src/runtime/traceback.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package runtime

 import "unsafe"

 // The code in this file implements stack trace walking for all architectures.
 // The most important fact about a given architecture is whether it uses a link register.
 // On systems with link registers, the prologue for a non-leaf function stores the
 // incoming value of LR at the bottom of the newly allocated stack frame.
 // On systems without link registers, the architecture pushes a return PC during
 // the call instruction, so the return PC ends up above the stack frame.
 // In this file, the return PC is always called LR, no matter how it was found.
 //
 // To date, the opposite of a link register architecture is an x86 architecture.
 // This code may need to change if some other kind of non-link-register
 // architecture comes along.
 //
 // The other important fact is the size of a pointer: on 32-bit systems the LR
 // takes up only 4 bytes on the stack, while on 64-bit systems it takes up 8 bytes.
 // Typically this is ptrSize.
 //
 // As an exception, amd64p32 has ptrSize == 4 but the CALL instruction still
 // stores an 8-byte return PC onto the stack. To accommodate this, we use regSize
 // as the size of the architecture-pushed return PC.
 //
 // usesLR is defined below. ptrSize and regSize are defined in stubs.go.

 const usesLR = GOARCH != "amd64" && GOARCH != "amd64p32" && GOARCH != "386"

 var (
 	// initialized in tracebackinit
 	goexitPC             uintptr
 	jmpdeferPC           uintptr
 	mcallPC              uintptr
 	morestackPC          uintptr
 	mstartPC             uintptr
 	rt0_goPC             uintptr
 	sigpanicPC           uintptr
 	runfinqPC            uintptr
 	backgroundgcPC       uintptr
 	bgsweepPC            uintptr
 	forcegchelperPC      uintptr
 	timerprocPC          uintptr
 	gcBgMarkWorkerPC     uintptr
 	systemstack_switchPC uintptr

 	externalthreadhandlerp uintptr // initialized elsewhere
 )

 func tracebackinit() {
 	// Go variable initialization happens late during runtime startup.
 	// Instead of initializing the variables above in the declarations,
 	// schedinit calls this function so that the variables are
 	// initialized and available earlier in the startup sequence.
 	goexitPC = funcPC(goexit)
 	jmpdeferPC = funcPC(jmpdefer)
 	mcallPC = funcPC(mcall)
 	morestackPC = funcPC(morestack)
 	mstartPC = funcPC(mstart)
 	rt0_goPC = funcPC(rt0_go)
 	sigpanicPC = funcPC(sigpanic)
 	runfinqPC = funcPC(runfinq)
 	backgroundgcPC = funcPC(backgroundgc)
 	bgsweepPC = funcPC(bgsweep)
 	forcegchelperPC = funcPC(forcegchelper)
 	timerprocPC = funcPC(timerproc)
 	gcBgMarkWorkerPC = funcPC(gcBgMarkWorker)
 	systemstack_switchPC = funcPC(systemstack_switch)
 }

 // Traceback over the deferred function calls.
 // Report them like calls that have been invoked but not started executing yet.
 func tracebackdefers(gp *g, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer) {
 	var frame stkframe
 	for d := gp._defer; d != nil; d = d.link {
 		fn := d.fn
 		if fn == nil {
 			// Defer of nil function. Args don't matter.
 			frame.pc = 0
 			frame.fn = nil
 			frame.argp = 0
 			frame.arglen = 0
 			frame.argmap = nil
 		} else {
 			frame.pc = uintptr(fn.fn)
 			f := findfunc(frame.pc)
 			if f == nil {
 				print("runtime: unknown pc in defer ", hex(frame.pc), "\n")
 				throw("unknown pc")
 			}
 			frame.fn = f
 			frame.argp = uintptr(deferArgs(d))
 			setArgInfo(&frame, f, true)
 		}
 		frame.continpc = frame.pc
 		if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
 			return
 		}
 	}
 }

 // Generic traceback.  Handles runtime stack prints (pcbuf == nil),
 // the runtime.Callers function (pcbuf != nil), as well as the garbage
 // collector (callback != nil).  A little clunky to merge these, but avoids
 // duplicating the code and all its subtlety.
 func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max int, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer, flags uint) int {
 	if goexitPC == 0 {
 		throw("gentraceback before goexitPC initialization")
 	}
 	g := getg()
 	if g == gp && g == g.m.curg {
 		// The starting sp has been passed in as a uintptr, and the caller may
 		// have other uintptr-typed stack references as well.
 		// If during one of the calls that got us here or during one of the
 		// callbacks below the stack must be grown, all these uintptr references
 		// to the stack will not be updated, and gentraceback will continue
 		// to inspect the old stack memory, which may no longer be valid.
 		// Even if all the variables were updated correctly, it is not clear that
 		// we want to expose a traceback that begins on one stack and ends
 		// on another stack. That could confuse callers quite a bit.
 		// Instead, we require that gentraceback and any other function that
 		// accepts an sp for the current goroutine (typically obtained by
 		// calling getcallersp) must not run on that goroutine's stack but
 		// instead on the g0 stack.
 		throw("gentraceback cannot trace user goroutine on its own stack")
 	}
 	gotraceback := gotraceback(nil)
 	if pc0 == ^uintptr(0) && sp0 == ^uintptr(0) { // Signal to fetch saved values from gp.
 		if gp.syscallsp != 0 {
 			pc0 = gp.syscallpc
 			sp0 = gp.syscallsp
 			if usesLR {
 				lr0 = 0
 			}
 		} else {
 			pc0 = gp.sched.pc
 			sp0 = gp.sched.sp
 			if usesLR {
 				lr0 = gp.sched.lr
 			}
 		}
 	}

 	nprint := 0
 	var frame stkframe
 	frame.pc = pc0
 	frame.sp = sp0
 	if usesLR {
 		frame.lr = lr0
 	}
 	waspanic := false
 	printing := pcbuf == nil && callback == nil
 	_defer := gp._defer

 	for _defer != nil && uintptr(_defer.sp) == _NoArgs {
 		_defer = _defer.link
 	}

 	// If the PC is zero, it's likely a nil function call.
 	// Start in the caller's frame.
 	if frame.pc == 0 {
 		if usesLR {
 			frame.pc = *(*uintptr)(unsafe.Pointer(frame.sp))
 			frame.lr = 0
 		} else {
 			frame.pc = uintptr(*(*uintreg)(unsafe.Pointer(frame.sp)))
 			frame.sp += regSize
 		}
 	}

 	f := findfunc(frame.pc)
 	if f == nil {
 		if callback != nil {
 			print("runtime: unknown pc ", hex(frame.pc), "\n")
 			throw("unknown pc")
 		}
 		return 0
 	}
 	frame.fn = f

 	n := 0
 	for n < max {
 		// Typically:
 		//	pc is the PC of the running function.
 		//	sp is the stack pointer at that program counter.
 		//	fp is the frame pointer (caller's stack pointer) at that program counter, or nil if unknown.
 		//	stk is the stack containing sp.
 		//	The caller's program counter is lr, unless lr is zero, in which case it is *(uintptr*)sp.
 		f = frame.fn

 		// Found an actual function.
 		// Derive frame pointer and link register.
 		if frame.fp == 0 {
 			frame.fp = frame.sp + uintptr(funcspdelta(f, frame.pc))
 			if !usesLR {
 				// On x86, call instruction pushes return PC before entering new function.
 				frame.fp += regSize
 			}
 		}
 		var flr *_func
 		if topofstack(f) {
 			frame.lr = 0
 			flr = nil
 		} else if usesLR && f.entry == jmpdeferPC {
 			// jmpdefer modifies SP/LR/PC non-atomically.
 			// If a profiling interrupt arrives during jmpdefer,
 			// the stack unwind may see a mismatched register set
 			// and get confused. Stop if we see PC within jmpdefer
 			// to avoid that confusion.
 			// See golang.org/issue/8153.
 			if callback != nil {
 				throw("traceback_arm: found jmpdefer when tracing with callback")
 			}
 			frame.lr = 0
 		} else {
 			if usesLR {
 				if n == 0 && frame.sp < frame.fp || frame.lr == 0 {
 					frame.lr = *(*uintptr)(unsafe.Pointer(frame.sp))
 				}
 			} else {
 				if frame.lr == 0 {
 					frame.lr = uintptr(*(*uintreg)(unsafe.Pointer(frame.fp - regSize)))
 				}
 			}
 			flr = findfunc(frame.lr)
 			if flr == nil {
 				// This happens if you get a profiling interrupt at just the wrong time.
 				// In that context it is okay to stop early.
 				// But if callback is set, we're doing a garbage collection and must
 				// get everything, so crash loudly.
 				if callback != nil {
 					print("runtime: unexpected return pc for ", funcname(f), " called from ", hex(frame.lr), "\n")
 					throw("unknown caller pc")
 				}
 			}
 		}

 		frame.varp = frame.fp
 		if !usesLR {
 			// On x86, call instruction pushes return PC before entering new function.
 			frame.varp -= regSize
 		}

 		// If framepointer_enabled and there's a frame, then
 		// there's a saved bp here.
 		if framepointer_enabled && GOARCH == "amd64" && frame.varp > frame.sp {
 			frame.varp -= regSize
 		}

 		// Derive size of arguments.
 		// Most functions have a fixed-size argument block,
 		// so we can use metadata about the function f.
 		// Not all, though: there are some variadic functions
 		// in package runtime and reflect, and for those we use call-specific
 		// metadata recorded by f's caller.
 		if callback != nil || printing {
 			frame.argp = frame.fp
 			if usesLR {
 				frame.argp += ptrSize
 			}
 			setArgInfo(&frame, f, callback != nil)
 		}

 		// Determine frame's 'continuation PC', where it can continue.
 		// Normally this is the return address on the stack, but if sigpanic
 		// is immediately below this function on the stack, then the frame
 		// stopped executing due to a trap, and frame.pc is probably not
 		// a safe point for looking up liveness information. In this panicking case,
 		// the function either doesn't return at all (if it has no defers or if the
 		// defers do not recover) or it returns from one of the calls to
 		// deferproc a second time (if the corresponding deferred func recovers).
 		// It suffices to assume that the most recent deferproc is the one that
 		// returns; everything live at earlier deferprocs is still live at that one.
 		frame.continpc = frame.pc
 		if waspanic {
 			if _defer != nil && _defer.sp == frame.sp {
 				frame.continpc = _defer.pc
 			} else {
 				frame.continpc = 0
 			}
 		}

 		// Unwind our local defer stack past this frame.
 		for _defer != nil && (_defer.sp == frame.sp || _defer.sp == _NoArgs) {
 			_defer = _defer.link
 		}

 		if skip > 0 {
 			skip--
 			goto skipped
 		}

 		if pcbuf != nil {
 			(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = frame.pc
 		}
 		if callback != nil {
 			if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
 				return n
 			}
 		}
 		if printing {
 			if (flags&_TraceRuntimeFrames) != 0 || showframe(f, gp) {
 				// Print during crash.
 				//	main(0x1, 0x2, 0x3)
 				//		/home/rsc/go/src/runtime/x.go:23 +0xf
 				//
 				tracepc := frame.pc // back up to CALL instruction for funcline.
 				if (n > 0 || flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
 					tracepc--
 				}
 				print(funcname(f), "(")
 				argp := (*[100]uintptr)(unsafe.Pointer(frame.argp))
 				for i := uintptr(0); i < frame.arglen/ptrSize; i++ {
 					if i >= 10 {
 						print(", ...")
 						break
 					}
 					if i != 0 {
 						print(", ")
 					}
 					print(hex(argp[i]))
 				}
 				print(")\n")
 				file, line := funcline(f, tracepc)
 				print("\t", file, ":", line)
 				if frame.pc > f.entry {
 					print(" +", hex(frame.pc-f.entry))
 				}
 				if g.m.throwing > 0 && gp == g.m.curg || gotraceback >= 2 {
 					print(" fp=", hex(frame.fp), " sp=", hex(frame.sp))
 				}
 				print("\n")
 				nprint++
 			}
 		}
 		n++

 	skipped:
 		waspanic = f.entry == sigpanicPC

 		// Do not unwind past the bottom of the stack.
 		if flr == nil {
 			break
 		}

 		// Unwind to next frame.
 		frame.fn = flr
 		frame.pc = frame.lr
 		frame.lr = 0
 		frame.sp = frame.fp
 		frame.fp = 0
 		frame.argmap = nil

 		// On link register architectures, sighandler saves the LR on stack
 		// before faking a call to sigpanic.
 		if usesLR && waspanic {
 			x := *(*uintptr)(unsafe.Pointer(frame.sp))
 			frame.sp += ptrSize
 			if GOARCH == "arm64" {
 				// arm64 needs 16-byte aligned SP, always
 				frame.sp += ptrSize
 			}
 			f = findfunc(frame.pc)
 			frame.fn = f
 			if f == nil {
 				frame.pc = x
 			} else if funcspdelta(f, frame.pc) == 0 {
 				frame.lr = x
 			}
 		}
 	}

 	if printing {
 		n = nprint
 	}

 	// If callback != nil, we're being called to gather stack information during
 	// garbage collection or stack growth. In that context, require that we used
 	// up the entire defer stack. If not, then there is a bug somewhere and the
 	// garbage collection or stack growth may not have seen the correct picture
 	// of the stack. Crash now instead of silently executing the garbage collection
 	// or stack copy incorrectly and setting up for a mysterious crash later.
 	//
 	// Note that panic != nil is okay here: there can be leftover panics,
 	// because the defers on the panic stack do not nest in frame order as
 	// they do on the defer stack. If you have:
 	//
 	//	frame 1 defers d1
 	//	frame 2 defers d2
 	//	frame 3 defers d3
 	//	frame 4 panics
 	//	frame 4's panic starts running defers
 	//	frame 5, running d3, defers d4
 	//	frame 5 panics
 	//	frame 5's panic starts running defers
 	//	frame 6, running d4, garbage collects
 	//	frame 6, running d2, garbage collects
 	//
 	// During the execution of d4, the panic stack is d4 -> d3, which
 	// is nested properly, and we'll treat frame 3 as resumable, because we
 	// can find d3. (And in fact frame 3 is resumable. If d4 recovers
 	// and frame 5 continues running, d3, d3 can recover and we'll
 	// resume execution in (returning from) frame 3.)
 	//
 	// During the execution of d2, however, the panic stack is d2 -> d3,
 	// which is inverted. The scan will match d2 to frame 2 but having
 	// d2 on the stack until then means it will not match d3 to frame 3.
 	// This is okay: if we're running d2, then all the defers after d2 have
 	// completed and their corresponding frames are dead. Not finding d3
 	// for frame 3 means we'll set frame 3's continpc == 0, which is correct
 	// (frame 3 is dead). At the end of the walk the panic stack can thus
 	// contain defers (d3 in this case) for dead frames. The inversion here
 	// always indicates a dead frame, and the effect of the inversion on the
 	// scan is to hide those dead frames, so the scan is still okay:
 	// what's left on the panic stack are exactly (and only) the dead frames.
 	//
 	// We require callback != nil here because only when callback != nil
 	// do we know that gentraceback is being called in a "must be correct"
 	// context as opposed to a "best effort" context. The tracebacks with
 	// callbacks only happen when everything is stopped nicely.
 	// At other times, such as when gathering a stack for a profiling signal
 	// or when printing a traceback during a crash, everything may not be
 	// stopped nicely, and the stack walk may not be able to complete.
 	// It's okay in those situations not to use up the entire defer stack:
 	// incomplete information then is still better than nothing.
 	if callback != nil && n < max && _defer != nil {
 		if _defer != nil {
 			print("runtime: g", gp.goid, ": leftover defer sp=", hex(_defer.sp), " pc=", hex(_defer.pc), "\n")
 		}
 		for _defer = gp._defer; _defer != nil; _defer = _defer.link {
 			print("\tdefer ", _defer, " sp=", hex(_defer.sp), " pc=", hex(_defer.pc), "\n")
 		}
 		throw("traceback has leftover defers")
 	}

 	return n
 }

 func setArgInfo(frame *stkframe, f *_func, needArgMap bool) {
 	frame.arglen = uintptr(f.args)
 	if needArgMap && f.args == _ArgsSizeUnknown {
 		// Extract argument bitmaps for reflect stubs from the calls they made to reflect.
 		switch funcname(f) {
 		case "reflect.makeFuncStub", "reflect.methodValueCall":
 			arg0 := frame.sp
 			if usesLR {
 				arg0 += ptrSize
 			}
 			fn := *(**[2]uintptr)(unsafe.Pointer(arg0))
 			if fn[0] != f.entry {
 				print("runtime: confused by ", funcname(f), "\n")
 				throw("reflect mismatch")
 			}
 			bv := (*bitvector)(unsafe.Pointer(fn[1]))
 			frame.arglen = uintptr(bv.n / 2 * ptrSize)
 			frame.argmap = bv
 		}
 	}
 }

 func printcreatedby(gp *g) {
 	// Show what created goroutine, except main goroutine (goid 1).
 	pc := gp.gopc
 	f := findfunc(pc)
 	if f != nil && showframe(f, gp) && gp.goid != 1 {
 		print("created by ", funcname(f), "\n")
 		tracepc := pc // back up to CALL instruction for funcline.
 		if pc > f.entry {
 			tracepc -= _PCQuantum
 		}
 		file, line := funcline(f, tracepc)
 		print("\t", file, ":", line)
 		if pc > f.entry {
 			print(" +", hex(pc-f.entry))
 		}
 		print("\n")
 	}
 }

 func traceback(pc, sp, lr uintptr, gp *g) {
 	traceback1(pc, sp, lr, gp, 0)
 }

 // tracebacktrap is like traceback but expects that the PC and SP were obtained
 // from a trap, not from gp->sched or gp->syscallpc/gp->syscallsp or getcallerpc/getcallersp.
 // Because they are from a trap instead of from a saved pair,
 // the initial PC must not be rewound to the previous instruction.
 // (All the saved pairs record a PC that is a return address, so we
 // rewind it into the CALL instruction.)
 func tracebacktrap(pc, sp, lr uintptr, gp *g) {
 	traceback1(pc, sp, lr, gp, _TraceTrap)
 }

 func traceback1(pc, sp, lr uintptr, gp *g, flags uint) {
 	var n int
 	if readgstatus(gp)&^_Gscan == _Gsyscall {
 		// Override registers if blocked in system call.
 		pc = gp.syscallpc
 		sp = gp.syscallsp
 		flags &^= _TraceTrap
 	}
 	// Print traceback. By default, omits runtime frames.
 	// If that means we print nothing at all, repeat forcing all frames printed.
 	n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags)
 	if n == 0 && (flags&_TraceRuntimeFrames) == 0 {
 		n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags|_TraceRuntimeFrames)
 	}
 	if n == _TracebackMaxFrames {
 		print("...additional frames elided...\n")
 	}
 	printcreatedby(gp)
 }

 func callers(skip int, pcbuf []uintptr) int {
 	sp := getcallersp(unsafe.Pointer(&skip))
 	pc := uintptr(getcallerpc(unsafe.Pointer(&skip)))
 	var n int
 	systemstack(func() {
 		n = gentraceback(pc, sp, 0, getg(), skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
 	})
 	return n
 }

 func gcallers(gp *g, skip int, pcbuf []uintptr) int {
 	return gentraceback(^uintptr(0), ^uintptr(0), 0, gp, skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
 }

 func showframe(f *_func, gp *g) bool {
 	g := getg()
 	if g.m.throwing > 0 && gp != nil && (gp == g.m.curg || gp == g.m.caughtsig.ptr()) {
 		return true
 	}
 	traceback := gotraceback(nil)
 	name := funcname(f)

 	// Special case: always show runtime.panic frame, so that we can
 	// see where a panic started in the middle of a stack trace.
 	// See golang.org/issue/5832.
 	if name == "runtime.panic" {
 		return true
 	}

 	return traceback > 1 || f != nil && contains(name, ".") && (!hasprefix(name, "runtime.") || isExportedRuntime(name))
 }

 // isExportedRuntime reports whether name is an exported runtime function.
 // It is only for runtime functions, so ASCII A-Z is fine.
 func isExportedRuntime(name string) bool {
 	const n = len("runtime.")
 	return len(name) > n && name[:n] == "runtime." && 'A' <= name[n] && name[n] <= 'Z'
 }

 var gStatusStrings = [...]string{
 	_Gidle:      "idle",
 	_Grunnable:  "runnable",
 	_Grunning:   "running",
 	_Gsyscall:   "syscall",
 	_Gwaiting:   "waiting",
 	_Gdead:      "dead",
 	_Genqueue:   "enqueue",
 	_Gcopystack: "copystack",
 }

 var gScanStatusStrings = [...]string{
 	0:          "scan",
 	_Grunnable: "scanrunnable",
 	_Grunning:  "scanrunning",
 	_Gsyscall:  "scansyscall",
 	_Gwaiting:  "scanwaiting",
 	_Gdead:     "scandead",
 	_Genqueue:  "scanenqueue",
 }

 func goroutineheader(gp *g) {
 	gpstatus := readgstatus(gp)

 	// Basic string status
 	var status string
 	if 0 <= gpstatus && gpstatus < uint32(len(gStatusStrings)) {
 		status = gStatusStrings[gpstatus]
 	} else if gpstatus&_Gscan != 0 && 0 <= gpstatus&^_Gscan && gpstatus&^_Gscan < uint32(len(gStatusStrings)) {
 		status = gStatusStrings[gpstatus&^_Gscan]
 	} else {
 		status = "???"
 	}

 	// Override.
 	if (gpstatus == _Gwaiting || gpstatus == _Gscanwaiting) && gp.waitreason != "" {
 		status = gp.waitreason
 	}

 	// approx time the G is blocked, in minutes
 	var waitfor int64
 	gpstatus &^= _Gscan // drop the scan bit
 	if (gpstatus == _Gwaiting || gpstatus == _Gsyscall) && gp.waitsince != 0 {
 		waitfor = (nanotime() - gp.waitsince) / 60e9
 	}
 	print("goroutine ", gp.goid, " [", status)
 	if waitfor >= 1 {
 		print(", ", waitfor, " minutes")
 	}
 	if gp.lockedm != nil {
 		print(", locked to thread")
 	}
 	print("]:\n")
 }

 func tracebackothers(me *g) {
 	level := gotraceback(nil)

 	// Show the current goroutine first, if we haven't already.
 	g := getg()
 	gp := g.m.curg
 	if gp != nil && gp != me {
 		print("\n")
 		goroutineheader(gp)
 		traceback(^uintptr(0), ^uintptr(0), 0, gp)
 	}

 	lock(&allglock)
 	for _, gp := range allgs {
 		if gp == me || gp == g.m.curg || readgstatus(gp) == _Gdead || isSystemGoroutine(gp) && level < 2 {
 			continue
 		}
 		print("\n")
 		goroutineheader(gp)
 		// Note: gp.m == g.m occurs when tracebackothers is
 		// called from a signal handler initiated during a
 		// systemstack call.  The original G is still in the
 		// running state, and we want to print its stack.
 		if gp.m != g.m && readgstatus(gp)&^_Gscan == _Grunning {
 			print("\tgoroutine running on other thread; stack unavailable\n")
 			printcreatedby(gp)
 		} else {
 			traceback(^uintptr(0), ^uintptr(0), 0, gp)
 		}
 	}
 	unlock(&allglock)
 }

 // Does f mark the top of a goroutine stack?
 func topofstack(f *_func) bool {
 	pc := f.entry
 	return pc == goexitPC ||
 		pc == mstartPC ||
 		pc == mcallPC ||
 		pc == morestackPC ||
 		pc == rt0_goPC ||
 		externalthreadhandlerp != 0 && pc == externalthreadhandlerp
 }

 // isSystemGoroutine reports whether the goroutine g must be omitted in
 // stack dumps and deadlock detector.
 func isSystemGoroutine(gp *g) bool {
 	pc := gp.startpc
 	return pc == runfinqPC && !fingRunning ||
 		pc == backgroundgcPC ||
 		pc == bgsweepPC ||
 		pc == forcegchelperPC ||
 		pc == timerprocPC ||
 		pc == gcBgMarkWorkerPC
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package runtime

	import "unsafe"

	// The code in this file implements stack trace walking for all architectures.
	// The most important fact about a given architecture is whether it uses a link register.
	// On systems with link registers, the prologue for a non-leaf function stores the
	// incoming value of LR at the bottom of the newly allocated stack frame.
	// On systems without link registers, the architecture pushes a return PC during
	// the call instruction, so the return PC ends up above the stack frame.
	// In this file, the return PC is always called LR, no matter how it was found.
	//
	// To date, the opposite of a link register architecture is an x86 architecture.
	// This code may need to change if some other kind of non-link-register
	// architecture comes along.
	//
	// The other important fact is the size of a pointer: on 32-bit systems the LR
	// takes up only 4 bytes on the stack, while on 64-bit systems it takes up 8 bytes.
	// Typically this is ptrSize.
	//
	// As an exception, amd64p32 has ptrSize == 4 but the CALL instruction still
	// stores an 8-byte return PC onto the stack. To accommodate this, we use regSize
	// as the size of the architecture-pushed return PC.
	//
	// usesLR is defined below. ptrSize and regSize are defined in stubs.go.

	const usesLR = GOARCH != "amd64" && GOARCH != "amd64p32" && GOARCH != "386"

	var (
	// initialized in tracebackinit
	goexitPC uintptr
	jmpdeferPC uintptr
	mcallPC uintptr
	morestackPC uintptr
	mstartPC uintptr
	rt0_goPC uintptr
	sigpanicPC uintptr
	runfinqPC uintptr
	backgroundgcPC uintptr
	bgsweepPC uintptr
	forcegchelperPC uintptr
	timerprocPC uintptr
	gcBgMarkWorkerPC uintptr
	systemstack_switchPC uintptr

	externalthreadhandlerp uintptr // initialized elsewhere
	)

	func tracebackinit() {
	// Go variable initialization happens late during runtime startup.
	// Instead of initializing the variables above in the declarations,
	// schedinit calls this function so that the variables are
	// initialized and available earlier in the startup sequence.
	goexitPC = funcPC(goexit)
	jmpdeferPC = funcPC(jmpdefer)
	mcallPC = funcPC(mcall)
	morestackPC = funcPC(morestack)
	mstartPC = funcPC(mstart)
	rt0_goPC = funcPC(rt0_go)
	sigpanicPC = funcPC(sigpanic)
	runfinqPC = funcPC(runfinq)
	backgroundgcPC = funcPC(backgroundgc)
	bgsweepPC = funcPC(bgsweep)
	forcegchelperPC = funcPC(forcegchelper)
	timerprocPC = funcPC(timerproc)
	gcBgMarkWorkerPC = funcPC(gcBgMarkWorker)
	systemstack_switchPC = funcPC(systemstack_switch)
	}

	// Traceback over the deferred function calls.
	// Report them like calls that have been invoked but not started executing yet.
	func tracebackdefers(gp g, callback func(stkframe, unsafe.Pointer) bool, v unsafe.Pointer) {
	var frame stkframe
	for d := gp._defer; d != nil; d = d.link {
	fn := d.fn
	if fn == nil {
	// Defer of nil function. Args don't matter.
	frame.pc = 0
	frame.fn = nil
	frame.argp = 0
	frame.arglen = 0
	frame.argmap = nil
	} else {
	frame.pc = uintptr(fn.fn)
	f := findfunc(frame.pc)
	if f == nil {
	print("runtime: unknown pc in defer ", hex(frame.pc), "\n")
	throw("unknown pc")
	}
	frame.fn = f
	frame.argp = uintptr(deferArgs(d))
	setArgInfo(&frame, f, true)
	}
	frame.continpc = frame.pc
	if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
	return
	}
	}
	}

	// Generic traceback. Handles runtime stack prints (pcbuf == nil),
	// the runtime.Callers function (pcbuf != nil), as well as the garbage
	// collector (callback != nil). A little clunky to merge these, but avoids
	// duplicating the code and all its subtlety.
	func gentraceback(pc0, sp0, lr0 uintptr, gp g, skip int, pcbuf uintptr, max int, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer, flags uint) int {
	if goexitPC == 0 {
	throw("gentraceback before goexitPC initialization")
	}
	g := getg()
	if g == gp && g == g.m.curg {
	// The starting sp has been passed in as a uintptr, and the caller may
	// have other uintptr-typed stack references as well.
	// If during one of the calls that got us here or during one of the
	// callbacks below the stack must be grown, all these uintptr references
	// to the stack will not be updated, and gentraceback will continue
	// to inspect the old stack memory, which may no longer be valid.
	// Even if all the variables were updated correctly, it is not clear that
	// we want to expose a traceback that begins on one stack and ends
	// on another stack. That could confuse callers quite a bit.
	// Instead, we require that gentraceback and any other function that
	// accepts an sp for the current goroutine (typically obtained by
	// calling getcallersp) must not run on that goroutine's stack but
	// instead on the g0 stack.
	throw("gentraceback cannot trace user goroutine on its own stack")
	}
	gotraceback := gotraceback(nil)
	if pc0 == ^uintptr(0) && sp0 == ^uintptr(0) { // Signal to fetch saved values from gp.
	if gp.syscallsp != 0 {
	pc0 = gp.syscallpc
	sp0 = gp.syscallsp
	if usesLR {
	lr0 = 0
	}
	} else {
	pc0 = gp.sched.pc
	sp0 = gp.sched.sp
	if usesLR {
	lr0 = gp.sched.lr
	}
	}
	}

	nprint := 0
	var frame stkframe
	frame.pc = pc0
	frame.sp = sp0
	if usesLR {
	frame.lr = lr0
	}
	waspanic := false
	printing := pcbuf == nil && callback == nil
	_defer := gp._defer

	for _defer != nil && uintptr(_defer.sp) == _NoArgs {
	_defer = _defer.link
	}

	// If the PC is zero, it's likely a nil function call.
	// Start in the caller's frame.
	if frame.pc == 0 {
	if usesLR {
	frame.pc = (uintptr)(unsafe.Pointer(frame.sp))
	frame.lr = 0
	} else {
	frame.pc = uintptr((uintreg)(unsafe.Pointer(frame.sp)))
	frame.sp += regSize
	}
	}

	f := findfunc(frame.pc)
	if f == nil {
	if callback != nil {
	print("runtime: unknown pc ", hex(frame.pc), "\n")
	throw("unknown pc")
	}
	return 0
	}
	frame.fn = f

	n := 0
	for n < max {
	// Typically:
	// pc is the PC of the running function.
	// sp is the stack pointer at that program counter.
	// fp is the frame pointer (caller's stack pointer) at that program counter, or nil if unknown.
	// stk is the stack containing sp.
	// The caller's program counter is lr, unless lr is zero, in which case it is (uintptr)sp.
	f = frame.fn

	// Found an actual function.
	// Derive frame pointer and link register.
	if frame.fp == 0 {
	frame.fp = frame.sp + uintptr(funcspdelta(f, frame.pc))
	if !usesLR {
	// On x86, call instruction pushes return PC before entering new function.
	frame.fp += regSize
	}
	}
	var flr *_func
	if topofstack(f) {
	frame.lr = 0
	flr = nil
	} else if usesLR && f.entry == jmpdeferPC {
	// jmpdefer modifies SP/LR/PC non-atomically.
	// If a profiling interrupt arrives during jmpdefer,
	// the stack unwind may see a mismatched register set
	// and get confused. Stop if we see PC within jmpdefer
	// to avoid that confusion.
	// See golang.org/issue/8153.
	if callback != nil {
	throw("traceback_arm: found jmpdefer when tracing with callback")
	}
	frame.lr = 0
	} else {
	if usesLR {
	if n == 0 && frame.sp < frame.fp \|\| frame.lr == 0 {
	frame.lr = (uintptr)(unsafe.Pointer(frame.sp))
	}
	} else {
	if frame.lr == 0 {
	frame.lr = uintptr((uintreg)(unsafe.Pointer(frame.fp - regSize)))
	}
	}
	flr = findfunc(frame.lr)
	if flr == nil {
	// This happens if you get a profiling interrupt at just the wrong time.
	// In that context it is okay to stop early.
	// But if callback is set, we're doing a garbage collection and must
	// get everything, so crash loudly.
	if callback != nil {
	print("runtime: unexpected return pc for ", funcname(f), " called from ", hex(frame.lr), "\n")
	throw("unknown caller pc")
	}
	}
	}

	frame.varp = frame.fp
	if !usesLR {
	// On x86, call instruction pushes return PC before entering new function.
	frame.varp -= regSize
	}

	// If framepointer_enabled and there's a frame, then
	// there's a saved bp here.
	if framepointer_enabled && GOARCH == "amd64" && frame.varp > frame.sp {
	frame.varp -= regSize
	}

	// Derive size of arguments.
	// Most functions have a fixed-size argument block,
	// so we can use metadata about the function f.
	// Not all, though: there are some variadic functions
	// in package runtime and reflect, and for those we use call-specific
	// metadata recorded by f's caller.
	if callback != nil \|\| printing {
	frame.argp = frame.fp
	if usesLR {
	frame.argp += ptrSize
	}
	setArgInfo(&frame, f, callback != nil)
	}

	// Determine frame's 'continuation PC', where it can continue.
	// Normally this is the return address on the stack, but if sigpanic
	// is immediately below this function on the stack, then the frame
	// stopped executing due to a trap, and frame.pc is probably not
	// a safe point for looking up liveness information. In this panicking case,
	// the function either doesn't return at all (if it has no defers or if the
	// defers do not recover) or it returns from one of the calls to
	// deferproc a second time (if the corresponding deferred func recovers).
	// It suffices to assume that the most recent deferproc is the one that
	// returns; everything live at earlier deferprocs is still live at that one.
	frame.continpc = frame.pc
	if waspanic {
	if _defer != nil && _defer.sp == frame.sp {
	frame.continpc = _defer.pc
	} else {
	frame.continpc = 0
	}
	}

	// Unwind our local defer stack past this frame.
	for _defer != nil && (_defer.sp == frame.sp \|\| _defer.sp == _NoArgs) {
	_defer = _defer.link
	}

	if skip > 0 {
	skip--
	goto skipped
	}

	if pcbuf != nil {
	(*[1 << 20]uintptr)(unsafe.Pointer(pcbuf))[n] = frame.pc
	}
	if callback != nil {
	if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
	return n
	}
	}
	if printing {
	if (flags&_TraceRuntimeFrames) != 0 \|\| showframe(f, gp) {
	// Print during crash.
	// main(0x1, 0x2, 0x3)
	// /home/rsc/go/src/runtime/x.go:23 +0xf
	//
	tracepc := frame.pc // back up to CALL instruction for funcline.
	if (n > 0 \|\| flags&_TraceTrap == 0) && frame.pc > f.entry && !waspanic {
	tracepc--
	}
	print(funcname(f), "(")
	argp := (*[100]uintptr)(unsafe.Pointer(frame.argp))
	for i := uintptr(0); i < frame.arglen/ptrSize; i++ {
	if i >= 10 {
	print(", ...")
	break
	}
	if i != 0 {
	print(", ")
	}
	print(hex(argp[i]))
	}
	print(")\n")
	file, line := funcline(f, tracepc)
	print("\t", file, ":", line)
	if frame.pc > f.entry {
	print(" +", hex(frame.pc-f.entry))
	}
	if g.m.throwing > 0 && gp == g.m.curg \|\| gotraceback >= 2 {
	print(" fp=", hex(frame.fp), " sp=", hex(frame.sp))
	}
	print("\n")
	nprint++
	}
	}
	n++

	skipped:
	waspanic = f.entry == sigpanicPC

	// Do not unwind past the bottom of the stack.
	if flr == nil {
	break
	}

	// Unwind to next frame.
	frame.fn = flr
	frame.pc = frame.lr
	frame.lr = 0
	frame.sp = frame.fp
	frame.fp = 0
	frame.argmap = nil

	// On link register architectures, sighandler saves the LR on stack
	// before faking a call to sigpanic.
	if usesLR && waspanic {
	x := (uintptr)(unsafe.Pointer(frame.sp))
	frame.sp += ptrSize
	if GOARCH == "arm64" {
	// arm64 needs 16-byte aligned SP, always
	frame.sp += ptrSize
	}
	f = findfunc(frame.pc)
	frame.fn = f
	if f == nil {
	frame.pc = x
	} else if funcspdelta(f, frame.pc) == 0 {
	frame.lr = x
	}
	}
	}

	if printing {
	n = nprint
	}

	// If callback != nil, we're being called to gather stack information during
	// garbage collection or stack growth. In that context, require that we used
	// up the entire defer stack. If not, then there is a bug somewhere and the
	// garbage collection or stack growth may not have seen the correct picture
	// of the stack. Crash now instead of silently executing the garbage collection
	// or stack copy incorrectly and setting up for a mysterious crash later.
	//
	// Note that panic != nil is okay here: there can be leftover panics,
	// because the defers on the panic stack do not nest in frame order as
	// they do on the defer stack. If you have:
	//
	// frame 1 defers d1
	// frame 2 defers d2
	// frame 3 defers d3
	// frame 4 panics
	// frame 4's panic starts running defers
	// frame 5, running d3, defers d4
	// frame 5 panics
	// frame 5's panic starts running defers
	// frame 6, running d4, garbage collects
	// frame 6, running d2, garbage collects
	//
	// During the execution of d4, the panic stack is d4 -> d3, which
	// is nested properly, and we'll treat frame 3 as resumable, because we
	// can find d3. (And in fact frame 3 is resumable. If d4 recovers
	// and frame 5 continues running, d3, d3 can recover and we'll
	// resume execution in (returning from) frame 3.)
	//
	// During the execution of d2, however, the panic stack is d2 -> d3,
	// which is inverted. The scan will match d2 to frame 2 but having
	// d2 on the stack until then means it will not match d3 to frame 3.
	// This is okay: if we're running d2, then all the defers after d2 have
	// completed and their corresponding frames are dead. Not finding d3
	// for frame 3 means we'll set frame 3's continpc == 0, which is correct
	// (frame 3 is dead). At the end of the walk the panic stack can thus
	// contain defers (d3 in this case) for dead frames. The inversion here
	// always indicates a dead frame, and the effect of the inversion on the
	// scan is to hide those dead frames, so the scan is still okay:
	// what's left on the panic stack are exactly (and only) the dead frames.
	//
	// We require callback != nil here because only when callback != nil
	// do we know that gentraceback is being called in a "must be correct"
	// context as opposed to a "best effort" context. The tracebacks with
	// callbacks only happen when everything is stopped nicely.
	// At other times, such as when gathering a stack for a profiling signal
	// or when printing a traceback during a crash, everything may not be
	// stopped nicely, and the stack walk may not be able to complete.
	// It's okay in those situations not to use up the entire defer stack:
	// incomplete information then is still better than nothing.
	if callback != nil && n < max && _defer != nil {
	if _defer != nil {
	print("runtime: g", gp.goid, ": leftover defer sp=", hex(_defer.sp), " pc=", hex(_defer.pc), "\n")
	}
	for _defer = gp._defer; _defer != nil; _defer = _defer.link {
	print("\tdefer ", _defer, " sp=", hex(_defer.sp), " pc=", hex(_defer.pc), "\n")
	}
	throw("traceback has leftover defers")
	}

	return n
	}

	func setArgInfo(frame stkframe, f _func, needArgMap bool) {
	frame.arglen = uintptr(f.args)
	if needArgMap && f.args == _ArgsSizeUnknown {
	// Extract argument bitmaps for reflect stubs from the calls they made to reflect.
	switch funcname(f) {
	case "reflect.makeFuncStub", "reflect.methodValueCall":
	arg0 := frame.sp
	if usesLR {
	arg0 += ptrSize
	}
	fn := (*[2]uintptr)(unsafe.Pointer(arg0))
	if fn[0] != f.entry {
	print("runtime: confused by ", funcname(f), "\n")
	throw("reflect mismatch")
	}
	bv := (*bitvector)(unsafe.Pointer(fn[1]))
	frame.arglen = uintptr(bv.n / 2 * ptrSize)
	frame.argmap = bv
	}
	}
	}

	func printcreatedby(gp *g) {
	// Show what created goroutine, except main goroutine (goid 1).
	pc := gp.gopc
	f := findfunc(pc)
	if f != nil && showframe(f, gp) && gp.goid != 1 {
	print("created by ", funcname(f), "\n")
	tracepc := pc // back up to CALL instruction for funcline.
	if pc > f.entry {
	tracepc -= _PCQuantum
	}
	file, line := funcline(f, tracepc)
	print("\t", file, ":", line)
	if pc > f.entry {
	print(" +", hex(pc-f.entry))
	}
	print("\n")
	}
	}

	func traceback(pc, sp, lr uintptr, gp *g) {
	traceback1(pc, sp, lr, gp, 0)
	}

	// tracebacktrap is like traceback but expects that the PC and SP were obtained
	// from a trap, not from gp->sched or gp->syscallpc/gp->syscallsp or getcallerpc/getcallersp.
	// Because they are from a trap instead of from a saved pair,
	// the initial PC must not be rewound to the previous instruction.
	// (All the saved pairs record a PC that is a return address, so we
	// rewind it into the CALL instruction.)
	func tracebacktrap(pc, sp, lr uintptr, gp *g) {
	traceback1(pc, sp, lr, gp, _TraceTrap)
	}

	func traceback1(pc, sp, lr uintptr, gp *g, flags uint) {
	var n int
	if readgstatus(gp)&^_Gscan == _Gsyscall {
	// Override registers if blocked in system call.
	pc = gp.syscallpc
	sp = gp.syscallsp
	flags &^= _TraceTrap
	}
	// Print traceback. By default, omits runtime frames.
	// If that means we print nothing at all, repeat forcing all frames printed.
	n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags)
	if n == 0 && (flags&_TraceRuntimeFrames) == 0 {
	n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags\|_TraceRuntimeFrames)
	}
	if n == _TracebackMaxFrames {
	print("...additional frames elided...\n")
	}
	printcreatedby(gp)
	}

	func callers(skip int, pcbuf []uintptr) int {
	sp := getcallersp(unsafe.Pointer(&skip))
	pc := uintptr(getcallerpc(unsafe.Pointer(&skip)))
	var n int
	systemstack(func() {
	n = gentraceback(pc, sp, 0, getg(), skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
	})
	return n
	}

	func gcallers(gp *g, skip int, pcbuf []uintptr) int {
	return gentraceback(^uintptr(0), ^uintptr(0), 0, gp, skip, &pcbuf[0], len(pcbuf), nil, nil, 0)
	}

	func showframe(f _func, gp g) bool {
	g := getg()
	if g.m.throwing > 0 && gp != nil && (gp == g.m.curg \|\| gp == g.m.caughtsig.ptr()) {
	return true
	}
	traceback := gotraceback(nil)
	name := funcname(f)

	// Special case: always show runtime.panic frame, so that we can
	// see where a panic started in the middle of a stack trace.
	// See golang.org/issue/5832.
	if name == "runtime.panic" {
	return true
	}

	return traceback > 1 \|\| f != nil && contains(name, ".") && (!hasprefix(name, "runtime.") \|\| isExportedRuntime(name))
	}

	// isExportedRuntime reports whether name is an exported runtime function.
	// It is only for runtime functions, so ASCII A-Z is fine.
	func isExportedRuntime(name string) bool {
	const n = len("runtime.")
	return len(name) > n && name[:n] == "runtime." && 'A' <= name[n] && name[n] <= 'Z'
	}

	var gStatusStrings = [...]string{
	_Gidle: "idle",
	_Grunnable: "runnable",
	_Grunning: "running",
	_Gsyscall: "syscall",
	_Gwaiting: "waiting",
	_Gdead: "dead",
	_Genqueue: "enqueue",
	_Gcopystack: "copystack",
	}

	var gScanStatusStrings = [...]string{
	0: "scan",
	_Grunnable: "scanrunnable",
	_Grunning: "scanrunning",
	_Gsyscall: "scansyscall",
	_Gwaiting: "scanwaiting",
	_Gdead: "scandead",
	_Genqueue: "scanenqueue",
	}

	func goroutineheader(gp *g) {
	gpstatus := readgstatus(gp)

	// Basic string status
	var status string
	if 0 <= gpstatus && gpstatus < uint32(len(gStatusStrings)) {
	status = gStatusStrings[gpstatus]
	} else if gpstatus&_Gscan != 0 && 0 <= gpstatus&^_Gscan && gpstatus&^_Gscan < uint32(len(gStatusStrings)) {
	status = gStatusStrings[gpstatus&^_Gscan]
	} else {
	status = "???"
	}

	// Override.
	if (gpstatus == _Gwaiting \|\| gpstatus == _Gscanwaiting) && gp.waitreason != "" {
	status = gp.waitreason
	}

	// approx time the G is blocked, in minutes
	var waitfor int64
	gpstatus &^= _Gscan // drop the scan bit
	if (gpstatus == _Gwaiting \|\| gpstatus == _Gsyscall) && gp.waitsince != 0 {
	waitfor = (nanotime() - gp.waitsince) / 60e9
	}
	print("goroutine ", gp.goid, " [", status)
	if waitfor >= 1 {
	print(", ", waitfor, " minutes")
	}
	if gp.lockedm != nil {
	print(", locked to thread")
	}
	print("]:\n")
	}

	func tracebackothers(me *g) {
	level := gotraceback(nil)

	// Show the current goroutine first, if we haven't already.
	g := getg()
	gp := g.m.curg
	if gp != nil && gp != me {
	print("\n")
	goroutineheader(gp)
	traceback(^uintptr(0), ^uintptr(0), 0, gp)
	}

	lock(&allglock)
	for _, gp := range allgs {
	if gp == me \|\| gp == g.m.curg \|\| readgstatus(gp) == _Gdead \|\| isSystemGoroutine(gp) && level < 2 {
	continue
	}
	print("\n")
	goroutineheader(gp)
	// Note: gp.m == g.m occurs when tracebackothers is
	// called from a signal handler initiated during a
	// systemstack call. The original G is still in the
	// running state, and we want to print its stack.
	if gp.m != g.m && readgstatus(gp)&^_Gscan == _Grunning {
	print("\tgoroutine running on other thread; stack unavailable\n")
	printcreatedby(gp)
	} else {
	traceback(^uintptr(0), ^uintptr(0), 0, gp)
	}
	}
	unlock(&allglock)
	}

	// Does f mark the top of a goroutine stack?
	func topofstack(f *_func) bool {
	pc := f.entry
	return pc == goexitPC \|\|
	pc == mstartPC \|\|
	pc == mcallPC \|\|
	pc == morestackPC \|\|
	pc == rt0_goPC \|\|
	externalthreadhandlerp != 0 && pc == externalthreadhandlerp
	}

	// isSystemGoroutine reports whether the goroutine g must be omitted in
	// stack dumps and deadlock detector.
	func isSystemGoroutine(gp *g) bool {
	pc := gp.startpc
	return pc == runfinqPC && !fingRunning \|\|
	pc == backgroundgcPC \|\|
	pc == bgsweepPC \|\|
	pc == forcegchelperPC \|\|
	pc == timerprocPC \|\|
	pc == gcBgMarkWorkerPC
	}