trace/simple.c

   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, &timestamp_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(void)
 284 {
 285     uint64_t type = TRACE_RECORD_TYPE_MAPPING;
 286     TraceEventIter iter;
 287     TraceEvent *ev;
 288
 289     trace_event_iter_init(&iter, NULL);
 290     while ((ev = trace_event_iter_next(&iter)) != NULL) {
 291         uint64_t id = trace_event_get_id(ev);
 292         const char *name = trace_event_get_name(ev);
 293         uint32_t len = strlen(name);
 294         if (fwrite(&type, sizeof(type), 1, trace_fp) != 1 ||
 295             fwrite(&id, sizeof(id), 1, trace_fp) != 1 ||
 296             fwrite(&len, sizeof(len), 1, trace_fp) != 1 ||
 297             fwrite(name, len, 1, trace_fp) != 1) {
 298             return -1;
 299         }
 300     }
 301
 302     return 0;
 303 }
 304
 305 /**
 306  * Enable / disable tracing, return whether it was enabled.
 307  *
 308  * @enable: enable if %true, else disable.
 309  */
 310 bool st_set_trace_file_enabled(bool enable)
 311 {
 312     bool was_enabled = trace_fp;
 313
 314     if (enable == !!trace_fp) {
 315         return was_enabled;     /* no change */
 316     }
 317
 318     /* Halt trace writeout */
 319     flush_trace_file(true);
 320     trace_writeout_enabled = false;
 321     flush_trace_file(true);
 322
 323     if (enable) {
 324         static const TraceLogHeader header = {
 325             .header_event_id = HEADER_EVENT_ID,
 326             .header_magic = HEADER_MAGIC,
 327             /* Older log readers will check for version at next location */
 328             .header_version = HEADER_VERSION,
 329         };
 330
 331         trace_fp = fopen(trace_file_name, "wb");
 332         if (!trace_fp) {
 333             return was_enabled;
 334         }
 335
 336         if (fwrite(&header, sizeof header, 1, trace_fp) != 1 ||
 337             st_write_event_mapping() < 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, (pid_t)getpid());
 368     } else {
 369         trace_file_name = g_strdup_printf("%s", 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 }