github.com/AESNooper/go/src@v0.0.0-20220218095104-b56a4ab1bbbb/runtime/trace.go (about) 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. 4 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. 12 13 package runtime 14 15 import ( 16 "internal/goarch" 17 "runtime/internal/atomic" 18 "runtime/internal/sys" 19 "unsafe" 20 ) 21 22 // Event types in the trace, args are given in square brackets. 23 const ( 24 traceEvNone = 0 // unused 25 traceEvBatch = 1 // start of per-P batch of events [pid, timestamp] 26 traceEvFrequency = 2 // contains tracer timer frequency [frequency (ticks per second)] 27 traceEvStack = 3 // stack [stack id, number of PCs, array of {PC, func string ID, file string ID, line}] 28 traceEvGomaxprocs = 4 // current value of GOMAXPROCS [timestamp, GOMAXPROCS, stack id] 29 traceEvProcStart = 5 // start of P [timestamp, thread id] 30 traceEvProcStop = 6 // stop of P [timestamp] 31 traceEvGCStart = 7 // GC start [timestamp, seq, stack id] 32 traceEvGCDone = 8 // GC done [timestamp] 33 traceEvGCSTWStart = 9 // GC STW start [timestamp, kind] 34 traceEvGCSTWDone = 10 // GC STW done [timestamp] 35 traceEvGCSweepStart = 11 // GC sweep start [timestamp, stack id] 36 traceEvGCSweepDone = 12 // GC sweep done [timestamp, swept, reclaimed] 37 traceEvGoCreate = 13 // goroutine creation [timestamp, new goroutine id, new stack id, stack id] 38 traceEvGoStart = 14 // goroutine starts running [timestamp, goroutine id, seq] 39 traceEvGoEnd = 15 // goroutine ends [timestamp] 40 traceEvGoStop = 16 // goroutine stops (like in select{}) [timestamp, stack] 41 traceEvGoSched = 17 // goroutine calls Gosched [timestamp, stack] 42 traceEvGoPreempt = 18 // goroutine is preempted [timestamp, stack] 43 traceEvGoSleep = 19 // goroutine calls Sleep [timestamp, stack] 44 traceEvGoBlock = 20 // goroutine blocks [timestamp, stack] 45 traceEvGoUnblock = 21 // goroutine is unblocked [timestamp, goroutine id, seq, stack] 46 traceEvGoBlockSend = 22 // goroutine blocks on chan send [timestamp, stack] 47 traceEvGoBlockRecv = 23 // goroutine blocks on chan recv [timestamp, stack] 48 traceEvGoBlockSelect = 24 // goroutine blocks on select [timestamp, stack] 49 traceEvGoBlockSync = 25 // goroutine blocks on Mutex/RWMutex [timestamp, stack] 50 traceEvGoBlockCond = 26 // goroutine blocks on Cond [timestamp, stack] 51 traceEvGoBlockNet = 27 // goroutine blocks on network [timestamp, stack] 52 traceEvGoSysCall = 28 // syscall enter [timestamp, stack] 53 traceEvGoSysExit = 29 // syscall exit [timestamp, goroutine id, seq, real timestamp] 54 traceEvGoSysBlock = 30 // syscall blocks [timestamp] 55 traceEvGoWaiting = 31 // denotes that goroutine is blocked when tracing starts [timestamp, goroutine id] 56 traceEvGoInSyscall = 32 // denotes that goroutine is in syscall when tracing starts [timestamp, goroutine id] 57 traceEvHeapAlloc = 33 // gcController.heapLive change [timestamp, heap_alloc] 58 traceEvHeapGoal = 34 // gcController.heapGoal (formerly next_gc) change [timestamp, heap goal in bytes] 59 traceEvTimerGoroutine = 35 // not currently used; previously denoted timer goroutine [timer goroutine id] 60 traceEvFutileWakeup = 36 // denotes that the previous wakeup of this goroutine was futile [timestamp] 61 traceEvString = 37 // string dictionary entry [ID, length, string] 62 traceEvGoStartLocal = 38 // goroutine starts running on the same P as the last event [timestamp, goroutine id] 63 traceEvGoUnblockLocal = 39 // goroutine is unblocked on the same P as the last event [timestamp, goroutine id, stack] 64 traceEvGoSysExitLocal = 40 // syscall exit on the same P as the last event [timestamp, goroutine id, real timestamp] 65 traceEvGoStartLabel = 41 // goroutine starts running with label [timestamp, goroutine id, seq, label string id] 66 traceEvGoBlockGC = 42 // goroutine blocks on GC assist [timestamp, stack] 67 traceEvGCMarkAssistStart = 43 // GC mark assist start [timestamp, stack] 68 traceEvGCMarkAssistDone = 44 // GC mark assist done [timestamp] 69 traceEvUserTaskCreate = 45 // trace.NewContext [timestamp, internal task id, internal parent task id, stack, name string] 70 traceEvUserTaskEnd = 46 // end of a task [timestamp, internal task id, stack] 71 traceEvUserRegion = 47 // trace.WithRegion [timestamp, internal task id, mode(0:start, 1:end), stack, name string] 72 traceEvUserLog = 48 // trace.Log [timestamp, internal task id, key string id, stack, value string] 73 traceEvCount = 49 74 // Byte is used but only 6 bits are available for event type. 75 // The remaining 2 bits are used to specify the number of arguments. 76 // That means, the max event type value is 63. 77 ) 78 79 const ( 80 // Timestamps in trace are cputicks/traceTickDiv. 81 // This makes absolute values of timestamp diffs smaller, 82 // and so they are encoded in less number of bytes. 83 // 64 on x86 is somewhat arbitrary (one tick is ~20ns on a 3GHz machine). 84 // The suggested increment frequency for PowerPC's time base register is 85 // 512 MHz according to Power ISA v2.07 section 6.2, so we use 16 on ppc64 86 // and ppc64le. 87 // Tracing won't work reliably for architectures where cputicks is emulated 88 // by nanotime, so the value doesn't matter for those architectures. 89 traceTickDiv = 16 + 48*(goarch.Is386|goarch.IsAmd64) 90 // Maximum number of PCs in a single stack trace. 91 // Since events contain only stack id rather than whole stack trace, 92 // we can allow quite large values here. 93 traceStackSize = 128 94 // Identifier of a fake P that is used when we trace without a real P. 95 traceGlobProc = -1 96 // Maximum number of bytes to encode uint64 in base-128. 97 traceBytesPerNumber = 10 98 // Shift of the number of arguments in the first event byte. 99 traceArgCountShift = 6 100 // Flag passed to traceGoPark to denote that the previous wakeup of this 101 // goroutine was futile. For example, a goroutine was unblocked on a mutex, 102 // but another goroutine got ahead and acquired the mutex before the first 103 // goroutine is scheduled, so the first goroutine has to block again. 104 // Such wakeups happen on buffered channels and sync.Mutex, 105 // but are generally not interesting for end user. 106 traceFutileWakeup byte = 128 107 ) 108 109 // trace is global tracing context. 110 var trace struct { 111 lock mutex // protects the following members 112 lockOwner *g // to avoid deadlocks during recursive lock locks 113 enabled bool // when set runtime traces events 114 shutdown bool // set when we are waiting for trace reader to finish after setting enabled to false 115 headerWritten bool // whether ReadTrace has emitted trace header 116 footerWritten bool // whether ReadTrace has emitted trace footer 117 shutdownSema uint32 // used to wait for ReadTrace completion 118 seqStart uint64 // sequence number when tracing was started 119 ticksStart int64 // cputicks when tracing was started 120 ticksEnd int64 // cputicks when tracing was stopped 121 timeStart int64 // nanotime when tracing was started 122 timeEnd int64 // nanotime when tracing was stopped 123 seqGC uint64 // GC start/done sequencer 124 reading traceBufPtr // buffer currently handed off to user 125 empty traceBufPtr // stack of empty buffers 126 fullHead traceBufPtr // queue of full buffers 127 fullTail traceBufPtr 128 reader guintptr // goroutine that called ReadTrace, or nil 129 stackTab traceStackTable // maps stack traces to unique ids 130 131 // Dictionary for traceEvString. 132 // 133 // TODO: central lock to access the map is not ideal. 134 // option: pre-assign ids to all user annotation region names and tags 135 // option: per-P cache 136 // option: sync.Map like data structure 137 stringsLock mutex 138 strings map[string]uint64 139 stringSeq uint64 140 141 // markWorkerLabels maps gcMarkWorkerMode to string ID. 142 markWorkerLabels [len(gcMarkWorkerModeStrings)]uint64 143 144 bufLock mutex // protects buf 145 buf traceBufPtr // global trace buffer, used when running without a p 146 } 147 148 // traceBufHeader is per-P tracing buffer. 149 type traceBufHeader struct { 150 link traceBufPtr // in trace.empty/full 151 lastTicks uint64 // when we wrote the last event 152 pos int // next write offset in arr 153 stk [traceStackSize]uintptr // scratch buffer for traceback 154 } 155 156 // traceBuf is per-P tracing buffer. 157 // 158 //go:notinheap 159 type traceBuf struct { 160 traceBufHeader 161 arr [64<<10 - unsafe.Sizeof(traceBufHeader{})]byte // underlying buffer for traceBufHeader.buf 162 } 163 164 // traceBufPtr is a *traceBuf that is not traced by the garbage 165 // collector and doesn't have write barriers. traceBufs are not 166 // allocated from the GC'd heap, so this is safe, and are often 167 // manipulated in contexts where write barriers are not allowed, so 168 // this is necessary. 169 // 170 // TODO: Since traceBuf is now go:notinheap, this isn't necessary. 171 type traceBufPtr uintptr 172 173 func (tp traceBufPtr) ptr() *traceBuf { return (*traceBuf)(unsafe.Pointer(tp)) } 174 func (tp *traceBufPtr) set(b *traceBuf) { *tp = traceBufPtr(unsafe.Pointer(b)) } 175 func traceBufPtrOf(b *traceBuf) traceBufPtr { 176 return traceBufPtr(unsafe.Pointer(b)) 177 } 178 179 // StartTrace enables tracing for the current process. 180 // While tracing, the data will be buffered and available via ReadTrace. 181 // StartTrace returns an error if tracing is already enabled. 182 // Most clients should use the runtime/trace package or the testing package's 183 // -test.trace flag instead of calling StartTrace directly. 184 func StartTrace() error { 185 // Stop the world so that we can take a consistent snapshot 186 // of all goroutines at the beginning of the trace. 187 // Do not stop the world during GC so we ensure we always see 188 // a consistent view of GC-related events (e.g. a start is always 189 // paired with an end). 190 stopTheWorldGC("start tracing") 191 192 // Prevent sysmon from running any code that could generate events. 193 lock(&sched.sysmonlock) 194 195 // We are in stop-the-world, but syscalls can finish and write to trace concurrently. 196 // Exitsyscall could check trace.enabled long before and then suddenly wake up 197 // and decide to write to trace at a random point in time. 198 // However, such syscall will use the global trace.buf buffer, because we've 199 // acquired all p's by doing stop-the-world. So this protects us from such races. 200 lock(&trace.bufLock) 201 202 if trace.enabled || trace.shutdown { 203 unlock(&trace.bufLock) 204 unlock(&sched.sysmonlock) 205 startTheWorldGC() 206 return errorString("tracing is already enabled") 207 } 208 209 // Can't set trace.enabled yet. While the world is stopped, exitsyscall could 210 // already emit a delayed event (see exitTicks in exitsyscall) if we set trace.enabled here. 211 // That would lead to an inconsistent trace: 212 // - either GoSysExit appears before EvGoInSyscall, 213 // - or GoSysExit appears for a goroutine for which we don't emit EvGoInSyscall below. 214 // To instruct traceEvent that it must not ignore events below, we set startingtrace. 215 // trace.enabled is set afterwards once we have emitted all preliminary events. 216 _g_ := getg() 217 _g_.m.startingtrace = true 218 219 // Obtain current stack ID to use in all traceEvGoCreate events below. 220 mp := acquirem() 221 stkBuf := make([]uintptr, traceStackSize) 222 stackID := traceStackID(mp, stkBuf, 2) 223 releasem(mp) 224 225 // World is stopped, no need to lock. 226 forEachGRace(func(gp *g) { 227 status := readgstatus(gp) 228 if status != _Gdead { 229 gp.traceseq = 0 230 gp.tracelastp = getg().m.p 231 // +PCQuantum because traceFrameForPC expects return PCs and subtracts PCQuantum. 232 id := trace.stackTab.put([]uintptr{gp.startpc + sys.PCQuantum}) 233 traceEvent(traceEvGoCreate, -1, uint64(gp.goid), uint64(id), stackID) 234 } 235 if status == _Gwaiting { 236 // traceEvGoWaiting is implied to have seq=1. 237 gp.traceseq++ 238 traceEvent(traceEvGoWaiting, -1, uint64(gp.goid)) 239 } 240 if status == _Gsyscall { 241 gp.traceseq++ 242 traceEvent(traceEvGoInSyscall, -1, uint64(gp.goid)) 243 } else { 244 gp.sysblocktraced = false 245 } 246 }) 247 traceProcStart() 248 traceGoStart() 249 // Note: ticksStart needs to be set after we emit traceEvGoInSyscall events. 250 // If we do it the other way around, it is possible that exitsyscall will 251 // query sysexitticks after ticksStart but before traceEvGoInSyscall timestamp. 252 // It will lead to a false conclusion that cputicks is broken. 253 trace.ticksStart = cputicks() 254 trace.timeStart = nanotime() 255 trace.headerWritten = false 256 trace.footerWritten = false 257 258 // string to id mapping 259 // 0 : reserved for an empty string 260 // remaining: other strings registered by traceString 261 trace.stringSeq = 0 262 trace.strings = make(map[string]uint64) 263 264 trace.seqGC = 0 265 _g_.m.startingtrace = false 266 trace.enabled = true 267 268 // Register runtime goroutine labels. 269 _, pid, bufp := traceAcquireBuffer() 270 for i, label := range gcMarkWorkerModeStrings[:] { 271 trace.markWorkerLabels[i], bufp = traceString(bufp, pid, label) 272 } 273 traceReleaseBuffer(pid) 274 275 unlock(&trace.bufLock) 276 277 unlock(&sched.sysmonlock) 278 279 startTheWorldGC() 280 return nil 281 } 282 283 // StopTrace stops tracing, if it was previously enabled. 284 // StopTrace only returns after all the reads for the trace have completed. 285 func StopTrace() { 286 // Stop the world so that we can collect the trace buffers from all p's below, 287 // and also to avoid races with traceEvent. 288 stopTheWorldGC("stop tracing") 289 290 // See the comment in StartTrace. 291 lock(&sched.sysmonlock) 292 293 // See the comment in StartTrace. 294 lock(&trace.bufLock) 295 296 if !trace.enabled { 297 unlock(&trace.bufLock) 298 unlock(&sched.sysmonlock) 299 startTheWorldGC() 300 return 301 } 302 303 traceGoSched() 304 305 // Loop over all allocated Ps because dead Ps may still have 306 // trace buffers. 307 for _, p := range allp[:cap(allp)] { 308 buf := p.tracebuf 309 if buf != 0 { 310 traceFullQueue(buf) 311 p.tracebuf = 0 312 } 313 } 314 if trace.buf != 0 { 315 buf := trace.buf 316 trace.buf = 0 317 if buf.ptr().pos != 0 { 318 traceFullQueue(buf) 319 } 320 } 321 322 for { 323 trace.ticksEnd = cputicks() 324 trace.timeEnd = nanotime() 325 // Windows time can tick only every 15ms, wait for at least one tick. 326 if trace.timeEnd != trace.timeStart { 327 break 328 } 329 osyield() 330 } 331 332 trace.enabled = false 333 trace.shutdown = true 334 unlock(&trace.bufLock) 335 336 unlock(&sched.sysmonlock) 337 338 startTheWorldGC() 339 340 // The world is started but we've set trace.shutdown, so new tracing can't start. 341 // Wait for the trace reader to flush pending buffers and stop. 342 semacquire(&trace.shutdownSema) 343 if raceenabled { 344 raceacquire(unsafe.Pointer(&trace.shutdownSema)) 345 } 346 347 // The lock protects us from races with StartTrace/StopTrace because they do stop-the-world. 348 lock(&trace.lock) 349 for _, p := range allp[:cap(allp)] { 350 if p.tracebuf != 0 { 351 throw("trace: non-empty trace buffer in proc") 352 } 353 } 354 if trace.buf != 0 { 355 throw("trace: non-empty global trace buffer") 356 } 357 if trace.fullHead != 0 || trace.fullTail != 0 { 358 throw("trace: non-empty full trace buffer") 359 } 360 if trace.reading != 0 || trace.reader != 0 { 361 throw("trace: reading after shutdown") 362 } 363 for trace.empty != 0 { 364 buf := trace.empty 365 trace.empty = buf.ptr().link 366 sysFree(unsafe.Pointer(buf), unsafe.Sizeof(*buf.ptr()), &memstats.other_sys) 367 } 368 trace.strings = nil 369 trace.shutdown = false 370 unlock(&trace.lock) 371 } 372 373 // ReadTrace returns the next chunk of binary tracing data, blocking until data 374 // is available. If tracing is turned off and all the data accumulated while it 375 // was on has been returned, ReadTrace returns nil. The caller must copy the 376 // returned data before calling ReadTrace again. 377 // ReadTrace must be called from one goroutine at a time. 378 func ReadTrace() []byte { 379 // This function may need to lock trace.lock recursively 380 // (goparkunlock -> traceGoPark -> traceEvent -> traceFlush). 381 // To allow this we use trace.lockOwner. 382 // Also this function must not allocate while holding trace.lock: 383 // allocation can call heap allocate, which will try to emit a trace 384 // event while holding heap lock. 385 lock(&trace.lock) 386 trace.lockOwner = getg() 387 388 if trace.reader != 0 { 389 // More than one goroutine reads trace. This is bad. 390 // But we rather do not crash the program because of tracing, 391 // because tracing can be enabled at runtime on prod servers. 392 trace.lockOwner = nil 393 unlock(&trace.lock) 394 println("runtime: ReadTrace called from multiple goroutines simultaneously") 395 return nil 396 } 397 // Recycle the old buffer. 398 if buf := trace.reading; buf != 0 { 399 buf.ptr().link = trace.empty 400 trace.empty = buf 401 trace.reading = 0 402 } 403 // Write trace header. 404 if !trace.headerWritten { 405 trace.headerWritten = true 406 trace.lockOwner = nil 407 unlock(&trace.lock) 408 return []byte("go 1.11 trace\x00\x00\x00") 409 } 410 // Wait for new data. 411 if trace.fullHead == 0 && !trace.shutdown { 412 trace.reader.set(getg()) 413 goparkunlock(&trace.lock, waitReasonTraceReaderBlocked, traceEvGoBlock, 2) 414 lock(&trace.lock) 415 } 416 // Write a buffer. 417 if trace.fullHead != 0 { 418 buf := traceFullDequeue() 419 trace.reading = buf 420 trace.lockOwner = nil 421 unlock(&trace.lock) 422 return buf.ptr().arr[:buf.ptr().pos] 423 } 424 // Write footer with timer frequency. 425 if !trace.footerWritten { 426 trace.footerWritten = true 427 // Use float64 because (trace.ticksEnd - trace.ticksStart) * 1e9 can overflow int64. 428 freq := float64(trace.ticksEnd-trace.ticksStart) * 1e9 / float64(trace.timeEnd-trace.timeStart) / traceTickDiv 429 trace.lockOwner = nil 430 unlock(&trace.lock) 431 var data []byte 432 data = append(data, traceEvFrequency|0<<traceArgCountShift) 433 data = traceAppend(data, uint64(freq)) 434 // This will emit a bunch of full buffers, we will pick them up 435 // on the next iteration. 436 trace.stackTab.dump() 437 return data 438 } 439 // Done. 440 if trace.shutdown { 441 trace.lockOwner = nil 442 unlock(&trace.lock) 443 if raceenabled { 444 // Model synchronization on trace.shutdownSema, which race 445 // detector does not see. This is required to avoid false 446 // race reports on writer passed to trace.Start. 447 racerelease(unsafe.Pointer(&trace.shutdownSema)) 448 } 449 // trace.enabled is already reset, so can call traceable functions. 450 semrelease(&trace.shutdownSema) 451 return nil 452 } 453 // Also bad, but see the comment above. 454 trace.lockOwner = nil 455 unlock(&trace.lock) 456 println("runtime: spurious wakeup of trace reader") 457 return nil 458 } 459 460 // traceReader returns the trace reader that should be woken up, if any. 461 func traceReader() *g { 462 if trace.reader == 0 || (trace.fullHead == 0 && !trace.shutdown) { 463 return nil 464 } 465 lock(&trace.lock) 466 if trace.reader == 0 || (trace.fullHead == 0 && !trace.shutdown) { 467 unlock(&trace.lock) 468 return nil 469 } 470 gp := trace.reader.ptr() 471 trace.reader.set(nil) 472 unlock(&trace.lock) 473 return gp 474 } 475 476 // traceProcFree frees trace buffer associated with pp. 477 func traceProcFree(pp *p) { 478 buf := pp.tracebuf 479 pp.tracebuf = 0 480 if buf == 0 { 481 return 482 } 483 lock(&trace.lock) 484 traceFullQueue(buf) 485 unlock(&trace.lock) 486 } 487 488 // traceFullQueue queues buf into queue of full buffers. 489 func traceFullQueue(buf traceBufPtr) { 490 buf.ptr().link = 0 491 if trace.fullHead == 0 { 492 trace.fullHead = buf 493 } else { 494 trace.fullTail.ptr().link = buf 495 } 496 trace.fullTail = buf 497 } 498 499 // traceFullDequeue dequeues from queue of full buffers. 500 func traceFullDequeue() traceBufPtr { 501 buf := trace.fullHead 502 if buf == 0 { 503 return 0 504 } 505 trace.fullHead = buf.ptr().link 506 if trace.fullHead == 0 { 507 trace.fullTail = 0 508 } 509 buf.ptr().link = 0 510 return buf 511 } 512 513 // traceEvent writes a single event to trace buffer, flushing the buffer if necessary. 514 // ev is event type. 515 // If skip > 0, write current stack id as the last argument (skipping skip top frames). 516 // If skip = 0, this event type should contain a stack, but we don't want 517 // to collect and remember it for this particular call. 518 func traceEvent(ev byte, skip int, args ...uint64) { 519 mp, pid, bufp := traceAcquireBuffer() 520 // Double-check trace.enabled now that we've done m.locks++ and acquired bufLock. 521 // This protects from races between traceEvent and StartTrace/StopTrace. 522 523 // The caller checked that trace.enabled == true, but trace.enabled might have been 524 // turned off between the check and now. Check again. traceLockBuffer did mp.locks++, 525 // StopTrace does stopTheWorld, and stopTheWorld waits for mp.locks to go back to zero, 526 // so if we see trace.enabled == true now, we know it's true for the rest of the function. 527 // Exitsyscall can run even during stopTheWorld. The race with StartTrace/StopTrace 528 // during tracing in exitsyscall is resolved by locking trace.bufLock in traceLockBuffer. 529 // 530 // Note trace_userTaskCreate runs the same check. 531 if !trace.enabled && !mp.startingtrace { 532 traceReleaseBuffer(pid) 533 return 534 } 535 536 if skip > 0 { 537 if getg() == mp.curg { 538 skip++ // +1 because stack is captured in traceEventLocked. 539 } 540 } 541 traceEventLocked(0, mp, pid, bufp, ev, skip, args...) 542 traceReleaseBuffer(pid) 543 } 544 545 func traceEventLocked(extraBytes int, mp *m, pid int32, bufp *traceBufPtr, ev byte, skip int, args ...uint64) { 546 buf := bufp.ptr() 547 // TODO: test on non-zero extraBytes param. 548 maxSize := 2 + 5*traceBytesPerNumber + extraBytes // event type, length, sequence, timestamp, stack id and two add params 549 if buf == nil || len(buf.arr)-buf.pos < maxSize { 550 buf = traceFlush(traceBufPtrOf(buf), pid).ptr() 551 bufp.set(buf) 552 } 553 554 // NOTE: ticks might be same after tick division, although the real cputicks is 555 // linear growth. 556 ticks := uint64(cputicks()) / traceTickDiv 557 tickDiff := ticks - buf.lastTicks 558 if tickDiff == 0 { 559 ticks = buf.lastTicks + 1 560 tickDiff = 1 561 } 562 563 buf.lastTicks = ticks 564 narg := byte(len(args)) 565 if skip >= 0 { 566 narg++ 567 } 568 // We have only 2 bits for number of arguments. 569 // If number is >= 3, then the event type is followed by event length in bytes. 570 if narg > 3 { 571 narg = 3 572 } 573 startPos := buf.pos 574 buf.byte(ev | narg<<traceArgCountShift) 575 var lenp *byte 576 if narg == 3 { 577 // Reserve the byte for length assuming that length < 128. 578 buf.varint(0) 579 lenp = &buf.arr[buf.pos-1] 580 } 581 buf.varint(tickDiff) 582 for _, a := range args { 583 buf.varint(a) 584 } 585 if skip == 0 { 586 buf.varint(0) 587 } else if skip > 0 { 588 buf.varint(traceStackID(mp, buf.stk[:], skip)) 589 } 590 evSize := buf.pos - startPos 591 if evSize > maxSize { 592 throw("invalid length of trace event") 593 } 594 if lenp != nil { 595 // Fill in actual length. 596 *lenp = byte(evSize - 2) 597 } 598 } 599 600 func traceStackID(mp *m, buf []uintptr, skip int) uint64 { 601 _g_ := getg() 602 gp := mp.curg 603 var nstk int 604 if gp == _g_ { 605 nstk = callers(skip+1, buf) 606 } else if gp != nil { 607 gp = mp.curg 608 nstk = gcallers(gp, skip, buf) 609 } 610 if nstk > 0 { 611 nstk-- // skip runtime.goexit 612 } 613 if nstk > 0 && gp.goid == 1 { 614 nstk-- // skip runtime.main 615 } 616 id := trace.stackTab.put(buf[:nstk]) 617 return uint64(id) 618 } 619 620 // traceAcquireBuffer returns trace buffer to use and, if necessary, locks it. 621 func traceAcquireBuffer() (mp *m, pid int32, bufp *traceBufPtr) { 622 mp = acquirem() 623 if p := mp.p.ptr(); p != nil { 624 return mp, p.id, &p.tracebuf 625 } 626 lock(&trace.bufLock) 627 return mp, traceGlobProc, &trace.buf 628 } 629 630 // traceReleaseBuffer releases a buffer previously acquired with traceAcquireBuffer. 631 func traceReleaseBuffer(pid int32) { 632 if pid == traceGlobProc { 633 unlock(&trace.bufLock) 634 } 635 releasem(getg().m) 636 } 637 638 // traceFlush puts buf onto stack of full buffers and returns an empty buffer. 639 func traceFlush(buf traceBufPtr, pid int32) traceBufPtr { 640 owner := trace.lockOwner 641 dolock := owner == nil || owner != getg().m.curg 642 if dolock { 643 lock(&trace.lock) 644 } 645 if buf != 0 { 646 traceFullQueue(buf) 647 } 648 if trace.empty != 0 { 649 buf = trace.empty 650 trace.empty = buf.ptr().link 651 } else { 652 buf = traceBufPtr(sysAlloc(unsafe.Sizeof(traceBuf{}), &memstats.other_sys)) 653 if buf == 0 { 654 throw("trace: out of memory") 655 } 656 } 657 bufp := buf.ptr() 658 bufp.link.set(nil) 659 bufp.pos = 0 660 661 // initialize the buffer for a new batch 662 ticks := uint64(cputicks()) / traceTickDiv 663 if ticks == bufp.lastTicks { 664 ticks = bufp.lastTicks + 1 665 } 666 bufp.lastTicks = ticks 667 bufp.byte(traceEvBatch | 1<<traceArgCountShift) 668 bufp.varint(uint64(pid)) 669 bufp.varint(ticks) 670 671 if dolock { 672 unlock(&trace.lock) 673 } 674 return buf 675 } 676 677 // traceString adds a string to the trace.strings and returns the id. 678 func traceString(bufp *traceBufPtr, pid int32, s string) (uint64, *traceBufPtr) { 679 if s == "" { 680 return 0, bufp 681 } 682 683 lock(&trace.stringsLock) 684 if raceenabled { 685 // raceacquire is necessary because the map access 686 // below is race annotated. 687 raceacquire(unsafe.Pointer(&trace.stringsLock)) 688 } 689 690 if id, ok := trace.strings[s]; ok { 691 if raceenabled { 692 racerelease(unsafe.Pointer(&trace.stringsLock)) 693 } 694 unlock(&trace.stringsLock) 695 696 return id, bufp 697 } 698 699 trace.stringSeq++ 700 id := trace.stringSeq 701 trace.strings[s] = id 702 703 if raceenabled { 704 racerelease(unsafe.Pointer(&trace.stringsLock)) 705 } 706 unlock(&trace.stringsLock) 707 708 // memory allocation in above may trigger tracing and 709 // cause *bufp changes. Following code now works with *bufp, 710 // so there must be no memory allocation or any activities 711 // that causes tracing after this point. 712 713 buf := bufp.ptr() 714 size := 1 + 2*traceBytesPerNumber + len(s) 715 if buf == nil || len(buf.arr)-buf.pos < size { 716 buf = traceFlush(traceBufPtrOf(buf), pid).ptr() 717 bufp.set(buf) 718 } 719 buf.byte(traceEvString) 720 buf.varint(id) 721 722 // double-check the string and the length can fit. 723 // Otherwise, truncate the string. 724 slen := len(s) 725 if room := len(buf.arr) - buf.pos; room < slen+traceBytesPerNumber { 726 slen = room 727 } 728 729 buf.varint(uint64(slen)) 730 buf.pos += copy(buf.arr[buf.pos:], s[:slen]) 731 732 bufp.set(buf) 733 return id, bufp 734 } 735 736 // traceAppend appends v to buf in little-endian-base-128 encoding. 737 func traceAppend(buf []byte, v uint64) []byte { 738 for ; v >= 0x80; v >>= 7 { 739 buf = append(buf, 0x80|byte(v)) 740 } 741 buf = append(buf, byte(v)) 742 return buf 743 } 744 745 // varint appends v to buf in little-endian-base-128 encoding. 746 func (buf *traceBuf) varint(v uint64) { 747 pos := buf.pos 748 for ; v >= 0x80; v >>= 7 { 749 buf.arr[pos] = 0x80 | byte(v) 750 pos++ 751 } 752 buf.arr[pos] = byte(v) 753 pos++ 754 buf.pos = pos 755 } 756 757 // byte appends v to buf. 758 func (buf *traceBuf) byte(v byte) { 759 buf.arr[buf.pos] = v 760 buf.pos++ 761 } 762 763 // traceStackTable maps stack traces (arrays of PC's) to unique uint32 ids. 764 // It is lock-free for reading. 765 type traceStackTable struct { 766 lock mutex 767 seq uint32 768 mem traceAlloc 769 tab [1 << 13]traceStackPtr 770 } 771 772 // traceStack is a single stack in traceStackTable. 773 type traceStack struct { 774 link traceStackPtr 775 hash uintptr 776 id uint32 777 n int 778 stk [0]uintptr // real type [n]uintptr 779 } 780 781 type traceStackPtr uintptr 782 783 func (tp traceStackPtr) ptr() *traceStack { return (*traceStack)(unsafe.Pointer(tp)) } 784 785 // stack returns slice of PCs. 786 func (ts *traceStack) stack() []uintptr { 787 return (*[traceStackSize]uintptr)(unsafe.Pointer(&ts.stk))[:ts.n] 788 } 789 790 // put returns a unique id for the stack trace pcs and caches it in the table, 791 // if it sees the trace for the first time. 792 func (tab *traceStackTable) put(pcs []uintptr) uint32 { 793 if len(pcs) == 0 { 794 return 0 795 } 796 hash := memhash(unsafe.Pointer(&pcs[0]), 0, uintptr(len(pcs))*unsafe.Sizeof(pcs[0])) 797 // First, search the hashtable w/o the mutex. 798 if id := tab.find(pcs, hash); id != 0 { 799 return id 800 } 801 // Now, double check under the mutex. 802 lock(&tab.lock) 803 if id := tab.find(pcs, hash); id != 0 { 804 unlock(&tab.lock) 805 return id 806 } 807 // Create new record. 808 tab.seq++ 809 stk := tab.newStack(len(pcs)) 810 stk.hash = hash 811 stk.id = tab.seq 812 stk.n = len(pcs) 813 stkpc := stk.stack() 814 for i, pc := range pcs { 815 stkpc[i] = pc 816 } 817 part := int(hash % uintptr(len(tab.tab))) 818 stk.link = tab.tab[part] 819 atomicstorep(unsafe.Pointer(&tab.tab[part]), unsafe.Pointer(stk)) 820 unlock(&tab.lock) 821 return stk.id 822 } 823 824 // find checks if the stack trace pcs is already present in the table. 825 func (tab *traceStackTable) find(pcs []uintptr, hash uintptr) uint32 { 826 part := int(hash % uintptr(len(tab.tab))) 827 Search: 828 for stk := tab.tab[part].ptr(); stk != nil; stk = stk.link.ptr() { 829 if stk.hash == hash && stk.n == len(pcs) { 830 for i, stkpc := range stk.stack() { 831 if stkpc != pcs[i] { 832 continue Search 833 } 834 } 835 return stk.id 836 } 837 } 838 return 0 839 } 840 841 // newStack allocates a new stack of size n. 842 func (tab *traceStackTable) newStack(n int) *traceStack { 843 return (*traceStack)(tab.mem.alloc(unsafe.Sizeof(traceStack{}) + uintptr(n)*goarch.PtrSize)) 844 } 845 846 // allFrames returns all of the Frames corresponding to pcs. 847 func allFrames(pcs []uintptr) []Frame { 848 frames := make([]Frame, 0, len(pcs)) 849 ci := CallersFrames(pcs) 850 for { 851 f, more := ci.Next() 852 frames = append(frames, f) 853 if !more { 854 return frames 855 } 856 } 857 } 858 859 // dump writes all previously cached stacks to trace buffers, 860 // releases all memory and resets state. 861 func (tab *traceStackTable) dump() { 862 var tmp [(2 + 4*traceStackSize) * traceBytesPerNumber]byte 863 bufp := traceFlush(0, 0) 864 for _, stk := range tab.tab { 865 stk := stk.ptr() 866 for ; stk != nil; stk = stk.link.ptr() { 867 tmpbuf := tmp[:0] 868 tmpbuf = traceAppend(tmpbuf, uint64(stk.id)) 869 frames := allFrames(stk.stack()) 870 tmpbuf = traceAppend(tmpbuf, uint64(len(frames))) 871 for _, f := range frames { 872 var frame traceFrame 873 frame, bufp = traceFrameForPC(bufp, 0, f) 874 tmpbuf = traceAppend(tmpbuf, uint64(f.PC)) 875 tmpbuf = traceAppend(tmpbuf, uint64(frame.funcID)) 876 tmpbuf = traceAppend(tmpbuf, uint64(frame.fileID)) 877 tmpbuf = traceAppend(tmpbuf, uint64(frame.line)) 878 } 879 // Now copy to the buffer. 880 size := 1 + traceBytesPerNumber + len(tmpbuf) 881 if buf := bufp.ptr(); len(buf.arr)-buf.pos < size { 882 bufp = traceFlush(bufp, 0) 883 } 884 buf := bufp.ptr() 885 buf.byte(traceEvStack | 3<<traceArgCountShift) 886 buf.varint(uint64(len(tmpbuf))) 887 buf.pos += copy(buf.arr[buf.pos:], tmpbuf) 888 } 889 } 890 891 lock(&trace.lock) 892 traceFullQueue(bufp) 893 unlock(&trace.lock) 894 895 tab.mem.drop() 896 *tab = traceStackTable{} 897 lockInit(&((*tab).lock), lockRankTraceStackTab) 898 } 899 900 type traceFrame struct { 901 funcID uint64 902 fileID uint64 903 line uint64 904 } 905 906 // traceFrameForPC records the frame information. 907 // It may allocate memory. 908 func traceFrameForPC(buf traceBufPtr, pid int32, f Frame) (traceFrame, traceBufPtr) { 909 bufp := &buf 910 var frame traceFrame 911 912 fn := f.Function 913 const maxLen = 1 << 10 914 if len(fn) > maxLen { 915 fn = fn[len(fn)-maxLen:] 916 } 917 frame.funcID, bufp = traceString(bufp, pid, fn) 918 frame.line = uint64(f.Line) 919 file := f.File 920 if len(file) > maxLen { 921 file = file[len(file)-maxLen:] 922 } 923 frame.fileID, bufp = traceString(bufp, pid, file) 924 return frame, (*bufp) 925 } 926 927 // traceAlloc is a non-thread-safe region allocator. 928 // It holds a linked list of traceAllocBlock. 929 type traceAlloc struct { 930 head traceAllocBlockPtr 931 off uintptr 932 } 933 934 // traceAllocBlock is a block in traceAlloc. 935 // 936 // traceAllocBlock is allocated from non-GC'd memory, so it must not 937 // contain heap pointers. Writes to pointers to traceAllocBlocks do 938 // not need write barriers. 939 // 940 //go:notinheap 941 type traceAllocBlock struct { 942 next traceAllocBlockPtr 943 data [64<<10 - goarch.PtrSize]byte 944 } 945 946 // TODO: Since traceAllocBlock is now go:notinheap, this isn't necessary. 947 type traceAllocBlockPtr uintptr 948 949 func (p traceAllocBlockPtr) ptr() *traceAllocBlock { return (*traceAllocBlock)(unsafe.Pointer(p)) } 950 func (p *traceAllocBlockPtr) set(x *traceAllocBlock) { *p = traceAllocBlockPtr(unsafe.Pointer(x)) } 951 952 // alloc allocates n-byte block. 953 func (a *traceAlloc) alloc(n uintptr) unsafe.Pointer { 954 n = alignUp(n, goarch.PtrSize) 955 if a.head == 0 || a.off+n > uintptr(len(a.head.ptr().data)) { 956 if n > uintptr(len(a.head.ptr().data)) { 957 throw("trace: alloc too large") 958 } 959 block := (*traceAllocBlock)(sysAlloc(unsafe.Sizeof(traceAllocBlock{}), &memstats.other_sys)) 960 if block == nil { 961 throw("trace: out of memory") 962 } 963 block.next.set(a.head.ptr()) 964 a.head.set(block) 965 a.off = 0 966 } 967 p := &a.head.ptr().data[a.off] 968 a.off += n 969 return unsafe.Pointer(p) 970 } 971 972 // drop frees all previously allocated memory and resets the allocator. 973 func (a *traceAlloc) drop() { 974 for a.head != 0 { 975 block := a.head.ptr() 976 a.head.set(block.next.ptr()) 977 sysFree(unsafe.Pointer(block), unsafe.Sizeof(traceAllocBlock{}), &memstats.other_sys) 978 } 979 } 980 981 // The following functions write specific events to trace. 982 983 func traceGomaxprocs(procs int32) { 984 traceEvent(traceEvGomaxprocs, 1, uint64(procs)) 985 } 986 987 func traceProcStart() { 988 traceEvent(traceEvProcStart, -1, uint64(getg().m.id)) 989 } 990 991 func traceProcStop(pp *p) { 992 // Sysmon and stopTheWorld can stop Ps blocked in syscalls, 993 // to handle this we temporary employ the P. 994 mp := acquirem() 995 oldp := mp.p 996 mp.p.set(pp) 997 traceEvent(traceEvProcStop, -1) 998 mp.p = oldp 999 releasem(mp) 1000 } 1001 1002 func traceGCStart() { 1003 traceEvent(traceEvGCStart, 3, trace.seqGC) 1004 trace.seqGC++ 1005 } 1006 1007 func traceGCDone() { 1008 traceEvent(traceEvGCDone, -1) 1009 } 1010 1011 func traceGCSTWStart(kind int) { 1012 traceEvent(traceEvGCSTWStart, -1, uint64(kind)) 1013 } 1014 1015 func traceGCSTWDone() { 1016 traceEvent(traceEvGCSTWDone, -1) 1017 } 1018 1019 // traceGCSweepStart prepares to trace a sweep loop. This does not 1020 // emit any events until traceGCSweepSpan is called. 1021 // 1022 // traceGCSweepStart must be paired with traceGCSweepDone and there 1023 // must be no preemption points between these two calls. 1024 func traceGCSweepStart() { 1025 // Delay the actual GCSweepStart event until the first span 1026 // sweep. If we don't sweep anything, don't emit any events. 1027 _p_ := getg().m.p.ptr() 1028 if _p_.traceSweep { 1029 throw("double traceGCSweepStart") 1030 } 1031 _p_.traceSweep, _p_.traceSwept, _p_.traceReclaimed = true, 0, 0 1032 } 1033 1034 // traceGCSweepSpan traces the sweep of a single page. 1035 // 1036 // This may be called outside a traceGCSweepStart/traceGCSweepDone 1037 // pair; however, it will not emit any trace events in this case. 1038 func traceGCSweepSpan(bytesSwept uintptr) { 1039 _p_ := getg().m.p.ptr() 1040 if _p_.traceSweep { 1041 if _p_.traceSwept == 0 { 1042 traceEvent(traceEvGCSweepStart, 1) 1043 } 1044 _p_.traceSwept += bytesSwept 1045 } 1046 } 1047 1048 func traceGCSweepDone() { 1049 _p_ := getg().m.p.ptr() 1050 if !_p_.traceSweep { 1051 throw("missing traceGCSweepStart") 1052 } 1053 if _p_.traceSwept != 0 { 1054 traceEvent(traceEvGCSweepDone, -1, uint64(_p_.traceSwept), uint64(_p_.traceReclaimed)) 1055 } 1056 _p_.traceSweep = false 1057 } 1058 1059 func traceGCMarkAssistStart() { 1060 traceEvent(traceEvGCMarkAssistStart, 1) 1061 } 1062 1063 func traceGCMarkAssistDone() { 1064 traceEvent(traceEvGCMarkAssistDone, -1) 1065 } 1066 1067 func traceGoCreate(newg *g, pc uintptr) { 1068 newg.traceseq = 0 1069 newg.tracelastp = getg().m.p 1070 // +PCQuantum because traceFrameForPC expects return PCs and subtracts PCQuantum. 1071 id := trace.stackTab.put([]uintptr{pc + sys.PCQuantum}) 1072 traceEvent(traceEvGoCreate, 2, uint64(newg.goid), uint64(id)) 1073 } 1074 1075 func traceGoStart() { 1076 _g_ := getg().m.curg 1077 _p_ := _g_.m.p 1078 _g_.traceseq++ 1079 if _p_.ptr().gcMarkWorkerMode != gcMarkWorkerNotWorker { 1080 traceEvent(traceEvGoStartLabel, -1, uint64(_g_.goid), _g_.traceseq, trace.markWorkerLabels[_p_.ptr().gcMarkWorkerMode]) 1081 } else if _g_.tracelastp == _p_ { 1082 traceEvent(traceEvGoStartLocal, -1, uint64(_g_.goid)) 1083 } else { 1084 _g_.tracelastp = _p_ 1085 traceEvent(traceEvGoStart, -1, uint64(_g_.goid), _g_.traceseq) 1086 } 1087 } 1088 1089 func traceGoEnd() { 1090 traceEvent(traceEvGoEnd, -1) 1091 } 1092 1093 func traceGoSched() { 1094 _g_ := getg() 1095 _g_.tracelastp = _g_.m.p 1096 traceEvent(traceEvGoSched, 1) 1097 } 1098 1099 func traceGoPreempt() { 1100 _g_ := getg() 1101 _g_.tracelastp = _g_.m.p 1102 traceEvent(traceEvGoPreempt, 1) 1103 } 1104 1105 func traceGoPark(traceEv byte, skip int) { 1106 if traceEv&traceFutileWakeup != 0 { 1107 traceEvent(traceEvFutileWakeup, -1) 1108 } 1109 traceEvent(traceEv & ^traceFutileWakeup, skip) 1110 } 1111 1112 func traceGoUnpark(gp *g, skip int) { 1113 _p_ := getg().m.p 1114 gp.traceseq++ 1115 if gp.tracelastp == _p_ { 1116 traceEvent(traceEvGoUnblockLocal, skip, uint64(gp.goid)) 1117 } else { 1118 gp.tracelastp = _p_ 1119 traceEvent(traceEvGoUnblock, skip, uint64(gp.goid), gp.traceseq) 1120 } 1121 } 1122 1123 func traceGoSysCall() { 1124 traceEvent(traceEvGoSysCall, 1) 1125 } 1126 1127 func traceGoSysExit(ts int64) { 1128 if ts != 0 && ts < trace.ticksStart { 1129 // There is a race between the code that initializes sysexitticks 1130 // (in exitsyscall, which runs without a P, and therefore is not 1131 // stopped with the rest of the world) and the code that initializes 1132 // a new trace. The recorded sysexitticks must therefore be treated 1133 // as "best effort". If they are valid for this trace, then great, 1134 // use them for greater accuracy. But if they're not valid for this 1135 // trace, assume that the trace was started after the actual syscall 1136 // exit (but before we actually managed to start the goroutine, 1137 // aka right now), and assign a fresh time stamp to keep the log consistent. 1138 ts = 0 1139 } 1140 _g_ := getg().m.curg 1141 _g_.traceseq++ 1142 _g_.tracelastp = _g_.m.p 1143 traceEvent(traceEvGoSysExit, -1, uint64(_g_.goid), _g_.traceseq, uint64(ts)/traceTickDiv) 1144 } 1145 1146 func traceGoSysBlock(pp *p) { 1147 // Sysmon and stopTheWorld can declare syscalls running on remote Ps as blocked, 1148 // to handle this we temporary employ the P. 1149 mp := acquirem() 1150 oldp := mp.p 1151 mp.p.set(pp) 1152 traceEvent(traceEvGoSysBlock, -1) 1153 mp.p = oldp 1154 releasem(mp) 1155 } 1156 1157 func traceHeapAlloc() { 1158 traceEvent(traceEvHeapAlloc, -1, gcController.heapLive) 1159 } 1160 1161 func traceHeapGoal() { 1162 if heapGoal := atomic.Load64(&gcController.heapGoal); heapGoal == ^uint64(0) { 1163 // Heap-based triggering is disabled. 1164 traceEvent(traceEvHeapGoal, -1, 0) 1165 } else { 1166 traceEvent(traceEvHeapGoal, -1, heapGoal) 1167 } 1168 } 1169 1170 // To access runtime functions from runtime/trace. 1171 // See runtime/trace/annotation.go 1172 1173 //go:linkname trace_userTaskCreate runtime/trace.userTaskCreate 1174 func trace_userTaskCreate(id, parentID uint64, taskType string) { 1175 if !trace.enabled { 1176 return 1177 } 1178 1179 // Same as in traceEvent. 1180 mp, pid, bufp := traceAcquireBuffer() 1181 if !trace.enabled && !mp.startingtrace { 1182 traceReleaseBuffer(pid) 1183 return 1184 } 1185 1186 typeStringID, bufp := traceString(bufp, pid, taskType) 1187 traceEventLocked(0, mp, pid, bufp, traceEvUserTaskCreate, 3, id, parentID, typeStringID) 1188 traceReleaseBuffer(pid) 1189 } 1190 1191 //go:linkname trace_userTaskEnd runtime/trace.userTaskEnd 1192 func trace_userTaskEnd(id uint64) { 1193 traceEvent(traceEvUserTaskEnd, 2, id) 1194 } 1195 1196 //go:linkname trace_userRegion runtime/trace.userRegion 1197 func trace_userRegion(id, mode uint64, name string) { 1198 if !trace.enabled { 1199 return 1200 } 1201 1202 mp, pid, bufp := traceAcquireBuffer() 1203 if !trace.enabled && !mp.startingtrace { 1204 traceReleaseBuffer(pid) 1205 return 1206 } 1207 1208 nameStringID, bufp := traceString(bufp, pid, name) 1209 traceEventLocked(0, mp, pid, bufp, traceEvUserRegion, 3, id, mode, nameStringID) 1210 traceReleaseBuffer(pid) 1211 } 1212 1213 //go:linkname trace_userLog runtime/trace.userLog 1214 func trace_userLog(id uint64, category, message string) { 1215 if !trace.enabled { 1216 return 1217 } 1218 1219 mp, pid, bufp := traceAcquireBuffer() 1220 if !trace.enabled && !mp.startingtrace { 1221 traceReleaseBuffer(pid) 1222 return 1223 } 1224 1225 categoryID, bufp := traceString(bufp, pid, category) 1226 1227 extraSpace := traceBytesPerNumber + len(message) // extraSpace for the value string 1228 traceEventLocked(extraSpace, mp, pid, bufp, traceEvUserLog, 3, id, categoryID) 1229 // traceEventLocked reserved extra space for val and len(val) 1230 // in buf, so buf now has room for the following. 1231 buf := bufp.ptr() 1232 1233 // double-check the message and its length can fit. 1234 // Otherwise, truncate the message. 1235 slen := len(message) 1236 if room := len(buf.arr) - buf.pos; room < slen+traceBytesPerNumber { 1237 slen = room 1238 } 1239 buf.varint(uint64(slen)) 1240 buf.pos += copy(buf.arr[buf.pos:], message[:slen]) 1241 1242 traceReleaseBuffer(pid) 1243 }