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