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#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 */
  40static GMutex trace_lock;
  41static GCond trace_available_cond;
  42static GCond trace_empty_cond;
  43
  44static bool trace_available;
  45static bool trace_writeout_enabled;
  46
  47enum {
  48    TRACE_BUF_LEN = 4096 * 64,
  49    TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4,
  50};
  51
  52uint8_t trace_buf[TRACE_BUF_LEN];
  53static volatile gint trace_idx;
  54static unsigned int writeout_idx;
  55static volatile gint dropped_events;
  56static uint32_t trace_pid;
  57static FILE *trace_fp;
  58static char *trace_file_name;
  59
  60#define TRACE_RECORD_TYPE_MAPPING 0
  61#define TRACE_RECORD_TYPE_EVENT   1
  62
  63/* * Trace buffer entry */
  64typedef 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
  72typedef 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
  79static void read_from_buffer(unsigned int idx, void *dataptr, size_t size);
  80static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size);
  81
  82static 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 */
 101static 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 */
 133static 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
 146static 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
 157static 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
 199void 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
 204void 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
 212int 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
 244static 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
 256static 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
 269void 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
 283static 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 */
 308bool 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 */
 359void 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_printf("%s", file);
 370    }
 371
 372    st_set_trace_file_enabled(saved_enable);
 373}
 374
 375void 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
 381void 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 */
 391static 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
 410bool 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
 426void 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}
 437