xref: /openbmc/qemu/trace/simple.c (revision 0955d66e)
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  */
40 static GMutex trace_lock;
41 static GCond trace_available_cond;
42 static GCond trace_empty_cond;
43 
44 static bool trace_available;
45 static bool trace_writeout_enabled;
46 
47 enum {
48     TRACE_BUF_LEN = 4096 * 64,
49     TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4,
50 };
51 
52 uint8_t trace_buf[TRACE_BUF_LEN];
53 static volatile gint trace_idx;
54 static unsigned int writeout_idx;
55 static volatile gint dropped_events;
56 static uint32_t trace_pid;
57 static FILE *trace_fp;
58 static char *trace_file_name;
59 
60 #define TRACE_RECORD_TYPE_MAPPING 0
61 #define TRACE_RECORD_TYPE_EVENT   1
62 
63 /* * Trace buffer entry */
64 typedef 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 
72 typedef 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 
79 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size);
80 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size);
81 
clear_buffer_range(unsigned int idx,size_t len)82 static 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  */
get_trace_record(unsigned int idx,TraceRecord ** recordptr)101 static 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  */
flush_trace_file(bool wait)133 static 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 
wait_for_trace_records_available(void)146 static 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 
writeout_thread(gpointer opaque)157 static 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 
trace_record_write_u64(TraceBufferRecord * rec,uint64_t val)199 void 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 
trace_record_write_str(TraceBufferRecord * rec,const char * s,uint32_t slen)204 void 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 
trace_record_start(TraceBufferRecord * rec,uint32_t event,size_t datasize)212 int 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 
read_from_buffer(unsigned int idx,void * dataptr,size_t size)244 static 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 
write_to_buffer(unsigned int idx,void * dataptr,size_t size)256 static 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 
trace_record_finish(TraceBufferRecord * rec)269 void 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 
st_write_event_mapping(TraceEventIter * iter)283 static 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  */
st_set_trace_file_enabled(bool enable)308 bool 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  */
st_set_trace_file(const char * file)359 void 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 
st_print_trace_file_status(void)375 void 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 
st_flush_trace_buffer(void)381 void 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  */
trace_thread_create(GThreadFunc fn)391 static 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 
st_init(void)410 bool 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 
st_init_group(size_t group)426 void 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