diff --git a/libgo/MERGE b/libgo/MERGE
index ad43e29..a84f1e3 100644
--- a/libgo/MERGE
+++ b/libgo/MERGE
@@ -1,4 +1,4 @@
-3e8f6b0791a670e52d25d76813d669daa68acfb4
+c4f8cb43caf0bcd0c730d7d04a3fce129393cecc
 
 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 0bcf07d..2d962d8 100644
--- a/libgo/VERSION
+++ b/libgo/VERSION
@@ -1 +1 @@
-go1.15rc1
+go1.15rc2
diff --git a/libgo/go/cmd/cgo/out.go b/libgo/go/cmd/cgo/out.go
index a5a22c8..1d23fc1 100644
--- a/libgo/go/cmd/cgo/out.go
+++ b/libgo/go/cmd/cgo/out.go
@@ -128,7 +128,9 @@
 		// Moreover, empty file name makes compile emit no source debug info at all.
 		var buf bytes.Buffer
 		noSourceConf.Fprint(&buf, fset, def.Go)
-		if bytes.HasPrefix(buf.Bytes(), []byte("_Ctype_")) {
+		if bytes.HasPrefix(buf.Bytes(), []byte("_Ctype_")) ||
+			strings.HasPrefix(name, "_Ctype_enum_") ||
+			strings.HasPrefix(name, "_Ctype_union_") {
 			// This typedef is of the form `typedef a b` and should be an alias.
 			fmt.Fprintf(fgo2, "= ")
 		}
diff --git a/libgo/go/cmd/go/internal/load/pkg.go b/libgo/go/cmd/go/internal/load/pkg.go
index e146e34..28220ce 100644
--- a/libgo/go/cmd/go/internal/load/pkg.go
+++ b/libgo/go/cmd/go/internal/load/pkg.go
@@ -239,11 +239,25 @@
 		err = &NoGoError{Package: p}
 	}
 
+	// Take only the first error from a scanner.ErrorList. PackageError only
+	// has room for one position, so we report the first error with a position
+	// instead of all of the errors without a position.
+	var pos string
+	var isScanErr bool
+	if scanErr, ok := err.(scanner.ErrorList); ok && len(scanErr) > 0 {
+		isScanErr = true // For stack push/pop below.
+
+		scanPos := scanErr[0].Pos
+		scanPos.Filename = base.ShortPath(scanPos.Filename)
+		pos = scanPos.String()
+		err = errors.New(scanErr[0].Msg)
+	}
+
 	// Report the error on the importing package if the problem is with the import declaration
 	// for example, if the package doesn't exist or if the import path is malformed.
 	// On the other hand, don't include a position if the problem is with the imported package,
 	// for example there are no Go files (NoGoError), or there's a problem in the imported
-	// package's source files themselves.
+	// package's source files themselves (scanner errors).
 	//
 	// TODO(matloob): Perhaps make each of those the errors in the first group
 	// (including modload.ImportMissingError, and the corresponding
@@ -254,22 +268,11 @@
 	// to make it easier to check for them? That would save us from having to
 	// move the modload errors into this package to avoid a package import cycle,
 	// and from having to export an error type for the errors produced in build.
-	if !isMatchErr && nogoErr != nil {
+	if !isMatchErr && (nogoErr != nil || isScanErr) {
 		stk.Push(path)
 		defer stk.Pop()
 	}
 
-	// Take only the first error from a scanner.ErrorList. PackageError only
-	// has room for one position, so we report the first error with a position
-	// instead of all of the errors without a position.
-	var pos string
-	if scanErr, ok := err.(scanner.ErrorList); ok && len(scanErr) > 0 {
-		scanPos := scanErr[0].Pos
-		scanPos.Filename = base.ShortPath(scanPos.Filename)
-		pos = scanPos.String()
-		err = errors.New(scanErr[0].Msg)
-	}
-
 	p.Error = &PackageError{
 		ImportStack: stk.Copy(),
 		Pos:         pos,
diff --git a/libgo/go/crypto/ed25519/ed25519.go b/libgo/go/crypto/ed25519/ed25519.go
index 5766970..6f59bb5 100644
--- a/libgo/go/crypto/ed25519/ed25519.go
+++ b/libgo/go/crypto/ed25519/ed25519.go
@@ -154,7 +154,7 @@
 	return signature
 }
 
-func signGeneric(signature, privateKey, message []byte) {
+func sign(signature, privateKey, message []byte) {
 	if l := len(privateKey); l != PrivateKeySize {
 		panic("ed25519: bad private key length: " + strconv.Itoa(l))
 	}
@@ -201,10 +201,6 @@
 // Verify reports whether sig is a valid signature of message by publicKey. It
 // will panic if len(publicKey) is not PublicKeySize.
 func Verify(publicKey PublicKey, message, sig []byte) bool {
-	return verify(publicKey, message, sig)
-}
-
-func verifyGeneric(publicKey PublicKey, message, sig []byte) bool {
 	if l := len(publicKey); l != PublicKeySize {
 		panic("ed25519: bad public key length: " + strconv.Itoa(l))
 	}
diff --git a/libgo/go/crypto/ed25519/ed25519_noasm.go b/libgo/go/crypto/ed25519/ed25519_noasm.go
deleted file mode 100644
index 4425bb2..0000000
--- a/libgo/go/crypto/ed25519/ed25519_noasm.go
+++ /dev/null
@@ -1,15 +0,0 @@
-// Copyright 2020 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.
-
-// -build !s390x
-
-package ed25519
-
-func sign(signature, privateKey, message []byte) {
-	signGeneric(signature, privateKey, message)
-}
-
-func verify(publicKey PublicKey, message, sig []byte) bool {
-	return verifyGeneric(publicKey, message, sig)
-}
diff --git a/libgo/go/crypto/ed25519/ed25519_s390x.go b/libgo/go/crypto/ed25519/ed25519_s390x.go
deleted file mode 100644
index d7e5243..0000000
--- a/libgo/go/crypto/ed25519/ed25519_s390x.go
+++ /dev/null
@@ -1,53 +0,0 @@
-// Copyright 2020 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.
-
-// +build ignore_for_gccgo
-
-package ed25519
-
-import (
-	"internal/cpu"
-	"strconv"
-)
-
-//go:noescape
-func kdsaSign(message, signature, privateKey []byte) bool
-
-//go:noescape
-func kdsaVerify(message, signature, publicKey []byte) bool
-
-// sign does a check to see if hardware has Edwards Curve instruction available.
-// If it does, use the hardware implementation. Otherwise, use the generic version.
-func sign(signature, privateKey, message []byte) {
-	if cpu.S390X.HasEDDSA {
-		if l := len(privateKey); l != PrivateKeySize {
-			panic("ed25519: bad private key length: " + strconv.Itoa(l))
-		}
-
-		ret := kdsaSign(message, signature, privateKey[:32])
-		if !ret {
-			panic("ed25519: kdsa sign has a failure")
-		}
-		return
-	}
-	signGeneric(signature, privateKey, message)
-}
-
-// verify does a check to see if hardware has Edwards Curve instruction available.
-// If it does, use the hardware implementation for eddsa verfication. Otherwise, the generic
-// version is used
-func verify(publicKey PublicKey, message, sig []byte) bool {
-	if cpu.S390X.HasEDDSA {
-		if l := len(publicKey); l != PublicKeySize {
-			panic("ed25519: bad public key length: " + strconv.Itoa(l))
-		}
-
-		if len(sig) != SignatureSize || sig[63]&224 != 0 {
-			return false
-		}
-
-		return kdsaVerify(message, sig, publicKey)
-	}
-	return verifyGeneric(publicKey, message, sig)
-}
diff --git a/libgo/go/crypto/ed25519/ed25519_test.go b/libgo/go/crypto/ed25519/ed25519_test.go
index f77d463..adb09e4 100644
--- a/libgo/go/crypto/ed25519/ed25519_test.go
+++ b/libgo/go/crypto/ed25519/ed25519_test.go
@@ -26,14 +26,6 @@
 	return len(buf), nil
 }
 
-// signGenericWrapper is identical to Sign except that it unconditionally calls signGeneric directly
-// rather than going through the sign function that might call assembly code.
-func signGenericWrapper(privateKey PrivateKey, msg []byte) []byte {
-	sig := make([]byte, SignatureSize)
-	signGeneric(sig, privateKey, msg)
-	return sig
-}
-
 func TestUnmarshalMarshal(t *testing.T) {
 	pub, _, _ := GenerateKey(rand.Reader)
 
@@ -53,33 +45,22 @@
 }
 
 func TestSignVerify(t *testing.T) {
-	t.Run("Generic", func(t *testing.T) { testSignVerify(t, signGenericWrapper, verifyGeneric) })
-	t.Run("Native", func(t *testing.T) { testSignVerify(t, Sign, Verify) })
-}
-
-func testSignVerify(t *testing.T, signImpl func(privateKey PrivateKey, message []byte) []byte,
-	verifyImpl func(publicKey PublicKey, message, sig []byte) bool) {
 	var zero zeroReader
 	public, private, _ := GenerateKey(zero)
 
 	message := []byte("test message")
-	sig := signImpl(private, message)
-	if !verifyImpl(public, message, sig) {
+	sig := Sign(private, message)
+	if !Verify(public, message, sig) {
 		t.Errorf("valid signature rejected")
 	}
 
 	wrongMessage := []byte("wrong message")
-	if verifyImpl(public, wrongMessage, sig) {
+	if Verify(public, wrongMessage, sig) {
 		t.Errorf("signature of different message accepted")
 	}
 }
 
 func TestCryptoSigner(t *testing.T) {
-	t.Run("Generic", func(t *testing.T) { testCryptoSigner(t, verifyGeneric) })
-	t.Run("Native", func(t *testing.T) { testCryptoSigner(t, Verify) })
-}
-
-func testCryptoSigner(t *testing.T, verifyImpl func(publicKey PublicKey, message, sig []byte) bool) {
 	var zero zeroReader
 	public, private, _ := GenerateKey(zero)
 
@@ -102,7 +83,7 @@
 		t.Fatalf("error from Sign(): %s", err)
 	}
 
-	if !verifyImpl(public, message, signature) {
+	if !Verify(public, message, signature) {
 		t.Errorf("Verify failed on signature from Sign()")
 	}
 }
@@ -130,12 +111,6 @@
 }
 
 func TestGolden(t *testing.T) {
-	t.Run("Generic", func(t *testing.T) { testGolden(t, signGenericWrapper, verifyGeneric) })
-	t.Run("Native", func(t *testing.T) { testGolden(t, Sign, Verify) })
-}
-
-func testGolden(t *testing.T, signImpl func(privateKey PrivateKey, message []byte) []byte,
-	verifyImpl func(publicKey PublicKey, message, sig []byte) bool) {
 	// sign.input.gz is a selection of test cases from
 	// https://ed25519.cr.yp.to/python/sign.input
 	testDataZ, err := os.Open("testdata/sign.input.gz")
@@ -177,12 +152,12 @@
 		copy(priv[:], privBytes)
 		copy(priv[32:], pubKey)
 
-		sig2 := signImpl(priv[:], msg)
+		sig2 := Sign(priv[:], msg)
 		if !bytes.Equal(sig, sig2[:]) {
 			t.Errorf("different signature result on line %d: %x vs %x", lineNo, sig, sig2)
 		}
 
-		if !verifyImpl(pubKey, msg, sig2) {
+		if !Verify(pubKey, msg, sig2) {
 			t.Errorf("signature failed to verify on line %d", lineNo)
 		}
 
@@ -206,11 +181,6 @@
 }
 
 func TestMalleability(t *testing.T) {
-	t.Run("Generic", func(t *testing.T) { testMalleability(t, verifyGeneric) })
-	t.Run("Native", func(t *testing.T) { testMalleability(t, Verify) })
-}
-
-func testMalleability(t *testing.T, verifyImpl func(publicKey PublicKey, message, sig []byte) bool) {
 	// https://tools.ietf.org/html/rfc8032#section-5.1.7 adds an additional test
 	// that s be in [0, order). This prevents someone from adding a multiple of
 	// order to s and obtaining a second valid signature for the same message.
@@ -229,7 +199,7 @@
 		0xb1, 0x08, 0xc3, 0xbd, 0xae, 0x36, 0x9e, 0xf5, 0x49, 0xfa,
 	}
 
-	if verifyImpl(publicKey, msg, sig) {
+	if Verify(publicKey, msg, sig) {
 		t.Fatal("non-canonical signature accepted")
 	}
 }
diff --git a/libgo/go/encoding/binary/varint.go b/libgo/go/encoding/binary/varint.go
index bcb8ac9..38af610 100644
--- a/libgo/go/encoding/binary/varint.go
+++ b/libgo/go/encoding/binary/varint.go
@@ -106,13 +106,13 @@
 func ReadUvarint(r io.ByteReader) (uint64, error) {
 	var x uint64
 	var s uint
-	for i := 0; ; i++ {
+	for i := 0; i < MaxVarintLen64; i++ {
 		b, err := r.ReadByte()
 		if err != nil {
 			return x, err
 		}
 		if b < 0x80 {
-			if i > 9 || i == 9 && b > 1 {
+			if i == 9 && b > 1 {
 				return x, overflow
 			}
 			return x | uint64(b)<<s, nil
@@ -120,6 +120,7 @@
 		x |= uint64(b&0x7f) << s
 		s += 7
 	}
+	return x, overflow
 }
 
 // ReadVarint reads an encoded signed integer from r and returns it as an int64.
diff --git a/libgo/go/encoding/binary/varint_test.go b/libgo/go/encoding/binary/varint_test.go
index ca411ec..6ef4c99 100644
--- a/libgo/go/encoding/binary/varint_test.go
+++ b/libgo/go/encoding/binary/varint_test.go
@@ -121,21 +121,27 @@
 	}
 }
 
-func testOverflow(t *testing.T, buf []byte, n0 int, err0 error) {
+func testOverflow(t *testing.T, buf []byte, x0 uint64, n0 int, err0 error) {
 	x, n := Uvarint(buf)
 	if x != 0 || n != n0 {
 		t.Errorf("Uvarint(%v): got x = %d, n = %d; want 0, %d", buf, x, n, n0)
 	}
 
-	x, err := ReadUvarint(bytes.NewReader(buf))
-	if x != 0 || err != err0 {
-		t.Errorf("ReadUvarint(%v): got x = %d, err = %s; want 0, %s", buf, x, err, err0)
+	r := bytes.NewReader(buf)
+	len := r.Len()
+	x, err := ReadUvarint(r)
+	if x != x0 || err != err0 {
+		t.Errorf("ReadUvarint(%v): got x = %d, err = %s; want %d, %s", buf, x, err, x0, err0)
+	}
+	if read := len - r.Len(); read > MaxVarintLen64 {
+		t.Errorf("ReadUvarint(%v): read more than MaxVarintLen64 bytes, got %d", buf, read)
 	}
 }
 
 func TestOverflow(t *testing.T) {
-	testOverflow(t, []byte{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x2}, -10, overflow)
-	testOverflow(t, []byte{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x1, 0, 0}, -13, overflow)
+	testOverflow(t, []byte{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x2}, 0, -10, overflow)
+	testOverflow(t, []byte{0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x1, 0, 0}, 0, -13, overflow)
+	testOverflow(t, []byte{0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}, 1<<64-1, 0, overflow) // 11 bytes, should overflow
 }
 
 func TestNonCanonicalZero(t *testing.T) {
diff --git a/libgo/go/net/http/transport.go b/libgo/go/net/http/transport.go
index a41e732..d37b52b 100644
--- a/libgo/go/net/http/transport.go
+++ b/libgo/go/net/http/transport.go
@@ -100,7 +100,7 @@
 	idleLRU      connLRU
 
 	reqMu       sync.Mutex
-	reqCanceler map[*Request]func(error)
+	reqCanceler map[cancelKey]func(error)
 
 	altMu    sync.Mutex   // guards changing altProto only
 	altProto atomic.Value // of nil or map[string]RoundTripper, key is URI scheme
@@ -273,6 +273,13 @@
 	ForceAttemptHTTP2 bool
 }
 
+// A cancelKey is the key of the reqCanceler map.
+// We wrap the *Request in this type since we want to use the original request,
+// not any transient one created by roundTrip.
+type cancelKey struct {
+	req *Request
+}
+
 func (t *Transport) writeBufferSize() int {
 	if t.WriteBufferSize > 0 {
 		return t.WriteBufferSize
@@ -433,9 +440,10 @@
 // optional extra headers to write and stores any error to return
 // from roundTrip.
 type transportRequest struct {
-	*Request                        // original request, not to be mutated
-	extra    Header                 // extra headers to write, or nil
-	trace    *httptrace.ClientTrace // optional
+	*Request                         // original request, not to be mutated
+	extra     Header                 // extra headers to write, or nil
+	trace     *httptrace.ClientTrace // optional
+	cancelKey cancelKey
 
 	mu  sync.Mutex // guards err
 	err error      // first setError value for mapRoundTripError to consider
@@ -512,6 +520,7 @@
 	}
 
 	origReq := req
+	cancelKey := cancelKey{origReq}
 	req = setupRewindBody(req)
 
 	if altRT := t.alternateRoundTripper(req); altRT != nil {
@@ -546,7 +555,7 @@
 		}
 
 		// treq gets modified by roundTrip, so we need to recreate for each retry.
-		treq := &transportRequest{Request: req, trace: trace}
+		treq := &transportRequest{Request: req, trace: trace, cancelKey: cancelKey}
 		cm, err := t.connectMethodForRequest(treq)
 		if err != nil {
 			req.closeBody()
@@ -559,7 +568,7 @@
 		// to send it requests.
 		pconn, err := t.getConn(treq, cm)
 		if err != nil {
-			t.setReqCanceler(req, nil)
+			t.setReqCanceler(cancelKey, nil)
 			req.closeBody()
 			return nil, err
 		}
@@ -567,7 +576,7 @@
 		var resp *Response
 		if pconn.alt != nil {
 			// HTTP/2 path.
-			t.setReqCanceler(req, nil) // not cancelable with CancelRequest
+			t.setReqCanceler(cancelKey, nil) // not cancelable with CancelRequest
 			resp, err = pconn.alt.RoundTrip(req)
 		} else {
 			resp, err = pconn.roundTrip(treq)
@@ -753,14 +762,14 @@
 // cancelable context instead. CancelRequest cannot cancel HTTP/2
 // requests.
 func (t *Transport) CancelRequest(req *Request) {
-	t.cancelRequest(req, errRequestCanceled)
+	t.cancelRequest(cancelKey{req}, errRequestCanceled)
 }
 
 // Cancel an in-flight request, recording the error value.
-func (t *Transport) cancelRequest(req *Request, err error) {
+func (t *Transport) cancelRequest(key cancelKey, err error) {
 	t.reqMu.Lock()
-	cancel := t.reqCanceler[req]
-	delete(t.reqCanceler, req)
+	cancel := t.reqCanceler[key]
+	delete(t.reqCanceler, key)
 	t.reqMu.Unlock()
 	if cancel != nil {
 		cancel(err)
@@ -1093,16 +1102,16 @@
 	return removed
 }
 
-func (t *Transport) setReqCanceler(r *Request, fn func(error)) {
+func (t *Transport) setReqCanceler(key cancelKey, fn func(error)) {
 	t.reqMu.Lock()
 	defer t.reqMu.Unlock()
 	if t.reqCanceler == nil {
-		t.reqCanceler = make(map[*Request]func(error))
+		t.reqCanceler = make(map[cancelKey]func(error))
 	}
 	if fn != nil {
-		t.reqCanceler[r] = fn
+		t.reqCanceler[key] = fn
 	} else {
-		delete(t.reqCanceler, r)
+		delete(t.reqCanceler, key)
 	}
 }
 
@@ -1110,17 +1119,17 @@
 // for the request, we don't set the function and return false.
 // Since CancelRequest will clear the canceler, we can use the return value to detect if
 // the request was canceled since the last setReqCancel call.
-func (t *Transport) replaceReqCanceler(r *Request, fn func(error)) bool {
+func (t *Transport) replaceReqCanceler(key cancelKey, fn func(error)) bool {
 	t.reqMu.Lock()
 	defer t.reqMu.Unlock()
-	_, ok := t.reqCanceler[r]
+	_, ok := t.reqCanceler[key]
 	if !ok {
 		return false
 	}
 	if fn != nil {
-		t.reqCanceler[r] = fn
+		t.reqCanceler[key] = fn
 	} else {
-		delete(t.reqCanceler, r)
+		delete(t.reqCanceler, key)
 	}
 	return true
 }
@@ -1324,12 +1333,12 @@
 		// set request canceler to some non-nil function so we
 		// can detect whether it was cleared between now and when
 		// we enter roundTrip
-		t.setReqCanceler(req, func(error) {})
+		t.setReqCanceler(treq.cancelKey, func(error) {})
 		return pc, nil
 	}
 
 	cancelc := make(chan error, 1)
-	t.setReqCanceler(req, func(err error) { cancelc <- err })
+	t.setReqCanceler(treq.cancelKey, func(err error) { cancelc <- err })
 
 	// Queue for permission to dial.
 	t.queueForDial(w)
@@ -2078,7 +2087,7 @@
 		}
 
 		if !hasBody || bodyWritable {
-			pc.t.setReqCanceler(rc.req, nil)
+			pc.t.setReqCanceler(rc.cancelKey, nil)
 
 			// Put the idle conn back into the pool before we send the response
 			// so if they process it quickly and make another request, they'll
@@ -2151,7 +2160,7 @@
 		// reading the response body. (or for cancellation or death)
 		select {
 		case bodyEOF := <-waitForBodyRead:
-			pc.t.setReqCanceler(rc.req, nil) // before pc might return to idle pool
+			pc.t.setReqCanceler(rc.cancelKey, nil) // before pc might return to idle pool
 			alive = alive &&
 				bodyEOF &&
 				!pc.sawEOF &&
@@ -2165,7 +2174,7 @@
 			pc.t.CancelRequest(rc.req)
 		case <-rc.req.Context().Done():
 			alive = false
-			pc.t.cancelRequest(rc.req, rc.req.Context().Err())
+			pc.t.cancelRequest(rc.cancelKey, rc.req.Context().Err())
 		case <-pc.closech:
 			alive = false
 		}
@@ -2408,9 +2417,10 @@
 }
 
 type requestAndChan struct {
-	_   incomparable
-	req *Request
-	ch  chan responseAndError // unbuffered; always send in select on callerGone
+	_         incomparable
+	req       *Request
+	cancelKey cancelKey
+	ch        chan responseAndError // unbuffered; always send in select on callerGone
 
 	// whether the Transport (as opposed to the user client code)
 	// added the Accept-Encoding gzip header. If the Transport
@@ -2472,7 +2482,7 @@
 
 func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err error) {
 	testHookEnterRoundTrip()
-	if !pc.t.replaceReqCanceler(req.Request, pc.cancelRequest) {
+	if !pc.t.replaceReqCanceler(req.cancelKey, pc.cancelRequest) {
 		pc.t.putOrCloseIdleConn(pc)
 		return nil, errRequestCanceled
 	}
@@ -2524,7 +2534,7 @@
 
 	defer func() {
 		if err != nil {
-			pc.t.setReqCanceler(req.Request, nil)
+			pc.t.setReqCanceler(req.cancelKey, nil)
 		}
 	}()
 
@@ -2540,6 +2550,7 @@
 	resc := make(chan responseAndError)
 	pc.reqch <- requestAndChan{
 		req:        req.Request,
+		cancelKey:  req.cancelKey,
 		ch:         resc,
 		addedGzip:  requestedGzip,
 		continueCh: continueCh,
@@ -2591,10 +2602,10 @@
 			}
 			return re.res, nil
 		case <-cancelChan:
-			pc.t.CancelRequest(req.Request)
+			pc.t.cancelRequest(req.cancelKey, errRequestCanceled)
 			cancelChan = nil
 		case <-ctxDoneChan:
-			pc.t.cancelRequest(req.Request, req.Context().Err())
+			pc.t.cancelRequest(req.cancelKey, req.Context().Err())
 			cancelChan = nil
 			ctxDoneChan = nil
 		}
diff --git a/libgo/go/net/http/transport_test.go b/libgo/go/net/http/transport_test.go
index 7153e3c..5c5ae3f 100644
--- a/libgo/go/net/http/transport_test.go
+++ b/libgo/go/net/http/transport_test.go
@@ -2368,6 +2368,50 @@
 	}
 }
 
+func testTransportCancelRequestInDo(t *testing.T, body io.Reader) {
+	setParallel(t)
+	defer afterTest(t)
+	if testing.Short() {
+		t.Skip("skipping test in -short mode")
+	}
+	unblockc := make(chan bool)
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		<-unblockc
+	}))
+	defer ts.Close()
+	defer close(unblockc)
+
+	c := ts.Client()
+	tr := c.Transport.(*Transport)
+
+	donec := make(chan bool)
+	req, _ := NewRequest("GET", ts.URL, body)
+	go func() {
+		defer close(donec)
+		c.Do(req)
+	}()
+	start := time.Now()
+	timeout := 10 * time.Second
+	for time.Since(start) < timeout {
+		time.Sleep(100 * time.Millisecond)
+		tr.CancelRequest(req)
+		select {
+		case <-donec:
+			return
+		default:
+		}
+	}
+	t.Errorf("Do of canceled request has not returned after %v", timeout)
+}
+
+func TestTransportCancelRequestInDo(t *testing.T) {
+	testTransportCancelRequestInDo(t, nil)
+}
+
+func TestTransportCancelRequestWithBodyInDo(t *testing.T) {
+	testTransportCancelRequestInDo(t, bytes.NewBuffer([]byte{0}))
+}
+
 func TestTransportCancelRequestInDial(t *testing.T) {
 	defer afterTest(t)
 	if testing.Short() {
diff --git a/libgo/go/runtime/lockrank_off.go b/libgo/go/runtime/lockrank_off.go
index 891589c..425ca8d 100644
--- a/libgo/go/runtime/lockrank_off.go
+++ b/libgo/go/runtime/lockrank_off.go
@@ -1,3 +1,7 @@
+// Copyright 2020 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.
+
 // +build !goexperiment.staticlockranking
 
 package runtime
diff --git a/libgo/go/runtime/lockrank_on.go b/libgo/go/runtime/lockrank_on.go
index cf4151f..fbc5ff5 100644
--- a/libgo/go/runtime/lockrank_on.go
+++ b/libgo/go/runtime/lockrank_on.go
@@ -1,3 +1,7 @@
+// Copyright 2020 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.
+
 // +build goexperiment.staticlockranking
 
 package runtime
diff --git a/libgo/go/runtime/mpagealloc.go b/libgo/go/runtime/mpagealloc.go
index 60f7f9f..8b3c62c 100644
--- a/libgo/go/runtime/mpagealloc.go
+++ b/libgo/go/runtime/mpagealloc.go
@@ -233,16 +233,12 @@
 
 	// The address to start an allocation search with. It must never
 	// point to any memory that is not contained in inUse, i.e.
-	// inUse.contains(searchAddr) must always be true.
+	// inUse.contains(searchAddr.addr()) must always be true. The one
+	// exception to this rule is that it may take on the value of
+	// maxOffAddr to indicate that the heap is exhausted.
 	//
-	// When added with arenaBaseOffset, we guarantee that
-	// all valid heap addresses (when also added with
-	// arenaBaseOffset) below this value are allocated and
-	// not worth searching.
-	//
-	// Note that adding in arenaBaseOffset transforms addresses
-	// to a new address space with a linear view of the full address
-	// space on architectures with segmented address spaces.
+	// We guarantee that all valid heap addresses below this value
+	// are allocated and not worth searching.
 	searchAddr offAddr
 
 	// start and end represent the chunk indices
@@ -518,6 +514,30 @@
 	return uintptr(scav) * pageSize
 }
 
+// findMappedAddr returns the smallest mapped offAddr that is
+// >= addr. That is, if addr refers to mapped memory, then it is
+// returned. If addr is higher than any mapped region, then
+// it returns maxOffAddr.
+//
+// s.mheapLock must be held.
+func (s *pageAlloc) findMappedAddr(addr offAddr) offAddr {
+	// If we're not in a test, validate first by checking mheap_.arenas.
+	// This is a fast path which is only safe to use outside of testing.
+	ai := arenaIndex(addr.addr())
+	if s.test || mheap_.arenas[ai.l1()] == nil || mheap_.arenas[ai.l1()][ai.l2()] == nil {
+		vAddr, ok := s.inUse.findAddrGreaterEqual(addr.addr())
+		if ok {
+			return offAddr{vAddr}
+		} else {
+			// The candidate search address is greater than any
+			// known address, which means we definitely have no
+			// free memory left.
+			return maxOffAddr
+		}
+	}
+	return addr
+}
+
 // find searches for the first (address-ordered) contiguous free region of
 // npages in size and returns a base address for that region.
 //
@@ -526,6 +546,7 @@
 //
 // find also computes and returns a candidate s.searchAddr, which may or
 // may not prune more of the address space than s.searchAddr already does.
+// This candidate is always a valid s.searchAddr.
 //
 // find represents the slow path and the full radix tree search.
 //
@@ -695,7 +716,7 @@
 			// We found a sufficiently large run of free pages straddling
 			// some boundary, so compute the address and return it.
 			addr := levelIndexToOffAddr(l, i).add(uintptr(base) * pageSize).addr()
-			return addr, firstFree.base
+			return addr, s.findMappedAddr(firstFree.base)
 		}
 		if l == 0 {
 			// We're at level zero, so that means we've exhausted our search.
@@ -741,7 +762,7 @@
 	// found an even narrower free window.
 	searchAddr := chunkBase(ci) + uintptr(searchIdx)*pageSize
 	foundFree(offAddr{searchAddr}, chunkBase(ci+1)-searchAddr)
-	return addr, firstFree.base
+	return addr, s.findMappedAddr(firstFree.base)
 }
 
 // alloc allocates npages worth of memory from the page heap, returning the base
diff --git a/libgo/go/runtime/mpagealloc_test.go b/libgo/go/runtime/mpagealloc_test.go
index 89a4a25..65ba71d 100644
--- a/libgo/go/runtime/mpagealloc_test.go
+++ b/libgo/go/runtime/mpagealloc_test.go
@@ -612,6 +612,63 @@
 				baseChunkIdx + chunkIdxBigJump:     {{0, PallocChunkPages}},
 			},
 		}
+
+		// Test to check for issue #40191. Essentially, the candidate searchAddr
+		// discovered by find may not point to mapped memory, so we need to handle
+		// that explicitly.
+		//
+		// chunkIdxSmallOffset is an offset intended to be used within chunkIdxBigJump.
+		// It is far enough within chunkIdxBigJump that the summaries at the beginning
+		// of an address range the size of chunkIdxBigJump will not be mapped in.
+		const chunkIdxSmallOffset = 0x503
+		tests["DiscontiguousBadSearchAddr"] = test{
+			before: map[ChunkIdx][]BitRange{
+				// The mechanism for the bug involves three chunks, A, B, and C, which are
+				// far apart in the address space. In particular, B is chunkIdxBigJump +
+				// chunkIdxSmalloffset chunks away from B, and C is 2*chunkIdxBigJump chunks
+				// away from A. A has 1 page free, B has several (NOT at the end of B), and
+				// C is totally free.
+				// Note that B's free memory must not be at the end of B because the fast
+				// path in the page allocator will check if the searchAddr even gives us
+				// enough space to place the allocation in a chunk before accessing the
+				// summary.
+				BaseChunkIdx + chunkIdxBigJump*0: {{0, PallocChunkPages - 1}},
+				BaseChunkIdx + chunkIdxBigJump*1 + chunkIdxSmallOffset: {
+					{0, PallocChunkPages - 10},
+					{PallocChunkPages - 1, 1},
+				},
+				BaseChunkIdx + chunkIdxBigJump*2: {},
+			},
+			scav: map[ChunkIdx][]BitRange{
+				BaseChunkIdx + chunkIdxBigJump*0:                       {},
+				BaseChunkIdx + chunkIdxBigJump*1 + chunkIdxSmallOffset: {},
+				BaseChunkIdx + chunkIdxBigJump*2:                       {},
+			},
+			hits: []hit{
+				// We first allocate into A to set the page allocator's searchAddr to the
+				// end of that chunk. That is the only purpose A serves.
+				{1, PageBase(BaseChunkIdx, PallocChunkPages-1), 0},
+				// Then, we make a big allocation that doesn't fit into B, and so must be
+				// fulfilled by C.
+				//
+				// On the way to fulfilling the allocation into C, we estimate searchAddr
+				// using the summary structure, but that will give us a searchAddr of
+				// B's base address minus chunkIdxSmallOffset chunks. These chunks will
+				// not be mapped.
+				{100, PageBase(baseChunkIdx+chunkIdxBigJump*2, 0), 0},
+				// Now we try to make a smaller allocation that can be fulfilled by B.
+				// In an older implementation of the page allocator, this will segfault,
+				// because this last allocation will first try to access the summary
+				// for B's base address minus chunkIdxSmallOffset chunks in the fast path,
+				// and this will not be mapped.
+				{9, PageBase(baseChunkIdx+chunkIdxBigJump*1+chunkIdxSmallOffset, PallocChunkPages-10), 0},
+			},
+			after: map[ChunkIdx][]BitRange{
+				BaseChunkIdx + chunkIdxBigJump*0:                       {{0, PallocChunkPages}},
+				BaseChunkIdx + chunkIdxBigJump*1 + chunkIdxSmallOffset: {{0, PallocChunkPages}},
+				BaseChunkIdx + chunkIdxBigJump*2:                       {{0, 100}},
+			},
+		}
 	}
 	for name, v := range tests {
 		v := v
diff --git a/libgo/go/runtime/mranges.go b/libgo/go/runtime/mranges.go
index e23d077..2c0eb2c 100644
--- a/libgo/go/runtime/mranges.go
+++ b/libgo/go/runtime/mranges.go
@@ -188,6 +188,25 @@
 	return len(a.ranges)
 }
 
+// findAddrGreaterEqual returns the smallest address represented by a
+// that is >= addr. Thus, if the address is represented by a,
+// then it returns addr. The second return value indicates whether
+// such an address exists for addr in a. That is, if addr is larger than
+// any address known to a, the second return value will be false.
+func (a *addrRanges) findAddrGreaterEqual(addr uintptr) (uintptr, bool) {
+	i := a.findSucc(addr)
+	if i == 0 {
+		return a.ranges[0].base.addr(), true
+	}
+	if a.ranges[i-1].contains(addr) {
+		return addr, true
+	}
+	if i < len(a.ranges) {
+		return a.ranges[i].base.addr(), true
+	}
+	return 0, false
+}
+
 // contains returns true if a covers the address addr.
 func (a *addrRanges) contains(addr uintptr) bool {
 	i := a.findSucc(addr)
diff --git a/libgo/go/runtime/proc.go b/libgo/go/runtime/proc.go
index 8f6eb6c..84070e4 100644
--- a/libgo/go/runtime/proc.go
+++ b/libgo/go/runtime/proc.go
@@ -176,7 +176,7 @@
 
 	if GOARCH != "wasm" { // no threads on wasm yet, so no sysmon
 		systemstack(func() {
-			newm(sysmon, nil)
+			newm(sysmon, nil, -1)
 		})
 	}
 
@@ -567,7 +567,7 @@
 
 	mallocinit()
 	fastrandinit() // must run before mcommoninit
-	mcommoninit(_g_.m)
+	mcommoninit(_g_.m, -1)
 	cpuinit() // must run before alginit
 	alginit() // maps must not be used before this call
 
@@ -633,7 +633,22 @@
 	}
 }
 
-func mcommoninit(mp *m) {
+// mReserveID returns the next ID to use for a new m. This new m is immediately
+// considered 'running' by checkdead.
+//
+// sched.lock must be held.
+func mReserveID() int64 {
+	if sched.mnext+1 < sched.mnext {
+		throw("runtime: thread ID overflow")
+	}
+	id := sched.mnext
+	sched.mnext++
+	checkmcount()
+	return id
+}
+
+// Pre-allocated ID may be passed as 'id', or omitted by passing -1.
+func mcommoninit(mp *m, id int64) {
 	_g_ := getg()
 
 	// g0 stack won't make sense for user (and is not necessary unwindable).
@@ -642,12 +657,12 @@
 	}
 
 	lock(&sched.lock)
-	if sched.mnext+1 < sched.mnext {
-		throw("runtime: thread ID overflow")
+
+	if id >= 0 {
+		mp.id = id
+	} else {
+		mp.id = mReserveID()
 	}
-	mp.id = sched.mnext
-	sched.mnext++
-	checkmcount()
 
 	mp.fastrand[0] = uint32(int64Hash(uint64(mp.id), fastrandseed))
 	mp.fastrand[1] = uint32(int64Hash(uint64(cputicks()), ^fastrandseed))
@@ -1052,7 +1067,7 @@
 			notewakeup(&mp.park)
 		} else {
 			// Start M to run P.  Do not start another M below.
-			newm(nil, p)
+			newm(nil, p, -1)
 		}
 	}
 
@@ -1379,12 +1394,13 @@
 // Allocate a new m unassociated with any thread.
 // Can use p for allocation context if needed.
 // fn is recorded as the new m's m.mstartfn.
+// id is optional pre-allocated m ID. Omit by passing -1.
 //
 // This function is allowed to have write barriers even if the caller
 // isn't because it borrows _p_.
 //
 //go:yeswritebarrierrec
-func allocm(_p_ *p, fn func(), allocatestack bool) (mp *m, g0Stack unsafe.Pointer, g0StackSize uintptr) {
+func allocm(_p_ *p, fn func(), id int64, allocatestack bool) (mp *m, g0Stack unsafe.Pointer, g0StackSize uintptr) {
 	_g_ := getg()
 	acquirem() // disable GC because it can be called from sysmon
 	if _g_.m.p == 0 {
@@ -1413,7 +1429,7 @@
 
 	mp = new(m)
 	mp.mstartfn = fn
-	mcommoninit(mp)
+	mcommoninit(mp, id)
 
 	mp.g0 = malg(allocatestack, false, &g0Stack, &g0StackSize)
 	mp.g0.m = mp
@@ -1540,7 +1556,7 @@
 	// The sched.pc will never be returned to, but setting it to
 	// goexit makes clear to the traceback routines where
 	// the goroutine stack ends.
-	mp, g0SP, g0SPSize := allocm(nil, nil, true)
+	mp, g0SP, g0SPSize := allocm(nil, nil, -1, true)
 	gp := malg(true, false, nil, nil)
 	// malg returns status as _Gidle. Change to _Gdead before
 	// adding to allg where GC can see it. We use _Gdead to hide
@@ -1715,9 +1731,11 @@
 // Create a new m. It will start off with a call to fn, or else the scheduler.
 // fn needs to be static and not a heap allocated closure.
 // May run with m.p==nil, so write barriers are not allowed.
+//
+// id is optional pre-allocated m ID. Omit by passing -1.
 //go:nowritebarrierrec
-func newm(fn func(), _p_ *p) {
-	mp, _, _ := allocm(_p_, fn, false)
+func newm(fn func(), _p_ *p, id int64) {
+	mp, _, _ := allocm(_p_, fn, id, false)
 	mp.nextp.set(_p_)
 	mp.sigmask = initSigmask
 	if gp := getg(); gp != nil && gp.m != nil && (gp.m.lockedExt != 0 || gp.m.incgo) && GOOS != "plan9" {
@@ -1770,7 +1788,7 @@
 		releasem(mp)
 		return
 	}
-	newm(templateThread, nil)
+	newm(templateThread, nil, -1)
 	releasem(mp)
 }
 
@@ -1865,16 +1883,31 @@
 		}
 	}
 	mp := mget()
-	unlock(&sched.lock)
 	if mp == nil {
+		// No M is available, we must drop sched.lock and call newm.
+		// However, we already own a P to assign to the M.
+		//
+		// Once sched.lock is released, another G (e.g., in a syscall),
+		// could find no idle P while checkdead finds a runnable G but
+		// no running M's because this new M hasn't started yet, thus
+		// throwing in an apparent deadlock.
+		//
+		// Avoid this situation by pre-allocating the ID for the new M,
+		// thus marking it as 'running' before we drop sched.lock. This
+		// new M will eventually run the scheduler to execute any
+		// queued G's.
+		id := mReserveID()
+		unlock(&sched.lock)
+
 		var fn func()
 		if spinning {
 			// The caller incremented nmspinning, so set m.spinning in the new M.
 			fn = mspinning
 		}
-		newm(fn, _p_)
+		newm(fn, _p_, id)
 		return
 	}
+	unlock(&sched.lock)
 	if mp.spinning {
 		throw("startm: m is spinning")
 	}
@@ -4897,7 +4930,9 @@
 
 	atomic.StoreRel(&pp.runqtail, t)
 	if !q.empty() {
+		lock(&sched.lock)
 		globrunqputbatch(q, int32(qsize))
+		unlock(&sched.lock)
 	}
 }
 
diff --git a/libgo/go/sync/runtime2.go b/libgo/go/sync/runtime2.go
index 931edad..f10c4e8 100644
--- a/libgo/go/sync/runtime2.go
+++ b/libgo/go/sync/runtime2.go
@@ -1,3 +1,7 @@
+// Copyright 2020 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.
+
 // +build !goexperiment.staticlockranking
 
 package sync
diff --git a/libgo/go/sync/runtime2_lockrank.go b/libgo/go/sync/runtime2_lockrank.go
index 5a68e90..aaa1c27 100644
--- a/libgo/go/sync/runtime2_lockrank.go
+++ b/libgo/go/sync/runtime2_lockrank.go
@@ -1,3 +1,7 @@
+// Copyright 2020 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.
+
 // +build goexperiment.staticlockranking
 
 package sync
diff --git a/libgo/go/testing/testing.go b/libgo/go/testing/testing.go
index 6f09358..dee77f7 100644
--- a/libgo/go/testing/testing.go
+++ b/libgo/go/testing/testing.go
@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // Package testing provides support for automated testing of Go packages.
-// It is intended to be used in concert with the ``go test'' command, which automates
+// It is intended to be used in concert with the "go test" command, which automates
 // execution of any function of the form
 //     func TestXxx(*testing.T)
 // where Xxx does not start with a lowercase letter. The function name
@@ -14,8 +14,8 @@
 // To write a new test suite, create a file whose name ends _test.go that
 // contains the TestXxx functions as described here. Put the file in the same
 // package as the one being tested. The file will be excluded from regular
-// package builds but will be included when the ``go test'' command is run.
-// For more detail, run ``go help test'' and ``go help testflag''.
+// package builds but will be included when the "go test" command is run.
+// For more detail, run "go help test" and "go help testflag".
 //
 // A simple test function looks like this:
 //
diff --git a/libgo/misc/cgo/test/test.go b/libgo/misc/cgo/test/test.go
index 8c69ad9..35bc3a1 100644
--- a/libgo/misc/cgo/test/test.go
+++ b/libgo/misc/cgo/test/test.go
@@ -901,6 +901,12 @@
 // issue 38649
 // Test that #define'd type aliases work.
 #define netbsd_gid unsigned int
+
+// issue 40494
+// Inconsistent handling of tagged enum and union types.
+enum Enum40494 { X_40494 };
+union Union40494 { int x; };
+void issue40494(enum Enum40494 e, union Union40494* up) {}
 */
 import "C"
 
@@ -2204,3 +2210,10 @@
 // issue 39877
 
 var issue39877 *C.void = nil
+
+// issue 40494
+// No runtime test; just make sure it compiles.
+
+func Issue40494() {
+	C.issue40494(C.enum_Enum40494(C.X_40494), (*C.union_Union40494)(nil))
+}
diff --git a/libgo/misc/cgo/testshared/shared_test.go b/libgo/misc/cgo/testshared/shared_test.go
index f8dabbe..5e08937 100644
--- a/libgo/misc/cgo/testshared/shared_test.go
+++ b/libgo/misc/cgo/testshared/shared_test.go
@@ -462,6 +462,7 @@
 	run(t, "trivial executable", "../../bin/trivial")
 	AssertIsLinkedTo(t, "../../bin/trivial", soname)
 	AssertHasRPath(t, "../../bin/trivial", gorootInstallDir)
+	checkSize(t, "../../bin/trivial", 100000) // it is 19K on linux/amd64, 100K should be enough
 }
 
 // Build a trivial program in PIE mode that links against the shared runtime and check it runs.
@@ -470,6 +471,18 @@
 	run(t, "trivial executable", "./trivial.pie")
 	AssertIsLinkedTo(t, "./trivial.pie", soname)
 	AssertHasRPath(t, "./trivial.pie", gorootInstallDir)
+	checkSize(t, "./trivial.pie", 100000) // it is 19K on linux/amd64, 100K should be enough
+}
+
+// Check that the file size does not exceed a limit.
+func checkSize(t *testing.T, f string, limit int64) {
+	fi, err := os.Stat(f)
+	if err != nil {
+		t.Fatalf("stat failed: %v", err)
+	}
+	if sz := fi.Size(); sz > limit {
+		t.Errorf("file too large: got %d, want <= %d", sz, limit)
+	}
 }
 
 // Build a division test program and check it runs.