diff --git a/libgo/MERGE b/libgo/MERGE
index 8cae45f..07547d0 100644
--- a/libgo/MERGE
+++ b/libgo/MERGE
@@ -1,4 +1,4 @@
-96745b980cfde139e8611772e2bc0c59a8e6cdf7
+83b181c68bf332ac7948f145f33d128377a09c42
 
 The first line of this file holds the git revision number of the
 last merge done from the master library sources.
diff --git a/libgo/VERSION b/libgo/VERSION
index 864916e..d8281a2 100644
--- a/libgo/VERSION
+++ b/libgo/VERSION
@@ -1 +1 @@
-go1.14.2
+go1.14.4
diff --git a/libgo/go/cmd/cgo/gcc.go b/libgo/go/cmd/cgo/gcc.go
index 310316b..e389729 100644
--- a/libgo/go/cmd/cgo/gcc.go
+++ b/libgo/go/cmd/cgo/gcc.go
@@ -2082,6 +2082,10 @@
 // that may contain a pointer. This is used for cgo pointer checking.
 var unionWithPointer = make(map[ast.Expr]bool)
 
+// anonymousStructTag provides a consistent tag for an anonymous struct.
+// The same dwarf.StructType pointer will always get the same tag.
+var anonymousStructTag = make(map[*dwarf.StructType]string)
+
 func (c *typeConv) Init(ptrSize, intSize int64) {
 	c.ptrSize = ptrSize
 	c.intSize = intSize
@@ -2430,8 +2434,12 @@
 			break
 		}
 		if tag == "" {
-			tag = "__" + strconv.Itoa(tagGen)
-			tagGen++
+			tag = anonymousStructTag[dt]
+			if tag == "" {
+				tag = "__" + strconv.Itoa(tagGen)
+				tagGen++
+				anonymousStructTag[dt] = tag
+			}
 		} else if t.C.Empty() {
 			t.C.Set(dt.Kind + " " + tag)
 		}
diff --git a/libgo/go/encoding/json/decode.go b/libgo/go/encoding/json/decode.go
index b434846..b60e2bb 100644
--- a/libgo/go/encoding/json/decode.go
+++ b/libgo/go/encoding/json/decode.go
@@ -1217,6 +1217,11 @@
 	if r == -1 {
 		return s, true
 	}
+	// Only perform up to one safe unquote for each re-scanned string
+	// literal. In some edge cases, the decoder unquotes a literal a second
+	// time, even after another literal has been re-scanned. Thus, only the
+	// first unquote can safely use safeUnquote.
+	d.safeUnquote = 0
 
 	b := make([]byte, len(s)+2*utf8.UTFMax)
 	w := copy(b, s[0:r])
diff --git a/libgo/go/encoding/json/decode_test.go b/libgo/go/encoding/json/decode_test.go
index 498bd97..a49181e 100644
--- a/libgo/go/encoding/json/decode_test.go
+++ b/libgo/go/encoding/json/decode_test.go
@@ -2419,7 +2419,7 @@
 	return nil
 }
 
-// Test unmarshal to a map, with map key is a user defined type.
+// Test unmarshal to a map, where the map key is a user defined type.
 // See golang.org/issues/34437.
 func TestUnmarshalMapWithTextUnmarshalerStringKey(t *testing.T) {
 	var p map[textUnmarshalerString]string
@@ -2428,6 +2428,35 @@
 	}
 
 	if _, ok := p["foo"]; !ok {
-		t.Errorf(`Key "foo" is not existed in map: %v`, p)
+		t.Errorf(`Key "foo" does not exist in map: %v`, p)
+	}
+}
+
+func TestUnmarshalRescanLiteralMangledUnquote(t *testing.T) {
+	// See golang.org/issues/38105.
+	var p map[textUnmarshalerString]string
+	if err := Unmarshal([]byte(`{"开源":"12345开源"}`), &p); err != nil {
+		t.Fatalf("Unmarshal unexpected error: %v", err)
+	}
+	if _, ok := p["开源"]; !ok {
+		t.Errorf(`Key "开源" does not exist in map: %v`, p)
+	}
+
+	// See golang.org/issues/38126.
+	type T struct {
+		F1 string `json:"F1,string"`
+	}
+	t1 := T{"aaa\tbbb"}
+
+	b, err := Marshal(t1)
+	if err != nil {
+		t.Fatalf("Marshal unexpected error: %v", err)
+	}
+	var t2 T
+	if err := Unmarshal(b, &t2); err != nil {
+		t.Fatalf("Unmarshal unexpected error: %v", err)
+	}
+	if t1 != t2 {
+		t.Errorf("Marshal and Unmarshal roundtrip mismatch: want %q got %q", t1, t2)
 	}
 }
diff --git a/libgo/go/encoding/json/encode.go b/libgo/go/encoding/json/encode.go
index 39cdaeb..b351cf3 100644
--- a/libgo/go/encoding/json/encode.go
+++ b/libgo/go/encoding/json/encode.go
@@ -635,11 +635,12 @@
 		return
 	}
 	if opts.quoted {
-		b := make([]byte, 0, v.Len()+2)
-		b = append(b, '"')
-		b = append(b, []byte(v.String())...)
-		b = append(b, '"')
-		e.stringBytes(b, opts.escapeHTML)
+		e2 := newEncodeState()
+		// Since we encode the string twice, we only need to escape HTML
+		// the first time.
+		e2.string(v.String(), opts.escapeHTML)
+		e.stringBytes(e2.Bytes(), false)
+		encodeStatePool.Put(e2)
 	} else {
 		e.string(v.String(), opts.escapeHTML)
 	}
diff --git a/libgo/go/encoding/json/encode_test.go b/libgo/go/encoding/json/encode_test.go
index 5110c7d..7290eca 100644
--- a/libgo/go/encoding/json/encode_test.go
+++ b/libgo/go/encoding/json/encode_test.go
@@ -79,37 +79,66 @@
 	NumberStr  Number  `json:",string"`
 }
 
-var stringTagExpected = `{
- "BoolStr": "true",
- "IntStr": "42",
- "UintptrStr": "44",
- "StrStr": "\"xzbit\"",
- "NumberStr": "46"
-}`
+func TestRoundtripStringTag(t *testing.T) {
+	tests := []struct {
+		name string
+		in   StringTag
+		want string // empty to just test that we roundtrip
+	}{
+		{
+			name: "AllTypes",
+			in: StringTag{
+				BoolStr:    true,
+				IntStr:     42,
+				UintptrStr: 44,
+				StrStr:     "xzbit",
+				NumberStr:  "46",
+			},
+			want: `{
+				"BoolStr": "true",
+				"IntStr": "42",
+				"UintptrStr": "44",
+				"StrStr": "\"xzbit\"",
+				"NumberStr": "46"
+			}`,
+		},
+		{
+			// See golang.org/issues/38173.
+			name: "StringDoubleEscapes",
+			in: StringTag{
+				StrStr:    "\b\f\n\r\t\"\\",
+				NumberStr: "0", // just to satisfy the roundtrip
+			},
+			want: `{
+				"BoolStr": "false",
+				"IntStr": "0",
+				"UintptrStr": "0",
+				"StrStr": "\"\\u0008\\u000c\\n\\r\\t\\\"\\\\\"",
+				"NumberStr": "0"
+			}`,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			// Indent with a tab prefix to make the multi-line string
+			// literals in the table nicer to read.
+			got, err := MarshalIndent(&test.in, "\t\t\t", "\t")
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got := string(got); got != test.want {
+				t.Fatalf(" got: %s\nwant: %s\n", got, test.want)
+			}
 
-func TestStringTag(t *testing.T) {
-	var s StringTag
-	s.BoolStr = true
-	s.IntStr = 42
-	s.UintptrStr = 44
-	s.StrStr = "xzbit"
-	s.NumberStr = "46"
-	got, err := MarshalIndent(&s, "", " ")
-	if err != nil {
-		t.Fatal(err)
-	}
-	if got := string(got); got != stringTagExpected {
-		t.Fatalf(" got: %s\nwant: %s\n", got, stringTagExpected)
-	}
-
-	// Verify that it round-trips.
-	var s2 StringTag
-	err = NewDecoder(bytes.NewReader(got)).Decode(&s2)
-	if err != nil {
-		t.Fatalf("Decode: %v", err)
-	}
-	if !reflect.DeepEqual(s, s2) {
-		t.Fatalf("decode didn't match.\nsource: %#v\nEncoded as:\n%s\ndecode: %#v", s, string(got), s2)
+			// Verify that it round-trips.
+			var s2 StringTag
+			if err := Unmarshal(got, &s2); err != nil {
+				t.Fatalf("Decode: %v", err)
+			}
+			if !reflect.DeepEqual(test.in, s2) {
+				t.Fatalf("decode didn't match.\nsource: %#v\nEncoded as:\n%s\ndecode: %#v", test.in, string(got), s2)
+			}
+		})
 	}
 }
 
diff --git a/libgo/go/encoding/json/stream_test.go b/libgo/go/encoding/json/stream_test.go
index ebb4f23..c9e5334 100644
--- a/libgo/go/encoding/json/stream_test.go
+++ b/libgo/go/encoding/json/stream_test.go
@@ -144,14 +144,15 @@
 		},
 		{
 			"stringOption", stringOption,
-			`{"bar":"\"\u003chtml\u003efoobar\u003c/html\u003e\""}`,
+			`{"bar":"\"\\u003chtml\\u003efoobar\\u003c/html\\u003e\""}`,
 			`{"bar":"\"<html>foobar</html>\""}`,
 		},
 	} {
 		var buf bytes.Buffer
 		enc := NewEncoder(&buf)
 		if err := enc.Encode(tt.v); err != nil {
-			t.Fatalf("Encode(%s): %s", tt.name, err)
+			t.Errorf("Encode(%s): %s", tt.name, err)
+			continue
 		}
 		if got := strings.TrimSpace(buf.String()); got != tt.wantEscape {
 			t.Errorf("Encode(%s) = %#q, want %#q", tt.name, got, tt.wantEscape)
@@ -159,7 +160,8 @@
 		buf.Reset()
 		enc.SetEscapeHTML(false)
 		if err := enc.Encode(tt.v); err != nil {
-			t.Fatalf("SetEscapeHTML(false) Encode(%s): %s", tt.name, err)
+			t.Errorf("SetEscapeHTML(false) Encode(%s): %s", tt.name, err)
+			continue
 		}
 		if got := strings.TrimSpace(buf.String()); got != tt.want {
 			t.Errorf("SetEscapeHTML(false) Encode(%s) = %#q, want %#q",
diff --git a/libgo/go/go/doc/example.go b/libgo/go/go/doc/example.go
index a010d3a..ebf8118 100644
--- a/libgo/go/go/doc/example.go
+++ b/libgo/go/go/doc/example.go
@@ -62,9 +62,6 @@
 			if !ok || f.Recv != nil {
 				continue
 			}
-			if params := f.Type.Params; len(params.List) != 0 {
-				continue // function has params; not a valid example
-			}
 			numDecl++
 			name := f.Name.Name
 			if isTest(name, "Test") || isTest(name, "Benchmark") {
@@ -74,6 +71,9 @@
 			if !isTest(name, "Example") {
 				continue
 			}
+			if params := f.Type.Params; len(params.List) != 0 {
+				continue // function has params; not a valid example
+			}
 			if f.Body == nil { // ast.File.Body nil dereference (see issue 28044)
 				continue
 			}
diff --git a/libgo/go/go/doc/example_test.go b/libgo/go/go/doc/example_test.go
index cd2f469..32db3cd 100644
--- a/libgo/go/go/doc/example_test.go
+++ b/libgo/go/go/doc/example_test.go
@@ -331,25 +331,65 @@
 }
 `
 
+const exampleWholeFileFunction = `package foo_test
+
+func Foo(x int) {
+}
+
+func Example() {
+	fmt.Println("Hello, world!")
+	// Output: Hello, world!
+}
+`
+
+const exampleWholeFileFunctionOutput = `package main
+
+func Foo(x int) {
+}
+
+func main() {
+	fmt.Println("Hello, world!")
+}
+`
+
+var exampleWholeFileTestCases = []struct {
+	Title, Source, Play, Output string
+}{
+	{
+		"Methods",
+		exampleWholeFile,
+		exampleWholeFileOutput,
+		"Hello, world!\n",
+	},
+	{
+		"Function",
+		exampleWholeFileFunction,
+		exampleWholeFileFunctionOutput,
+		"Hello, world!\n",
+	},
+}
+
 func TestExamplesWholeFile(t *testing.T) {
-	fset := token.NewFileSet()
-	file, err := parser.ParseFile(fset, "test.go", strings.NewReader(exampleWholeFile), parser.ParseComments)
-	if err != nil {
-		t.Fatal(err)
-	}
-	es := doc.Examples(file)
-	if len(es) != 1 {
-		t.Fatalf("wrong number of examples; got %d want 1", len(es))
-	}
-	e := es[0]
-	if e.Name != "" {
-		t.Errorf("got Name == %q, want %q", e.Name, "")
-	}
-	if g, w := formatFile(t, fset, e.Play), exampleWholeFileOutput; g != w {
-		t.Errorf("got Play == %q, want %q", g, w)
-	}
-	if g, w := e.Output, "Hello, world!\n"; g != w {
-		t.Errorf("got Output == %q, want %q", g, w)
+	for _, c := range exampleWholeFileTestCases {
+		fset := token.NewFileSet()
+		file, err := parser.ParseFile(fset, "test.go", strings.NewReader(c.Source), parser.ParseComments)
+		if err != nil {
+			t.Fatal(err)
+		}
+		es := doc.Examples(file)
+		if len(es) != 1 {
+			t.Fatalf("%s: wrong number of examples; got %d want 1", c.Title, len(es))
+		}
+		e := es[0]
+		if e.Name != "" {
+			t.Errorf("%s: got Name == %q, want %q", c.Title, e.Name, "")
+		}
+		if g, w := formatFile(t, fset, e.Play), c.Play; g != w {
+			t.Errorf("%s: got Play == %q, want %q", c.Title, g, w)
+		}
+		if g, w := e.Output, c.Output; g != w {
+			t.Errorf("%s: got Output == %q, want %q", c.Title, g, w)
+		}
 	}
 }
 
diff --git a/libgo/go/go/parser/interface.go b/libgo/go/go/parser/interface.go
index 500c98d..54f9d7b 100644
--- a/libgo/go/go/parser/interface.go
+++ b/libgo/go/go/parser/interface.go
@@ -133,13 +133,7 @@
 // first error encountered are returned.
 //
 func ParseDir(fset *token.FileSet, path string, filter func(os.FileInfo) bool, mode Mode) (pkgs map[string]*ast.Package, first error) {
-	fd, err := os.Open(path)
-	if err != nil {
-		return nil, err
-	}
-	defer fd.Close()
-
-	list, err := fd.Readdir(-1)
+	list, err := ioutil.ReadDir(path)
 	if err != nil {
 		return nil, err
 	}
diff --git a/libgo/go/math/big/nat.go b/libgo/go/math/big/nat.go
index 1b771ca..c31ec51 100644
--- a/libgo/go/math/big/nat.go
+++ b/libgo/go/math/big/nat.go
@@ -740,7 +740,8 @@
 // The remainder overwrites input u.
 //
 // Precondition:
-// - len(q) >= len(u)-len(v)
+// - q is large enough to hold the quotient u / v
+//   which has a maximum length of len(u)-len(v)+1.
 func (q nat) divBasic(u, v nat) {
 	n := len(v)
 	m := len(u) - n
@@ -779,6 +780,8 @@
 		}
 
 		// D4.
+		// Compute the remainder u - (q̂*v) << (_W*j).
+		// The subtraction may overflow if q̂ estimate was off by one.
 		qhatv[n] = mulAddVWW(qhatv[0:n], v, qhat, 0)
 		qhl := len(qhatv)
 		if j+qhl > len(u) && qhatv[n] == 0 {
@@ -787,7 +790,11 @@
 		c := subVV(u[j:j+qhl], u[j:], qhatv)
 		if c != 0 {
 			c := addVV(u[j:j+n], u[j:], v)
-			u[j+n] += c
+			// If n == qhl, the carry from subVV and the carry from addVV
+			// cancel out and don't affect u[j+n].
+			if n < qhl {
+				u[j+n] += c
+			}
 			qhat--
 		}
 
@@ -827,6 +834,10 @@
 	putNat(tmp)
 }
 
+// divRecursiveStep computes the division of u by v.
+// - z must be large enough to hold the quotient
+// - the quotient will overwrite z
+// - the remainder will overwrite u
 func (z nat) divRecursiveStep(u, v nat, depth int, tmp *nat, temps []*nat) {
 	u = u.norm()
 	v = v.norm()
diff --git a/libgo/go/math/big/nat_test.go b/libgo/go/math/big/nat_test.go
index 32f29e3..89e913f 100644
--- a/libgo/go/math/big/nat_test.go
+++ b/libgo/go/math/big/nat_test.go
@@ -786,3 +786,21 @@
 		}
 	}
 }
+
+// TestIssue37499 triggers the edge case of divBasic where
+// the inaccurate estimate of the first word's quotient
+// happens at the very beginning of the loop.
+func TestIssue37499(t *testing.T) {
+	// Choose u and v such that v is slightly larger than u >> N.
+	// This tricks divBasic into choosing 1 as the first word
+	// of the quotient. This works in both 32-bit and 64-bit settings.
+	u := natFromString("0x2b6c385a05be027f5c22005b63c42a1165b79ff510e1706b39f8489c1d28e57bb5ba4ef9fd9387a3e344402c0a453381")
+	v := natFromString("0x2b6c385a05be027f5c22005b63c42a1165b79ff510e1706c")
+
+	q := nat(nil).make(8)
+	q.divBasic(u, v)
+	q = q.norm()
+	if s := string(q.utoa(16)); s != "fffffffffffffffffffffffffffffffffffffffffffffffb" {
+		t.Fatalf("incorrect quotient: %s", s)
+	}
+}
diff --git a/libgo/go/os/os_test.go b/libgo/go/os/os_test.go
index a19b46d..8ec6de7 100644
--- a/libgo/go/os/os_test.go
+++ b/libgo/go/os/os_test.go
@@ -2450,3 +2450,38 @@
 		}
 	}
 }
+
+// Test that opening a file does not change its permissions.  Issue 38225.
+func TestOpenFileKeepsPermissions(t *testing.T) {
+	t.Parallel()
+	dir, err := ioutil.TempDir("", "TestOpenFileKeepsPermissions")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer RemoveAll(dir)
+	name := filepath.Join(dir, "x")
+	f, err := Create(name)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := f.Close(); err != nil {
+		t.Error(err)
+	}
+	f, err = OpenFile(name, O_WRONLY|O_CREATE|O_TRUNC, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if fi, err := f.Stat(); err != nil {
+		t.Error(err)
+	} else if fi.Mode()&0222 == 0 {
+		t.Errorf("f.Stat.Mode after OpenFile is %v, should be writable", fi.Mode())
+	}
+	if err := f.Close(); err != nil {
+		t.Error(err)
+	}
+	if fi, err := Stat(name); err != nil {
+		t.Error(err)
+	} else if fi.Mode()&0222 == 0 {
+		t.Errorf("Stat after OpenFile is %v, should be writable", fi.Mode())
+	}
+}
diff --git a/libgo/go/runtime/crash_test.go b/libgo/go/runtime/crash_test.go
index 6268f2e..aa97cf7 100644
--- a/libgo/go/runtime/crash_test.go
+++ b/libgo/go/runtime/crash_test.go
@@ -55,6 +55,16 @@
 		t.Fatal(err)
 	}
 
+	return runBuiltTestProg(t, exe, name, env...)
+}
+
+func runBuiltTestProg(t *testing.T, exe, name string, env ...string) string {
+	if *flagQuick {
+		t.Skip("-quick")
+	}
+
+	testenv.MustHaveGoBuild(t)
+
 	cmd := testenv.CleanCmdEnv(exec.Command(exe, name))
 	cmd.Env = append(cmd.Env, env...)
 	if testing.Short() {
@@ -64,7 +74,7 @@
 	cmd.Stdout = &b
 	cmd.Stderr = &b
 	if err := cmd.Start(); err != nil {
-		t.Fatalf("starting %s %s: %v", binary, name, err)
+		t.Fatalf("starting %s %s: %v", exe, name, err)
 	}
 
 	// If the process doesn't complete within 1 minute,
@@ -92,7 +102,7 @@
 	}()
 
 	if err := cmd.Wait(); err != nil {
-		t.Logf("%s %s exit status: %v", binary, name, err)
+		t.Logf("%s %s exit status: %v", exe, name, err)
 	}
 	close(done)
 
diff --git a/libgo/go/runtime/mgcscavenge.go b/libgo/go/runtime/mgcscavenge.go
index 3b60b3d..d4b527c 100644
--- a/libgo/go/runtime/mgcscavenge.go
+++ b/libgo/go/runtime/mgcscavenge.go
@@ -288,6 +288,28 @@
 			continue
 		}
 
+		if released < physPageSize {
+			// If this happens, it means that we may have attempted to release part
+			// of a physical page, but the likely effect of that is that it released
+			// the whole physical page, some of which may have still been in-use.
+			// This could lead to memory corruption. Throw.
+			throw("released less than one physical page of memory")
+		}
+
+		// On some platforms we may see crit as zero if the time it takes to scavenge
+		// memory is less than the minimum granularity of its clock (e.g. Windows).
+		// In this case, just assume scavenging takes 10 µs per regular physical page
+		// (determined empirically), and conservatively ignore the impact of huge pages
+		// on timing.
+		//
+		// We shouldn't ever see a crit value less than zero unless there's a bug of
+		// some kind, either on our side or in the platform we're running on, but be
+		// defensive in that case as well.
+		const approxCritNSPerPhysicalPage = 10e3
+		if crit <= 0 {
+			crit = approxCritNSPerPhysicalPage * float64(released/physPageSize)
+		}
+
 		// Multiply the critical time by 1 + the ratio of the costs of using
 		// scavenged memory vs. scavenging memory. This forces us to pay down
 		// the cost of reusing this memory eagerly by sleeping for a longer period
diff --git a/libgo/go/runtime/mpagecache.go b/libgo/go/runtime/mpagecache.go
index 9fc338b..a074961 100644
--- a/libgo/go/runtime/mpagecache.go
+++ b/libgo/go/runtime/mpagecache.go
@@ -148,9 +148,14 @@
 	// Update as an allocation, but note that it's not contiguous.
 	s.update(c.base, pageCachePages, false, true)
 
-	// We're always searching for the first free page, and we always know the
-	// up to pageCache size bits will be allocated, so we can always move the
-	// searchAddr past the cache.
-	s.searchAddr = c.base + pageSize*pageCachePages
+	// Set the search address to the last page represented by the cache.
+	// Since all of the pages in this block are going to the cache, and we
+	// searched for the first free page, we can confidently start at the
+	// next page.
+	//
+	// However, s.searchAddr is not allowed to point into unmapped heap memory
+	// unless it is maxSearchAddr, so make it the last page as opposed to
+	// the page after.
+	s.searchAddr = c.base + pageSize*(pageCachePages-1)
 	return c
 }
diff --git a/libgo/go/runtime/mpagecache_test.go b/libgo/go/runtime/mpagecache_test.go
index b8cc0bd..2ed0c0a 100644
--- a/libgo/go/runtime/mpagecache_test.go
+++ b/libgo/go/runtime/mpagecache_test.go
@@ -260,12 +260,13 @@
 	if GOOS == "openbsd" && testing.Short() {
 		t.Skip("skipping because virtual memory is limited; see #36210")
 	}
-	tests := map[string]struct {
+	type test struct {
 		before map[ChunkIdx][]BitRange
 		scav   map[ChunkIdx][]BitRange
 		hits   []PageCache // expected base addresses and patterns
 		after  map[ChunkIdx][]BitRange
-	}{
+	}
+	tests := map[string]test{
 		"AllFree": {
 			before: map[ChunkIdx][]BitRange{
 				BaseChunkIdx: {},
@@ -349,6 +350,34 @@
 			},
 		},
 	}
+	if PageAlloc64Bit != 0 {
+		const chunkIdxBigJump = 0x100000 // chunk index offset which translates to O(TiB)
+
+		// This test is similar to the one with the same name for
+		// pageAlloc.alloc and serves the same purpose.
+		// See mpagealloc_test.go for details.
+		sumsPerPhysPage := ChunkIdx(PhysPageSize / PallocSumBytes)
+		baseChunkIdx := BaseChunkIdx &^ (sumsPerPhysPage - 1)
+		tests["DiscontiguousMappedSumBoundary"] = test{
+			before: map[ChunkIdx][]BitRange{
+				baseChunkIdx + sumsPerPhysPage - 1: {{0, PallocChunkPages - 1}},
+				baseChunkIdx + chunkIdxBigJump:     {{1, PallocChunkPages - 1}},
+			},
+			scav: map[ChunkIdx][]BitRange{
+				baseChunkIdx + sumsPerPhysPage - 1: {},
+				baseChunkIdx + chunkIdxBigJump:     {},
+			},
+			hits: []PageCache{
+				NewPageCache(PageBase(baseChunkIdx+sumsPerPhysPage-1, PallocChunkPages-64), 1<<63, 0),
+				NewPageCache(PageBase(baseChunkIdx+chunkIdxBigJump, 0), 1, 0),
+				NewPageCache(0, 0, 0),
+			},
+			after: map[ChunkIdx][]BitRange{
+				baseChunkIdx + sumsPerPhysPage - 1: {{0, PallocChunkPages}},
+				baseChunkIdx + chunkIdxBigJump:     {{0, PallocChunkPages}},
+			},
+		}
+	}
 	for name, v := range tests {
 		v := v
 		t.Run(name, func(t *testing.T) {
diff --git a/libgo/go/runtime/proc.go b/libgo/go/runtime/proc.go
index f75cacf..e098137 100644
--- a/libgo/go/runtime/proc.go
+++ b/libgo/go/runtime/proc.go
@@ -1704,10 +1704,16 @@
 	if GOARCH == "wasm" { // no threads on wasm yet
 		return
 	}
+
+	// Disable preemption to guarantee that the template thread will be
+	// created before a park once haveTemplateThread is set.
+	mp := acquirem()
 	if !atomic.Cas(&newmHandoff.haveTemplateThread, 0, 1) {
+		releasem(mp)
 		return
 	}
 	newm(templateThread, nil)
+	releasem(mp)
 }
 
 // templateThread is a thread in a known-good state that exists solely
diff --git a/libgo/go/runtime/proc_test.go b/libgo/go/runtime/proc_test.go
index a693937..5f96d64 100644
--- a/libgo/go/runtime/proc_test.go
+++ b/libgo/go/runtime/proc_test.go
@@ -6,6 +6,7 @@
 
 import (
 	"fmt"
+	"internal/testenv"
 	"math"
 	"net"
 	"runtime"
@@ -930,6 +931,29 @@
 	}
 }
 
+func TestLockOSThreadTemplateThreadRace(t *testing.T) {
+	testenv.MustHaveGoRun(t)
+
+	exe, err := buildTestProg(t, "testprog")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	iterations := 100
+	if testing.Short() {
+		// Reduce run time to ~100ms, with much lower probability of
+		// catching issues.
+		iterations = 5
+	}
+	for i := 0; i < iterations; i++ {
+		want := "OK\n"
+		output := runBuiltTestProg(t, exe, "LockOSThreadTemplateThreadRace")
+		if output != want {
+			t.Fatalf("run %d: want %q, got %q", i, want, output)
+		}
+	}
+}
+
 // fakeSyscall emulates a system call.
 //go:nosplit
 func fakeSyscall(duration time.Duration) {
diff --git a/libgo/go/runtime/testdata/testprog/lockosthread.go b/libgo/go/runtime/testdata/testprog/lockosthread.go
index fd3123e..098cc4d 100644
--- a/libgo/go/runtime/testdata/testprog/lockosthread.go
+++ b/libgo/go/runtime/testdata/testprog/lockosthread.go
@@ -7,6 +7,7 @@
 import (
 	"os"
 	"runtime"
+	"sync"
 	"time"
 )
 
@@ -30,6 +31,7 @@
 		runtime.LockOSThread()
 	})
 	register("LockOSThreadAvoidsStatePropagation", LockOSThreadAvoidsStatePropagation)
+	register("LockOSThreadTemplateThreadRace", LockOSThreadTemplateThreadRace)
 }
 
 func LockOSThreadMain() {
@@ -195,3 +197,50 @@
 	runtime.UnlockOSThread()
 	println("OK")
 }
+
+func LockOSThreadTemplateThreadRace() {
+	// This test attempts to reproduce the race described in
+	// golang.org/issue/38931. To do so, we must have a stop-the-world
+	// (achieved via ReadMemStats) racing with two LockOSThread calls.
+	//
+	// While this test attempts to line up the timing, it is only expected
+	// to fail (and thus hang) around 2% of the time if the race is
+	// present.
+
+	// Ensure enough Ps to actually run everything in parallel. Though on
+	// <4 core machines, we are still at the whim of the kernel scheduler.
+	runtime.GOMAXPROCS(4)
+
+	go func() {
+		// Stop the world; race with LockOSThread below.
+		var m runtime.MemStats
+		for {
+			runtime.ReadMemStats(&m)
+		}
+	}()
+
+	// Try to synchronize both LockOSThreads.
+	start := time.Now().Add(10*time.Millisecond)
+
+	var wg sync.WaitGroup
+	wg.Add(2)
+
+	for i := 0; i < 2; i++ {
+		go func() {
+			for time.Now().Before(start) {
+			}
+
+			// Add work to the local runq to trigger early startm
+			// in handoffp.
+			go func(){}()
+
+			runtime.LockOSThread()
+			runtime.Gosched()  // add a preemption point.
+			wg.Done()
+		}()
+	}
+
+	wg.Wait()
+	// If both LockOSThreads completed then we did not hit the race.
+	println("OK")
+}
diff --git a/libgo/misc/cgo/test/testx.go b/libgo/misc/cgo/test/testx.go
index 42979b5..eb9d7fa 100644
--- a/libgo/misc/cgo/test/testx.go
+++ b/libgo/misc/cgo/test/testx.go
@@ -124,6 +124,11 @@
 } Issue31891B;
 
 void callIssue31891(void);
+
+typedef struct {
+	int i;
+} Issue38408, *PIssue38408;
+
 */
 import "C"
 
@@ -552,3 +557,8 @@
 func test31891(t *testing.T) {
 	C.callIssue31891()
 }
+
+// issue 38408
+// A typedef pointer can be used as the element type.
+// No runtime test; just make sure it compiles.
+var _ C.PIssue38408 = &C.Issue38408{i: 1}