/* * 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 "qemu/osdep.h" #ifndef _WIN32 #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 3 /** 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 CompatGMutex trace_lock; static CompatGCond trace_available_cond; static CompatGCond trace_empty_cond; 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 uint32_t trace_pid; 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 pid; 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); /* don't 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_mutex_lock(&trace_lock); trace_available = true; g_cond_signal(&trace_available_cond); if (wait) { g_cond_wait(&trace_empty_cond, &trace_lock); } g_mutex_unlock(&trace_lock); } static void wait_for_trace_records_available(void) { g_mutex_lock(&trace_lock); while (!(trace_available && trace_writeout_enabled)) { g_cond_signal(&trace_empty_cond); g_cond_wait(&trace_available_cond, &trace_lock); } trace_available = false; g_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.pid = trace_pid; 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); /* don't 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, ×tamp_ns, sizeof(timestamp_ns)); rec_off = write_to_buffer(rec_off, &rec_len, sizeof(rec_len)); rec_off = write_to_buffer(rec_off, &trace_pid, sizeof(trace_pid)); 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 */ void st_set_trace_file(const char *file) { st_set_trace_file_enabled(false); g_free(trace_file_name); if (!file) { /* Type cast needed for Windows where getpid() returns an int. */ trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE, (pid_t)getpid()); } else { trace_file_name = g_strdup_printf("%s", file); } st_set_trace_file_enabled(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); } /* 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 thread = g_thread_new("trace-thread", fn, NULL); #ifndef _WIN32 pthread_sigmask(SIG_SETMASK, &oldset, NULL); #endif return thread; } bool st_init(void) { GThread *thread; trace_pid = getpid(); 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); return true; }