Adding upstream version 1.21.8.upstream/1.21.8

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1640 insertions, 0 deletions

diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go
new file mode 100644
index 0000000..32a5385
--- /dev/null
+++ b/src/runtime/traceback.go
@@ -0,0 +1,1640 @@
+// 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 (
+	"internal/abi"
+	"internal/bytealg"
+	"internal/goarch"
+	"runtime/internal/sys"
+	"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 (x86), 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.
+
+const usesLR = sys.MinFrameSize > 0
+
+const (
+	// tracebackInnerFrames is the number of innermost frames to print in a
+	// stack trace. The total maximum frames is tracebackInnerFrames +
+	// tracebackOuterFrames.
+	tracebackInnerFrames = 50
+
+	// tracebackOuterFrames is the number of outermost frames to print in a
+	// stack trace.
+	tracebackOuterFrames = 50
+)
+
+// unwindFlags control the behavior of various unwinders.
+type unwindFlags uint8
+
+const (
+	// unwindPrintErrors indicates that if unwinding encounters an error, it
+	// should print a message and stop without throwing. This is used for things
+	// like stack printing, where it's better to get incomplete information than
+	// to crash. This is also used in situations where everything may not be
+	// stopped nicely and the stack walk may not be able to complete, such as
+	// during profiling signals or during a crash.
+	//
+	// If neither unwindPrintErrors or unwindSilentErrors are set, unwinding
+	// performs extra consistency checks and throws on any error.
+	//
+	// Note that there are a small number of fatal situations that will throw
+	// regardless of unwindPrintErrors or unwindSilentErrors.
+	unwindPrintErrors unwindFlags = 1 << iota
+
+	// unwindSilentErrors silently ignores errors during unwinding.
+	unwindSilentErrors
+
+	// unwindTrap indicates that the initial PC and SP are from a trap, not a
+	// return PC from a call.
+	//
+	// The unwindTrap flag is updated during unwinding. If set, frame.pc is the
+	// address of a faulting instruction instead of the return address of a
+	// call. It also means the liveness at pc may not be known.
+	//
+	// TODO: Distinguish frame.continpc, which is really the stack map PC, from
+	// the actual continuation PC, which is computed differently depending on
+	// this flag and a few other things.
+	unwindTrap
+
+	// unwindJumpStack indicates that, if the traceback is on a system stack, it
+	// should resume tracing at the user stack when the system stack is
+	// exhausted.
+	unwindJumpStack
+)
+
+// An unwinder iterates the physical stack frames of a Go sack.
+//
+// Typical use of an unwinder looks like:
+//
+//	var u unwinder
+//	for u.init(gp, 0); u.valid(); u.next() {
+//		// ... use frame info in u ...
+//	}
+//
+// Implementation note: This is carefully structured to be pointer-free because
+// tracebacks happen in places that disallow write barriers (e.g., signals).
+// Even if this is stack-allocated, its pointer-receiver methods don't know that
+// their receiver is on the stack, so they still emit write barriers. Here we
+// address that by carefully avoiding any pointers in this type. Another
+// approach would be to split this into a mutable part that's passed by pointer
+// but contains no pointers itself and an immutable part that's passed and
+// returned by value and can contain pointers. We could potentially hide that
+// we're doing that in trivial methods that are inlined into the caller that has
+// the stack allocation, but that's fragile.
+type unwinder struct {
+	// frame is the current physical stack frame, or all 0s if
+	// there is no frame.
+	frame stkframe
+
+	// g is the G who's stack is being unwound. If the
+	// unwindJumpStack flag is set and the unwinder jumps stacks,
+	// this will be different from the initial G.
+	g guintptr
+
+	// cgoCtxt is the index into g.cgoCtxt of the next frame on the cgo stack.
+	// The cgo stack is unwound in tandem with the Go stack as we find marker frames.
+	cgoCtxt int
+
+	// calleeFuncID is the function ID of the caller of the current
+	// frame.
+	calleeFuncID abi.FuncID
+
+	// flags are the flags to this unwind. Some of these are updated as we
+	// unwind (see the flags documentation).
+	flags unwindFlags
+
+	// cache is used to cache pcvalue lookups.
+	cache pcvalueCache
+}
+
+// init initializes u to start unwinding gp's stack and positions the
+// iterator on gp's innermost frame. gp must not be the current G.
+//
+// A single unwinder can be reused for multiple unwinds.
+func (u *unwinder) init(gp *g, flags unwindFlags) {
+	// Implementation note: This starts the iterator on the first frame and we
+	// provide a "valid" method. Alternatively, this could start in a "before
+	// the first frame" state and "next" could return whether it was able to
+	// move to the next frame, but that's both more awkward to use in a "for"
+	// loop and is harder to implement because we have to do things differently
+	// for the first frame.
+	u.initAt(^uintptr(0), ^uintptr(0), ^uintptr(0), gp, flags)
+}
+
+func (u *unwinder) initAt(pc0, sp0, lr0 uintptr, gp *g, flags unwindFlags) {
+	// Don't call this "g"; it's too easy get "g" and "gp" confused.
+	if ourg := getg(); ourg == gp && ourg == ourg.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 traceback 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 initAt 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("cannot trace user goroutine on its own stack")
+	}
+
+	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
+			}
+		}
+	}
+
+	var frame stkframe
+	frame.pc = pc0
+	frame.sp = sp0
+	if usesLR {
+		frame.lr = lr0
+	}
+
+	// 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(*(*uintptr)(unsafe.Pointer(frame.sp)))
+			frame.sp += goarch.PtrSize
+		}
+	}
+
+	// runtime/internal/atomic functions call into kernel helpers on
+	// arm < 7. See runtime/internal/atomic/sys_linux_arm.s.
+	//
+	// Start in the caller's frame.
+	if GOARCH == "arm" && goarm < 7 && GOOS == "linux" && frame.pc&0xffff0000 == 0xffff0000 {
+		// Note that the calls are simple BL without pushing the return
+		// address, so we use LR directly.
+		//
+		// The kernel helpers are frameless leaf functions, so SP and
+		// LR are not touched.
+		frame.pc = frame.lr
+		frame.lr = 0
+	}
+
+	f := findfunc(frame.pc)
+	if !f.valid() {
+		if flags&unwindSilentErrors == 0 {
+			print("runtime: g ", gp.goid, ": unknown pc ", hex(frame.pc), "\n")
+			tracebackHexdump(gp.stack, &frame, 0)
+		}
+		if flags&(unwindPrintErrors|unwindSilentErrors) == 0 {
+			throw("unknown pc")
+		}
+		*u = unwinder{}
+		return
+	}
+	frame.fn = f
+
+	// Populate the unwinder.
+	*u = unwinder{
+		frame:        frame,
+		g:            gp.guintptr(),
+		cgoCtxt:      len(gp.cgoCtxt) - 1,
+		calleeFuncID: abi.FuncIDNormal,
+		flags:        flags,
+	}
+
+	isSyscall := frame.pc == pc0 && frame.sp == sp0 && pc0 == gp.syscallpc && sp0 == gp.syscallsp
+	u.resolveInternal(true, isSyscall)
+}
+
+func (u *unwinder) valid() bool {
+	return u.frame.pc != 0
+}
+
+// resolveInternal fills in u.frame based on u.frame.fn, pc, and sp.
+//
+// innermost indicates that this is the first resolve on this stack. If
+// innermost is set, isSyscall indicates that the PC/SP was retrieved from
+// gp.syscall*; this is otherwise ignored.
+//
+// On entry, u.frame contains:
+//   - fn is the running function.
+//   - pc is the PC in the running function.
+//   - sp is the stack pointer at that program counter.
+//   - For the innermost frame on LR machines, lr is the program counter that called fn.
+//
+// On return, u.frame contains:
+//   - fp is the stack pointer of the caller.
+//   - lr is the program counter that called fn.
+//   - varp, argp, and continpc are populated for the current frame.
+//
+// If fn is a stack-jumping function, resolveInternal can change the entire
+// frame state to follow that stack jump.
+//
+// This is internal to unwinder.
+func (u *unwinder) resolveInternal(innermost, isSyscall bool) {
+	frame := &u.frame
+	gp := u.g.ptr()
+
+	f := frame.fn
+	if f.pcsp == 0 {
+		// No frame information, must be external function, like race support.
+		// See golang.org/issue/13568.
+		u.finishInternal()
+		return
+	}
+
+	// Compute function info flags.
+	flag := f.flag
+	if f.funcID == abi.FuncID_cgocallback {
+		// cgocallback does write SP to switch from the g0 to the curg stack,
+		// but it carefully arranges that during the transition BOTH stacks
+		// have cgocallback frame valid for unwinding through.
+		// So we don't need to exclude it with the other SP-writing functions.
+		flag &^= abi.FuncFlagSPWrite
+	}
+	if isSyscall {
+		// Some Syscall functions write to SP, but they do so only after
+		// saving the entry PC/SP using entersyscall.
+		// Since we are using the entry PC/SP, the later SP write doesn't matter.
+		flag &^= abi.FuncFlagSPWrite
+	}
+
+	// Found an actual function.
+	// Derive frame pointer.
+	if frame.fp == 0 {
+		// Jump over system stack transitions. If we're on g0 and there's a user
+		// goroutine, try to jump. Otherwise this is a regular call.
+		// We also defensively check that this won't switch M's on us,
+		// which could happen at critical points in the scheduler.
+		// This ensures gp.m doesn't change from a stack jump.
+		if u.flags&unwindJumpStack != 0 && gp == gp.m.g0 && gp.m.curg != nil && gp.m.curg.m == gp.m {
+			switch f.funcID {
+			case abi.FuncID_morestack:
+				// morestack does not return normally -- newstack()
+				// gogo's to curg.sched. Match that.
+				// This keeps morestack() from showing up in the backtrace,
+				// but that makes some sense since it'll never be returned
+				// to.
+				gp = gp.m.curg
+				u.g.set(gp)
+				frame.pc = gp.sched.pc
+				frame.fn = findfunc(frame.pc)
+				f = frame.fn
+				flag = f.flag
+				frame.lr = gp.sched.lr
+				frame.sp = gp.sched.sp
+				u.cgoCtxt = len(gp.cgoCtxt) - 1
+			case abi.FuncID_systemstack:
+				// systemstack returns normally, so just follow the
+				// stack transition.
+				if usesLR && funcspdelta(f, frame.pc, &u.cache) == 0 {
+					// We're at the function prologue and the stack
+					// switch hasn't happened, or epilogue where we're
+					// about to return. Just unwind normally.
+					// Do this only on LR machines because on x86
+					// systemstack doesn't have an SP delta (the CALL
+					// instruction opens the frame), therefore no way
+					// to check.
+					flag &^= abi.FuncFlagSPWrite
+					break
+				}
+				gp = gp.m.curg
+				u.g.set(gp)
+				frame.sp = gp.sched.sp
+				u.cgoCtxt = len(gp.cgoCtxt) - 1
+				flag &^= abi.FuncFlagSPWrite
+			}
+		}
+		frame.fp = frame.sp + uintptr(funcspdelta(f, frame.pc, &u.cache))
+		if !usesLR {
+			// On x86, call instruction pushes return PC before entering new function.
+			frame.fp += goarch.PtrSize
+		}
+	}
+
+	// Derive link register.
+	if flag&abi.FuncFlagTopFrame != 0 {
+		// This function marks the top of the stack. Stop the traceback.
+		frame.lr = 0
+	} else if flag&abi.FuncFlagSPWrite != 0 && (!innermost || u.flags&(unwindPrintErrors|unwindSilentErrors) != 0) {
+		// The function we are in does a write to SP that we don't know
+		// how to encode in the spdelta table. Examples include context
+		// switch routines like runtime.gogo but also any code that switches
+		// to the g0 stack to run host C code.
+		// We can't reliably unwind the SP (we might not even be on
+		// the stack we think we are), so stop the traceback here.
+		//
+		// The one exception (encoded in the complex condition above) is that
+		// we assume if we're doing a precise traceback, and this is the
+		// innermost frame, that the SPWRITE function voluntarily preempted itself on entry
+		// during the stack growth check. In that case, the function has
+		// not yet had a chance to do any writes to SP and is safe to unwind.
+		// isAsyncSafePoint does not allow assembly functions to be async preempted,
+		// and preemptPark double-checks that SPWRITE functions are not async preempted.
+		// So for GC stack traversal, we can safely ignore SPWRITE for the innermost frame,
+		// but farther up the stack we'd better not find any.
+		// This is somewhat imprecise because we're just guessing that we're in the stack
+		// growth check. It would be better if SPWRITE were encoded in the spdelta
+		// table so we would know for sure that we were still in safe code.
+		//
+		// uSE uPE inn | action
+		//  T   _   _  | frame.lr = 0
+		//  F   T   _  | frame.lr = 0
+		//  F   F   F  | print; panic
+		//  F   F   T  | ignore SPWrite
+		if u.flags&(unwindPrintErrors|unwindSilentErrors) == 0 && !innermost {
+			println("traceback: unexpected SPWRITE function", funcname(f))
+			throw("traceback")
+		}
+		frame.lr = 0
+	} else {
+		var lrPtr uintptr
+		if usesLR {
+			if innermost && frame.sp < frame.fp || frame.lr == 0 {
+				lrPtr = frame.sp
+				frame.lr = *(*uintptr)(unsafe.Pointer(lrPtr))
+			}
+		} else {
+			if frame.lr == 0 {
+				lrPtr = frame.fp - goarch.PtrSize
+				frame.lr = *(*uintptr)(unsafe.Pointer(lrPtr))
+			}
+		}
+	}
+
+	frame.varp = frame.fp
+	if !usesLR {
+		// On x86, call instruction pushes return PC before entering new function.
+		frame.varp -= goarch.PtrSize
+	}
+
+	// For architectures with frame pointers, if there's
+	// a frame, then there's a saved frame pointer here.
+	//
+	// NOTE: This code is not as general as it looks.
+	// On x86, the ABI is to save the frame pointer word at the
+	// top of the stack frame, so we have to back down over it.
+	// On arm64, the frame pointer should be at the bottom of
+	// the stack (with R29 (aka FP) = RSP), in which case we would
+	// not want to do the subtraction here. But we started out without
+	// any frame pointer, and when we wanted to add it, we didn't
+	// want to break all the assembly doing direct writes to 8(RSP)
+	// to set the first parameter to a called function.
+	// So we decided to write the FP link *below* the stack pointer
+	// (with R29 = RSP - 8 in Go functions).
+	// This is technically ABI-compatible but not standard.
+	// And it happens to end up mimicking the x86 layout.
+	// Other architectures may make different decisions.
+	if frame.varp > frame.sp && framepointer_enabled {
+		frame.varp -= goarch.PtrSize
+	}
+
+	frame.argp = frame.fp + sys.MinFrameSize
+
+	// 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).
+	// In the latter case, use a deferreturn call site as the continuation pc.
+	frame.continpc = frame.pc
+	if u.calleeFuncID == abi.FuncID_sigpanic {
+		if frame.fn.deferreturn != 0 {
+			frame.continpc = frame.fn.entry() + uintptr(frame.fn.deferreturn) + 1
+			// Note: this may perhaps keep return variables alive longer than
+			// strictly necessary, as we are using "function has a defer statement"
+			// as a proxy for "function actually deferred something". It seems
+			// to be a minor drawback. (We used to actually look through the
+			// gp._defer for a defer corresponding to this function, but that
+			// is hard to do with defer records on the stack during a stack copy.)
+			// Note: the +1 is to offset the -1 that
+			// stack.go:getStackMap does to back up a return
+			// address make sure the pc is in the CALL instruction.
+		} else {
+			frame.continpc = 0
+		}
+	}
+}
+
+func (u *unwinder) next() {
+	frame := &u.frame
+	f := frame.fn
+	gp := u.g.ptr()
+
+	// Do not unwind past the bottom of the stack.
+	if frame.lr == 0 {
+		u.finishInternal()
+		return
+	}
+	flr := findfunc(frame.lr)
+	if !flr.valid() {
+		// This happens if you get a profiling interrupt at just the wrong time.
+		// In that context it is okay to stop early.
+		// But if no error flags are set, we're doing a garbage collection and must
+		// get everything, so crash loudly.
+		fail := u.flags&(unwindPrintErrors|unwindSilentErrors) == 0
+		doPrint := u.flags&unwindSilentErrors == 0
+		if doPrint && gp.m.incgo && f.funcID == abi.FuncID_sigpanic {
+			// We can inject sigpanic
+			// calls directly into C code,
+			// in which case we'll see a C
+			// return PC. Don't complain.
+			doPrint = false
+		}
+		if fail || doPrint {
+			print("runtime: g ", gp.goid, ": unexpected return pc for ", funcname(f), " called from ", hex(frame.lr), "\n")
+			tracebackHexdump(gp.stack, frame, 0)
+		}
+		if fail {
+			throw("unknown caller pc")
+		}
+		frame.lr = 0
+		u.finishInternal()
+		return
+	}
+
+	if frame.pc == frame.lr && frame.sp == frame.fp {
+		// If the next frame is identical to the current frame, we cannot make progress.
+		print("runtime: traceback stuck. pc=", hex(frame.pc), " sp=", hex(frame.sp), "\n")
+		tracebackHexdump(gp.stack, frame, frame.sp)
+		throw("traceback stuck")
+	}
+
+	injectedCall := f.funcID == abi.FuncID_sigpanic || f.funcID == abi.FuncID_asyncPreempt || f.funcID == abi.FuncID_debugCallV2
+	if injectedCall {
+		u.flags |= unwindTrap
+	} else {
+		u.flags &^= unwindTrap
+	}
+
+	// Unwind to next frame.
+	u.calleeFuncID = f.funcID
+	frame.fn = flr
+	frame.pc = frame.lr
+	frame.lr = 0
+	frame.sp = frame.fp
+	frame.fp = 0
+
+	// On link register architectures, sighandler saves the LR on stack
+	// before faking a call.
+	if usesLR && injectedCall {
+		x := *(*uintptr)(unsafe.Pointer(frame.sp))
+		frame.sp += alignUp(sys.MinFrameSize, sys.StackAlign)
+		f = findfunc(frame.pc)
+		frame.fn = f
+		if !f.valid() {
+			frame.pc = x
+		} else if funcspdelta(f, frame.pc, &u.cache) == 0 {
+			frame.lr = x
+		}
+	}
+
+	u.resolveInternal(false, false)
+}
+
+// finishInternal is an unwinder-internal helper called after the stack has been
+// exhausted. It sets the unwinder to an invalid state and checks that it
+// successfully unwound the entire stack.
+func (u *unwinder) finishInternal() {
+	u.frame.pc = 0
+
+	// 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.
+	gp := u.g.ptr()
+	if u.flags&(unwindPrintErrors|unwindSilentErrors) == 0 && u.frame.sp != gp.stktopsp {
+		print("runtime: g", gp.goid, ": frame.sp=", hex(u.frame.sp), " top=", hex(gp.stktopsp), "\n")
+		print("\tstack=[", hex(gp.stack.lo), "-", hex(gp.stack.hi), "\n")
+		throw("traceback did not unwind completely")
+	}
+}
+
+// symPC returns the PC that should be used for symbolizing the current frame.
+// Specifically, this is the PC of the last instruction executed in this frame.
+//
+// If this frame did a normal call, then frame.pc is a return PC, so this will
+// return frame.pc-1, which points into the CALL instruction. If the frame was
+// interrupted by a signal (e.g., profiler, segv, etc) then frame.pc is for the
+// trapped instruction, so this returns frame.pc. See issue #34123. Finally,
+// frame.pc can be at function entry when the frame is initialized without
+// actually running code, like in runtime.mstart, in which case this returns
+// frame.pc because that's the best we can do.
+func (u *unwinder) symPC() uintptr {
+	if u.flags&unwindTrap == 0 && u.frame.pc > u.frame.fn.entry() {
+		// Regular call.
+		return u.frame.pc - 1
+	}
+	// Trapping instruction or we're at the function entry point.
+	return u.frame.pc
+}
+
+// cgoCallers populates pcBuf with the cgo callers of the current frame using
+// the registered cgo unwinder. It returns the number of PCs written to pcBuf.
+// If the current frame is not a cgo frame or if there's no registered cgo
+// unwinder, it returns 0.
+func (u *unwinder) cgoCallers(pcBuf []uintptr) int {
+	if cgoTraceback == nil || u.frame.fn.funcID != abi.FuncID_cgocallback || u.cgoCtxt < 0 {
+		// We don't have a cgo unwinder (typical case), or we do but we're not
+		// in a cgo frame or we're out of cgo context.
+		return 0
+	}
+
+	ctxt := u.g.ptr().cgoCtxt[u.cgoCtxt]
+	u.cgoCtxt--
+	cgoContextPCs(ctxt, pcBuf)
+	for i, pc := range pcBuf {
+		if pc == 0 {
+			return i
+		}
+	}
+	return len(pcBuf)
+}
+
+// tracebackPCs populates pcBuf with the return addresses for each frame from u
+// and returns the number of PCs written to pcBuf. The returned PCs correspond
+// to "logical frames" rather than "physical frames"; that is if A is inlined
+// into B, this will still return a PCs for both A and B. This also includes PCs
+// generated by the cgo unwinder, if one is registered.
+//
+// If skip != 0, this skips this many logical frames.
+//
+// Callers should set the unwindSilentErrors flag on u.
+func tracebackPCs(u *unwinder, skip int, pcBuf []uintptr) int {
+	var cgoBuf [32]uintptr
+	n := 0
+	for ; n < len(pcBuf) && u.valid(); u.next() {
+		f := u.frame.fn
+		cgoN := u.cgoCallers(cgoBuf[:])
+
+		// TODO: Why does &u.cache cause u to escape? (Same in traceback2)
+		for iu, uf := newInlineUnwinder(f, u.symPC(), noEscapePtr(&u.cache)); n < len(pcBuf) && uf.valid(); uf = iu.next(uf) {
+			sf := iu.srcFunc(uf)
+			if sf.funcID == abi.FuncIDWrapper && elideWrapperCalling(u.calleeFuncID) {
+				// ignore wrappers
+			} else if skip > 0 {
+				skip--
+			} else {
+				// Callers expect the pc buffer to contain return addresses
+				// and do the -1 themselves, so we add 1 to the call PC to
+				// create a return PC.
+				pcBuf[n] = uf.pc + 1
+				n++
+			}
+			u.calleeFuncID = sf.funcID
+		}
+		// Add cgo frames (if we're done skipping over the requested number of
+		// Go frames).
+		if skip == 0 {
+			n += copy(pcBuf[n:], cgoBuf[:cgoN])
+		}
+	}
+	return n
+}
+
+// printArgs prints function arguments in traceback.
+func printArgs(f funcInfo, argp unsafe.Pointer, pc uintptr) {
+	// The "instruction" of argument printing is encoded in _FUNCDATA_ArgInfo.
+	// See cmd/compile/internal/ssagen.emitArgInfo for the description of the
+	// encoding.
+	// These constants need to be in sync with the compiler.
+	const (
+		_endSeq         = 0xff
+		_startAgg       = 0xfe
+		_endAgg         = 0xfd
+		_dotdotdot      = 0xfc
+		_offsetTooLarge = 0xfb
+	)
+
+	const (
+		limit    = 10                       // print no more than 10 args/components
+		maxDepth = 5                        // no more than 5 layers of nesting
+		maxLen   = (maxDepth*3+2)*limit + 1 // max length of _FUNCDATA_ArgInfo (see the compiler side for reasoning)
+	)
+
+	p := (*[maxLen]uint8)(funcdata(f, abi.FUNCDATA_ArgInfo))
+	if p == nil {
+		return
+	}
+
+	liveInfo := funcdata(f, abi.FUNCDATA_ArgLiveInfo)
+	liveIdx := pcdatavalue(f, abi.PCDATA_ArgLiveIndex, pc, nil)
+	startOffset := uint8(0xff) // smallest offset that needs liveness info (slots with a lower offset is always live)
+	if liveInfo != nil {
+		startOffset = *(*uint8)(liveInfo)
+	}
+
+	isLive := func(off, slotIdx uint8) bool {
+		if liveInfo == nil || liveIdx <= 0 {
+			return true // no liveness info, always live
+		}
+		if off < startOffset {
+			return true
+		}
+		bits := *(*uint8)(add(liveInfo, uintptr(liveIdx)+uintptr(slotIdx/8)))
+		return bits&(1<<(slotIdx%8)) != 0
+	}
+
+	print1 := func(off, sz, slotIdx uint8) {
+		x := readUnaligned64(add(argp, uintptr(off)))
+		// mask out irrelevant bits
+		if sz < 8 {
+			shift := 64 - sz*8
+			if goarch.BigEndian {
+				x = x >> shift
+			} else {
+				x = x << shift >> shift
+			}
+		}
+		print(hex(x))
+		if !isLive(off, slotIdx) {
+			print("?")
+		}
+	}
+
+	start := true
+	printcomma := func() {
+		if !start {
+			print(", ")
+		}
+	}
+	pi := 0
+	slotIdx := uint8(0) // register arg spill slot index
+printloop:
+	for {
+		o := p[pi]
+		pi++
+		switch o {
+		case _endSeq:
+			break printloop
+		case _startAgg:
+			printcomma()
+			print("{")
+			start = true
+			continue
+		case _endAgg:
+			print("}")
+		case _dotdotdot:
+			printcomma()
+			print("...")
+		case _offsetTooLarge:
+			printcomma()
+			print("_")
+		default:
+			printcomma()
+			sz := p[pi]
+			pi++
+			print1(o, sz, slotIdx)
+			if o >= startOffset {
+				slotIdx++
+			}
+		}
+		start = false
+	}
+}
+
+// funcNamePiecesForPrint returns the function name for printing to the user.
+// It returns three pieces so it doesn't need an allocation for string
+// concatenation.
+func funcNamePiecesForPrint(name string) (string, string, string) {
+	// Replace the shape name in generic function with "...".
+	i := bytealg.IndexByteString(name, '[')
+	if i < 0 {
+		return name, "", ""
+	}
+	j := len(name) - 1
+	for name[j] != ']' {
+		j--
+	}
+	if j <= i {
+		return name, "", ""
+	}
+	return name[:i], "[...]", name[j+1:]
+}
+
+// funcNameForPrint returns the function name for printing to the user.
+func funcNameForPrint(name string) string {
+	a, b, c := funcNamePiecesForPrint(name)
+	return a + b + c
+}
+
+// printFuncName prints a function name. name is the function name in
+// the binary's func data table.
+func printFuncName(name string) {
+	if name == "runtime.gopanic" {
+		print("panic")
+		return
+	}
+	a, b, c := funcNamePiecesForPrint(name)
+	print(a, b, c)
+}
+
+func printcreatedby(gp *g) {
+	// Show what created goroutine, except main goroutine (goid 1).
+	pc := gp.gopc
+	f := findfunc(pc)
+	if f.valid() && showframe(f.srcFunc(), gp, false, abi.FuncIDNormal) && gp.goid != 1 {
+		printcreatedby1(f, pc, gp.parentGoid)
+	}
+}
+
+func printcreatedby1(f funcInfo, pc uintptr, goid uint64) {
+	print("created by ")
+	printFuncName(funcname(f))
+	if goid != 0 {
+		print(" in goroutine ", goid)
+	}
+	print("\n")
+	tracepc := pc // back up to CALL instruction for funcline.
+	if pc > f.entry() {
+		tracepc -= sys.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.)
+// If gp.m.libcall{g,pc,sp} information is available, it uses that information in preference to
+// the pc/sp/lr passed in.
+func tracebacktrap(pc, sp, lr uintptr, gp *g) {
+	if gp.m.libcallsp != 0 {
+		// We're in C code somewhere, traceback from the saved position.
+		traceback1(gp.m.libcallpc, gp.m.libcallsp, 0, gp.m.libcallg.ptr(), 0)
+		return
+	}
+	traceback1(pc, sp, lr, gp, unwindTrap)
+}
+
+func traceback1(pc, sp, lr uintptr, gp *g, flags unwindFlags) {
+	// If the goroutine is in cgo, and we have a cgo traceback, print that.
+	if iscgo && gp.m != nil && gp.m.ncgo > 0 && gp.syscallsp != 0 && gp.m.cgoCallers != nil && gp.m.cgoCallers[0] != 0 {
+		// Lock cgoCallers so that a signal handler won't
+		// change it, copy the array, reset it, unlock it.
+		// We are locked to the thread and are not running
+		// concurrently with a signal handler.
+		// We just have to stop a signal handler from interrupting
+		// in the middle of our copy.
+		gp.m.cgoCallersUse.Store(1)
+		cgoCallers := *gp.m.cgoCallers
+		gp.m.cgoCallers[0] = 0
+		gp.m.cgoCallersUse.Store(0)
+
+		printCgoTraceback(&cgoCallers)
+	}
+
+	if readgstatus(gp)&^_Gscan == _Gsyscall {
+		// Override registers if blocked in system call.
+		pc = gp.syscallpc
+		sp = gp.syscallsp
+		flags &^= unwindTrap
+	}
+	if gp.m != nil && gp.m.vdsoSP != 0 {
+		// Override registers if running in VDSO. This comes after the
+		// _Gsyscall check to cover VDSO calls after entersyscall.
+		pc = gp.m.vdsoPC
+		sp = gp.m.vdsoSP
+		flags &^= unwindTrap
+	}
+
+	// Print traceback.
+	//
+	// We print the first tracebackInnerFrames frames, and the last
+	// tracebackOuterFrames frames. There are many possible approaches to this.
+	// There are various complications to this:
+	//
+	// - We'd prefer to walk the stack once because in really bad situations
+	//   traceback may crash (and we want as much output as possible) or the stack
+	//   may be changing.
+	//
+	// - Each physical frame can represent several logical frames, so we might
+	//   have to pause in the middle of a physical frame and pick up in the middle
+	//   of a physical frame.
+	//
+	// - The cgo symbolizer can expand a cgo PC to more than one logical frame,
+	//   and involves juggling state on the C side that we don't manage. Since its
+	//   expansion state is managed on the C side, we can't capture the expansion
+	//   state part way through, and because the output strings are managed on the
+	//   C side, we can't capture the output. Thus, our only choice is to replay a
+	//   whole expansion, potentially discarding some of it.
+	//
+	// Rejected approaches:
+	//
+	// - Do two passes where the first pass just counts and the second pass does
+	//   all the printing. This is undesirable if the stack is corrupted or changing
+	//   because we won't see a partial stack if we panic.
+	//
+	// - Keep a ring buffer of the last N logical frames and use this to print
+	//   the bottom frames once we reach the end of the stack. This works, but
+	//   requires keeping a surprising amount of state on the stack, and we have
+	//   to run the cgo symbolizer twice—once to count frames, and a second to
+	//   print them—since we can't retain the strings it returns.
+	//
+	// Instead, we print the outer frames, and if we reach that limit, we clone
+	// the unwinder, count the remaining frames, and then skip forward and
+	// finish printing from the clone. This makes two passes over the outer part
+	// of the stack, but the single pass over the inner part ensures that's
+	// printed immediately and not revisited. It keeps minimal state on the
+	// stack. And through a combination of skip counts and limits, we can do all
+	// of the steps we need with a single traceback printer implementation.
+	//
+	// We could be more lax about exactly how many frames we print, for example
+	// always stopping and resuming on physical frame boundaries, or at least
+	// cgo expansion boundaries. It's not clear that's much simpler.
+	flags |= unwindPrintErrors
+	var u unwinder
+	tracebackWithRuntime := func(showRuntime bool) int {
+		const maxInt int = 0x7fffffff
+		u.initAt(pc, sp, lr, gp, flags)
+		n, lastN := traceback2(&u, showRuntime, 0, tracebackInnerFrames)
+		if n < tracebackInnerFrames {
+			// We printed the whole stack.
+			return n
+		}
+		// Clone the unwinder and figure out how many frames are left. This
+		// count will include any logical frames already printed for u's current
+		// physical frame.
+		u2 := u
+		remaining, _ := traceback2(&u, showRuntime, maxInt, 0)
+		elide := remaining - lastN - tracebackOuterFrames
+		if elide > 0 {
+			print("...", elide, " frames elided...\n")
+			traceback2(&u2, showRuntime, lastN+elide, tracebackOuterFrames)
+		} else if elide <= 0 {
+			// There are tracebackOuterFrames or fewer frames left to print.
+			// Just print the rest of the stack.
+			traceback2(&u2, showRuntime, lastN, tracebackOuterFrames)
+		}
+		return n
+	}
+	// By default, omits runtime frames. If that means we print nothing at all,
+	// repeat forcing all frames printed.
+	if tracebackWithRuntime(false) == 0 {
+		tracebackWithRuntime(true)
+	}
+	printcreatedby(gp)
+
+	if gp.ancestors == nil {
+		return
+	}
+	for _, ancestor := range *gp.ancestors {
+		printAncestorTraceback(ancestor)
+	}
+}
+
+// traceback2 prints a stack trace starting at u. It skips the first "skip"
+// logical frames, after which it prints at most "max" logical frames. It
+// returns n, which is the number of logical frames skipped and printed, and
+// lastN, which is the number of logical frames skipped or printed just in the
+// physical frame that u references.
+func traceback2(u *unwinder, showRuntime bool, skip, max int) (n, lastN int) {
+	// commitFrame commits to a logical frame and returns whether this frame
+	// should be printed and whether iteration should stop.
+	commitFrame := func() (pr, stop bool) {
+		if skip == 0 && max == 0 {
+			// Stop
+			return false, true
+		}
+		n++
+		lastN++
+		if skip > 0 {
+			// Skip
+			skip--
+			return false, false
+		}
+		// Print
+		max--
+		return true, false
+	}
+
+	gp := u.g.ptr()
+	level, _, _ := gotraceback()
+	var cgoBuf [32]uintptr
+	for ; u.valid(); u.next() {
+		lastN = 0
+		f := u.frame.fn
+		for iu, uf := newInlineUnwinder(f, u.symPC(), noEscapePtr(&u.cache)); uf.valid(); uf = iu.next(uf) {
+			sf := iu.srcFunc(uf)
+			callee := u.calleeFuncID
+			u.calleeFuncID = sf.funcID
+			if !(showRuntime || showframe(sf, gp, n == 0, callee)) {
+				continue
+			}
+
+			if pr, stop := commitFrame(); stop {
+				return
+			} else if !pr {
+				continue
+			}
+
+			name := sf.name()
+			file, line := iu.fileLine(uf)
+			// Print during crash.
+			//	main(0x1, 0x2, 0x3)
+			//		/home/rsc/go/src/runtime/x.go:23 +0xf
+			//
+			printFuncName(name)
+			print("(")
+			if iu.isInlined(uf) {
+				print("...")
+			} else {
+				argp := unsafe.Pointer(u.frame.argp)
+				printArgs(f, argp, u.symPC())
+			}
+			print(")\n")
+			print("\t", file, ":", line)
+			if !iu.isInlined(uf) {
+				if u.frame.pc > f.entry() {
+					print(" +", hex(u.frame.pc-f.entry()))
+				}
+				if gp.m != nil && gp.m.throwing >= throwTypeRuntime && gp == gp.m.curg || level >= 2 {
+					print(" fp=", hex(u.frame.fp), " sp=", hex(u.frame.sp), " pc=", hex(u.frame.pc))
+				}
+			}
+			print("\n")
+		}
+
+		// Print cgo frames.
+		if cgoN := u.cgoCallers(cgoBuf[:]); cgoN > 0 {
+			var arg cgoSymbolizerArg
+			anySymbolized := false
+			stop := false
+			for _, pc := range cgoBuf[:cgoN] {
+				if cgoSymbolizer == nil {
+					if pr, stop := commitFrame(); stop {
+						break
+					} else if pr {
+						print("non-Go function at pc=", hex(pc), "\n")
+					}
+				} else {
+					stop = printOneCgoTraceback(pc, commitFrame, &arg)
+					anySymbolized = true
+					if stop {
+						break
+					}
+				}
+			}
+			if anySymbolized {
+				// Free symbolization state.
+				arg.pc = 0
+				callCgoSymbolizer(&arg)
+			}
+			if stop {
+				return
+			}
+		}
+	}
+	return n, 0
+}
+
+// printAncestorTraceback prints the traceback of the given ancestor.
+// TODO: Unify this with gentraceback and CallersFrames.
+func printAncestorTraceback(ancestor ancestorInfo) {
+	print("[originating from goroutine ", ancestor.goid, "]:\n")
+	for fidx, pc := range ancestor.pcs {
+		f := findfunc(pc) // f previously validated
+		if showfuncinfo(f.srcFunc(), fidx == 0, abi.FuncIDNormal) {
+			printAncestorTracebackFuncInfo(f, pc)
+		}
+	}
+	if len(ancestor.pcs) == tracebackInnerFrames {
+		print("...additional frames elided...\n")
+	}
+	// Show what created goroutine, except main goroutine (goid 1).
+	f := findfunc(ancestor.gopc)
+	if f.valid() && showfuncinfo(f.srcFunc(), false, abi.FuncIDNormal) && ancestor.goid != 1 {
+		// In ancestor mode, we'll already print the goroutine ancestor.
+		// Pass 0 for the goid parameter so we don't print it again.
+		printcreatedby1(f, ancestor.gopc, 0)
+	}
+}
+
+// printAncestorTracebackFuncInfo prints the given function info at a given pc
+// within an ancestor traceback. The precision of this info is reduced
+// due to only have access to the pcs at the time of the caller
+// goroutine being created.
+func printAncestorTracebackFuncInfo(f funcInfo, pc uintptr) {
+	u, uf := newInlineUnwinder(f, pc, nil)
+	file, line := u.fileLine(uf)
+	printFuncName(u.srcFunc(uf).name())
+	print("(...)\n")
+	print("\t", file, ":", line)
+	if pc > f.entry() {
+		print(" +", hex(pc-f.entry()))
+	}
+	print("\n")
+}
+
+func callers(skip int, pcbuf []uintptr) int {
+	sp := getcallersp()
+	pc := getcallerpc()
+	gp := getg()
+	var n int
+	systemstack(func() {
+		var u unwinder
+		u.initAt(pc, sp, 0, gp, unwindSilentErrors)
+		n = tracebackPCs(&u, skip, pcbuf)
+	})
+	return n
+}
+
+func gcallers(gp *g, skip int, pcbuf []uintptr) int {
+	var u unwinder
+	u.init(gp, unwindSilentErrors)
+	return tracebackPCs(&u, skip, pcbuf)
+}
+
+// showframe reports whether the frame with the given characteristics should
+// be printed during a traceback.
+func showframe(sf srcFunc, gp *g, firstFrame bool, calleeID abi.FuncID) bool {
+	mp := getg().m
+	if mp.throwing >= throwTypeRuntime && gp != nil && (gp == mp.curg || gp == mp.caughtsig.ptr()) {
+		return true
+	}
+	return showfuncinfo(sf, firstFrame, calleeID)
+}
+
+// showfuncinfo reports whether a function with the given characteristics should
+// be printed during a traceback.
+func showfuncinfo(sf srcFunc, firstFrame bool, calleeID abi.FuncID) bool {
+	level, _, _ := gotraceback()
+	if level > 1 {
+		// Show all frames.
+		return true
+	}
+
+	if sf.funcID == abi.FuncIDWrapper && elideWrapperCalling(calleeID) {
+		return false
+	}
+
+	name := sf.name()
+
+	// Special case: always show runtime.gopanic frame
+	// in the middle of a stack trace, so that we can
+	// see the boundary between ordinary code and
+	// panic-induced deferred code.
+	// See golang.org/issue/5832.
+	if name == "runtime.gopanic" && !firstFrame {
+		return true
+	}
+
+	return bytealg.IndexByteString(name, '.') >= 0 && (!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.
+// TODO: this handles exported functions but not exported methods.
+func isExportedRuntime(name string) bool {
+	const n = len("runtime.")
+	return len(name) > n && name[:n] == "runtime." && 'A' <= name[n] && name[n] <= 'Z'
+}
+
+// elideWrapperCalling reports whether a wrapper function that called
+// function id should be elided from stack traces.
+func elideWrapperCalling(id abi.FuncID) bool {
+	// If the wrapper called a panic function instead of the
+	// wrapped function, we want to include it in stacks.
+	return !(id == abi.FuncID_gopanic || id == abi.FuncID_sigpanic || id == abi.FuncID_panicwrap)
+}
+
+var gStatusStrings = [...]string{
+	_Gidle:      "idle",
+	_Grunnable:  "runnable",
+	_Grunning:   "running",
+	_Gsyscall:   "syscall",
+	_Gwaiting:   "waiting",
+	_Gdead:      "dead",
+	_Gcopystack: "copystack",
+	_Gpreempted: "preempted",
+}
+
+func goroutineheader(gp *g) {
+	gpstatus := readgstatus(gp)
+
+	isScan := gpstatus&_Gscan != 0
+	gpstatus &^= _Gscan // drop the scan bit
+
+	// Basic string status
+	var status string
+	if 0 <= gpstatus && gpstatus < uint32(len(gStatusStrings)) {
+		status = gStatusStrings[gpstatus]
+	} else {
+		status = "???"
+	}
+
+	// Override.
+	if gpstatus == _Gwaiting && gp.waitreason != waitReasonZero {
+		status = gp.waitreason.String()
+	}
+
+	// approx time the G is blocked, in minutes
+	var waitfor int64
+	if (gpstatus == _Gwaiting || gpstatus == _Gsyscall) && gp.waitsince != 0 {
+		waitfor = (nanotime() - gp.waitsince) / 60e9
+	}
+	print("goroutine ", gp.goid, " [", status)
+	if isScan {
+		print(" (scan)")
+	}
+	if waitfor >= 1 {
+		print(", ", waitfor, " minutes")
+	}
+	if gp.lockedm != 0 {
+		print(", locked to thread")
+	}
+	print("]:\n")
+}
+
+func tracebackothers(me *g) {
+	level, _, _ := gotraceback()
+
+	// Show the current goroutine first, if we haven't already.
+	curgp := getg().m.curg
+	if curgp != nil && curgp != me {
+		print("\n")
+		goroutineheader(curgp)
+		traceback(^uintptr(0), ^uintptr(0), 0, curgp)
+	}
+
+	// We can't call locking forEachG here because this may be during fatal
+	// throw/panic, where locking could be out-of-order or a direct
+	// deadlock.
+	//
+	// Instead, use forEachGRace, which requires no locking. We don't lock
+	// against concurrent creation of new Gs, but even with allglock we may
+	// miss Gs created after this loop.
+	forEachGRace(func(gp *g) {
+		if gp == me || gp == curgp || readgstatus(gp) == _Gdead || isSystemGoroutine(gp, false) && level < 2 {
+			return
+		}
+		print("\n")
+		goroutineheader(gp)
+		// Note: gp.m == getg().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 != getg().m && readgstatus(gp)&^_Gscan == _Grunning {
+			print("\tgoroutine running on other thread; stack unavailable\n")
+			printcreatedby(gp)
+		} else {
+			traceback(^uintptr(0), ^uintptr(0), 0, gp)
+		}
+	})
+}
+
+// tracebackHexdump hexdumps part of stk around frame.sp and frame.fp
+// for debugging purposes. If the address bad is included in the
+// hexdumped range, it will mark it as well.
+func tracebackHexdump(stk stack, frame *stkframe, bad uintptr) {
+	const expand = 32 * goarch.PtrSize
+	const maxExpand = 256 * goarch.PtrSize
+	// Start around frame.sp.
+	lo, hi := frame.sp, frame.sp
+	// Expand to include frame.fp.
+	if frame.fp != 0 && frame.fp < lo {
+		lo = frame.fp
+	}
+	if frame.fp != 0 && frame.fp > hi {
+		hi = frame.fp
+	}
+	// Expand a bit more.
+	lo, hi = lo-expand, hi+expand
+	// But don't go too far from frame.sp.
+	if lo < frame.sp-maxExpand {
+		lo = frame.sp - maxExpand
+	}
+	if hi > frame.sp+maxExpand {
+		hi = frame.sp + maxExpand
+	}
+	// And don't go outside the stack bounds.
+	if lo < stk.lo {
+		lo = stk.lo
+	}
+	if hi > stk.hi {
+		hi = stk.hi
+	}
+
+	// Print the hex dump.
+	print("stack: frame={sp:", hex(frame.sp), ", fp:", hex(frame.fp), "} stack=[", hex(stk.lo), ",", hex(stk.hi), ")\n")
+	hexdumpWords(lo, hi, func(p uintptr) byte {
+		switch p {
+		case frame.fp:
+			return '>'
+		case frame.sp:
+			return '<'
+		case bad:
+			return '!'
+		}
+		return 0
+	})
+}
+
+// isSystemGoroutine reports whether the goroutine g must be omitted
+// in stack dumps and deadlock detector. This is any goroutine that
+// starts at a runtime.* entry point, except for runtime.main,
+// runtime.handleAsyncEvent (wasm only) and sometimes runtime.runfinq.
+//
+// If fixed is true, any goroutine that can vary between user and
+// system (that is, the finalizer goroutine) is considered a user
+// goroutine.
+func isSystemGoroutine(gp *g, fixed bool) bool {
+	// Keep this in sync with internal/trace.IsSystemGoroutine.
+	f := findfunc(gp.startpc)
+	if !f.valid() {
+		return false
+	}
+	if f.funcID == abi.FuncID_runtime_main || f.funcID == abi.FuncID_handleAsyncEvent {
+		return false
+	}
+	if f.funcID == abi.FuncID_runfinq {
+		// We include the finalizer goroutine if it's calling
+		// back into user code.
+		if fixed {
+			// This goroutine can vary. In fixed mode,
+			// always consider it a user goroutine.
+			return false
+		}
+		return fingStatus.Load()&fingRunningFinalizer == 0
+	}
+	return hasPrefix(funcname(f), "runtime.")
+}
+
+// SetCgoTraceback records three C functions to use to gather
+// traceback information from C code and to convert that traceback
+// information into symbolic information. These are used when printing
+// stack traces for a program that uses cgo.
+//
+// The traceback and context functions may be called from a signal
+// handler, and must therefore use only async-signal safe functions.
+// The symbolizer function may be called while the program is
+// crashing, and so must be cautious about using memory.  None of the
+// functions may call back into Go.
+//
+// The context function will be called with a single argument, a
+// pointer to a struct:
+//
+//	struct {
+//		Context uintptr
+//	}
+//
+// In C syntax, this struct will be
+//
+//	struct {
+//		uintptr_t Context;
+//	};
+//
+// If the Context field is 0, the context function is being called to
+// record the current traceback context. It should record in the
+// Context field whatever information is needed about the current
+// point of execution to later produce a stack trace, probably the
+// stack pointer and PC. In this case the context function will be
+// called from C code.
+//
+// If the Context field is not 0, then it is a value returned by a
+// previous call to the context function. This case is called when the
+// context is no longer needed; that is, when the Go code is returning
+// to its C code caller. This permits the context function to release
+// any associated resources.
+//
+// While it would be correct for the context function to record a
+// complete a stack trace whenever it is called, and simply copy that
+// out in the traceback function, in a typical program the context
+// function will be called many times without ever recording a
+// traceback for that context. Recording a complete stack trace in a
+// call to the context function is likely to be inefficient.
+//
+// The traceback function will be called with a single argument, a
+// pointer to a struct:
+//
+//	struct {
+//		Context    uintptr
+//		SigContext uintptr
+//		Buf        *uintptr
+//		Max        uintptr
+//	}
+//
+// In C syntax, this struct will be
+//
+//	struct {
+//		uintptr_t  Context;
+//		uintptr_t  SigContext;
+//		uintptr_t* Buf;
+//		uintptr_t  Max;
+//	};
+//
+// The Context field will be zero to gather a traceback from the
+// current program execution point. In this case, the traceback
+// function will be called from C code.
+//
+// Otherwise Context will be a value previously returned by a call to
+// the context function. The traceback function should gather a stack
+// trace from that saved point in the program execution. The traceback
+// function may be called from an execution thread other than the one
+// that recorded the context, but only when the context is known to be
+// valid and unchanging. The traceback function may also be called
+// deeper in the call stack on the same thread that recorded the
+// context. The traceback function may be called multiple times with
+// the same Context value; it will usually be appropriate to cache the
+// result, if possible, the first time this is called for a specific
+// context value.
+//
+// If the traceback function is called from a signal handler on a Unix
+// system, SigContext will be the signal context argument passed to
+// the signal handler (a C ucontext_t* cast to uintptr_t). This may be
+// used to start tracing at the point where the signal occurred. If
+// the traceback function is not called from a signal handler,
+// SigContext will be zero.
+//
+// Buf is where the traceback information should be stored. It should
+// be PC values, such that Buf[0] is the PC of the caller, Buf[1] is
+// the PC of that function's caller, and so on.  Max is the maximum
+// number of entries to store.  The function should store a zero to
+// indicate the top of the stack, or that the caller is on a different
+// stack, presumably a Go stack.
+//
+// Unlike runtime.Callers, the PC values returned should, when passed
+// to the symbolizer function, return the file/line of the call
+// instruction.  No additional subtraction is required or appropriate.
+//
+// On all platforms, the traceback function is invoked when a call from
+// Go to C to Go requests a stack trace. On linux/amd64, linux/ppc64le,
+// linux/arm64, and freebsd/amd64, the traceback function is also invoked
+// when a signal is received by a thread that is executing a cgo call.
+// The traceback function should not make assumptions about when it is
+// called, as future versions of Go may make additional calls.
+//
+// The symbolizer function will be called with a single argument, a
+// pointer to a struct:
+//
+//	struct {
+//		PC      uintptr // program counter to fetch information for
+//		File    *byte   // file name (NUL terminated)
+//		Lineno  uintptr // line number
+//		Func    *byte   // function name (NUL terminated)
+//		Entry   uintptr // function entry point
+//		More    uintptr // set non-zero if more info for this PC
+//		Data    uintptr // unused by runtime, available for function
+//	}
+//
+// In C syntax, this struct will be
+//
+//	struct {
+//		uintptr_t PC;
+//		char*     File;
+//		uintptr_t Lineno;
+//		char*     Func;
+//		uintptr_t Entry;
+//		uintptr_t More;
+//		uintptr_t Data;
+//	};
+//
+// The PC field will be a value returned by a call to the traceback
+// function.
+//
+// The first time the function is called for a particular traceback,
+// all the fields except PC will be 0. The function should fill in the
+// other fields if possible, setting them to 0/nil if the information
+// is not available. The Data field may be used to store any useful
+// information across calls. The More field should be set to non-zero
+// if there is more information for this PC, zero otherwise. If More
+// is set non-zero, the function will be called again with the same
+// PC, and may return different information (this is intended for use
+// with inlined functions). If More is zero, the function will be
+// called with the next PC value in the traceback. When the traceback
+// is complete, the function will be called once more with PC set to
+// zero; this may be used to free any information. Each call will
+// leave the fields of the struct set to the same values they had upon
+// return, except for the PC field when the More field is zero. The
+// function must not keep a copy of the struct pointer between calls.
+//
+// When calling SetCgoTraceback, the version argument is the version
+// number of the structs that the functions expect to receive.
+// Currently this must be zero.
+//
+// The symbolizer function may be nil, in which case the results of
+// the traceback function will be displayed as numbers. If the
+// traceback function is nil, the symbolizer function will never be
+// called. The context function may be nil, in which case the
+// traceback function will only be called with the context field set
+// to zero.  If the context function is nil, then calls from Go to C
+// to Go will not show a traceback for the C portion of the call stack.
+//
+// SetCgoTraceback should be called only once, ideally from an init function.
+func SetCgoTraceback(version int, traceback, context, symbolizer unsafe.Pointer) {
+	if version != 0 {
+		panic("unsupported version")
+	}
+
+	if cgoTraceback != nil && cgoTraceback != traceback ||
+		cgoContext != nil && cgoContext != context ||
+		cgoSymbolizer != nil && cgoSymbolizer != symbolizer {
+		panic("call SetCgoTraceback only once")
+	}
+
+	cgoTraceback = traceback
+	cgoContext = context
+	cgoSymbolizer = symbolizer
+
+	// The context function is called when a C function calls a Go
+	// function. As such it is only called by C code in runtime/cgo.
+	if _cgo_set_context_function != nil {
+		cgocall(_cgo_set_context_function, context)
+	}
+}
+
+var cgoTraceback unsafe.Pointer
+var cgoContext unsafe.Pointer
+var cgoSymbolizer unsafe.Pointer
+
+// cgoTracebackArg is the type passed to cgoTraceback.
+type cgoTracebackArg struct {
+	context    uintptr
+	sigContext uintptr
+	buf        *uintptr
+	max        uintptr
+}
+
+// cgoContextArg is the type passed to the context function.
+type cgoContextArg struct {
+	context uintptr
+}
+
+// cgoSymbolizerArg is the type passed to cgoSymbolizer.
+type cgoSymbolizerArg struct {
+	pc       uintptr
+	file     *byte
+	lineno   uintptr
+	funcName *byte
+	entry    uintptr
+	more     uintptr
+	data     uintptr
+}
+
+// printCgoTraceback prints a traceback of callers.
+func printCgoTraceback(callers *cgoCallers) {
+	if cgoSymbolizer == nil {
+		for _, c := range callers {
+			if c == 0 {
+				break
+			}
+			print("non-Go function at pc=", hex(c), "\n")
+		}
+		return
+	}
+
+	commitFrame := func() (pr, stop bool) { return true, false }
+	var arg cgoSymbolizerArg
+	for _, c := range callers {
+		if c == 0 {
+			break
+		}
+		printOneCgoTraceback(c, commitFrame, &arg)
+	}
+	arg.pc = 0
+	callCgoSymbolizer(&arg)
+}
+
+// printOneCgoTraceback prints the traceback of a single cgo caller.
+// This can print more than one line because of inlining.
+// It returns the "stop" result of commitFrame.
+func printOneCgoTraceback(pc uintptr, commitFrame func() (pr, stop bool), arg *cgoSymbolizerArg) bool {
+	arg.pc = pc
+	for {
+		if pr, stop := commitFrame(); stop {
+			return true
+		} else if !pr {
+			continue
+		}
+
+		callCgoSymbolizer(arg)
+		if arg.funcName != nil {
+			// Note that we don't print any argument
+			// information here, not even parentheses.
+			// The symbolizer must add that if appropriate.
+			println(gostringnocopy(arg.funcName))
+		} else {
+			println("non-Go function")
+		}
+		print("\t")
+		if arg.file != nil {
+			print(gostringnocopy(arg.file), ":", arg.lineno, " ")
+		}
+		print("pc=", hex(pc), "\n")
+		if arg.more == 0 {
+			return false
+		}
+	}
+}
+
+// callCgoSymbolizer calls the cgoSymbolizer function.
+func callCgoSymbolizer(arg *cgoSymbolizerArg) {
+	call := cgocall
+	if panicking.Load() > 0 || getg().m.curg != getg() {
+		// We do not want to call into the scheduler when panicking
+		// or when on the system stack.
+		call = asmcgocall
+	}
+	if msanenabled {
+		msanwrite(unsafe.Pointer(arg), unsafe.Sizeof(cgoSymbolizerArg{}))
+	}
+	if asanenabled {
+		asanwrite(unsafe.Pointer(arg), unsafe.Sizeof(cgoSymbolizerArg{}))
+	}
+	call(cgoSymbolizer, noescape(unsafe.Pointer(arg)))
+}
+
+// cgoContextPCs gets the PC values from a cgo traceback.
+func cgoContextPCs(ctxt uintptr, buf []uintptr) {
+	if cgoTraceback == nil {
+		return
+	}
+	call := cgocall
+	if panicking.Load() > 0 || getg().m.curg != getg() {
+		// We do not want to call into the scheduler when panicking
+		// or when on the system stack.
+		call = asmcgocall
+	}
+	arg := cgoTracebackArg{
+		context: ctxt,
+		buf:     (*uintptr)(noescape(unsafe.Pointer(&buf[0]))),
+		max:     uintptr(len(buf)),
+	}
+	if msanenabled {
+		msanwrite(unsafe.Pointer(&arg), unsafe.Sizeof(arg))
+	}
+	if asanenabled {
+		asanwrite(unsafe.Pointer(&arg), unsafe.Sizeof(arg))
+	}
+	call(cgoTraceback, noescape(unsafe.Pointer(&arg)))
+}