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