Archipelago » qemu

/*

 * Simple trace backend

 *

 * Copyright IBM, Corp. 2010

 *

 * This work is licensed under the terms of the GNU GPL, version 2.  See

 * the COPYING file in the top-level directory.

 *

 */

#include <stdlib.h>

#include <stdint.h>

#include <stdio.h>

#include <time.h>

#ifndef _WIN32

#include <signal.h>

#include <pthread.h>

#endif

#include "qemu/timer.h"

#include "trace.h"

#include "trace/control.h"

#include "trace/simple.h"

/** Trace file header event ID */

#define HEADER_EVENT_ID (~(uint64_t)0) /* avoids conflicting with TraceEventIDs */

/** Trace file magic number */

#define HEADER_MAGIC 0xf2b177cb0aa429b4ULL

/** Trace file version number, bump if format changes */

#define HEADER_VERSION 2

/** Records were dropped event ID */

#define DROPPED_EVENT_ID (~(uint64_t)0 - 1)

/** Trace record is valid */

#define TRACE_RECORD_VALID ((uint64_t)1 << 63)

/*

 * Trace records are written out by a dedicated thread.  The thread waits for

 * records to become available, writes them out, and then waits again.

 */

static GStaticMutex trace_lock = G_STATIC_MUTEX_INIT;

/* g_cond_new() was deprecated in glib 2.31 but we still need to support it */

#if GLIB_CHECK_VERSION(2, 31, 0)

static GCond the_trace_available_cond;

static GCond the_trace_empty_cond;

static GCond *trace_available_cond = &the_trace_available_cond;

static GCond *trace_empty_cond = &the_trace_empty_cond;

#else

static GCond *trace_available_cond;

static GCond *trace_empty_cond;

#endif

static bool trace_available;

static bool trace_writeout_enabled;

enum {

    TRACE_BUF_LEN = 4096 * 64,

    TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4,

};

uint8_t trace_buf[TRACE_BUF_LEN];

static volatile gint trace_idx;

static unsigned int writeout_idx;

static volatile gint dropped_events;

static FILE *trace_fp;

static char *trace_file_name;

/* * Trace buffer entry */

typedef struct {

    uint64_t event; /*   TraceEventID */

    uint64_t timestamp_ns;

    uint32_t length;   /*    in bytes */

    uint32_t reserved; /*    unused */

    uint64_t arguments[];

} TraceRecord;

typedef struct {

    uint64_t header_event_id; /* HEADER_EVENT_ID */

    uint64_t header_magic;    /* HEADER_MAGIC    */

    uint64_t header_version;  /* HEADER_VERSION  */

} TraceLogHeader;

static void read_from_buffer(unsigned int idx, void *dataptr, size_t size);

static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size);

static void clear_buffer_range(unsigned int idx, size_t len)

{

    uint32_t num = 0;

    while (num < len) {

        if (idx >= TRACE_BUF_LEN) {

            idx = idx % TRACE_BUF_LEN;

        }

        trace_buf[idx++] = 0;

        num++;

    }

}

/**

 * Read a trace record from the trace buffer

 *

 * @idx         Trace buffer index

 * @record      Trace record to fill

 *

 * Returns false if the record is not valid.

 */

static bool get_trace_record(unsigned int idx, TraceRecord **recordptr)

{

    uint64_t event_flag = 0;

    TraceRecord record;

    /* read the event flag to see if its a valid record */

    read_from_buffer(idx, &record, sizeof(event_flag));

    if (!(record.event & TRACE_RECORD_VALID)) {

        return false;

    }

    smp_rmb(); /* read memory barrier before accessing record */

    /* read the record header to know record length */

    read_from_buffer(idx, &record, sizeof(TraceRecord));

    *recordptr = malloc(record.length); /* dont use g_malloc, can deadlock when traced */

    /* make a copy of record to avoid being overwritten */

    read_from_buffer(idx, *recordptr, record.length);

    smp_rmb(); /* memory barrier before clearing valid flag */

    (*recordptr)->event &= ~TRACE_RECORD_VALID;

    /* clear the trace buffer range for consumed record otherwise any byte

     * with its MSB set may be considered as a valid event id when the writer

     * thread crosses this range of buffer again.

     */

    clear_buffer_range(idx, record.length);

    return true;

}

/**

 * Kick writeout thread

 *

 * @wait        Whether to wait for writeout thread to complete

 */

static void flush_trace_file(bool wait)

{

    g_static_mutex_lock(&trace_lock);

    trace_available = true;

    g_cond_signal(trace_available_cond);

    if (wait) {

        g_cond_wait(trace_empty_cond, g_static_mutex_get_mutex(&trace_lock));

    }

    g_static_mutex_unlock(&trace_lock);

}

static void wait_for_trace_records_available(void)

{

    g_static_mutex_lock(&trace_lock);

    while (!(trace_available && trace_writeout_enabled)) {

        g_cond_signal(trace_empty_cond);

        g_cond_wait(trace_available_cond,

                    g_static_mutex_get_mutex(&trace_lock));

    }

    trace_available = false;

    g_static_mutex_unlock(&trace_lock);

}

static gpointer writeout_thread(gpointer opaque)

{

    TraceRecord *recordptr;

    union {

        TraceRecord rec;

        uint8_t bytes[sizeof(TraceRecord) + sizeof(uint64_t)];

    } dropped;

    unsigned int idx = 0;

    int dropped_count;

    size_t unused __attribute__ ((unused));

    for (;;) {

        wait_for_trace_records_available();

        if (g_atomic_int_get(&dropped_events)) {

            dropped.rec.event = DROPPED_EVENT_ID,

            dropped.rec.timestamp_ns = get_clock();

            dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t),

            dropped.rec.reserved = 0;

            do {

                dropped_count = g_atomic_int_get(&dropped_events);

            } while (!g_atomic_int_compare_and_exchange(&dropped_events,

                                                        dropped_count, 0));

            dropped.rec.arguments[0] = dropped_count;

            unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp);

        }

        while (get_trace_record(idx, &recordptr)) {

            unused = fwrite(recordptr, recordptr->length, 1, trace_fp);

            writeout_idx += recordptr->length;

            free(recordptr); /* dont use g_free, can deadlock when traced */

            idx = writeout_idx % TRACE_BUF_LEN;

        }

        fflush(trace_fp);

    }

    return NULL;

}

void trace_record_write_u64(TraceBufferRecord *rec, uint64_t val)

{

    rec->rec_off = write_to_buffer(rec->rec_off, &val, sizeof(uint64_t));

}

void trace_record_write_str(TraceBufferRecord *rec, const char *s, uint32_t slen)

{

    /* Write string length first */

    rec->rec_off = write_to_buffer(rec->rec_off, &slen, sizeof(slen));

    /* Write actual string now */

    rec->rec_off = write_to_buffer(rec->rec_off, (void*)s, slen);

}

int trace_record_start(TraceBufferRecord *rec, TraceEventID event, size_t datasize)

{

    unsigned int idx, rec_off, old_idx, new_idx;

    uint32_t rec_len = sizeof(TraceRecord) + datasize;

    uint64_t event_u64 = event;

    uint64_t timestamp_ns = get_clock();

    do {

        old_idx = g_atomic_int_get(&trace_idx);

        smp_rmb();

        new_idx = old_idx + rec_len;

        if (new_idx - writeout_idx > TRACE_BUF_LEN) {

            /* Trace Buffer Full, Event dropped ! */

            g_atomic_int_inc(&dropped_events);

            return -ENOSPC;

        }

    } while (!g_atomic_int_compare_and_exchange(&trace_idx, old_idx, new_idx));

    idx = old_idx % TRACE_BUF_LEN;

    rec_off = idx;

    rec_off = write_to_buffer(rec_off, &event_u64, sizeof(event_u64));

    rec_off = write_to_buffer(rec_off, &timestamp_ns, sizeof(timestamp_ns));

    rec_off = write_to_buffer(rec_off, &rec_len, sizeof(rec_len));

    rec->tbuf_idx = idx;

    rec->rec_off  = (idx + sizeof(TraceRecord)) % TRACE_BUF_LEN;

    return 0;

}

static void read_from_buffer(unsigned int idx, void *dataptr, size_t size)

{

    uint8_t *data_ptr = dataptr;

    uint32_t x = 0;

    while (x < size) {

        if (idx >= TRACE_BUF_LEN) {

            idx = idx % TRACE_BUF_LEN;

        }

        data_ptr[x++] = trace_buf[idx++];

    }

}

static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size)

{

    uint8_t *data_ptr = dataptr;

    uint32_t x = 0;

    while (x < size) {

        if (idx >= TRACE_BUF_LEN) {

            idx = idx % TRACE_BUF_LEN;

        }

        trace_buf[idx++] = data_ptr[x++];

    }

    return idx; /* most callers wants to know where to write next */

}

void trace_record_finish(TraceBufferRecord *rec)

{

    TraceRecord record;

    read_from_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));

    smp_wmb(); /* write barrier before marking as valid */

    record.event |= TRACE_RECORD_VALID;

    write_to_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));

    if (((unsigned int)g_atomic_int_get(&trace_idx) - writeout_idx)

        > TRACE_BUF_FLUSH_THRESHOLD) {

        flush_trace_file(false);

    }

}

void st_set_trace_file_enabled(bool enable)

{

    if (enable == !!trace_fp) {

        return; /* no change */

    }

    /* Halt trace writeout */

    flush_trace_file(true);

    trace_writeout_enabled = false;

    flush_trace_file(true);

    if (enable) {

        static const TraceLogHeader header = {

            .header_event_id = HEADER_EVENT_ID,

            .header_magic = HEADER_MAGIC,

            /* Older log readers will check for version at next location */

            .header_version = HEADER_VERSION,

        };

        trace_fp = fopen(trace_file_name, "wb");

        if (!trace_fp) {

            return;

        }

        if (fwrite(&header, sizeof header, 1, trace_fp) != 1) {

            fclose(trace_fp);

            trace_fp = NULL;

            return;

        }

        /* Resume trace writeout */

        trace_writeout_enabled = true;

        flush_trace_file(false);

    } else {

        fclose(trace_fp);

        trace_fp = NULL;

    }

}

/**

 * Set the name of a trace file

 *

 * @file        The trace file name or NULL for the default name-<pid> set at

 *              config time

 */

bool st_set_trace_file(const char *file)

{

    st_set_trace_file_enabled(false);

    g_free(trace_file_name);

    if (!file) {

        trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE, getpid());

    } else {

        trace_file_name = g_strdup_printf("%s", file);

    }

    st_set_trace_file_enabled(true);

    return true;

}

void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...))

{

    stream_printf(stream, "Trace file \"%s\" %s.\n",

                  trace_file_name, trace_fp ? "on" : "off");

}

void st_flush_trace_buffer(void)

{

    flush_trace_file(true);

}

void trace_print_events(FILE *stream, fprintf_function stream_printf)

{

    unsigned int i;

    for (i = 0; i < trace_event_count(); i++) {

        TraceEvent *ev = trace_event_id(i);

        stream_printf(stream, "%s [Event ID %u] : state %u\n",

                      trace_event_get_name(ev), i, trace_event_get_state_dynamic(ev));

    }

}

void trace_event_set_state_dynamic_backend(TraceEvent *ev, bool state)

{

    ev->dstate = state;

}

/* Helper function to create a thread with signals blocked.  Use glib's

 * portable threads since QEMU abstractions cannot be used due to reentrancy in

 * the tracer.  Also note the signal masking on POSIX hosts so that the thread

 * does not steal signals when the rest of the program wants them blocked.

 */

static GThread *trace_thread_create(GThreadFunc fn)

{

    GThread *thread;

#ifndef _WIN32

    sigset_t set, oldset;

    sigfillset(&set);

    pthread_sigmask(SIG_SETMASK, &set, &oldset);

#endif

#if GLIB_CHECK_VERSION(2, 31, 0)

    thread = g_thread_new("trace-thread", fn, NULL);

#else

    thread = g_thread_create(fn, NULL, FALSE, NULL);

#endif

#ifndef _WIN32

    pthread_sigmask(SIG_SETMASK, &oldset, NULL);

#endif

    return thread;

}

bool trace_backend_init(const char *events, const char *file)

{

    GThread *thread;

    if (!g_thread_supported()) {

#if !GLIB_CHECK_VERSION(2, 31, 0)

        g_thread_init(NULL);

#else

        fprintf(stderr, "glib threading failed to initialize.\n");

        exit(1);

#endif

    }

#if !GLIB_CHECK_VERSION(2, 31, 0)

    trace_available_cond = g_cond_new();

    trace_empty_cond = g_cond_new();

#endif

    thread = trace_thread_create(writeout_thread);

    if (!thread) {

        fprintf(stderr, "warning: unable to initialize simple trace backend\n");

        return false;

    }

    atexit(st_flush_trace_buffer);

    trace_backend_init_events(events);

    st_set_trace_file(file);

    return true;

}