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 <stdlib.h>
  12 #include <stdint.h>
  13 #include <stdio.h>
  14 #include <time.h>
  15 #ifndef _WIN32
  16 #include <signal.h>
  17 #include <pthread.h>
  18 #endif
  19 #include "qemu-timer.h"
  20 #include "trace.h"
  21 #include "trace/control.h"
  22
  23 /** Trace file header event ID */
  24 #define HEADER_EVENT_ID (~(uint64_t)0) /* avoids conflicting with TraceEventIDs */
  25
  26 /** Trace file magic number */
  27 #define HEADER_MAGIC 0xf2b177cb0aa429b4ULL
  28
  29 /** Trace file version number, bump if format changes */
  30 #define HEADER_VERSION 0
  31
  32 /** Records were dropped event ID */
  33 #define DROPPED_EVENT_ID (~(uint64_t)0 - 1)
  34
  35 /** Trace record is valid */
  36 #define TRACE_RECORD_VALID ((uint64_t)1 << 63)
  37
  38 /** Trace buffer entry */
  39 typedef struct {
  40     uint64_t event;
  41     uint64_t timestamp_ns;
  42     uint64_t x1;
  43     uint64_t x2;
  44     uint64_t x3;
  45     uint64_t x4;
  46     uint64_t x5;
  47     uint64_t x6;
  48 } TraceRecord;
  49
  50 enum {
  51     TRACE_BUF_LEN = 4096,
  52     TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4,
  53 };
  54
  55 /*
  56  * Trace records are written out by a dedicated thread.  The thread waits for
  57  * records to become available, writes them out, and then waits again.
  58  */
  59 static GStaticMutex trace_lock = G_STATIC_MUTEX_INIT;
  60 static GCond *trace_available_cond;
  61 static GCond *trace_empty_cond;
  62 static bool trace_available;
  63 static bool trace_writeout_enabled;
  64
  65 static TraceRecord trace_buf[TRACE_BUF_LEN];
  66 static unsigned int trace_idx;
  67 static FILE *trace_fp;
  68 static char *trace_file_name = NULL;
  69
  70 /**
  71  * Read a trace record from the trace buffer
  72  *
  73  * @idx         Trace buffer index
  74  * @record      Trace record to fill
  75  *
  76  * Returns false if the record is not valid.
  77  */
  78 static bool get_trace_record(unsigned int idx, TraceRecord *record)
  79 {
  80     if (!(trace_buf[idx].event & TRACE_RECORD_VALID)) {
  81         return false;
  82     }
  83
  84     __sync_synchronize(); /* read memory barrier before accessing record */
  85
  86     *record = trace_buf[idx];
  87     record->event &= ~TRACE_RECORD_VALID;
  88     return true;
  89 }
  90
  91 /**
  92  * Kick writeout thread
  93  *
  94  * @wait        Whether to wait for writeout thread to complete
  95  */
  96 static void flush_trace_file(bool wait)
  97 {
  98     g_static_mutex_lock(&trace_lock);
  99     trace_available = true;
 100     g_cond_signal(trace_available_cond);
 101
 102     if (wait) {
 103         g_cond_wait(trace_empty_cond, g_static_mutex_get_mutex(&trace_lock));
 104     }
 105
 106     g_static_mutex_unlock(&trace_lock);
 107 }
 108
 109 static void wait_for_trace_records_available(void)
 110 {
 111     g_static_mutex_lock(&trace_lock);
 112     while (!(trace_available && trace_writeout_enabled)) {
 113         g_cond_signal(trace_empty_cond);
 114         g_cond_wait(trace_available_cond,
 115                     g_static_mutex_get_mutex(&trace_lock));
 116     }
 117     trace_available = false;
 118     g_static_mutex_unlock(&trace_lock);
 119 }
 120
 121 static gpointer writeout_thread(gpointer opaque)
 122 {
 123     TraceRecord record;
 124     unsigned int writeout_idx = 0;
 125     unsigned int num_available, idx;
 126     size_t unused __attribute__ ((unused));
 127
 128     for (;;) {
 129         wait_for_trace_records_available();
 130
 131         num_available = trace_idx - writeout_idx;
 132         if (num_available > TRACE_BUF_LEN) {
 133             record = (TraceRecord){
 134                 .event = DROPPED_EVENT_ID,
 135                 .x1 = num_available,
 136             };
 137             unused = fwrite(&record, sizeof(record), 1, trace_fp);
 138             writeout_idx += num_available;
 139         }
 140
 141         idx = writeout_idx % TRACE_BUF_LEN;
 142         while (get_trace_record(idx, &record)) {
 143             trace_buf[idx].event = 0; /* clear valid bit */
 144             unused = fwrite(&record, sizeof(record), 1, trace_fp);
 145             idx = ++writeout_idx % TRACE_BUF_LEN;
 146         }
 147
 148         fflush(trace_fp);
 149     }
 150     return NULL;
 151 }
 152
 153 static void trace(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3,
 154                   uint64_t x4, uint64_t x5, uint64_t x6)
 155 {
 156     unsigned int idx;
 157     uint64_t timestamp;
 158
 159     if (!trace_list[event].state) {
 160         return;
 161     }
 162
 163     timestamp = get_clock();
 164
 165     idx = g_atomic_int_exchange_and_add((gint *)&trace_idx, 1) % TRACE_BUF_LEN;
 166     trace_buf[idx] = (TraceRecord){
 167         .event = event,
 168         .timestamp_ns = timestamp,
 169         .x1 = x1,
 170         .x2 = x2,
 171         .x3 = x3,
 172         .x4 = x4,
 173         .x5 = x5,
 174         .x6 = x6,
 175     };
 176     __sync_synchronize(); /* write barrier before marking as valid */
 177     trace_buf[idx].event |= TRACE_RECORD_VALID;
 178
 179     if ((idx + 1) % TRACE_BUF_FLUSH_THRESHOLD == 0) {
 180         flush_trace_file(false);
 181     }
 182 }
 183
 184 void trace0(TraceEventID event)
 185 {
 186     trace(event, 0, 0, 0, 0, 0, 0);
 187 }
 188
 189 void trace1(TraceEventID event, uint64_t x1)
 190 {
 191     trace(event, x1, 0, 0, 0, 0, 0);
 192 }
 193
 194 void trace2(TraceEventID event, uint64_t x1, uint64_t x2)
 195 {
 196     trace(event, x1, x2, 0, 0, 0, 0);
 197 }
 198
 199 void trace3(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3)
 200 {
 201     trace(event, x1, x2, x3, 0, 0, 0);
 202 }
 203
 204 void trace4(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4)
 205 {
 206     trace(event, x1, x2, x3, x4, 0, 0);
 207 }
 208
 209 void trace5(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4, uint64_t x5)
 210 {
 211     trace(event, x1, x2, x3, x4, x5, 0);
 212 }
 213
 214 void trace6(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4, uint64_t x5, uint64_t x6)
 215 {
 216     trace(event, x1, x2, x3, x4, x5, x6);
 217 }
 218
 219 void st_set_trace_file_enabled(bool enable)
 220 {
 221     if (enable == !!trace_fp) {
 222         return; /* no change */
 223     }
 224
 225     /* Halt trace writeout */
 226     flush_trace_file(true);
 227     trace_writeout_enabled = false;
 228     flush_trace_file(true);
 229
 230     if (enable) {
 231         static const TraceRecord header = {
 232             .event = HEADER_EVENT_ID,
 233             .timestamp_ns = HEADER_MAGIC,
 234             .x1 = HEADER_VERSION,
 235         };
 236
 237         trace_fp = fopen(trace_file_name, "w");
 238         if (!trace_fp) {
 239             return;
 240         }
 241
 242         if (fwrite(&header, sizeof header, 1, trace_fp) != 1) {
 243             fclose(trace_fp);
 244             trace_fp = NULL;
 245             return;
 246         }
 247
 248         /* Resume trace writeout */
 249         trace_writeout_enabled = true;
 250         flush_trace_file(false);
 251     } else {
 252         fclose(trace_fp);
 253         trace_fp = NULL;
 254     }
 255 }
 256
 257 /**
 258  * Set the name of a trace file
 259  *
 260  * @file        The trace file name or NULL for the default name-<pid> set at
 261  *              config time
 262  */
 263 bool st_set_trace_file(const char *file)
 264 {
 265     st_set_trace_file_enabled(false);
 266
 267     free(trace_file_name);
 268
 269     if (!file) {
 270         if (asprintf(&trace_file_name, CONFIG_TRACE_FILE, getpid()) < 0) {
 271             trace_file_name = NULL;
 272             return false;
 273         }
 274     } else {
 275         if (asprintf(&trace_file_name, "%s", file) < 0) {
 276             trace_file_name = NULL;
 277             return false;
 278         }
 279     }
 280
 281     st_set_trace_file_enabled(true);
 282     return true;
 283 }
 284
 285 void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...))
 286 {
 287     stream_printf(stream, "Trace file \"%s\" %s.\n",
 288                   trace_file_name, trace_fp ? "on" : "off");
 289 }
 290
 291 void st_print_trace(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...))
 292 {
 293     unsigned int i;
 294
 295     for (i = 0; i < TRACE_BUF_LEN; i++) {
 296         TraceRecord record;
 297
 298         if (!get_trace_record(i, &record)) {
 299             continue;
 300         }
 301         stream_printf(stream, "Event %" PRIu64 " : %" PRIx64 " %" PRIx64
 302                       " %" PRIx64 " %" PRIx64 " %" PRIx64 " %" PRIx64 "\n",
 303                       record.event, record.x1, record.x2,
 304                       record.x3, record.x4, record.x5,
 305                       record.x6);
 306     }
 307 }
 308
 309 void st_flush_trace_buffer(void)
 310 {
 311     flush_trace_file(true);
 312 }
 313
 314 void trace_print_events(FILE *stream, fprintf_function stream_printf)
 315 {
 316     unsigned int i;
 317
 318     for (i = 0; i < NR_TRACE_EVENTS; i++) {
 319         stream_printf(stream, "%s [Event ID %u] : state %u\n",
 320                       trace_list[i].tp_name, i, trace_list[i].state);
 321     }
 322 }
 323
 324 bool trace_event_set_state(const char *name, bool state)
 325 {
 326     unsigned int i;
 327
 328     for (i = 0; i < NR_TRACE_EVENTS; i++) {
 329         if (!strcmp(trace_list[i].tp_name, name)) {
 330             trace_list[i].state = state;
 331             return true;
 332         }
 333     }
 334     return false;
 335 }
 336
 337 /* Helper function to create a thread with signals blocked.  Use glib's
 338  * portable threads since QEMU abstractions cannot be used due to reentrancy in
 339  * the tracer.  Also note the signal masking on POSIX hosts so that the thread
 340  * does not steal signals when the rest of the program wants them blocked.
 341  */
 342 static GThread *trace_thread_create(GThreadFunc fn)
 343 {
 344     GThread *thread;
 345 #ifndef _WIN32
 346     sigset_t set, oldset;
 347
 348     sigfillset(&set);
 349     pthread_sigmask(SIG_SETMASK, &set, &oldset);
 350 #endif
 351     thread = g_thread_create(writeout_thread, NULL, FALSE, NULL);
 352 #ifndef _WIN32
 353     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 354 #endif
 355
 356     return thread;
 357 }
 358
 359 bool trace_backend_init(const char *events, const char *file)
 360 {
 361     GThread *thread;
 362
 363     if (!g_thread_supported()) {
 364         g_thread_init(NULL);
 365     }
 366
 367     trace_available_cond = g_cond_new();
 368     trace_empty_cond = g_cond_new();
 369
 370     thread = trace_thread_create(writeout_thread);
 371     if (!thread) {
 372         fprintf(stderr, "warning: unable to initialize simple trace backend\n");
 373         return false;
 374     }
 375
 376     atexit(st_flush_trace_buffer);
 377     trace_backend_init_events(events);
 378     st_set_trace_file(file);
 379     return true;
 380 }