libgo: update to Go1.18rc1 release

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/386594

23 files changed, 718 insertions, 280 deletions

diff --git a/libgo/go/runtime/crash_cgo_test.go b/libgo/go/runtime/crash_cgo_test.go
index 615892d..7344a93 100644
--- a/libgo/go/runtime/crash_cgo_test.go
+++ b/libgo/go/runtime/crash_cgo_test.go
@@ -216,6 +216,19 @@ func TestCgoCCodeSIGPROF(t *testing.T) {
 	}
 }
 
+func TestCgoPprofCallback(t *testing.T) {
+	t.Parallel()
+	switch runtime.GOOS {
+	case "windows", "plan9":
+		t.Skipf("skipping cgo pprof callback test on %s", runtime.GOOS)
+	}
+	got := runTestProg(t, "testprogcgo", "CgoPprofCallback")
+	want := "OK\n"
+	if got != want {
+		t.Errorf("expected %q got %v", want, got)
+	}
+}
+
 func TestCgoCrashTraceback(t *testing.T) {
 	t.Parallel()
 	switch platform := runtime.GOOS + "/" + runtime.GOARCH; platform {
@@ -614,6 +627,9 @@ func TestSegv(t *testing.T) {
 			t.Log(got)
 			want := "SIGSEGV"
 			if !strings.Contains(got, want) {
+				if runtime.GOOS == "darwin" && runtime.GOARCH == "amd64" && strings.Contains(got, "fatal: morestack on g0") {
+					testenv.SkipFlaky(t, 39457)
+				}
 				t.Errorf("did not see %q in output", want)
 			}
 
@@ -628,13 +644,11 @@ func TestSegv(t *testing.T) {
 					// a VDSO call via asmcgocall.
 					testenv.SkipFlaky(t, 50504)
 				}
-				if testenv.Builder() == "linux-mips64le-mengzhuo" && strings.Contains(got, "runtime: unknown pc") {
-					// Runtime sometimes throw "unknown pc" when generating the traceback.
-					// Curiously, that doesn't seem to happen on the linux-mips64le-rtrk
-					// builder.
-					testenv.SkipFlaky(t, 50605)
-				}
 			}
+			if test == "SegvInCgo" && strings.Contains(got, "runtime: unknown pc") {
+				testenv.SkipFlaky(t, 50979)
+			}
+
 			nowant := "runtime: "
 			if strings.Contains(got, nowant) {
 				t.Errorf("unexpectedly saw %q in output", nowant)
diff --git a/libgo/go/runtime/crash_unix_test.go b/libgo/go/runtime/crash_unix_test.go
index b7ca811..ab94aff 100644
--- a/libgo/go/runtime/crash_unix_test.go
+++ b/libgo/go/runtime/crash_unix_test.go
@@ -132,7 +132,7 @@ func TestCrashDumpsAllThreads(t *testing.T) {
 	out := outbuf.Bytes()
 	n := bytes.Count(out, []byte("main.crashDumpsAllThreadsLoop"))
 	if n != 4 {
-		t.Errorf("found %d instances of main.loop; expected 4", n)
+		t.Errorf("found %d instances of main.crashDumpsAllThreadsLoop; expected 4", n)
 		t.Logf("%s", out)
 	}
 }
diff --git a/libgo/go/runtime/debug/mod.go b/libgo/go/runtime/debug/mod.go
index 61b15ad..5184a02 100644
--- a/libgo/go/runtime/debug/mod.go
+++ b/libgo/go/runtime/debug/mod.go
@@ -5,9 +5,9 @@
 package debug
 
 import (
-	"bytes"
 	"fmt"
 	"runtime"
+	"strconv"
 	"strings"
 	_ "unsafe" // for go:linkname
 )
@@ -24,8 +24,8 @@ func ReadBuildInfo() (info *BuildInfo, ok bool) {
 		return nil, false
 	}
 	data = data[16 : len(data)-16]
-	bi := &BuildInfo{}
-	if err := bi.UnmarshalText([]byte(data)); err != nil {
+	bi, err := ParseBuildInfo(data)
+	if err != nil {
 		return nil, false
 	}
 
@@ -64,8 +64,18 @@ type BuildSetting struct {
 	Key, Value string
 }
 
-func (bi *BuildInfo) MarshalText() ([]byte, error) {
-	buf := &bytes.Buffer{}
+// quoteKey reports whether key is required to be quoted.
+func quoteKey(key string) bool {
+	return len(key) == 0 || strings.ContainsAny(key, "= \t\r\n\"`")
+}
+
+// quoteValue reports whether value is required to be quoted.
+func quoteValue(value string) bool {
+	return strings.ContainsAny(value, " \t\r\n\"`")
+}
+
+func (bi *BuildInfo) String() string {
+	buf := new(strings.Builder)
 	if bi.GoVersion != "" {
 		fmt.Fprintf(buf, "go\t%s\n", bi.GoVersion)
 	}
@@ -77,12 +87,8 @@ func (bi *BuildInfo) MarshalText() ([]byte, error) {
 		buf.WriteString(word)
 		buf.WriteByte('\t')
 		buf.WriteString(m.Path)
-		mv := m.Version
-		if mv == "" {
-			mv = "(devel)"
-		}
 		buf.WriteByte('\t')
-		buf.WriteString(mv)
+		buf.WriteString(m.Version)
 		if m.Replace == nil {
 			buf.WriteByte('\t')
 			buf.WriteString(m.Sum)
@@ -92,27 +98,28 @@ func (bi *BuildInfo) MarshalText() ([]byte, error) {
 		}
 		buf.WriteByte('\n')
 	}
-	if bi.Main.Path != "" {
+	if bi.Main != (Module{}) {
 		formatMod("mod", bi.Main)
 	}
 	for _, dep := range bi.Deps {
 		formatMod("dep", *dep)
 	}
 	for _, s := range bi.Settings {
-		if strings.ContainsAny(s.Key, "= \t\n") {
-			return nil, fmt.Errorf("invalid build setting key %q", s.Key)
+		key := s.Key
+		if quoteKey(key) {
+			key = strconv.Quote(key)
 		}
-		if strings.Contains(s.Value, "\n") {
-			return nil, fmt.Errorf("invalid build setting value for key %q: contains newline", s.Value)
+		value := s.Value
+		if quoteValue(value) {
+			value = strconv.Quote(value)
 		}
-		fmt.Fprintf(buf, "build\t%s=%s\n", s.Key, s.Value)
+		fmt.Fprintf(buf, "build\t%s=%s\n", key, value)
 	}
 
-	return buf.Bytes(), nil
+	return buf.String()
 }
 
-func (bi *BuildInfo) UnmarshalText(data []byte) (err error) {
-	*bi = BuildInfo{}
+func ParseBuildInfo(data string) (bi *BuildInfo, err error) {
 	lineNum := 1
 	defer func() {
 		if err != nil {
@@ -121,67 +128,69 @@ func (bi *BuildInfo) UnmarshalText(data []byte) (err error) {
 	}()
 
 	var (
-		pathLine  = []byte("path\t")
-		modLine   = []byte("mod\t")
-		depLine   = []byte("dep\t")
-		repLine   = []byte("=>\t")
-		buildLine = []byte("build\t")
-		newline   = []byte("\n")
-		tab       = []byte("\t")
+		pathLine  = "path\t"
+		modLine   = "mod\t"
+		depLine   = "dep\t"
+		repLine   = "=>\t"
+		buildLine = "build\t"
+		newline   = "\n"
+		tab       = "\t"
 	)
 
-	readModuleLine := func(elem [][]byte) (Module, error) {
+	readModuleLine := func(elem []string) (Module, error) {
 		if len(elem) != 2 && len(elem) != 3 {
 			return Module{}, fmt.Errorf("expected 2 or 3 columns; got %d", len(elem))
 		}
+		version := elem[1]
 		sum := ""
 		if len(elem) == 3 {
-			sum = string(elem[2])
+			sum = elem[2]
 		}
 		return Module{
-			Path:    string(elem[0]),
-			Version: string(elem[1]),
+			Path:    elem[0],
+			Version: version,
 			Sum:     sum,
 		}, nil
 	}
 
+	bi = new(BuildInfo)
 	var (
 		last *Module
-		line []byte
+		line string
 		ok   bool
 	)
 	// Reverse of BuildInfo.String(), except for go version.
 	for len(data) > 0 {
-		line, data, ok = bytes.Cut(data, newline)
+		line, data, ok = strings.Cut(data, newline)
 		if !ok {
 			break
 		}
 		switch {
-		case bytes.HasPrefix(line, pathLine):
+		case strings.HasPrefix(line, pathLine):
 			elem := line[len(pathLine):]
 			bi.Path = string(elem)
-		case bytes.HasPrefix(line, modLine):
-			elem := bytes.Split(line[len(modLine):], tab)
+		case strings.HasPrefix(line, modLine):
+			elem := strings.Split(line[len(modLine):], tab)
 			last = &bi.Main
 			*last, err = readModuleLine(elem)
 			if err != nil {
-				return err
+				return nil, err
 			}
-		case bytes.HasPrefix(line, depLine):
-			elem := bytes.Split(line[len(depLine):], tab)
+		case strings.HasPrefix(line, depLine):
+			elem := strings.Split(line[len(depLine):], tab)
 			last = new(Module)
 			bi.Deps = append(bi.Deps, last)
 			*last, err = readModuleLine(elem)
 			if err != nil {
-				return err
+				return nil, err
 			}
-		case bytes.HasPrefix(line, repLine):
-			elem := bytes.Split(line[len(repLine):], tab)
+		case strings.HasPrefix(line, repLine):
+			elem := strings.Split(line[len(repLine):], tab)
 			if len(elem) != 3 {
-				return fmt.Errorf("expected 3 columns for replacement; got %d", len(elem))
+				return nil, fmt.Errorf("expected 3 columns for replacement; got %d", len(elem))
 			}
 			if last == nil {
-				return fmt.Errorf("replacement with no module on previous line")
+				return nil, fmt.Errorf("replacement with no module on previous line")
 			}
 			last.Replace = &Module{
 				Path:    string(elem[0]),
@@ -189,17 +198,63 @@ func (bi *BuildInfo) UnmarshalText(data []byte) (err error) {
 				Sum:     string(elem[2]),
 			}
 			last = nil
-		case bytes.HasPrefix(line, buildLine):
-			key, val, ok := strings.Cut(string(line[len(buildLine):]), "=")
-			if !ok {
-				return fmt.Errorf("invalid build line")
+		case strings.HasPrefix(line, buildLine):
+			kv := line[len(buildLine):]
+			if len(kv) < 1 {
+				return nil, fmt.Errorf("build line missing '='")
+			}
+
+			var key, rawValue string
+			switch kv[0] {
+			case '=':
+				return nil, fmt.Errorf("build line with missing key")
+
+			case '`', '"':
+				rawKey, err := strconv.QuotedPrefix(kv)
+				if err != nil {
+					return nil, fmt.Errorf("invalid quoted key in build line")
+				}
+				if len(kv) == len(rawKey) {
+					return nil, fmt.Errorf("build line missing '=' after quoted key")
+				}
+				if c := kv[len(rawKey)]; c != '=' {
+					return nil, fmt.Errorf("unexpected character after quoted key: %q", c)
+				}
+				key, _ = strconv.Unquote(rawKey)
+				rawValue = kv[len(rawKey)+1:]
+
+			default:
+				var ok bool
+				key, rawValue, ok = strings.Cut(kv, "=")
+				if !ok {
+					return nil, fmt.Errorf("build line missing '=' after key")
+				}
+				if quoteKey(key) {
+					return nil, fmt.Errorf("unquoted key %q must be quoted", key)
+				}
 			}
-			if key == "" {
-				return fmt.Errorf("empty key")
+
+			var value string
+			if len(rawValue) > 0 {
+				switch rawValue[0] {
+				case '`', '"':
+					var err error
+					value, err = strconv.Unquote(rawValue)
+					if err != nil {
+						return nil, fmt.Errorf("invalid quoted value in build line")
+					}
+
+				default:
+					value = rawValue
+					if quoteValue(value) {
+						return nil, fmt.Errorf("unquoted value %q must be quoted", value)
+					}
+				}
 			}
-			bi.Settings = append(bi.Settings, BuildSetting{Key: key, Value: val})
+
+			bi.Settings = append(bi.Settings, BuildSetting{Key: key, Value: value})
 		}
 		lineNum++
 	}
-	return nil
+	return bi, nil
 }
diff --git a/libgo/go/runtime/debug/mod_test.go b/libgo/go/runtime/debug/mod_test.go
new file mode 100644
index 0000000..b291769
--- /dev/null
+++ b/libgo/go/runtime/debug/mod_test.go
@@ -0,0 +1,75 @@
+// Copyright 2022 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 debug_test
+
+import (
+	"reflect"
+	"runtime/debug"
+	"strings"
+	"testing"
+)
+
+// strip removes two leading tabs after each newline of s.
+func strip(s string) string {
+	replaced := strings.ReplaceAll(s, "\n\t\t", "\n")
+	if len(replaced) > 0 && replaced[0] == '\n' {
+		replaced = replaced[1:]
+	}
+	return replaced
+}
+
+func FuzzParseBuildInfoRoundTrip(f *testing.F) {
+	// Package built from outside a module, missing some fields..
+	f.Add(strip(`
+		path	rsc.io/fortune
+		mod	rsc.io/fortune	v1.0.0
+		`))
+
+	// Package built from the standard library, missing some fields..
+	f.Add(`path	cmd/test2json`)
+
+	// Package built from inside a module.
+	f.Add(strip(`
+		go	1.18
+		path	example.com/m
+		mod	example.com/m	(devel)	
+		build	-compiler=gc
+		`))
+
+	// Package built in GOPATH mode.
+	f.Add(strip(`
+		go	1.18
+		path	example.com/m
+		build	-compiler=gc
+		`))
+
+	// Escaped build info.
+	f.Add(strip(`
+		go 1.18
+		path example.com/m
+		build CRAZY_ENV="requires\nescaping"
+		`))
+
+	f.Fuzz(func(t *testing.T, s string) {
+		bi, err := debug.ParseBuildInfo(s)
+		if err != nil {
+			// Not a round-trippable BuildInfo string.
+			t.Log(err)
+			return
+		}
+
+		// s2 could have different escaping from s.
+		// However, it should parse to exactly the same contents.
+		s2 := bi.String()
+		bi2, err := debug.ParseBuildInfo(s2)
+		if err != nil {
+			t.Fatalf("%v:\n%s", err, s2)
+		}
+
+		if !reflect.DeepEqual(bi2, bi) {
+			t.Fatalf("Parsed representation differs.\ninput:\n%s\noutput:\n%s", s, s2)
+		}
+	})
+}
diff --git a/libgo/go/runtime/export_test.go b/libgo/go/runtime/export_test.go
index 468e3a1..85d6f61 100644
--- a/libgo/go/runtime/export_test.go
+++ b/libgo/go/runtime/export_test.go
@@ -1202,6 +1202,8 @@ func (th *TimeHistogram) Record(duration int64) {
 
 var Pusestackmaps = &usestackmaps
 
+var TimeHistogramMetricsBuckets = timeHistogramMetricsBuckets
+
 func FinalizerGAsleep() bool {
 	lock(&finlock)
 	result := fingwait
@@ -1318,3 +1320,21 @@ func Releasem() {
 }
 
 var Timediv = timediv
+
+type PIController struct {
+	piController
+}
+
+func NewPIController(kp, ti, tt, min, max float64) *PIController {
+	return &PIController{piController{
+		kp:  kp,
+		ti:  ti,
+		tt:  tt,
+		min: min,
+		max: max,
+	}}
+}
+
+func (c *PIController) Next(input, setpoint, period float64) (float64, bool) {
+	return c.piController.next(input, setpoint, period)
+}
diff --git a/libgo/go/runtime/histogram.go b/libgo/go/runtime/histogram.go
index 0cccbcc..cd7e29a 100644
--- a/libgo/go/runtime/histogram.go
+++ b/libgo/go/runtime/histogram.go
@@ -47,7 +47,7 @@ const (
 	//    │  └---- Next 4 bits -> sub-bucket 1
 	//    └------- Bit 5 set -> super-bucket 2
 	//
-	// Following this pattern, bucket 45 will have the bit 48 set. We don't
+	// Following this pattern, super-bucket 44 will have the bit 47 set. We don't
 	// have any buckets for higher values, so the highest sub-bucket will
 	// contain values of 2^48-1 nanoseconds or approx. 3 days. This range is
 	// more than enough to handle durations produced by the runtime.
@@ -139,36 +139,30 @@ func float64NegInf() float64 {
 func timeHistogramMetricsBuckets() []float64 {
 	b := make([]float64, timeHistTotalBuckets+1)
 	b[0] = float64NegInf()
-	for i := 0; i < timeHistNumSuperBuckets; i++ {
-		superBucketMin := uint64(0)
-		// The (inclusive) minimum for the first non-negative bucket is 0.
-		if i > 0 {
-			// The minimum for the second bucket will be
-			// 1 << timeHistSubBucketBits, indicating that all
-			// sub-buckets are represented by the next timeHistSubBucketBits
-			// bits.
-			// Thereafter, we shift up by 1 each time, so we can represent
-			// this pattern as (i-1)+timeHistSubBucketBits.
-			superBucketMin = uint64(1) << uint(i-1+timeHistSubBucketBits)
-		}
-		// subBucketShift is the amount that we need to shift the sub-bucket
-		// index to combine it with the bucketMin.
-		subBucketShift := uint(0)
-		if i > 1 {
-			// The first two super buckets are exact with respect to integers,
-			// so we'll never have to shift the sub-bucket index. Thereafter,
-			// we shift up by 1 with each subsequent bucket.
-			subBucketShift = uint(i - 2)
-		}
+	// Super-bucket 0 has no bits above timeHistSubBucketBits
+	// set, so just iterate over each bucket and assign the
+	// incrementing bucket.
+	for i := 0; i < timeHistNumSubBuckets; i++ {
+		bucketNanos := uint64(i)
+		b[i+1] = float64(bucketNanos) / 1e9
+	}
+	// Generate the rest of the super-buckets. It's easier to reason
+	// about if we cut out the 0'th bucket, so subtract one since
+	// we just handled that bucket.
+	for i := 0; i < timeHistNumSuperBuckets-1; i++ {
 		for j := 0; j < timeHistNumSubBuckets; j++ {
-			// j is the sub-bucket index. By shifting the index into position to
-			// combine with the bucket minimum, we obtain the minimum value for that
-			// sub-bucket.
-			subBucketMin := superBucketMin + (uint64(j) << subBucketShift)
-
-			// Convert the subBucketMin which is in nanoseconds to a float64 seconds value.
+			// Set the super-bucket bit.
+			bucketNanos := uint64(1) << (i + timeHistSubBucketBits)
+			// Set the sub-bucket bits.
+			bucketNanos |= uint64(j) << i
+			// The index for this bucket is going to be the (i+1)'th super bucket
+			// (note that we're starting from zero, but handled the first super-bucket
+			// earlier, so we need to compensate), and the j'th sub bucket.
+			// Add 1 because we left space for -Inf.
+			bucketIndex := (i+1)*timeHistNumSubBuckets + j + 1
+			// Convert nanoseconds to seconds via a division.
 			// These values will all be exactly representable by a float64.
-			b[i*timeHistNumSubBuckets+j+1] = float64(subBucketMin) / 1e9
+			b[bucketIndex] = float64(bucketNanos) / 1e9
 		}
 	}
 	b[len(b)-1] = float64Inf()
diff --git a/libgo/go/runtime/histogram_test.go b/libgo/go/runtime/histogram_test.go
index dbc64fa..b12b65a 100644
--- a/libgo/go/runtime/histogram_test.go
+++ b/libgo/go/runtime/histogram_test.go
@@ -68,3 +68,43 @@ func TestTimeHistogram(t *testing.T) {
 
 	dummyTimeHistogram = TimeHistogram{}
 }
+
+func TestTimeHistogramMetricsBuckets(t *testing.T) {
+	buckets := TimeHistogramMetricsBuckets()
+
+	nonInfBucketsLen := TimeHistNumSubBuckets * TimeHistNumSuperBuckets
+	expBucketsLen := nonInfBucketsLen + 2 // Count -Inf and +Inf.
+	if len(buckets) != expBucketsLen {
+		t.Fatalf("unexpected length of buckets: got %d, want %d", len(buckets), expBucketsLen)
+	}
+	// Check the first non-Inf 2*TimeHistNumSubBuckets buckets in order, skipping the
+	// first bucket which should be -Inf (checked later).
+	//
+	// Because of the way this scheme works, the bottom TimeHistNumSubBuckets
+	// buckets are fully populated, and then the next TimeHistNumSubBuckets
+	// have the TimeHistSubBucketBits'th bit set, while the bottom are once
+	// again fully populated.
+	for i := 1; i <= 2*TimeHistNumSubBuckets+1; i++ {
+		if got, want := buckets[i], float64(i-1)/1e9; got != want {
+			t.Errorf("expected bucket %d to have value %e, got %e", i, want, got)
+		}
+	}
+	// Check some values.
+	idxToBucket := map[int]float64{
+		0:                 math.Inf(-1),
+		33:                float64(0x10<<1) / 1e9,
+		34:                float64(0x11<<1) / 1e9,
+		49:                float64(0x10<<2) / 1e9,
+		58:                float64(0x19<<2) / 1e9,
+		65:                float64(0x10<<3) / 1e9,
+		513:               float64(0x10<<31) / 1e9,
+		519:               float64(0x16<<31) / 1e9,
+		expBucketsLen - 2: float64(0x1f<<43) / 1e9,
+		expBucketsLen - 1: math.Inf(1),
+	}
+	for idx, bucket := range idxToBucket {
+		if got, want := buckets[idx], bucket; got != want {
+			t.Errorf("expected bucket %d to have value %e, got %e", idx, want, got)
+		}
+	}
+}
diff --git a/libgo/go/runtime/internal/syscall/errno.c b/libgo/go/runtime/internal/syscall/errno.c
new file mode 100644
index 0000000..2bc5900
--- /dev/null
+++ b/libgo/go/runtime/internal/syscall/errno.c
@@ -0,0 +1,27 @@
+/* errno.c -- functions for getting and setting errno
+
+   Copyright 2022 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.  */
+#include <errno.h>
+#include <stdint.h>
+
+#include "runtime.h"
+
+/* errno is typically a macro. These functions set and get errno
+   specific to the libc being used.  */
+
+uintptr_t getErrno(void) __asm__ (GOSYM_PREFIX "runtime_1internal_1syscall.getErrno");
+void setErrno(uintptr_t) __asm__ (GOSYM_PREFIX "runtime_1internal_1syscall.setErrno");
+
+uintptr_t
+getErrno(void)
+{
+  return (uintptr_t) errno;
+}
+
+void
+setErrno(uintptr_t value)
+{
+  errno = (int) value;
+}
diff --git a/libgo/go/runtime/internal/syscall/syscall_linux.go b/libgo/go/runtime/internal/syscall/syscall_linux.go
new file mode 100644
index 0000000..a4e9358
--- /dev/null
+++ b/libgo/go/runtime/internal/syscall/syscall_linux.go
@@ -0,0 +1,23 @@
+// Copyright 2022 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 syscall provides the syscall primitives required for the runtime.
+package syscall
+
+// TODO(https://go.dev/issue/51087): This package is incomplete and currently
+// only contains very minimal support for Linux.
+
+//extern __go_syscall6
+func syscall6(num uintptr, a1, a2, a3, a4, a5, a6 uintptr) uintptr
+
+func getErrno() uintptr
+func setErrno(uintptr)
+
+// Syscall6 calls system call number 'num' with arguments a1-6.
+func Syscall6(num, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2, errno uintptr) {
+	setErrno(0)
+	r := syscall6(num, a1, a2, a3, a4, a5, a6)
+	errno = getErrno()
+	return r, 0, errno
+}
diff --git a/libgo/go/runtime/mbarrier.go b/libgo/go/runtime/mbarrier.go
index 4982fd4..94eebc9 100644
--- a/libgo/go/runtime/mbarrier.go
+++ b/libgo/go/runtime/mbarrier.go
@@ -204,7 +204,7 @@ func reflectlite_typedmemmove(typ *_type, dst, src unsafe.Pointer) {
 
 // typedmemmovepartial is like typedmemmove but assumes that
 // dst and src point off bytes into the value and only copies size bytes.
-// off must be a multiple of sys.PtrSize.
+// off must be a multiple of goarch.PtrSize.
 //go:linkname reflect_typedmemmovepartial reflect.typedmemmovepartial
 func reflect_typedmemmovepartial(typ *_type, dst, src unsafe.Pointer, off, size uintptr) {
 	if writeBarrier.needed && typ.ptrdata > off && size >= goarch.PtrSize {
diff --git a/libgo/go/runtime/mbitmap.go b/libgo/go/runtime/mbitmap.go
index 019ca34..33cfa72 100644
--- a/libgo/go/runtime/mbitmap.go
+++ b/libgo/go/runtime/mbitmap.go
@@ -862,7 +862,7 @@ func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
 	// size is sizeof(_defer{}) (at least 6 words) and dataSize may be
 	// arbitrarily larger.
 	//
-	// The checks for size == sys.PtrSize and size == 2*sys.PtrSize can therefore
+	// The checks for size == goarch.PtrSize and size == 2*goarch.PtrSize can therefore
 	// assume that dataSize == size without checking it explicitly.
 
 	if goarch.PtrSize == 8 && size == goarch.PtrSize {
@@ -912,7 +912,7 @@ func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
 			}
 			return
 		}
-		// Otherwise typ.size must be 2*sys.PtrSize,
+		// Otherwise typ.size must be 2*goarch.PtrSize,
 		// and typ.kind&kindGCProg == 0.
 		if doubleCheck {
 			if typ.size != 2*goarch.PtrSize || typ.kind&kindGCProg != 0 {
@@ -1114,8 +1114,8 @@ func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
 			// Replicate ptrmask to fill entire pbits uintptr.
 			// Doubling and truncating is fewer steps than
 			// iterating by nb each time. (nb could be 1.)
-			// Since we loaded typ.ptrdata/sys.PtrSize bits
-			// but are pretending to have typ.size/sys.PtrSize,
+			// Since we loaded typ.ptrdata/goarch.PtrSize bits
+			// but are pretending to have typ.size/goarch.PtrSize,
 			// there might be no replication necessary/possible.
 			pbits = b
 			endnb = nb
@@ -1583,7 +1583,7 @@ func heapBitsSetTypeGCProg(h heapBits, progSize, elemSize, dataSize, allocSize u
 
 // progToPointerMask returns the 1-bit pointer mask output by the GC program prog.
 // size the size of the region described by prog, in bytes.
-// The resulting bitvector will have no more than size/sys.PtrSize bits.
+// The resulting bitvector will have no more than size/goarch.PtrSize bits.
 func progToPointerMask(prog *byte, size uintptr) bitvector {
 	n := (size/goarch.PtrSize + 7) / 8
 	x := (*[1 << 30]byte)(persistentalloc(n+1, 1, &memstats.buckhash_sys))[:n+1]
@@ -1716,7 +1716,7 @@ Run:
 		// into a register and use that register for the entire loop
 		// instead of repeatedly reading from memory.
 		// Handling fewer than 8 bits here makes the general loop simpler.
-		// The cutoff is sys.PtrSize*8 - 7 to guarantee that when we add
+		// The cutoff is goarch.PtrSize*8 - 7 to guarantee that when we add
 		// the pattern to a bit buffer holding at most 7 bits (a partial byte)
 		// it will not overflow.
 		src := dst
diff --git a/libgo/go/runtime/mgcmark.go b/libgo/go/runtime/mgcmark.go
index 6bc7094..3b568dd 100644
--- a/libgo/go/runtime/mgcmark.go
+++ b/libgo/go/runtime/mgcmark.go
@@ -338,7 +338,7 @@ func markrootSpans(gcw *gcWork, shard int) {
 }
 
 // gcAssistAlloc performs GC work to make gp's assist debt positive.
-// gp must be the calling user gorountine.
+// gp must be the calling user goroutine.
 //
 // This must be called with preemption enabled.
 func gcAssistAlloc(gp *g) {
diff --git a/libgo/go/runtime/mgcpacer.go b/libgo/go/runtime/mgcpacer.go
index 5e940b0..0fff13c 100644
--- a/libgo/go/runtime/mgcpacer.go
+++ b/libgo/go/runtime/mgcpacer.go
@@ -154,6 +154,8 @@ type gcControllerState struct {
 	// For goexperiment.PacerRedesign.
 	consMarkController piController
 
+	_ uint32 // Padding for atomics on 32-bit platforms.
+
 	// heapGoal is the goal heapLive for when next GC ends.
 	// Set to ^uint64(0) if disabled.
 	//
@@ -670,10 +672,31 @@ func (c *gcControllerState) endCycle(now int64, procs int, userForced bool) floa
 		currentConsMark := (float64(c.heapLive-c.trigger) * (utilization + idleUtilization)) /
 			(float64(scanWork) * (1 - utilization))
 
-		// Update cons/mark controller.
-		// Period for this is 1 GC cycle.
+		// Update cons/mark controller. The time period for this is 1 GC cycle.
+		//
+		// This use of a PI controller might seem strange. So, here's an explanation:
+		//
+		// currentConsMark represents the consMark we *should've* had to be perfectly
+		// on-target for this cycle. Given that we assume the next GC will be like this
+		// one in the steady-state, it stands to reason that we should just pick that
+		// as our next consMark. In practice, however, currentConsMark is too noisy:
+		// we're going to be wildly off-target in each GC cycle if we do that.
+		//
+		// What we do instead is make a long-term assumption: there is some steady-state
+		// consMark value, but it's obscured by noise. By constantly shooting for this
+		// noisy-but-perfect consMark value, the controller will bounce around a bit,
+		// but its average behavior, in aggregate, should be less noisy and closer to
+		// the true long-term consMark value, provided its tuned to be slightly overdamped.
+		var ok bool
 		oldConsMark := c.consMark
-		c.consMark = c.consMarkController.next(c.consMark, currentConsMark, 1.0)
+		c.consMark, ok = c.consMarkController.next(c.consMark, currentConsMark, 1.0)
+		if !ok {
+			// The error spiraled out of control. This is incredibly unlikely seeing
+			// as this controller is essentially just a smoothing function, but it might
+			// mean that something went very wrong with how currentConsMark was calculated.
+			// Just reset consMark and keep going.
+			c.consMark = 0
+		}
 
 		if debug.gcpacertrace > 0 {
 			printlock()
@@ -681,6 +704,9 @@ func (c *gcControllerState) endCycle(now int64, procs int, userForced bool) floa
 			print("pacer: ", int(utilization*100), "% CPU (", int(goal), " exp.) for ")
 			print(c.heapScanWork.Load(), "+", c.stackScanWork.Load(), "+", c.globalsScanWork.Load(), " B work (", c.lastHeapScan+c.stackScan+c.globalsScan, " B exp.) ")
 			print("in ", c.trigger, " B -> ", c.heapLive, " B (∆goal ", int64(c.heapLive)-int64(c.heapGoal), ", cons/mark ", oldConsMark, ")")
+			if !ok {
+				print("[controller reset]")
+			}
 			println()
 			printunlock()
 		}
@@ -1263,15 +1289,38 @@ type piController struct {
 	// PI controller state.
 
 	errIntegral float64 // Integral of the error from t=0 to now.
+
+	// Error flags.
+	errOverflow   bool // Set if errIntegral ever overflowed.
+	inputOverflow bool // Set if an operation with the input overflowed.
 }
 
-func (c *piController) next(input, setpoint, period float64) float64 {
+// next provides a new sample to the controller.
+//
+// input is the sample, setpoint is the desired point, and period is how much
+// time (in whatever unit makes the most sense) has passed since the last sample.
+//
+// Returns a new value for the variable it's controlling, and whether the operation
+// completed successfully. One reason this might fail is if error has been growing
+// in an unbounded manner, to the point of overflow.
+//
+// In the specific case of an error overflow occurs, the errOverflow field will be
+// set and the rest of the controller's internal state will be fully reset.
+func (c *piController) next(input, setpoint, period float64) (float64, bool) {
 	// Compute the raw output value.
 	prop := c.kp * (setpoint - input)
 	rawOutput := prop + c.errIntegral
 
 	// Clamp rawOutput into output.
 	output := rawOutput
+	if isInf(output) || isNaN(output) {
+		// The input had a large enough magnitude that either it was already
+		// overflowed, or some operation with it overflowed.
+		// Set a flag and reset. That's the safest thing to do.
+		c.reset()
+		c.inputOverflow = true
+		return c.min, false
+	}
 	if output < c.min {
 		output = c.min
 	} else if output > c.max {
@@ -1281,6 +1330,19 @@ func (c *piController) next(input, setpoint, period float64) float64 {
 	// Update the controller's state.
 	if c.ti != 0 && c.tt != 0 {
 		c.errIntegral += (c.kp*period/c.ti)*(setpoint-input) + (period/c.tt)*(output-rawOutput)
+		if isInf(c.errIntegral) || isNaN(c.errIntegral) {
+			// So much error has accumulated that we managed to overflow.
+			// The assumptions around the controller have likely broken down.
+			// Set a flag and reset. That's the safest thing to do.
+			c.reset()
+			c.errOverflow = true
+			return c.min, false
+		}
 	}
-	return output
+	return output, true
+}
+
+// reset resets the controller state, except for controller error flags.
+func (c *piController) reset() {
+	c.errIntegral = 0
 }
diff --git a/libgo/go/runtime/mgcpacer_test.go b/libgo/go/runtime/mgcpacer_test.go
index 9ec0e51..10a8ca2 100644
--- a/libgo/go/runtime/mgcpacer_test.go
+++ b/libgo/go/runtime/mgcpacer_test.go
@@ -715,3 +715,48 @@ func (f float64Stream) limit(min, max float64) float64Stream {
 		return v
 	}
 }
+
+func FuzzPIController(f *testing.F) {
+	isNormal := func(x float64) bool {
+		return !math.IsInf(x, 0) && !math.IsNaN(x)
+	}
+	isPositive := func(x float64) bool {
+		return isNormal(x) && x > 0
+	}
+	// Seed with constants from controllers in the runtime.
+	// It's not critical that we keep these in sync, they're just
+	// reasonable seed inputs.
+	f.Add(0.3375, 3.2e6, 1e9, 0.001, 1000.0, 0.01)
+	f.Add(0.9, 4.0, 1000.0, -1000.0, 1000.0, 0.84)
+	f.Fuzz(func(t *testing.T, kp, ti, tt, min, max, setPoint float64) {
+		// Ignore uninteresting invalid parameters. These parameters
+		// are constant, so in practice surprising values will be documented
+		// or will be other otherwise immediately visible.
+		//
+		// We just want to make sure that given a non-Inf, non-NaN input,
+		// we always get a non-Inf, non-NaN output.
+		if !isPositive(kp) || !isPositive(ti) || !isPositive(tt) {
+			return
+		}
+		if !isNormal(min) || !isNormal(max) || min > max {
+			return
+		}
+		// Use a random source, but make it deterministic.
+		rs := rand.New(rand.NewSource(800))
+		randFloat64 := func() float64 {
+			return math.Float64frombits(rs.Uint64())
+		}
+		p := NewPIController(kp, ti, tt, min, max)
+		state := float64(0)
+		for i := 0; i < 100; i++ {
+			input := randFloat64()
+			// Ignore the "ok" parameter. We're just trying to break it.
+			// state is intentionally completely uncorrelated with the input.
+			var ok bool
+			state, ok = p.Next(input, setPoint, 1.0)
+			if !isNormal(state) {
+				t.Fatalf("got NaN or Inf result from controller: %f %v", state, ok)
+			}
+		}
+	})
+}
diff --git a/libgo/go/runtime/mgcscavenge.go b/libgo/go/runtime/mgcscavenge.go
index adf2b05..9d6e0bd 100644
--- a/libgo/go/runtime/mgcscavenge.go
+++ b/libgo/go/runtime/mgcscavenge.go
@@ -165,11 +165,12 @@ func gcPaceScavenger(heapGoal, lastHeapGoal uint64) {
 
 // Sleep/wait state of the background scavenger.
 var scavenge struct {
-	lock       mutex
-	g          *g
-	parked     bool
-	timer      *timer
-	sysmonWake uint32 // Set atomically.
+	lock                 mutex
+	g                    *g
+	parked               bool
+	timer                *timer
+	sysmonWake           uint32 // Set atomically.
+	printControllerReset bool   // Whether the scavenger is in cooldown.
 }
 
 // readyForScavenger signals sysmon to wake the scavenger because
@@ -297,8 +298,14 @@ func bgscavenge(c chan int) {
 		max: 1000.0, // 1000:1
 	}
 	// It doesn't really matter what value we start at, but we can't be zero, because
-	// that'll cause divide-by-zero issues.
-	critSleepRatio := 0.001
+	// that'll cause divide-by-zero issues. Pick something conservative which we'll
+	// also use as a fallback.
+	const startingCritSleepRatio = 0.001
+	critSleepRatio := startingCritSleepRatio
+	// Duration left in nanoseconds during which we avoid using the controller and
+	// we hold critSleepRatio at a conservative value. Used if the controller's
+	// assumptions fail to hold.
+	controllerCooldown := int64(0)
 	for {
 		released := uintptr(0)
 		crit := float64(0)
@@ -385,9 +392,22 @@ func bgscavenge(c chan int) {
 		// because of the additional overheads of using scavenged memory.
 		crit *= 1 + scavengeCostRatio
 
-		// Go to sleep for our current sleepNS.
+		// Go to sleep based on how much time we spent doing work.
 		slept := scavengeSleep(int64(crit / critSleepRatio))
 
+		// Stop here if we're cooling down from the controller.
+		if controllerCooldown > 0 {
+			// crit and slept aren't exact measures of time, but it's OK to be a bit
+			// sloppy here. We're just hoping we're avoiding some transient bad behavior.
+			t := slept + int64(crit)
+			if t > controllerCooldown {
+				controllerCooldown = 0
+			} else {
+				controllerCooldown -= t
+			}
+			continue
+		}
+
 		// Calculate the CPU time spent.
 		//
 		// This may be slightly inaccurate with respect to GOMAXPROCS, but we're
@@ -397,7 +417,20 @@ func bgscavenge(c chan int) {
 		cpuFraction := float64(crit) / ((float64(slept) + crit) * float64(gomaxprocs))
 
 		// Update the critSleepRatio, adjusting until we reach our ideal fraction.
-		critSleepRatio = critSleepController.next(cpuFraction, idealFraction, float64(slept)+crit)
+		var ok bool
+		critSleepRatio, ok = critSleepController.next(cpuFraction, idealFraction, float64(slept)+crit)
+		if !ok {
+			// The core assumption of the controller, that we can get a proportional
+			// response, broke down. This may be transient, so temporarily switch to
+			// sleeping a fixed, conservative amount.
+			critSleepRatio = startingCritSleepRatio
+			controllerCooldown = 5e9 // 5 seconds.
+
+			// Signal the scav trace printer to output this.
+			lock(&scavenge.lock)
+			scavenge.printControllerReset = true
+			unlock(&scavenge.lock)
+		}
 	}
 }
 
@@ -436,7 +469,11 @@ func (p *pageAlloc) scavenge(nbytes uintptr) uintptr {
 // released should be the amount of memory released since the last time this
 // was called, and forced indicates whether the scavenge was forced by the
 // application.
+//
+// scavenge.lock must be held.
 func printScavTrace(gen uint32, released uintptr, forced bool) {
+	assertLockHeld(&scavenge.lock)
+
 	printlock()
 	print("scav ", gen, " ",
 		released>>10, " KiB work, ",
@@ -445,6 +482,9 @@ func printScavTrace(gen uint32, released uintptr, forced bool) {
 	)
 	if forced {
 		print(" (forced)")
+	} else if scavenge.printControllerReset {
+		print(" [controller reset]")
+		scavenge.printControllerReset = false
 	}
 	println()
 	printunlock()
diff --git a/libgo/go/runtime/pprof/pprof_test.go b/libgo/go/runtime/pprof/pprof_test.go
index def49c1..983d4d4 100644
--- a/libgo/go/runtime/pprof/pprof_test.go
+++ b/libgo/go/runtime/pprof/pprof_test.go
@@ -798,7 +798,7 @@ func TestBlockProfile(t *testing.T) {
 	t.Skip("lots of details are different for gccgo; FIXME")
 	type TestCase struct {
 		name string
-		f    func()
+		f    func(*testing.T)
 		stk  []string
 		re   string
 	}
@@ -907,7 +907,7 @@ func TestBlockProfile(t *testing.T) {
 	runtime.SetBlockProfileRate(1)
 	defer runtime.SetBlockProfileRate(0)
 	for _, test := range tests {
-		test.f()
+		test.f(t)
 	}
 
 	t.Run("debug=1", func(t *testing.T) {
@@ -983,42 +983,73 @@ func containsStack(got [][]string, want []string) bool {
 	return false
 }
 
-const blockDelay = 10 * time.Millisecond
+// awaitBlockedGoroutine spins on runtime.Gosched until a runtime stack dump
+// shows a goroutine in the given state with a stack frame in
+// runtime/pprof.<fName>.
+func awaitBlockedGoroutine(t *testing.T, state, fName string) {
+	re := fmt.Sprintf(`(?m)^goroutine \d+ \[%s\]:\n(?:.+\n\t.+\n)*runtime/pprof\.%s`, regexp.QuoteMeta(state), fName)
+	r := regexp.MustCompile(re)
 
-func blockChanRecv() {
+	if deadline, ok := t.Deadline(); ok {
+		if d := time.Until(deadline); d > 1*time.Second {
+			timer := time.AfterFunc(d-1*time.Second, func() {
+				debug.SetTraceback("all")
+				panic(fmt.Sprintf("timed out waiting for %#q", re))
+			})
+			defer timer.Stop()
+		}
+	}
+
+	buf := make([]byte, 64<<10)
+	for {
+		runtime.Gosched()
+		n := runtime.Stack(buf, true)
+		if n == len(buf) {
+			// Buffer wasn't large enough for a full goroutine dump.
+			// Resize it and try again.
+			buf = make([]byte, 2*len(buf))
+			continue
+		}
+		if r.Match(buf[:n]) {
+			return
+		}
+	}
+}
+
+func blockChanRecv(t *testing.T) {
 	c := make(chan bool)
 	go func() {
-		time.Sleep(blockDelay)
+		awaitBlockedGoroutine(t, "chan receive", "blockChanRecv")
 		c <- true
 	}()
 	<-c
 }
 
-func blockChanSend() {
+func blockChanSend(t *testing.T) {
 	c := make(chan bool)
 	go func() {
-		time.Sleep(blockDelay)
+		awaitBlockedGoroutine(t, "chan send", "blockChanSend")
 		<-c
 	}()
 	c <- true
 }
 
-func blockChanClose() {
+func blockChanClose(t *testing.T) {
 	c := make(chan bool)
 	go func() {
-		time.Sleep(blockDelay)
+		awaitBlockedGoroutine(t, "chan receive", "blockChanClose")
 		close(c)
 	}()
 	<-c
 }
 
-func blockSelectRecvAsync() {
+func blockSelectRecvAsync(t *testing.T) {
 	const numTries = 3
 	c := make(chan bool, 1)
 	c2 := make(chan bool, 1)
 	go func() {
 		for i := 0; i < numTries; i++ {
-			time.Sleep(blockDelay)
+			awaitBlockedGoroutine(t, "select", "blockSelectRecvAsync")
 			c <- true
 		}
 	}()
@@ -1030,11 +1061,11 @@ func blockSelectRecvAsync() {
 	}
 }
 
-func blockSelectSendSync() {
+func blockSelectSendSync(t *testing.T) {
 	c := make(chan bool)
 	c2 := make(chan bool)
 	go func() {
-		time.Sleep(blockDelay)
+		awaitBlockedGoroutine(t, "select", "blockSelectSendSync")
 		<-c
 	}()
 	select {
@@ -1043,11 +1074,11 @@ func blockSelectSendSync() {
 	}
 }
 
-func blockMutex() {
+func blockMutex(t *testing.T) {
 	var mu sync.Mutex
 	mu.Lock()
 	go func() {
-		time.Sleep(blockDelay)
+		awaitBlockedGoroutine(t, "semacquire", "blockMutex")
 		mu.Unlock()
 	}()
 	// Note: Unlock releases mu before recording the mutex event,
@@ -1057,12 +1088,12 @@ func blockMutex() {
 	mu.Lock()
 }
 
-func blockCond() {
+func blockCond(t *testing.T) {
 	var mu sync.Mutex
 	c := sync.NewCond(&mu)
 	mu.Lock()
 	go func() {
-		time.Sleep(blockDelay)
+		awaitBlockedGoroutine(t, "sync.Cond.Wait", "blockCond")
 		mu.Lock()
 		c.Signal()
 		mu.Unlock()
@@ -1148,7 +1179,7 @@ func TestMutexProfile(t *testing.T) {
 		t.Fatalf("need MutexProfileRate 0, got %d", old)
 	}
 
-	blockMutex()
+	blockMutex(t)
 
 	t.Run("debug=1", func(t *testing.T) {
 		var w bytes.Buffer
diff --git a/libgo/go/runtime/proc.go b/libgo/go/runtime/proc.go
index db1e2b4..881793b 100644
--- a/libgo/go/runtime/proc.go
+++ b/libgo/go/runtime/proc.go
@@ -212,10 +212,6 @@ func main(unsafe.Pointer) {
 	mainStarted = true
 
 	if GOARCH != "wasm" { // no threads on wasm yet, so no sysmon
-		// For runtime_syscall_doAllThreadsSyscall, we
-		// register sysmon is not ready for the world to be
-		// stopped.
-		atomic.Store(&sched.sysmonStarting, 1)
 		systemstack(func() {
 			newm(sysmon, nil, -1)
 		})
@@ -232,7 +228,6 @@ func main(unsafe.Pointer) {
 	if g.m != &m0 {
 		throw("runtime.main not on m0")
 	}
-	m0.doesPark = true
 
 	// Record when the world started.
 	// Must be before doInit for tracing init.
@@ -801,7 +796,13 @@ func mcommoninit(mp *m, id int64) {
 	if lo|hi == 0 {
 		hi = 1
 	}
-	mp.fastrand = uint64(hi)<<32 | uint64(lo)
+	// Same behavior as for 1.17.
+	// TODO: Simplify ths.
+	if goarch.BigEndian {
+		mp.fastrand = uint64(lo)<<32 | uint64(hi)
+	} else {
+		mp.fastrand = uint64(hi)<<32 | uint64(lo)
+	}
 
 	mpreinit(mp)
 
@@ -1363,22 +1364,12 @@ func mstartm0() {
 	initsig(false)
 }
 
-// mPark causes a thread to park itself - temporarily waking for
-// fixups but otherwise waiting to be fully woken. This is the
-// only way that m's should park themselves.
+// mPark causes a thread to park itself, returning once woken.
 //go:nosplit
 func mPark() {
-	g := getg()
-	for {
-		notesleep(&g.m.park)
-		// Note, because of signal handling by this parked m,
-		// a preemptive mDoFixup() may actually occur via
-		// mDoFixupAndOSYield(). (See golang.org/issue/44193)
-		noteclear(&g.m.park)
-		if !mDoFixup() {
-			return
-		}
-	}
+	gp := getg()
+	notesleep(&gp.m.park)
+	noteclear(&gp.m.park)
 }
 
 // mexit tears down and exits the current thread.
@@ -1623,8 +1614,14 @@ func runSafePointFn() {
 //
 //go:yeswritebarrierrec
 func allocm(_p_ *p, fn func(), id int64, allocatestack bool) (mp *m, g0Stack unsafe.Pointer, g0StackSize uintptr) {
+	allocmLock.rlock()
+
+	// The caller owns _p_, but we may borrow (i.e., acquirep) it. We must
+	// disable preemption to ensure it is not stolen, which would make the
+	// caller lose ownership.
+	acquirem()
+
 	_g_ := getg()
-	acquirem() // disable GC because it can be called from sysmon
 	if _g_.m.p == 0 {
 		acquirep(_p_) // temporarily borrow p for mallocs in this function
 	}
@@ -1664,8 +1661,9 @@ func allocm(_p_ *p, fn func(), id int64, allocatestack bool) (mp *m, g0Stack uns
 	if _p_ == _g_.m.p.ptr() {
 		releasep()
 	}
-	releasem(_g_.m)
 
+	releasem(_g_.m)
+	allocmLock.runlock()
 	return mp, g0Stack, g0StackSize
 }
 
@@ -1940,9 +1938,17 @@ func unlockextra(mp *m) {
 	atomic.Storeuintptr(&extram, uintptr(unsafe.Pointer(mp)))
 }
 
-// execLock serializes exec and clone to avoid bugs or unspecified behaviour
-// around exec'ing while creating/destroying threads.  See issue #19546.
-var execLock rwmutex
+var (
+	// allocmLock is locked for read when creating new Ms in allocm and their
+	// addition to allm. Thus acquiring this lock for write blocks the
+	// creation of new Ms.
+	allocmLock rwmutex
+
+	// execLock serializes exec and clone to avoid bugs or unspecified
+	// behaviour around exec'ing while creating/destroying threads. See
+	// issue #19546.
+	execLock rwmutex
+)
 
 // newmHandoff contains a list of m structures that need new OS threads.
 // This is used by newm in situations where newm itself can't safely
@@ -1972,8 +1978,19 @@ var newmHandoff struct {
 // id is optional pre-allocated m ID. Omit by passing -1.
 //go:nowritebarrierrec
 func newm(fn func(), _p_ *p, id int64) {
+	// allocm adds a new M to allm, but they do not start until created by
+	// the OS in newm1 or the template thread.
+	//
+	// doAllThreadsSyscall requires that every M in allm will eventually
+	// start and be signal-able, even with a STW.
+	//
+	// Disable preemption here until we start the thread to ensure that
+	// newm is not preempted between allocm and starting the new thread,
+	// ensuring that anything added to allm is guaranteed to eventually
+	// start.
+	acquirem()
+
 	mp, _, _ := allocm(_p_, fn, id, false)
-	mp.doesPark = (_p_ != nil)
 	mp.nextp.set(_p_)
 	mp.sigmask = initSigmask
 	if gp := getg(); gp != nil && gp.m != nil && (gp.m.lockedExt != 0 || gp.m.incgo) && GOOS != "plan9" {
@@ -1999,9 +2016,14 @@ func newm(fn func(), _p_ *p, id int64) {
 			notewakeup(&newmHandoff.wake)
 		}
 		unlock(&newmHandoff.lock)
+		// The M has not started yet, but the template thread does not
+		// participate in STW, so it will always process queued Ms and
+		// it is safe to releasem.
+		releasem(getg().m)
 		return
 	}
 	newm1(mp)
+	releasem(getg().m)
 }
 
 func newm1(mp *m) {
@@ -2030,67 +2052,6 @@ func startTemplateThread() {
 	releasem(mp)
 }
 
-// mFixupRace is used to temporarily borrow the race context from the
-// coordinating m during a syscall_runtime_doAllThreadsSyscall and
-// loan it out to each of the m's of the runtime so they can execute a
-// mFixup.fn in that context.
-var mFixupRace struct {
-	lock mutex
-	ctx  uintptr
-}
-
-// mDoFixup runs any outstanding fixup function for the running m.
-// Returns true if a fixup was outstanding and actually executed.
-//
-// Note: to avoid deadlocks, and the need for the fixup function
-// itself to be async safe, signals are blocked for the working m
-// while it holds the mFixup lock. (See golang.org/issue/44193)
-//
-//go:nosplit
-func mDoFixup() bool {
-	_g_ := getg()
-	if used := atomic.Load(&_g_.m.mFixup.used); used == 0 {
-		return false
-	}
-
-	// slow path - if fixup fn is used, block signals and lock.
-	var sigmask sigset
-	sigsave(&sigmask)
-	sigblock(false)
-	lock(&_g_.m.mFixup.lock)
-	fn := _g_.m.mFixup.fn
-	if fn != nil {
-		if gcphase != _GCoff {
-			// We can't have a write barrier in this
-			// context since we may not have a P, but we
-			// clear fn to signal that we've executed the
-			// fixup. As long as fn is kept alive
-			// elsewhere, technically we should have no
-			// issues with the GC, but fn is likely
-			// generated in a different package altogether
-			// that may change independently. Just assert
-			// the GC is off so this lack of write barrier
-			// is more obviously safe.
-			throw("GC must be disabled to protect validity of fn value")
-		}
-		*(*uintptr)(unsafe.Pointer(&_g_.m.mFixup.fn)) = 0
-		fn(false)
-	}
-	unlock(&_g_.m.mFixup.lock)
-	msigrestore(sigmask)
-	return fn != nil
-}
-
-// mDoFixupAndOSYield is called when an m is unable to send a signal
-// because the allThreadsSyscall mechanism is in progress. That is, an
-// mPark() has been interrupted with this signal handler so we need to
-// ensure the fixup is executed from this context.
-//go:nosplit
-func mDoFixupAndOSYield() {
-	mDoFixup()
-	osyield()
-}
-
 // templateThread is a thread in a known-good state that exists solely
 // to start new threads in known-good states when the calling thread
 // may not be in a good state.
@@ -2127,7 +2088,6 @@ func templateThread() {
 		noteclear(&newmHandoff.wake)
 		unlock(&newmHandoff.lock)
 		notesleep(&newmHandoff.wake)
-		mDoFixup()
 	}
 }
 
@@ -4826,10 +4786,6 @@ func sysmon() {
 	checkdead()
 	unlock(&sched.lock)
 
-	// For syscall_runtime_doAllThreadsSyscall, sysmon is
-	// sufficiently up to participate in fixups.
-	atomic.Store(&sched.sysmonStarting, 0)
-
 	lasttrace := int64(0)
 	idle := 0 // how many cycles in succession we had not wokeup somebody
 	delay := uint32(0)
@@ -4844,7 +4800,6 @@ func sysmon() {
 			delay = 10 * 1000
 		}
 		usleep(delay)
-		mDoFixup()
 
 		// sysmon should not enter deep sleep if schedtrace is enabled so that
 		// it can print that information at the right time.
@@ -4881,7 +4836,6 @@ func sysmon() {
 						osRelax(true)
 					}
 					syscallWake = notetsleep(&sched.sysmonnote, sleep)
-					mDoFixup()
 					if shouldRelax {
 						osRelax(false)
 					}
@@ -4924,7 +4878,6 @@ func sysmon() {
 				incidlelocked(1)
 			}
 		}
-		mDoFixup()
 		if GOOS == "netbsd" && needSysmonWorkaround {
 			// netpoll is responsible for waiting for timer
 			// expiration, so we typically don't have to worry
diff --git a/libgo/go/runtime/runtime2.go b/libgo/go/runtime/runtime2.go
index 3c0348f..7885fbb 100644
--- a/libgo/go/runtime/runtime2.go
+++ b/libgo/go/runtime/runtime2.go
@@ -593,7 +593,6 @@ type m struct {
 	ncgo        int32  // number of cgo calls currently in progress
 	// Not for gccgo: cgoCallersUse uint32      // if non-zero, cgoCallers in use temporarily
 	// Not for gccgo: cgoCallers    *cgoCallers // cgo traceback if crashing in cgo call
-	doesPark      bool // non-P running threads: sysmon and newmHandoff never use .park
 	park          note
 	alllink       *m // on allm
 	schedlink     muintptr
@@ -610,16 +609,6 @@ type m struct {
 	syscalltick   uint32
 	freelink      *m // on sched.freem
 
-	// mFixup is used to synchronize OS related m state
-	// (credentials etc) use mutex to access. To avoid deadlocks
-	// an atomic.Load() of used being zero in mDoFixupFn()
-	// guarantees fn is nil.
-	mFixup struct {
-		lock mutex
-		used uint32
-		fn   func(bool) bool
-	}
-
 	// these are here because they are too large to be on the stack
 	// of low-level NOSPLIT functions.
 	// Not for gccgo: libcall   libcall
@@ -869,10 +858,6 @@ type schedt struct {
 	sysmonwait uint32
 	sysmonnote note
 
-	// While true, sysmon not ready for mFixup calls.
-	// Accessed atomically.
-	sysmonStarting uint32
-
 	// safepointFn should be called on each P at the next GC
 	// safepoint if p.runSafePointFn is set.
 	safePointFn   func(*p)
@@ -890,6 +875,8 @@ type schedt struct {
 	// with the rest of the runtime.
 	sysmonlock mutex
 
+	_ uint32 // for alignment
+
 	// timeToRun is a distribution of scheduling latencies, defined
 	// as the sum of time a G spends in the _Grunnable state before
 	// it transitions to _Grunning.
@@ -906,7 +893,7 @@ const (
 	_SigPanic                // if the signal is from the kernel, panic
 	_SigDefault              // if the signal isn't explicitly requested, don't monitor it
 	_SigGoExit               // cause all runtime procs to exit (only used on Plan 9).
-	_SigSetStack             // add SA_ONSTACK to libc handler
+	_SigSetStack             // Don't explicitly install handler, but add SA_ONSTACK to existing libc handler
 	_SigUnblock              // always unblock; see blockableSig
 	_SigIgn                  // _SIG_DFL action is to ignore the signal
 )
diff --git a/libgo/go/runtime/sigqueue.go b/libgo/go/runtime/sigqueue.go
index da2491d..49754f5 100644
--- a/libgo/go/runtime/sigqueue.go
+++ b/libgo/go/runtime/sigqueue.go
@@ -11,18 +11,18 @@
 //
 // sigsend is called by the signal handler to queue a new signal.
 // signal_recv is called by the Go program to receive a newly queued signal.
+//
 // Synchronization between sigsend and signal_recv is based on the sig.state
-// variable. It can be in 4 states: sigIdle, sigReceiving, sigSending and sigFixup.
-// sigReceiving means that signal_recv is blocked on sig.Note and there are no
-// new pending signals.
-// sigSending means that sig.mask *may* contain new pending signals,
-// signal_recv can't be blocked in this state.
-// sigIdle means that there are no new pending signals and signal_recv is not blocked.
-// sigFixup is a transient state that can only exist as a short
-// transition from sigReceiving and then on to sigIdle: it is
-// used to ensure the AllThreadsSyscall()'s mDoFixup() operation
-// occurs on the sleeping m, waiting to receive a signal.
+// variable. It can be in three states:
+// * sigReceiving means that signal_recv is blocked on sig.Note and there are
+//   no new pending signals.
+// * sigSending means that sig.mask *may* contain new pending signals,
+//   signal_recv can't be blocked in this state.
+// * sigIdle means that there are no new pending signals and signal_recv is not
+//   blocked.
+//
 // Transitions between states are done atomically with CAS.
+//
 // When signal_recv is unblocked, it resets sig.Note and rechecks sig.mask.
 // If several sigsends and signal_recv execute concurrently, it can lead to
 // unnecessary rechecks of sig.mask, but it cannot lead to missed signals
@@ -63,7 +63,6 @@ const (
 	sigIdle = iota
 	sigReceiving
 	sigSending
-	sigFixup
 )
 
 // sigsend delivers a signal from sighandler to the internal signal delivery queue.
@@ -117,9 +116,6 @@ Send:
 				notewakeup(&sig.note)
 				break Send
 			}
-		case sigFixup:
-			// nothing to do - we need to wait for sigIdle.
-			mDoFixupAndOSYield()
 		}
 	}
 
@@ -127,19 +123,6 @@ Send:
 	return true
 }
 
-// sigRecvPrepareForFixup is used to temporarily wake up the
-// signal_recv() running thread while it is blocked waiting for the
-// arrival of a signal. If it causes the thread to wake up, the
-// sig.state travels through this sequence: sigReceiving -> sigFixup
-// -> sigIdle -> sigReceiving and resumes. (This is only called while
-// GC is disabled.)
-//go:nosplit
-func sigRecvPrepareForFixup() {
-	if atomic.Cas(&sig.state, sigReceiving, sigFixup) {
-		notewakeup(&sig.note)
-	}
-}
-
 // Called to receive the next queued signal.
 // Must only be called from a single goroutine at a time.
 //go:linkname signal_recv os_1signal.signal__recv
@@ -167,16 +150,7 @@ func signal_recv() uint32 {
 					}
 					notetsleepg(&sig.note, -1)
 					noteclear(&sig.note)
-					if !atomic.Cas(&sig.state, sigFixup, sigIdle) {
-						break Receive
-					}
-					// Getting here, the code will
-					// loop around again to sleep
-					// in state sigReceiving. This
-					// path is taken when
-					// sigRecvPrepareForFixup()
-					// has been called by another
-					// thread.
+					break Receive
 				}
 			case sigSending:
 				if atomic.Cas(&sig.state, sigSending, sigIdle) {
diff --git a/libgo/go/runtime/slice.go b/libgo/go/runtime/slice.go
index 7c8b458..8c85712 100644
--- a/libgo/go/runtime/slice.go
+++ b/libgo/go/runtime/slice.go
@@ -228,7 +228,7 @@ func growslice(et *_type, oldarray unsafe.Pointer, oldlen, oldcap, cap int) slic
 	var lenmem, newlenmem, capmem uintptr
 	// Specialize for common values of et.size.
 	// For 1 we don't need any division/multiplication.
-	// For sys.PtrSize, compiler will optimize division/multiplication into a shift by a constant.
+	// For goarch.PtrSize, compiler will optimize division/multiplication into a shift by a constant.
 	// For powers of 2, use a variable shift.
 	switch {
 	case et.size == 1:
diff --git a/libgo/go/runtime/testdata/testprogcgo/aprof.go b/libgo/go/runtime/testdata/testprogcgo/aprof.go
index 44a15b0..c70d633 100644
--- a/libgo/go/runtime/testdata/testprogcgo/aprof.go
+++ b/libgo/go/runtime/testdata/testprogcgo/aprof.go
@@ -7,8 +7,11 @@ package main
 // Test that SIGPROF received in C code does not crash the process
 // looking for the C code's func pointer.
 
-// The test fails when the function is the first C function.
-// The exported functions are the first C functions, so we use that.
+// This is a regression test for issue 14599, where profiling fails when the
+// function is the first C function. Exported functions are the first C
+// functions, so we use an exported function. Exported functions are created in
+// lexigraphical order of source files, so this file is named aprof.go to
+// ensure its function is first.
 
 // extern void CallGoNop();
 import "C"
diff --git a/libgo/go/runtime/testdata/testprogcgo/pprof_callback.go b/libgo/go/runtime/testdata/testprogcgo/pprof_callback.go
new file mode 100644
index 0000000..e345643
--- /dev/null
+++ b/libgo/go/runtime/testdata/testprogcgo/pprof_callback.go
@@ -0,0 +1,89 @@
+// Copyright 2022 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.
+
+//go:build !plan9 && !windows
+
+package main
+
+// Make many C-to-Go callback while collecting a CPU profile.
+//
+// This is a regression test for issue 50936.
+
+/*
+#include <unistd.h>
+
+void goCallbackPprof();
+
+static void callGo() {
+	// Spent >20us in C so this thread is eligible for sysmon to retake its
+	// P.
+	usleep(50);
+	goCallbackPprof();
+}
+*/
+import "C"
+
+import (
+	"fmt"
+	"os"
+	"runtime/pprof"
+	"runtime"
+	"time"
+)
+
+func init() {
+	register("CgoPprofCallback", CgoPprofCallback)
+}
+
+//export goCallbackPprof
+func goCallbackPprof() {
+	// No-op. We want to stress the cgocall and cgocallback internals,
+	// landing as many pprof signals there as possible.
+}
+
+func CgoPprofCallback() {
+	// Issue 50936 was a crash in the SIGPROF handler when the signal
+	// arrived during the exitsyscall following a cgocall(back) in dropg or
+	// execute, when updating mp.curg.
+	//
+	// These are reachable only when exitsyscall finds no P available. Thus
+	// we make C calls from significantly more Gs than there are available
+	// Ps. Lots of runnable work combined with >20us spent in callGo makes
+	// it possible for sysmon to retake Ps, forcing C calls to go down the
+	// desired exitsyscall path.
+	//
+	// High GOMAXPROCS is used to increase opportunities for failure on
+	// high CPU machines.
+	const (
+		P = 16
+		G = 64
+	)
+	runtime.GOMAXPROCS(P)
+
+	f, err := os.CreateTemp("", "prof")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+	}
+	defer f.Close()
+
+	if err := pprof.StartCPUProfile(f); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+	}
+
+	for i := 0; i < G; i++ {
+		go func() {
+			for {
+				C.callGo()
+			}
+		}()
+	}
+
+	time.Sleep(time.Second)
+
+	pprof.StopCPUProfile()
+
+	fmt.Println("OK")
+}
diff --git a/libgo/go/runtime/trace.go b/libgo/go/runtime/trace.go
index 5d7eb75..9678144 100644
--- a/libgo/go/runtime/trace.go
+++ b/libgo/go/runtime/trace.go
@@ -230,7 +230,7 @@ func StartTrace() error {
 			gp.traceseq = 0
 			gp.tracelastp = getg().m.p
 			// +PCQuantum because traceFrameForPC expects return PCs and subtracts PCQuantum.
-			id := trace.stackTab.put([]location{location{pc: gp.startpc + sys.PCQuantum}})
+			id := trace.stackTab.put([]location{location{pc: startPCforTrace(gp.startpc) + sys.PCQuantum}})
 			traceEvent(traceEvGoCreate, -1, uint64(gp.goid), uint64(id), stackID)
 		}
 		if status == _Gwaiting {
@@ -1066,7 +1066,7 @@ func traceGoCreate(newg *g, pc uintptr) {
 	newg.traceseq = 0
 	newg.tracelastp = getg().m.p
 	// +PCQuantum because traceFrameForPC expects return PCs and subtracts PCQuantum.
-	id := trace.stackTab.put([]location{location{pc: pc + sys.PCQuantum}})
+	id := trace.stackTab.put([]location{location{pc: startPCforTrace(pc) + sys.PCQuantum}})
 	traceEvent(traceEvGoCreate, 2, uint64(newg.goid), uint64(id))
 }
 
@@ -1239,3 +1239,9 @@ func trace_userLog(id uint64, category, message string) {
 
 	traceReleaseBuffer(pid)
 }
+
+// the start PC of a goroutine for tracing purposes. If pc is a wrapper,
+// it returns the PC of the wrapped function. Otherwise it returns pc.
+func startPCforTrace(pc uintptr) uintptr {
+	return pc
+}