1 // Copyright 2014 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Go execution tracer.
6 // The tracer captures a wide range of execution events like goroutine
7 // creation/blocking/unblocking, syscall enter/exit/block, GC-related events,
8 // changes of heap size, processor start/stop, etc and writes them to a buffer
9 // in a compact form. A precise nanosecond-precision timestamp and a stack
10 // trace is captured for most events.
11 // See https://golang.org/s/go15trace for more info.
19 "runtime/internal/atomic"
20 "runtime/internal/sys"
24 // Event types in the trace, args are given in square brackets.
26 traceEvNone = 0 // unused
27 traceEvBatch = 1 // start of per-P batch of events [pid, timestamp]
28 traceEvFrequency = 2 // contains tracer timer frequency [frequency (ticks per second)]
29 traceEvStack = 3 // stack [stack id, number of PCs, array of {PC, func string ID, file string ID, line}]
30 traceEvGomaxprocs = 4 // current value of GOMAXPROCS [timestamp, GOMAXPROCS, stack id]
31 traceEvProcStart = 5 // start of P [timestamp, thread id]
32 traceEvProcStop = 6 // stop of P [timestamp]
33 traceEvGCStart = 7 // GC start [timestamp, seq, stack id]
34 traceEvGCDone = 8 // GC done [timestamp]
35 traceEvSTWStart = 9 // STW start [timestamp, kind]
36 traceEvSTWDone = 10 // STW done [timestamp]
37 traceEvGCSweepStart = 11 // GC sweep start [timestamp, stack id]
38 traceEvGCSweepDone = 12 // GC sweep done [timestamp, swept, reclaimed]
39 traceEvGoCreate = 13 // goroutine creation [timestamp, new goroutine id, new stack id, stack id]
40 traceEvGoStart = 14 // goroutine starts running [timestamp, goroutine id, seq]
41 traceEvGoEnd = 15 // goroutine ends [timestamp]
42 traceEvGoStop = 16 // goroutine stops (like in select{}) [timestamp, stack]
43 traceEvGoSched = 17 // goroutine calls Gosched [timestamp, stack]
44 traceEvGoPreempt = 18 // goroutine is preempted [timestamp, stack]
45 traceEvGoSleep = 19 // goroutine calls Sleep [timestamp, stack]
46 traceEvGoBlock = 20 // goroutine blocks [timestamp, stack]
47 traceEvGoUnblock = 21 // goroutine is unblocked [timestamp, goroutine id, seq, stack]
48 traceEvGoBlockSend = 22 // goroutine blocks on chan send [timestamp, stack]
49 traceEvGoBlockRecv = 23 // goroutine blocks on chan recv [timestamp, stack]
50 traceEvGoBlockSelect = 24 // goroutine blocks on select [timestamp, stack]
51 traceEvGoBlockSync = 25 // goroutine blocks on Mutex/RWMutex [timestamp, stack]
52 traceEvGoBlockCond = 26 // goroutine blocks on Cond [timestamp, stack]
53 traceEvGoBlockNet = 27 // goroutine blocks on network [timestamp, stack]
54 traceEvGoSysCall = 28 // syscall enter [timestamp, stack]
55 traceEvGoSysExit = 29 // syscall exit [timestamp, goroutine id, seq, real timestamp]
56 traceEvGoSysBlock = 30 // syscall blocks [timestamp]
57 traceEvGoWaiting = 31 // denotes that goroutine is blocked when tracing starts [timestamp, goroutine id]
58 traceEvGoInSyscall = 32 // denotes that goroutine is in syscall when tracing starts [timestamp, goroutine id]
59 traceEvHeapAlloc = 33 // gcController.heapLive change [timestamp, heap_alloc]
60 traceEvHeapGoal = 34 // gcController.heapGoal() (formerly next_gc) change [timestamp, heap goal in bytes]
61 traceEvTimerGoroutine = 35 // not currently used; previously denoted timer goroutine [timer goroutine id]
62 traceEvFutileWakeup = 36 // not currently used; denotes that the previous wakeup of this goroutine was futile [timestamp]
63 traceEvString = 37 // string dictionary entry [ID, length, string]
64 traceEvGoStartLocal = 38 // goroutine starts running on the same P as the last event [timestamp, goroutine id]
65 traceEvGoUnblockLocal = 39 // goroutine is unblocked on the same P as the last event [timestamp, goroutine id, stack]
66 traceEvGoSysExitLocal = 40 // syscall exit on the same P as the last event [timestamp, goroutine id, real timestamp]
67 traceEvGoStartLabel = 41 // goroutine starts running with label [timestamp, goroutine id, seq, label string id]
68 traceEvGoBlockGC = 42 // goroutine blocks on GC assist [timestamp, stack]
69 traceEvGCMarkAssistStart = 43 // GC mark assist start [timestamp, stack]
70 traceEvGCMarkAssistDone = 44 // GC mark assist done [timestamp]
71 traceEvUserTaskCreate = 45 // trace.NewTask [timestamp, internal task id, internal parent task id, name string, stack]
72 traceEvUserTaskEnd = 46 // end of a task [timestamp, internal task id, stack]
73 traceEvUserRegion = 47 // trace.WithRegion [timestamp, internal task id, mode(0:start, 1:end), name string, stack]
74 traceEvUserLog = 48 // trace.Log [timestamp, internal task id, key string id, stack, value string]
75 traceEvCPUSample = 49 // CPU profiling sample [timestamp, real timestamp, real P id (-1 when absent), goroutine id, stack]
77 // Byte is used but only 6 bits are available for event type.
78 // The remaining 2 bits are used to specify the number of arguments.
79 // That means, the max event type value is 63.
82 // traceBlockReason is an enumeration of reasons a goroutine might block.
83 // This is the interface the rest of the runtime uses to tell the
84 // tracer why a goroutine blocked. The tracer then propagates this information
85 // into the trace however it sees fit.
87 // Note that traceBlockReasons should not be compared, since reasons that are
88 // distinct by name may *not* be distinct by value.
89 type traceBlockReason uint8
91 // For maximal efficiency, just map the trace block reason directly to a trace
94 traceBlockGeneric traceBlockReason = traceEvGoBlock
95 traceBlockForever = traceEvGoStop
96 traceBlockNet = traceEvGoBlockNet
97 traceBlockSelect = traceEvGoBlockSelect
98 traceBlockCondWait = traceEvGoBlockCond
99 traceBlockSync = traceEvGoBlockSync
100 traceBlockChanSend = traceEvGoBlockSend
101 traceBlockChanRecv = traceEvGoBlockRecv
102 traceBlockGCMarkAssist = traceEvGoBlockGC
103 traceBlockGCSweep = traceEvGoBlock
104 traceBlockSystemGoroutine = traceEvGoBlock
105 traceBlockPreempted = traceEvGoBlock
106 traceBlockDebugCall = traceEvGoBlock
107 traceBlockUntilGCEnds = traceEvGoBlock
108 traceBlockSleep = traceEvGoSleep
112 // Timestamps in trace are cputicks/traceTickDiv.
113 // This makes absolute values of timestamp diffs smaller,
114 // and so they are encoded in less number of bytes.
115 // 64 on x86 is somewhat arbitrary (one tick is ~20ns on a 3GHz machine).
116 // The suggested increment frequency for PowerPC's time base register is
117 // 512 MHz according to Power ISA v2.07 section 6.2, so we use 16 on ppc64
119 traceTimeDiv = 16 + 48*(goarch.Is386|goarch.IsAmd64)
120 // Maximum number of PCs in a single stack trace.
121 // Since events contain only stack id rather than whole stack trace,
122 // we can allow quite large values here.
124 // Identifier of a fake P that is used when we trace without a real P.
126 // Maximum number of bytes to encode uint64 in base-128.
127 traceBytesPerNumber = 10
128 // Shift of the number of arguments in the first event byte.
129 traceArgCountShift = 6
132 // trace is global tracing context.
134 // trace.lock must only be acquired on the system stack where
135 // stack splits cannot happen while it is held.
136 lock mutex // protects the following members
137 enabled bool // when set runtime traces events
138 shutdown bool // set when we are waiting for trace reader to finish after setting enabled to false
139 headerWritten bool // whether ReadTrace has emitted trace header
140 footerWritten bool // whether ReadTrace has emitted trace footer
141 shutdownSema uint32 // used to wait for ReadTrace completion
142 seqStart uint64 // sequence number when tracing was started
143 startTicks int64 // cputicks when tracing was started
144 endTicks int64 // cputicks when tracing was stopped
145 startNanotime int64 // nanotime when tracing was started
146 endNanotime int64 // nanotime when tracing was stopped
147 startTime traceTime // traceClockNow when tracing started
148 endTime traceTime // traceClockNow when tracing stopped
149 seqGC uint64 // GC start/done sequencer
150 reading traceBufPtr // buffer currently handed off to user
151 empty traceBufPtr // stack of empty buffers
152 fullHead traceBufPtr // queue of full buffers
154 stackTab traceStackTable // maps stack traces to unique ids
155 // cpuLogRead accepts CPU profile samples from the signal handler where
156 // they're generated. It uses a two-word header to hold the IDs of the P and
157 // G (respectively) that were active at the time of the sample. Because
158 // profBuf uses a record with all zeros in its header to indicate overflow,
159 // we make sure to make the P field always non-zero: The ID of a real P will
160 // start at bit 1, and bit 0 will be set. Samples that arrive while no P is
161 // running (such as near syscalls) will set the first header field to 0b10.
162 // This careful handling of the first header field allows us to store ID of
163 // the active G directly in the second field, even though that will be 0
166 // cpuLogBuf is a trace buffer to hold events corresponding to CPU profile
167 // samples, which arrive out of band and not directly connected to a
169 cpuLogBuf traceBufPtr
171 reader atomic.Pointer[g] // goroutine that called ReadTrace, or nil
173 signalLock atomic.Uint32 // protects use of the following member, only usable in signal handlers
174 cpuLogWrite *profBuf // copy of cpuLogRead for use in signal handlers, set without signalLock
176 // Dictionary for traceEvString.
178 // TODO: central lock to access the map is not ideal.
179 // option: pre-assign ids to all user annotation region names and tags
180 // option: per-P cache
181 // option: sync.Map like data structure
183 strings map[string]uint64
186 // markWorkerLabels maps gcMarkWorkerMode to string ID.
187 markWorkerLabels [len(gcMarkWorkerModeStrings)]uint64
189 bufLock mutex // protects buf
190 buf traceBufPtr // global trace buffer, used when running without a p
193 // gTraceState is per-G state for the tracer.
194 type gTraceState struct {
195 sysExitTime traceTime // timestamp when syscall has returned
196 tracedSyscallEnter bool // syscall or cgo was entered while trace was enabled or StartTrace has emitted EvGoInSyscall about this goroutine
197 seq uint64 // trace event sequencer
198 lastP puintptr // last P emitted an event for this goroutine
201 // mTraceState is per-M state for the tracer.
202 type mTraceState struct {
203 startingTrace bool // this M is in TraceStart, potentially before traceEnabled is true
204 tracedSTWStart bool // this M traced a STW start, so it should trace an end
207 // pTraceState is per-P state for the tracer.
208 type pTraceState struct {
211 // inSweep indicates the sweep events should be traced.
212 // This is used to defer the sweep start event until a span
213 // has actually been swept.
216 // swept and reclaimed track the number of bytes swept and reclaimed
217 // by sweeping in the current sweep loop (while inSweep was true).
218 swept, reclaimed uintptr
221 // traceLockInit initializes global trace locks.
222 func traceLockInit() {
223 lockInit(&trace.bufLock, lockRankTraceBuf)
224 lockInit(&trace.stringsLock, lockRankTraceStrings)
225 lockInit(&trace.lock, lockRankTrace)
226 lockInit(&trace.stackTab.lock, lockRankTraceStackTab)
229 // traceBufHeader is per-P tracing buffer.
230 type traceBufHeader struct {
231 link traceBufPtr // in trace.empty/full
232 lastTime traceTime // when we wrote the last event
233 pos int // next write offset in arr
234 stk [traceStackSize]uintptr // scratch buffer for traceback
237 // traceBuf is per-P tracing buffer.
238 type traceBuf struct {
241 arr [64<<10 - unsafe.Sizeof(traceBufHeader{})]byte // underlying buffer for traceBufHeader.buf
244 // traceBufPtr is a *traceBuf that is not traced by the garbage
245 // collector and doesn't have write barriers. traceBufs are not
246 // allocated from the GC'd heap, so this is safe, and are often
247 // manipulated in contexts where write barriers are not allowed, so
248 // this is necessary.
250 // TODO: Since traceBuf is now embedded runtime/internal/sys.NotInHeap, this isn't necessary.
251 type traceBufPtr uintptr
253 func (tp traceBufPtr) ptr() *traceBuf { return (*traceBuf)(unsafe.Pointer(tp)) }
254 func (tp *traceBufPtr) set(b *traceBuf) { *tp = traceBufPtr(unsafe.Pointer(b)) }
255 func traceBufPtrOf(b *traceBuf) traceBufPtr {
256 return traceBufPtr(unsafe.Pointer(b))
259 // traceEnabled returns true if the trace is currently enabled.
261 // nosplit because it's called on the syscall path when stack movement is forbidden.
264 func traceEnabled() bool {
268 // traceShuttingDown returns true if the trace is currently shutting down.
271 func traceShuttingDown() bool {
272 return trace.shutdown
275 // traceLocker represents an M writing trace events. While a traceLocker value
276 // is valid, the tracer observes all operations on the G/M/P or trace events being
277 // written as happening atomically.
279 // This doesn't do much for the current tracer, because the current tracer doesn't
280 // need atomicity around non-trace runtime operations. All the state it needs it
281 // collects carefully during a STW.
282 type traceLocker struct {
286 // traceAcquire prepares this M for writing one or more trace events.
288 // This exists for compatibility with the upcoming new tracer; it doesn't do much
289 // in the current tracer.
291 // nosplit because it's called on the syscall path when stack movement is forbidden.
294 func traceAcquire() traceLocker {
296 return traceLocker{false}
298 return traceLocker{true}
301 // ok returns true if the traceLocker is valid (i.e. tracing is enabled).
303 // nosplit because it's called on the syscall path when stack movement is forbidden.
306 func (tl traceLocker) ok() bool {
310 // traceRelease indicates that this M is done writing trace events.
312 // This exists for compatibility with the upcoming new tracer; it doesn't do anything
313 // in the current tracer.
315 // nosplit because it's called on the syscall path when stack movement is forbidden.
318 func traceRelease(tl traceLocker) {
321 // StartTrace enables tracing for the current process.
322 // While tracing, the data will be buffered and available via ReadTrace.
323 // StartTrace returns an error if tracing is already enabled.
324 // Most clients should use the runtime/trace package or the testing package's
325 // -test.trace flag instead of calling StartTrace directly.
326 func StartTrace() error {
327 // Stop the world so that we can take a consistent snapshot
328 // of all goroutines at the beginning of the trace.
329 // Do not stop the world during GC so we ensure we always see
330 // a consistent view of GC-related events (e.g. a start is always
331 // paired with an end).
332 stopTheWorldGC(stwStartTrace)
334 // Prevent sysmon from running any code that could generate events.
335 lock(&sched.sysmonlock)
337 // We are in stop-the-world, but syscalls can finish and write to trace concurrently.
338 // Exitsyscall could check trace.enabled long before and then suddenly wake up
339 // and decide to write to trace at a random point in time.
340 // However, such syscall will use the global trace.buf buffer, because we've
341 // acquired all p's by doing stop-the-world. So this protects us from such races.
344 if trace.enabled || trace.shutdown {
345 unlock(&trace.bufLock)
346 unlock(&sched.sysmonlock)
348 return errorString("tracing is already enabled")
351 // Can't set trace.enabled yet. While the world is stopped, exitsyscall could
352 // already emit a delayed event (see exitTicks in exitsyscall) if we set trace.enabled here.
353 // That would lead to an inconsistent trace:
354 // - either GoSysExit appears before EvGoInSyscall,
355 // - or GoSysExit appears for a goroutine for which we don't emit EvGoInSyscall below.
356 // To instruct traceEvent that it must not ignore events below, we set trace.startingTrace.
357 // trace.enabled is set afterwards once we have emitted all preliminary events.
359 mp.trace.startingTrace = true
361 // Obtain current stack ID to use in all traceEvGoCreate events below.
362 stkBuf := make([]uintptr, traceStackSize)
363 stackID := traceStackID(mp, stkBuf, 2)
365 profBuf := newProfBuf(2, profBufWordCount, profBufTagCount) // after the timestamp, header is [pp.id, gp.goid]
366 trace.cpuLogRead = profBuf
368 // We must not acquire trace.signalLock outside of a signal handler: a
369 // profiling signal may arrive at any time and try to acquire it, leading to
370 // deadlock. Because we can't use that lock to protect updates to
371 // trace.cpuLogWrite (only use of the structure it references), reads and
372 // writes of the pointer must be atomic. (And although this field is never
373 // the sole pointer to the profBuf value, it's best to allow a write barrier
375 atomicstorep(unsafe.Pointer(&trace.cpuLogWrite), unsafe.Pointer(profBuf))
377 // World is stopped, no need to lock.
378 forEachGRace(func(gp *g) {
379 status := readgstatus(gp)
380 if status != _Gdead {
382 gp.trace.lastP = getg().m.p
383 // +PCQuantum because traceFrameForPC expects return PCs and subtracts PCQuantum.
384 id := trace.stackTab.put([]uintptr{logicalStackSentinel, startPCforTrace(gp.startpc) + sys.PCQuantum})
385 traceEvent(traceEvGoCreate, -1, gp.goid, uint64(id), stackID)
387 if status == _Gwaiting {
388 // traceEvGoWaiting is implied to have seq=1.
390 traceEvent(traceEvGoWaiting, -1, gp.goid)
392 if status == _Gsyscall {
394 gp.trace.tracedSyscallEnter = true
395 traceEvent(traceEvGoInSyscall, -1, gp.goid)
396 } else if status == _Gdead && gp.m != nil && gp.m.isextra {
397 // Trigger two trace events for the dead g in the extra m,
398 // since the next event of the g will be traceEvGoSysExit in exitsyscall,
399 // while calling from C thread to Go.
401 gp.trace.lastP = getg().m.p
402 // +PCQuantum because traceFrameForPC expects return PCs and subtracts PCQuantum.
403 id := trace.stackTab.put([]uintptr{logicalStackSentinel, startPCforTrace(0) + sys.PCQuantum}) // no start pc
404 traceEvent(traceEvGoCreate, -1, gp.goid, uint64(id), stackID)
406 gp.trace.tracedSyscallEnter = true
407 traceEvent(traceEvGoInSyscall, -1, gp.goid)
409 // We need to explicitly clear the flag. A previous trace might have ended with a goroutine
410 // not emitting a GoSysExit and clearing the flag, leaving it in a stale state. Clearing
411 // it here makes it unambiguous to any goroutine exiting a syscall racing with us that
412 // no EvGoInSyscall event was emitted for it. (It's not racy to set this flag here, because
413 // it'll only get checked when the goroutine runs again, which will be after the world starts
415 gp.trace.tracedSyscallEnter = false
418 // Use a dummy traceLocker. The trace isn't enabled yet, but we can still write events.
422 // Note: startTicks needs to be set after we emit traceEvGoInSyscall events.
423 // If we do it the other way around, it is possible that exitsyscall will
424 // query sysExitTime after startTicks but before traceEvGoInSyscall timestamp.
425 // It will lead to a false conclusion that cputicks is broken.
426 trace.startTime = traceClockNow()
427 trace.startTicks = cputicks()
428 trace.startNanotime = nanotime()
429 trace.headerWritten = false
430 trace.footerWritten = false
432 // string to id mapping
433 // 0 : reserved for an empty string
434 // remaining: other strings registered by traceString
436 trace.strings = make(map[string]uint64)
439 mp.trace.startingTrace = false
442 // Register runtime goroutine labels.
443 _, pid, bufp := traceAcquireBuffer()
444 for i, label := range gcMarkWorkerModeStrings[:] {
445 trace.markWorkerLabels[i], bufp = traceString(bufp, pid, label)
447 traceReleaseBuffer(mp, pid)
449 unlock(&trace.bufLock)
451 unlock(&sched.sysmonlock)
453 // Record the current state of HeapGoal to avoid information loss in trace.
455 // Use the same dummy trace locker. The trace can't end until after we start
456 // the world, and we can safely trace from here.
463 // StopTrace stops tracing, if it was previously enabled.
464 // StopTrace only returns after all the reads for the trace have completed.
466 // Stop the world so that we can collect the trace buffers from all p's below,
467 // and also to avoid races with traceEvent.
468 stopTheWorldGC(stwStopTrace)
470 // See the comment in StartTrace.
471 lock(&sched.sysmonlock)
473 // See the comment in StartTrace.
477 unlock(&trace.bufLock)
478 unlock(&sched.sysmonlock)
483 // Trace GoSched for us, and use a dummy locker. The world is stopped
484 // and we control whether the trace is enabled, so this is safe.
488 atomicstorep(unsafe.Pointer(&trace.cpuLogWrite), nil)
489 trace.cpuLogRead.close()
492 // Loop over all allocated Ps because dead Ps may still have
494 for _, p := range allp[:cap(allp)] {
504 if buf.ptr().pos != 0 {
508 if trace.cpuLogBuf != 0 {
509 buf := trace.cpuLogBuf
511 if buf.ptr().pos != 0 {
516 // Wait for startNanotime != endNanotime. On Windows the default interval between
517 // system clock ticks is typically between 1 and 15 milliseconds, which may not
518 // have passed since the trace started. Without nanotime moving forward, trace
519 // tooling has no way of identifying how much real time each cputicks time deltas
522 trace.endTime = traceClockNow()
523 trace.endTicks = cputicks()
524 trace.endNanotime = nanotime()
526 if trace.endNanotime != trace.startNanotime || faketime != 0 {
532 trace.enabled = false
533 trace.shutdown = true
534 unlock(&trace.bufLock)
536 unlock(&sched.sysmonlock)
540 // The world is started but we've set trace.shutdown, so new tracing can't start.
541 // Wait for the trace reader to flush pending buffers and stop.
542 semacquire(&trace.shutdownSema)
544 raceacquire(unsafe.Pointer(&trace.shutdownSema))
548 // The lock protects us from races with StartTrace/StopTrace because they do stop-the-world.
550 for _, p := range allp[:cap(allp)] {
551 if p.trace.buf != 0 {
552 throw("trace: non-empty trace buffer in proc")
556 throw("trace: non-empty global trace buffer")
558 if trace.fullHead != 0 || trace.fullTail != 0 {
559 throw("trace: non-empty full trace buffer")
561 if trace.reading != 0 || trace.reader.Load() != nil {
562 throw("trace: reading after shutdown")
564 for trace.empty != 0 {
566 trace.empty = buf.ptr().link
567 sysFree(unsafe.Pointer(buf), unsafe.Sizeof(*buf.ptr()), &memstats.other_sys)
570 trace.shutdown = false
571 trace.cpuLogRead = nil
576 // ReadTrace returns the next chunk of binary tracing data, blocking until data
577 // is available. If tracing is turned off and all the data accumulated while it
578 // was on has been returned, ReadTrace returns nil. The caller must copy the
579 // returned data before calling ReadTrace again.
580 // ReadTrace must be called from one goroutine at a time.
581 func ReadTrace() []byte {
586 buf, park = readTrace0()
589 gopark(func(gp *g, _ unsafe.Pointer) bool {
590 if !trace.reader.CompareAndSwapNoWB(nil, gp) {
591 // We're racing with another reader.
592 // Wake up and handle this case.
596 if g2 := traceReader(); gp == g2 {
597 // New data arrived between unlocking
598 // and the CAS and we won the wake-up
599 // race, so wake up directly.
601 } else if g2 != nil {
603 println("runtime: got trace reader", g2, g2.goid)
604 throw("unexpected trace reader")
608 }, nil, waitReasonTraceReaderBlocked, traceBlockSystemGoroutine, 2)
615 // readTrace0 is ReadTrace's continuation on g0. This must run on the
616 // system stack because it acquires trace.lock.
619 func readTrace0() (buf []byte, park bool) {
621 // g0 doesn't have a race context. Borrow the user G's.
622 if getg().racectx != 0 {
623 throw("expected racectx == 0")
625 getg().racectx = getg().m.curg.racectx
626 // (This defer should get open-coded, which is safe on
627 // the system stack.)
628 defer func() { getg().racectx = 0 }()
631 // Optimistically look for CPU profile samples. This may write new stack
632 // records, and may write new tracing buffers. This must be done with the
633 // trace lock not held. footerWritten and shutdown are safe to access
634 // here. They are only mutated by this goroutine or during a STW.
635 if !trace.footerWritten && !trace.shutdown {
639 // This function must not allocate while holding trace.lock:
640 // allocation can call heap allocate, which will try to emit a trace
641 // event while holding heap lock.
644 if trace.reader.Load() != nil {
645 // More than one goroutine reads trace. This is bad.
646 // But we rather do not crash the program because of tracing,
647 // because tracing can be enabled at runtime on prod servers.
649 println("runtime: ReadTrace called from multiple goroutines simultaneously")
652 // Recycle the old buffer.
653 if buf := trace.reading; buf != 0 {
654 buf.ptr().link = trace.empty
658 // Write trace header.
659 if !trace.headerWritten {
660 trace.headerWritten = true
662 return []byte("go 1.21 trace\x00\x00\x00"), false
664 // Wait for new data.
665 if trace.fullHead == 0 && !trace.shutdown {
666 // We don't simply use a note because the scheduler
667 // executes this goroutine directly when it wakes up
668 // (also a note would consume an M).
673 assertLockHeld(&trace.lock)
675 if trace.fullHead != 0 {
676 buf := traceFullDequeue()
679 return buf.ptr().arr[:buf.ptr().pos], false
682 // Write footer with timer frequency.
683 if !trace.footerWritten {
684 trace.footerWritten = true
685 freq := (float64(trace.endTicks-trace.startTicks) / traceTimeDiv) / (float64(trace.endNanotime-trace.startNanotime) / 1e9)
687 throw("trace: ReadTrace got invalid frequency")
691 // Write frequency event.
692 bufp := traceFlush(0, 0)
694 buf.byte(traceEvFrequency | 0<<traceArgCountShift)
695 buf.varint(uint64(freq))
698 // This will emit a bunch of full buffers, we will pick them up
699 // on the next iteration.
700 bufp = trace.stackTab.dump(bufp)
702 // Flush final buffer.
705 goto newFull // trace.lock should be held at newFull
711 // Model synchronization on trace.shutdownSema, which race
712 // detector does not see. This is required to avoid false
713 // race reports on writer passed to trace.Start.
714 racerelease(unsafe.Pointer(&trace.shutdownSema))
716 // trace.enabled is already reset, so can call traceable functions.
717 semrelease(&trace.shutdownSema)
720 // Also bad, but see the comment above.
722 println("runtime: spurious wakeup of trace reader")
726 // traceReader returns the trace reader that should be woken up, if any.
727 // Callers should first check that trace.enabled or trace.shutdown is set.
729 // This must run on the system stack because it acquires trace.lock.
732 func traceReader() *g {
733 // Optimistic check first
734 if traceReaderAvailable() == nil {
738 gp := traceReaderAvailable()
739 if gp == nil || !trace.reader.CompareAndSwapNoWB(gp, nil) {
747 // traceReaderAvailable returns the trace reader if it is not currently
748 // scheduled and should be. Callers should first check that trace.enabled
749 // or trace.shutdown is set.
750 func traceReaderAvailable() *g {
751 if trace.fullHead != 0 || trace.shutdown {
752 return trace.reader.Load()
757 // traceProcFree frees trace buffer associated with pp.
759 // This must run on the system stack because it acquires trace.lock.
762 func traceProcFree(pp *p) {
773 // traceFullQueue queues buf into queue of full buffers.
774 func traceFullQueue(buf traceBufPtr) {
776 if trace.fullHead == 0 {
779 trace.fullTail.ptr().link = buf
784 // traceFullDequeue dequeues from queue of full buffers.
785 func traceFullDequeue() traceBufPtr {
786 buf := trace.fullHead
790 trace.fullHead = buf.ptr().link
791 if trace.fullHead == 0 {
798 // traceEvent writes a single event to trace buffer, flushing the buffer if necessary.
800 // If skip > 0, write current stack id as the last argument (skipping skip top frames).
801 // If skip = 0, this event type should contain a stack, but we don't want
802 // to collect and remember it for this particular call.
803 func traceEvent(ev byte, skip int, args ...uint64) {
804 mp, pid, bufp := traceAcquireBuffer()
805 // Double-check trace.enabled now that we've done m.locks++ and acquired bufLock.
806 // This protects from races between traceEvent and StartTrace/StopTrace.
808 // The caller checked that trace.enabled == true, but trace.enabled might have been
809 // turned off between the check and now. Check again. traceLockBuffer did mp.locks++,
810 // StopTrace does stopTheWorld, and stopTheWorld waits for mp.locks to go back to zero,
811 // so if we see trace.enabled == true now, we know it's true for the rest of the function.
812 // Exitsyscall can run even during stopTheWorld. The race with StartTrace/StopTrace
813 // during tracing in exitsyscall is resolved by locking trace.bufLock in traceLockBuffer.
815 // Note trace_userTaskCreate runs the same check.
816 if !trace.enabled && !mp.trace.startingTrace {
817 traceReleaseBuffer(mp, pid)
822 if getg() == mp.curg {
823 skip++ // +1 because stack is captured in traceEventLocked.
826 traceEventLocked(0, mp, pid, bufp, ev, 0, skip, args...)
827 traceReleaseBuffer(mp, pid)
830 // traceEventLocked writes a single event of type ev to the trace buffer bufp,
831 // flushing the buffer if necessary. pid is the id of the current P, or
832 // traceGlobProc if we're tracing without a real P.
834 // Preemption is disabled, and if running without a real P the global tracing
837 // Events types that do not include a stack set skip to -1. Event types that
838 // include a stack may explicitly reference a stackID from the trace.stackTab
839 // (obtained by an earlier call to traceStackID). Without an explicit stackID,
840 // this function will automatically capture the stack of the goroutine currently
841 // running on mp, skipping skip top frames or, if skip is 0, writing out an
842 // empty stack record.
844 // It records the event's args to the traceBuf, and also makes an effort to
845 // reserve extraBytes bytes of additional space immediately following the event,
846 // in the same traceBuf.
847 func traceEventLocked(extraBytes int, mp *m, pid int32, bufp *traceBufPtr, ev byte, stackID uint32, skip int, args ...uint64) {
849 // TODO: test on non-zero extraBytes param.
850 maxSize := 2 + 5*traceBytesPerNumber + extraBytes // event type, length, sequence, timestamp, stack id and two add params
851 if buf == nil || len(buf.arr)-buf.pos < maxSize {
853 buf = traceFlush(traceBufPtrOf(buf), pid).ptr()
858 ts := traceClockNow()
859 if ts <= buf.lastTime {
860 ts = buf.lastTime + 1
862 tsDiff := uint64(ts - buf.lastTime)
864 narg := byte(len(args))
865 if stackID != 0 || skip >= 0 {
868 // We have only 2 bits for number of arguments.
869 // If number is >= 3, then the event type is followed by event length in bytes.
874 buf.byte(ev | narg<<traceArgCountShift)
877 // Reserve the byte for length assuming that length < 128.
879 lenp = &buf.arr[buf.pos-1]
882 for _, a := range args {
886 buf.varint(uint64(stackID))
887 } else if skip == 0 {
890 buf.varint(traceStackID(mp, buf.stk[:], skip))
892 evSize := buf.pos - startPos
893 if evSize > maxSize {
894 throw("invalid length of trace event")
897 // Fill in actual length.
898 *lenp = byte(evSize - 2)
902 // traceCPUSample writes a CPU profile sample stack to the execution tracer's
903 // profiling buffer. It is called from a signal handler, so is limited in what
905 func traceCPUSample(gp *g, pp *p, stk []uintptr) {
907 // Tracing is usually turned off; don't spend time acquiring the signal
908 // lock unless it's active.
912 // Match the clock used in traceEventLocked
913 now := traceClockNow()
914 // The "header" here is the ID of the P that was running the profiled code,
915 // followed by the ID of the goroutine. (For normal CPU profiling, it's
916 // usually the number of samples with the given stack.) Near syscalls, pp
917 // may be nil. Reporting goid of 0 is fine for either g0 or a nil gp.
920 // Overflow records in profBuf have all header values set to zero. Make
921 // sure that real headers have at least one bit set.
922 hdr[0] = uint64(pp.id)<<1 | 0b1
930 // Allow only one writer at a time
931 for !trace.signalLock.CompareAndSwap(0, 1) {
932 // TODO: Is it safe to osyield here? https://go.dev/issue/52672
936 if log := (*profBuf)(atomic.Loadp(unsafe.Pointer(&trace.cpuLogWrite))); log != nil {
937 // Note: we don't pass a tag pointer here (how should profiling tags
938 // interact with the execution tracer?), but if we did we'd need to be
939 // careful about write barriers. See the long comment in profBuf.write.
940 log.write(nil, int64(now), hdr[:], stk)
943 trace.signalLock.Store(0)
946 func traceReadCPU() {
947 bufp := &trace.cpuLogBuf
950 data, tags, _ := trace.cpuLogRead.read(profBufNonBlocking)
955 if len(data) < 4 || data[0] > uint64(len(data)) {
956 break // truncated profile
958 if data[0] < 4 || tags != nil && len(tags) < 1 {
959 break // malformed profile
962 break // mismatched profile records and tags
966 if hasP := (data[2] & 0b1) != 0; !hasP {
970 stk := data[4:data[0]]
971 empty := len(stk) == 1 && data[2] == 0 && data[3] == 0
972 data = data[data[0]:]
973 // No support here for reporting goroutine tags at the moment; if
974 // that information is to be part of the execution trace, we'd
975 // probably want to see when the tags are applied and when they
976 // change, instead of only seeing them when we get a CPU sample.
980 // Looks like an overflow record from the profBuf. Not much to
981 // do here, we only want to report full records.
983 // TODO: should we start a goroutine to drain the profBuf,
984 // rather than relying on a high-enough volume of tracing events
985 // to keep ReadTrace busy? https://go.dev/issue/52674
992 *bufp = traceFlush(*bufp, 0)
997 buf.stk[0] = logicalStackSentinel
998 for ; nstk < len(buf.stk) && nstk-1 < len(stk); nstk++ {
999 buf.stk[nstk] = uintptr(stk[nstk-1])
1001 stackID := trace.stackTab.put(buf.stk[:nstk])
1003 traceEventLocked(0, nil, 0, bufp, traceEvCPUSample, stackID, 1, timestamp, ppid, goid)
1008 // logicalStackSentinel is a sentinel value at pcBuf[0] signifying that
1009 // pcBuf[1:] holds a logical stack requiring no further processing. Any other
1010 // value at pcBuf[0] represents a skip value to apply to the physical stack in
1011 // pcBuf[1:] after inline expansion.
1012 const logicalStackSentinel = ^uintptr(0)
1014 // traceStackID captures a stack trace into pcBuf, registers it in the trace
1015 // stack table, and returns its unique ID. pcBuf should have a length equal to
1016 // traceStackSize. skip controls the number of leaf frames to omit in order to
1017 // hide tracer internals from stack traces, see CL 5523.
1018 func traceStackID(mp *m, pcBuf []uintptr, skip int) uint64 {
1022 if tracefpunwindoff() || mp.hasCgoOnStack() {
1023 // Slow path: Unwind using default unwinder. Used when frame pointer
1024 // unwinding is unavailable or disabled (tracefpunwindoff), or might
1025 // produce incomplete results or crashes (hasCgoOnStack). Note that no
1026 // cgo callback related crashes have been observed yet. The main
1027 // motivation is to take advantage of a potentially registered cgo
1029 pcBuf[0] = logicalStackSentinel
1031 nstk += callers(skip+1, pcBuf[1:])
1032 } else if curgp != nil {
1033 nstk += gcallers(curgp, skip, pcBuf[1:])
1036 // Fast path: Unwind using frame pointers.
1037 pcBuf[0] = uintptr(skip)
1039 nstk += fpTracebackPCs(unsafe.Pointer(getfp()), pcBuf[1:])
1040 } else if curgp != nil {
1041 // We're called on the g0 stack through mcall(fn) or systemstack(fn). To
1042 // behave like gcallers above, we start unwinding from sched.bp, which
1043 // points to the caller frame of the leaf frame on g's stack. The return
1044 // address of the leaf frame is stored in sched.pc, which we manually
1046 pcBuf[1] = curgp.sched.pc
1047 nstk += 1 + fpTracebackPCs(unsafe.Pointer(curgp.sched.bp), pcBuf[2:])
1051 nstk-- // skip runtime.goexit
1053 if nstk > 0 && curgp.goid == 1 {
1054 nstk-- // skip runtime.main
1056 id := trace.stackTab.put(pcBuf[:nstk])
1060 // tracefpunwindoff returns true if frame pointer unwinding for the tracer is
1061 // disabled via GODEBUG or not supported by the architecture.
1062 // TODO(#60254): support frame pointer unwinding on plan9/amd64.
1063 func tracefpunwindoff() bool {
1064 return debug.tracefpunwindoff != 0 || (goarch.ArchFamily != goarch.AMD64 && goarch.ArchFamily != goarch.ARM64) || goos.IsPlan9 == 1
1067 // fpTracebackPCs populates pcBuf with the return addresses for each frame and
1068 // returns the number of PCs written to pcBuf. The returned PCs correspond to
1069 // "physical frames" rather than "logical frames"; that is if A is inlined into
1070 // B, this will return a PC for only B.
1071 func fpTracebackPCs(fp unsafe.Pointer, pcBuf []uintptr) (i int) {
1072 for i = 0; i < len(pcBuf) && fp != nil; i++ {
1073 // return addr sits one word above the frame pointer
1074 pcBuf[i] = *(*uintptr)(unsafe.Pointer(uintptr(fp) + goarch.PtrSize))
1075 // follow the frame pointer to the next one
1076 fp = unsafe.Pointer(*(*uintptr)(fp))
1081 // traceAcquireBuffer returns trace buffer to use and, if necessary, locks it.
1082 func traceAcquireBuffer() (mp *m, pid int32, bufp *traceBufPtr) {
1083 // Any time we acquire a buffer, we may end up flushing it,
1084 // but flushes are rare. Record the lock edge even if it
1085 // doesn't happen this time.
1086 lockRankMayTraceFlush()
1089 if p := mp.p.ptr(); p != nil {
1090 return mp, p.id, &p.trace.buf
1092 lock(&trace.bufLock)
1093 return mp, traceGlobProc, &trace.buf
1096 // traceReleaseBuffer releases a buffer previously acquired with traceAcquireBuffer.
1097 func traceReleaseBuffer(mp *m, pid int32) {
1098 if pid == traceGlobProc {
1099 unlock(&trace.bufLock)
1104 // lockRankMayTraceFlush records the lock ranking effects of a
1105 // potential call to traceFlush.
1106 func lockRankMayTraceFlush() {
1107 lockWithRankMayAcquire(&trace.lock, getLockRank(&trace.lock))
1110 // traceFlush puts buf onto stack of full buffers and returns an empty buffer.
1112 // This must run on the system stack because it acquires trace.lock.
1115 func traceFlush(buf traceBufPtr, pid int32) traceBufPtr {
1120 if trace.empty != 0 {
1122 trace.empty = buf.ptr().link
1124 buf = traceBufPtr(sysAlloc(unsafe.Sizeof(traceBuf{}), &memstats.other_sys))
1126 throw("trace: out of memory")
1133 // initialize the buffer for a new batch
1134 ts := traceClockNow()
1135 if ts <= bufp.lastTime {
1136 ts = bufp.lastTime + 1
1139 bufp.byte(traceEvBatch | 1<<traceArgCountShift)
1140 bufp.varint(uint64(pid))
1141 bufp.varint(uint64(ts))
1147 // traceString adds a string to the trace.strings and returns the id.
1148 func traceString(bufp *traceBufPtr, pid int32, s string) (uint64, *traceBufPtr) {
1153 lock(&trace.stringsLock)
1155 // raceacquire is necessary because the map access
1156 // below is race annotated.
1157 raceacquire(unsafe.Pointer(&trace.stringsLock))
1160 if id, ok := trace.strings[s]; ok {
1162 racerelease(unsafe.Pointer(&trace.stringsLock))
1164 unlock(&trace.stringsLock)
1170 id := trace.stringSeq
1171 trace.strings[s] = id
1174 racerelease(unsafe.Pointer(&trace.stringsLock))
1176 unlock(&trace.stringsLock)
1178 // memory allocation in above may trigger tracing and
1179 // cause *bufp changes. Following code now works with *bufp,
1180 // so there must be no memory allocation or any activities
1181 // that causes tracing after this point.
1184 size := 1 + 2*traceBytesPerNumber + len(s)
1185 if buf == nil || len(buf.arr)-buf.pos < size {
1186 systemstack(func() {
1187 buf = traceFlush(traceBufPtrOf(buf), pid).ptr()
1191 buf.byte(traceEvString)
1194 // double-check the string and the length can fit.
1195 // Otherwise, truncate the string.
1197 if room := len(buf.arr) - buf.pos; room < slen+traceBytesPerNumber {
1201 buf.varint(uint64(slen))
1202 buf.pos += copy(buf.arr[buf.pos:], s[:slen])
1208 // varint appends v to buf in little-endian-base-128 encoding.
1209 func (buf *traceBuf) varint(v uint64) {
1211 for ; v >= 0x80; v >>= 7 {
1212 buf.arr[pos] = 0x80 | byte(v)
1215 buf.arr[pos] = byte(v)
1220 // varintAt writes varint v at byte position pos in buf. This always
1221 // consumes traceBytesPerNumber bytes. This is intended for when the
1222 // caller needs to reserve space for a varint but can't populate it
1224 func (buf *traceBuf) varintAt(pos int, v uint64) {
1225 for i := 0; i < traceBytesPerNumber; i++ {
1226 if i < traceBytesPerNumber-1 {
1227 buf.arr[pos] = 0x80 | byte(v)
1229 buf.arr[pos] = byte(v)
1236 // byte appends v to buf.
1237 func (buf *traceBuf) byte(v byte) {
1238 buf.arr[buf.pos] = v
1242 // traceStackTable maps stack traces (arrays of PC's) to unique uint32 ids.
1243 // It is lock-free for reading.
1244 type traceStackTable struct {
1245 lock mutex // Must be acquired on the system stack
1248 tab [1 << 13]traceStackPtr
1251 // traceStack is a single stack in traceStackTable.
1252 type traceStack struct {
1257 stk [0]uintptr // real type [n]uintptr
1260 type traceStackPtr uintptr
1262 func (tp traceStackPtr) ptr() *traceStack { return (*traceStack)(unsafe.Pointer(tp)) }
1264 // stack returns slice of PCs.
1265 func (ts *traceStack) stack() []uintptr {
1266 return (*[traceStackSize]uintptr)(unsafe.Pointer(&ts.stk))[:ts.n]
1269 // put returns a unique id for the stack trace pcs and caches it in the table,
1270 // if it sees the trace for the first time.
1271 func (tab *traceStackTable) put(pcs []uintptr) uint32 {
1275 hash := memhash(unsafe.Pointer(&pcs[0]), 0, uintptr(len(pcs))*unsafe.Sizeof(pcs[0]))
1276 // First, search the hashtable w/o the mutex.
1277 if id := tab.find(pcs, hash); id != 0 {
1280 // Now, double check under the mutex.
1281 // Switch to the system stack so we can acquire tab.lock
1283 systemstack(func() {
1285 if id = tab.find(pcs, hash); id != 0 {
1289 // Create new record.
1291 stk := tab.newStack(len(pcs))
1296 stkpc := stk.stack()
1298 part := int(hash % uintptr(len(tab.tab)))
1299 stk.link = tab.tab[part]
1300 atomicstorep(unsafe.Pointer(&tab.tab[part]), unsafe.Pointer(stk))
1306 // find checks if the stack trace pcs is already present in the table.
1307 func (tab *traceStackTable) find(pcs []uintptr, hash uintptr) uint32 {
1308 part := int(hash % uintptr(len(tab.tab)))
1310 for stk := tab.tab[part].ptr(); stk != nil; stk = stk.link.ptr() {
1311 if stk.hash == hash && stk.n == len(pcs) {
1312 for i, stkpc := range stk.stack() {
1313 if stkpc != pcs[i] {
1323 // newStack allocates a new stack of size n.
1324 func (tab *traceStackTable) newStack(n int) *traceStack {
1325 return (*traceStack)(tab.mem.alloc(unsafe.Sizeof(traceStack{}) + uintptr(n)*goarch.PtrSize))
1328 // traceFrames returns the frames corresponding to pcs. It may
1329 // allocate and may emit trace events.
1330 func traceFrames(bufp traceBufPtr, pcs []uintptr) ([]traceFrame, traceBufPtr) {
1331 frames := make([]traceFrame, 0, len(pcs))
1332 ci := CallersFrames(pcs)
1334 var frame traceFrame
1335 f, more := ci.Next()
1336 frame, bufp = traceFrameForPC(bufp, 0, f)
1337 frames = append(frames, frame)
1344 // dump writes all previously cached stacks to trace buffers,
1345 // releases all memory and resets state.
1347 // This must run on the system stack because it calls traceFlush.
1350 func (tab *traceStackTable) dump(bufp traceBufPtr) traceBufPtr {
1351 for i := range tab.tab {
1352 stk := tab.tab[i].ptr()
1353 for ; stk != nil; stk = stk.link.ptr() {
1354 var frames []traceFrame
1355 frames, bufp = traceFrames(bufp, fpunwindExpand(stk.stack()))
1357 // Estimate the size of this record. This
1358 // bound is pretty loose, but avoids counting
1359 // lots of varint sizes.
1360 maxSize := 1 + traceBytesPerNumber + (2+4*len(frames))*traceBytesPerNumber
1361 // Make sure we have enough buffer space.
1362 if buf := bufp.ptr(); len(buf.arr)-buf.pos < maxSize {
1363 bufp = traceFlush(bufp, 0)
1366 // Emit header, with space reserved for length.
1368 buf.byte(traceEvStack | 3<<traceArgCountShift)
1370 buf.pos += traceBytesPerNumber
1374 buf.varint(uint64(stk.id))
1375 buf.varint(uint64(len(frames)))
1376 for _, frame := range frames {
1377 buf.varint(uint64(frame.PC))
1378 buf.varint(frame.funcID)
1379 buf.varint(frame.fileID)
1380 buf.varint(frame.line)
1383 // Fill in size header.
1384 buf.varintAt(lenPos, uint64(buf.pos-recPos))
1389 *tab = traceStackTable{}
1390 lockInit(&((*tab).lock), lockRankTraceStackTab)
1395 // fpunwindExpand checks if pcBuf contains logical frames (which include inlined
1396 // frames) or physical frames (produced by frame pointer unwinding) using a
1397 // sentinel value in pcBuf[0]. Logical frames are simply returned without the
1398 // sentinel. Physical frames are turned into logical frames via inline unwinding
1399 // and by applying the skip value that's stored in pcBuf[0].
1400 func fpunwindExpand(pcBuf []uintptr) []uintptr {
1401 if len(pcBuf) > 0 && pcBuf[0] == logicalStackSentinel {
1402 // pcBuf contains logical rather than inlined frames, skip has already been
1403 // applied, just return it without the sentinel value in pcBuf[0].
1408 lastFuncID = abi.FuncIDNormal
1409 newPCBuf = make([]uintptr, 0, traceStackSize)
1411 // skipOrAdd skips or appends retPC to newPCBuf and returns true if more
1412 // pcs can be added.
1413 skipOrAdd = func(retPC uintptr) bool {
1417 newPCBuf = append(newPCBuf, retPC)
1419 return len(newPCBuf) < cap(newPCBuf)
1424 for _, retPC := range pcBuf[1:] {
1426 fi := findfunc(callPC)
1428 // There is no funcInfo if callPC belongs to a C function. In this case
1429 // we still keep the pc, but don't attempt to expand inlined frames.
1430 if more := skipOrAdd(retPC); !more {
1436 u, uf := newInlineUnwinder(fi, callPC)
1437 for ; uf.valid(); uf = u.next(uf) {
1439 if sf.funcID == abi.FuncIDWrapper && elideWrapperCalling(lastFuncID) {
1441 } else if more := skipOrAdd(uf.pc + 1); !more {
1444 lastFuncID = sf.funcID
1450 type traceFrame struct {
1457 // traceFrameForPC records the frame information.
1458 // It may allocate memory.
1459 func traceFrameForPC(buf traceBufPtr, pid int32, f Frame) (traceFrame, traceBufPtr) {
1461 var frame traceFrame
1465 const maxLen = 1 << 10
1466 if len(fn) > maxLen {
1467 fn = fn[len(fn)-maxLen:]
1469 frame.funcID, bufp = traceString(bufp, pid, fn)
1470 frame.line = uint64(f.Line)
1472 if len(file) > maxLen {
1473 file = file[len(file)-maxLen:]
1475 frame.fileID, bufp = traceString(bufp, pid, file)
1476 return frame, (*bufp)
1479 // traceAlloc is a non-thread-safe region allocator.
1480 // It holds a linked list of traceAllocBlock.
1481 type traceAlloc struct {
1482 head traceAllocBlockPtr
1486 // traceAllocBlock is a block in traceAlloc.
1488 // traceAllocBlock is allocated from non-GC'd memory, so it must not
1489 // contain heap pointers. Writes to pointers to traceAllocBlocks do
1490 // not need write barriers.
1491 type traceAllocBlock struct {
1493 next traceAllocBlockPtr
1494 data [64<<10 - goarch.PtrSize]byte
1497 // TODO: Since traceAllocBlock is now embedded runtime/internal/sys.NotInHeap, this isn't necessary.
1498 type traceAllocBlockPtr uintptr
1500 func (p traceAllocBlockPtr) ptr() *traceAllocBlock { return (*traceAllocBlock)(unsafe.Pointer(p)) }
1501 func (p *traceAllocBlockPtr) set(x *traceAllocBlock) { *p = traceAllocBlockPtr(unsafe.Pointer(x)) }
1503 // alloc allocates n-byte block.
1504 func (a *traceAlloc) alloc(n uintptr) unsafe.Pointer {
1505 n = alignUp(n, goarch.PtrSize)
1506 if a.head == 0 || a.off+n > uintptr(len(a.head.ptr().data)) {
1507 if n > uintptr(len(a.head.ptr().data)) {
1508 throw("trace: alloc too large")
1510 block := (*traceAllocBlock)(sysAlloc(unsafe.Sizeof(traceAllocBlock{}), &memstats.other_sys))
1512 throw("trace: out of memory")
1514 block.next.set(a.head.ptr())
1518 p := &a.head.ptr().data[a.off]
1520 return unsafe.Pointer(p)
1523 // drop frees all previously allocated memory and resets the allocator.
1524 func (a *traceAlloc) drop() {
1526 block := a.head.ptr()
1527 a.head.set(block.next.ptr())
1528 sysFree(unsafe.Pointer(block), unsafe.Sizeof(traceAllocBlock{}), &memstats.other_sys)
1532 // The following functions write specific events to trace.
1534 func (_ traceLocker) Gomaxprocs(procs int32) {
1535 traceEvent(traceEvGomaxprocs, 1, uint64(procs))
1538 func (_ traceLocker) ProcStart() {
1539 traceEvent(traceEvProcStart, -1, uint64(getg().m.id))
1542 func (_ traceLocker) ProcStop(pp *p) {
1543 // Sysmon and stopTheWorld can stop Ps blocked in syscalls,
1544 // to handle this we temporary employ the P.
1548 traceEvent(traceEvProcStop, -1)
1553 func (_ traceLocker) GCStart() {
1554 traceEvent(traceEvGCStart, 3, trace.seqGC)
1558 func (_ traceLocker) GCDone() {
1559 traceEvent(traceEvGCDone, -1)
1562 func (_ traceLocker) STWStart(reason stwReason) {
1563 // Don't trace if this STW is for trace start/stop, since traceEnabled
1564 // switches during a STW.
1565 if reason == stwStartTrace || reason == stwStopTrace {
1568 getg().m.trace.tracedSTWStart = true
1569 traceEvent(traceEvSTWStart, -1, uint64(reason))
1572 func (_ traceLocker) STWDone() {
1574 if !mp.trace.tracedSTWStart {
1577 mp.trace.tracedSTWStart = false
1578 traceEvent(traceEvSTWDone, -1)
1581 // traceGCSweepStart prepares to trace a sweep loop. This does not
1582 // emit any events until traceGCSweepSpan is called.
1584 // traceGCSweepStart must be paired with traceGCSweepDone and there
1585 // must be no preemption points between these two calls.
1586 func (_ traceLocker) GCSweepStart() {
1587 // Delay the actual GCSweepStart event until the first span
1588 // sweep. If we don't sweep anything, don't emit any events.
1589 pp := getg().m.p.ptr()
1590 if pp.trace.inSweep {
1591 throw("double traceGCSweepStart")
1593 pp.trace.inSweep, pp.trace.swept, pp.trace.reclaimed = true, 0, 0
1596 // traceGCSweepSpan traces the sweep of a single page.
1598 // This may be called outside a traceGCSweepStart/traceGCSweepDone
1599 // pair; however, it will not emit any trace events in this case.
1600 func (_ traceLocker) GCSweepSpan(bytesSwept uintptr) {
1601 pp := getg().m.p.ptr()
1602 if pp.trace.inSweep {
1603 if pp.trace.swept == 0 {
1604 traceEvent(traceEvGCSweepStart, 1)
1606 pp.trace.swept += bytesSwept
1610 func (_ traceLocker) GCSweepDone() {
1611 pp := getg().m.p.ptr()
1612 if !pp.trace.inSweep {
1613 throw("missing traceGCSweepStart")
1615 if pp.trace.swept != 0 {
1616 traceEvent(traceEvGCSweepDone, -1, uint64(pp.trace.swept), uint64(pp.trace.reclaimed))
1618 pp.trace.inSweep = false
1621 func (_ traceLocker) GCMarkAssistStart() {
1622 traceEvent(traceEvGCMarkAssistStart, 1)
1625 func (_ traceLocker) GCMarkAssistDone() {
1626 traceEvent(traceEvGCMarkAssistDone, -1)
1629 func (_ traceLocker) GoCreate(newg *g, pc uintptr) {
1631 newg.trace.lastP = getg().m.p
1632 // +PCQuantum because traceFrameForPC expects return PCs and subtracts PCQuantum.
1633 id := trace.stackTab.put([]uintptr{logicalStackSentinel, startPCforTrace(pc) + sys.PCQuantum})
1634 traceEvent(traceEvGoCreate, 2, newg.goid, uint64(id))
1637 func (_ traceLocker) GoStart() {
1641 if pp.ptr().gcMarkWorkerMode != gcMarkWorkerNotWorker {
1642 traceEvent(traceEvGoStartLabel, -1, gp.goid, gp.trace.seq, trace.markWorkerLabels[pp.ptr().gcMarkWorkerMode])
1643 } else if gp.trace.lastP == pp {
1644 traceEvent(traceEvGoStartLocal, -1, gp.goid)
1647 traceEvent(traceEvGoStart, -1, gp.goid, gp.trace.seq)
1651 func (_ traceLocker) GoEnd() {
1652 traceEvent(traceEvGoEnd, -1)
1655 func (_ traceLocker) GoSched() {
1657 gp.trace.lastP = gp.m.p
1658 traceEvent(traceEvGoSched, 1)
1661 func (_ traceLocker) GoPreempt() {
1663 gp.trace.lastP = gp.m.p
1664 traceEvent(traceEvGoPreempt, 1)
1667 func (_ traceLocker) GoPark(reason traceBlockReason, skip int) {
1668 // Convert the block reason directly to a trace event type.
1669 // See traceBlockReason for more information.
1670 traceEvent(byte(reason), skip)
1673 func (_ traceLocker) GoUnpark(gp *g, skip int) {
1676 if gp.trace.lastP == pp {
1677 traceEvent(traceEvGoUnblockLocal, skip, gp.goid)
1680 traceEvent(traceEvGoUnblock, skip, gp.goid, gp.trace.seq)
1684 func (_ traceLocker) GoSysCall() {
1687 case tracefpunwindoff():
1688 // Unwind by skipping 1 frame relative to gp.syscallsp which is captured 3
1689 // frames above this frame. For frame pointer unwinding we produce the same
1690 // results by hard coding the number of frames in between our caller and the
1691 // actual syscall, see cases below.
1692 // TODO(felixge): Implement gp.syscallbp to avoid this workaround?
1694 case GOOS == "solaris" || GOOS == "illumos":
1695 // These platforms don't use a libc_read_trampoline.
1698 // Skip the extra trampoline frame used on most systems.
1701 getg().m.curg.trace.tracedSyscallEnter = true
1702 traceEvent(traceEvGoSysCall, skip)
1705 func (_ traceLocker) GoSysExit() {
1707 if !gp.trace.tracedSyscallEnter {
1708 // There was no syscall entry traced for us at all, so there's definitely
1709 // no EvGoSysBlock or EvGoInSyscall before us, which EvGoSysExit requires.
1712 gp.trace.tracedSyscallEnter = false
1713 ts := gp.trace.sysExitTime
1714 if ts != 0 && ts < trace.startTime {
1715 // There is a race between the code that initializes sysExitTimes
1716 // (in exitsyscall, which runs without a P, and therefore is not
1717 // stopped with the rest of the world) and the code that initializes
1718 // a new trace. The recorded sysExitTime must therefore be treated
1719 // as "best effort". If they are valid for this trace, then great,
1720 // use them for greater accuracy. But if they're not valid for this
1721 // trace, assume that the trace was started after the actual syscall
1722 // exit (but before we actually managed to start the goroutine,
1723 // aka right now), and assign a fresh time stamp to keep the log consistent.
1726 gp.trace.sysExitTime = 0
1728 gp.trace.lastP = gp.m.p
1729 traceEvent(traceEvGoSysExit, -1, gp.goid, gp.trace.seq, uint64(ts))
1732 func (_ traceLocker) GoSysBlock(pp *p) {
1733 // Sysmon and stopTheWorld can declare syscalls running on remote Ps as blocked,
1734 // to handle this we temporary employ the P.
1738 traceEvent(traceEvGoSysBlock, -1)
1743 func (_ traceLocker) HeapAlloc(live uint64) {
1744 traceEvent(traceEvHeapAlloc, -1, live)
1747 func (_ traceLocker) HeapGoal() {
1748 heapGoal := gcController.heapGoal()
1749 if heapGoal == ^uint64(0) {
1750 // Heap-based triggering is disabled.
1751 traceEvent(traceEvHeapGoal, -1, 0)
1753 traceEvent(traceEvHeapGoal, -1, heapGoal)
1757 // To access runtime functions from runtime/trace.
1758 // See runtime/trace/annotation.go
1760 //go:linkname trace_userTaskCreate runtime/trace.userTaskCreate
1761 func trace_userTaskCreate(id, parentID uint64, taskType string) {
1766 // Same as in traceEvent.
1767 mp, pid, bufp := traceAcquireBuffer()
1768 if !trace.enabled && !mp.trace.startingTrace {
1769 traceReleaseBuffer(mp, pid)
1773 typeStringID, bufp := traceString(bufp, pid, taskType)
1774 traceEventLocked(0, mp, pid, bufp, traceEvUserTaskCreate, 0, 3, id, parentID, typeStringID)
1775 traceReleaseBuffer(mp, pid)
1778 //go:linkname trace_userTaskEnd runtime/trace.userTaskEnd
1779 func trace_userTaskEnd(id uint64) {
1780 traceEvent(traceEvUserTaskEnd, 2, id)
1783 //go:linkname trace_userRegion runtime/trace.userRegion
1784 func trace_userRegion(id, mode uint64, name string) {
1789 mp, pid, bufp := traceAcquireBuffer()
1790 if !trace.enabled && !mp.trace.startingTrace {
1791 traceReleaseBuffer(mp, pid)
1795 nameStringID, bufp := traceString(bufp, pid, name)
1796 traceEventLocked(0, mp, pid, bufp, traceEvUserRegion, 0, 3, id, mode, nameStringID)
1797 traceReleaseBuffer(mp, pid)
1800 //go:linkname trace_userLog runtime/trace.userLog
1801 func trace_userLog(id uint64, category, message string) {
1806 mp, pid, bufp := traceAcquireBuffer()
1807 if !trace.enabled && !mp.trace.startingTrace {
1808 traceReleaseBuffer(mp, pid)
1812 categoryID, bufp := traceString(bufp, pid, category)
1814 // The log message is recorded after all of the normal trace event
1815 // arguments, including the task, category, and stack IDs. We must ask
1816 // traceEventLocked to reserve extra space for the length of the message
1817 // and the message itself.
1818 extraSpace := traceBytesPerNumber + len(message)
1819 traceEventLocked(extraSpace, mp, pid, bufp, traceEvUserLog, 0, 3, id, categoryID)
1822 // double-check the message and its length can fit.
1823 // Otherwise, truncate the message.
1824 slen := len(message)
1825 if room := len(buf.arr) - buf.pos; room < slen+traceBytesPerNumber {
1828 buf.varint(uint64(slen))
1829 buf.pos += copy(buf.arr[buf.pos:], message[:slen])
1831 traceReleaseBuffer(mp, pid)
1834 // the start PC of a goroutine for tracing purposes. If pc is a wrapper,
1835 // it returns the PC of the wrapped function. Otherwise it returns pc.
1836 func startPCforTrace(pc uintptr) uintptr {
1839 return pc // may happen for locked g in extra M since its pc is 0.
1841 w := funcdata(f, abi.FUNCDATA_WrapInfo)
1843 return pc // not a wrapper
1845 return f.datap.textAddr(*(*uint32)(w))
1848 // OneNewExtraM registers the fact that a new extra M was created with
1849 // the tracer. This matters if the M (which has an attached G) is used while
1850 // the trace is still active because if it is, we need the fact that it exists
1851 // to show up in the final trace.
1852 func (tl traceLocker) OneNewExtraM(gp *g) {
1853 // Trigger two trace events for the locked g in the extra m,
1854 // since the next event of the g will be traceEvGoSysExit in exitsyscall,
1855 // while calling from C thread to Go.
1856 tl.GoCreate(gp, 0) // no start pc
1858 traceEvent(traceEvGoInSyscall, -1, gp.goid)
1861 // traceTime represents a timestamp for the trace.
1862 type traceTime uint64
1864 // traceClockNow returns a monotonic timestamp. The clock this function gets
1865 // the timestamp from is specific to tracing, and shouldn't be mixed with other
1868 // nosplit because it's called from exitsyscall, which is nosplit.
1871 func traceClockNow() traceTime {
1872 return traceTime(cputicks() / traceTimeDiv)