20 files changed, 248 insertions, 83 deletions

diff --git a/libgo/go/encoding/ascii85/ascii85_test.go b/libgo/go/encoding/ascii85/ascii85_test.go
index 1a3a87a..c6371039 100644
--- a/libgo/go/encoding/ascii85/ascii85_test.go
+++ b/libgo/go/encoding/ascii85/ascii85_test.go
@@ -7,7 +7,6 @@ package ascii85
 import (
 	"bytes"
 	"io"
-	"io/ioutil"
 	"strings"
 	"testing"
 )
@@ -118,7 +117,7 @@ func TestDecode(t *testing.T) {
 func TestDecoder(t *testing.T) {
 	for _, p := range pairs {
 		decoder := NewDecoder(strings.NewReader(p.encoded))
-		dbuf, err := ioutil.ReadAll(decoder)
+		dbuf, err := io.ReadAll(decoder)
 		if err != nil {
 			t.Fatal("Read failed", err)
 		}
@@ -187,7 +186,7 @@ func TestBig(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Encoder.Close() = %v want nil", err)
 	}
-	decoded, err := ioutil.ReadAll(NewDecoder(encoded))
+	decoded, err := io.ReadAll(NewDecoder(encoded))
 	if err != nil {
 		t.Fatalf("io.ReadAll(NewDecoder(...)): %v", err)
 	}
@@ -205,7 +204,7 @@ func TestBig(t *testing.T) {
 
 func TestDecoderInternalWhitespace(t *testing.T) {
 	s := strings.Repeat(" ", 2048) + "z"
-	decoded, err := ioutil.ReadAll(NewDecoder(strings.NewReader(s)))
+	decoded, err := io.ReadAll(NewDecoder(strings.NewReader(s)))
 	if err != nil {
 		t.Errorf("Decode gave error %v", err)
 	}
diff --git a/libgo/go/encoding/asn1/asn1.go b/libgo/go/encoding/asn1/asn1.go
index d809dde..7c260b4 100644
--- a/libgo/go/encoding/asn1/asn1.go
+++ b/libgo/go/encoding/asn1/asn1.go
@@ -851,53 +851,37 @@ func parseField(v reflect.Value, bytes []byte, initOffset int, params fieldParam
 	offset += t.length
 
 	// We deal with the structures defined in this package first.
-	switch fieldType {
-	case rawValueType:
-		result := RawValue{t.class, t.tag, t.isCompound, innerBytes, bytes[initOffset:offset]}
-		v.Set(reflect.ValueOf(result))
+	switch v := v.Addr().Interface().(type) {
+	case *RawValue:
+		*v = RawValue{t.class, t.tag, t.isCompound, innerBytes, bytes[initOffset:offset]}
 		return
-	case objectIdentifierType:
-		newSlice, err1 := parseObjectIdentifier(innerBytes)
-		v.Set(reflect.MakeSlice(v.Type(), len(newSlice), len(newSlice)))
-		if err1 == nil {
-			reflect.Copy(v, reflect.ValueOf(newSlice))
-		}
-		err = err1
+	case *ObjectIdentifier:
+		*v, err = parseObjectIdentifier(innerBytes)
 		return
-	case bitStringType:
-		bs, err1 := parseBitString(innerBytes)
-		if err1 == nil {
-			v.Set(reflect.ValueOf(bs))
-		}
-		err = err1
+	case *BitString:
+		*v, err = parseBitString(innerBytes)
 		return
-	case timeType:
-		var time time.Time
-		var err1 error
+	case *time.Time:
 		if universalTag == TagUTCTime {
-			time, err1 = parseUTCTime(innerBytes)
-		} else {
-			time, err1 = parseGeneralizedTime(innerBytes)
-		}
-		if err1 == nil {
-			v.Set(reflect.ValueOf(time))
+			*v, err = parseUTCTime(innerBytes)
+			return
 		}
-		err = err1
+		*v, err = parseGeneralizedTime(innerBytes)
 		return
-	case enumeratedType:
+	case *Enumerated:
 		parsedInt, err1 := parseInt32(innerBytes)
 		if err1 == nil {
-			v.SetInt(int64(parsedInt))
+			*v = Enumerated(parsedInt)
 		}
 		err = err1
 		return
-	case flagType:
-		v.SetBool(true)
+	case *Flag:
+		*v = true
 		return
-	case bigIntType:
+	case **big.Int:
 		parsedInt, err1 := parseBigInt(innerBytes)
 		if err1 == nil {
-			v.Set(reflect.ValueOf(parsedInt))
+			*v = parsedInt
 		}
 		err = err1
 		return
@@ -1035,7 +1019,8 @@ func setDefaultValue(v reflect.Value, params fieldParameters) (ok bool) {
 // Unmarshal parses the DER-encoded ASN.1 data structure b
 // and uses the reflect package to fill in an arbitrary value pointed at by val.
 // Because Unmarshal uses the reflect package, the structs
-// being written to must use upper case field names.
+// being written to must use upper case field names. If val
+// is nil or not a pointer, Unmarshal returns an error.
 //
 // After parsing b, any bytes that were leftover and not used to fill
 // val will be returned in rest. When parsing a SEQUENCE into a struct,
@@ -1085,9 +1070,10 @@ func setDefaultValue(v reflect.Value, params fieldParameters) (ok bool) {
 // If the type of the first field of a structure is RawContent then the raw
 // ASN1 contents of the struct will be stored in it.
 //
-// If the type name of a slice element ends with "SET" then it's treated as if
-// the "set" tag was set on it. This can be used with nested slices where a
-// struct tag cannot be given.
+// If the name of a slice type ends with "SET" then it's treated as if
+// the "set" tag was set on it. This results in interpreting the type as a
+// SET OF x rather than a SEQUENCE OF x. This can be used with nested slices
+// where a struct tag cannot be given.
 //
 // Other ASN.1 types are not supported; if it encounters them,
 // Unmarshal returns a parse error.
@@ -1095,11 +1081,31 @@ func Unmarshal(b []byte, val interface{}) (rest []byte, err error) {
 	return UnmarshalWithParams(b, val, "")
 }
 
+// An invalidUnmarshalError describes an invalid argument passed to Unmarshal.
+// (The argument to Unmarshal must be a non-nil pointer.)
+type invalidUnmarshalError struct {
+	Type reflect.Type
+}
+
+func (e *invalidUnmarshalError) Error() string {
+	if e.Type == nil {
+		return "asn1: Unmarshal recipient value is nil"
+	}
+
+	if e.Type.Kind() != reflect.Ptr {
+		return "asn1: Unmarshal recipient value is non-pointer " + e.Type.String()
+	}
+	return "asn1: Unmarshal recipient value is nil " + e.Type.String()
+}
+
 // UnmarshalWithParams allows field parameters to be specified for the
 // top-level element. The form of the params is the same as the field tags.
 func UnmarshalWithParams(b []byte, val interface{}, params string) (rest []byte, err error) {
-	v := reflect.ValueOf(val).Elem()
-	offset, err := parseField(v, b, 0, parseFieldParameters(params))
+	v := reflect.ValueOf(val)
+	if v.Kind() != reflect.Ptr || v.IsNil() {
+		return nil, &invalidUnmarshalError{reflect.TypeOf(val)}
+	}
+	offset, err := parseField(v.Elem(), b, 0, parseFieldParameters(params))
 	if err != nil {
 		return nil, err
 	}
diff --git a/libgo/go/encoding/asn1/asn1_test.go b/libgo/go/encoding/asn1/asn1_test.go
index 8daae97..8985538 100644
--- a/libgo/go/encoding/asn1/asn1_test.go
+++ b/libgo/go/encoding/asn1/asn1_test.go
@@ -518,6 +518,29 @@ func TestUnmarshal(t *testing.T) {
 	}
 }
 
+func TestUnmarshalWithNilOrNonPointer(t *testing.T) {
+	tests := []struct {
+		b    []byte
+		v    interface{}
+		want string
+	}{
+		{b: []byte{0x05, 0x00}, v: nil, want: "asn1: Unmarshal recipient value is nil"},
+		{b: []byte{0x05, 0x00}, v: RawValue{}, want: "asn1: Unmarshal recipient value is non-pointer asn1.RawValue"},
+		{b: []byte{0x05, 0x00}, v: (*RawValue)(nil), want: "asn1: Unmarshal recipient value is nil *asn1.RawValue"},
+	}
+
+	for _, test := range tests {
+		_, err := Unmarshal(test.b, test.v)
+		if err == nil {
+			t.Errorf("Unmarshal expecting error, got nil")
+			continue
+		}
+		if g, w := err.Error(), test.want; g != w {
+			t.Errorf("InvalidUnmarshalError mismatch\nGot:  %q\nWant: %q", g, w)
+		}
+	}
+}
+
 type Certificate struct {
 	TBSCertificate     TBSCertificate
 	SignatureAlgorithm AlgorithmIdentifier
diff --git a/libgo/go/encoding/asn1/common.go b/libgo/go/encoding/asn1/common.go
index e2aa8bd..1c712e1 100644
--- a/libgo/go/encoding/asn1/common.go
+++ b/libgo/go/encoding/asn1/common.go
@@ -92,7 +92,16 @@ type fieldParameters struct {
 // parseFieldParameters will parse it into a fieldParameters structure,
 // ignoring unknown parts of the string.
 func parseFieldParameters(str string) (ret fieldParameters) {
-	for _, part := range strings.Split(str, ",") {
+	var part string
+	for len(str) > 0 {
+		// This loop uses IndexByte and explicit slicing
+		// instead of strings.Split(str, ",") to reduce allocations.
+		i := strings.IndexByte(str, ',')
+		if i < 0 {
+			part, str = str, ""
+		} else {
+			part, str = str[:i], str[i+1:]
+		}
 		switch {
 		case part == "optional":
 			ret.optional = true
diff --git a/libgo/go/encoding/asn1/marshal_test.go b/libgo/go/encoding/asn1/marshal_test.go
index 5290522..e3a7d8f 100644
--- a/libgo/go/encoding/asn1/marshal_test.go
+++ b/libgo/go/encoding/asn1/marshal_test.go
@@ -376,3 +376,31 @@ func TestSetEncoderSETSliceSuffix(t *testing.T) {
 		t.Errorf("Unexpected SET content. got: %s, want: %s", resultSet, expectedOrder)
 	}
 }
+
+func BenchmarkUnmarshal(b *testing.B) {
+	b.ReportAllocs()
+
+	type testCase struct {
+		in  []byte
+		out interface{}
+	}
+	var testData []testCase
+	for _, test := range unmarshalTestData {
+		pv := reflect.New(reflect.TypeOf(test.out).Elem())
+		inCopy := make([]byte, len(test.in))
+		copy(inCopy, test.in)
+		outCopy := pv.Interface()
+
+		testData = append(testData, testCase{
+			in:  inCopy,
+			out: outCopy,
+		})
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		for _, testCase := range testData {
+			_, _ = Unmarshal(testCase.in, testCase.out)
+		}
+	}
+}
diff --git a/libgo/go/encoding/base32/base32_test.go b/libgo/go/encoding/base32/base32_test.go
index 0b611db..8fb22b9 100644
--- a/libgo/go/encoding/base32/base32_test.go
+++ b/libgo/go/encoding/base32/base32_test.go
@@ -8,7 +8,6 @@ import (
 	"bytes"
 	"errors"
 	"io"
-	"io/ioutil"
 	"strings"
 	"testing"
 )
@@ -361,9 +360,9 @@ func TestBig(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Encoder.Close() = %v want nil", err)
 	}
-	decoded, err := ioutil.ReadAll(NewDecoder(StdEncoding, encoded))
+	decoded, err := io.ReadAll(NewDecoder(StdEncoding, encoded))
 	if err != nil {
-		t.Fatalf("ioutil.ReadAll(NewDecoder(...)): %v", err)
+		t.Fatalf("io.ReadAll(NewDecoder(...)): %v", err)
 	}
 
 	if !bytes.Equal(raw, decoded) {
@@ -428,14 +427,14 @@ LNEBUWIIDFON2CA3DBMJXXE5LNFY==
 	encodedShort := strings.ReplaceAll(encoded, "\n", "")
 
 	dec := NewDecoder(StdEncoding, strings.NewReader(encoded))
-	res1, err := ioutil.ReadAll(dec)
+	res1, err := io.ReadAll(dec)
 	if err != nil {
 		t.Errorf("ReadAll failed: %v", err)
 	}
 
 	dec = NewDecoder(StdEncoding, strings.NewReader(encodedShort))
 	var res2 []byte
-	res2, err = ioutil.ReadAll(dec)
+	res2, err = io.ReadAll(dec)
 	if err != nil {
 		t.Errorf("ReadAll failed: %v", err)
 	}
@@ -619,7 +618,7 @@ func TestBufferedDecodingSameError(t *testing.T) {
 			}()
 
 			decoder := NewDecoder(StdEncoding, pr)
-			_, err := ioutil.ReadAll(decoder)
+			_, err := io.ReadAll(decoder)
 
 			if err != testcase.expected {
 				t.Errorf("Expected %v, got %v; case %s %+v", testcase.expected, err, testcase.prefix, chunks)
@@ -718,7 +717,7 @@ func TestDecodeReadAll(t *testing.T) {
 				encoded = strings.ReplaceAll(encoded, "=", "")
 			}
 
-			decReader, err := ioutil.ReadAll(NewDecoder(encoding, strings.NewReader(encoded)))
+			decReader, err := io.ReadAll(NewDecoder(encoding, strings.NewReader(encoded)))
 			if err != nil {
 				t.Errorf("NewDecoder error: %v", err)
 			}
diff --git a/libgo/go/encoding/base64/base64_test.go b/libgo/go/encoding/base64/base64_test.go
index c2c9478..5104740 100644
--- a/libgo/go/encoding/base64/base64_test.go
+++ b/libgo/go/encoding/base64/base64_test.go
@@ -9,7 +9,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"reflect"
 	"runtime/debug"
 	"strings"
@@ -324,9 +323,9 @@ func TestBig(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Encoder.Close() = %v want nil", err)
 	}
-	decoded, err := ioutil.ReadAll(NewDecoder(StdEncoding, encoded))
+	decoded, err := io.ReadAll(NewDecoder(StdEncoding, encoded))
 	if err != nil {
-		t.Fatalf("ioutil.ReadAll(NewDecoder(...)): %v", err)
+		t.Fatalf("io.ReadAll(NewDecoder(...)): %v", err)
 	}
 
 	if !bytes.Equal(raw, decoded) {
@@ -403,7 +402,7 @@ func TestDecoderIssue3577(t *testing.T) {
 	})
 	errc := make(chan error, 1)
 	go func() {
-		_, err := ioutil.ReadAll(d)
+		_, err := io.ReadAll(d)
 		errc <- err
 	}()
 	select {
@@ -436,14 +435,14 @@ bqbPb06551Y4
 	encodedShort := strings.ReplaceAll(encoded, "\n", "")
 
 	dec := NewDecoder(StdEncoding, strings.NewReader(encoded))
-	res1, err := ioutil.ReadAll(dec)
+	res1, err := io.ReadAll(dec)
 	if err != nil {
 		t.Errorf("ReadAll failed: %v", err)
 	}
 
 	dec = NewDecoder(StdEncoding, strings.NewReader(encodedShort))
 	var res2 []byte
-	res2, err = ioutil.ReadAll(dec)
+	res2, err = io.ReadAll(dec)
 	if err != nil {
 		t.Errorf("ReadAll failed: %v", err)
 	}
@@ -517,14 +516,14 @@ func TestDecoderRaw(t *testing.T) {
 
 	// Through reader. Used to fail.
 	r := NewDecoder(RawURLEncoding, bytes.NewReader([]byte(source)))
-	dec2, err := ioutil.ReadAll(io.LimitReader(r, 100))
+	dec2, err := io.ReadAll(io.LimitReader(r, 100))
 	if err != nil || !bytes.Equal(dec2, want) {
 		t.Errorf("reading NewDecoder(RawURLEncoding, %q) = %x, %v, want %x, nil", source, dec2, err, want)
 	}
 
 	// Should work with padding.
 	r = NewDecoder(URLEncoding, bytes.NewReader([]byte(source+"==")))
-	dec3, err := ioutil.ReadAll(r)
+	dec3, err := io.ReadAll(r)
 	if err != nil || !bytes.Equal(dec3, want) {
 		t.Errorf("reading NewDecoder(URLEncoding, %q) = %x, %v, want %x, nil", source+"==", dec3, err, want)
 	}
diff --git a/libgo/go/encoding/binary/binary.go b/libgo/go/encoding/binary/binary.go
index a99ca01..a311499 100644
--- a/libgo/go/encoding/binary/binary.go
+++ b/libgo/go/encoding/binary/binary.go
@@ -306,7 +306,7 @@ func Write(w io.Writer, order ByteOrder, data interface{}) error {
 		case uint8:
 			bs[0] = v
 		case []uint8:
-			bs = v // TODO(josharian): avoid allocating bs in this case?
+			bs = v
 		case *int16:
 			order.PutUint16(bs, uint16(*v))
 		case int16:
diff --git a/libgo/go/encoding/binary/binary_test.go b/libgo/go/encoding/binary/binary_test.go
index aeb4212..83af89e 100644
--- a/libgo/go/encoding/binary/binary_test.go
+++ b/libgo/go/encoding/binary/binary_test.go
@@ -8,7 +8,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math"
 	"reflect"
 	"strings"
@@ -524,7 +523,7 @@ func BenchmarkWriteStruct(b *testing.B) {
 	b.SetBytes(int64(Size(&s)))
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		Write(ioutil.Discard, BigEndian, &s)
+		Write(io.Discard, BigEndian, &s)
 	}
 }
 
@@ -706,3 +705,27 @@ func BenchmarkWriteSlice1000Float32s(b *testing.B) {
 	}
 	b.StopTimer()
 }
+
+func BenchmarkReadSlice1000Uint8s(b *testing.B) {
+	bsr := &byteSliceReader{}
+	slice := make([]uint8, 1000)
+	buf := make([]byte, len(slice))
+	b.SetBytes(int64(len(buf)))
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		bsr.remain = buf
+		Read(bsr, BigEndian, slice)
+	}
+}
+
+func BenchmarkWriteSlice1000Uint8s(b *testing.B) {
+	slice := make([]uint8, 1000)
+	buf := new(bytes.Buffer)
+	var w io.Writer = buf
+	b.SetBytes(1000)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		buf.Reset()
+		Write(w, BigEndian, slice)
+	}
+}
diff --git a/libgo/go/encoding/binary/varint.go b/libgo/go/encoding/binary/varint.go
index 38af610..1fa325d 100644
--- a/libgo/go/encoding/binary/varint.go
+++ b/libgo/go/encoding/binary/varint.go
@@ -62,7 +62,7 @@ func Uvarint(buf []byte) (uint64, int) {
 	var s uint
 	for i, b := range buf {
 		if b < 0x80 {
-			if i > 9 || i == 9 && b > 1 {
+			if i >= MaxVarintLen64 || i == MaxVarintLen64-1 && b > 1 {
 				return 0, -(i + 1) // overflow
 			}
 			return x | uint64(b)<<s, i + 1
@@ -112,7 +112,7 @@ func ReadUvarint(r io.ByteReader) (uint64, error) {
 			return x, err
 		}
 		if b < 0x80 {
-			if i == 9 && b > 1 {
+			if i == MaxVarintLen64-1 && b > 1 {
 				return x, overflow
 			}
 			return x | uint64(b)<<s, nil
diff --git a/libgo/go/encoding/gob/encoder_test.go b/libgo/go/encoding/gob/encoder_test.go
index 825f0d6..fe27749 100644
--- a/libgo/go/encoding/gob/encoder_test.go
+++ b/libgo/go/encoding/gob/encoder_test.go
@@ -8,7 +8,7 @@ import (
 	"bytes"
 	"encoding/hex"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"reflect"
 	"strings"
 	"testing"
@@ -938,7 +938,7 @@ func encodeAndRecover(value interface{}) (encodeErr, panicErr error) {
 		}
 	}()
 
-	encodeErr = NewEncoder(ioutil.Discard).Encode(value)
+	encodeErr = NewEncoder(io.Discard).Encode(value)
 	return
 }
 
diff --git a/libgo/go/encoding/hex/hex_test.go b/libgo/go/encoding/hex/hex_test.go
index 31e3f68..7593e20 100644
--- a/libgo/go/encoding/hex/hex_test.go
+++ b/libgo/go/encoding/hex/hex_test.go
@@ -8,7 +8,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"strings"
 	"testing"
 )
@@ -150,7 +149,7 @@ func TestEncoderDecoder(t *testing.T) {
 func TestDecoderErr(t *testing.T) {
 	for _, tt := range errTests {
 		dec := NewDecoder(strings.NewReader(tt.in))
-		out, err := ioutil.ReadAll(dec)
+		out, err := io.ReadAll(dec)
 		wantErr := tt.err
 		// Decoder is reading from stream, so it reports io.ErrUnexpectedEOF instead of ErrLength.
 		if wantErr == ErrLength {
diff --git a/libgo/go/encoding/json/bench_test.go b/libgo/go/encoding/json/bench_test.go
index 4a5fe7e..73c7b09 100644
--- a/libgo/go/encoding/json/bench_test.go
+++ b/libgo/go/encoding/json/bench_test.go
@@ -15,7 +15,7 @@ import (
 	"compress/gzip"
 	"fmt"
 	"internal/testenv"
-	"io/ioutil"
+	"io"
 	"os"
 	"reflect"
 	"runtime"
@@ -52,7 +52,7 @@ func codeInit() {
 	if err != nil {
 		panic(err)
 	}
-	data, err := ioutil.ReadAll(gz)
+	data, err := io.ReadAll(gz)
 	if err != nil {
 		panic(err)
 	}
@@ -89,7 +89,7 @@ func BenchmarkCodeEncoder(b *testing.B) {
 		b.StartTimer()
 	}
 	b.RunParallel(func(pb *testing.PB) {
-		enc := NewEncoder(ioutil.Discard)
+		enc := NewEncoder(io.Discard)
 		for pb.Next() {
 			if err := enc.Encode(&codeStruct); err != nil {
 				b.Fatal("Encode:", err)
@@ -399,7 +399,7 @@ func BenchmarkEncodeMarshaler(b *testing.B) {
 	}{}
 
 	b.RunParallel(func(pb *testing.PB) {
-		enc := NewEncoder(ioutil.Discard)
+		enc := NewEncoder(io.Discard)
 
 		for pb.Next() {
 			if err := enc.Encode(&m); err != nil {
diff --git a/libgo/go/encoding/json/encode.go b/libgo/go/encoding/json/encode.go
index 578d551..483b9d8 100644
--- a/libgo/go/encoding/json/encode.go
+++ b/libgo/go/encoding/json/encode.go
@@ -236,6 +236,8 @@ func (e *UnsupportedTypeError) Error() string {
 	return "json: unsupported type: " + e.Type.String()
 }
 
+// An UnsupportedValueError is returned by Marshal when attempting
+// to encode an unsupported value.
 type UnsupportedValueError struct {
 	Value reflect.Value
 	Str   string
@@ -779,6 +781,16 @@ func (me mapEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
 		e.WriteString("null")
 		return
 	}
+	if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
+		// We're a large number of nested ptrEncoder.encode calls deep;
+		// start checking if we've run into a pointer cycle.
+		ptr := v.Pointer()
+		if _, ok := e.ptrSeen[ptr]; ok {
+			e.error(&UnsupportedValueError{v, fmt.Sprintf("encountered a cycle via %s", v.Type())})
+		}
+		e.ptrSeen[ptr] = struct{}{}
+		defer delete(e.ptrSeen, ptr)
+	}
 	e.WriteByte('{')
 
 	// Extract and sort the keys.
@@ -801,6 +813,7 @@ func (me mapEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
 		me.elemEnc(e, v.MapIndex(kv.v), opts)
 	}
 	e.WriteByte('}')
+	e.ptrLevel--
 }
 
 func newMapEncoder(t reflect.Type) encoderFunc {
@@ -857,7 +870,23 @@ func (se sliceEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
 		e.WriteString("null")
 		return
 	}
+	if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
+		// We're a large number of nested ptrEncoder.encode calls deep;
+		// start checking if we've run into a pointer cycle.
+		// Here we use a struct to memorize the pointer to the first element of the slice
+		// and its length.
+		ptr := struct {
+			ptr uintptr
+			len int
+		}{v.Pointer(), v.Len()}
+		if _, ok := e.ptrSeen[ptr]; ok {
+			e.error(&UnsupportedValueError{v, fmt.Sprintf("encountered a cycle via %s", v.Type())})
+		}
+		e.ptrSeen[ptr] = struct{}{}
+		defer delete(e.ptrSeen, ptr)
+	}
 	se.arrayEnc(e, v, opts)
+	e.ptrLevel--
 }
 
 func newSliceEncoder(t reflect.Type) encoderFunc {
@@ -946,7 +975,7 @@ func isValidTag(s string) bool {
 	}
 	for _, c := range s {
 		switch {
-		case strings.ContainsRune("!#$%&()*+-./:<=>?@[]^_{|}~ ", c):
+		case strings.ContainsRune("!#$%&()*+-./:;<=>?@[]^_{|}~ ", c):
 			// Backslash and quote chars are reserved, but
 			// otherwise any punctuation chars are allowed
 			// in a tag name.
diff --git a/libgo/go/encoding/json/encode_test.go b/libgo/go/encoding/json/encode_test.go
index 7290eca..42bb09d 100644
--- a/libgo/go/encoding/json/encode_test.go
+++ b/libgo/go/encoding/json/encode_test.go
@@ -183,7 +183,15 @@ type PointerCycleIndirect struct {
 	Ptrs []interface{}
 }
 
-var pointerCycleIndirect = &PointerCycleIndirect{}
+type RecursiveSlice []RecursiveSlice
+
+var (
+	pointerCycleIndirect = &PointerCycleIndirect{}
+	mapCycle             = make(map[string]interface{})
+	sliceCycle           = []interface{}{nil}
+	sliceNoCycle         = []interface{}{nil, nil}
+	recursiveSliceCycle  = []RecursiveSlice{nil}
+)
 
 func init() {
 	ptr := &SamePointerNoCycle{}
@@ -192,6 +200,14 @@ func init() {
 
 	pointerCycle.Ptr = pointerCycle
 	pointerCycleIndirect.Ptrs = []interface{}{pointerCycleIndirect}
+
+	mapCycle["x"] = mapCycle
+	sliceCycle[0] = sliceCycle
+	sliceNoCycle[1] = sliceNoCycle[:1]
+	for i := startDetectingCyclesAfter; i > 0; i-- {
+		sliceNoCycle = []interface{}{sliceNoCycle}
+	}
+	recursiveSliceCycle[0] = recursiveSliceCycle
 }
 
 func TestSamePointerNoCycle(t *testing.T) {
@@ -200,12 +216,21 @@ func TestSamePointerNoCycle(t *testing.T) {
 	}
 }
 
+func TestSliceNoCycle(t *testing.T) {
+	if _, err := Marshal(sliceNoCycle); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
 var unsupportedValues = []interface{}{
 	math.NaN(),
 	math.Inf(-1),
 	math.Inf(1),
 	pointerCycle,
 	pointerCycleIndirect,
+	mapCycle,
+	sliceCycle,
+	recursiveSliceCycle,
 }
 
 func TestUnsupportedValues(t *testing.T) {
diff --git a/libgo/go/encoding/json/stream_test.go b/libgo/go/encoding/json/stream_test.go
index c9e5334..c284f2d 100644
--- a/libgo/go/encoding/json/stream_test.go
+++ b/libgo/go/encoding/json/stream_test.go
@@ -7,7 +7,6 @@ package json
 import (
 	"bytes"
 	"io"
-	"io/ioutil"
 	"log"
 	"net"
 	"net/http"
@@ -215,7 +214,7 @@ func TestDecoderBuffered(t *testing.T) {
 	if m.Name != "Gopher" {
 		t.Errorf("Name = %q; want Gopher", m.Name)
 	}
-	rest, err := ioutil.ReadAll(d.Buffered())
+	rest, err := io.ReadAll(d.Buffered())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -318,7 +317,7 @@ func BenchmarkEncoderEncode(b *testing.B) {
 	v := &T{"foo", "bar"}
 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
-			if err := NewEncoder(ioutil.Discard).Encode(v); err != nil {
+			if err := NewEncoder(io.Discard).Encode(v); err != nil {
 				b.Fatal(err)
 			}
 		}
diff --git a/libgo/go/encoding/json/tagkey_test.go b/libgo/go/encoding/json/tagkey_test.go
index f77c49c..bbb4e6a 100644
--- a/libgo/go/encoding/json/tagkey_test.go
+++ b/libgo/go/encoding/json/tagkey_test.go
@@ -41,7 +41,7 @@ type percentSlashTag struct {
 }
 
 type punctuationTag struct {
-	V string `json:"!#$%&()*+-./:<=>?@[]^_{|}~"` // https://golang.org/issue/3546
+	V string `json:"!#$%&()*+-./:;<=>?@[]^_{|}~ "` // https://golang.org/issue/3546
 }
 
 type dashTag struct {
@@ -90,7 +90,7 @@ var structTagObjectKeyTests = []struct {
 	{badFormatTag{"Orfevre"}, "Orfevre", "Y"},
 	{badCodeTag{"Reliable Man"}, "Reliable Man", "Z"},
 	{percentSlashTag{"brut"}, "brut", "text/html%"},
-	{punctuationTag{"Union Rags"}, "Union Rags", "!#$%&()*+-./:<=>?@[]^_{|}~"},
+	{punctuationTag{"Union Rags"}, "Union Rags", "!#$%&()*+-./:;<=>?@[]^_{|}~ "},
 	{spaceTag{"Perreddu"}, "Perreddu", "With space"},
 	{unicodeTag{"Loukanikos"}, "Loukanikos", "Ελλάδα"},
 }
diff --git a/libgo/go/encoding/pem/pem_test.go b/libgo/go/encoding/pem/pem_test.go
index 8515b46..b2b6b15 100644
--- a/libgo/go/encoding/pem/pem_test.go
+++ b/libgo/go/encoding/pem/pem_test.go
@@ -6,7 +6,7 @@ package pem
 
 import (
 	"bytes"
-	"io/ioutil"
+	"io"
 	"reflect"
 	"strings"
 	"testing"
@@ -271,7 +271,7 @@ func BenchmarkEncode(b *testing.B) {
 	data := &Block{Bytes: make([]byte, 65536)}
 	b.SetBytes(int64(len(data.Bytes)))
 	for i := 0; i < b.N; i++ {
-		Encode(ioutil.Discard, data)
+		Encode(io.Discard, data)
 	}
 }
 
diff --git a/libgo/go/encoding/xml/marshal.go b/libgo/go/encoding/xml/marshal.go
index 0554b0d..d8a04a9 100644
--- a/libgo/go/encoding/xml/marshal.go
+++ b/libgo/go/encoding/xml/marshal.go
@@ -345,8 +345,11 @@ func (p *printer) createAttrPrefix(url string) string {
 	if prefix == "" || !isName([]byte(prefix)) || strings.Contains(prefix, ":") {
 		prefix = "_"
 	}
-	if strings.HasPrefix(prefix, "xml") {
-		// xmlanything is reserved.
+	// xmlanything is reserved and any variant of it regardless of
+	// case should be matched, so:
+	//    (('X'|'x') ('M'|'m') ('L'|'l'))
+	// See Section 2.3 of https://www.w3.org/TR/REC-xml/
+	if len(prefix) >= 3 && strings.EqualFold(prefix[:3], "xml") {
 		prefix = "_" + prefix
 	}
 	if p.attrNS[prefix] != "" {
diff --git a/libgo/go/encoding/xml/marshal_test.go b/libgo/go/encoding/xml/marshal_test.go
index 31309ef..d2e5137 100644
--- a/libgo/go/encoding/xml/marshal_test.go
+++ b/libgo/go/encoding/xml/marshal_test.go
@@ -2283,6 +2283,30 @@ var encodeTokenTests = []struct {
 		}},
 	},
 	want: `<foo xmlns="space"><bar xmlns="space" xmlns:space="space" space:attr="value">`,
+}, {
+	desc: "reserved namespace prefix -- all lower case",
+	toks: []Token{
+		StartElement{Name{"", "foo"}, []Attr{
+			{Name{"http://www.w3.org/2001/xmlSchema-instance", "nil"}, "true"},
+		}},
+	},
+	want: `<foo xmlns:_xmlSchema-instance="http://www.w3.org/2001/xmlSchema-instance" _xmlSchema-instance:nil="true">`,
+}, {
+	desc: "reserved namespace prefix -- all upper case",
+	toks: []Token{
+		StartElement{Name{"", "foo"}, []Attr{
+			{Name{"http://www.w3.org/2001/XMLSchema-instance", "nil"}, "true"},
+		}},
+	},
+	want: `<foo xmlns:_XMLSchema-instance="http://www.w3.org/2001/XMLSchema-instance" _XMLSchema-instance:nil="true">`,
+}, {
+	desc: "reserved namespace prefix -- all mixed case",
+	toks: []Token{
+		StartElement{Name{"", "foo"}, []Attr{
+			{Name{"http://www.w3.org/2001/XmLSchema-instance", "nil"}, "true"},
+		}},
+	},
+	want: `<foo xmlns:_XmLSchema-instance="http://www.w3.org/2001/XmLSchema-instance" _XmLSchema-instance:nil="true">`,
 }}
 
 func TestEncodeToken(t *testing.T) {