) |
| 284 | { |
| 285 | uint64_t type = TRACE_RECORD_TYPE_MAPPING; |
| 286 | TraceEvent *ev; |
| 287 | |
| 288 | while ((ev = trace_event_iter_next(iter)) != NULL) { |
| 289 | uint64_t id = trace_event_get_id(ev); |
| 290 | const char *name = trace_event_get_name(ev); |
| 291 | uint32_t len = strlen(name); |
| 292 | if (fwrite(&type, sizeof(type), 1, trace_fp) != 1 || |
| 293 | fwrite(&id, sizeof(id), 1, trace_fp) != 1 || |
| 294 | fwrite(&len, sizeof(len), 1, trace_fp) != 1 || |
| 295 | fwrite(name, len, 1, trace_fp) != 1) { |
| 296 | return -1; |
| 297 | } |
| 298 | } |
| 299 | |
| 300 | return 0; |
| 301 | } |
| 302 | |
| 303 | /** |
| 304 | * Enable / disable tracing, return whether it was enabled. |
| 305 | * |
| 306 | * @enable: enable if %true, else disable. |
| 307 | */ |
| 308 | bool st_set_trace_file_enabled(bool enable) |
| 309 | { |
| 310 | TraceEventIter iter; |
| 311 | bool was_enabled = trace_fp; |
| 312 | |
| 313 | if (enable == !!trace_fp) { |
| 314 | return was_enabled; /* no change */ |
| 315 | } |
| 316 | |
| 317 | /* Halt trace writeout */ |
| 318 | flush_trace_file(true); |
| 319 | trace_writeout_enabled = false; |
| 320 | flush_trace_file(true); |
| 321 | |
| 322 | if (enable) { |
| 323 | static const TraceLogHeader header = { |
| 324 | .header_event_id = HEADER_EVENT_ID, |
| 325 | .header_magic = HEADER_MAGIC, |
| 326 | /* Older log readers will check for version at next location */ |
| 327 | .header_version = HEADER_VERSION, |
| 328 | }; |
| 329 | |
| 330 | trace_fp = fopen(trace_file_name, "wb"); |
| 331 | if (!trace_fp) { |
| 332 | return was_enabled; |
| 333 | } |
| 334 | |
| 335 | trace_event_iter_init_all(&iter); |
| 336 | if (fwrite(&header, sizeof header, 1, trace_fp) != 1 || |
| 337 | st_write_event_mapping(&iter) < 0) { |
| 338 | fclose(trace_fp); |
| 339 | trace_fp = NULL; |
| 340 | return was_enabled; |
| 341 | } |
| 342 | |
| 343 | /* Resume trace writeout */ |
| 344 | trace_writeout_enabled = true; |
| 345 | flush_trace_file(false); |
| 346 | } else { |
| 347 | fclose(trace_fp); |
| 348 | trace_fp = NULL; |
| 349 | } |
| 350 | return was_enabled; |
| 351 | } |
| 352 | |
| 353 | /** |
| 354 | * Set the name of a trace file |
| 355 | * |
| 356 | * @file The trace file name or NULL for the default name-<pid> set at |
| 357 | * config time |
| 358 | */ |
| 359 | void st_set_trace_file(const char *file) |
| 360 | { |
| 361 | bool saved_enable = st_set_trace_file_enabled(false); |
| 362 | |
| 363 | g_free(trace_file_name); |
| 364 | |
| 365 | if (!file) { |
| 366 | /* Type cast needed for Windows where getpid() returns an int. */ |
| 367 | trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE "-" FMT_pid, (pid_t)getpid()); |
| 368 | } else { |
| 369 | trace_file_name = g_strdup(file); |
| 370 | } |
| 371 | |
| 372 | st_set_trace_file_enabled(saved_enable); |
| 373 | } |
| 374 | |
| 375 | void st_print_trace_file_status(void) |
| 376 | { |
| 377 | qemu_printf("Trace file \"%s\" %s.\n", |
| 378 | trace_file_name, trace_fp ? "on" : "off"); |
| 379 | } |
| 380 | |
| 381 | void st_flush_trace_buffer(void) |
| 382 | { |
| 383 | flush_trace_file(true); |
| 384 | } |
| 385 | |
| 386 | /* Helper function to create a thread with signals blocked. Use glib's |
| 387 | * portable threads since QEMU abstractions cannot be used due to reentrancy in |
| 388 | * the tracer. Also note the signal masking on POSIX hosts so that the thread |
| 389 | * does not steal signals when the rest of the program wants them blocked. |
| 390 | */ |
| 391 | static GThread *trace_thread_create(GThreadFunc fn) |
| 392 | { |
| 393 | GThread *thread; |
| 394 | #ifndef _WIN32 |
| 395 | sigset_t set, oldset; |
| 396 | |
| 397 | sigfillset(&set); |
| 398 | pthread_sigmask(SIG_SETMASK, &set, &oldset); |
| 399 | #endif |
| 400 | |
| 401 | thread = g_thread_new("trace-thread", fn, NULL); |
| 402 | |
| 403 | #ifndef _WIN32 |
| 404 | pthread_sigmask(SIG_SETMASK, &oldset, NULL); |
| 405 | #endif |
| 406 | |
| 407 | return thread; |
| 408 | } |
| 409 | |
| 410 | bool st_init(void) |
| 411 | { |
| 412 | GThread *thread; |
| 413 | |
| 414 | trace_pid = getpid(); |
| 415 | |
| 416 | thread = trace_thread_create(writeout_thread); |
| 417 | if (!thread) { |
| 418 | warn_report("unable to initialize simple trace backend"); |
| 419 | return false; |
| 420 | } |
| 421 | |
| 422 | atexit(st_flush_trace_buffer); |
| 423 | return true; |
| 424 | } |
| 425 | |
| 426 | void st_init_group(size_t group) |
| 427 | { |
| 428 | TraceEventIter iter; |
| 429 | |
| 430 | if (!trace_writeout_enabled) { |
| 431 | return; |
| 432 | } |
| 433 | |
| 434 | trace_event_iter_init_group(&iter, group); |
| 435 | st_write_event_mapping(&iter); |
| 436 | } |