Adding upstream version 1.16.10.upstream/1.16.10upstream

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

1 files changed, 894 insertions, 0 deletions

diff --git a/src/runtime/stack_test.go b/src/runtime/stack_test.go
new file mode 100644
index 0000000..43fc5ca
--- /dev/null
+++ b/src/runtime/stack_test.go
@@ -0,0 +1,894 @@
+// Copyright 2012 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_test
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"reflect"
+	"regexp"
+	. "runtime"
+	"strconv"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+	_ "unsafe" // for go:linkname
+)
+
+// TestStackMem measures per-thread stack segment cache behavior.
+// The test consumed up to 500MB in the past.
+func TestStackMem(t *testing.T) {
+	const (
+		BatchSize      = 32
+		BatchCount     = 256
+		ArraySize      = 1024
+		RecursionDepth = 128
+	)
+	if testing.Short() {
+		return
+	}
+	defer GOMAXPROCS(GOMAXPROCS(BatchSize))
+	s0 := new(MemStats)
+	ReadMemStats(s0)
+	for b := 0; b < BatchCount; b++ {
+		c := make(chan bool, BatchSize)
+		for i := 0; i < BatchSize; i++ {
+			go func() {
+				var f func(k int, a [ArraySize]byte)
+				f = func(k int, a [ArraySize]byte) {
+					if k == 0 {
+						time.Sleep(time.Millisecond)
+						return
+					}
+					f(k-1, a)
+				}
+				f(RecursionDepth, [ArraySize]byte{})
+				c <- true
+			}()
+		}
+		for i := 0; i < BatchSize; i++ {
+			<-c
+		}
+
+		// The goroutines have signaled via c that they are ready to exit.
+		// Give them a chance to exit by sleeping. If we don't wait, we
+		// might not reuse them on the next batch.
+		time.Sleep(10 * time.Millisecond)
+	}
+	s1 := new(MemStats)
+	ReadMemStats(s1)
+	consumed := int64(s1.StackSys - s0.StackSys)
+	t.Logf("Consumed %vMB for stack mem", consumed>>20)
+	estimate := int64(8 * BatchSize * ArraySize * RecursionDepth) // 8 is to reduce flakiness.
+	if consumed > estimate {
+		t.Fatalf("Stack mem: want %v, got %v", estimate, consumed)
+	}
+	// Due to broken stack memory accounting (https://golang.org/issue/7468),
+	// StackInuse can decrease during function execution, so we cast the values to int64.
+	inuse := int64(s1.StackInuse) - int64(s0.StackInuse)
+	t.Logf("Inuse %vMB for stack mem", inuse>>20)
+	if inuse > 4<<20 {
+		t.Fatalf("Stack inuse: want %v, got %v", 4<<20, inuse)
+	}
+}
+
+// Test stack growing in different contexts.
+func TestStackGrowth(t *testing.T) {
+	if *flagQuick {
+		t.Skip("-quick")
+	}
+
+	if GOARCH == "wasm" {
+		t.Skip("fails on wasm (too slow?)")
+	}
+
+	// Don't make this test parallel as this makes the 20 second
+	// timeout unreliable on slow builders. (See issue #19381.)
+
+	var wg sync.WaitGroup
+
+	// in a normal goroutine
+	var growDuration time.Duration // For debugging failures
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		start := time.Now()
+		growStack(nil)
+		growDuration = time.Since(start)
+	}()
+	wg.Wait()
+
+	// in locked goroutine
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		LockOSThread()
+		growStack(nil)
+		UnlockOSThread()
+	}()
+	wg.Wait()
+
+	// in finalizer
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		done := make(chan bool)
+		var startTime time.Time
+		var started, progress uint32
+		go func() {
+			s := new(string)
+			SetFinalizer(s, func(ss *string) {
+				startTime = time.Now()
+				atomic.StoreUint32(&started, 1)
+				growStack(&progress)
+				done <- true
+			})
+			s = nil
+			done <- true
+		}()
+		<-done
+		GC()
+
+		timeout := 20 * time.Second
+		if s := os.Getenv("GO_TEST_TIMEOUT_SCALE"); s != "" {
+			scale, err := strconv.Atoi(s)
+			if err == nil {
+				timeout *= time.Duration(scale)
+			}
+		}
+
+		select {
+		case <-done:
+		case <-time.After(timeout):
+			if atomic.LoadUint32(&started) == 0 {
+				t.Log("finalizer did not start")
+			} else {
+				t.Logf("finalizer started %s ago and finished %d iterations", time.Since(startTime), atomic.LoadUint32(&progress))
+			}
+			t.Log("first growStack took", growDuration)
+			t.Error("finalizer did not run")
+			return
+		}
+	}()
+	wg.Wait()
+}
+
+// ... and in init
+//func init() {
+//	growStack()
+//}
+
+func growStack(progress *uint32) {
+	n := 1 << 10
+	if testing.Short() {
+		n = 1 << 8
+	}
+	for i := 0; i < n; i++ {
+		x := 0
+		growStackIter(&x, i)
+		if x != i+1 {
+			panic("stack is corrupted")
+		}
+		if progress != nil {
+			atomic.StoreUint32(progress, uint32(i))
+		}
+	}
+	GC()
+}
+
+// This function is not an anonymous func, so that the compiler can do escape
+// analysis and place x on stack (and subsequently stack growth update the pointer).
+func growStackIter(p *int, n int) {
+	if n == 0 {
+		*p = n + 1
+		GC()
+		return
+	}
+	*p = n + 1
+	x := 0
+	growStackIter(&x, n-1)
+	if x != n {
+		panic("stack is corrupted")
+	}
+}
+
+func TestStackGrowthCallback(t *testing.T) {
+	t.Parallel()
+	var wg sync.WaitGroup
+
+	// test stack growth at chan op
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		c := make(chan int, 1)
+		growStackWithCallback(func() {
+			c <- 1
+			<-c
+		})
+	}()
+
+	// test stack growth at map op
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		m := make(map[int]int)
+		growStackWithCallback(func() {
+			_, _ = m[1]
+			m[1] = 1
+		})
+	}()
+
+	// test stack growth at goroutine creation
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		growStackWithCallback(func() {
+			done := make(chan bool)
+			go func() {
+				done <- true
+			}()
+			<-done
+		})
+	}()
+	wg.Wait()
+}
+
+func growStackWithCallback(cb func()) {
+	var f func(n int)
+	f = func(n int) {
+		if n == 0 {
+			cb()
+			return
+		}
+		f(n - 1)
+	}
+	for i := 0; i < 1<<10; i++ {
+		f(i)
+	}
+}
+
+// TestDeferPtrs tests the adjustment of Defer's argument pointers (p aka &y)
+// during a stack copy.
+func set(p *int, x int) {
+	*p = x
+}
+func TestDeferPtrs(t *testing.T) {
+	var y int
+
+	defer func() {
+		if y != 42 {
+			t.Errorf("defer's stack references were not adjusted appropriately")
+		}
+	}()
+	defer set(&y, 42)
+	growStack(nil)
+}
+
+type bigBuf [4 * 1024]byte
+
+// TestDeferPtrsGoexit is like TestDeferPtrs but exercises the possibility that the
+// stack grows as part of starting the deferred function. It calls Goexit at various
+// stack depths, forcing the deferred function (with >4kB of args) to be run at
+// the bottom of the stack. The goal is to find a stack depth less than 4kB from
+// the end of the stack. Each trial runs in a different goroutine so that an earlier
+// stack growth does not invalidate a later attempt.
+func TestDeferPtrsGoexit(t *testing.T) {
+	for i := 0; i < 100; i++ {
+		c := make(chan int, 1)
+		go testDeferPtrsGoexit(c, i)
+		if n := <-c; n != 42 {
+			t.Fatalf("defer's stack references were not adjusted appropriately (i=%d n=%d)", i, n)
+		}
+	}
+}
+
+func testDeferPtrsGoexit(c chan int, i int) {
+	var y int
+	defer func() {
+		c <- y
+	}()
+	defer setBig(&y, 42, bigBuf{})
+	useStackAndCall(i, Goexit)
+}
+
+func setBig(p *int, x int, b bigBuf) {
+	*p = x
+}
+
+// TestDeferPtrsPanic is like TestDeferPtrsGoexit, but it's using panic instead
+// of Goexit to run the Defers. Those two are different execution paths
+// in the runtime.
+func TestDeferPtrsPanic(t *testing.T) {
+	for i := 0; i < 100; i++ {
+		c := make(chan int, 1)
+		go testDeferPtrsGoexit(c, i)
+		if n := <-c; n != 42 {
+			t.Fatalf("defer's stack references were not adjusted appropriately (i=%d n=%d)", i, n)
+		}
+	}
+}
+
+func testDeferPtrsPanic(c chan int, i int) {
+	var y int
+	defer func() {
+		if recover() == nil {
+			c <- -1
+			return
+		}
+		c <- y
+	}()
+	defer setBig(&y, 42, bigBuf{})
+	useStackAndCall(i, func() { panic(1) })
+}
+
+//go:noinline
+func testDeferLeafSigpanic1() {
+	// Cause a sigpanic to be injected in this frame.
+	//
+	// This function has to be declared before
+	// TestDeferLeafSigpanic so the runtime will crash if we think
+	// this function's continuation PC is in
+	// TestDeferLeafSigpanic.
+	*(*int)(nil) = 0
+}
+
+// TestDeferLeafSigpanic tests defer matching around leaf functions
+// that sigpanic. This is tricky because on LR machines the outer
+// function and the inner function have the same SP, but it's critical
+// that we match up the defer correctly to get the right liveness map.
+// See issue #25499.
+func TestDeferLeafSigpanic(t *testing.T) {
+	// Push a defer that will walk the stack.
+	defer func() {
+		if err := recover(); err == nil {
+			t.Fatal("expected panic from nil pointer")
+		}
+		GC()
+	}()
+	// Call a leaf function. We must set up the exact call stack:
+	//
+	//  defering function -> leaf function -> sigpanic
+	//
+	// On LR machines, the leaf function will have the same SP as
+	// the SP pushed for the defer frame.
+	testDeferLeafSigpanic1()
+}
+
+// TestPanicUseStack checks that a chain of Panic structs on the stack are
+// updated correctly if the stack grows during the deferred execution that
+// happens as a result of the panic.
+func TestPanicUseStack(t *testing.T) {
+	pc := make([]uintptr, 10000)
+	defer func() {
+		recover()
+		Callers(0, pc) // force stack walk
+		useStackAndCall(100, func() {
+			defer func() {
+				recover()
+				Callers(0, pc) // force stack walk
+				useStackAndCall(200, func() {
+					defer func() {
+						recover()
+						Callers(0, pc) // force stack walk
+					}()
+					panic(3)
+				})
+			}()
+			panic(2)
+		})
+	}()
+	panic(1)
+}
+
+func TestPanicFar(t *testing.T) {
+	var xtree *xtreeNode
+	pc := make([]uintptr, 10000)
+	defer func() {
+		// At this point we created a large stack and unwound
+		// it via recovery. Force a stack walk, which will
+		// check the stack's consistency.
+		Callers(0, pc)
+	}()
+	defer func() {
+		recover()
+	}()
+	useStackAndCall(100, func() {
+		// Kick off the GC and make it do something nontrivial.
+		// (This used to force stack barriers to stick around.)
+		xtree = makeTree(18)
+		// Give the GC time to start scanning stacks.
+		time.Sleep(time.Millisecond)
+		panic(1)
+	})
+	_ = xtree
+}
+
+type xtreeNode struct {
+	l, r *xtreeNode
+}
+
+func makeTree(d int) *xtreeNode {
+	if d == 0 {
+		return new(xtreeNode)
+	}
+	return &xtreeNode{makeTree(d - 1), makeTree(d - 1)}
+}
+
+// use about n KB of stack and call f
+func useStackAndCall(n int, f func()) {
+	if n == 0 {
+		f()
+		return
+	}
+	var b [1024]byte // makes frame about 1KB
+	useStackAndCall(n-1+int(b[99]), f)
+}
+
+func useStack(n int) {
+	useStackAndCall(n, func() {})
+}
+
+func growing(c chan int, done chan struct{}) {
+	for n := range c {
+		useStack(n)
+		done <- struct{}{}
+	}
+	done <- struct{}{}
+}
+
+func TestStackCache(t *testing.T) {
+	// Allocate a bunch of goroutines and grow their stacks.
+	// Repeat a few times to test the stack cache.
+	const (
+		R = 4
+		G = 200
+		S = 5
+	)
+	for i := 0; i < R; i++ {
+		var reqchans [G]chan int
+		done := make(chan struct{})
+		for j := 0; j < G; j++ {
+			reqchans[j] = make(chan int)
+			go growing(reqchans[j], done)
+		}
+		for s := 0; s < S; s++ {
+			for j := 0; j < G; j++ {
+				reqchans[j] <- 1 << uint(s)
+			}
+			for j := 0; j < G; j++ {
+				<-done
+			}
+		}
+		for j := 0; j < G; j++ {
+			close(reqchans[j])
+		}
+		for j := 0; j < G; j++ {
+			<-done
+		}
+	}
+}
+
+func TestStackOutput(t *testing.T) {
+	b := make([]byte, 1024)
+	stk := string(b[:Stack(b, false)])
+	if !strings.HasPrefix(stk, "goroutine ") {
+		t.Errorf("Stack (len %d):\n%s", len(stk), stk)
+		t.Errorf("Stack output should begin with \"goroutine \"")
+	}
+}
+
+func TestStackAllOutput(t *testing.T) {
+	b := make([]byte, 1024)
+	stk := string(b[:Stack(b, true)])
+	if !strings.HasPrefix(stk, "goroutine ") {
+		t.Errorf("Stack (len %d):\n%s", len(stk), stk)
+		t.Errorf("Stack output should begin with \"goroutine \"")
+	}
+}
+
+func TestStackPanic(t *testing.T) {
+	// Test that stack copying copies panics correctly. This is difficult
+	// to test because it is very unlikely that the stack will be copied
+	// in the middle of gopanic. But it can happen.
+	// To make this test effective, edit panic.go:gopanic and uncomment
+	// the GC() call just before freedefer(d).
+	defer func() {
+		if x := recover(); x == nil {
+			t.Errorf("recover failed")
+		}
+	}()
+	useStack(32)
+	panic("test panic")
+}
+
+func BenchmarkStackCopyPtr(b *testing.B) {
+	c := make(chan bool)
+	for i := 0; i < b.N; i++ {
+		go func() {
+			i := 1000000
+			countp(&i)
+			c <- true
+		}()
+		<-c
+	}
+}
+
+func countp(n *int) {
+	if *n == 0 {
+		return
+	}
+	*n--
+	countp(n)
+}
+
+func BenchmarkStackCopy(b *testing.B) {
+	c := make(chan bool)
+	for i := 0; i < b.N; i++ {
+		go func() {
+			count(1000000)
+			c <- true
+		}()
+		<-c
+	}
+}
+
+func count(n int) int {
+	if n == 0 {
+		return 0
+	}
+	return 1 + count(n-1)
+}
+
+func BenchmarkStackCopyNoCache(b *testing.B) {
+	c := make(chan bool)
+	for i := 0; i < b.N; i++ {
+		go func() {
+			count1(1000000)
+			c <- true
+		}()
+		<-c
+	}
+}
+
+func count1(n int) int {
+	if n <= 0 {
+		return 0
+	}
+	return 1 + count2(n-1)
+}
+
+func count2(n int) int  { return 1 + count3(n-1) }
+func count3(n int) int  { return 1 + count4(n-1) }
+func count4(n int) int  { return 1 + count5(n-1) }
+func count5(n int) int  { return 1 + count6(n-1) }
+func count6(n int) int  { return 1 + count7(n-1) }
+func count7(n int) int  { return 1 + count8(n-1) }
+func count8(n int) int  { return 1 + count9(n-1) }
+func count9(n int) int  { return 1 + count10(n-1) }
+func count10(n int) int { return 1 + count11(n-1) }
+func count11(n int) int { return 1 + count12(n-1) }
+func count12(n int) int { return 1 + count13(n-1) }
+func count13(n int) int { return 1 + count14(n-1) }
+func count14(n int) int { return 1 + count15(n-1) }
+func count15(n int) int { return 1 + count16(n-1) }
+func count16(n int) int { return 1 + count17(n-1) }
+func count17(n int) int { return 1 + count18(n-1) }
+func count18(n int) int { return 1 + count19(n-1) }
+func count19(n int) int { return 1 + count20(n-1) }
+func count20(n int) int { return 1 + count21(n-1) }
+func count21(n int) int { return 1 + count22(n-1) }
+func count22(n int) int { return 1 + count23(n-1) }
+func count23(n int) int { return 1 + count1(n-1) }
+
+type structWithMethod struct{}
+
+func (s structWithMethod) caller() string {
+	_, file, line, ok := Caller(1)
+	if !ok {
+		panic("Caller failed")
+	}
+	return fmt.Sprintf("%s:%d", file, line)
+}
+
+func (s structWithMethod) callers() []uintptr {
+	pc := make([]uintptr, 16)
+	return pc[:Callers(0, pc)]
+}
+
+func (s structWithMethod) stack() string {
+	buf := make([]byte, 4<<10)
+	return string(buf[:Stack(buf, false)])
+}
+
+func (s structWithMethod) nop() {}
+
+func TestStackWrapperCaller(t *testing.T) {
+	var d structWithMethod
+	// Force the compiler to construct a wrapper method.
+	wrapper := (*structWithMethod).caller
+	// Check that the wrapper doesn't affect the stack trace.
+	if dc, ic := d.caller(), wrapper(&d); dc != ic {
+		t.Fatalf("direct caller %q != indirect caller %q", dc, ic)
+	}
+}
+
+func TestStackWrapperCallers(t *testing.T) {
+	var d structWithMethod
+	wrapper := (*structWithMethod).callers
+	// Check that <autogenerated> doesn't appear in the stack trace.
+	pcs := wrapper(&d)
+	frames := CallersFrames(pcs)
+	for {
+		fr, more := frames.Next()
+		if fr.File == "<autogenerated>" {
+			t.Fatalf("<autogenerated> appears in stack trace: %+v", fr)
+		}
+		if !more {
+			break
+		}
+	}
+}
+
+func TestStackWrapperStack(t *testing.T) {
+	var d structWithMethod
+	wrapper := (*structWithMethod).stack
+	// Check that <autogenerated> doesn't appear in the stack trace.
+	stk := wrapper(&d)
+	if strings.Contains(stk, "<autogenerated>") {
+		t.Fatalf("<autogenerated> appears in stack trace:\n%s", stk)
+	}
+}
+
+type I interface {
+	M()
+}
+
+func TestStackWrapperStackPanic(t *testing.T) {
+	t.Run("sigpanic", func(t *testing.T) {
+		// nil calls to interface methods cause a sigpanic.
+		testStackWrapperPanic(t, func() { I.M(nil) }, "runtime_test.I.M")
+	})
+	t.Run("panicwrap", func(t *testing.T) {
+		// Nil calls to value method wrappers call panicwrap.
+		wrapper := (*structWithMethod).nop
+		testStackWrapperPanic(t, func() { wrapper(nil) }, "runtime_test.(*structWithMethod).nop")
+	})
+}
+
+func testStackWrapperPanic(t *testing.T, cb func(), expect string) {
+	// Test that the stack trace from a panicking wrapper includes
+	// the wrapper, even though elide these when they don't panic.
+	t.Run("CallersFrames", func(t *testing.T) {
+		defer func() {
+			err := recover()
+			if err == nil {
+				t.Fatalf("expected panic")
+			}
+			pcs := make([]uintptr, 10)
+			n := Callers(0, pcs)
+			frames := CallersFrames(pcs[:n])
+			for {
+				frame, more := frames.Next()
+				t.Log(frame.Function)
+				if frame.Function == expect {
+					return
+				}
+				if !more {
+					break
+				}
+			}
+			t.Fatalf("panicking wrapper %s missing from stack trace", expect)
+		}()
+		cb()
+	})
+	t.Run("Stack", func(t *testing.T) {
+		defer func() {
+			err := recover()
+			if err == nil {
+				t.Fatalf("expected panic")
+			}
+			buf := make([]byte, 4<<10)
+			stk := string(buf[:Stack(buf, false)])
+			if !strings.Contains(stk, "\n"+expect) {
+				t.Fatalf("panicking wrapper %s missing from stack trace:\n%s", expect, stk)
+			}
+		}()
+		cb()
+	})
+}
+
+func TestCallersFromWrapper(t *testing.T) {
+	// Test that invoking CallersFrames on a stack where the first
+	// PC is an autogenerated wrapper keeps the wrapper in the
+	// trace. Normally we elide these, assuming that the wrapper
+	// calls the thing you actually wanted to see, but in this
+	// case we need to keep it.
+	pc := reflect.ValueOf(I.M).Pointer()
+	frames := CallersFrames([]uintptr{pc})
+	frame, more := frames.Next()
+	if frame.Function != "runtime_test.I.M" {
+		t.Fatalf("want function %s, got %s", "runtime_test.I.M", frame.Function)
+	}
+	if more {
+		t.Fatalf("want 1 frame, got > 1")
+	}
+}
+
+func TestTracebackSystemstack(t *testing.T) {
+	if GOARCH == "ppc64" || GOARCH == "ppc64le" {
+		t.Skip("systemstack tail call not implemented on ppc64x")
+	}
+
+	// Test that profiles correctly jump over systemstack,
+	// including nested systemstack calls.
+	pcs := make([]uintptr, 20)
+	pcs = pcs[:TracebackSystemstack(pcs, 5)]
+	// Check that runtime.TracebackSystemstack appears five times
+	// and that we see TestTracebackSystemstack.
+	countIn, countOut := 0, 0
+	frames := CallersFrames(pcs)
+	var tb bytes.Buffer
+	for {
+		frame, more := frames.Next()
+		fmt.Fprintf(&tb, "\n%s+0x%x %s:%d", frame.Function, frame.PC-frame.Entry, frame.File, frame.Line)
+		switch frame.Function {
+		case "runtime.TracebackSystemstack":
+			countIn++
+		case "runtime_test.TestTracebackSystemstack":
+			countOut++
+		}
+		if !more {
+			break
+		}
+	}
+	if countIn != 5 || countOut != 1 {
+		t.Fatalf("expected 5 calls to TracebackSystemstack and 1 call to TestTracebackSystemstack, got:%s", tb.String())
+	}
+}
+
+func TestTracebackAncestors(t *testing.T) {
+	goroutineRegex := regexp.MustCompile(`goroutine [0-9]+ \[`)
+	for _, tracebackDepth := range []int{0, 1, 5, 50} {
+		output := runTestProg(t, "testprog", "TracebackAncestors", fmt.Sprintf("GODEBUG=tracebackancestors=%d", tracebackDepth))
+
+		numGoroutines := 3
+		numFrames := 2
+		ancestorsExpected := numGoroutines
+		if numGoroutines > tracebackDepth {
+			ancestorsExpected = tracebackDepth
+		}
+
+		matches := goroutineRegex.FindAllStringSubmatch(output, -1)
+		if len(matches) != 2 {
+			t.Fatalf("want 2 goroutines, got:\n%s", output)
+		}
+
+		// Check functions in the traceback.
+		fns := []string{"main.recurseThenCallGo", "main.main", "main.printStack", "main.TracebackAncestors"}
+		for _, fn := range fns {
+			if !strings.Contains(output, "\n"+fn+"(") {
+				t.Fatalf("expected %q function in traceback:\n%s", fn, output)
+			}
+		}
+
+		if want, count := "originating from goroutine", ancestorsExpected; strings.Count(output, want) != count {
+			t.Errorf("output does not contain %d instances of %q:\n%s", count, want, output)
+		}
+
+		if want, count := "main.recurseThenCallGo(...)", ancestorsExpected*(numFrames+1); strings.Count(output, want) != count {
+			t.Errorf("output does not contain %d instances of %q:\n%s", count, want, output)
+		}
+
+		if want, count := "main.recurseThenCallGo(0x", 1; strings.Count(output, want) != count {
+			t.Errorf("output does not contain %d instances of %q:\n%s", count, want, output)
+		}
+	}
+}
+
+// Test that defer closure is correctly scanned when the stack is scanned.
+func TestDeferLiveness(t *testing.T) {
+	output := runTestProg(t, "testprog", "DeferLiveness", "GODEBUG=clobberfree=1")
+	if output != "" {
+		t.Errorf("output:\n%s\n\nwant no output", output)
+	}
+}
+
+func TestDeferHeapAndStack(t *testing.T) {
+	P := 4     // processors
+	N := 10000 //iterations
+	D := 200   // stack depth
+
+	if testing.Short() {
+		P /= 2
+		N /= 10
+		D /= 10
+	}
+	c := make(chan bool)
+	for p := 0; p < P; p++ {
+		go func() {
+			for i := 0; i < N; i++ {
+				if deferHeapAndStack(D) != 2*D {
+					panic("bad result")
+				}
+			}
+			c <- true
+		}()
+	}
+	for p := 0; p < P; p++ {
+		<-c
+	}
+}
+
+// deferHeapAndStack(n) computes 2*n
+func deferHeapAndStack(n int) (r int) {
+	if n == 0 {
+		return 0
+	}
+	if n%2 == 0 {
+		// heap-allocated defers
+		for i := 0; i < 2; i++ {
+			defer func() {
+				r++
+			}()
+		}
+	} else {
+		// stack-allocated defers
+		defer func() {
+			r++
+		}()
+		defer func() {
+			r++
+		}()
+	}
+	r = deferHeapAndStack(n - 1)
+	escapeMe(new([1024]byte)) // force some GCs
+	return
+}
+
+// Pass a value to escapeMe to force it to escape.
+var escapeMe = func(x interface{}) {}
+
+// Test that when F -> G is inlined and F is excluded from stack
+// traces, G still appears.
+func TestTracebackInlineExcluded(t *testing.T) {
+	defer func() {
+		recover()
+		buf := make([]byte, 4<<10)
+		stk := string(buf[:Stack(buf, false)])
+
+		t.Log(stk)
+
+		if not := "tracebackExcluded"; strings.Contains(stk, not) {
+			t.Errorf("found but did not expect %q", not)
+		}
+		if want := "tracebackNotExcluded"; !strings.Contains(stk, want) {
+			t.Errorf("expected %q in stack", want)
+		}
+	}()
+	tracebackExcluded()
+}
+
+// tracebackExcluded should be excluded from tracebacks. There are
+// various ways this could come up. Linking it to a "runtime." name is
+// rather synthetic, but it's easy and reliable. See issue #42754 for
+// one way this happened in real code.
+//
+//go:linkname tracebackExcluded runtime.tracebackExcluded
+//go:noinline
+func tracebackExcluded() {
+	// Call an inlined function that should not itself be excluded
+	// from tracebacks.
+	tracebackNotExcluded()
+}
+
+// tracebackNotExcluded should be inlined into tracebackExcluded, but
+// should not itself be excluded from the traceback.
+func tracebackNotExcluded() {
+	var x *int
+	*x = 0
+}