Imported Upstream version 1.4upstream/1.4

1 files changed, 659 insertions, 0 deletions

diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go
new file mode 100644
index 000000000..1c6ce6e64
--- /dev/null
+++ b/src/runtime/traceback.go
@@ -0,0 +1,659 @@
+// 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
+	deferprocPC uintptr
+	goexitPC    uintptr
+	jmpdeferPC  uintptr
+	mcallPC     uintptr
+	morestackPC uintptr
+	mstartPC    uintptr
+	newprocPC   uintptr
+	rt0_goPC    uintptr
+	sigpanicPC  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.
+	deferprocPC = funcPC(deferproc)
+	goexitPC = funcPC(goexit)
+	jmpdeferPC = funcPC(jmpdefer)
+	mcallPC = funcPC(mcall)
+	morestackPC = funcPC(morestack)
+	mstartPC = funcPC(mstart)
+	newprocPC = funcPC(newproc)
+	rt0_goPC = funcPC(rt0_go)
+	sigpanicPC = funcPC(sigpanic)
+}
+
+// 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")
+				gothrow("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 uintptr, sp0 uintptr, 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 {
+		gothrow("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.
+		gothrow("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
+	wasnewproc := false
+	printing := pcbuf == nil && callback == nil
+	_defer := gp._defer
+
+	for _defer != nil && uintptr(_defer.argp) == _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")
+			gothrow("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 {
+				gothrow("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 ", gofuncname(f), " called from ", hex(frame.lr), "\n")
+					gothrow("unknown caller pc")
+				}
+			}
+		}
+
+		frame.varp = frame.fp
+		if !usesLR {
+			// On x86, call instruction pushes return PC before entering new function.
+			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 function SP where deferproc would find its arguments.
+		var sparg uintptr
+		if usesLR {
+			// On link register architectures, that's the standard bottom-of-stack plus 1 word
+			// for the saved LR. If the previous frame was a direct call to newproc/deferproc,
+			// however, the SP is three words lower than normal.
+			// If the function has no frame at all - perhaps it just started, or perhaps
+			// it is a leaf with no local variables - then we cannot possibly find its
+			// SP in a defer, and we might confuse its SP for its caller's SP, so
+			// leave sparg=0 in that case.
+			if frame.fp != frame.sp {
+				sparg = frame.sp + regSize
+				if wasnewproc {
+					sparg += 3 * regSize
+				}
+			}
+		} else {
+			// On x86 that's the standard bottom-of-stack, so SP exactly.
+			// If the previous frame was a direct call to newproc/deferproc, however,
+			// the SP is two words lower than normal.
+			sparg = frame.sp
+			if wasnewproc {
+				sparg += 2 * ptrSize
+			}
+		}
+
+		// 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.argp == sparg {
+				frame.continpc = _defer.pc
+			} else {
+				frame.continpc = 0
+			}
+		}
+
+		// Unwind our local defer stack past this frame.
+		for _defer != nil && (_defer.argp == sparg || _defer.argp == _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(gofuncname(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")
+				var file string
+				line := funcline(f, tracepc, &file)
+				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
+		wasnewproc = f.entry == newprocPC || f.entry == deferprocPC
+
+		// 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
+			f = findfunc(frame.pc)
+			frame.fn = f
+			if f == nil {
+				frame.pc = x
+			} else if f.frame == 0 {
+				frame.lr = x
+			}
+		}
+	}
+
+	if pcbuf == nil && callback == nil {
+		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 argp=", hex(_defer.argp), " pc=", hex(_defer.pc), "\n")
+		}
+		for _defer = gp._defer; _defer != nil; _defer = _defer.link {
+			print("\tdefer ", _defer, " argp=", hex(_defer.argp), " pc=", hex(_defer.pc), "\n")
+		}
+		gothrow("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 gofuncname(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 ", gofuncname(f), "\n")
+				gothrow("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 ", gofuncname(f), "\n")
+		tracepc := pc // back up to CALL instruction for funcline.
+		if pc > f.entry {
+			tracepc -= _PCQuantum
+		}
+		var file string
+		line := funcline(f, tracepc, &file)
+		print("\t", file, ":", line)
+		if pc > f.entry {
+			print(" +", hex(pc-f.entry))
+		}
+		print("\n")
+	}
+}
+
+func traceback(pc uintptr, sp uintptr, 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 uintptr, sp uintptr, lr uintptr, gp *g) {
+	traceback1(pc, sp, lr, gp, _TraceTrap)
+}
+
+func traceback1(pc uintptr, sp uintptr, 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, m int) int {
+	sp := getcallersp(unsafe.Pointer(&skip))
+	pc := uintptr(getcallerpc(unsafe.Pointer(&skip)))
+	var n int
+	onM(func() {
+		n = gentraceback(pc, sp, 0, getg(), skip, pcbuf, m, nil, nil, 0)
+	})
+	return n
+}
+
+func gcallers(gp *g, skip int, pcbuf *uintptr, m int) int {
+	return gentraceback(^uintptr(0), ^uintptr(0), 0, gp, skip, pcbuf, m, 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) {
+		return true
+	}
+	traceback := gotraceback(nil)
+	name := gostringnocopy(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 || gp.issystem && level < 2 {
+			continue
+		}
+		print("\n")
+		goroutineheader(gp)
+		if 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
+}